Analysis and Mapping of Post-Fire 

Hydrologic Hazards for the 2002 Hayman, 

Coal Seam, and Missionary Ridge 

Wildfires, Colorado

By J.G. Elliott, M.E. Smith, M.J. Friedel, M.R. Stevens, C.R. Bossong, D.W. Litke, 

R.S. Parker, C. Costello, J. Wagner, S.J. Char, M.A. Bauer, and S.R. Wilds

Prepared in cooperation with the

Federal Emergency Management Agency

Scientific Investigations Report 2004–5300

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

For more information about the Federal Emergency Management Agency, Region VIII, and their work on this report:

Jeanine D. Petterson, Division Director

Robert Ives, Branch Chief

John Liou, Regional Hydrologist

Denver Federal Center, Building 719

P.O. Box 25267

Denver, CO 80225–0267

http://www.fema.gov/regions/viii/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Elliott, J.G., Smith, M.E., Friedel, M.J., Stevens, M.R., Bossong, C.R., Litke, D.W., Parker, R.S., Costello, C., Wagner, 

J., Char, S.J., Bauer, M.A., and Wilds, S.R., 2005, Analysis and mapping of post-fire hydrologic hazards for the 2002 

Hayman, Coal Seam, and Missionary Ridge wildfires, Colorado: U.S. Geological Survey Scientific Investigations 

Report 2004–5300, 104 p.
iii

Contents

Abstract ................................................................................................... 1

Introduction ................................................................................................ 2

Purpose and Scope ................................................................................. 2

Acknowledgments ................................................................................. 4

Study Areas ................................................................................................ 4

Reconnaissance of 2002 Wildfires—Phase 1 ......................................................... 4

Major 2002 Colorado Wildfires through July 2, 2002 .......................................... 4

High-Priority Wildfires Selected for Detailed Hydrologic Analyses ........................... 5

Hayman Wildfire Area ........................................................................ 5

Coal Seam Wildfire Area ..................................................................... 5

Missionary Ridge Wildfire Area ............................................................ 6

Dominant Post-Fire Hazard Processes ......................................................... 6

Methods for Post-Fire Flood Hazard Analysis—Phase 2 ............................................. 6

Short-Term Post-Fire Effects and Long-Term Recovery ....................................... 6

Preparation of Digital Elevation Data ............................................................ 6

Rainfall-Runoff Model Calibration and Simulation ............................................. 7

Pre-Burn Model Calibration .................................................................. 7

Post-Burn Adjustment of Model Parameters ............................................. 8

Sediment Bulking of Estimated Discharge ...................................................... 9

Water-Flow Routing and Computation of Flood Elevations .................................... 9

Delineation of the 100-Year Flood Plain ......................................................... 9

Methods for Post-Fire Debris-Flow Hazard Analysis—Phase 2 .................................... 9

Debris-Flow Mechanisms ........................................................................ 9

Post-Fire Debris-Flow Peak Discharge Estimates ............................................. 10

Debris-Flow Modeling in Colorado Wildfire Areas ............................................. 11

Debris-Flow Routing with FLO-2D ............................................................... 11

Post-Fire Flood and Debris-Flow Hazard Maps ................................................ 13

Method for Determination of Drainage Basin Recovery—Phase 3 ................................. 13

Post-Fire Hydrologic Hazards for the Hayman Wildfire ............................................. 14

South Platte River “Limited-Detail” Hydrologic Analysis—Phase 2 ........................ 14

South Platte River Inflow Conditions ...................................................... 15

South Platte River Tributary Rainfall-Runoff Modeling ................................. 16

Rainfall-Runoff Model Methodology for the Hayman Wildfire ..................... 16

Step 1, Modeling of Unburned Conditions, South Platte River 

Tributaries ............................................................... 16

Step 2, Modeling of Burned Conditions, South Platte River 

Tributaries ............................................................... 18

Sediment Bulking of Discharge for Hayman Wildfire-Area Tributaries ............... 20

Estimated Peak Discharges, South Platte River Tributaries ........................... 21

Estimated Peak Discharges, Selected Reaches of the South Platte River ............ 22

South Platte River Hydrology and Peak Flow Analysis for Long-Term 

Recovery—Phase 3 ........................................................................ 22

South Platte River “Detailed” Hydraulic Analysis ............................................. 23
iv

Post-Fire Hydrologic Hazards for the Coal Seam Wildfire .......................................... 24

Hydrologic Analysis of Mitchell Creek—Phase 2 ............................................. 24

Mitchell Creek Tributary Rainfall-Runoff Modeling ....................................... 29

Step 1, Modeling of Unburned Conditions, Mitchell Creek Tributaries ......... 29

Step 2, Modeling of Burned Conditions, Mitchell Creek Tributaries ............ 30

Sediment Bulking and Peak Flood Discharge for Mitchell Creek ..................... 31

Mitchell Creek Hydrology and Peak Flow Modeling for Long-Term 

Recovery—Phase 3 ........................................................................ 32

Analysis of Debris-Flow-Producing Drainage Basins, Coal Seam 

Wildfire—Phase 2 ........................................................................ 32

Post-Fire Hydrologic Hazards for the Missionary Ridge Wildfire ................................. 34

Analysis of Debris-Flow-Producing Drainage Basins, Missionary Ridge 

Wildfire—Phase 2 ........................................................................ 34

Summary ................................................................................................... 35

Hayman Wildfire .................................................................................... 38

Coal Seam Wildfire ................................................................................. 40

Missionary Ridge Wildfire ........................................................................ 41

References Cited .......................................................................................... 41

Appendix 1. Summary of Methods for Post-Fire and Debris-Flow Hazard Analyses ......... 47

Appendix 2. The Manual Calibration Method for the Hayman Burned Area ..................... 49

Appendix 3. Appendix Tables 3–1—3–14 ............................................................ 57

Appendix 4. Appendix Tables 4–1—4–2 ............................................................ 97

Appendix 5. Appendix Tables 5–1—5–4 ............................................................101

Figures

1. Map showing location of Colorado wildfires, 2002 ....................................... 3

2. Example of pre- and post-burn runoff hydrographs and sediment-concentration 

hydrograph used in debris-flow modeling, 100-year, 1-hour storm ..................... 12

3. Graph showing estimated recovery curves for runoff-curve numbers in a 

drainage basin with a pre-burn runoff-curve number of 50 .............................. 14

 4. Hayman Drainage Basin overview map ................................................... 5

 5. Hayman Drainage Basin index map ...................................................... 5

6. Graph showing 100-year flood peaks in relation to drainage area and the best-fit 

regression line using an ordinary-least-squares regression model ..................... 18

7. Graph showing comparison of post-fire runoff sediment-bulking methods, as a 

percentage of results from Moody and Martin’s (2001a) Spring Creek regression 

on total drainage-basin area to a 25-percent bulking factor applied to moderately 

and severely burned areas compared to percentage of drainage basin moderately 

or severely burned ........................................................................... 21

 8. Hayman Drainage Basin cross-section map 1—South Platte River .................. 5

 9. Hayman Drainage Basin cross-section map 2—South Platte River .................. 5

 10. Hayman Drainage Basin cross-section map 3—South Platte River .................. 5

 11. Hayman Drainage Basin cross-section map 4—South Platte River .................. 5

 12. Hayman cross-section detail map 1—South Platte River, Deckers .................. 5

 13. Hayman cross-section detail map 2—South Platte River, Trumbull .................. 5
v

 14. Hayman cross-section detail map 3—South Platte River, South Platte ............... 5

15. Cross-section location map for South Platte River detailed hydraulic study ......... 23

16. Flood-profile plots of the South Platte River, Colorado, detailed study reach ......... 25

 17. Coal Seam Drainage Basin overview map—Debris-flow study areas ............... 5

 18. Coal Seam debris-flow inundation map 2 ................................................ 5

 19. Coal Seam debris-flow inundation map 2 ................................................ 5

 20. Missionary Ridge overview map ............................................................ 5

 21. Missionary Ridge west of Lemon Reservoir debris-flow inundation map 1 ......... 5

 22. Missionary Ridge east of Lemon Reservoir debris-flow inundation map 2 ............ 5

Tables

1. Characteristics of streamflow-gaging stations used for calibration of 100-year 

peak discharge for pre-burn conditions, South Platte River drainage basin in 

Colorado ....................................................................................... 17

2. Subbasin characteristics, modeling parameters, and computed 100-year peak 

discharges for pre-burn, post-burn, and post-burn bulked floods for 19 selected

subbasins affected by the Hayman wildfire, objective calibration method ............ 19

3. Subbasin characteristics, modeling parameters, and computed peak discharge 

for pre- and post-burn subbasin conditions, Mitchell Creek ........................... 30

4. Computed 100-year peak discharges for pre-burn, post-burn, and post-burn 

(bulked) runoff conditions for modeled subbasins in the Mitchell Creek drainage

basin ............................................................................................. 31

5. Estimated 100-year debris-flow peak discharges for selected Coal Seam burned 

area tributary subbasins ..................................................................... 33

6. Estimated 100-year debris-flow peak discharges for selected Missionary Ridge 

burned area tributary subbasins ............................................................ 35

Appendix Figure

2–1. Relation of 100-year flood peaks and drainage area showing the best-fit 

regression line using an ordinary-least-squares regression model ..................... 51

Appendix Tables

2–1. Characteristics of streamflow-gaging stations used for calibration of 100-year 

peak discharge for pre-burn conditions, South Platte River drainage basin ......... 50

2–2. Drainage-basin characteristics, modeling parameters, and computed peak 

discharges for pre-burn, post-burn, and post-burn (bulked) conditions in the 

19 principal drainage basins affected by the Hayman fire .............................. 54

2–3. Channel cross-section properties (normal-depth computation) for South Platte 

River reaches upstream and downstream from Cheesman Reservoir .................. 56
vi

3–1. South Platte River basins and subbasins used in the HEC-HMS model upstream 

and downstream from Cheesman Reservoir ............................................. 57

3–2. Burn data for South Platte River basins and subbasins upstream and downstream 

from Cheesman Reservoir ..................................................................... 60

3–3. Pre- and post-burn model parameters for South Platte River basins and subbasins 

upstream and downstream from Cheesman Reservoir used in the manual calibration 

method ................................................................................................... 65

3–4. Post-burn model parameters for South Platte River basins upstream and 

downstream from Cheesman Reservoir used in the manual calibration method ...... 68

3–5. Channel routing parameters used in the HEC-HMS model for South Platte River 

reaches upstream and downstream from Cheesman Reservoir used in the manual 

calibration method ........................................................................... 72

3–6. HEC-HMS model results for South Platte River basins and subbasins upstream 

and downstream from Cheesman Reservoir used in the manual calibration 

method .......................................................................................... 73

3–7. Peak flows and recovered model parameters for South Platte River subbasins 

upstream and downstream from Cheesman Reservoir ................................. 79

3–8. South Platte River Basin rainfall distribution ............................................. 82

3–9. Flood peak flows through the Deckers-to-Trumbull reach, South Platte River ......... 84

3–10. Summary of Manning’s n values for roughness and downstream reach lengths ...... 85

3–11. Results of step-backwater computations using HEC-RAS program ..................... 86

3–12. Floodway data for the Deckers to Trumbull reach, South Platte River, computed 

in HEC-RAS .................................................................................... 91

3–13. Comparison of 1978 study 100-year flood elevations at selected cross sections

to 2004 study 100-year flood elevations at the same cross sections .................. 92

3–14. Pre- and post-burn model parameters for South Platte River subbasins upstream 

and downstream from Cheesman Reservoir used in the objective calibration 

method .......................................................................................... 93

4–1. Global Positioning System positions for South Platte River cross sections used 

in post-fire hazard analysis .................................................................. 97

4–2. Global Positioning System positions for South Platte River cross sections used 

in detailed hydraulic analysis of recovered conditions ................................. 99

5–1. Mitchell Creek subbasin characteristics and pre-burn model parameters ............101

5–2. Mitchell Creek subbasin characteristics and post-burn model parameters. ...............101

5–3. Results of rainfall-runoff modeling using recurrence intervals for the 1-hour 

storm in the Coal Seam burned area ......................................................102

5–4. Mitchell Creek rainfall distribution .........................................................103
vii

Conversion Factors, Abbreviations, and Datums

Multiply By To obtain

millimeter (mm) 0.03937 inch

meter (m) 3.281 foot (ft) 

kilogram per square meter (kg/m2) 0.2048 pound per square foot (lb/ft2)

newton per square meter (N/m2) 0.02088 pound per square foot (lb/ft2)

newton per cubic meter (N/m3) 0.006365 pound per cubic foot (lb/ft3)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

acre 4,047 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

foot per second (ft/s) 0.3048 meter per second (m/s)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

acre-foot (acre-ft) 1,233 cubic meter (m3)

ton, short 0.9072 megagram (Mg)

Vertical coordinate information is referenced to the North Geodetic Vertical Datum of 1929 

(NGVD 29) and to the North American Vertical Datum of 1988 (NAV 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
Abstract

Wildfires caused extreme changes in the hydrologic, 

hydraulic, and geomorphologic characteristics of many 

Colorado drainage basins in the summer of 2002. Detailed 

assessments were made of the short-term effects of three 

wildfires on burned and adjacent unburned parts of drainage 

basins. These were the Hayman, Coal Seam, and Missionary 

Ridge wildfires. Longer term runoff characteristics that reflect 

post-fire drainage basin recovery expected to develop over a 

period of several years also were analyzed for two affected 

stream reaches: the South Platte River between Deckers and 

Trumbull, and Mitchell Creek in Glenwood Springs. The 10-, 

50-, 100-, and 500-year flood-plain boundaries and watersurface profiles were computed in a detailed hydraulic study 

of the Deckers-to-Trumbull reach.

The Hayman wildfire burned approximately 138,000 acres

(216 square miles) in granitic terrain near Denver, and the predominant potential hazard in this area is flooding by sedimentladen water along the large tributaries to and the main stem of 

the South Platte River. The Coal Seam wildfire burned approximately 12,200 acres (19.1 square miles) near Glenwood Springs, 

and the Missionary Ridge wildfire burned approximately 

70,500 acres (110 square miles) near Durango, both in areas 

underlain by marine shales where the predominant potential 

hazard is debris-flow inundation of low-lying areas.

Hydrographs and peak discharges for pre-burn and postburn scenarios were computed for each drainage basin and 

tributary subbasin by using rainfall-runoff models because 

streamflow data for most tributary subbasins were not available. An objective rainfall-runoff model calibration method 

based on nonlinear regression and referred to as the “objective 

calibration method” was developed and applied to rainfallrunoff models for three burned areas. The HEC–1 rainfallrunoff model was used to simulate the pre-burn rainfall-runoff 

processes in response to the 100-year storm, and HEC-HMS 

was used for runoff hydrograph generation.

Post-burn rainfall-runoff parameters were determined by 

adjusting the runoff-curve numbers on the basis of a weighting procedure derived from the U.S. Soil Conservation Service 

(now the National Resources Conservation Service) equation 

for precipitation excess and the effect of burn severity. This 

weighting procedure was determined to be more appropriate 

than simple area weighting because of the potentially marked 

effect of even small burned areas on the runoff hydrograph 

in individual drainage basins. Computed water-peak discharges from HEC-HMS models were increased volumetrically to account for increased sediment concentrations that 

are expected as a result of accelerated erosion after burning. 

Peak discharge estimates for potential floods in the South 

Platte River were increased by a factor that assumed a volumetric sediment concentration (Cv

) of 20 percent. Flood hydrographs for the South Platte River and Mitchell Creek were 

routed down main-stem channels using watershed-routing 

algorithms included in the HEC-HMS rainfall-runoff model.

In areas subject to debris flows in the Coal Seam and 

Missionary Ridge burned areas, debris-flow discharges were 

simulated by 100-year rainfall events, and the inflow hydrographs at tributary mouths were simulated by using the objective calibration method. Sediment concentrations (Cv

) used 

in debris-flow simulations were varied through the event, and 

were initial Cv 20 percent, mean Cv approximately 31 percent, 

maximum Cv 48 percent, Cv 43 percent at the time of the water 

hydrograph peak, and Cv 20 percent for the duration of the 

event. The FLO-2D flood- and debris-flow routing model was 

used to delineate the area of unconfined debris-flow inundation on selected alluvial fan and valley floor areas.

A method was developed to objectively determine the 

post-fire recovery period for the Hayman and Coal Seam 

burned areas using runoff-curve numbers (RCN) for all drainage basins for a 50-year period. A time assumed to be the 

recovery period was determined when the rate of change in the 

estimated 100-year flood peak became less than 5 percent per 

year. The method was based on a limited amount of historical 

data collected in drainage basins that were monitored during 

the post-fire recovery process.

Analysis and Mapping of Post-Fire Hydrologic Hazards 

for the 2002 Hayman, Coal Seam, and Missionary Ridge 

Wildfires, Colorado

By J.G. Elliott, M.E. Smith, M.J. Friedel, M.R. Stevens, C.R. Bossong, D.W. Litke, R.S. Parker, C. Costello, 

J. Wagner, S.J. Char, M.A. Bauer, and S.R. Wilds
2 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

The simulated post-burn 100-year peak discharges for 

19 subbasins, routed to the point of confluence with the South 

Platte River, are expected to increase 3 to 90 times the preburn peaks in the short term. Among subbasins with greater 

than 50 percent moderately to severely burned areas, post-burn 

peak discharges are expected to be 28 to 91 times greater than 

pre-burn peaks. Post-fire recovery-time estimates are estimated 

to be 6 years for the Platte River upstream and downstream 

from Cheesman Reservoir.

Potential post-fire hazards in the Coal Seam burned area 

are waterflooding in Mitchell Creek and debris flows from 

smaller tributaries. Post-burn, sediment-bulked 100-year 

peak water flows for Mitchell Creek tributaries are expected 

to increase 2 to 21 times the pre-burn peaks. Post-burn peak 

discharges for points along the main stem of Mitchell Creek 

are expected to increase 3 to 4 times over the pre-burn peaks. 

Debris-flow analysis was done for 26 tributaries with drainage areas that ranged from 0.01 to 0.75 square mile. Estimates 

of the increase in 100-year discharge resulting from post-fire 

debris flows, relative to unburned conditions, range from 8 to 

14 times in the Red Mountain area, 2 to 9 times in the West 

Glenwood Springs area, and 8 to 14 times for selected tributaries of Mitchell Creek. Post-fire recovery-time estimates were 

not made for the smaller subbasins burned by the Coal Seam

wildfire; however, the estimated recovery time for Mitchell 

Creek is about 4 years.

Short-term effects of 100-year storm-generated debris 

flows in 25 tributaries in the Missionary Ridge burned area 

with drainage areas that range from 0.07 to 9.78 square miles 

were evaluated. The largest increase from estimated preburn discharge to post-burn debris flow 100-year discharge 

is expected to occur in Coon Creek where peak discharges 

could increase by a factor of greater than 240. Increases range 

from 9 to 38 times in other Animas River tributaries. In the 

Florida River area, increases range from 22 to 31 times, and 

in the Vallecito Reservoir and Los Pinos River areas, from 9 

to 30 times.

Introduction

Drought conditions in Colorado made the 2002 wildfire

season unusually active. At least 16 wildfires were burning or 

had burned as of July 2, 2002 (fig. 1). These wildfires caused 

extreme changes in the hydrologic, hydraulic, and geomorphologic characteristics of the affected drainage basins. Post-fire 

basin conditions increase the risk of flood and debris-flow 

damage to homes, roads, bridges, and other infrastructure. In 

cooperation with the Federal Emergency Management Agency 

(FEMA), a team of scientists from the U.S. Geological Survey 

(USGS) and the Bureau of Reclamation (BOR): (1) assessed 

and ranked the 16 existing Colorado wildfires (as of July 2, 

2002) in terms of relative hazard to population centers and 

infrastructure; (2) conducted detailed assessments of the 

hydrologic, hydraulic, and geomorphologic effects of selected, 

high-priority wildfires on burned and adjacent unburned 

parts of the drainage basins; and (3) summarized hydrologic

information for use by water managers about the effects of

wildfire on runoff and sediment from burned drainage basins. 

Additional wildfires in 2002 started after early July (fig. 1); 

however, these wildfires were not evaluated in this study.

The technical assessment focused on population centers 

and infrastructure affected by the wildfires. Pre-fire National 

Flood Insurance Program (NFIP) maps (where they exist) 

needed to be revised to reflect post-fire drainage-basin conditions. The technical response team, consisting of experts 

in hydrology, hydraulics, sediment transport, geomorphology, and geographical information system (GIS) mapping, 

used NFIP study data to evaluate post-fire changes to floodinundation maps where these data existed.

Purpose and Scope

The purpose of this report is to document analyses and 

mapping of post-fire hydrologic hazards for the 2002 Hayman, 

Coal Seam, and Missionary Ridge wildfires in Colorado. The 

wildfires in Colorado caused extreme changes in the hydrologic, hydraulic, and geomorphologic characteristics of the 

affected drainage basins. A rapid technical assessment of these 

changes was needed to evaluate their effects on flood plains, 

population centers, infrastructure, and transportation systems 

within and downstream from the burned areas. Accordingly, a 

three-phase hydrologic analysis was undertaken for the areas 

affected by the 16 Colorado wildfires that had burned or were 

burning as of July 2, 2002.

Phase 1.—Post-wildfire reconnaissance-hazard maps 

were created for analysis of the 16 Colorado wildfires 

identified as of July 2, 2002. Each map was produced at 

1:24,000 scale, and fire perimeter, fire intensity (if available), 

and other types of readily available information were depicted. 

These maps then were used to rank the relative priority of 

each of the wildfires in terms of anticipated hydrologic hazard 

(category 1 = high; category 2 = moderate; category 3 = low). 

These maps were developed for reconnaissance purposes only 

and are not included in this report. Category 1 wildfires were 

selected for detailed hydrologic analysis under Phase 2 of the 

study.

Phase 2.—Detailed hydrologic studies were conducted 

for the Category 1 wildfires, leading to the production of postfire flood- or debris-flow hazard maps for areas with existing 

National Flood Insurance Program (NFIP) maps and for other 

flood-prone areas where post-fire flooding could threaten 

downstream population centers or infrastructure.

Phase 3.—Phase 3 studies include analysis of longterm runoff characteristics that reflect post-fire drainagebasin recovery and stabilizing hydrologic conditions expected 

to develop over a period of several years after the wildfire. 

Past studies of post-fire hydrology indicate that a drainagebasin recovery period of about 5 years may be typical (Moody 

and Martin, 2001a; USDA Forest Service, 2002a). The longterm 100-year flood elevations from Phase 3 studies will be 

used by the FEMA for regulatory purposes.
Figure 1. Location of Colorado wildfires, 2002.

t

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Co ol rado

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EXPLANATION

Wildfire incident locations with

significant acreage burned

16 wildfire incident locations with

evaluated hydroanalysis

Meeker

Introduction 3
4 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Two specific study reaches were identified in which 

followup studies would be conducted to develop detailed 10-, 

50-, 100-, and 500-year flood-plain maps. These reaches are 

the South Platte River between Deckers and Trumbull, and 

Mitchell Creek in Glenwood Springs. Results from the study 

of the South Platte River between Deckers and Trumbull are 

included in this report. Hydraulic modeling and flood-plain 

mapping of Mitchell Creek are being completed as part of a 

separate project and are not covered by this report.

Acknowledgments

This study was conducted with interagency and interdisciplinary USGS collaboration and was authorized under 

Presidential Disaster Declaration FEMA_DR–1421, Colorado 

(a wildland fire disaster declared on June 19, 2002) due to 

extreme post-fire hazards and changes in flood plains and 

affected areas (http://www.fema.gov/news/dfrn.fema?id=712, 

accessed October 1, 2004). Because the study is being done to 

meet FEMA standards for flood-plain mapping, the data also 

will be used in the long term for National Flood Insurance 

Program mapping under the National Flood Insurance Act 

of 1968 and the Flood Disaster Protection Act of 1973. The 

funding for this study was provided by the President’s Disaster 

Relief Fund and under the authority of FEMA Region VIII. 

FEMA Region VIII staff provided the guidance and direction 

for this study.

The authors thank John Liou, FEMA project officer, 

for his assistance in this project; Ben Glass, Mickey Messer, 

Greg Smith, Dick Orr, and Bob Stull (USGS) for their help 

with onsite surveys and measurements used in the hydrologic 

and hydraulic analyses; and Sue Cannon and John Michael 

(USGS) for providing drainage-basin characteristics and preliminary estimates of potential debris-flow discharge magnitudes from severely burned areas. Jon Major (USGS) provided many helpful comments on the analysis of debris-flow 

hazards. Alexis Ellis and Jennifer Stefanacci (USGS) assisted 

with preparation of the overview and hazard mitigation maps. 

Technical reviews of an early draft of this report were made by 

Kathy Chase and Chuck Parrett.

Study Areas

The initial (Phase 1) study area included most of the 

mountainous and forested regions of Colorado. The 16 

wildfires that had burned or were burning as of July 2, 2002, 

ranged from the Trinidad Complex Fire in south-central 

Colorado, to the Pinyon Ridge Fire near Meeker in northwestern Colorado, to the Missionary Ridge Fire near Durango 

in southwestern Colorado (fig. 1). Three wildfires were 

determined to be Category 1 wildfires with high anticipated 

hazard and potential threat to infrastructure and life and were 

selected for additional, more detailed hydrologic assessments 

in Phase 2. Category 1 wildfires were the Hayman wildfire in 

the Colorado Front Range mountains southwest of Denver, 

the Coal Seam wildfire at the southern edge of the Flat Tops 

region and along the Colorado River near Glenwood Springs, 

and the Missionary Ridge wildfire in the southern San Juan 

Mountains near Durango. Each Category 1 wildfire is treated 

in a separate section that follows in this report.

Reconnaissance of 2002 Wildfires—

Phase 1

Major 2002 Colorado Wildfires through 

July 2, 2002

The 16 wildfires that had burned or were burning as 

of July 2, 2002, (fig. 1) listed in no particular order, are the 

following:

1. Hayman (137,760 acres)

2. Coal Seam (12,209 acres)

3. Missionary Ridge (70,485 acres)

4. Iron Mountain (4,439 acres)

5. Million (9,346 acres)

6. Spring Creek (13,493 acres)

7. Trinidad Complex (33,000 acres)

8. Bear (4,800 acres)

9. Black Mountain (200 acres)

10. Cuerna Verde (500 acres)

11. Dietrich/Miracle Complex (3,951 acres)

12. Pinyon Ridge (2,400 acres)

13. Schoonover (3,852 acres)

14. Snaking (2,590 acres)

15. Ute Pass (60 acres)

16. Wiley Ridge (1,084 acres)

The existing Colorado wildfires (as of July 2, 2002) 

were assessed during this study on the basis of areal extent 

and intensity of the wildfire, mapped infrastructure and 

inhabited areas, terrain, drainage networks, geology, and 

other information, when available. “Fire intensity,” used in 

the reconnaissance phase of the study, is contrasted with 

“burn severity,” used in the subsequent detailed hydrologic 

analyses. Fire intensity is related to fire behavior and the fire 

effect on overstory vegetation. Early estimates of fire intensity for the 16 wildfires were made on the basis of remotely 
sensed (satellite imagery) vegetation changes. Burn severity is 

specifically related to the effects of fire on soil conditions and 

hydrologic function, such as the amount of surface litter and 

duff, ash depth, soil structure and erodibility, hydrophobicity, and residual fuels (USDA Forest Service, 2002b, p. 109). 

Burn severities were estimated by the Burned Area Emergency 

Rehabilitation (BAER) teams, interagency groups formed to 

evaluate each wildfire.

Fire-intensity mapping was an integral layer on the 

reconnaissance hazard maps. Fire intensity was derived 

using remotely sensed Landsat Thematic Mapper (TM) and 

Enhanced Thematic Mapper Plus (ETM+) data and a technique called the Normalized Burn Ratio (NBR). NBR was 

developed for post-fire assessment by remote sensing on 

National Park Service lands by determining the difference 

between NBR data sets to enhance contrast and detection of 

wildfires through a scale of change from before fire (pre-burn) 

to after fire (post-burn) (Key and Benson, 2002). Pre- and 

post-fire Landsat images are used to calculate the NBR, an 

estimate of fire intensity ranging from low to high. Areas that 

are not affected by wildfire also are interpreted.

Potential hazards were associated with each burned area; 

however, 9 of the 16 wildfires were determined to have a lesser 

associated potential risk to infrastructure and life than the others and were excluded from additional evaluation in this study. 

These were the Bear, Black Mountain, Cuerna Verde, Dietrich/

Miracle Complex, Pinyon Ridge, Schoonover, Snaking, Ute 

Pass, and Wiley Ridge wildfires. Three wildfires received 

additional scrutiny after the initial assessment but also were 

found to have a lesser associated risk: the Iron Mountain, 

Spring Creek, and Trinidad Complex wildfires.

High-Priority Wildfires Selected for Detailed 

Hydrologic Analyses

Three wildfires were determined to have substantially 

greater potential hazards than the others, and areas affected by 

these wildfires were selected for additional Phase 2 analyses 

described in separate sections in this report. Detailed assessments of the hydrologic, hydraulic, and geomorphologic 

effects of these high-priority wildfires on burned and adjacent unburned parts of the drainage basins were made, and 

the effects of wildfire on runoff and sediment from burned 

drainage basins were analyzed. These were the Hayman 

(figs. 4, 5, 8–14), Coal Seam (figs. 17–19), and Missionary 

Ridge wildfires (figs. 20–22). Because of its proximity to the 

Hayman wildfire, the area burned by the Schoonover wildfire 

was combined with that of the Hayman wildfire in subsequent 

hydrologic analyses. A fourth wildfire, the Million wildfire, 

also was determined to have a greater potential flood hazard. 

Hydrologic assessment of the Million wildfire is being done 

in another USGS study and is not addressed in this report.

Hayman Wildfire Area

The Hayman wildfire (fig. 4) started in June 2002 near 

Lake George in the South Platte River Basin and burned 

approximately 138,000 acres (216 mi2). Elevations in the 

burned area ranged from 6,289 to more than 11,000 ft (USDA 

Forest Service, 2002a). The drainage area of the South Platte 

River just upstream from the confluence with the North Fork 

of the South Platte is about 2,580 mi2. The South Platte River 

flows from southwest to the northeast through the interior of 

the burned area. Perennial tributaries affected by the wildfire 

include Horse Creek, Fourmile Creek, Goose Creek, Wigwam 

Creek, West Creek, and Turkey Creek.

Cheesman Reservoir is a major impoundment on the 

South Platte River and is located near the center of the burned 

area. Strontia Springs Reservoir is another important impoundment on the South Platte River and is located downstream 

from the burned area. These reservoirs, owned and operated by 

the Denver Water Board, are important water-supply facilities 

for the Denver metropolitan area. Approximately 44 percent of 

the burned area drains into the South Platte River downstream 

from Cheesman Reservoir Dam, whereas about 56 percent of 

the burned area drains either directly into Cheesman Reservoir 

or into the South Platte River upstream from Cheesman 

Reservoir.

Most of the burned area is composed of shallow, easily eroded, weathered granitic soils from the Precambrian 

Pikes Peak batholith. The landscape is highly dissected in the 

upland forested part of the burned area. Annual precipitation 

is composed of snowfall during the winter and high intensity 

rainstorms during the summer. There are several roads, trails, 

and forest recreation sites within the burned area as well as a 

summer camp, recreation residences, and year-round residences (USDA Forest Service, 2002a).

Coal Seam Wildfire Area

The Coal Seam wildfire (fig. 17) started on June 8, 2002, 

near Glenwood Springs, Colorado, and burned approximately 

12,200 acres (19.1 mi2) and several homes. Elevations in the 

burned area ranged from 5,800 to 10,500 ft (USDA Forest 

Service, 2002b). Abundant, fine-grained sediment is available for debris-flow entrainment in the Coal Seam area. The 

sediment originates from tributaries underlain by weathered 

Paleozoic sedimentary rocks of the Maroon and other formations (Cannon, Michael, and Gartner, 2003; USDA Forest 

Service, 2002a). Infrastructure that survived the wildfire, 

including homes, businesses, the Municipal Operations Center, 

roads, bridges, and a railroad, is potentially threatened by 

subsequent flooding and debris flows. Flooding in Mitchell 

Creek, a major tributary entering the Glenwood Springs area 

from the north, is another potential hazard in the Coal Seam 

area. Approximately 25 percent of Mitchell Creek’s 11.9-mi2

drainage area was burned by the Coal Seam wildfire.

Reconnaissance of 2002 Wildfires—Phase 1 5
6 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Missionary Ridge Wildfire Area

The Missionary Ridge wildfire (fig. 20) burned 

from June 9 to July 14, 2002, and affected approximately 

70,500 acres (110 mi2) of Federal, State, and private land 

in La Plata County, Colorado. Elevations in the burned area 

ranged from approximately 6,500 to 11,400 ft (USDA Forest 

Service, 2002c). The wildfire destroyed several homes and 

other structures in three major drainage basins near Durango: 

the Animas, Florida, and Los Pinos River drainage basins. 

Approximately 61 percent of the area was burned with a moderate or high severity (USDA Forest Service, 2002c). Most of 

the area affected by the wildfire is underlain by sedimentary 

rocks including the Paleozoic Cutler and Hermosa Formations

and the Mesozoic Morrison Formation, which are known 

sources of debris-flow sediments (USDA Forest Service, 

2002c). Infrastructure that survived the wildfire, including 

homes, businesses, several major roads, bridges, and the dams 

at Lemon and Vallecito Reservoirs, is potentially threatened by 

subsequent flooding and debris flows.

Dominant Post-Fire Hazard Processes

Low-relief areas, valley floors, and alluvial fans in the 

Colorado mountains are subject to periodic flooding and 

debris flows; these processes become more severe after wildfires have devegetated the upland drainage basins, consumed 

organic litter, and changed the infiltration characteristics of the 

soil (Moody and Martin, 2001b). Stratigraphic evidence indicates that prehistoric forest fires in the Colorado Front Range 

and elsewhere have been followed by transport and deposition 

of large amounts of sediment in tributary and main-stem channels (Elliott and Parker, 2001).

The predominant potential hazard process in the Hayman 

wildfire area is flooding by sediment-laden water in the large 

tributaries to, and in the main stem of, the South Platte River. 

Although much sediment is available for erosion and transport 

by storm runoff in the Hayman area, there is little potential for 

debris-flow activity because the amount of silt- and clay-size 

material derived from the weathered parent rock is relatively 

small (S.H. Cannon, U.S. Geological Survey, oral commun., 

July 2002). The area is underlain by granitic material of the 

Pikes Peak batholith, a lithology whose weathering products 

are not associated with debris flows.

The other two high-priority burned areas are subject 

to debris-flow activity that could adversely affect life and 

infrastructure. The Coal Seam and Missionary Ridge wildfires burned in forests over geologic materials similar to those 

exposed by the 1994 South Canyon wildfire near Glenwood 

Springs. Debris flows that occurred after a summer thunderstorm soon after the South Canyon wildfire in 1994 blocked a 

1.2-mile length of Interstate 70 near Glenwood Springs. These 

debris flows were generated from basins adjacent to those 

burned in the 2002 Coal Seam wildfire (Cannon and others, 

1998, 2001). The marine shales exposed in formations within 

the Coal Seam and Missionary Ridge burned areas weather 

into fine-grain sediments including clays that are essential 

to the mobility and transport competence of debris flows 

(Griffiths and others, 1996).

Methods for Post-Fire Flood Hazard 

Analysis—Phase 2

The following section describes methods used to analyze potential hazards caused from flooding in perennial 

and ephemeral streams by sediment-laden water originating 

in burned areas. Methods used to analyze potential hazards 

from debris flows are described in a subsequent section 

of the report, “Methods for Post-Fire Debris-Flow Hazard 

Analysis—Phase 2.”

Short-Term Post-Fire Effects and Long-Term 

Recovery

Hydrologic responses are greatest immediately after a 

wildfire and persist for several years. As vegetation becomes 

reestablished, hydrophobic soil conditions change, organic litter accumulates on the land surface, and hydrologic conditions 

return to near pre-fire conditions. Both short-term hydrologic 

responses and long-term recovery hydrologic responses are 

evaluated in this study.

Short-term hydrologic responses have been defined on 

the basis of burned area and severity, and long-term hydrologic 

responses during the post-fire recovery period have been characterized on the basis of the pre-fire and post-fire conditions 

and streamflow data from two burned basins in New Mexico 

(Veenhuis, 2002).

Preparation of Digital Elevation Data

Many rainfall-runoff model parameters are extracted 

from the topography captured in digital elevation models 

(DEMs). Ten- or 30-m digital elevation model (DEM) data and 

Interferometric Synthetic Aperture Radar (IFSAR) 2.5-m data 

were prepared for this study. The source material for preparing 10-m DEM data is elevation contour lines (hypsography) 

from standard USGS 1:24,000-scale topographic maps. The 

USGS uses a software program named LT4X to process the 

digitally scanned source material (Infotek, 1993); this software 

calculates elevations for 10-m-square grid cells overlain on the 

hypsography map. Research has shown that a 10-m cell size 

is sufficient to capture all of the elevation information present 

on a 1:24,000-scale map (D.W. Litke, U.S. Geological Survey, 

oral commun., 2002). Elevations at cells located between 

contour lines are estimated using bilateral interpolation. The 
accuracy of the 10-m DEM elevation data is the same as the 

original hypsography data, which is plus or minus one-half of 

a contour interval. Contour intervals on maps in the study area 

generally are 40 ft in mountainous areas and 20 ft in flatter 

areas; therefore, the corresponding accuracy of an elevation 

value in the 10-m DEM is plus or minus 20 ft in mountainous 

areas and plus or minus 10 ft in flatter areas. The ground condition represented in the elevation data is that of the original 

orthophotography used to produce each 1:24,000 quadrangle 

map. In general, orthophotography for the study area was 

made from flights between 1950 and 1980.

IFSAR data provided by Intermap Technologies for

the Hayman burned area were used to develop a more accurate DEM. IFSAR is an aircraft-mounted sensor designed to 

measure surface elevation, which is used to produce topographic imagery. The sensor sends radar pulses to the Earth, 

which are received by two antennas that record elevations (z) 

at specific ground coordinates (x, y). The ground coordinates 

are determined by Global Positioning System (GPS) technology. The 2.5-m DEMs were then used to generate 10-ft 

contours of the study area for delineation of the 100-year 

flood plain. Shaded-relief imagery also was generated from 

the IFSAR DEMs to provide a visual base layer for various 

hazard-map products.

Rainfall-Runoff Model Calibration and 

Simulation

Measured streamflow information for most drainage 

basins and subbasins affected by the Hayman, Coal Seam, 

and Missionary Ridge wildfires were not available; therefore, hydrographs and peak discharges for pre- and post-burn 

conditions were simulated using a rainfall-runoff model. The 

ability of a rainfall-runoff model to provide reliable simulations depends on the adequacy of the conceptual model and 

model parameterization. Assuming that the conceptual model 

is adequate, model parameterization typically proceeds by 

assigning values to parameters that control the rate exchange 

of fluxes within the drainage basins and subbasins. Whereas 

parameters might be determined by relating them to observable characteristics of the drainage basin or subbasin, most 

model parameters are abstract conceptual representations of 

nonmeasurable characteristics that must be estimated through 

a calibration process.

Pre-Burn Model Calibration

Two model-calibration approaches were used to estimate the pre-burn parameter values in the course of this 

study: manual calibration and objective calibration based 

on nonlinear regression. Manual calibration of the Hayman 

rainfall-runoff model involved trial-and-error estimation of 

parameter values for all contributing basins and subbasins. 

The manual calibration approach was used in the initial 

Hayman modeling study (U.S. Geological Survey, written 

commun., 2003) and is described in Appendix 2.

Because two of the three basin parameter values being 

estimated are functions of a third unknown parameter value, 

the estimation problem is intrinsically nonlinear and difficult 

to solve using the manual approach. More problematic is that 

there is no way to ensure the optimal estimation of parameter 

values or to quantify the degree of uniqueness and(or) uncertainty associated with the estimated parameter values. For 

this reason, a second approach based on nonlinear regression 

(Doherty, 1998, 2001) was used to recalibrate the Hayman 

rainfall-runoff model; this approach is termed the objective 

calibration method. The objective calibration method was used 

exclusively to calibrate rainfall-runoff models for the Coal 

Seam and Missionary Ridge burned areas.

The objective calibration method was used to estimate 

pre-burn parameter values that minimized a predefined 

objective function. The predefined objective function was 

based on a least-squares formulation defined by the following 

equation:

�m wi

i = 1

N

� Qri� � t x y , , Qsi � – � � p � 2 = (1)

where Φm is a measurement objective function that is composed of the sum of weighted squared differences between 

regional and simulated estimates of peak discharge values Q; 

p is the vector of parameter values being estimated; r and s

are subscripts indicating regional and simulated values; N is 

the number of peak flood discharge measurements; and i is an 

index. The weights t, x, and y were chosen to be unity so that 

all measurements had the same influence on the estimation 

process. The actual number of measurement objective function 

terms used during the model calibration process is dependent 

on the number of measurements used to condition the inverse 

procedure.

Whereas the regional peak discharge values were determined using regional peak discharge equations (Vaill, 2000), 

the simulated peak discharge values were computed using the 

HEC–1 rainfall-runoff model (U.S. Army Corps of Engineers, 

1998). The HEC–1 model components were based on simple 

mathematical relations that were intended to represent the 

meteorologic, hydrologic, and hydraulic processes constituting 

the rainfall-runoff processes in the drainage basins. Meteorological input to the model was based on the 100-year recurrent 

rainfall defined by amount, duration, and cumulative density 

function; these data were available from the National Oceanic 

and Atmospheric Administration (NOAA) atlas (Miller, and 

others, 1973). By characterizing rainfall in this way, the rainfall was assumed to represent a basin or subbasin average; that 

is, the rainfall was assumed to be uniformly distributed over 

each basin or subbasin.

Methods for Post-Fire Flood Hazard Analysis—Phase 2 7
8 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Various basin and subbasin characteristics and model 

parameter values are required as input to the HEC–1 model 

to compute the hydrologic processes. Basin and subbasin 

characteristics were derived using GIS and included drainage 

area, length, and slope. Model parameter values that require 

estimation through a model calibration process—such as 

runoff-curve number, initial abstraction (an adjustment 

to precipitation that describes the amount of precipitation 

not expected to run off due to interception, surface-depression 

storage, evaporation, and other factors), and lag time—

were defined by the equations (Soil Conservation Service, 

1985):

Tlag L

0.8 � � S + 1 0.7

1 900 Y0.5 ,

-------------------------

� � � � � � = (2)

IA = S * 0.2 (3)

S 1,000

RCN

-------------

� � � � � � = – 10 (4)

where

Tlag

is the SCS lag time;

L is the hydraulic length of drainage basin, 

in feet;

S is the maximum retention in the drainage 

basin, in inches;

Y is the drainage basin slope, in percent;

IA is the initial abstraction;

and

RCN is the runoff-curve number for the drainage 

basin as defined by the SCS curve-number 

loss method.

On the basis of equations 1 to 4, sets of optimal pre-burn 

model parameters were estimated through an iterative process 

that minimized the measurement objective function (eq. 1) 

and simulated the resultant (calibrated) rainfall-runoff relation 

using HEC–1.

Post-Burn Adjustment of Model Parameters

The post-burn rainfall-runoff parameter values are 

determined by adjusting the runoff-curve numbers according 

to the observed burn conditions in each basin or subbasin. 

Typically this is done using a simple area-weighting procedure. However, because the relation between runoff-curve 

number and precipitation excess is nonlinear, area weighting tends to incorrectly account for small, severely burned 

areas (high RCN) within a basin or subbasin. In this study, 

the weighting procedure was based on the SCS equation for 

precipitation excess (Soil Conservation Service, 1985) and 

was designed to account for the combined effects of unburned, 

low burn, and medium-high burn areas within a basin or subbasin. The SCS equation for precipitation excess has the form:

Pe

P 0.2 1,000

RCN

------------- 10 – � � � � 2–

P 0.8 1,000

RCN

------------- 10 – � � � � +

= -------------------------------------------------- (5)

where

Pe is the precipitation excess, in inches;

P is the 100-year precipitation depth, in inches;

and

RCN is the runoff-curve number.

For basins or subbasins that included both burned (low, 

moderate, or high burn severity) and unburned areas, the postburn precipitation excess was computed assuming a linearweighted combination of runoff associated with burned and 

unburned conditions given by:

 Pe,subbasin = (Pe,u DAu) + (Pe,1 DA1) + (Pe,mh DAmh) (6)

where

Pe,subbasin is post-burn basin or subbasin precipitation 

excess, in inches;

Pe,u is precipitation excess for unburned area, in 

inches;

DAu is percentage of basin or subbasin drainage 

area unburned;

Pe,1 is precipitation excess for low-severity burned 

areas;

DA1 is percentage of basin or subbasin drainage 

area burned at low severity;

Pe,mh is precipitation excess for moderate- and 

high-severity burned areas;

and

DAmh is percentage of basin or subbasin area burned 

at moderate and high severity.

Initial abstraction values generally decrease as a result 

of moderate to severe burned conditions (URS Corporation, 

2000). In the SCS method, initial abstraction is a function of 

RCN. An RCN value of 95 produced an initial abstraction of 

0.11 inch; an RCN value of 98 produced an initial abstraction 

of 0.04 inch. Runoff data and field observations made by the 

USGS (Robert Jarrett, U.S. Geological Survey, oral commun., 2002) indicate that runoff in burned areas of the 1996 

Buffalo Creek wildfire and 2002 Hayman wildfire (as well as 

other wildfires in the Western United States) can occur with 

as little as 0.1 inch of rainfall, indicating that initial abstractions (especially where burned soils may be hydrophobic) 

may be less than 0.1 inch. In view of these observations, a 

lower limit (conservative) abstraction value of 0.04 inch was 
used for areas of moderate-to-high burn severity (based on 

an assumed RCN of 98). An RCN of 85 was assumed for 

areas of low-burn severity, and the pre-burn RCN (estimated 

by the pre-burn calibration process) was used for unburned 

areas. The assigned moderate-to-high burn and low-burn 

RCN values were based on BAER team reports (USDA Forest 

Service, 2002a, 2002b, 2002c) and consensus among experts 

from FEMA and State and local agencies (John Liou, Federal 

Emergency Management Agency; Tom Browning, Colorado 

Water Conservation Board; Garth Englund, Douglas County, 

Colorado; oral communs., 2003). The values of precipitation 

excess for moderate- and high-severity burned areas, lowseverity burned areas, and unburned areas were computed 

using equation 5.

Weighted, post-burn RCN values for individual basins 

and subbasins were computed by setting equations 5 and 6 

equal and solving iteratively for values of RCN. Using the 

post-burn RCN values, the associated initial abstraction and 

lag-time values were computed using equations 2, 3, and 4 for 

use in post-burn rainfall-runoff simulations. After the weighting and computation process was complete, the post-burn 

subbasin parameter values and associated GIS information 

were used as input to the HEC-HMS rainfall-runoff model 

for hydrograph generation (U.S. Army Corps of Engineers, 

2001b). HEC-HMS is a widely accepted, public-domain 

rainfall-runoff model commonly used by FEMA to conduct 

detailed rainfall-runoff analyses.

Sediment Bulking of Estimated Discharge

Studies of post-fire hydrology in the Western United 

States have shown that sediment loads can increase substantially during flooding in burned drainage basins (O’Brien and 

Fullerton, 1989; Moody and Martin, 2001a). The physical 

behavior of combined water-and-sediment flows depends on 

the concentration of sediment. Several investigators have identified a sediment-concentration limit of 20 percent by volume, 

up to which a water-sediment mixture has the characteristics 

of purely water flow. At volumetric concentrations greater 

than 20 percent, the mixture has the characteristics of a hyperconcentrated flow (mud flood) or a debris flow (mudflow) 

(Pierson and Costa, 1987; Costa, 1988; O’Brien, 2001).

Computed water-peak discharges from the HEC-HMS 

modeling were bulked, or increased volumetrically, to account 

for increased sediment concentrations that are expected to 

occur as a result of accelerated erosion after burning. Bulking 

analyses and computations were based on previous studies of post-fire runoff in other areas of the Western United 

States, and on published research documenting the physical 

behavior of combined water and sediment flows (Pierson and 

Costa, 1987; Costa, 1988; O’Brien, 2001). The amount of 

sediment bulking varied in the study, depending on whether 

predominantly water floods or debris flows were anticipated 

in response to the 100-year storm.

Water-Flow Routing and Computation of Flood 

Elevations

Hydrologic routing of flood hydrographs down mainstem channels was performed using routing algorithms 

included in the HEC-HMS rainfall-runoff model. Hydrologic 

routing methods used in each model (including Muskingum, 

Muskingum-Cunge, and Modified Puls reservoir routing) are 

discussed in greater detail in subsequent sections of the report 

covering the post-fire hydrologic hazards for the Hayman, 

Coal Seam, and Missionary Ridge wildfires.

Post-fire flood elevations were computed for bulked peak 

discharges at selected cross-section locations in each reach 

of the South Platte River, and the resulting flood plain was 

delineated on a topographic map. Flood boundaries between 

cross sections were interpolated by hydrologists and mapping experts. The accuracy of these interpolations depends on 

the available map scale and the cross-section spacing in each 

study area.

Delineation of the 100-Year Flood Plain

Delineation of the revised 100-year flood plain of the 

South Platte River (Phase 2 analysis) incorporated IFSAR 

elevation data and the simulated discharge values for the 

burned drainage basins and subbasins. The USGS surveyed 

and monumented representative cross sections through the 

study reach, spaced 1 to 2 mi apart. Post-fire, 100-year flood 

levels were computed for each cross section using the normaldepth computation method in the Quick-2 computer program 

(Federal Emergency Management Agency, written commun., 

2003). Interpolation of the flood plain between surveyed 

cross sections was based on the contours generated from the 

2.5-m IFSAR elevation data to generate the 100-year flood 

plain polygon using ArcGIS Spatial Analyst (Environmental 

Systems Research Institute, 2004).

Methods for Post-Fire Debris-Flow 

Hazard Analysis—Phase 2

The following section describes methods used to analyze potential hazards caused by debris flows originating in 

burned areas. Methods used to analyze potential flooding by 

sediment-laden water are described in the section “Methods 

for Post-Fire Flood Hazard Analysis—Phase 2.”

Debris-Flow Mechanisms

Wildfire can have profound effects on a drainage basin 

through the consumption of the rainfall-intercepting canopy 

and the soil-mantling litter and duff and through the formation 

of water-repellent soils. These changes can result in decreased 

Methods for Post-Fire Debris-Flow Hazard Analysis—Phase 2 9
10 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

rainfall infiltration into the soil and, subsequently, a significant 

increase in overland flow and runoff in channels. Removal 

of obstructions by wildfire can enhance the erosive power of 

overland flow, resulting in accelerated erosion of material from 

hillslopes. Increased runoff also can erode substantial volumes 

of material from channels, the net result being the transport 

and deposition of large volumes of sediment both within and 

downstream from the burned area (Cannon, 2001).

Flow and fluid properties gradually begin to change 

with increasing sediment concentration. Sediment-particle fall 

velocity decreases, and fluid density and viscosity increase. The 

upper limit of sediment concentration, by volume, in a typical 

“water flood” is 20 percent (Costa, 1988). Volumetric sediment 

concentration in a “hyperconcentrated flow” ranges from 20 

to 47 percent (Costa, 1988). Rapid runoff with extremely high 

concentrations of entrained sediment (47 to 77 percent, Costa, 

1988) is known as a “mudflow” or “debris flow.” Mudflows 

are runoff events with no more than 50 percent of the sediment 

coarser than gravel size (particle intermediate diameter greater 

than 2.0 mm, or 0.079 inch) (Varnes, 1978). Because most 

runoff events in rugged areas with a high sediment concentration transport sediment particles ranging in size from clay to 

boulders, the term “debris flow” is used in this study.

Debris flows are produced frequently in response to 

summer convective thunderstorm activity over drainage basins 

burned by wildfire (Cannon, 2001). Debris flows pose a hazard 

distinct from other sediment-laden flows because of their 

unique destructive power; debris flows can occur with little 

warning and can exert great impulsive loads on objects in their 

paths. Even small debris flows can strip vegetation, block drainageways, damage structures, and endanger human life (Cannon, 

Michael, and Gartner, 2003). Debris-flow peak velocities are 

dependent on flow depth and can range from 3 to 30 m/s (10 to 

100 ft/s) (Hungr and others, 1984; Pierson and Costa, 1987).

Debris-flow behavior is dependent on the concentration and particle-size range of the entrained sediment (Costa 

and Jarrett, 1981) and on the relative proportion of inertial 

and viscous forces (Pierson and Costa, 1987). A relatively 

high proportion of clay-size particles (particle diameter less 

than 0.004 mm, or 0.0002 inch) in the transported sediment 

increases debris-flow matrix strength and helps maintain the 

high pore pressure necessary to support larger particles in the 

flow (Griffiths and others, 1996).

The volumetric sediment concentration (Cv) is difficult 

to measure precisely and varies during a debris-flow event. 

Several researchers have estimated or calculated concentration ranges for different periods during a debris flow. Pierson 

and Scott (1985) reported mean Cv greater than 57 percent 

in volcanic lahar-derived debris flows. Pierson and Scott 

also reported mean Cv of 30–35 percent and a maximum Cv

of 37 percent in non-Newtonian hyperconcentrated flows. 

Pierson and Costa (1987) observed the range of mean Cv

between 20 and 60 percent for hyperconcentrated flows. 

O’Brien (J.S. O’Brien, FLO Engineering, Inc., oral commun., December 2002) assumes a mean Cv

 of between 30 

and 35 percent for debris flows, a maximum Cv of between 

45 and 53 percent, and a Cv between 40 and 45 percent at the 

water hydrograph peak when calibrating the FLO-2D twodimensional flood-routing model (FLO-2D; O’Brien, 1993, 

2001) used for debris-flow analysis in this report.

Cannon and others (2003a and 2003b) categorized the 

potential debris-flow peak-discharge in the Coal Seam and 

Missionary Ridge burned areas on the basis of a regression 

equation developed from data measured in previously burned, 

mountainous areas (Cannon, 2001). These peak discharge 

categories, existing infrastructure, and input from local 

authorities were used to prioritize drainage basins for the 

further debris-flow analysis described in this report. This study 

includes a select group of tributaries to illustrate the potential 

for debris-flow inundation on existing alluvial fans and lowgradient features such as valley floors and flood plains. Other 

tributaries not included in this study also have the potential to 

produce floods and debris flows that could do great damage to 

other types of infrastructure, such as roads, bridges, railroads, 

utility lines, and isolated structures.

Post-Fire Debris-Flow Peak Discharge 

Estimates

Cannon (2001) developed a multiple regression model 

to define the range of potential peak discharges generated by 

post-fire debris flows. Cannon and others (2003) and Cannon, 

Michael, and Gartner (2003) revised the relation by using data 

measured from 49 burned drainage basins located throughout 

the Western United States; of these basins, 7 were in the Coal 

Seam burned area and 10 were in the Missionary Ridge burned 

area. The regression model relies on indirect peak discharge 

measurements (computed using either slope-area, critical flow, 

or super-elevation techniques from field surveys) and consists 

of a physical representation of peak discharge relative to average rainfall intensity (Qp

/I) as a function of basin gradient and 

burned extent where Qp is the peak discharge (in cubic meters 

per second) and I is the average storm rainfall intensity (in 

meters per second). The slope-area method for determination 

of peak discharge generally is not assumed to be applicable 

for non-Newtonian debris flows; however, it does allow for at 

least a relative measure of the debris-flow response of burned 

drainage basins. For the steep basins and hillslopes from 

which Cannon’s measurements were made, it generally was 

assumed that the discharges estimated using this approach are 

conservative in the context of engineering design (Cannon and 

others, 2003; Cannon, Michael, and Gartner, 2003).

All debris flows in Cannon’s analysis were reported to be 

triggered by summer convective thunderstorms. Although the 

adjusted R2 of 0.34 for Cannon’s relation indicates significant scatter in the data used in the regression, and thus great 

uncertainty in the predicted values, Cannon and others (2003) 

and Cannon, Michael, and Gartner (2003) used the relation 

to estimate potential debris-flow peak discharges for several 

tributaries in the Coal Seam and Missionary Ridge burned 

areas on the basis of measured gradient extracted from 10-m 
DEMs and estimated rainfall. The peak debris-flow discharge 

estimates were used in this study to help rank tributaries for 

additional analysis.

Debris-Flow Modeling in Colorado Wildfire 

Areas

A two-dimensional flood-routing model (FLO-2D; 

O’Brien, 1993, 2001) was used to delineate the area of 

unconfined debris-flow inundation on selected alluvial fan 

and valley floor areas in the Coal Seam and Missionary Ridge 

wildfire areas. FLO-2D was used in this analysis at the request 

of FEMA. The model uses a specified input hydrograph, 

volumetric sediment concentration, and existing topography 

to route a debris flow from the originating tributary to the 

depositional zone.

The HEC-HMS rainfall-runoff model (U.S. Army Corps 

of Engineers, 2001b) was used to generate the FLO-2D input 

hydrograph from burned drainage basins. Sediment concentration of the debris flow was estimated on the basis of results from 

previous studies (Pierson and Scott, 1985; Pierson and Costa, 

1987; Costa, 1988; O’Brien, 2001). Topography of the debrisflow channel and alluvial fan area was extracted from 10-m 

DEMs prepared by the USGS. Model output is spatially and 

temporally varied and includes maximum depth and velocity.

Simulated flood and debris-flow discharges presented in 

this study were generated by 100-year rainfall events; however, the 25-year rainfall may be more representative of storms 

that generated debris flows in Cannon’s regression equation 

(Susan H. Cannon, U.S. Geological Survey, oral commun., 

2003). O’Brien (J.S. O’Brien, FLO Engineering, Inc., oral 

commun., 2002) notes that the 100-year storm may generate too much water relative to available sediment to produce 

debris flows, and that storms of less than a 25-year recurrence 

interval may not result in enough runoff to move a substantial

volume of sediment from source areas to the alluvial fan.

Debris flows from some subbasins in this study were 

simulated with the 25-year storm for comparison to the 

100-year storm. Simulated debris-flow inundations from the 

25-year storms were nearly indistinguishable from 100-year 

storm debris-flow inundations. Consequently, runoff from the 

100-year rainfall was used in this analysis for comparison to 

flood estimates from the Hayman and Mitchell Creek studies.

Debris-Flow Routing with FLO-2D

FLO-2D (O’Brien, 1993, 2001) was used to delineate 

the area of unconfined debris-flow inundation on selected 

alluvial fan and valley floor areas in the Coal Seam and 

Missionary Ridge areas. FLO-2D was used in several earlier 

studies to simulate debris flows in Telluride, Ouray, Aspen, 

Basalt, Glenwood Springs, and Colorado Springs, Colorado; 

Centerville, Utah; and along the north coast of Venezuela 

(O’Brien, 2001, p. 73–80).

As applied in this study, the FLO-2D model routes 

the water and sediment emanating from a burned tributary 

drainage basin onto an unconfined alluvial fan or flood-plain 

surface. FLO-2D conserves the hydrograph volume, predicts 

flood-wave attenuation, and predicts the area of inundation 

while routing the unconfined debris flow over nonuniform 

topography and roughness elements. The model uses either 

the diffusive-wave or the full dynamic-wave versions of the 

momentum equation. Model time steps are governed by 

wave celerity and are incremented according to flood-routing 

numerical stability criteria. Numerical stability is linked to 

flood-volume conservation. Model output is spatially and temporally varied. Maximum depth, velocity, and discharge can be 

reviewed numerically or graphically for the entire inundation 

surface or by the individual grid elements.

The FLO-2D model requires a representation of the 

potential flow-surface elevation in a square grid format; 

however, the USGS DEM map format is not directly readable 

by FLO-2D. Consequently, the 10-m DEMs were converted 

into an ArcGIS (Environmental Systems Research Institute, 

2002) GRID format that is readable by FLO-2D. The GRID 

data sets were then subdivided into subsets for each area to 

be modeled using ArcGIS software. Output from the ArcGIS 

software included an ASCII point file of elevation data in the 

form of [x-location, y-location, z-elevation] and a georeferenced tagged image format (TIF) file of a portion of the USGS 

topographic map for each area to be modeled. These data 

sets were then loaded into the Grid Developer System (GDS) 

module of FLO-2D. The GDS was used to prepare the model 

grid files (CadPTS.DAT and FPlain.DAT) that are used in the 

FLO-2D model.

The inflow hydrograph at the alluvial fan head or 

tributary mouth was generated with the objective calibration 

method described in the section “Methods for Post-Fire Flood 

Hazard Analysis—Phase 2.” The 100-year, 1-hour storm was 

used to simulate debris flows. For the Coal Seam area, the 

100-year, 1-hour rainfall was 1.64 inches. For the Missionary

Ridge area, the 100-year, 1-hour rainfall was 1.77 inches 

(Miller and others, 1973).

Drainage-basin geomorphic characteristics were derived 

with GIS methods by using the 10-m DEMs. Burned area and 

burn severity were taken from the BAER reports for the Coal 

Seam and Missionary Ridge areas (USDA Forest Service, 

2002b and 2002c). An RCN for each delineated drainage basin 

was computed by area weighting the subbasin RCNs (percentage of area in each burn-severity category observed in the subbasin) and deriving a composite RCN from SCS equations 5

and 6.

The rheological properties (deformation and flow 

behavior) of debris flows are extremely sensitive to changes 

in sediment concentration (Major, 1993). Debris flows and 

hyperconcentrated flows are simulated in the FLO-2D model 

by assuming viscosity and yield-stress relations are a function of volumetric sediment concentration (Cv

). Based on the 

Methods for Post-Fire Debris-Flow Hazard Analysis—Phase 2 11
12 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

post-fire assessments by Cannon (Cannon and others, 2003; 

Cannon, Michael, and Gartner, 2003), tributary subbasins were 

assumed to contain an abundant supply of sediment, and most 

of the sediment was assumed to originate from in- and nearchannel erosion rather than from landsliding or mass failure 

into the flow path.

The sediment concentrations used in simulations at 

Coal Seam and Missionary Ridge are based on results from 

previous studies (Pierson and Scott, 1985; Pierson and Costa, 

1987; Costa, 1988; O’Brien, 2001). Post-fire runoff was not 

bulked with sediment before being input into the FLO-2D as 

it was for the water floods described elsewhere in this report. 

The assumed volumetric concentrations for the input debrisflow hydrograph were varied through the event, and for this 

study, they were initial Cv 20 percent, mean Cv approximately 

31 percent, maximum Cv 48 percent (preceding the input water 

hydrograph peak), Cv at the time of the input water hydrograph peak 43 percent, and Cv

 for the duration of the event 

20 percent. Examples of runoff and sediment-concentration 

hydrographs used in the debris-flow simulations are presented 

in figure 2.

FLO-2D treats debris-flow composition as a temporally and spatially unvarying mixture; coarse material does 

not settle out during the simulation as it does in actual mud 

and debris flows. When the input sediment concentrations 

are decreased in FLO-2D, the debris-flow mixture travels 

a farther distance down a fan or valley; when concentrations are increased, the debris flow travels a shorter distance 

before stopping.

Interpretation of FLO-2D model output is limited by 

several factors. The FLO-2D model is a quasi-two-dimensional 

model and, although often used in unconfined flow situations, 

only routes flow in a downslope direction toward the nearest 

neighbor grid cell rather than in a truly lateral or transverse 

direction. Outflow from one square grid element into an adjacent 

square grid element is limited to eight possible directions (N, 

NE, E, SE, S, SW, W, NW). Model output is limited by the 

resolution of the topographic data supplied; in this study, 10-m 

digital elevation data. Most roughness elements less than 10 m,

or 32.8 ft, in size are not accounted for. Also, the original topography remains static during a model run and is insensitive to 

large-scale channel scour or aggradation. Small-scale differences 

in grid-cell elevation values influence the direction of cell-to-cell 

flow propagation. Errors in the input elevation values or changes 

in elevation over time, such as from land use or subsequent 

debris-flow deposition, could render the existing model output 

inaccurate.

Inundation areas and depositional depths generated in 

these FLO-2D simulations reflect the median of predicted 

values. Minimum and maximum likelihood areas and depths are 

not presented in the model output, and there is large, unquantified variability in the expected outcome of the 100-year storm. 

Another limitation of the analyses is that estimated inundation areas and depths from the model output are not verifiable. 

No post-fire data exist at this time with which to compare the 

FLO-2D simulations; however, future debris flows from areas 

within the Missionary Ridge and Coal Seam burned areas where 

precipitation gages are operating may facilitate verification.

Figure 2. Example of pre- and post-burn runoff hydrographs and sediment-concentration hydrograph 

used in debris-flow modeling, 100-year, 1-hour storm.

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Post-Fire Flood and Debris-Flow Hazard Maps

Various map products were created for the three 

burned areas determined to have high priority in the Phase 1 

assessment—the Hayman, Coal Seam, and Missionary Ridge 

wildfires (see figs. 1, 4, 17, 20). The maps were compiled 

using the following raster data sources: 1-m imagery from 

the 133 Urban Area Initiative, USGS Digital Raster Graphics 

(DRG), 2.5-m IFSAR elevation data, USGS 30-m National 

Elevation Data (NED), and USGS 10-m DEMs. Vector data 

that complemented the raster data sets include the 100-year 

cross-section and flood-plain vectors, debris flow/alluvial fan 

data sets, fire perimeters, USGS transportation and hydrography data, and public-land survey reference data. The scale 

of the map determined the type of base layer imagery to be 

used in the map product. NED or USGS DRGs were used as 

background images on small-scale maps, depicting the entire 

extent of the wildfire (see figs. 4, 5, 17, 20). The large-scale 

maps used 1-m color imagery from the 133 Urban Area 

Initiative as the background layer (see figs. 12, 13, 14, 18, 19). 

At this scale the user can view potential structures at risk in 

the revised 100-year flood plain.

Method for Determination of Drainage 

Basin Recovery—Phase 3

Hydrologic responses during the post-fire recovery period 

are estimated in this report for the Hayman and Coal Seam 

burned areas based on the following assumptions:

1. A wildfire will raise the RCN in a burned drainage basin 

from a pre-fire RCN to a post-fire RCN as a function of 

burned area and severity.

2. During the recovery period, the value of the larger postfire RCN will attenuate with time and eventually approach, or 

decay to, the value of the smaller pre-fire RCN.

3. Although it is recognized as a simplification, for the purposes of this report, recovery will be characterized as a decay 

function that reduces the post-fire RCN with time.

4. Initial decay will be the most rapid and will take place as 

a function of the magnitude of the pre-fire RCN and the difference between pre- and post-fire RCNs.

Pre- and post-fire RCNs were estimated for all subbasins in the Hayman and Coal Seam burned areas for use in 

the HEC-HMS model as described in the “Rainfall-Runoff

Model Calibration and Simulation” section. Although very few 

systematic field data exist that characterize post-fire recovery, 

Veenhuis (2002) provides a nearly complete description of postfire drainage-basin recovery in the Frijoles Canyon at Bandolier 

National Monument, New Mexico, on the basis of streamflow 

data collected in a burned area. The data indicate that the 

magnitude and frequency of post-fire flood peaks both decayed 

with time and that most of the decay occurred in 5 to 10 years; 

however, the report states that flood magnitudes remained above 

pre-fire levels 22 years after the wildfire. These results were

used in the Hayman and Coal Seam wildfire recovery characterizations developed for this analysis as the general framework 

for a post-fire recovery equation that is a function of initial 

RCN, change in RCN (due to wildfire), and time. The equation 

has the form of an exponential decay equation:

CNt = PCN + (DCN) e (-t/TC) (7)

where

CNt is RCN at time t in the recovery period,

PCN is pre-fire RCN number,

DCN is post-fire RCN minus PCN,

TC is a function of pre-fire RCN,

and

t is time, in years.

Equation 7 can be used to estimate an RCN at any point in 

the recovery process. In this analysis, equation 7 was used 

to develop estimates for parameters used in the HEC–1 and 

HEC-HMS models, and the models were then used to develop 

a time series of annual flood peaks of the 100-year design 

storm to characterize long-term recovery.

An example discussing the results from equation 7 is 

helpful to indicate how the equation was used in this analysis. Figure 3 indicates a family of curves generated with 

equation 7 that begin at the y-axis and intersect or closely 

approach the x-axis. These curves are RCN estimates for a 

recovery period beginning with post-fire conditions and continuing for 50 years in a hypothetical drainage basin with an 

assumed pre-fire RCN of 50, raised to post-fire RCNs of 55 to

100 in increments of 5. The first, or lowest, curve in figure 3

is for a drainage basin burned and raised to a post-fire curve 

number of 55. Likewise, the second curve shows the estimated 

response for a drainage basin burned and raised to a postfire RCN of 60, and so on. In figure 3, the third curve from 

the top indicates RCN recovery for the hypothetical burned 

drainage basin having a post-fire RCN raised to 90. The curve 

intersects the y-axis at 90 and indicates that after 5 years it is 

estimated the RCN would recover from 90 to about 68, about 

a 55-percent reduction of the RCN increase attributed to this 

hypothetical wildfire.

In this report, “long-term recovery” is used to indicate an 

estimate of the period of time it takes for post-fire hydrologic 

responses to stabilize or reach a point where change occurs at a 

relatively slow and steady rate. In order to obtain an estimate of 

long-term recovery in each wildfire area, equation 7 was used to 

determine values for RCN for all subbasins for a period beginning with post-fire conditions and continuing through 50 years. 

For this exercise, pre-and post-fire RCNs in the Hayman and 

Coal Seam wildfire areas used in equation 7 were obtained 

using methods described in the “Rainfall-Runoff Model 

Calibration and Simulation” section. Initial abstractions were 

calculated on the basis of RCN by using equation 3, and lag 

times were calculated using equation 2.

Method for Determination of Drainage Basin Recovery—Phase 3 13
14 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

The calculated values for RCN, initial abstraction, and 

lag times were used to prepare batch input for the HEC–1 

model and obtain a time series of 100-year storm flood-peak 

estimates, on the basis of the 100-year storm, in the Hayman 

and Coal Seam burned areas. The resultant time-series values 

were evaluated to identify a time in the recovery process when 

the change in estimated 100-year flood peak became less than 

5 percent, per year, of the RCN change due to wildfire. Estimates were made for three locations: two represent outlets for 

the burned areas upstream and downstream from Cheesman

Reservoir for the Hayman wildfire, and a third represents the 

burned area of Mitchell Creek for the Coal Seam wildfire. 

Although the times determined here do not represent the time 

to full recovery, they will be referred to, for convenience, as 

long-term recovery times. The long-term recovery times were 

rounded to the nearest whole year and used as the basis to prepare input for HEC-HMS to obtain estimates of the 100-year 

flood peak at the recovery time for the three outlet locations.

The estimated periods for long-term recovery are 

6 years for the South Platte River upstream from Cheesman 

Reservoir, 6 years for the South Platte River downstream from 

Cheesman Reservoir, and 4 years for Mitchell Creek. Times in 

this range are consistent with BAER-team estimates of about 

5 years to recovery due to the mitigating effects of vegetation reestablishment (USDA Forest Service, 2002a and b), 

and with field observations from the USGS National Research 

Program of about 3 to 7 years at drainage basins affected by 

other wildfires near the Hayman burned area (Robert Jarrett, 

U.S. Geological Survey, oral commun., February 2004). Additional details about the results of the HEC-HMS simulations 

are described in the sections “South Platte River Hydrology and 

Peak Flow Modeling for Long-Term Recovery—Phase 3” and 

“Mitchell Creek Hydrology and Peak Flow Modeling for LongTerm Recovery—Phase 3.” Finally, it is important to note, as 

suggested in the initial assumptions, that recovery is only generally a function of time. In reality, recovery is likely a complicated function of many variables such as storm characteristics 

(frequency, magnitude, and intensity), storm distribution, and 

vegetation reestablishment in the years following a wildfire.

Post-Fire Hydrologic Hazards for the 

Hayman Wildfire

South Platte River “Limited-Detail” Hydrologic 

Analysis—Phase 2

Post-fire hydrologic analyses were conducted to evaluate 

the effects of the 100-year peak flow on burned and adjacent 

unburned areas of the South Platte River Basin. Overview and 

index maps of the Hayman wildfire area are shown in figures 4

and 5, oversized maps that accompany this report. Analyses 

were designed to characterize increased runoff produced by 

Figure 3. Estimated recovery curves for runoff-curve numbers in a drainage basin with a 

pre-burn runoff-curve number of 50. Plotted curves represent estimated post-burn response 

of runoff-curve numbers 55 through 100, incrementing by 5.

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rainstorms within and near the fire perimeter and to reflect 

drainage-basin conditions that are expected to exist during the 

next several years (before substantial regrowth of vegetation 

in the burned areas). The results of these analyses (known to 

FEMA as a “Limited Detail Analysis”) were used to delineate 

a hazard-mitigation map for post-fire, 100-year flooding of the 

South Platte River. The map, shown in figures 12, 13, and 14, 

characterizes runoff conditions over the short term (approximately the first 6 years after the 2002 wildfire) and will not be 

used for regulatory purposes (John Liou, Federal Emergency 

Management Agency, oral commun., 2003).

Long-term hydrologic analysis reflecting more stable 

drainage-basin conditions (after a recovery period of approximately 6 years) and a more detailed hydraulic analysis (using 

step-backwater modeling routines) also have been made for 

the South Platte River Basin. Results of these analyses are 

presented in later sections of this report.

The approach to the post-fire “limited-detail” hydrologic 

analyses included the following steps and assumptions:

1. Inflow conditions were established for the South Platte 

River at the upstream boundary of the burned area and for the 

South Platte River downstream from Cheesman Dam.

2. A rainfall-runoff model was developed for pre-fire 

(unburned) conditions in the affected subbasins tributary to 

the South Platte River. Model parameters for runoff generated 

by the 100-year, 6-hour rainstorm (2.4 inches) were calibrated 

on the basis of regional estimates of computed 100-year peak 

discharge at selected stream-gage sites in the study area.

3. Peak discharges associated with the 100-year, 6-hour 

storm were simulated for post-fire conditions in burned subbasins tributary to the South Platte River. Hydrologic routing 

was used in the larger, multibasin drainages.

4. Peak discharges for burned subbasins were increased 

using a bulking factor to reflect the increased runoff volume 

due to large sediment loads.

5. Bulked peak discharges for selected reaches of the South 

Platte River (within and downstream from the burned area) 

were computed using a hydrograph routing algorithm.

Two rainfall-runoff calibration methods were used in 

the Hayman burned-area analysis: manual calibration and 

objective calibration. Initial model calibration was done using 

manual adjustment of drainage-basin parameters to produce a 

target 100-year peak discharge for each subbasin at the point 

of confluence with the South Platte River. Results of the manual calibration method, including the simulated 100-year peak 

discharges used to develop short-term (hazard-mitigation) 

flood maps, are described in Appendix 2.

The objective calibration method was used for the 

analysis of drainage basin-recovery (long term) conditions. 

The objective calibration method was developed subsequent 

to completion of the short-term flood-hazard assessment and 

is considered to be unbiased and more robust than the manual 

calibration method. Results from the objective calibration 

method are presented in this section.

South Platte River Inflow Conditions

The South Platte River within and downstream from 

the Hayman burned area is regulated by a series of reservoirs 

owned and operated by the Denver Water Board. In order to 

assess the effects of the 100-year storm and subsequent flooding on burned and adjacent unburned areas of the South Platte 

River Basin, boundary flow conditions were needed at the 

upstream edge of the fire perimeter and at the outflow from 

Cheesman Dam. Boundary flow conditions were established 

as follows.

Upstream Edge of Fire Perimeter.—Because of the large 

contributing drainage area of the South Platte River Basin 

upstream from the wildfire area (figs. 4 and 5) and the substantial regulation/storage capacity of upstream reservoirs, it is 

extremely unlikely that a 100-year flood would occur throughout the entire drainage basin during a single runoff event. To 

account for potential antecedent runoff and reservoir releases 

into the burned area, a 10-year peak discharge was selected as 

the boundary inflow condition. The 10-year peak discharge 

for streamflow-gaging station 06696000 (South Platte River 

near Lake George; drainage area 963 mi2; period of record 

1933–98 since completion of Elevenmile Canyon Reservoir) 

is 840 ft3/s. Adjustment of discharge for contributing drainage 

area between the gage and the Hayman fire perimeter using a 

relation developed by Vaill (2000) resulted in a 10-year peak 

discharge of 940 ft3/s. A similar analysis was used to compute the pre-burn discharge for Tarryall Creek, which also is 

regulated. The computed 10-year peak discharge was 715 ft3/s 

(Tarryall Creek near Lake George). Tarryall Creek flows into 

the burned area of the Hayman wildfire and was treated as a 

boundary inflow point.

Outflow from Cheesman Dam.—Cheesman Reservoir 

is operated as a water-supply reservoir for the City of Denver. 

It is not designated for flood control, so hydrologic analysis 

of the 100-year flood assumes fill-and-spill operation of the 

dam. That is, the reservoir is allowed to fill to capacity, then 

freely spill excess over the spillway. Based on discussions with 

staff of the Denver Water Board (Robert Steger, Denver Water 

Board, oral commun., 2003), the following boundary conditions at Cheesman Dam were used:

1. Reservoir full, with uncontrolled flow over the spillway 

in response to upstream runoff.

2. Outlet works (release capacity 1,400 ft3/s) closed.

3. Spillway (release capacity 22,370 ft3/s) passes the entire 

flood (subject to peak attenuation by the reservoir).

4. Peak flow over the spillway is the inflow boundary condition for modeling of the South Platte River downstream from 

the dam. Outflow from Cheesman Dam is assumed to contain 

no sediment.

Cheesman Reservoir could be filled with water at any 

time after the 2002 wildfire in response to either operational 

considerations (Cheesman evaporation rates are smaller than 

Post-Fire Hydrologic Hazards for the Hayman Wildfire 15
16 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

upstream reservoirs on the South Platte River Basin) or natural 

runoff. As a result, both short-term (hazard-mitigation) and 

long-term modeling scenarios reflect a full-reservoir condition. 

The Modified Puls reservoir routing routine in HEC-HMS 

was used to route the computed flood hydrograph through 

Cheesman Reservoir and over the spillway to the downstream 

reach.

South Platte River Tributary Rainfall-Runoff 

Modeling

Because the study reach of the South Platte River is 

affected by flow regulation (Elevenmile Canyon and Cheesman

Reservoirs), flood-frequency analyses of streamflow-gaging

stations on the South Platte River were not used. Instead, 

rainfall-runoff modeling was used to develop post-fire hydrographs for 19 selected drainage basins (subbasins) tributary 

to the South Platte River within and downstream from the 

Hayman burned area. These 19 subbasins and an additional 

22 minor contributing subbasins were delineated using a 30-m 

DEM. The U.S. Army Corps of Engineers (USACE) HECHMS computer model (U.S. Army Corps of Engineers, 2001b) 

was used for the analysis along with the 100-year, 6-hour storm 

(2.4 inches). The 100-year, 6-hour storm also was used by the 

USACE for hydrologic analysis of the 2000 Cerro Grande

wildfire in New Mexico (URS Corporation, 2000).

Rainfall-Runoff Model Methodology for the Hayman 

Wildfire

Rainfall-runoff modeling was conducted in two steps to 

simulate (1) preburned or unburned conditions, and (2) burned 

conditions.

Step 1, Modeling of Unburned Conditions, South Platte River 

Tributaries

The runoff hydrograph for the 100-year peak discharge 

was developed for natural, unburned conditions of each subbasin. Because streamflow data for most subbasins were not 

available, a hydrograph and peak discharge for each tributary were computed using a rainfall-runoff model. Hydrographs were generated using the SCS curve-number loss 

method (Soil Conservation Service, 1985) as described in the 

“Rainfall-Runoff Model Calibration and Simulation” section 

of this report.

Calibration of simulated peak discharges by using 

regional regression equations developed from measured peakflow data was desirable. However, a comparison of measured 

100-year peak flows (Interagency Advisory Committee on 

Water Data, 1982) at five stream gages in the Goose and 

Tarryall Creek subbasins with the results of regional regression equations developed for mountain areas of Colorado 

(Vaill, 2000; Browning, 2001; Kircher and others, 1985) 

showed that the regional equations substantially overestimated the observed 100-year peaks (by a factor of 2 or more). 

It was apparent that existing regional equations do not fit 

this area of relatively low rainfall runoff (Jarrett and Costa, 

1988). The landscape assessment for the Upper South Platte 

Watershed Protection and Restoration Project (Foster Wheeler 

Environmental Corporation, 1999) notes that the montane 

study area was heavily forested with ponderosa pine, Douglas 

fir, and lodgepole pine before the wildfire. The crown closure, which is the percentage of ground cover not visible 

from an aerial view looking straight down at the forest land, 

across most of the pre-fire study area was estimated to be 71 

to 100 percent, and in four subbasins (Cheesman Reservoir, 

Horse Creek, Waterton/Deckers, and West Creek) was estimated to be greater than 90 percent. The presence of this protective canopy and a thick duff layer on the ground, coupled 

with historically low precipitation amounts (Hansen and 

others, 1978; Robert Jarrett, U.S. Geological Survey, oral commun., 2002), probably explains the anomalously low 100-year, 

gaged peak discharges as compared to those predicted by the 

regional regression equations.

As an alternative, the five streamflow gages in the Goose 

and Tarryall Creek subbasins were used to develop a local 

regional equation for the study area (table 1). The period of 

annual peak discharge at three of the sites (1978–86) is less 

than 10 years, which generally is considered the minimum 

required for flood-frequency analysis. In an effort to evaluate 

the 1978–86 period in terms of its hydro-climatic characteristics relative to long-term conditions, a flood-frequency 

analysis of peak discharges for 1978–84 at streamflow-gaging 

station 06700500 (Goose Creek above Cheesman Lake) 

was compared with that for the period of record (1924–84). 

Annual peaks for 1983 and 1984 at the Goose Creek gage 

were provided by the Colorado Division of Water Resources, 

subsequent to the completion of regional regression analysis; peaks for 1985 and 1986 were not available because the 

gage was discontinued. The 100-year peak discharge for 

1978–84 was 857 ft3/s, which lies within the 95-percent confidence interval for the analysis spanning the longer 1924–84 

period. The 95-percent confidence interval for the long-term 

period of record was 546 to 884 ft3/s.

In this comparison, peak discharges for 1978–84 generally can be considered representative of those for the period 

of record. Unfortunately, other acceptable comparison sites in 

the same general hydro-climatic region (and with appropriate 

periods of record) were not available. A review of available 

precipitation data for the Cheesman Reservoir precipitation 

gage indicates that the 1978–84 period generally is representative of long-term precipitation for the period 1949–99. The 

average annual precipitation for 1978–86 was 17.6 inches, and 

the long-term average was 17.1 inches. On the basis of the 

peak-flow comparison at the Goose Creek gage and the analysis of average annual precipitation for the study area, the short 

period of record (1978–86) used to develop the local regional 

equation is considered reasonable.
Table 1 gives a summary of the drainage-basin characteristics and the predicted 100-year peak discharges used 

to develop the relation (Interagency Advisory Committee 

on Water Data, 1982). The resulting peak discharges computed using the local regression model, along with those 

predicted by the Vaill regional equation (2000), are shown in 

table 1 for comparison. The sites generally are unaffected by 

regulation and are considered to reflect meteorological and 

hydrological characteristics representative of the burned and 

adjacent unburned subbasins affected by the wildfire. Because 

of the limited period of historical record for each gage, no 

mixed-population analyses (snowmelt and rainfall peaks) 

were done.

An ordinary-least-squares regression model to predict 

100-year peak discharge, Q100, as a function of drainage area, 

A, was developed using the streamflow-gaging station data 

shown in table 1. The resulting equation and regression statistics were:

R squared

Standard error 

of estimate

Q100 = 14.21 A0.823 0.995 28 percent (8)

The regression coefficient (14.21) in the equation 

includes a bias correction factor to correct for bias introduced 

in the process of converting the results of log-space regression 

analysis back to rectangular coordinates (Duan, 1983).

Similar one-parameter models for Q100 have been developed by Browning (2001) and by Jarrett and Costa (1988). 

A plot of the new regression analysis showing the best-fit 

line defined by the equation is shown in figure 6; all five data 

points lie within the computed 95-percent confidence intervals 

(not shown) for the regression. The regression line generally 

plots lower and parallel to the equation defined by Jarrett and 

Costa (1988) (not shown) for a larger data set (basins below 

8,000 ft elevation) developed for the South Platte River Basin.

The regression model was used as the basis for calibration of the pre-burn, 100-year peak discharge of subbasins 

simulated using HEC-HMS. The regression model is limited 

by the small number of streamflow gages available for analysis

within the study area and by the relatively short period of 

record at each gage (which reduces the reliability of the peakflow statistics).

The HEC-HMS rainfall-runoff model (U.S. Army 

Corps of Engineers, 2001b) was used to simulate the preburn rainfall-runoff processes in burned and adjacent unburned 

areas of the South Platte River Basin. The HEC-HMS model 

was composed of 19 selected drainage basins and consisted 

of subbasins and other single basins. Data for the basins and 

subbasins are provided in Appendix tables 3–1, 3–2, and 3–14. 

The name and basin identification number convention for 

basins and subbasins is explained in Appendix table 3–2.

The objective calibration method, described in the 

“Rainfall-Runoff Model Calibration and Simulation” section 

of this report, was used to calculate optimal pre-burn rainfallrunoff parameters. The objective calibration method used an 

optimization algorithm (Doherty, 1998, 2001), in conjunction with HEC-HMS, to estimate a set of drainage-basin 

parameters that minimized a predefined objective function. 

In this study, the objective function was defined as the sum 

of squared residuals between regional and simulated 100-year 

peak discharges; the regional peak discharges for pre-burn 

conditions were computed using equation 8. The objective

calibration method resulted in a set of unbiased drainage-basin 

parameters (RCN, initial abstraction, and lag time) based on a 

robust, mathematical optimization procedure.

Five larger drainage basins were divided into smaller contributing subbasins that generally corresponded to basin delineations defined by the BAER team (USDA Forest Service, 

2002a) in their post-fire analysis of the Hayman area. The SCS 

curve-number method was used to estimate drainage-basin 

losses in individual, smaller tributaries. Subbasin hydrographs 

were routed to the mouths of the larger, composite drainage 

Table 1. Characteristics of streamflow-gaging stations used for calibration of 100-year peak discharge for pre-burn conditions, 

South Platte River drainage basin in Colorado.

[mi2, square mile; ft, foot; ft/ft/, foot per foot; ft3/s, cubic feet per second; Q100, 100-year peak discharge]

Streamflow-gaging station Period 

of record

Drainage 

area 

(mi2)

Gage 

elevation 

above 

sea level 

(ft)

Subbasin 

slope 

(ft/ft)

Q100

at gage 

(ft3/s)

Predicted 

Q100, 

equation 8 

(ft3/s)

Predicted 

Q100, 

Vaill1

(ft3/s)

Tarryall Creek at Upper Station near Como 

(06696980)

1978–86 23.7 9,935 0.316 236 192 569

Michigan Creek above Jefferson (06697450) 1978–86 23.1 9,503 0.246 196 188 513

Jefferson Creek near Jefferson (06698000) 1978–86 11.8 9,600 0.333 81 108 355

Tarryall Creek below Rock Creek, near Jefferson 

(06699005)

1983–97 236 9,020 0.182 1,050 1,270 2,390

Goose Creek above Cheesman Lake (06700500) 1924–84 86.6 6,910 0.317 646 559 1,410

1

Vaill, 2000.

Post-Fire Hydrologic Hazards for the Hayman Wildfire 17
18 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

basins. On the basis of existing reports that describe prefire drainage-basin conditions within the study area (Foster 

Wheeler Environmental Corporation, 1999; USDA Forest 

Service, 2002a) and assessment of aerial photography, preburn RCNs between 55 and 67 were selected for each subbasin

(pre-burn RCNs used in this study are somewhat lower than 

those selected by the BAER team). In addition to subbasin 

RCN values, the initial abstraction (infiltration) and the percentage of impervious area were entered into the model. The 

pre-burn abstraction values were selected using default model 

computations based on pre-burn drainage-basin characteristics 

and are reflective of the weathered rock soils that dominate 

the area. Limited field observations from nearby areas appear 

to corroborate pre-burn abstraction values computed by the 

model (David Stannard, U.S. Geological Survey, oral commun., 2002). Impervious areas (rock outcrops, roads, and so 

forth) were mapped by the BAER team and were accounted 

for in the model by adjusting RCNs for those areas.

Flow routing within the five larger basins (table 2) was 

performed using the Muskingum method (McCuen, 1989). 

Because observed hydrograph or field data were not available 

for calibration of the routing parameters, values of Muskingum 

K (that defines the time of travel for a flood wave traversing the 

basin) and X (a weighting factor that describes the backwater 

storage effects of a channel) were selected within the range of 

commonly used values for channels in steep, upland drainage basins (or subbasins) (McCuen, 1989; John Liou, Federal 

Emergency Management Agency, oral commun., 2003):

• Muskingum K = 0.6 hour

• Muskingum X = 0.4, to reflect channels with little 

over-bank storage

A summary of pre-burn calibration data (RCN, abstraction, lag-time factors) for all principal and minor subbasins is 

provided in Appendix table 3–14.

Step 2, Modeling of Burned Conditions, South Platte River 

Tributaries

Adjustments of the calibrated, pre-burn drainage-basin 

parameters were made to reflect the burned conditions within 

each subbasin. Existing studies documenting the hydrologic 

response of burned drainage basins in other areas were used 

to guide the calibration for post-burn conditions. The BAER 

team’s burned-area emergency stabilization and rehabilitation 

plan for the Hayman wildfire (USDA Forest Service, 2002a) 

was used to guide the selection of RCNs for post-burn conditions. Because of the detailed mapping of the post-burn subbasins (including burn severity, rock outcrops, unburned area, 

and water courses) conducted by the BAER team, and because 

of extensive USDA Forest Service experience with post-fire 

hydrology, the post-burn RCNs selected by the BAER team 

generally were adopted for this study. Exceptions were the use 

of lowered RCNs for some unburned areas, previously noted 

in the “Step 1, Modeling of Unburned Conditions, South Platte 

River Tributaries” section, and a slightly higher RCN for areas 

of moderate to high burn severity (explained herein).

• Rocky areas = 90

• Unburned forest = 55–60

• Low burn severity = 85

• Moderate and high burn severity = 98 (BAER team 

used 95)

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Figure 6. 100-Year flood peaks in relation to drainage area and the best-fit regression line using an ordinary-leastsquares regression model.
Table 2. Subbasin characteristics, modeling parameters, and computed 100-year peak discharges for pre-burn, post-burn, and post-burn bulked floods for 19 selected 

subbasins affected by the Hayman wildfire, objective calibration method.[mi2, square miles; %, percent; in, inches; Q100, 100-year discharge; ft3/s, cubic feet per second; Qu, pre-burn 100-year discharge; Qb, post-burn 100-year discharge; Qbb, post-burn bulked 100-year discharge; N/A, not applicable]

Subbasin name and number 

(downstream order)

Drainage 

area 

(mi2

)

Area of 

low burn 

(%)

Area of 

moderate to 

high burn 

(%)

Rainfall 

depth1

(in)

Curve number* 100-Year peak discharge

Ratio 

Qbb/Qu Pre-burn Post-burn (weighted)

Q100 

Unburned 

(ft3/s) 

Qu

Q100

Burned 

(ft3/s) 

Qb

Q100

Post-burn 

bulked 

(ft3/s) 

Qbb

Qbb

(ft3/s 

per mi2

)

Vermillion Creek (1) 4.93 50.0 27.6 2.4 57 86 50.8 1,060 1,130 230 22.3Crystal Creek (2) 5.27 46.4 29.0 2.4 57 86 52.8 1,120 1,200 228 22.8Beaver Creek (3) 3.54 51.5 33.7 2.4 56 89 37.8 994 1,080 304 28.5Hackett Gulch (4) 6.56 37.2 33.2 2.4 55 86 63.1 1,650 1,790 272 28.3Tarryall Creek (5) 443 0.96 0.89 2.4 N/A 86 78.1 2,180 2,180 4.93 28.0Longwater Gulch (6) 2.34 29.3 67.6 2.4 53 94 17.6 1,350 1,580 674 89.7Corral Creek (7) 4.38 15.7 70.3 2.4 54 94 44.3 2,770 3,260 744 73.5Northrup Gulch (8) 3.84 37.2 58.2 2.4 56 94 40.7 1,630 1,870 486 45.9Turkey Creek (9) 28.2 32.4 50.6 2.4 55–60 82–98 224 5,380 6,060 215 27.1Goose Creek (10) 95.2 5.29 15.1 2.4 57–58 55–97 471 7,100 7,370 77.4 15.6

Cheesman Reservoir

Schoonover Gulch (11) 1.71 11.7 85.4 2.4 55 96 21.0 1,350 1,640 958 78.0Sixmile/Wigwam Creek (12) 36.7 13.7 34.2 2.4 54–59 78–96 638 3,760 4,080 111 6.40Fourmile Creek (13) 8.22 11.7 59.7 2.4 58 90 77.2 1,850 2,130 259 27.5Horse Creek (14) 212 9.06 12.8 2.4 52–61 58–98 1,340 5,710 5,890 27.8 4.40Lazy Gulch (15) 1.23 54.2 39.0 2.4 55 90 16.0 650 713 580 44.6Brush Creek (16) 2.33 29.2 59.3 2.4 56 92 27.6 1,130 1,300 557 47.0Unnamed drainage (17) 1.16 0.00 0.00 2.4 55 N/A 15.4 N/A N/A N/ASaloon Gulch (18) 1.26 39.7 46.6 2.4 55 90 16.6 619 691 548 41.6Gunbarrel/Kelsey Creek (19) 10.2 8.00 2.00 2.4 55–56 55–62 103 276 277 27.2 2.69

*Runoff-curve numbers for the five larger subbasins are shown as a range of values determined for the subbasins within each drainage basin. Model data for the 19 selected subbasins, and other contributing 

subbasins in the Hayman burned area are in Appendix tables 3–1, 3–2, and 3–14.

1National Oceanic and Atmospheric Administration Atlas 2, Volume III—Colorado (Miller and others, 1973).

Post-Fire Hydrologic Hazards for the Hayman Wildfire 19
20 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Removal of surface vegetation by wildfire can be 

expected to decrease the runoff lag time in an affected drainage basin (URS Corporation, 2000; U.S. Army Corps of 

Engineers, 2000). Adjustment of post-burn lag times was 

made according to the SCS lag-time equation (eq. 1), which 

is a function of the post-burn RCN. Post-burn lag times range 

from 24 to 93 percent of pre-burn lag times in South Platte 

River subbasins, depending on the amount of burned area 

in the subbasin. A summary of post-burn calibration data 

(RCNs, abstractions, lag-time factors) for all principal and 

minor subbasins is in Appendix table 3–14. Table 2 shows 

the 19 selected subbasins for which modeling was conducted 

and the results of the pre- and post-burn runoff calibrations. 

A rainfall depth of 2.4 inches (100-year, 6-hour storm) was 

applied uniformly over each subbasin, with no areal distribution of the storm (Miller and others, 1973).

Sediment Bulking of Discharge for Hayman 

Wildfire-Area Tributaries

Most of the Hayman wildfire area “is comprised of shallow, weathered soils from the Pikes Peak batholith” (USDA 

Forest Service, 2002a). This weathered granite is easily eroded 

and, although not expected to result in debris flows, can be 

expected to produce large sediment loads during flooding. To 

account for the potential sediment bulking of floodflows in 

burned subbasins, computed peak discharges were increased 

according to the assumption that sediment concentrations 

by volume (Cv) could reach the maximum water-flood limit 

of 20 percent (Costa, 1988). O’Brien and Fullerton (1989) 

computed the bulking factor (BF) applied to water discharge 

according to the equation:

BF = 1/(1 – Cv) (9)

For a Cv of 20 percent, the corresponding BF is 1.25. 

The BF was applied to peak water discharges computed by 

the HEC-HMS model for areas of moderate to high burn 

severity and was weighted according to relative burned area 

within each of the modeled subbasins. Studies indicate that 

sediment concentration in natural streams varies over the 

water-discharge hydrograph and, for most streams, tends to 

reach a maximum in advance of the water-discharge peak 

(Guy, 1970). Application of the BF to the peak discharge 

therefore may represent a conservative adjustment to the 

modeling results.

The reasonableness of the 1.25 BF was evaluated using 

the results of a study of the Buffalo Creek wildfire in Colorado 

(Moody and Martin, 2001a). Moody and Martin derived a 

regression equation from discharge, suspended-sediment, and 

bedload-sediment measurements at Spring Creek, a drainage 

basin severely burned by the 1996 Buffalo Creek wildfire. 

Like the Hayman burned area, weathered Pikes Peak batholith materials are exposed throughout the Spring Creek and 

Buffalo Creek drainage basins. The 1996 wildfire burned 

approximately 79 percent of the Spring Creek drainage basin, 

and 63 percent of the entire burned area (both drainage basins) 

was classified as severely burned. Data were collected at the 

mouth of Spring Creek from July 1997, one year after the 

Buffalo Creek wildfire, through the summer of 2000. Several 

floods were sampled; however, the initial large post-fire floods 

of 1996 and before July 1997 were not sampled.

Moody and Martin’s (2001a) relation for total sediment 

transport (suspended and bedload) is:

 Qs = 23 Q1.3 R2 = 0.96 (10)

where

Qs is sediment discharge, in kilograms per second;

Q is water discharge, in cubic meters per second;

and

R2 is the coefficient of determination.

Post-fire, unbulked tributary peak discharges (Qb in 

table 2) were converted to cubic meters per second and 

used in equation 10. The predicted sediment discharges were 

converted from kilograms per second to cubic feet per second 

by using a units conversion and an assumed sediment specific 

weight of 165.36 pounds per cubic foot. The estimated sediment volume was added to the post-fire tributary discharge 

to determine the post-fire bulked tributary discharge. Bulked 

Hayman tributary discharges estimated using Moody and 

Martin’s (2001a) Spring Creek regression equation (eq. 10) 

were smaller than bulked discharges estimated with the 

1.25 bulking factor (eq. 9) for most tributaries. Estimates from 

the two methods diverged as the percentage of the drainagebasin area moderately or severely burned increased (fig. 7). 

For Hayman subbasins with 0 to about 20 percent of the drainage basin moderately or severely burned, bulked discharge 

estimates using equation 10 were within about ±5 percent of 

estimates from the 1.25 bulking factor method. However, for 

subbasins with greater than 50 percent area moderately or 

severely burned, the difference was greater than 10 percent, 

with the two equations diverging steadily as the percentage 

of moderately and severely burned area increased.

One possible explanation for the difference in bulked 

discharges from the two methods could be that the 1.25 BF

was applied only to the actual burned portion of each tributary 

subbasin, whereas equation 10 was applied to the total tributary drainage-basin area. Moody and Martin’s (2001a) equation was derived from measurements at the mouth of the basin 

that integrated runoff and sediment from burned and unburned 

parts of the Spring Creek drainage basin and was applied in 

the same way to the Hayman subbasins.

Another explanation for the difference in bulked discharges could be that Moody and Martin’s (2001a) transport 

equation did not fully reflect the high sediment-transport 

rates of the first, unsampled floods in 1996 and early 1997. 

Vegetation cover and soil conditions in the Spring Creek drainage basin were rapidly evolving in the first 5 years after the
wildfire, and hillslope sediment production was declining 

yearly. Moody and Martin predicted that over time, hillslope 

sediment yield and fluvial transport of sediment would return 

to pre-fire rates (Moody and Martin, 2001a).

Yet another explanation could be that the 1.25 BF is 

insensitive to in-channel storage in valley bottoms and tends 

to overestimate the efficiency of fluvial transport from some 

drainage basins. An analysis of in-channel storage in tributary valley bottoms was beyond the scope of this report. The 

bulked discharges estimated using equation 10 can be considered to be conservative, whereas the discharges estimated 

using the 1.25 BF can be considered to be maximum values.

Estimated Peak Discharges, South Platte River 

Tributaries

Post-fire, unbulked tributary peak discharges were 

increased to reflect the anticipated increased sediment loads 

by using a 1.25 bulking factor applied to areas of moderate-tohigh burn severity. Simulated pre-burn, post-burn, and bulked 

100-year discharges for each of the 19 selected subbasins are 

shown in table 2. Post-burn 100-year peak discharges for the 

principal subbasins (routed to the point of confluence with the 

South Platte River) are expected to increase 3 to 90 times over 

pre-burn peaks. Among all modeled subbasins with substantial (greater than 50 percent) moderate to high burn-severity 

areas, post-burn bulked peak discharges are expected to be 

28 to 91 times greater than pre-burn peaks. For those drainage 

basins with substantial burned area, average predicted unitarea peak discharges for pre-burn conditions is 12.3 ft3

/s/mi2; 

average predicted bulked unit-area peak discharge for postburn conditions is 830 ft3

/s/mi2.

Predicted increases in post-burn peak discharge are in 

general agreement with the BAER team’s hydrologic assessment of the Hayman wildfire (USDA Forest Service, 2002a) 

and with hydrologic studies of other burned drainage basins 

(Rowe and others, 1954; Moody and Martin, 2001b; URS 

Corporation, 2000). The BAER team’s assessment included 

92 subbasins (all tributary to the 19 selected subbasins modeled in this study) directly affected by the Hayman wildfire. The BAER team analyzed the 25-year, 1-hour storm 

(1 inch/hour) and found that the average ratio of post- to preburn unit-area peak discharge for affected subbasins was about 

3; the highest ratios, as much as 7.5, were measured in very 

small, severely burned subbasins.

Rowe and others (1954) found that the ratio of unitarea peak discharge before and after wildfires in southern 

California increased as much as 40 times, depending on the 

recurrence interval of the rainstorm. Ratios tend to be highest in the year following the wildfire, then decrease in subsequent years as vegetation is reestablished and the drainage basin begins to recover (Moody and Martin, 2001a; URS 

Corporation, 2000).

Figure 7. Comparison of post-fire runoff sediment-bulking methods, as a percentage of results from Moody and 

Martin’s (2001a) Spring Creek regression on total drainage-basin area to a 25-percent bulking factor applied to 

moderately and severely burned areas compared to percentage of drainage basin moderately or severely burned.

Post-Fire Hydrologic Hazards for the Hayman Wildfire 21

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22 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Moody and Martin (2001b) studied post-fire peak discharges in three burned drainage basins of the Western United 

States and developed relations for unit-area peak discharge 

(Qbb/drainage area) as a function of the maximum 30-minute 

rainfall intensity. Equations developed by Moody and Martin 

for the Spring Creek drainage basin of Colorado (burned by 

the Buffalo Creek wildfire of 1996) and the Rendija Canyon 

drainage basin of New Mexico (burned by the Cerro Grande 

wildfire of 2000) were used to predict a range of peak discharges that might occur in burned subbasins of the Hayman 

burned area. The 100-year unit-area peak discharges for the 

Hayman area simulated using HEC-HMS lie within the range 

of predicted unit-area peak discharges for the Spring Creek 

relation (considered to be a lower estimate limit) and the 

Rendija Canyon relation (considered to be an upper estimate 

limit). Based on comparison with the results from other 

burned drainage-basin studies (Moody and Martin, 2001b), 

the modeling results for the Hayman wildfire are considered 

reasonable.

Estimated Peak Discharges, Selected Reaches 

of the South Platte River

Estimated peak discharges on the South Platte River for 

use in short-term hazard mapping were computed using the 

manual calibration method as presented to FEMA in 2003 

by J.G. Elliott and others (U.S. Geological Survey, written 

commun.) and described in Appendix 2. Computed peak discharges along the South Platte River, and associated short-term 

hazard maps, were not revised to reflect model recalibration 

using the objective calibration method because a comparison 

showed that model differences (cumulative peak discharges at 

the outlet of Cheesman Reservoir and at the downstream end 

of the HEC-HMS model reach) were less than 10 to 17 percent 

for the two calibration methods. These differences were considered minor with regard to the larger uncertainty associated 

with modeling post-burn flood peaks, and these differences 

would not produce substantial differences in mapped areas at 

the scale of the hazards maps.

Results of the analyses are summarized in a series of 

hazard maps (fig. 5). Cross sections showing the 100-year 

floodwater-surface elevation along the South Platte River are 

shown in figures 8–11, and the extent of the 100-year flood is 

shown in map view in figures 12–14. The locations of cross 

sections used in the hazard analysis are presented in Appendix 

table 4–1.

South Platte River Hydrology and Peak Flow 

Analysis for Long-Term Recovery—Phase 3

Peak flows were computed to evaluate hydrologic 

responses at a stage in the post-burn recovery process referred 

to as the “long-term recovery” period. The long-term recovery 

period was estimated using methods described in the “Method 

for Determination of Drainage Basin Recovery—Phase 3”

section. In the South Platte River Basin of the Hayman 

burned area, the long-term recovery period was estimated to 

be 6 years. Analyses were designed to characterize runoff produced by rainstorms in and near the burned area and to reflect 

drainage-basin conditions that are expected to exist at a point 

of recovery approximately 6 years after the wildfire. Values 

for the HEC-HMS input parameters RCN, initial abstraction, 

and lag time in individual subbasins were calculated for the 

long-term recovery by decreasing the RCN in accordance to 

the long-term recovery decay function and recomputing the 

initial abstraction and lag time. HEC-HMS was then used to 

obtain estimates of long-term recovery peak flows. Discharge 

results from these analyses then were used as input for hydraulic analysis.

Long-term hydrologic analyses were conducted to 

evaluate the effects of the 10-, 50-, 100-, and 500-year 6-hour 

rainfall on peak flows in the burned and adjacent delineated 

unburned South Platte River subbasins after the recovery 

period. The post-burn 10-, 50-, 100-, and 500-year peak 

discharges along the main stem of the South Platte River were 

computed for the Deckers-to-Trumbull detailed study reach. 

In-stream flow routing, to account for in-channel storage and 

peak attenuation at successive downstream cross sections, 

was performed using the routing routines in the HEC-HMS 

computer model. The Muskingum-Cunge routing routine, 

which incorporates cross-section and hydraulic properties of 

the surveyed cross sections, was used to route flows in reaches 

of the main-stem South Platte River. Routed peaks showed 

little attenuation. Sensitivity testing indicated that hydrograph 

attenuation was affected mainly by channel slope; the relatively steep slopes (measured as water-surface slope during 

the cross-section surveys) through the study reach preclude 

substantial attenuation. The Modified Puls reservoir routing 

routine in HEC-HMS was used to route the computed flood 

hydrograph through Cheesman Reservoir and over the spillway to the downstream reach. Water-surface profile elevations 

in the detailed study reach were plotted (fig. 16), and floodway 

computations were made using encroachment routines in the 

HEC-RAS program for the 100-year profile.

The approach to the long-term detailed hydrologic study 

included the following steps:

1. Inflow conditions upstream from the burned area were 

assumed to be the 10-year flood for the South Platte River 

at the upstream fire perimeter, the 10-year flood for Tarryall 

Creek at the upstream fire perimeter, and maximum outlet 

release (1,400 ft3/s) from Cheesman Reservoir for the South 

Platte River below Cheesman Dam.

2. Initial pre-flood storage in Cheesman Reservoir was 

assumed to be 54,039 acre-ft.

3. Drainage-basin parameters for the previously described 

long-term conditions in the burned subbasins tributary to the 

South Platte River were used in the HEC-HMS rainfall-runoff 

model (Appendix table 3–7).
4. Peak flow was simulated for the 10-, 50-, 100-, and 500-

year, 6-hour storms by using long-term drainage-basin parameters in burned subbasins tributary to the South Platte River.

5. Rainfall amounts and distributions were determined from 

the NOAA Atlas 2 guidance (Miller and others, 1973). The 

500-year 6-hour storm total was estimated by logarithmic 

extension of NOAA Atlas 2 data (Appendix table 3–8).

6. Peak flows for post-fire recovery were not bulked due 

to the probable lack of large sediment loads in the post-fire 

recovery period.

7. Peak flows for subbasins tributary to the South Platte 

River were computed (with routing of the runoff hydrograph 

through the primary subbasins) (Appendix table 3–7).

8. Peak flows for selected reaches of the South Platte River 

(within and downstream from the burned area) were computed 

using a hydrograph routing algorithm.

Peak-discharge water-surface elevations from the rainfallrunoff model can be used to create FEMA regulatory maps. 

However, because a larger flood study is being conducted and 

a digital flood-insurance rate map (DFIRM) is being created 

for Douglas County, these results will need to be integrated 

into the larger scope of the South Platte River. Therefore, no 

flood-insurance rate map (FIRM) was produced for this report. 

The flood elevations computed for this study do show overtopping of all three bridges in the detailed reach. The bridge at 

Trumbull (fig. 16A) was overtopped by the 10-yr recurrence 

floodflow. The next bridge upstream between Deckers and 

Trumbull (fig. 16C) was overtopped by the 50-yr floodflow. 

The bridge at Deckers (fig. 16C) also was overtopped by the 

50-yr floodflow. Comparison of the 100-yr flood elevations 

(Appendix table 3–13) from the 1978 Flood Insurance Study 

(FIS) (Federal Emergency Management Agency, 1978) to 

the results in this report for the same cross-section locations 

indicate that differences ranged from 4 ft higher to 3 ft lower 

in this study (2004). The median difference was zero.

South Platte River “Detailed” Hydraulic 

Analysis

Detailed flood hydraulics (known to FEMA as a 

“Detailed Study”) were computed for the recovered 

(Phase 3) hydrologic conditions using step-backwater 

routines in HEC-RAS (U.S. Army Corps of Engineers, 

2001a) for a stream reach from a point 5,040 ft upstream from 

the county road bridge over the South Platte River at Deckers 

to a point 2,455 ft downstream from the county road bridge 

over the South Platte River at Trumbull (fig. 15); in this report, 

this reach is referred to as “the detailed study reach.” Floodway elevations, defined by FEMA as “the channel of a river 

or other watercourse and the adjacent land areas that must be 

reserved in order to discharge the base flood without cumulatively increasing the water-surface elevation by more than a 

designated height” (1 ft in the case of the Deckers-to-Trumbull 

reach of the South Platte), also were computed for this reach.

V

P

N

O

Q R S T

U

A

B

C

D

E

F

G H

I

J

K L

M

Figure 15. Cross-section location map for South Platte River detailed hydraulic study.

Post-Fire Hydrologic Hazards for the Hayman Wildfire 23
24 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

The approach to the hydraulic analyses included the following steps and data:

1. Peak discharges (long-term recovery) based on the 10-, 

50-, 100-, and 500-year recurrence intervals (Appendix 

table 3–9) 6-hour design storm (objective calibration method) 

for the main-stem South Platte River were used in the detailed 

study reach.

2. Stream cross sections were delineated using USGS ground 

surveys and cross-section data from the 1978 detailed flood 

insurance study (FIS) of Douglas County (Federal Emergency 

Management Agency, 1978) that overlapped part of this 

detailed study reach (Appendix table 4–2).

3. Tributary inflows available from HEC-HMS modeling 

within the detailed study reach were added at the appropriate 

cross sections in the model to determine the main-stem South 

Platte peak flows (Appendix table 3–9).

4. Manning’s roughness coefficients and distances between 

cross sections were determined during ground surveys, global 

positioning system (GPS) surveys, and review of the 1978 

FIS data and flood-insurance rate map (FIRM) (Appendix 

table 3–10).

5. Water-surface elevations and flow characteristics were 

determined using the HEC-RAS hydraulic model assuming 

subcritical flow regime (Appendix table 3–11).

6. Water-surface profile elevations in the detailed study reach 

were plotted at NAVD 88 datum (fig. 16).

7. Floodway computations were made using encroachment 

routines in the HEC-RAS hydraulic model for the 100-year 

profile (Appendix table 3–12). For this analysis the flood plain 

was encroached such that maximum allowable water-surface 

increase was equal to or less than 1 ft.

Post-Fire Hydrologic Hazards for the 

Coal Seam Wildfire

The Coal Seam wildfire affected many small subbasins as 

well as the large subbasin of Mitchell Creek, a perennial tributary of the Colorado River at Glenwood Springs, Colorado 

(fig. 1). The Coal Seam fire perimeter and Mitchell Creek 

drainage basin are shown on an oversized map (fig. 17) that 

accompanies this report. Water flooding and debris flows are 

potential hazards in the Coal Seam area. Post-fire hydrologic 

analyses were conducted to evaluate the effects of the 100-year 

peak flow on the burned and adjacent unburned areas of the 

Mitchell Creek subbasin. Water-flood and debris-flow analyses 

also were conducted for subbasins within the Mitchell Creek 

subbasin. The Mitchell Creek debris-flow analysis is presented 

in a subsequent section of this report, “Analysis of DebrisFlow-Producing Drainage Basins, Coal Seam Wildfire.” For 

the purpose of flood-hazard mitigation in the present study, 

the results of a FLO-2D analysis, which includes a combined 

analysis of water flooding and debris flows in the Mitchell 

Creek subbasin, have been used to construct the Mitchell 

Creek hazard map (figs. 18 and 19). The following discussion 

pertains to water-flood conditions in subbasins and main-stem 

reaches of Mitchell Creek.

Hydrologic Analysis of Mitchell Creek—Phase 2

Water-flood analyses were designed to characterize 

increased runoff produced by rainstorms in and near the 

wildfire area and reflect drainage-basin conditions that are 

expected to exist during the next several years (before substantial regrowth of vegetation in the burned areas). The results of 

these analyses were used to delineate a limited-detail hazardmitigation map for post-fire flooding of Mitchell Creek. The 

map characterizes short-term (next 1–4 years) runoff conditions and should not be used for regulatory purposes.

Additional hydrologic analyses reflecting more stable 

drainage-basin conditions (after a recovery period of 5 years) 

also were performed and are presented in a subsequent section “Mitchell Creek Hydrology and Peak Flow Modeling 

for Long-Term Recovery—Phase 3.” An ongoing study is 

evaluating the flood hydraulics under long-term recovered 

conditions of Mitchell Creek in greater detail (known to 

FEMA as a “Detailed Study”), but findings from the Mitchell 

Creek long-term study are not included in this report. Results 

of the “detailed” hydraulic analyses will be used by FEMA to 

delineate a revised flood-plain map for regulatory purposes. 

The future map will include analyses of the 10-, 50-, 100-, and 

500-year floods.

Assumptions for the short-term, Phase 2 hydrologic 

hazard-mitigation analysis of Mitchell Creek are as follows:

1. Calibration of a rainfall-runoff model for pre-fire 

(unburned) conditions in drainage basins tributary to Mitchell 

Creek. Runoff generated by the 100-year, 1-hour rainstorm 

(1.64 inches) was calibrated to the existing 100-year discharge 

for the study area. The existing 100-year discharges are documented in a FEMA Flood Insurance Study (FIS) for Mitchell 

Creek (Simons, Li & Associates, Inc., 1983).

2. Rainfall runoff was simulated for the 100-year, 1-hour 

storm for post-fire conditions in burned drainage basins 

tributary to Mitchell Creek.

3. Peak discharges for selected reaches of Mitchell 

Creek were computed (with hydrologic routing of the 

runoff hydrograph).

4. Peak discharges for burned subbasins were increased 

using a bulking factor to reflect increased sediment loads.

5. Debris-flow hazards were analyzed separately and are 

covered in the “Analysis of Debris-Flow-Producing Drainage 

Basins, Coal Seam Wildfire—Phase 2” section of this report.
Post-Fire Hydrologic Hazards for the Coal Seam Wildfire 25 Figure 16. Flood-profile plots of the South Platte River, Colorado, detailed study reach.

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26 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

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28 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

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Mitchell Creek has a contributing drainage area of 

11.2 mi2 at Donegan Bridge in Glenwood Springs (fig. 17). 

A FEMA flood-insurance study (FIS) was completed in 1983 

by Simons, Li and Associates, Inc. The accepted 100-year 

peak discharge for the drainage basin is 360 ft3/s at a mainstem point upstream from Donegan Bridge (drainage area 

is 5.9 mi2). The 1983 hydrologic analysis was based on a 

detailed regional analysis of streamflow data recorded at 

nine streamflow-gaging stations. Flood-frequency statistics 

(log-Pearson III distribution) for Mitchell Creek were based 

on a regional analysis of Crystal River streamflow-gage data 

conducted by the U.S. Army Corps of Engineers (1979).

A drainage-area adjustment of this peak discharge was 

made during the present study to reflect hydrologic conditions 

in Mitchell Creek at Donegan Bridge. The area-adjusted peak 

discharge was computed using an equation relating peak discharge for gaged (simulated discharge using HEC-HMS) sites 

to ungaged sites as a function of relative drainage area (Vaill, 

2000). The following equation was used:

Q100(u) = Q100(g) (Au/Ag)X (11)

where

Q100(u) is the 100-year peak discharge, in cubic feet per 

second, at the ungaged (nonmodeled) site;

Q100(g) is the 100-year peak discharge, in cubic feet per 

second, at the gaged (modeled) site;

Au is the drainage area, in square miles, at the 

ungaged (nonmodeled) site;

Ag is the drainage area, in square miles, at the gaged 

(modeled) site;

and

X is the average exponent for drainage area in the 

flood region of interest, derived from regression analysis of historical streamflow data.

The computed 100-year peak discharge for Mitchell Creek at 

Donegan Bridge was 542 ft3/s.

Mitchell Creek Tributary Rainfall-Runoff 

Modeling

Rainfall-runoff modeling was used to develop post-fire 

hydrographs for each of the principal subbasins of Mitchell 

Creek. Fifteen subbasins (fig. 17, Appendix tables 5–1, 5–2) 

were delineated using a 10-m DEM. The U.S. Army Corps 

of Engineers HEC-HMS computer model was used for the 

analysis (U.S. Army Corps of Engineers, 2001b). The 100-year, 

1-hour storm was selected for analysis to reflect flood hazards 

resulting from spring and summer thunderstorms unique to 

the study area. Rainfall-runoff modeling was conducted in two 

steps.

Step 1, Modeling of Unburned Conditions, Mitchell Creek 

Tributaries

The runoff hydrograph for the 100-year peak discharge 

was developed for natural, unburned conditions of each 

subbasin. The accepted 100-year peak discharge of 360 ft3/s 

(drainage area of 5.9 mi2) and the extended 100-year peak 

discharge of 542 ft3/s (drainage area of 11.2 mi2) were used 

as target discharges for model calibration.

The 100-year, 1-hour storm, as determined from the 

NOAA Atlas 2 Volume III—Colorado (Miller and others, 

1973), is 1.64 inches for most areas of the Mitchell Creek subbasin. The USDA Forest Service BAER team (USDA Forest 

Service, 2002b) selected a larger rainfall depth (1.85 inches) 

for analysis in their post-fire study. The larger value reflects 

rainfall conditions in the most upstream areas of the headwater 

tributaries and is considered a conservative rainfall depth for 

the study area.

The U.S. Army Corps of Engineers (1998) used the 

1.64-inch rainfall depth for rainfall-runoff modeling in the 

Glenwood Springs area; a 1-hour storm distribution also was 

developed from locally measured rainfall data. This temporal distribution was used in the present study because it was 

derived from local measurements.

The SCS lag-time equation (eq. 2) (Soil Conservation 

Service, 1985) developed for drainage basins smaller than 

about 3.25 mi2 was used to compute the lag time. Drainagebasin areas in the Mitchell Creek subbasin ranged from 0.010 

to 4.418 mi2 (table 3). The SCS method, developed for such 

small drainage basins, required minimal parameter calibration in simulating the pre-burn, 100-year peak discharges; 

other methods required additional parameter adjustments for 

calibration.

The HEC-HMS drainage basin model (U.S. Army Corps 

of Engineers, 2001b) was used to simulate the pre-burn 

rainfall-runoff processes in Coal Seam burned area tributaries 

for (1) unsteady, one- and two-dimensional water flooding in 

Mitchell Creek and (2) unsteady, two-dimensional debris flows 

in smaller tributaries affected by the wildfire. An objective 

calibration method, described in the “Rainfall-Runoff Model 

Calibration and Simulation” section of this report, was used to 

calculate optimal pre-burn rainfall-runoff parameters.

Target 100-year peak discharges for each Mitchell Creek 

subbasin were computed using three published regional 

equations (Vaill, 2000; Browning, 2001; Kircher and others, 

1985). Resulting parameter sets (RCN, initial abstraction, and 

lag time) then were analyzed using the objective calibration 

method and HEC-HMS to compute the routed peak discharge 

at the mouth of Mitchell Creek. Comparison tests showed that 

the Vaill equation produced target subbasin discharges and 

resultant RCNs that yielded the best estimate of the accepted 

100-year discharge for the main stem of Mitchell Creek. The 

Vaill equation produced peak discharges that agreed closely 

with peak discharges from the existing flood insurance study 

(FIS) (Simons, Li and Associates, Inc., 1983):

Post-Fire Hydrologic Hazards for the Coal Seam Wildfire 29
30 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

• Accepted 100-year peak discharge (5.9 mi2) = 360 ft3/s

• Simulated 100-year peak discharge (Vaill, 2000) = 

366 ft3/s (1.67 percent difference)

• Accepted 100-year peak discharge (11.2 mi2) = 542 ft3/s

• Simulated 100-year peak discharge (Vaill, 2000) = 

587 ft3/s (8.30 percent difference)

Flow routing within the Mitchell Creek subbasin was performed using the Muskingum method. Values of Muskingum 

K (defines the time of travel for a flood wave traversing the 

basin) and X (a weighting factor that describes the backwater 

storage effects of a channel) were selected within the range of 

commonly used values for channels in steep, upland drainage basins (McCuen, 1989; John Liou, Federal Emergency 

Management Agency, oral commun., 2002):

• Muskingum K = 0.6 hour

• Muskingum X = 0.4, to reflect channels in the upper 

drainage basin with little overbank storage

• Muskingum X = 0.2, to reflect channels in the middle 

and lower drainage basin with more overbank storage

A summary of pre-burn calibration data (RCN, abstraction, lag-time factors) for all principal and minor subbasins in 

the Mitchell Creek drainage subbasin is provided in Appendix 

table 5–1.

Step 2, Modeling of Burned Conditions, Mitchell Creek 

Tributaries

About 25 percent of the Mitchell Creek drainage basin 

was burned by the 2002 Coal Seam wildfire. Adjustments to 

the pre-burn modeling parameters were made to reflect the 

burned condition within each subbasin. Existing studies documenting the hydrologic response of burned subbasins in other 

areas were used to guide the calibration for post-burn conditions. The BAER team “Coal Seam Fire Hydrology Report” 

(USDA Forest Service, 2002b) was used to guide the selection 

of RCNs for post-burn conditions. Key RCN values used for 

the present analysis are:

• Unburned drainage basin = 67 to 80

• Low burn severity = 85

• Moderate and high burn severity = 98 (BAER team 

used RCN = 95)

Where affected drainage basins and subbasins included 

burned and unburned areas, post-burn RCNs were computed 

as described in the previous section "Step 2, Modeling of 

Burned Conditions, South Platte River Tributaries." Post-burn 

lag times range from 40 to 87 percent of pre-burn lag times, 

depending on the amount of burned area in the subbasin. 

A summary of post-burn calibration data (RCNs, abstractions, lag-time factors) for all Mitchell Creek subbasins is 

Table 3. Subbasin characteristics, modeling parameters, and computed peak discharge for pre- and post-burn subbasin conditions, 

Mitchell Creek.

[mi2, square miles; %, percent; Q100, 100-year discharge; ft3/s, cubic feet per second]

Subbasin name 

and number

Drainage 

area 

(mi2)

Area of 

low burn 

(%)

Area of 

moderatehigh burn 

(%)

Runoff-curve number Q100

(ft3/s)

Pre-burn Post-burn Pre-burn

Qu

Post-burn

Qb

Storm King 1 (23) 0.201 6.7 74.2 72 95 38.4 415

Storm King 2 (24) 0.055 57.8 35.1 74 91 17.1 107

Mitchell E1 (25) 0.290 42.4 40.7 72 91 48.2 369

Mitchell E2 (26) 0.013 27.7 70.0 79 95 7.84 33.8

Mitchell E3 (27) 0.051 3.0 97.0 80 98 24.7 132

Mitchell E4 (28) 0.045 6.8 89.8 78 97 22.5 130

Mitchell W4–S (29) 0.010 8.6 91.4 79 97 7.80 34.7

Mitchell W3 (30) 0.116 10.5 79.5 74 96 36.8 323

Mitchell W2 (31) 0.133 7.8 76.6 73 95 37.8 353

Mitchell W1 (32) 0.147 24.8 37.5 74 89 40.4 223

Mitchell W4–N (33) 0.031 2.6 89.0 78 97 17.2 95.0

Upper Mitchell West (36) 2.372 11.8 4.1 70 75 175 362

Upper Mitchell East (37) 2.747 11.9 7.7 70 77 192 489

Fish hatchery (38) 0.575 30.3 55.2 67 93 49.2 918

Donegan Bridge (39) 4.418 4.4 5.7 69 74 228 472
in Appendix table 5–2. Table 3 lists the 15 Mitchell Creek 

subbasins that were modeled and the results of the pre- and 

post-burn runoff calibrations. A rainfall depth of 1.64 inches 

(100-year, 1-hour storm) was applied uniformly over each 

subbasin, with no areal distribution of the storm (Miller and 

others, 1973).

Sediment Bulking and Peak Flood Discharge for 

Mitchell Creek

Computed Mitchell Creek peak discharges were 

increased to account for potential sediment bulking of water 

floods according to the assumption that sediment concentrations by volume (Cv

) could reach the maximum water-flood 

limit of 20 percent. For the limiting sediment concentration 

Cv of 20 percent, the corresponding bulking factor is 1.25 

(eq. 9). This factor was applied to peak discharges computed 

for areas of moderate to high burn severity; the bulking factor 

was weighted according to the relative burned area within each 

of the modeled subbasins.

Simulated pre-burn, post-burn, and bulked 100-year discharges for each of the 15 Mitchell Creek subbasins are shown 

in table 4. Post-burn, bulked 100-year peak flows for Mitchell 

Creek subbasins are expected to increase 2 to 21 times pre-burn 

peaks (table 4). Post-burn peak discharges for composite subbasins along the main stem of Mitchell Creek (Upstream, Fish 

Hatchery, and Donegan Bridge) are expected to increase 3 to 

4 times pre-burn peaks. Based on comparison with the results 

of studies of other burned drainage basins (Rowe and others, 

1954; Moody and Martin, 2001b; URS Corporation, 2000), the 

modeling results for post-fire peak flows in Mitchell Creek are 

considered reasonable.

Combined routing of water-flood (HEC-RAS) and debrisflow (FLO-2D) components in Mitchell Creek are planned as 

part of a future “detailed” hydraulic study that will delineate 

the long-term (Phase 3) 10-, 50-, 100-, and 500-year floodplain (and floodway) boundaries for the Mitchell Creek drainage basin. Debris-flow potential in subbasins burned by the 

Coal Seam wildfire, including tributaries to Mitchell Creek, are 

evaluated in the subsequent section of this report, “Analysis of 

Debris-Flow Producing Drainage Basins, Coal Seam Wildfire.”

Table 4. Computed 100-year peak discharges for pre-burn, post-burn, and post-burn (bulked) runoff conditions for modeled subbasins in the Mitchell Creek drainage basin.

[mi2 , square miles; %, percent; Q100, 100-year discharge; ft3/s, cubic feet per second; Qu, pre-burn 100-year discharge; Qb, post-burn 100-year discharge; Qbb, 

post-burned bulked 100-year discharge; ft3/s/mi2, cubic feet per second per square mile; N/A, not applicable]

Subbasin name 

and number

Drainage 

area 

(mi2)

Area of 

low burn 

(%)

Area of 

moderatehigh 

burn 

(%)

Q100

(ft3/s)

Ratio 

Qbb Pre-burn /Qu

(Qu)

Post-burn 

(Qb)

Post-burn 

bulked 

(Qbb)

Qbb per mi2

(ft3/s)

Storm King 1 (23) 0.201 6.7 74.2 38.4 415 482 2,400 12.6

Storm King 2 (24) 0.055 57.8 35.1 17.1 107 120 2,170 7.0

Mitchell E1 (25) 0.290 42.4 40.7 48.2 369 407 1,400 8.4

Mitchell E2 (26) 0.013 27.7 70.0 7.84 33.8 39.7 3,050 5.1

Mitchell E3 (27) 0.051 3.0 97.0 24.7 132 164 3,200 6.6

Mitchell E4 (28) 0.045 6.8 89.8 22.5 130 159 3,560 7.1

Mitchell W4–S (29) 0.010 8.6 91.4 7.80 34.7 42.6 4,350 5.5

Mitchell W3 (30) 0.116 10.5 79.5 36.8 323 387 3,320 10.5

Mitchell W2 (31) 0.133 7.8 76.6 37.8 353 421 3,160 11.1

Mitchell W1 (32) 0.147 24.8 37.5 40.4 223 244 1,660 6.0

Mitchell W4–N (33) 0.031 2.6 89.0 17.2 95.0 116 3,800 6.8

Upper Mitchell West (36) 2.372 11.8 4.1 175 362 366 154 2.1

Upper Mitchell East (37) 2.747 11.9 7.7 192 489 498 181 2.6

Fish hatchery (38) 0.575 30.3 55.2 49.2 918 1,040 1,810 21.1

Donegan Bridge (39) 4.418 4.4 5.7 22.8 472 479 105 2.1

Composite basin name

Upstream main stem 5.12 11.8 6.0 216 844 857 167 4.0

Fish hatchery main stem 6.23 13.6 16.1 366 1,070 1,120 180 3.1

Donegan Bridge main stem 11.2 10.8 13.8 587 1,740 1,800 161 3.1

Post-Fire Hydrologic Hazards for the Coal Seam Wildfire 31
32 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Mitchell Creek Hydrology and Peak Flow 

Modeling for Long-Term Recovery—Phase 3

Hydrologic responses in Mitchell Creek were computed 

to evaluate peak flows at a point in the post-burn, long-term 

recovery period (Phase 3). The long-term recovery was identified using methods described in “Method for Determination 

of Drainage Basin Recovery—Phase 3” section. In the 

Mitchell Creek subbasin of the Coal Seam burned area, the 

long-term recovery was estimated to be 4 years. HEC-HMS 

input parameters (U.S. Army Corps of Engineers, 2001b) 

for individual subbasins were calculated for the long-term 

recovery to facilitate HEC-HMS modeling of peak flows. 

Discharge results from these analyses can be used as input for 

hydraulic analysis. Peak-flow hydrographs were developed for 

15 tributaries (subbasins) to Mitchell Creek within and downstream from the Coal Seam burned area. These subbasins were 

delineated using a 30-m DEM. The 1-hour storm duration and 

distribution used by the USACE for hydrologic analysis in the 

same area (U.S. Army Corps of Engineers, 1998) was used in 

this study.

The effects of the 10-, 50-, 100-, and 500-year 1-hour 

rainfall on peak flows in Mitchell Creek were evaluated. The 

analysis characterizes increased runoff produced by rainstorms 

in and near the burned area and reflects drainage-basin conditions that are expected to exist for a 4-year recovery period. 

The approach to the long-term hydrologic analysis is similar to 

the approach described previously for pre-burn and post-burn 

periods and included the following steps and assumptions:

1. Drainage-basin parameters for the previously described 

long-term conditions in the burned subbasins tributary to 

Mitchell Creek were used in the HEC-HMS rainfall-runoff 

model (Appendix table 5–2).

2. Peak flows were simulated in the HEC-HMS rainfallrunoff model for the 10-, 50-, 100-, and 500-year, 1-hour 

design storms using long-term recovery drainage-basin 

parameters in burned subbasins tributary to Mitchell Creek 

(Appendix table 5–3).

3. Rainfall amounts and distributions were determined from 

the NOAA Atlas 2 guidance. The 500-year 1-hour storm total 

was estimated by logarithmic extension of NOAA Atlas 2 data 

(Miller and others, 1973) (Appendix table 5–4).

4. Peak discharges for recovered subbasins were not volumetrically bulked because large sediment loads probably will 

not be typical in the period following recovery.

5. Peak discharges for subbasins tributary to Mitchell Creek 

were computed. Runoff hydrographs were routed through the 

larger subbasins (Appendix table 5–3).

Analysis of Debris-Flow-Producing Drainage 

Basins, Coal Seam Wildfire—Phase 2

Many of the small subbasins burned by the Coal Seam 

wildfire have the potential to produce damaging debris flows 

during the next several years before substantial vegetation 

regrowth in the burned areas (fig. 17). The Maroon Formation, 

widely exposed in this area, produced several large debris 

flows on nearby Storm King Mountain following a wildfire 

in 1994 (Cannon and others, 1998; Kirkham and others, 

2000). The potential for debris flows from larger rainstorms 

was evaluated in the Coal Seam burned area. Cannon, 

Michael, and Gartner (2003) and Cannon (Susan H. Cannon, 

U.S. Geological Survey, oral commun., 2003) assessed 

approximately 135 tributaries with some potential for flooding 

and debris flows and estimated the potential peak discharges 

with Cannon’s (2001) regression equation.

Additional debris-flow analysis with FLO-2D was done 

for 26 of the tributaries Cannon assessed (table 5). These 

tributaries were identified as having the greatest potential peak 

debris-flow discharges and for having the potential to damage 

habitable and commercial structures. Other tributaries also 

have a potential to produce floods and debris flows but were 

not included in this analysis. The Mitchell Creek flood potential is covered in the preceding section of this report.

Debris flows from small tributaries (subbasins) to 

Mitchell Creek were simulated with FLO-2D. A composite 

model of Mitchell Creek was created in which 10 heavily 

burned subbasins were modeled as debris-flow-producing 

tributaries (table 5), and other minimally burned subbasins 

were modeled as water-flood-producing tributaries. The 

procedures for simulating Coal Seam burned-area debris flows 

are presented in the previous section “Methods for Post-Fire 

Debris-Flow Hazard Analysis.”

Drainage areas for the Coal Seam wildfire study subbasins range from 0.01 to 0.75 mi2

. Most of these subbasins 

are located on Red Mountain south of the Colorado River, in 

the upland areas north of the golf course in West Glenwood 

Springs, and are tributaries to Mitchell Creek (fig. 17). All 

tributaries were modeled using a 10-m grid-element size. 

Delineation of the potential inundation areas and the maximum depths during the debris flow following a 100-year 

storm are indicated on maps showing the debris-flow subbasins, existing alluvial fans, and infrastructure visible on 

the current (2004) USGS topographic maps (figs. 18 and 19).

Debris-flow hydrographs, inundation areas, and maximum flow depths were created in FLO-2D. Subbasins with a 

relatively large area of moderate and high burn severity were 

characterized by marked increase in runoff and sediment yield. 

Estimates of the increase in 100-year discharge resulting from 

post-fire debris flows, relative to unburned conditions, range 

from 8 to 14 times in the Red Mountain area, 2 to 9 times 

in the West Glenwood Springs area, and 8 to 14 times for 

selected tributaries of Mitchell Creek (table 5). Runoff from 

tributaries included in the Coal Seam debris-flow analyses 
was not routed within the basin; runoff values used in FLO2D analyses represent a basin-mouth summary of discharge 

from the contributing drainage area and are therefore slightly 

different from the Mitchell Creek water-flood runoff estimates 

described in the previous Mitchell Creek hydrology section 

where flow routing was performed (tables 4 and 5).

The debris-flow depths shown in figures 18 and 19 are 

maximum depths that occurred at some time during the model 

simulation. In most locations in the depositional zone, depths 

increased to a maximum as the sediment and water mixture 

passed and then receded to lesser depths. The time of occurrence of maximum depth varied by location in the depositional 

zone; therefore these maps do not represent an instant in 

time of the debris-flow deposit or the final depths at the end 

of the event. Repetitious, echolike depth patterns on some 

debris-flow deposits, such as those seen in the West Glenwood 

Springs area, represent the passage of undulating wave forms 

during runoff (J.S. O’Brien, FLO Engineering, Inc., oral commun., June 2003).

Some of the simulated 100-year debris-flow depositional 

areas were extensive. Debris flows from several small subbasins in Red Mountain inundated large areas of the Wulfsohn

Fan, and maximum depths of 4 to 6 ft could occur near the 

west end of the fan (fig. 19). Debris-flow inundation in the 

West Glenwood Springs area also could be extensive and 

affect many residences and businesses. Maximum depths in 

Table 5. Estimated 100-year debris-flow peak discharges for selected Coal Seam burned area tributary subbasins.

[100-year, 1-hour storm total 1.64 inches; sediment concentration, Cv, at water peak = 0.43; USGS, U.S. Geological Survey; USACE, U.S. Army Corps of 

Engineers; BAER, Burned Area Emergency Rehabilitation team; mi2, square miles; ft3/s, cubic feet per second; --, not applicable]

Subbasin 

number

Tributary 

subbasin 

name 

USGS 

(fig. 17)

USACE 

report 

basin 

number1

BAER 

report 

basin 

number2

Tributary to

Drainage 

area 

(mi2)

Pre-fire 

100-year 

peak 

streamflow 

discharge 

(ft3/s)

Post-fire 

100-year 

peak 

streamflow 

discharge 

(ft3/s)

Post-fire 

100-year 

peak 

debris-flow 

discharge 

(ft3/s)

1 Red Mtn Basin 1 W–18 14 Wulfsohn Fan 0.07 25 207 363

2 Red Mtn Basin 2 -- 15 Wulfsohn Fan/Colo R 0.02 8 61 107

3 Red Mtn Basin 3 W–20 30 Wulfsohn Fan/Colo R 0.06 24 147 258

4 Red Mtn Basin 4 W–21 31 Wulfsohn Fan/Colo R 0.06 25 124 218

5 Red Mtn Basin 5 W–22a 32 Wulfsohn Fan/Colo R 0.06 24 173 304

6 Red Mtn Basin 6 -- 33 Wulfsohn Fan/Colo R 0.02 7 47 82

7 Red Mtn Basin 7 W–22b 13 Wulfsohn Fan/Colo R 0.08 28 223 391

8 Red Mtn Basin 9 -- 34 Wulfsohn Fan/Colo R 0.04 16 117 205

9 Red Mtn Basin 11 W–24 35 Colorado R 0.55 131 631 1,107

18 “Charo Rd” basin N–12 22 W Glenwood/Colo R 0.66 148 153 268

19 “Sunny Acres Rd” bsn N–11 W Glenwood/Colo R 0.11 39 71 125

20 “Cedar Crest Dr” bsn N–10a 23 W Glenwood/Colo R 0.18 55 270 474

21 “Rock Ledge Dr” bsn -- W Glenwood/Colo R 0.04 17 69 121

22 “Mel-Ray Rd” basin N–9 24 W Glenwood/Colo R 0.75 163 757 1,328

23 Storm King 1 -- 4 Mitchell Creek 0.20 15 407 714

24 Storm King 2 -- 5 Mitchell Creek 0.05 43 110 193

25 Mitchell E1 -- Mitchell Creek 0.29 48 369 647

26 Mitchell E2 -- Mitchell Creek 0.01 8 34 59

27 Mitchell E3 -- Mitchell Creek 0.05 25 132 232

28 Mitchell E4 -- Mitchell Creek 0.04 23 130 228

29 Mitchell W4-S -- Mitchell Creek 0.01 8 35 61

30 Mitchell W3 -- Mitchell Creek 0.12 37 323 567

31 Mitchell W2 -- Mitchell Creek 0.13 38 353 619

32 Mitchell W1 -- Mitchell Creek 0.15 40 223 391

34 “Ponderosa Dr W” N–7 W Glenwood/Colo R 0.10 34 130 228

35 “Ponderosa Dr E” N–8 W Glenwood/Colo R 0.05 19 51 89

1

Basin number used in U.S. Army Corps of Engineers (1998) report.

2

Basin number used in Burned Area Emergency Rehabilitation (2002) report.

Post-Fire Hydrologic Hazards for the Coal Seam Wildfire 33
34 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

the West Glenwood Springs area could approach 6 to 8 ft with 

a 100-year storm (fig. 19). If debris flows are generated simultaneously from multiple small tributary subbasins in Mitchell 

Creek (table 5), the combined maximum debris flows could 

exceed 10 to 15 feet in the main stem of Mitchell Creek and 

downstream from the Donegan Bridge (fig. 18).

Post-Fire Hydrologic Hazards for the 

Missionary Ridge Wildfire

Most of the area affected by the Missionary Ridge 

wildfire is underlain by sedimentary rocks including the 

Cutler, Hermosa, and Morrison Formations, known sources of 

debris-flow sediments (Cannon and others, 2003). Numerous 

steep drainage basins in the burned area have the potential to 

produce debris flows that threaten homes, businesses, several 

major roads, bridges, and the dams at Lemon and Vallecito 

Reservoirs during the next several years before substantial 

vegetation regrowth in the burned areas.

Analysis of Debris-Flow-Producing Drainage 

Basins, Missionary Ridge Wildfire—Phase 2

The potential for debris flows from larger rainstorms 

was evaluated in the Missionary Ridge burned area. The 

Missionary Ridge wildfire area is shown in figure 20. 

Cannon and others (2003) and Cannon (Susan H. Cannon, 

U.S. Geological Survey, oral commun., 2003) assessed 

approximately 121 tributaries with some potential for flooding 

and debris flows and estimated the potential peak discharges 

with Cannon’s (2001) regression equation.

Twenty-five of the tributaries Cannon assessed were 

selected for additional debris-flow analysis with FLO-2D 

(table 6). These tributaries were identified as having the 

greatest potential peak debris-flow discharges and for having 

the potential to damage habitable and commercial structures. 

The procedures for simulating Missionary Ridge burned-area 

debris flows are presented in the section “Methods for PostFire Debris-Flow Hazard Analysis.” Other tributaries also have 

a potential to produce floods and debris flows but were not 

included in this analysis.

Subbasins of the Missionary Ridge burned area differ 

greatly in size; drainage areas range from 0.07 to 9.78 mi2. 

These subbasins are tributaries to the Animas, Florida, and 

Los Pinos Rivers. A delineation of the potential inundation 

areas and the maximum depths during a debris flow following a 100-year, 1-hour storm (1.77 inches) are indicated in 

figures 21 and 22 showing the debris-flow subbasins, existing 

alluvial fans, and infrastructure visible on the current (2004) 

USGS topographic maps.

Debris-flow hydrographs, inundation areas, and maximum flow depths were created in FLO-2D. All tributaries 

initially were modeled using a 10-m grid-element size. Five 

large subbasins producing large peak discharges that inundated 

extensive areas were modeled with 30-m grid elements. These 

larger subbasins were Stevens Creek, a tributary of the Animas 

River; True, Shearer, and Red Creeks, tributaries of the Florida 

River; and Red Creek, a tributary of the Los Pinos River 

(figs. 21 and 22). The FLO-2D models for these five subbasins 

approached the grid-element number maximum when 10-m 

elements were used. Consequently, the outflow graphics from 

these five subbasins do not have the high resolution of the 

other subbasins in this study, but the extensive hazard area is 

adequately shown.

The debris-flow depths shown in figures 21 and 22 are 

maximum depths that occurred at some time during the model 

simulation. In most locations in the depositional zone, depths 

increased to a maximum as the sediment and water mixture 

passed and then receded to lesser depths. The time of occurrence of maximum depth varied by location in the depositional 

zone; therefore, these maps do not represent an instant in time 

of the debris-flow deposit or the final depths at the end of the 

debris flow.

The largest increase from estimated pre-burn discharge to 

post-burn debris flow 100-year discharge is expected to occur 

in the Coon Creek subbasin (fig. 21) where peak discharges 

could increase by a factor of greater than 240 (table 6). 

Approximately 96 percent of the 7.99-mi2 Coon Creek subbasin was burned by the Missionary Ridge wildfire, and 

78 percent of the subbasin was moderately to severely burned 

(USDA Forest Service, 2002c). Maximum debris-flow depths 

downstream from the Coon Creek canyon mouth could be in 

the range of 8 to 10 ft with isolated depths in excess of 15 ft. 

Estimates of the increase in 100-year discharge resulting from 

post-fire debris flows, relative to unburned conditions in most 

of the Missionary Ridge area, are not as great as those in Coon 

Creek. In the Animas River area, the increases range from 9 to 

38 times; in the Florida River area, from 22 to 31 times; and 

in the Vallecito Reservoir and Los Pinos River area, from 9 to 

30 times (figs. 21 and 22).

The large contributing drainage areas and large 

100-year debris-flow peak discharges from some Missionary 

Ridge burned-area tributaries (subbasins) result in extensive 

inundation areas (figs. 21 and 22). Existing topography in these 

areas includes older alluvial and debris fans, terraces, hillslopes, 

valley-floors, and flood plains. Isolated areas of deeper flow on 

the debris fan, such as those downstream from Freed Canyon, 

Haflin Canyon, Woodard Canyon, and Kroeger Canyon, are 

most likely the result of sediment and water accumulations in 

topographic low spots, such as at a terrace margin or in abandoned and active stream channels.

Repetitious, echolike depth patterns on some debris-flow 

deposits, such as for Coon Creek and Lost Creek, represent the 

passage of undulating wave forms during runoff (J.S. O’Brien, 

FLO Engineering, Inc., oral commun., June 2003). The 

repetitious fan-shaped inundation patterns, such as those 

downstream from Elkhorn Canyon, Stevens Creek, and Freed 

Canyon, may be the result of a prolonged debris-flow event 

advancing over a series of topographic irregularities, or 
they could be computational relicts related to the model limit 

of eight possible directions for the mixture to flow from one 

square grid element into an adjacent grid element.

Debris-flow deposition into water bodies, such as Lemon 

and Vallecito Reservoirs, was not accurately simulated by 

FLO-2D because no bathymetric data were available. Consequently, the reservoir water surface was treated in the model as 

a solid, planar feature. Debris-flow depths beyond the water’s 

edge are overstated by an undetermined amount; however, 

flow depths at the tributary mouth are within the tolerance of 

the model, and flow depths on the existing land surface are 

reasonably accurate where not affected by backwater effects 

from the artificial reservoir surface.

Summary

Drought conditions in Colorado made the 2002 wildfire season unusually active. Several wildfires substantially 

changed the hydrologic, hydraulic, and geomorphologic 

characteristics of the affected drainage basins. In cooperation 

with the Federal Emergency Management Agency (FEMA), 

a team from the U.S. Geological Survey (USGS) and the 

Bureau of Reclamation (BOR) assessed and ranked the 2002 

Colorado wildfires (as of July 2, 2002) in terms of relative 

hazard to population centers and infrastructure. The team also 

conducted detailed assessments of the hydrologic, hydraulic, 

Table 6. Estimated 100-year debris-flow peak discharges for selected Missionary Ridge burned area tributary subbasins.

[100-year, 1-hour storm total 1.77 inches; sediment concentration, Cv, at water peak = 0.43; USGS, U.S. Geological Survey; BAER, Burned Area Emergency 

Rehabilitation team; mi2, square miles; ft3/s, cubic feet per second; --, not applicable]

Subbasin 

number

Tributary 

subbasin 

name 

USGS 

(figs. 20–22)

BAER 

report basin 

number or 

name1

Tributary to

Drainage 

area 

(mi2)

Pre-fire 

100-year 

peak 

streamflow 

discharge 

(ft3/s)

Post-fire 

100-year 

peak 

streamflow 

discharge 

(ft3/s)

Post-fire 

100-year 

peak 

debris-flow 

discharge 

(ft3/s)

18 Coon Creek N Fk, M Fk, S Fk Animas River Valley 7.99 149 20,653 36,234

21 Unnamed 1st order -- Animas River Valley 2.16 182 3,946 6,923

30 Elkhorn Canyon -- Animas River Valley 0.46 79 1,075 1,886

35 Stevens Creek N10 Animas River Valley 6.02 414 2,186 3,835

50 Freed Canyon Freed Canyon Animas River Valley 2.16 216 4,094 7,183

66 Unnamed 1st order -- Animas River Valley 0.18 43 449 788

69 Unnamed 1st order -- Animas River Valley 0.07 26 156 274

71 Haflin Canyon X-Sec near N19 Animas River Valley 1.61 179 3,050 5,351

92 Woodard Canyon V21 Animas River Valley 0.91 124 1,817 3,188

106 Kroeger Canyon Kroeger Cr 2 Animas River Valley 1.22 150 2,555 4,482

61 Unnamed 2nd order E26 Lemon Reservoir and dam 0.57 90 1,276 2,239

83 True Creek -- Florida River 2.56 238 2,977 5,223

96 Shearer Creek -- Florida River 7.07 455 7,847 13,767

119 Red Creek E34 Red Creek Florida River 7.75 471 8,231 14,440

16 Lost Creek -- Grimes/Vallecito Creeks 2.30 225 1,157 2,030

23 Unnamed 2nd order -- Vallecito Reservoir 0.35 67 910 1,597

24 Unnamed 0 order -- Vallecito Reservoir 0.54 87 799 1,402

29 Freeman Creek E4-12 Vallecito Reservoir 2.32 226 2,965 5,202

53 Unnamed 1st order -- Vallecito Reservoir 0.24 53 607 1,065

55 Root Creek -- Vallecito Reservoir 0.72 105 1,590 2,789

63 Jack Creek E1 Jack Cr/E1A Vallecito Reservoir and dam 1.99 198 3,366 5,905

65 Wilson Creek Wilson Cr E23-25 Vallecito Reservoir 1.58 175 2,590 4,544

68 Gut Canyon -- Vallecito Reservoir 0.38 69 839 1,472

73 Red Creek -- Los Pinos River 9.78 560 9,459 16,595

111 Patton Canyon -- Vallecito Reservoir and dam 0.70 102 1,516 2,660

1

Basin number used in USDA Forest Service (2002c) report.

Post-Fire Hydrologic Hazards for the Missionary Ridge Wildfire 35
36 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

and geomorphologic effects of selected, high-priority wildfires 

on burned and adjacent unburned parts of the drainage basins, 

providing information for use by water managers about the 

effects of wildfire on runoff and sediment from burned drainage basins. The technical assessment focused on population 

centers and infrastructure affected by the wildfires. Existing 

National Flood Insurance Program (NFIP) maps (where available) needed to be revised to reflect post-fire drainage-basin 

conditions. The technical response team, consisting of experts 

in hydrology, hydraulics, sediment transport, geomorphology, 

and GIS mapping, used NFIP study data to evaluate post-fire 

changes to flood-inundation maps where these data existed.

The objective of this study was to conduct three phases of 

hydrologic activities in response to the Colorado wildfires in 

2002:

Phase 1.—Post-wildfire reconnaissance-hazard maps 

were created for 16 Colorado wildfires identified as of July 2, 

2002. These maps were used to rank the relative priority of 

each of the wildfires in terms of anticipated hydrologic hazard. 

These maps were developed for reconnaissance purposes only 

and are not included in this report. Three highest priority wildfires were selected for more detailed hydrologic analysis under 

Phase 2 of the study.

Phase 2.—More detailed hydrologic studies were conducted for those wildfires having the highest priority defined 

in Phase 1, leading to the production of revised flood- or 

debris-flow hazard maps for areas with existing NFIP maps 

and for other flood-prone areas where post-fire flooding could 

threaten downstream population centers or infrastructure.

Phase 3.—Long-term runoff characteristics that reflect 

post-fire drainage-basin recovery and stabilizing hydrologic 

conditions expected to develop over a period of several years 

after the wildfire also were analyzed for two channel reaches: 

the South Platte River between Deckers and Trumbull, Colo., 

and Mitchell Creek in Glenwood Springs, Colo.

An additional study task included a detailed hydraulic analysis of the South Platte River between Deckers and 

Trumbull. Detailed 10-, 50-, 100-, and 500-year flood-plain 

elevations were developed for the Deckers-to-Trumbull reach. 

Floodway elevations also were computed for this reach.

The 16 wildfires that had burned or were burning as of 

July 2, 2002, ranged from the Trinidad Complex wildfire in 

south-central Colorado to the Pinyon Ridge wildfire near 

Meeker in northwestern Colorado, to the Missionary Ridge 

wildfire near Durango, in southwestern Colorado. Three 

wildfires were determined to have a high priority in terms of 

anticipated hazard and potential threat to infrastructure and 

life and were selected for additional, more detailed hydrologic 

assessments. These were the Hayman wildfire in the Colorado 

Front Range Mountains southwest of Denver, the Coal Seam 

wildfire at the southern edge of the Flat Tops region and 

along the Colorado River near Glenwood Springs, and the 

Missionary Ridge wildfire in the southern San Juan Mountains 

near Durango.

The Hayman wildfire started in June 2002 near Lake 

George in the South Platte River Basin and burned approximately 138,000 acres (216 mi2

). Elevations in the burned 

area ranged from 6,289 to over 11,000 ft. The drainage area 

of the South Platte River at South Platte, Colo., is 2,580 mi2. 

The South Platte River flows from southwest to the northeast 

through the interior of the burned area. Most of the burned 

area is composed of shallow, easily eroded, weathered soils 

from the Pikes Peak batholith. The landscape is highly dissected in the upland forested part of the burned area. Annual 

precipitation is composed of snowfall during the winter and 

high-intensity rainstorms during the summer.

The Coal Seam wildfire started on June 8, 2002, near 

Glenwood Springs and burned approximately 12,200 acres 

(19.1 mi2). Elevations in the burned area ranged from 5,800 

to 10,500 ft. In the Coal Seam area, abundant, fine-grained 

sediment is available for debris-flow entrainment originating 

from tributaries underlain by weathered sedimentary rocks of 

the Maroon and other formations. Flooding in Mitchell Creek, 

a major tributary entering the Glenwood Springs area from 

the north, is another potential hazard in the Coal Seam burned 

area. Approximately 25 percent of Mitchell Creek’s 11.9-mi2

drainage area was burned by the Coal Seam wildfire.

The Missionary Ridge wildfire burned from June 9 

to July 14, 2002, and affected approximately 70,500 acres 

(110 mi2) in La Plata County, Colorado. Elevations in the 

burned area ranged from approximately 6,500 to 11,400 ft. 

The wildfire affected tributaries of three major drainage basins 

near Durango: the Animas, Florida, and Los Pinos River drainage basins. Approximately 61 percent of the area was burned 

with a moderate or high severity. Most of the area affected by 

the wildfire is underlain by sedimentary rocks including the 

Cutler, Hermosa, and Morrison Formations, which are known 

sources of debris-flow sediments.

The predominant potential hazard process in the Hayman

wildfire area is flooding by sediment-laden water along the 

large tributaries to, and the main stem of, the South Platte 

River. Although much sediment is available for erosion and 

transport by storm runoff in the Hayman area, there is little 

potential for debris-flow activity because the amount of siltand clay-size material derived from the weathered parent rock 

is relatively small. The other two high-priority burned areas 

had a substantial potential for debris-flow activity that could 

adversely affect life and infrastructure. Debris flows pose a 

hazard distinct from other sediment-laden flows because of 

their unique destructive power; debris flows can occur with 

little warning and can exert great impulsive loads on objects 

in their paths. Even small debris flows can strip vegetation, 

block drainageways, damage structures, and endanger human 

life. The marine shales exposed in formations within the 

Coal Seam and Missionary Ridge burned areas weather into 

fine-grained sediments including clays that are essential to the 

mobility and transport competence of debris flows.

Many of the rainfall-runoff model parameters used in this 

study were extracted from the topography captured in digital 

elevation models (DEMs). Ten-meter digital elevation model 
(10-m DEM) data and Intermap IFSAR 2.5-m data were 

prepared for this study with the LT4X program using elevation 

contour lines (hypsography) from standard USGS 1:24,000-

scale topographic maps. The accuracy of an elevation value in 

the 10-m DEM is ±20 ft in mountainous areas and ±10 ft in 

flatter areas. The ground condition represented in the elevation 

data is that of the original orthophotography used to produce 

each 1:24,000 quadrangle map; in general, for the study area, 

this orthophotography was flown between 1950 and 1980. 

Interferometric Synthetic Aperture Radar (IFSAR) data from 

Intermap Technologies was used over the Hayman burned area 

to provide a more accurate DEM.

Streamflow-gage data for most tributary drainage basins 

of the Hayman, Coal Seam, and Missionary Ridge drainage 

basins were not available; therefore, hydrographs and peak 

discharge values for pre-burn, post-burn short-term, and postburn long-term scenarios were simulated for each subbasin 

by using a rainfall-runoff model. Most model parameters are 

abstract conceptual representations of non-measurable characteristics that must be estimated through a calibration process.

Two calibration approaches were used to estimate the 

pre-burn parameter values in this study: the manual calibration method and the objective calibration method. The 

manual calibration method initially was used for the Hayman 

rainfall-runoff model and involved a trial-and-error estimation of parameter values for all subbasins. Because there was 

no way to ensure the optimal estimation of parameter values 

or to quantify the degree of uniqueness and(or) uncertainty 

associated with the estimated parameter values, a second 

approach, the objective calibration method based on nonlinear 

regression, was used to recalibrate the Hayman rainfall-runoff 

model. The objective calibration method was used to calibrate 

the Coal Seam and Missionary Ridge rainfall-runoff models.

Simulated peak discharge values were computed using 

the HEC–1 rainfall-runoff model. Subbasin characteristics 

were derived using a geographical information system and 

included area, length, and slope. The rainfall-runoff model 

parameters RCN, initial abstraction, and lag time were 

defined by the SCS curve number method. Where affected 

drainage basins and subbasins included both burned and 

unburned areas, post-burn RCNs were computed by weighting the respective drainage-basin conditions according to the 

equations of the SCS curve number method. After the model 

calibration process was complete, the post-burn parameter 

values and associated GIS information were used as input to 

the HEC-HMS rainfall-runoff model for drainage-basin hydrograph generation.

Computed water-peak discharges from the HEC-HMS 

modeling were “bulked,” or increased volumetrically, to 

account for increased sediment concentrations that are 

expected to occur as a result of accelerated erosion after 

burning. Bulking analyses and computations were based 

on previous studies of post-fire runoff in other areas of the 

Western United States and on published research documenting 

the physical behavior of combined water and sediment flows. 

The amount of sediment bulking varied in the study depending 

on whether predominantly water floods or debris flows were 

anticipated in response to the 100-year storm. Peak-discharge 

estimates for the predominant water floods anticipated in the 

South Platte River Basin were bulked by a factor that assumed 

a volumetric sediment concentration (Cv) of 20 percent. Flood 

hydrographs were routed down main-stem channels by using 

routing routines included in the HEC-HMS rainfall-runoff 

model, and post-fire flood elevations were computed for 

bulked peak discharges at selected cross-section locations 

in the South Platte River and Mitchell Creek.

Debris-flow behavior is dependent on the concentration and particle-size range of the entrained sediment and 

on the relative proportion of inertial and viscous forces. A 

relatively high proportion of clay-size particles (diameter less 

than 0.004 mm, or 0.0002 inch) in the transported sediment 

increases debris-flow matrix strength and helps maintain the 

high pore pressure necessary to support larger particles in the 

flow. Sediment concentrations used in simulations at Coal 

Seam and Missionary Ridge are based on results from previous studies. The assumed volumetric concentrations for the 

input debris-flow hydrograph were varied through the event 

and for this study were initial Cv 20 percent, mean Cv approximately 31 percent, maximum Cv

 48 percent (preceding the 

input water hydrograph peak), Cv at the time of the input water 

hydrograph peak 43 percent, and Cv for the duration of the 

event 20 percent.

A two-dimensional flood-routing model, FLO-2D, was 

used to delineate the area of unconfined debris-flow inundation on selected alluvial fan and valley floor areas in the Coal 

Seam and Missionary Ridge burned areas. The model uses a 

specified input hydrograph, volumetric sediment concentration, and existing topography to route a debris flow from the 

originating tributary to the depositional zone. Debris-flow 

discharges presented in this study were generated by 100-year 

rainfall events, and the inflow hydrographs at the alluvial fan 

heads or tributary mouths were generated with the objective 

calibration method used in the South Platte River analysis. The 

100-year, 1-hour rainfall was 1.64 inches for the Coal Seam 

area and 1.77 inches for the Missionary Ridge area.

Interpretation of FLO-2D model output is limited by 

several factors. FLO-2D treats debris-flow composition as a 

temporally and spatially unvarying mixture; coarse material 

does not settle out during the simulation as it does in actual 

mud and debris flows. When the input sediment concentrations are decreased in FLO-2D, the debris-flow mixture travels 

a farther distance down a fan or valley; when concentrations 

are increased, the debris flow travels a shorter distance before 

stopping. The FLO-2D model is a quasi-two-dimensional 

model and, although often used in unconfined flow situations, 

it only routes flow in a downslope direction toward the nearest 

neighbor grid cell rather than in a truly lateral or transverse 

direction. Outflow from one square grid element into an adjacent square grid element is limited to eight possible directions 

(N, NE, E, SE, S, SW, W, NW). Model output is limited by 

Summary 37
38 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

the resolution of the topographic data supplied; in this study, 

10-meter digital elevation data. Most roughness elements less 

than 10 m in size are not accounted for. Also, the original 

topography remains static during a model run and is insensitive to large-scale channel scour or aggradation. Small-scale 

differences in grid-cell elevation values influence the direction 

of cell-to-cell flow propagation. Errors in the input elevation 

values or changes in elevation over time, such as from land use 

or subsequent debris-flow deposition, could render the existing 

model output inaccurate.

Inundation areas and depositional depths generated in 

the FLO-2D simulations reflect the median of predicted values. Minimum and maximum likelihood areas and depths are 

not presented in the model output, and there is large, unquantified variability in the expected outcome of the 100-year storm. 

Another limitation of the analyses is that estimated inundation areas and depths from the model output are not verifiable 

without onsite observations of actual debris flows and the 

rainfall amounts that generated them.

Runoff characteristics that reflect post-fire drainagebasin recovery and stabilizing hydrologic conditions are 

expected to develop over a period of several years after the 

wildfire. A method was developed to objectively determine 

the number of years over which this recovery could occur. 

Assumptions for this method are that (1) a wildfire will raise 

the RCN in a burned drainage basin from a pre-fire RCN 

to a post-burn RCN as a function of burned area and severity; (2) during the recovery period, the post-burn RCN will 

“decay” back to some function of the pre-fire curve number; 

(3) although it is recognized as a simplification, recovery will 

be some function of time; and (4) initial decay will be the 

most rapid and will take place as a function of the magnitude 

of the pre-fire RCN and the difference between pre- and postfire RCNs.

Estimates for both pre- and post-fire RCNs are available 

for all subbasins in the Hayman and Coal Seam burned areas 

on the basis of HEC-HMS modeling. Although there are very 

few field data that describe post-burn recovery, a study in the 

Frijoles Canyon at Bandolier National Monument in New 

Mexico provides a nearly complete description of post-fire 

recovery based streamflow records collected in a burned area. 

The study describes post-fire recovery in terms of the magnitude and frequency of flood peaks; the description was used 

in Hayman and Coal Seam wildfire recovery characterizations 

developed here, as a basis for a post-fire recovery equation that 

is a function of initial RCN, change in RCN due to wildfire, 

and time. The equation has the form of an exponential decay 

equation and can be used to estimate an RCN at any point in 

the recovery process.

A family of curves was generated with this post-fire 

recovery equation. These curves indicate estimates for RCN 

for a recovery period beginning with post-fire conditions and 

continuing for 50 years in a hypothetical drainage basin with 

an assumed pre-burn RCN of 50, raised to post-burn RCNs of 

55 to 100 in increments of 5. In order to obtain an estimate of 

overall recovery in each wildfire area, the equation was used to 

determine values for RCN for all drainage basins for a period 

beginning with post-fire conditions and continuing through 

50 years. The resultant time-series values were evaluated to 

identify a time in the recovery process when the change in 

estimated 100-year flood peak became less than 5 percent per 

year. The recovery times were rounded to the nearest whole 

year and used as the basis to prepare input for HEC-HMS to 

obtain estimates of the 100-year flood peak at the recovery 

time. The recovery-time estimates are: 6 years upstream from 

Cheesman Reservoir; 6 years downstream from Cheesman 

Reservoir; and 4 years for Mitchell Creek. Times in this range 

are consistent with BAER-team estimates of about 5 years due 

to vegetation regrowth, and with field observations from the 

USGS National Research Program of about 6 to 7 years in the 

Buffalo Creek burned area.

Hayman Wildfire

The South Platte River within and downstream from 

the Hayman wildfire is regulated by a series of reservoirs. In 

order to assess the effects of the 100-yr storm and subsequent 

flooding on burned and adjacent unburned areas of the South 

Platte River drainage basin, boundary flow conditions were 

established at the upstream edge of the fire perimeter and at 

the outflow from Cheesman Dam.

Because of the large contributing drainage area of the 

South Platte River Basin upstream from the fire perimeter 

and the substantial regulation/storage capacity of upstream 

reservoirs, it is extremely unlikely that a 100-year flood would 

occur throughout the entire basin during a single runoff event; 

consequently, the 10-year peak discharge at streamflow-gaging 

station 06696000 South Platte River near Lake George was 

selected as the boundary inflow condition. The 10-year peak 

discharge was computed for the period of record since completion of Elevenmile Canyon Reservoir (1933–98). The 10-year 

peak discharge was adjusted to account for the contributing 

drainage area between the streamflow-gaging station and the 

upstream edge of the Hayman fire perimeter, using a regional 

regression equation developed by the USGS for mountain 

regions of Colorado. The adjusted 10-year peak discharge, 

940 ft3/s, was used as the inflow peak for the South Platte 

River at the upstream limit of the burned area.

Cheesman Reservoir is operated as a water-supply 

reservoir; therefore, the boundary condition at the outflow at 

Cheesman Dam was determined to be a full reservoir, with 

uncontrolled flow over the spillway in response to upstream 

runoff. The reservoir is assumed to pass the entire flood volume but none of the sediment entrained from upstream.

Rainfall-runoff modeling was used to develop post-fire 

hydrographs for 19 selected subbasins tributary to the South 

Platte River within and downstream from the Hayman burned 

area. The U.S. Army Corps of Engineers HEC-HMS computer 

model was used for the analysis with the 100-year, 6-hour 

storm (2.4 inches).
A comparison of measured 100-year peak flows at five 

stream gages on tributaries near Cheesman Reservoir with 

the results of the regional regression equations developed for 

mountain areas of Colorado showed that the regional equations substantially overestimated the observed 100-year peaks 

by a factor of 2 or more. As an alternative, the five streamflow 

gages in the Goose Creek and Tarryall Creek drainages were 

used to develop a local regional equation for the study area. 

An ordinary-least-squares regression model to predict 100-year 

peak discharge (Q100) as a function of drainage area (A) was 

developed using the stream-gage data. The regression model 

was used as the basis for calibration of the pre-burn, 100-year 

peak discharge of drainage basins modeled using HEC-HMS. 

Calibration of parameters in HEC-HMS was performed, to the 

extent possible, in the general range of drainage areas defined 

by the five streamflow gages used in the regression analysis.

The objective calibration method was used to estimate 

drainage-basin losses in all of the South Platte River tributaries 

(subbasins) affected by the Hayman wildfire. Larger drainage basins (Turkey Creek, Goose Creek, Wigwam Creek, and 

Horse Creek) were divided into smaller subbasins, and the 

subbasin hydrographs were routed to the basin mouth. Preburn runoff curve numbers (RCN) between 55 and 67 were 

selected for each subbasin. The pre-burn abstraction values 

were selected using default model computations based on preburn subbasin characteristics and are reflective of the weathered rock soils that dominate the area.

The SCS dimensionless unit hydrograph method was 

used to compute the resultant hydrograph. After examination 

of several lag-time equations, the SCS lag-time equation was 

selected for use in modeling. In the SCS equation, lag time is 

calculated directly from the RCN.

Simulated peak discharge for pre-burn conditions was 

calibrated to the 100-year peak discharge computed using 

the locally derived regional equation. Parameter estimation 

for each subbasin was done using the objective calibration 

method. Flow routing within the five larger subbasins was 

performed using the Muskingum method. Because observed 

hydrograph or field data were not available for calibration of 

the routing parameters, values of Muskingum K and X were 

selected within the range of commonly used values for channels in steep, upland subbasins.

Existing studies documenting the hydrologic response 

of burned drainage basins in other areas were used to guide 

the calibration for post-burn conditions. The post-burn 

RCNs selected by the BAER team were adopted for postburn-discharge estimates in South Platte River tributaries 

(subbasins). Where affected drainage basins and subbasins 

included burned and unburned areas, post-burn RCNs were 

computed by weighting the respective drainage-basin conditions according to the governing equations of the SCS curve 

number method. Post-burn lag times were adjusted according 

to the SCS lag-time equation, which is a function of the postburn RCN. Post-burn lag times were estimated using the SCS 

equation and ranged from 24 to 93 percent of pre-burn lag 

times in South Platte River subbasins.

To account for the potential sediment bulking of floodflows in burned drainage basins, computed peak discharges 

were increased according to the assumption that sediment 

concentrations by volume (Cv) could reach the maximum 

water-flood limit of 20 percent. For a Cv of 20 percent, the corresponding bulking factor (BF) is 1.25. This factor was applied 

to peak water discharges computed by the HEC-HMS model 

for areas of moderate to high burn severity; the bulking factor 

was weighted according to relative burned area within each of 

the modeled drainage basins.

Post-burn 100-year peak discharges for the 19 selected 

subbasins, routed to the point of confluence with the South 

Platte River, are expected to increase 3 to 90 times pre-burn 

peaks. Among all modeled drainage basins, including subbasins of the larger tributaries, with substantial (greater than 

50 percent) moderate to severe burned areas, post-burn bulked 

peak discharges are expected to be 28 to 91 times greater 

than pre-burn peaks. For those drainage basins with substantial burned area, average predicted unit-area peak discharge 

for pre-burn conditions is 12.3 ft3/s/mi2; average predicted 

bulked unit-area peak discharge for post-burn conditions is 

830 ft3/s/mi2. Predicted increases in post-burn peak discharge 

are in general agreement with the BAER team’s hydrologic 

assessment of the Hayman wildfire and with hydrologic studies of other burned drainage basins. Results of the analyses are 

summarized in a series of hazard maps showing the extent of 

the 100-year flood, and cross sections showing the 100-year 

flood water-surface elevation along the South Platte River.

The post-burn 10-, 50-, 100-, and 500-year peak discharges along the main stem of the South Platte River were 

computed for the Deckers-to-Trumbull detailed study reach. 

In-stream flow routing, to account for in-channel storage and 

peak attenuation at successive downstream cross sections, 

was performed using the routing routines in the HEC-HMS 

computer model. The Muskingum-Cunge routing routine, 

which incorporates cross-section and hydraulic properties of 

the surveyed cross sections, was used to route flows in reaches 

of the main-stem South Platte River. Routed peaks showed 

little attenuation. Sensitivity testing indicated that hydrograph 

attenuation was affected mainly by channel slope; the relatively steep slopes (measured as water-surface slope during 

the cross-section surveys) through the study reach preclude 

substantial attenuation. The Modified Puls reservoir routing 

routine in HEC-HMS was used to route the computed flood 

hydrograph through Cheesman Reservoir and over the spillway to the downstream reach.

Post-fire recovery-time estimates are 6 years for drainage basins upstream from Cheesman Reservoir, and 6 years 

for drainage basins downstream from Cheesman Reservoir. 

Detailed flood hydraulics were computed using stepbackwater routines in HEC-RAS for a stream reach from 

a point 5,040 ft upstream from the county road bridge over 

the South Platte River at Deckers to a point 2,455 ft downstream from the county road bridge over the South Platte 

River at Trumbull. Peak flows from the 10-, 50-, 100-, and 

Summary 39
40 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

500-year recurrence intervals 6-hour design storm for the 

main-stem South Platte River were used in the detailed reach. 

Water-surface profile elevations in the detailed study reach 

were plotted, and floodway computations were made using 

encroachment routines in the HEC-RAS program for the 

100-year profile.

Coal Seam Wildfire

The Coal Seam wildfire affected many small subbasins 

as well as the large subbasin of Mitchell Creek, a perennial 

tributary of the Colorado River at Glenwood Springs, Colo. 

Water flooding in Mitchell Creek and debris flows from 

smaller tributaries are potential hazards in the Coal Seam area. 

Post-fire hydrologic analyses were conducted to evaluate the 

effects of the 100-year, 1-hour storm (1.64 inch) on the burned 

and adjacent unburned areas of the Mitchell Creek subbasin 

and other subbasins.

Mitchell Creek has a contributing drainage area of 

11.2 mi2 at Donegan Bridge in Glenwood Springs. Earlier 

studies determined the 100-year peak discharge is 360 ft3/s at 

a main-stem point upstream from Donegan Bridge (drainage 

area is 5.9 mi2). A drainage-area adjustment of this peak discharge was made to reflect hydrologic conditions at Donegan 

Bridge. The area-adjusted peak discharge was computed using 

an equation relating peak discharge for gaged sites to ungaged 

sites as a function of relative drainage area. The computed, 

100-year peak discharge for Mitchell Creek at Donegan 

Bridge was 542 ft3/s. Rainfall-runoff modeling was used to 

develop post-fire hydrographs for 15 principal subbasin drainage basins of Mitchell Creek. Subbasin areas in the Mitchell 

Creek drainage ranged from 0.010 to 4.42 mi2.

Unburned conditions first were modeled using the 

100-year peak discharges of 360 ft3/s at the point upstream 

from the Donegan Bridge and 542 ft3/s at the Donegan Bridge 

as target discharges for model calibration. The SCS lag-time 

equation developed for drainage basins smaller than about 

3.25 mi2 was used to compute the lag time. The objective 

calibration method was used to estimate optimal pre-burn 

rainfall-runoff parameters for use in simulating the effects of 

wildfires on (1) unsteady, one- and two-dimensional water 

flooding and (2) unsteady, two-dimensional, debris flows. The 

HEC-HMS model was used to simulate the pre-burn rainfallrunoff processes. Model calibration was achieved by applying 

a nonlinear-parameter estimation algorithm to the HEC-HMS 

model.

Target 100-year peak discharges for each unburned 

Mitchell Creek subbasin were computed using three published regional equations. Resulting parameter sets (RCN, 

initial abstraction, and lag time) then were analyzed using the 

PEST algorithm and HEC-HMS to compute the routed peak 

discharge at the mouth of Mitchell Creek. Comparison tests 

showed that of the three regional equations evaluated, the Vaill 

equation produced target subbasin discharges and resultant 

RCNs that yielded the best estimate of the accepted 100-year 

discharge for the main stem of Mitchell Creek. The Vaill 

equation produced peak discharges that agreed closely with 

peak discharges from the existing flood-insurance study. Flow 

routing within the Mitchell Creek subbasin was performed 

using the Muskingum method.

About 25 percent of the Mitchell Creek drainage basin 

was burned by the Coal Seam wildfire in 2002. Adjustments 

to the pre-burn modeling parameters were made to reflect 

the burned condition within each subbasin as was done for 

tributaries to the South Platte River. The BAER team “Coal 

Seam Fire Hydrology Report” was used to guide the selection of RCNs for post-burn conditions in the Mitchell Creek 

subbasin. Post-burn lag times range from 40 to 87 percent of 

pre-burn lag times, depending on the amount of burned area in 

the subbasin.

Computed Mitchell Creek peak discharges were 

increased to account for potential sediment bulking of water 

floods according to the assumption that sediment concentrations by volume (Cv

) could reach the maximum water-flood 

limit of 20 percent. This factor was applied to peak discharges 

computed for areas of moderate to high burn severity; the 

bulking factor was weighted according to relative burned 

area within each of the modeled subbasins. Post-burn, bulked 

100-year peak flows for Mitchell Creek subbasins are expected 

to increase 2 to 21 times pre-burn peaks. Post-burn peak discharges for points along the main stem of Mitchell Creek are 

expected to increase 3 to 4 times pre-burn peaks.

Many of the small subbasins burned by the Coal Seam 

wildfire have the potential to produce damaging debris flows. 

Debris-flow analysis with FLO-2D was done for 26 tributaries (subbasins) identified as having the greatest potential peak 

debris-flow discharges and for having the potential to damage 

to habitable and commercial structures. Debris flows from 

10 small tributaries to Mitchell Creek also were simulated 

with FLO-2D. Drainage areas for the Coal Seam burnedarea subbasins range from 0.01 to 0.75 mi2

.

Subbasins with a relatively large area of moderate and 

high burn severity were characterized by marked increase 

in runoff and sediment yield. Estimates of the increase in 

100-year discharge resulting from post-fire debris flows, 

relative to unburned conditions, range from 8 to 14 times in 

the Red Mountain area, 2 to 9 times in the West Glenwood 

Springs area, and 8 to 14 times for selected tributaries of 

Mitchell Creek. Runoff from tributaries included in the Coal 

Seam debris-flow analyses was not routed within the Mitchell 

Creek drainage basin; runoff values used in FLO-2D analyses 

represent a basin-mouth summary of discharge from the contributing drainage area and are therefore slightly different from 

the Mitchell Creek water-flood runoff estimates where flow 

routing was performed. Post-fire recovery-time estimates were 

not made for the smaller subbasins burned by the Coal Seam 

wildfire; however, the estimated recovery time for Mitchell 

Creek is 4 years.
The debris-flow depths in this report are maximum depths 

that occurred at some time during the model simulation. In 

most locations in the depositional zone, depths increased to a 

maximum as the sediment and water mixture passed and then 

receded to lesser depths. The time of occurrence of maximum depth varied by location in the depositional zone. Some 

debris-flow depositional areas were extensive. Debris flows 

from several small subbasins in Red Mountain inundated large 

areas of the Wulfsohn Fan, and maximum depths of 4 to 6 ft 

could occur near the west end of the fan. Maximum depths in 

the West Glenwood Springs area could approach 6 to 8 ft with 

a 100-year storm, and if debris flows are generated simultaneously from multiple small tributary drainage basins in Mitchell 

Creek, the combined maximum debris flows could exceed 10 

to 15 ft in the main stem of Mitchell Creek and downstream 

from the Donegan Bridge.

Missionary Ridge Wildfire

Numerous steep drainage basins in the Missionary Ridge 

burned area have the potential to produce debris flows. Post-fire 

hydrologic analyses were conducted to evaluate the effects of the 

100-year, 1-hour storm (1.77 inch) in 25 burned tributaries. Subbasins of the Missionary Ridge burned area differ greatly in size; 

drainage areas range from 0.07 to 9.78 mi2. These subbasins are 

tributaries to the Animas, Florida, and Los Pinos Rivers.

Debris-flow hydrographs, inundation areas, and maximum flow depths were created in FLO-2D. All tributaries 

initially were modeled with FLO-2D using a 10-m gridelement size. Five subbasins with relatively large drainage 

areas producing large peak discharges that inundated extensive 

areas were modeled using 30-m grid elements. These drainage 

basins were Stevens Creek, a tributary of the Animas River; 

True, Shearer, and Red Creeks, tributaries of the Florida River; 

and Red Creek, a tributary of the Los Pinos River.

The debris-flow depositional depths in most locations 

increased to a maximum as the sediment and water mixture 

passed and then receded to lesser depths. The time of occurrence of maximum depth varied by location in the depositional 

zone. The largest increase from estimated pre-burn discharge 

to post-burn debris flow 100-year discharge is expected to 

occur in the Coon Creek subbasin where peak discharges 

could increase by a factor greater than 240. Approximately 

96 percent of the 7.99-mi2 Coon Creek subbasin was burned 

by the Missionary Ridge wildfire, and 78 percent of the 

subbasin was moderately to severely burned. Maximum 

debris-flow depths downstream of the Coon Creek canyon 

mouth could be in the range of 8 to 10 ft with isolated depths 

in excess of 15 ft. Estimates of the increase in 100-year 

discharge resulting from post-fire debris flows, relative to 

unburned conditions in most of the Missionary Ridge area, are 

not as great as those in Coon Creek. In the Animas River area, 

the increases range from 9 to 38 times; in the Florida River 

area, from 22 to 31 times; and in the Vallecito Reservoir and 

Los Pinos River area, from 9 to 30 times.

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References Cited 43
Appendixes
Procedures for All Hydrologic Hazards: 

Sediment-Laden Water Floods and 

Debris Flows

Short-Term Hazards

1. Determine the dominant hydrologic processes likely to 

create hazards in the short term (perhaps 3–6 years) before 

substantial drainage basin recovery from the effects of fire.

2. Acquire or construct digital elevation model (DEM) data 

for the burned drainage basins and downstream areas with 

potential for flood or debris-flow inundation. Identify the 

appropriate resolution of DEM data based on data availability, 

modeling requirements, and project cost. Compute drainagebasin area, length, and slope using a geographical information 

system (GIS).

3. Acquire or survey detailed channel cross sections along 

main stem of channels, if flood-plain mapping will be done.

4. Compile historical peak-discharge data from streamflowgaging stations located within or near the burned area (if 

available), or from drainage basins with similar climate and 

geography to those of the affected area. If recorded streamflow 

data are not available for the affected area, regional regression 

equations derived from gage data collected in hydrologically 

similar regions may be appropriate.

5. Acquire precipitation data from nearby weather stations or 

from the NOAA precipitation-frequency atlas (Miller and others, 1973). An observed or design hyetograph representative of 

the study area is needed for rainfall-runoff modeling.

6. Select an appropriate computer program to be used for 

rainfall-runoff modeling. In this study, the U.S. Army Corps 

of Engineers’ Hydrologic Modeling System (HEC-HMS) was 

selected (U.S. Army Corps of Engineers, 2000).

7. Select an appropriate mathematical model to estimate the 

precipitation-runoff and routing process. In this study, the SCS 

Curve Number Loss Model (Soil Conservation Service, 1985) 

was selected to estimate runoff volume as a function of the 

precipitation hyetograph and drainage-basin characteristics. 

The SCS Curve Number Loss Model includes a transformation to convert runoff volume to a streamflow hydrograph, and 

hydrologic routing to “account for storage and energy flux as 

water moves through stream channels” (U.S. Army Corps of 

Engineers, 2000).

8. Estimate pre-burn rainfall-runoff model parameters for all 

drainage basins in the burned area in terms of the loss/transform

model to be used. Parameters required for the SCS Curve 

Number Model are the runoff curve number, initial abstraction, and basin lag time. Calibration of pre-burn rainfall-runoff

model parameters may be done manually (trial-and-error), or by 

using an objective method based on nonlinear regression. In this 

study, the objective calibration method was used to incrementally adjust the parameter values until the modeled peak discharge at the basin outlet matched the “t-year” peak discharge 

(where the “t-year” value characterizes the recurrence interval 

of interest). In the objective calibration method, an appropriate

precipitation hyetograph, of specific depth-duration-frequency 

(such as the 6-hour, 100-year storm), is used in conjunction 

with a rainfall-runoff model and an optimization algorithm to 

estimate the optimal set of drainage-basin parameters.

9. Once the pre-burn rainfall-runoff model has been calibrated to local or regional hydrologic conditions, the pre-burn 

drainage-basin parameters are adjusted to reflect post-burn 

conditions. Post-burn runoff curve numbers for various burn 

severities, documented by the USDA Forest Service BAER 

Teams, were used in this study (see for example, USDA Forest 

Service, 2002c). Photogrammetric methods, which can provide a measure of the burn intensity, also may be used.

10. Where affected drainage basins and subbasins include 

burned and unburned areas, composite post-burn runoff curve 

numbers are derived using a weighting procedure based on the 

governing relation between runoff and precipitation excess. 

In this study, the weighting procedure was defined in terms 

of precipitation excess according to the governing equations 

of the SCS runoff curve number method (Soil Conservation 

Service, 1985).

11. Estimate post-burn peak discharges (t-year recurrence 

interval) and post-burn runoff hydrographs for the burned 

drainage basins, using the rainfall-runoff model (for example, 

HEC-HMS), the computed post-burn rainfall-runoff model 

parameters, and the t-year rainfall distribution defined by 

amount, duration, and cumulative density function (as previously selected).

12. Route the main-stem peak discharge for post-burn conditions using a hydraulic model such as HEC-RAS (U.S. Army 

Corps of Engineers, 2001a), and complete the flood-hazard 

map according to conventional procedures.

Appendix 1. Summary of Methods for Post-Fire Flood and Debris-Flow Hazard 

Analyses

[Methods are described in greater detail in the previous sections of this report]

Appendix 1. Summary of Methods for Post-Fire Flood and Debris-Flow Hazard Analyses 47
48 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Long-Term Hazards

1. Evaluate the post-fire recovery period and estimate hydrologic conditions for the drainage basin over a longer period of 

time. The long-term recovery period reflects the time in years 

for the drainage basin to reach a generally stable condition, not 

the time required for the drainage basin to return to pre-burn 

conditions.

2. In this study an exponential decay equation, developed on 

the basis of assumptions and a limited amount of measured 

data, was used to estimate input drainage-basin parameters for 

a time-series of 50 years, beginning with post-fire conditions. 

The rainfall-runoff model was then used to obtain a series of 

estimated peaks for t-year design storm at the downstream end 

of the modeled area.

3. The resultant series of estimated peaks was evaluated to 

identify the period of time (in years) in the recovery process 

for which the annual reduction in the estimated peak discharge 

becomes relatively stable (less than 5 percent per year). This 

period of time is called “long-term recovery.”

4. Estimate peak discharges and runoff hydrographs for 

long-term recovery (t-year recurrence interval), using the 

rainfall-runoff model (for example, HEC-HMS).

5. Route the main-stem peak discharge for long-term recovery using a hydraulic model such as HEC-RAS (U.S. Army 

Corps of Engineers, 2001a), and complete the flood-hazard 

map according to conventional procedures.

Additional Procedures for Sediment-Laden 

Water Floods

1. Bulk or increase the discharge hydrograph volumetrically, 

to account for the addition of entrained sediment (the result 

will be increased water discharge as surrogate for sediment 

load). In this study, a bulking factor was applied to basin areas 

determined to have moderate to high burn severity. Application of a bulking factor is an interpretive decision that will be 

based on the drainage-basin characteristics of a given study 

area. For water flooding, the theoretical upper limit of sediment concentration by volume is 20 percent. This may be 

considered the upper limit of adjustment of the hydrograph 

for sediment-laden water floods. A sediment concentration 

of 20 percent by volume translates to a bulking factor of 1.25, 

which was used in this study (O’Brien and Fullerton, 1989).

2. Route the sediment-adjusted flood hydrographs through 

the drainage basin by using hydrologic routing routines 

included in the rainfall-runoff model. In this study, Muskingum

and Muskingum-Cunge routing methods were applied in 

HEC-HMS.

3. Compute post-fire flood elevations for post-burn peak 

discharges at selected cross-section locations along the study 

reach using an appropriate hydraulic model (for example, 

HEC-RAS), and delineate the resulting flood-plain boundaries 

on a topographic map using DEM (or photogrammetric) data. 

This constitutes the short-term “Hazards Map.”

Additional Procedures for Debris Flows

1. Debris flows are modeled using an appropriate flood and 

debris-flow routing model. In this study, the FLO-2D twodimensional debris-flow-routing model was used (O’Brien, 

1993, 2001).

2. Convert DEM maps into an ArcGIS (Environmental 

Systems Research Institute, 2002) GRID format. Divide the 

grid data sets into subsets covering the channel and depositional areas to be modeled. Import the grid data into FLO-2D 

(or other appropriate debris-flow routing model).

3. Import the post-burn inflow hydrograph (generated using 

HEC-HMS) into FLO-2D. In this study, hydrographs corresponding to the 100-year post-burn peak discharges were used. 

Note: Procedures to compute the post-burn inflow hydrograph 

(water only, no sediment bulking) were described in the 

previous section (“Additional Procedures for Sediment-Laden 

Water Floods”).

4. Apply variable volumetric sediment concentrations (Cv) 

to the input hydrograph. In this study, the following concentrations were applied to each inflow hydrograph: initial Cv

20 percent, mean Cv approximately 31 percent, maximum Cv

48 percent (preceding the input water hydrograph peak), Cv

43 percent at the time of the input water hydrograph peak, 

and Cv 20 percent for the duration of the event.

5. Generate FLO-2D model output files, including maximum 

velocity and inundation depth files. In this study, maximum 

debris-flow depths in each grid element were overlaid on a 

topographic map.

6. Delineate debris-flow inundation maps using FLO-2D 

output files, DEM data, and an appropriate GIS.
This Appendix presents the results obtained with the 

manual calibration method. The manual calibration method 

involved incremental adjustment of runoff curve numbers 

(RCN) to obtain discharges at the mouth of each drainage 

basin tributary to the South Platte River to match results from 

the regional 100-year peak-flow equations. Results from the 

manual calibration method were the basis for the flood hazard 

maps presented in this report (figs. 8 through 14) and in a previously composed USGS Administrative Report presented to 

FEMA in July 2003 (J.G. Elliott and others, written commun.).

The material in this Appendix, including figures and 

tables, is the same as that presented in the USGS 2003 

Administrative Report to FEMA and are the final products for 

the short-term (approximately 1 to 5 years) hazard assessment 

of the Hayman burn area. The material in this Appendix is 

included for comparison to results from the objective rainfallrunoff model calibration method.

South Platte River “Limited-Detail” Hydrologic 

Analysis

Post-fire hydrologic analyses were conducted to evaluate the effects of the 100-year peak flow on the burned and 

adjacent unburned areas of the South Platte River drainage 

basin and reflect drainage-basin conditions that are expected 

to exist during the next several years (in the short-term, prior 

to substantial regrowth of vegetation in the burned areas). 

The results of these analyses (known to FEMA as a “Limited 

Detail Analysis”) were used to delineate a hazard-mitigation 

map for post-fire, 100-year flooding of the South Platte River 

and will not be used for regulatory purposes (John Liou, 

Federal Emergency Management Agency, oral commun., 

2003).

The approach to the post-fire “limited-detail” hydrologic 

analyses included the following steps:

1. Inflow conditions were established for the South Platte 

River at the upstream boundary of the burned area and for the 

South Platte River downstream from Cheesman Dam.

2. A rainfall-runoff model was calibrated for pre-fire 

(unburned) conditions in the affected drainage basins tributary 

to the South Platte River. Runoff generated by the 100-year, 

6-hour rainstorm (2.4 inches) was calibrated to computed 

100-year peak discharge (flood-frequency analysis) at selected 

stream-gage sites in the study area.

3. Rainfall-runoff of the 100-year, 6-hour storm for post-fire 

conditions in burned drainage basins tributary to the South 

Platte River was modeled.

4. Peak discharges for drainage basins tributary to the South 

Platte River were computed (with routing of the runoff hydrograph through the larger drainage basins).

5. Peak discharges for burned drainage basins were increased 

using a bulking factor to reflect the increased runoff volume 

due to large sediment loads.

6. Peak discharges (bulked flow) for selected reaches of the 

South Platte River (within and downstream from the burned 

area) were computed using a hydrograph routing algorithm.

South Platte River Inflow Conditions

Boundary flow conditions at the upstream edge of the 

fire perimeter and at the outflow from Cheesman Dam were 

established as follows.

Upstream Edge of Burn Perimeter

Discharge records for streamflow-gaging station 06696000 

(South Platte River near Lake George, drainage area 963 mi2) 

are available for the period 1930–98; the gage was located 

downstream from the outlet of Elevenmile Canyon Reservoir 

(owned and operated by the Denver Water Board). Because of 

the large contributing drainage area of the South Platte River 

basin upstream from the wildfire area and the substantial regulation/storage capacity of upstream reservoirs, it is extremely 

unlikely that a 100-year flood would occur throughout the entire 

basin during a single runoff event. To account for potential 

antecedent runoff and reservoir releases into the burned area, 

a 10-year peak discharge was selected as the boundary inflow 

condition. The 10-year peak discharge for streamflow-gaging 

station 06696000 was computed for the period of record since 

completion of Elevenmile Canyon Reservoir (1933–98). The 

resulting discharge is 840 ft3/s.

The 10-year peak discharge was adjusted to account 

for contributing drainage area between streamflow-gaging 

station 06696000 and the upstream edge of the Hayman fire 

perimeter (drainage area 1,133 mi2), using a regional regression equation for ungaged sites near gaging stations developed by the USGS for mountain regions of Colorado (Vaill, 

2000). The adjusted 10-year peak discharge is 940 ft3/s, which 

was used as the inflow peak for the South Platte River at the 

upstream edge of the fire perimeter. A similar analysis was 

used to compute the pre-burn discharge for Tarryall Creek, 

which also is regulated. The computed 10-year peak discharge 

was 715 ft3/s (Tarryall Creek near Lake George). Tarryall 

Creek flows into the burned area of the Hayman fire and 

was treated as a boundary inflow point.

Outflow from Cheesman Dam

Cheesman Reservoir is owned and operated by the Denver 

Water Board as a water-supply reservoir for the City of Denver. 

It is not designated for flood control, so hydrologic analysis 

of the 100-year flood assumes fill-and-spill operation of the 

Appendix 2. The Manual Calibration Method for the Hayman Burned Area

Appendix 2. The Manual Calibration Method for the Hayman Burned Area 49
50 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

dam. That is, the reservoir is allowed to fill to capacity then 

freely spill excess over the spillway. Based on discussions 

with staff of the Denver Water Board (Robert Steger, Denver 

Water Board, oral commun., 2003), the boundary condition 

at Cheesman Dam was determined to be a full reservoir, with 

uncontrolled flow over the spillway in response to upstream 

runoff. The outlet works (release capacity 1,400 ft3/s) 

were assumed to be closed; the spillway (release capacity 22,370 ft3

/s) would pass the entire flood (subject to peak 

attenuation by the reservoir) and produce the base flow to be 

used for modeling of the South Platte River downstream from 

the dam. Outflow from Cheesman Dam was assumed to contain no sediment.

Cheesman Reservoir could be filled with water at any 

time within 1 to 4 years after the fire, or more, in response 

to either operational considerations (Cheesman evaporation 

rates are smaller than upstream reservoirs on the South Platte 

River system) or natural runoff. As a result, both short-term 

(hazard-mitigation) and long-term modeling scenarios reflect 

a full-reservoir condition.

South Platte River Tributary Rainfall-Runoff 

Modeling—Manual Calibration Method

Rainfall-runoff modeling was used to develop post-fire 

hydrographs for 19 principal drainage basins tributary to the 

South Platte River within and downstream from the Hayman 

burn area. These principal drainage basins and an additional 

22 minor contributing drainages were analyzed with the 

U.S. Army Corps of Engineers HEC-HMS computer model 

(U.S. Army Corps of Engineers, 2001b) and by using the 

100-year, 6-hour storm (2.4 inches).

Rainfall-Runoff Model Methodology for the Hayman Fire

Rainfall-runoff modeling was conducted in two steps to 

simulate (1) preburned or unburned conditions, and (2) burned 

conditions.

Step 1, Modeling of Unburned Conditions

The runoff hydrograph for the 100-year peak discharge 

was developed for natural, unburned conditions of each drainage basin. Because streamflow data for most tributary drainage 

basins were not available, a hydrograph and peak discharge 

for each drainage basin were computed using the rainfallrunoff model; basin hydrographs were generated in the model 

using the Soil Conservation Service (SCS) Curve Number 

Loss model (Soil Conservation Service, 1985) as described 

previously in the “Rainfall-Runoff Model Calibration and 

Simulation” section of the report.

A comparison of measured 100-year peak flows 

(Interagency Advisory Committee on Water Data, 1982) at 

five streamflow gaging stations in the Goose and Tarryall 

Creek drainages with the results of regional regression equations developed for mountain areas of Colorado (Vaill, 2000; 

Browning, 2001; Kircher and others, 1985) showed that the 

regional equations substantially overestimated the observed 

100-year peaks (by a factor of 2 or more). As an alternative, 

the five streamflow gaging stations in the Goose and Tarryall Creek drainages were used to develop a local regional 

equation for the study area. Table 2–1 shows a summary of 

the drainage basin characteristics and the computed 100-year 

peak discharges used to develop the relation (Interagency 

Advisory Committee on Water Data, 1982). The resulting peak 

discharges computed using the local regression model, along 

with those predicted by the Vaill regional equation (2000), are 

shown in table 2–1 for comparison. The sites generally are 

unaffected by regulation and are considered to reflect meteorological and hydrological characteristics representative of the 

burned and adjacent unburned drainage basins affected by the 

fire. Because of the short period of historical record for each 

gage, no mixed-population analyses (snowmelt and rainfall 

peaks) were performed.

Table 2–1. Characteristics of streamflow-gaging stations used for calibration of 100-year peak discharge for pre-burn conditions, 

South Platte drainage basin.

[mi2, square miles; ft, feet; ft/ft, feet per feet; ft3/s, cubic feet per second; Q100, 100-year peak discharge]

Streamflow-gaging station Period 

of record

Drainage 

area 

(mi2)

Gage 

elevation 

(ft)

Basin 

slope 

(ft/ft)

Q100

at gage 

(ft3/s)

Predicted 

Q100, 

equation A–1 

(ft3/s)

Predicted 

Q100, 

Vaill1

(ft3/s)

Tarryall Creek at Upper Station near Como 

(06696980)

1978–86 23.7 9,935 0.316 236 192 569

Michigan Creek above Jefferson (06697450) 1978–86 23.1 9,503 0.246 196 188 513

Jefferson Creek near Jefferson (06698000) 1978–86 11.8 9,600 0.333 81 108 355

Tarryall Creek below Rock Creek, near Jefferson 

(06699005)

1983–97 236 9,020 0.182 1,050 1,270 2,390

Goose Creek above Cheesman Lake (06700500) 1924–82 86.6 6,910 0.317 646 559 1,410

1

Vaill, 2000.
An ordinary-least-squares regression model to predict 

100-year peak discharge, Q100, as a function of drainage area, 

A, was developed using the gage data shown in table 2–1. The 

resulting equation and regression statistics were:

R squared

Standard error 

of estimate (2–1)

Q100 = 14.21 A0.823 0.995 28 percent

The regression coefficient (14.21) in the equation 

includes a bias correction factor to correct for bias introduced 

in the process of converting the results of log-space regression 

analysis back to rectangular coordinates (Duan, 1983).

Similar one-parameter models for Q100 have been developed by Browning (2001) and by Jarrett and Costa (1988). A 

plot of the new regression analysis showing the best-fit line 

defined by the equation is shown in figure 2–1; all five data 

points lie within the computed 95-percent confidence intervals 

(not shown) for the regression. The regression line generally 

plots lower and parallel to the equation defined by Jarrett and 

Costa (not shown) for a larger dataset (basins below 8,000 ft 

elevation) developed for the South Platte River Basin.

The regression model was used as the basis for calibration of the pre-burn, 100-year peak discharge of drainage 

basins modeled using HEC-HMS. The regression model is 

limited by the small number of streamflow gages available 

for analysis within the study area and by the relatively short 

period of record at each gage (which reduces the reliability of 

the peak-flow statistics).

The Soil Conservation Service (SCS) curve number 

method was used to estimate rainfall-runoff losses in individual, smaller tributaries. The objective calibration method, 

described in the “Rainfall-Runoff Model Calibration and 

Simulation” section of the report, was used to estimate 

rainfall-runoff losses in the larger tributary drainage basins 

that were a composite of several smaller drainage basins 

(Turkey Creek, Goose Creek, Wigwam Creek, and Horse 

Creek) (fig. 4 of the main body of the report). These larger 

composite drainage basins were divided into smaller subbasins 

that generally correspond to basin delineations defined by the 

BAER Team (USDA Forest Service, 2002a) in their post-fire 

analysis of the Hayman area; routing of subbasin hydrographs 

to the basin mouth was conducted for these large basins. 

On the basis of existing reports that describe pre-fire drainage basin conditions within the study area (Foster Wheeler 

Environmental Corporation, 1999; USDA Forest Service, 

2002a) and assessment of aerial photography, pre-burn runoff 

curve numbers (RCN) between 55 and 67 were selected for 

each drainage basin (pre-burn RCNs used in this study are 

somewhat lower than those selected by the BAER Team). In 

addition to drainage basin RCN values, the initial abstraction (infiltration) and the percentage of impervious area were 

entered into the model. The pre-burn abstraction values were 

selected using default model computations based on pre-burn 

drainage basin characteristics and are reflective of the weathered rock soils that dominate the area. Impervious areas (rock 

outcrops, roads, and so forth) were mapped by the BAER 

Team and were accounted for in the model by adjusting RCNs 

for those areas.

The SCS dimensionless unit hydrograph method was 

used to compute the resultant hydrograph. The Taylor-Schwarz 

(1952) lag-time equation was selected for use in modeling 

after testing with several lag-time computation methods; other 

methods considered include the SCS lag-time equation (Soil 

Conservation Service, 1985) and the Denver lag-time equation 

(Wright-McLaughlin Engineers, 1975). The Taylor-Schwarz 

method required minimal parameter calibration in modeling 

Figure 2–1. Relation of 100-year flood peaks and drainage area showing the best-fit regression line using 

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Appendix 2. The Manual Calibration Method for the Hayman Burned Area 51
52 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

pre-burn, 100-year peak discharges for the study area. Other 

methods resulted in parameter values outside of the range of 

values that would be expected for the study area. The TaylorSchwarz equation has the following form:

Lt = Ct (LLca)

0.3 (2–2)

Ct = 0.6/S0.5 (2–3)

where

Lt is the Taylor-Schwarz lag time, in hours;

Ct is a coefficient of basin topography based on basin 

slope;

L is the basin length, measured along the main channel to the furthest point on the basin perimeter, 

in miles;

Lca is the length from the basin mouth to the basin 

centroid, measured along the main channel from 

its origin (as determined from the base map) to 

a point opposite the centroid, in miles; 

and

S is the average basin slope.

Simulated 100-year peak discharge for pre-burn conditions was calibrated to the 100-year peak discharge computed 

with equation 2-1. Calibration generally was conducted within 

the range of drainage area represented by the regression 

analysis. Calibration of the four larger basins (Turkey Creek, 

Goose Creek, Wigwam Creek, and Horse Creek) was designed 

to produce peak discharges that correspond to values predicted by equation 2–1 for the basin mouth (confluence with 

the South Platte River). Calibration of each drainage basin

was done manually, by adjusting RCN values (and associated 

initial abstractions) incrementally until the simulated peak

discharge at the drainage basin outlet was equal to the peak 

discharge predicted by equation 2–1.

Flow routing within the larger basins was performed using 

the Muskingum method (McCuen, 1989). Because observed 

hydrograph or field data were not available for calibration of 

the routing parameters, values of Muskingum K (defines the 

time of travel for a flood wave traversing the basin) and X (a 

weighting factor that describes the backwater storage effects of 

a channel) were selected within the range of commonly used 

values for channels in steep, upland drainage basins (McCuen, 

1989; John Liou, FEMA, oral commun., 2003):

• Muskingum K = 0.6 hour;

• Muskingum X = 0.4, to reflect channels with little 

over-bank storage.

A summary of pre-burn calibration data (RCN, abstraction, lag-time factors) for all principal and minor drainage 

basins is provided in Appendix table 3–3.

Step 2, Modeling of Burned Conditions

Adjustments of the pre-burn peak discharge were made 

to reflect the burned conditions within each drainage basin. 

Existing studies documenting the hydrologic response of 

burned drainage basins in other areas were used to guide 

the calibration for post-burn conditions. The “Hayman Fire 

Hydrology Report” (USDA Forest Service, 2002a) was used 

to guide the selection of RCNs for post-burn conditions. The 

BAER Team study reports that marked increases in runoff 

occur in areas of moderate-to-high burn severity; low burn 

severity also contributes to increased runoff. Because of the 

detailed mapping of the post-burn drainage basins (including burn severity, rock outcrops, unburned area, and water 

courses) conducted by the BAER Team, and because of extensive USDA Forest Service experience with post-fire hydrology, the post-burn runoff curve numbers selected by the BAER 

Team generally were adopted for this study. Exceptions were 

the use of lowered RCNs for some unburned areas (as noted 

previously), and a slightly higher RCN for areas of moderate 

to high severity burn (explained herein). RCNs used for the 

modeling described in this report are:

• Rocky areas = 90

• Unburned forest = 55–60

• Low burn severity = 85

• Moderate and high burn severity = 98 (BAER Team 

used 95)

Where affected drainage basins and subbasins included 

burned and unburned areas, post-burn RCNs were computed 

by weighting the respective drainage basin conditions according to the governing equations of the SCS curve number 

method. The relation between RCN and drainage-basin runoff 

is nonlinear, such that small burned areas can be expected to 

cause substantial increases in runoff. Initial abstraction values 

generally decrease as a result of moderate to severe burned 

conditions (URS Corporation, 2000). In the SCS method, 

initial abstraction is a function of RCN. An RCN value of 95 

produces an initial abstraction of 0.11 inch; an RCN value of 

98 produces an initial abstraction of 0.04 inch. Runoff data 

and field observations made by the USGS (Robert Jarrett, oral 

commun., 2002) suggest that runoff in burned areas of the 

Buffalo Creek fire and Hayman fire (as well as other fires in 

the Western United States) can occur with as little as 0.1 inch 

of rainfall, indicating that initial abstractions (especially where 

burned soils may be hydrophobic) may be less than 0.1 inch. 

In view of these observations, a lower limit (conservative) 

abstraction value of 0.04 inch was used for areas of moderatehigh burn severity (RCN = 98). This modification of RCN for 

moderate-high burn severity (from 95 to 98) resulted in an 

increase in computed peak discharges in the South Platte River 

of as much as 20 percent.

Removal of surface vegetation by wildfire can be 

expected to decrease the runoff lag time in an affected drainage basin (URS Corporation, 2000; U.S. Army Corps of 

Engineers, 2000). Because site-specific data are not available 

to calibrate this response, post-burn lag times were reduced as 

a function of the percentage of moderate-to-high burned area 

in each drainage basin. Adjustment of post-burn lag times was 

made using a lag-time equation developed by the BOR for the 

Rocky Mountain region (Cubworth, 1989, p. 74). The BOR 
equation has the same basic form as the Taylor-Schwarz equation, with the inclusion of a basin-slope parameter (U.S. Army 

Corps of Engineers, 1957). The BOR found that the TaylorSchwarz coefficient Ct

 was related to the average Manning’s n 

value representing the hydraulic characteristics of a drainage 

basin’s drainage network. The following equation was used to 

compute lag time, Lg (in hours):

Lg = 26Kn [(LLca)/S0.5]

0.33 (2–4)

where

Kn is the average Manning’s n value for the drainage 

basin;

L is the basin length, measured along the main channel from its origin (as determined from the base 

map) to the furthest point on the basin perimeter, in miles;

Lca is the length to the basin centroid, measured along 

the main channel to a point opposite the centroid, in miles;

and

S is the average basin slope.

Note that the term 26 Kn is a basin coefficient similar to 

the coefficient Ct in the Taylor-Schwarz equation. In order to 

better characterize the post-burn lag-time conditions, the following procedure was used:

1. Pre-burn lag times, calibrated using the Taylor-Schwarz 

equation and the regression equation for peak discharge 

data, were used to derive the corresponding value for Kn in 

equation 2-4; this essentially was a calibration process. The 

approach appears to fit well with the observed BOR data for 

the Rocky Mountains. Their relation predicts Manning’s n to 

be in the range of 0.050 to 0.073 for thunderstorm lag times in 

the Rocky Mountains. Most of the Hayman pre-burn lag times 

lie within this range.

2. Post-burn lag-time conditions were adjusted using n = 0.030 

for moderate-high burn areas and n = 0.040 for low-burn areas. 

A composite, weighted n value for each basin (based on percentage of unburned, low burn, and moderate-high burn areas) was 

used in the BOR lag-time equation. Manning’s n values for 

post-burn conditions were selected on the basis of professional 

judgment and are considered to be the lower bound for post-burn 

drainage basin roughness.

Weighted, post-burn lag times can be as low as 39 percent 

of pre-burn lag times, depending on the area of drainage basin

burned. A summary of post-burn calibration data (RCNs, 

abstractions, lag-time factors) for all principal and minor 

drainage basins is in Appendix table 3–4.

Table 2–2 shows the 19 principal drainage basins for 

which modeling was conducted and the results of the pre- and 

post-burn runoff calibrations. A rainfall depth of 2.4 inches 

(100-year, 6-hour storm) was applied uniformly over each 

basin, with no aerial distribution of the storm (Miller and others, 1973).

Runoff curve numbers for larger drainage basins are shown 

as a range of values determined for the subbasins within each 

drainage basin. Model data for all primary drainage basins, contributing subbasins, and minor drainages in the Hayman burn 

area are in Appendix tables 3–1, 3–2, 3–3, and 3–4.

Estimated Peak Discharges, South Platte River 

Tributaries

To account for the potential sediment bulking of floodflows 

in burned drainage basins, computed peak discharges were 

increased according to the assumption that sediment concentrations by volume (Cv

) could reach the maximum water-flood 

limit of 20 percent (Costa, 1988). The equation of O’Brien and 

Fullerton (1989) was used to compute the bulking factor (BF):

BF = 1/(1 – Cv) (2–5)

For a Cv of 20 percent, the corresponding BF is 1.25. This 

factor was applied to peak water discharges computed by the 

HEC-HMS model for areas of moderate to high burn severity. 

The bulking factor was weighted according to relative burned 

area within each of the modeled drainage basins.

Simulated pre-burn, post-burn, and bulked 100-year 

discharges for each of the principal drainage basins are shown 

in table 2–2. Post-burn 100-year peak discharges for the 19 

principal drainage basins (routed to the point of confluence 

with the South Platte River) are expected to increase 2 to 

34 times pre-burn peaks. Among all modeled drainage basins 

(including subbasins) with substantial (>50 percent) moderate to severe burned areas, post-burn peak discharges are 

expected to be 8 to 44 times greater than pre-burn peaks. For 

those drainage basins with substantial burned area, average 

predicted peak discharges per square mile for pre-burn conditions is 15.8 ft3

/s/mi2; average predicted peak discharges per 

square mile for post-burn conditions is 425 ft3/s/mi2. Predicted 

increases in post-burn peak discharge are in general agreement 

with the BAER Team’s hydrologic assessment of the Hayman 

fire (USDA Forest Service, 2002a) and with hydrologic studies of other burned drainage basins (Rowe and others, 1954; 

Martin and Moody, 2001b; URS Corporation, 2000).

Estimated Peak Discharges, Selected Reaches 

of the South Platte River

As part of the hydrologic assessment of the Hayman 

fire on affected reaches of the South Platte River, the 100-

year peak discharge for selected points along the river were 

computed on the basis of tributary inflow from drainage 

basins within and adjacent to the burned area. Cumulative 

peak discharge in the main-stem South Platte River was 

computed as the sum of the main-stem flow and tributary peak 

discharges (table 2–2) at the point of interest. In-stream flow 

routing, to account for in-channel storage and peak attenuation 

at successive downstream sections, was performed using the 

routing routines in the HEC-HMS computer model.

Appendix 2. The Manual Calibration Method for the Hayman Burned Area 53
54 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires Table 2–2. Drainage-basin characteristics, modeling parameters, and computed peak discharges for pre-burn, post-burn, and post-burn (bulked) conditions in the 19 principal drainage basins affected by the Hayman fire. [mi2, square miles; %, percent; Q100, 100-year discharge; in, inches; ft3/s, cubic feet per second; Qu, pre-burn 100-year discharge; Qb, post-burn 100-year discharge; Qbb, post-burned bulked 100-year discharge; ft3/s/mi2, cubic feet per second per square mile; N/A, not applicable] Basin name and number (downstream order) Drainage area (mi2

)

Area of 

low burn 

(%)

Area of 

moderate 

to high burn 

(%)

Rainfall 

depth1

(in)

Curve number*

Q100 (ft3/s)

Ratio 

Qbb/Qu Pre-burn Post-burn (weighted) Pre-burn, 

Qu

Post-burn, 

Qb

Post-burn 

(bulked), 

Qbb

Qbb 

(ft3/s/mi2

)

Vermillion Creek (1) 4.93 50.0 27.6 2.4 58 86 52.6 665 711 144 13.5Crystal Creek (2) 5.27 46.4 29.0 2.4 59 86 55.5 663 711 135 12.8Beaver Creek (3) 3.54 51.5 33.7 2.4 59 88 40.3 531 576 163 14.3Hackett Gulch (4) 6.56 37.2 33.2 2.4 56 86 66.4 954 1,030 157 15.5Tarryall Creek (5) 443 0.96 0.89 2.4 N/A 86 715 2,160 2,160 N/A N/ALongwater Gulch (6) 2.34 29.3 67.6 2.4 57 94 28.8 641 749 320 26.0Corral Creek (7) 4.38 15.7 70.3 2.4 55 93 47.6 1,150 1,350 308 28.4Northrup Gulch (8) 3.84 37.2 58.2 2.4 58 93 43.5 844 967 252 22.2Turkey Creek (9) 28.2 32.4 50.6 2.4 57–61 77–98 222 3.390 3,820 135 17.2Goose Creek (10) 95.2 5.29 15.1 2.4 57–58 58–98 607 4,120 4,280 45.0 7.1

Cheesman Reservoir

Schoonover Gulch (11) 1.71 11.7 85.4 2.4 57 96 22.0 607 737 431 33.5Sixmile/Wigwam Creek (12) 36.7 13.7 34.2 2.4 58–60 78–96 274 2,510 2,720 74.1 9.9Fourmile Creek (13) 8.22 11.7 59.7 2.4 61 90 80.8 958 1,100 134 13.6Horse Creek (14) 212 9.06 12.8 2.4 58–66 58–98 1,150 4,010 4,140 19.5 3.6Lazy Gulch (15) 1.23 54.2 39.0 2.4 56 90 17.0 309 339 276 19.9Brush Creek (16) 2.33 29.2 59.3 2.4 58 92 28.7 507 582 250 20.3Unnamed drainage (17) 1.16 0.00 0.00 2.4 57 57 15.8 15.8 15.8 N/A N/ASaloon Gulch (18) 1.26 39.7 46.6 2.4 58 90 17.2 290 324 257 18.8Gunbarrel/Kelsey Creek (19) 10.2 8.00 2.00 2.4 57 63 96.8 220 221 21.7 2.3

1NOAA Atlas 2 Volume III—Colorado (Miller and others, 1973).
Twenty river cross sections were surveyed through 

the study reach upstream and downstream from Cheesman 

Reservoir. These cross sections were located to improve the 

flood-plain delineation of the existing FEMA regulatory 

maps (designated by FEMA as an Approximate Study area) 

and to establish discrete flood elevations for the post-fire, 

100-year flood through the affected reach. Each cross section 

was surveyed to the North American Vertical Datum of 1988 

(NAVD88, vertical control) and to the North American Datum 

of 1983 (NAD83, horizontal control) by Global Positioning 

System (GPS) surveys. Left and right ends of each cross section were monumented (rebar rods with stamped, aluminum 

caps) to facilitate resurveys. Control coordinates (Universal 

Transverse Mercator) and elevations (NAVD88) for all cross 

sections are shown in Appendix 4; cross-section data (x-y coordinate pairs) are available from the U.S. Geological Survey, 

Colorado District, Denver, Colo.

Because of the distance between surveyed cross sections 

(generally 1 to 2 miles), water-surface elevations for computed 

peak discharges were determined using a normal-depth calculation (steady, uniform flow); step-backwater flow routing was 

not performed.

Main-Stem Peak Discharge Within the HEC-HMS 

Model Area

Cumulative drainage areas for each cross section were 

computed from GIS data. The 100-year peak discharge at 

each South Platte cross section within the HEC-HMS model 

area was determined from the routing computations. The 

Muskingum-Cunge routing routine, which incorporates crosssection and hydraulic properties of the surveyed cross sections, 

was used to route flows in reaches of the main-stem South 

Platte River. Routed peaks showed little attenuation. Sensitivity testing indicated that hydrograph attenuation was affected 

mainly by channel slope; the relatively steep slopes (measured as water-surface slope during the cross-section surveys) 

through the study reach preclude substantial attenuation.

The Modified Puls reservoir routing routine in HEC-HMS 

was used to route the computed flood hydrograph through 

Cheesman Reservoir and over the spillway to the downstream 

reach. As noted previously, the study assumes that Cheesman 

Reservoir is full, so that an inflow hydrograph would pass 

through the reservoir and over the spillway, into the downstream reach. The computed inflow hydrograph to Cheesman 

Reservoir consists of two components:

• Routed water-flood hydrograph, consisting of inflows 

from burned and unburned drainage basins.

• Computed sediment hydrograph to account for 

sediment bulking of South Platte River flows. The 

sediment hydrograph was computed by applying the 

bulking factor (eq. 2–5) to the portion of main-stem 

water discharge attributed to areas of moderate to high 

severity burn; the resulting peak was 1,750 ft3/s.

These two components were combined to form the bulked 

inflow hydrograph. Because most sediment is assumed deposited 

in Cheesman Reservoir, a clear water (equivalent to the waterflood hydrograph plus the water discharge resulting from the 

displaced volume of inflowing sediment) was routed through the 

reservoir and over the spillway. On the basis of the conditions 

described herein, the computed peak discharge for the combined 

inflow hydrograph to Cheesman Reservoir was 19,000 ft3/s; the 

computed total inflow volume was 19,800 acre-feet.

The routed outflow peak discharge (clear water) from 

Cheesman Reservoir was 11,900 ft3/s. Peak discharges (with 

sediment bulking) computed for cross sections surveyed along 

the South Platte River downstream from Cheesman Reservoir 

range from 12,900 ft3/s (at cross section DXS1) to 18,900 ft3/s 

(at cross section DXS7).

Main-Stem Peak Discharge Downstream from 

the HEC-HMS Model Area

For South Platte reaches downstream from the area 

modeled using HEC-HMS (and downstream from the burn 

perimeter), peak discharge was adjusted for contributing drainage area using an equation relating peak discharge for “gaged” 

(simulated discharge using HEC-HMS) sites to ungaged sites 

as a function of relative drainage area (Vaill, 2000). The following equation was used:

Q100(u) = Q100(g) (Au/Ag)

x (2–7)

where

Q100(u) is the 100-year peak discharge, in cubic feet per 

second, at the ungaged (unmodeled) site;

Q100(g is the 100-year peak discharge, in cubic feet per 

second, at the gaged (modeled) site;

Au is the drainage area, in square miles, at the 

ungaged (unmodeled) site;

Ag is the drainage area, in square miles, at the gaged 

(modeled) site;

and

X is the average exponent for drainage area in the 

flood region of interest, derived from regression analysis of historical streamflow data.

Peak discharges computed for channel cross sections 

surveyed along the South Platte River downstream from the 

burned area range from 18,900 ft3/s (at cross section DXS8), 

to 22,200 ft3/s (at cross section DXS13 downstream from 

the confluence with the North Fork South Platte River), and 

22,400 ft3/s (at cross section WXS3 in Waterton Canyon). 

A summary of peak discharge and computed water-surface 

elevations for all South Platte channel cross sections is shown 

in table 2–3. Hazard-mitigation maps were constructed from 

the computed water-surface elevations to assist State and local 

emergency-response officials in planning for possible post-fire 

flooding. These oversized maps, including cross sections, are 

presented in figures 8 through 14 and accompany this report.

Appendix 2. The Manual Calibration Method for the Hayman Burned Area 55
56 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires Table 2–3. Channel cross-section properties (normal-depth computation) for South Platte River reaches upstream and downstream from Cheesman Reservoir. [ft3/s, cubic feet per second; ft, feet; ft/ft, feet per feet; ft/s, feet per second; NAVD 88, North American Vertical Datum of 1988] Name of cross section Peak discharge (ft3/s) Water-surface elevation (ft) (NAVD88) Channel slope (ft/ft) Top width (ft) Mean depth (ft) Mean velocity (ft/s) Froude number Note Reach upstream from Cheesman Reservoir Cross section UXS1 9,670 7,116.29 0.0047 314 4.10 7.51 0.70 Used average cross-section properties for entire reach Cross section UXS2 10,400 6,950.71 0.0095 130 7.83 10.2 0.64 Cross section UXS3 10,400 6,855.61 0.0038 125 7.37 11.3 0.73 Reach downstream from Cheesman Reservoir Routed peak outflow over spillway = 11,400 ft3/s Cross section DXS1 12,900 6,490.90 0.0018 223 8.77 6.60 0.39 Above Wigwam Creek confluence Cross section DXS2 14,700 6,461.44 0.0027 203 8.97 8.07 0.48 Below Wigwam Creek confluence Cross section DXS3 15,800 6,425.48 0.0031 195 8.62 9.40 0.59 Below Fourmile Creek confluence Cross section DXS4 16,000 6,414.76 0.0067 145 9.54 11.6 0.66 Above Deckers and Horse Creek confluence Cross section DXS4.5 18,600 6,380.28 0.0025 140 11.7 11.4 0.61 Trumbull stream gage Cross section DXS5 18,700 6,359.44 0.0027 601 5.40 5.75 0.59 Cross section DXS6 18,900 6,342.79 0.0039 334 6.77 8.36 0.67 Wide, flat flood plain through this reach Cross section DXS7 18,900 6,298.31 0.0018 353 9.27 5.77 0.38 Cross section DXS8 18,900 6,285.51 0.0027 612 6.74 4.58 0.44 End Hayman burn perimeter

Cross section DXS8.5 18,900 6,269.91 0.0016 241 10.9 7.22 0.40Cross section DXS9 18,900 6,226.30 0.0013 253 10.5 7.14 0.42Cross section DXS10 19,000 6,194.24 0.0039 249 8.39 9.09 0.58Cross section DXS11 19,200 6,163.26 0.0010 202 13.1 7.23 0.35Cross section DXS12 19,200 6,117.41 0.0024 164 11.1 10.58 0.60Cross section DXS13 22,200 6,100.36 0.0031 186 12.8 9.33 0.47 Below confluence of N.F. South Platte

Reach downstream from Strontia Springs Reservoir (Waterton Canyon)

Cross section WXS2 22,300 5,725.81 0.0092 135 12.4 13.35 0.70 Waterton CanyonCross section WXS3 22,400 5,690.71 0.0038 204 11.0 9.96 0.54 Waterton Canyon
Appendix 3. Appendix Tables 3–1—3–14

Appendix 3. Appendix Tables 3–1—3–14 57

Table 3–1. South Platte River basins and subbasins used in the HEC-HMS model upstream and 

downstream from Cheesman Reservoir.

[mi2, square miles; BAER, Burned Area Emergency Rehabilitation; n/a, not applicable]

Model 

basin ID

Corresponding 

BAER basin(s)

Name of basin 

or drainage

Basin area 

(mi2)

South Platte River basins and subbasins upstream from Cheesman Dam

0.1 84 Unnamed 0.60

PA 80, 77, 75 South Platte Reach A 3.87

UBB1 - Unburned basin 1ac n/a

UBB2 - Unburned basin 2ac n/a

1 78 Vermillion Creek 4.93

UBB3 - Unburned basin 3ac n/a

2 76 Crystal Creek 5.27

UBB4 - Unburned basin 4ac 0.32

PB 891 South Platte Reach B 11.3

3 74 Beaver Creek 3.54

4 65 Hackett Gulch 6.56

5A 58 Tarryall Creek 8.42

5B 58, 72 Tarryall Creek 3.11

5C - Tarryall Creek (upstream) 431

6 63 Longwater Gulch 2.34

7 53 Corral Creek 4.38

7.1 57 Motberry Gulch 1.60

7.2 47 Wildcat Creek 1.98

8 51 Northrup Gulch 3.84

8.1 44 Unnamed drainage A 1.03

8.2 45 Unnamed drainage B 0.72

PC 892 South Platte Reach C 6.49

9A 37 Turkey Creek 0.61

9B 92 Turkey Creek 1.99

9C 46 Turkey Creek 8.09

9D 37 Turkey Creek 0.99

9E 40 Turkey Creek 0.97

9F 43 Turkey Creek 1.57

9G 91 Turkey Creek 6.44

9H 90 Turkey Creek 2.16

9I 54 Turkey Creek 0.27

9J 59 Turkey Creek 0.40

9K 62 Turkey Creek 0.48

9L 67 Turkey Creek 0.88

9M 73 Turkey Creek 2.97

9N 46 (partial) Turkey Creek 0.37

9.1 33 Unnamed drainage C 0.87

9.2 34 Sand Draw 0.67

9.3 31 Unnamed drainage D 0.75

10A 26 Goose Creek 2.13

10B 26 Goose Creek 4.67
58 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

10C 25 Goose Creek 2.82

10D 87 Goose Creek 7.38

10E 30 Goose Creek 1.88

10F 39 Goose Creek 6.27

10G 32 Goose Creek 3.55

10H - Goose Creek 7.64

10I - Goose Creek 4.69

10J - Goose Creek 5.48

10K - Goose Creek 10.9

10L - Goose Creek 12.2

10M - Goose Creek 13.9

10N - Goose Creek 11.7

Basins downstream from Cheesman Dam

11 28 Schoonover 1.71

12A 3 Sixmile and Wigwam 18.2

12B 2 Sixmile and Wigwam 5.22

12C 6 Sixmile and Wigwam 3.43

12D 5 Sixmile and Wigwam 7.78

12E 19 Sixmile and Wigwam 0.88

12F 22 Sixmile and Wigwam 1.19

13 21 Fourmile Creek 8.22

14A 11 Horse Creek 3.58

14B 23 Horse Creek 1.36

14C 24 Horse Creek 0.64

14D 20 Horse Creek 0.63

14E 11, 50, 52, 55,

61, 68, 70

Horse Creek 18.8

14F 27 Horse Creek 2.05

14G 29 Horse Creek 0.55

14H 36 Horse Creek 0.76

14I 38 Horse Creek 1.16

14J 42 Horse Creek 1.89

14K 49 Horse Creek 15.5

14L 56 Horse Creek 1.19

14M 60 Horse Creek 0.40

14N 64 Horse Creek 0.65

14O 66 Horse Creek 0.49

14P 71 Horse Creek 0.58

14Q None Horse Creek 12.3

14R None Horse Creek 12.8

14S 85 Horse Creek 17.4

14T 85 Horse Creek 8.85

14U 85 Horse Creek 7.39

14V 35 Horse Creek 2.71

Table 3–1. South Platte River basins and subbasins used in the HEC-HMS model upstream and 

downstream from Cheesman Reservoir.—Continued

[mi2, square miles; BAER, Burned Area Emergency Rehabilitation; n/a, not applicable]

Model 

basin ID

Corresponding 

BAER basin(s)

Name of basin 

or drainage

Basin area 

(mi2)

South Platte River basins and subbasins upstream from Cheesman Dam—Continued
Appendix 3. Appendix Tables 3–1—3–14 59

14W 85 Horse Creek 7.20

14X 88 Horse Creek 16.0

14Y 88 Horse Creek 12.8

14Z 88 Horse Creek 15.5

14AA None Horse Creek 1.83

14BB None Horse Creek 9.45

14CC None Horse Creek 6.43

14DD None Horse Creek 9.00

14EE None Horse Creek 13.3

14FF None Horse Creek 8.88

15 8 Lazy Gulch 1.23

16 7 Brush Creek 2.33

17 9 Unnamed drainage 1.16

UB1 None Unburned drainage 1bc 1.75

18 4 Saloon Gulch 1.26

UB2 None Unburned drainage 2bc 1.07

19A 1 Gunbarrel and Kelsey 0.69

19B 1 Gunbarrel and Kelsey 4.72

19C 1 Gunbarrel and Kelsey 4.79

UB3 None Unburned drainage 3bc 13.1

M1 893 South Platte Reach 1 3.26

M2 893 South Platte Reach 2 2.57

M3 93, 893 South Platte Reach 3 2.98

M4 93 South Platte Reach 4 4.19

Table 3–1. South Platte River basins and subbasins used in the HEC-HMS model upstream and 

downstream from Cheesman Reservoir.—Continued

[mi2, square miles; BAER, Burned Area Emergency Rehabilitation; n/a, not applicable]

Model 

basin ID

Corresponding 

BAER basin(s)

Name of basin 

or drainage

Basin area 

(mi2)

Basins downstream from Cheesman Dam—Continued
60 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires Model basin ID Name of basin or drainage Total basin area (mi2

)

Percentage 

of low 

burned area

Low 

burned area 

(mi2

)

Percentage of 

medium-high 

burned area

Medium-high 

burned area 

(mi2

)

Total 

burned 

area 

(%)

Total 

burned 

area 

(mi2

)

South Platte River basins and subbasins upstream from Cheesman Dam

0.1 Unnamed 0.60 44.00 0.27 19.62 0.119 63.62 0.384PA South Platte Reach A 3.87 82.00 3.17 4.50 0.174 86.50 3.35UBB1 Unburned basin 1ac 19.8 0.00 0.00 0.00 0.000 0.00 0.000UBB2 Unburned basin 2ac 8.70 0.00 0.00 0.00 0.000 0.00 0.0001 Vermillion Creek 4.93 50.00 2.47 27.58 1.360 77.58 3.82UBB3 Unburned basin 3ac 1.20 0.00 0.00 0.00 0.000 0.00 0.0002 Crystal Creek 5.27 46.40 2.45 29.05 1.531 75.45 3.98UBB4 Unburned basin 4ac 0.32 0.00 0.00 0.00 0.000 0.00 0.000PB South Platte Reach B 11.3 46.00 5.20 38.59 4.364 84.59 9.573 Beaver Creek 3.54 51.50 1.82 33.70 1.194 85.20 3.024 Hackett Gulch 6.56 37.20 2.44 33.19 2.177 70.39 4.625 Mouth of Tarryall Creek 443 0.96 4.27 0.89 3.922 1.85 8.195A Tarryall Creek 8.42 37.00 3.12 34.02 2.865 71.02 5.985B Tarryall Creek 3.11 37.00 1.15 34.02 1.057 71.02 2.215C Tarryall upstream (regulated in and above 5C) 431 0.00 0.00 0.00 0.000 0.00 0.0006 Longwater Gulch 2.34 29.00 0.68 67.64 1.583 96.64 2.267 Corral Creek 4.38 16.00 0.70 70.32 3.080 86.32 3.787.1 Motberry Gulch 1.60 20.00 0.32 80.12 1.282 100.12 1.607.2 Wildcat Creek 1.98 19.00 0.38 80.65 1.593 99.65 1.978 Northrup Gulch 3.84 37.00 1.42 58.22 2.234 95.22 3.658.1 Unnamed drainage A 1.03 22.00 0.23 77.95 0.803 99.95 1.038.2 Unnamed drainage B 0.72 18.00 0.13 81.67 0.591 99.67 0.722PC South Platte Reach C 6.49 21.00 1.36 61.42 3.987 82.42 5.359 Mouth of Turkey Creek 28.2 32.41 9.13 50.60 14.253 83.01 23.4

Table 3–2. Burn data for South Platte River basins and subbasins upstream and downstream from Cheesman Reservoir.[ID, identification number; mi2, square miles; %, percent; BAER, Burned Area Emergency Rehabilitation]

Single basins Composite basins Subbasins of composite basins
Appendix 3. Appendix Tables 3–1—3–14 61

9A Turkey Creek 0.61 1.00 0.01 98.72 0.599 99.72 0.6059B Turkey Creek 1.99 5.00 0.10 94.90 1.889 99.90 1.999C Turkey Creek 8.09 34.00 2.75 44.37 3.588 78.37 6.349D Turkey Creek 0.99 1.00 0.01 98.72 0.980 99.72 0.9909E Turkey Creek 0.97 0.00 0.00 100.00 0.968 100.00 0.9689F Turkey Creek 1.57 9.00 0.14 90.85 1.425 99.85 1.579G Turkey Creek 6.44 42.00 2.70 37.26 2.400 79.26 5.109H Turkey Creek 2.16 62.00 1.34 20.17 0.435 82.17 1.779I Turkey Creek 0.27 65.00 0.17 23.46 0.063 88.46 0.2369J Turkey Creek 0.40 50.00 0.20 3.67 0.015 53.67 0.2169K Turkey Creek 0.48 66.00 0.31 6.75 0.032 72.75 0.3479L Turkey Creek 0.88 43.00 0.38 42.11 0.369 85.11 0.7469M Turkey Creek 2.97 30.00 0.89 44.71 1.327 74.71 2.229N Turkey Creek 0.37 34.00 0.13 44.37 0.164 78.37 0.2909.1 Unnamed drainage C 0.87 4.00 0.03 95.57 0.831 99.57 0.8669.2 Sand Draw 0.67 4.00 0.03 96.33 0.641 100.33 0.6679.3 Unnamed drainage D 0.75 7.00 0.05 93.00 0.698 100.00 0.75010 Mouth of Goose Creek 95.2 5.29 5.04 15.06 14.335 20.35 19.410A Goose Creek 2.13 10.00 0.21 89.61 1.909 99.61 2.1210B Goose Creek 4.67 10.00 0.47 89.61 4.181 99.61 4.6510C Goose Creek 2.82 32.00 0.90 59.96 1.690 91.96 2.5910D Goose Creek 7.38 26.00 1.92 63.36 4.677 89.36 6.6010E Goose Creek 1.88 31.00 0.58 54.94 1.030 85.94 1.6110F Goose Creek 6.27 9.00 0.56 8.67 0.544 17.67 1.1110G Goose Creek 3.55 11.00 0.39 8.57 0.304 19.57 0.69510H Goose Creek 7.64 0.00 0.00 0.00 0.000 0.00 0.000

Model 

basin 

ID

Name of basin 

or drainage

Total 

basin area 

(mi2)

Percentage 

of low 

burned area

Low 

burned area 

(mi2)

Percentage of 

medium-high 

burned area

Medium-high 

burned area 

(mi2)

Total 

burned 

area 

(%)

Total 

burned 

area 

(mi2)

South Platte River basins and subbasins upstream from Cheesman Dam—Continued

Table 3–2. Burn data for South Platte River basins and subbasins upstream and downstream from Cheesman Reservoir.—Continued[ID, identification number; mi2, square miles; %, percent; BAER, Burned Area Emergency Rehabilitation]

Single basins Composite basins Subbasins of composite basins
62 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires 10I Goose Creek 4.69 0.00 0.00 0.00 0.000 0.00 0.000 10J Goose Creek 5.48 0.00 0.00 0.00 0.000 0.00 0.000 10K Goose Creek 10.9 0.00 0.00 0.00 0.000 0.00 0.000 10L Goose Creek 12.2 0.00 0.00 0.00 0.000 0.00 0.000 10M Goose Creek 13.9 0.00 0.00 0.00 0.000 0.00 0.000 10N Goose Creek 11.7 0.00 0.00 0.00 0.000 0.00 0.000 South Platte River basins and subbasins downstream from Cheesman Dam 11 Schoonover 1.71 11.70 0.20 85.37 1.461 97.07 1.66 12 Mouth of Sixmile and Wigwam 36.7 13.68 5.02 34.24 12.555 47.91 17.6 12A Sixmile and Wigwam 18.2 15.00 2.73 27.80 5.053 42.80 7.78 12B Sixmile and Wigwam 5.22 13.00 0.68 42.50 2.219 55.50 2.90 12C Sixmile and Wigwam 3.43 11.00 0.38 51.90 1.778 62.90 2.15 12D Sixmile and Wigwam 7.78 11.00 0.86 24.40 1.897 35.40 2.75

12E Sixmile and Wigwam 0.879 24.00 0.21 76.20 0.670 100.20 0.88112F Sixmile and Wigwam 1.19 14.00 0.17 78.70 0.938 92.70 1.1113 Fourmile Creek 8.22 11.70 0.96 59.71 4.906 71.41 5.8714 Mouth of Horse Creek 212 9.06 19.22 12.75 27.048 21.82 46.314A Horse Creek 3.58 33.00 1.18 20.65 0.738 53.65 1.9214B Horse Creek 1.36 18.00 0.24 75.30 1.021 93.30 1.2714C Horse Creek 0.641 0.00 0.00 100.00 0.641 100.00 0.64114D Horse Creek 0.633 48.00 0.30 45.80 0.290 93.80 0.59414E Horse Creek 18.8 27.00 5.08 36.10 6.788 63.10 11.914F Horse Creek 2.05 11.00 0.23 54.30 1.110 65.30 1.3414G Horse Creek 0.547 45.00 0.25 29.90 0.164 74.90 0.41014H Horse Creek 0.764 33.00 0.25 30.50 0.233 63.50 0.485

Table 3–2. Burn data for South Platte River basins and subbasins upstream and downstream from Cheesman Reservoir.—Continued[ID, identification number; mi2, square miles; %, percent; BAER, Burned Area Emergency Rehabilitation]

Single basins Composite basins Subbasins of composite basins

Model 

basin 

ID

Name of basin 

or drainage

Total 

basin area 

(mi2

)

Percentage 

of low 

burned area

Low 

burned area 

(mi2

)

Percentage of 

medium-high 

burned area

Medium-high 

burned area 

(mi2

)

Total 

burned 

area 

(%)

Total 

burned 

area 

(mi2

)

South Platte River basins and subbasins upstream from Cheesman Dam—Continued
Appendix 3. Appendix Tables 3–1—3–14 63

14I Horse Creek 1.16 46.00 0.53 44.10 0.509 90.10 1.0414J Horse Creek 1.89 50.00 0.94 30.30 0.572 80.30 1.5214K Horse Creek 15.5 33.00 5.13 41.00 6.370 74.00 11.514L Horse Creek 1.19 52.00 0.62 41.40 0.494 93.40 1.1114M Horse Creek 0.399 30.00 0.12 59.50 0.237 89.50 0.35714N Horse Creek 0.653 13.00 0.08 87.20 0.569 100.20 0.65414O Horse Creek 0.492 6.00 0.03 59.80 0.294 65.80 0.32414P Horse Creek 0.582 48.00 0.28 22.70 0.132 70.70 0.41114Q Horse Creek 12.3 0.00 0.00 3.00 0.369 3.00 0.36914R Horse Creek 12.8 0.00 0.00 0.00 0.000 0.00 0.00014S Horse Creek 17.4 5.00 0.87 4.77 0.831 9.77 1.7014T Horse Creek 8.85 5.00 0.44 4.77 0.422 9.77 0.86514U Horse Creek 7.39 5.00 0.37 4.77 0.353 9.77 0.72214V Horse Creek 2.71 38.00 1.03 59.24 1.603 97.24 2.6314W Horse Creek 7.20 5.00 0.36 4.77 0.343 9.77 0.70314X Horse Creek 16.0 2.00 0.32 3.18 0.509 5.18 0.82814Y Horse Creek 12.8 2.00 0.26 3.18 0.406 5.18 0.66214Z Horse Creek 15.5 2.00 0.31 3.18 0.494 5.18 0.80514AA Horse Creek 1.83 0.00 0.00 3.18 0.058 3.18 0.05814BB Horse Creek 9.45 0.00 0.00 3.18 0.300 3.18 0.30014CC Horse Creek 6.43 0.00 0.00 3.18 0.204 3.18 0.20414DD Horse Creek 9.00 0.00 0.00 3.18 0.286 3.18 0.28614EE Horse Creek 13.3 0.00 0.00 3.18 0.423 3.18 0.42314FF Horse Creek 8.88 0.00 0.00 3.18 0.282 3.18 0.282

Table 3–2. Burn data for South Platte River basins and subbasins upstream and downstream from Cheesman Reservoir.—Continued[ID, identification number; mi2, square miles; %, percent; BAER, Burned Area Emergency Rehabilitation]

Single basins Composite basins Subbasins of composite basins

Model 

basin 

ID

Name of basin 

or drainage

Total 

basin area 

(mi2)

Percentage 

of low 

burned area

Low 

burned area 

(mi2)

Percentage of 

medium-high 

burned area

Medium-high 

burned area 

(mi2)

Total 

burned 

area 

(%)

Total 

burned 

area 

(mi2)

South Platte River basins and subbasins downstream from Cheesman Dam—Continued
64 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires 15 Lazy Gulch 1.23 54.20 0.67 39.05 0.480 93.25 1.15 16 Brush Creek 2.33 29.20 0.68 59.31 1.380 88.51 2.06 17 Unnamed drainage 1.16 0.00 0.00 0.00 0.000 0.00 0.000 UB1 Unburned drainage 1bc 1.75 0.00 0.00 0.00 0.000 0.00 0.000 18 Saloon Gulch 1.26 39.70 0.50 46.63 0.588 86.33 1.088 UB2 Unburned drainage 2bc 1.07 0.00 0.00 0.00 0.000 0.00 0.000 19 Mouth of Gunbarrel and Kelsey 10.2 8.00 0.82 2.00 0.204 10.00 1.02 19A Gunbarrel and Kelsey 0.686 8.00 0.05 2.00 0.014 10.00 0.069

19B Gunbarrel and Kelsey 4.72 8.00 0.38 2.00 0.094 10.00 0.47219C Gunbarrel and Kelsey 4.79 8.00 0.38 2.00 0.096 10.00 0.479UB3 Unburned drainage 3bc 13.1 0.00 0.00 0.000 0.00 0.000M1 South Platte Reach 1 3.26 21.00 0.68 5.77 0.188 26.77 0.872M2 South Platte Reach 2 2.57 21.00 0.54 5.77 0.148 26.77 0.687M3 South Platte Reach 3 2.98 31.00 0.92 9.05 0.269 40.05 1.19M4 South Platte Reach 4 4.19 40.00 1.67 12.33 0.516 52.33 2.19

Model 

basin 

ID

Name of basin 

or drainage

Total 

basin area 

(mi2

)

Percentage 

of low 

burned area

Low 

burned area 

(mi2

)

Percentage of 

medium-high 

burned area

Medium-high 

burned area 

(mi2

)

Total 

burned 

area 

(%)

Total 

burned 

area 

(mi2

)

South Platte River basins and subbasins downstream from Cheesman Dam—Continued

Table 3–2. Burn data for South Platte River basins and subbasins upstream and downstream from Cheesman Reservoir.—Continued[ID, identification number; mi2, square miles; %, percent; BAER, Burned Area Emergency Rehabilitation]

Single basins Composite basins Subbasins of composite basins
Appendix 3. Appendix Tables 3–1—3–14 65

Table 3–3. Pre- and post-burn model parameters for South Platte River basins and subbasins upstream and downstream from 

Cheesman Reservoir used in the manual calibration method.

[ID, identification number; BAER, Burned Area Emergency Rehabilitation; mi2, square miles; RCN, runoff curve number; IA, initial abstraction; na, not 

applicable]

Model 

basin ID

Corresponding 

BAER basin(s)

Name of basin 

or drainage

Drainage 

area 

(mi2)

Preburned 

RCN

Default 

IA

Taylor 

lag time Remarks

South Platte River basins and subbasins upstream from Cheesman Dam

0.1 84 Unnamed 0.60 59 1.40 3.23

PA 80, 77, 75 South Platte Reach A 3.87 65 1.07 10.72

UBB1 - Unburned basin 1ac 19.82 62 1.25 9.86

UBB2 - Unburned basin 2ac 8.70 61 1.26 8.70

1 78 Vermillion Creek 4.93 58 1.42 4.76

UBB3 - Unburned basin 3ac 1.20 67 0.97 1.20

2 76 Crystal Creek 5.27 59 1.40 5.13

UBB4 - Unburned basin 4ac 0.32 56 1.57 1.05

PB 891 South Platte Reach B 11.31 63 1.17 10.56

3 74 Beaver Creek 3.54 59 1.39 4.84

4 65 Hackett Gulch 6.56 57 1.53 3.62

5A 58 Tarryall Creek 8.42 59 1.37 6.15

5B 58, 72 Tarryall Creek 3.11 57 1.50 3.38

5C - Tarryall upstream 431.05 na na na Tarryall is regulated in this area

6 63 Longwater Gulch 2.34 57 1.49 3.20

7 53 Corral Creek 4.38 56 1.60 2.53

7.1 57 Motberry Gulch 1.60 56 1.55 2.43

7.2 47 Wildcat Creek 1.98 56 1.55 2.54

8 51 Northrup Gulch 3.84 58 1.45 4.15

8.1 44 Unnamed drainage A 1.03 56 1.57 1.82

8.2 45 Unnamed drainage B 0.72 56 1.60 1.35

PC 892 South Platte Reach C 6.49 60 1.35 6.02

9A 37 Turkey Creek 0.61 57 1.50 1.84

9B 92 Turkey Creek 1.99 57 1.50 3.07

9C 46 Turkey Creek 8.09 59 1.39 6.99

9D 37 Turkey Creek 0.99 57 1.50 2.60

9E 40 Turkey Creek 0.97 58 1.46 2.95

9F 43 Turkey Creek 1.57 57 1.50 2.69

9G 91 Turkey Creek 6.44 61 1.26 9.13

9H 90 Turkey Creek 2.16 58 1.47 3.38

9I 54 Turkey Creek 0.27 57 1.50 1.73

9J 59 Turkey Creek 0.40 57 1.50 2.01

9K 62 Turkey Creek 0.48 57 1.50 2.05

9L 67 Turkey Creek 0.88 58 1.45 3.43

9M 73 Turkey Creek 2.97 58 1.45 3.84

9N 46 (partial) Turkey Creek 0.37 58 1.45 1.25

9.1 33 Unnamed drainage C 0.87 56 1.57 1.75

9.2 34 Sand Draw 0.67 57 1.50 2.17

9.3 31 Unnamed drainage D 0.75 58 1.47 2.59

10A 26 Goose Creek 2.13 58 1.46 2.96

10B 26 Goose Creek 4.67 58 1.46 3.63

10C 25 Goose Creek 2.82 58 1.46 2.29

10D 87 Goose Creek 7.38 59 1.42 4.88
66 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

10E 30 Goose Creek 1.88 58 1.45 1.83

10F 39 Goose Creek 6.27 58 1.45 3.45

10G 32 Goose Creek 3.55 58 1.46 2.90

10H - Goose Creek 7.64 58 1.43 4.68

10I - Goose Creek 4.69 58 1.45 3.26

10J - Goose Creek 5.48 58 1.46 3.19

10K - Goose Creek 10.95 58 1.45 3.84

10L - Goose Creek 12.16 58 1.44 5.98

10M - Goose Creek 13.86 58 1.46 6.73

10N - Goose Creek 11.70 59 1.41 8.04

South Platte River basins and subbasins downstream from Cheesman Dam

11 28 Schoonover 1.71 57 1.52 2.70

12A 3 Sixmile and Wigwam 18.18 60 1.33 8.80

12B 2 Sixmile and Wigwam 5.22 62 1.23 3.96

12C 6 Sixmile and Wigwam 3.43 61 1.28 3.74

12D 5 Sixmile and Wigwam 7.78 60 1.33 4.77

12E 19 Sixmile and Wigwam 0.88 60 1.33 1.81

12F 22 Sixmile and Wigwam 1.19 61 1.28 1.67

13 21 Fourmile Creek 8.22 62 1.25 8.22

14A 11 Horse Creek 3.58 59 1.37 5.26

14B 23 Horse Creek 1.36 61 1.26 1.99

14C 24 Horse Creek 0.64 58 1.42 1.67

14D 20 Horse Creek 0.63 62 1.21 1.56

14E 11, 50, 52, 55, 

61, 68, 70

Horse Creek 18.80 61 1.26 16.20

14F 27 Horse Creek 2.05 63 1.15 2.52

14G 29 Horse Creek 0.55 64 1.11 1.53

14H 36 Horse Creek 0.76 66 1.01 1.46

14I 38 Horse Creek 1.16 62 1.21 1.65

14J 42 Horse Creek 1.89 59 1.37 3.28

14K 49 Horse Creek 15.54 58 1.42 12.78

14L 56 Horse Creek 1.19 61 1.26 2.36

14M 60 Horse Creek 0.40 58 1.42 1.67

14N 64 Horse Creek 0.65 59 1.37 1.60

14O 66 Horse Creek 0.49 59 1.37 1.89

14P 71 Horse Creek 0.58 63 1.15 1.70

14Q None Horse Creek 12.29 59 1.37 10.35

14R None Horse Creek 12.75 58 1.42 9.84

14S 85 Horse Creek 17.42 60 1.31 6.62

14T 85 Horse Creek 8.85 60 1.31 7.82

14U 85 Horse Creek 7.39 60 1.31 5.84

14V 35 Horse Creek 2.71 59 1.37 3.77

14W 85 Horse Creek 7.20 60 1.31 6.09

Table 3–3. Pre- and post-burn model parameters for South Platte River basins and subbasins upstream and downstream from 

Cheesman Reservoir used in the manual calibration method.—Continued

[ID, identification number; BAER, Burned Area Emergency Rehabilitation; mi2, square miles; RCN, runoff curve number; IA, initial abstraction; na, not 

applicable]

Model 

basin ID

Corresponding 

BAER basin(s)

Name of basin 

or drainage

Drainage 

area 

(mi2)

Preburned 

RCN

Default 

IA

Taylor 

lag time Remarks

South Platte River basins and subbasins upstream from Cheesman Dam—Continued
Appendix 3. Appendix Tables 3–1—3–14 67

14X 88 Horse Creek 15.99 59 1.37 6.24

14Y 88 Horse Creek 12.78 59 1.37 5.64

14Z 88 Horse Creek 15.54 59 1.37 7.48

14AA None Horse Creek 1.83 58 1.42 2.90

14BB None Horse Creek 9.45 58 1.42 12.14

14CC None Horse Creek 6.43 58 1.42 6.47

14DD None Horse Creek 9.00 58 1.42 5.58

14EE None Horse Creek 13.32 58 1.42 7.61

14FF None Horse Creek 8.88 58 1.42 8.43

15 8 Lazy Gulch 1.23 57 1.54 2.21

16 7 Brush Creek 2.33 58 1.45 3.66

17 9 Unnamed drainage 1.16 57 1.50 2.67

UB1 None Unburned drainage 1bc 1.75 58 1.48 3.24

18 4 Saloon Gulch 1.26 57 1.51 2.57

UB2 None Unburned drainage 2bc 1.07 57 1.53 2.36

19A 1 Gunbarrel and Kelsey 0.69 57 1.50 2.33

19B 1 Gunbarrel and Kelsey 4.72 57 1.50 4.23

19C 1 Gunbarrel and Kelsey 4.79 57 1.50 4.07

UB3 None Unburned drainage 3bc 13.12 58 1.44 5.50

M1 893 South Platte Reach 1 3.26 58 1.44 4.16

M2 893 South Platte Reach 2 2.57 58 1.45 3.77

M3 93, 893 South Platte Reach 3 2.98 58 1.42 4.19

M4 93 South Platte Reach 4 4.19 58 1.42 4.60

Explanation of Parameters

Regr. Q = Local peak discharge regression equation, determined by Q = 14.21 × A0.823

Unburn RCN = RCN determined from composite and individual BAER team basins (base RCN for natural forest min. 55)

Default IA = Initial Abstraction value determined by SCS method, IA = 0.2 × [(1,000/RCN) – 10]

Taylor lag time = Lag time determined by Taylor-Schwartz method

Table 3–3. Pre- and post-burn model parameters for South Platte River basins and subbasins upstream and downstream from 

Cheesman Reservoir used in the manual calibration method.—Continued

[ID, identification number; BAER, Burned Area Emergency Rehabilitation; mi2, square miles; RCN, runoff curve number; IA, initial abstraction; na, not 

applicable]

Model 

basin ID

Corresponding 

BAER basin(s)

Name of basin 

or drainage

Drainage 

area 

(mi2)

Preburned 

RCN

Default 

IA

Taylor 

lag time Remarks

South Platte River basins and subbasins downstream from Cheesman Dam—Continued
68 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires Table 3–4. Post-burn model parameters for South Platte River basins upstream and downstream from Cheesman Reservoir used in the manual calibration method. [ID, identification number; BAER, Burned Area Emergency Rehabilitation; mi2, square miles; %, percent; RCN, runoff curve number; IA, initial abstraction; LT, lag time; BOR, Bureau of Reclamation source; na, not applicable] Model basin ID Corresponding BAER basin(s) Name of basin or drainage Area (mi2

)

Unburned 

RCN

Medium 

and high 

burn %

Burned 

RCN

Change 

in RCN

Burned 

default IA

Unburned 

Taylor LT

Burned 

LT BOR

Percentage 

of unburned 

LT

Note

South Platte River basins and subbasins upstream from Cheesman Dam

0.1 84 Unnamed 0.60 59 19.6 82.5 24 0.42 3.23 2.55 78.9PA 80, 77, 75 South Platte Reach A 3.87 65 4.5 84.1 19 0.38 10.72 4.11 38.4UBB1 - Unburned basin 1ac 19.82 62 0.0 Unburned Unburned 9.86 9.86 100.0UBB2 - Unburned basin 2ac 8.70 61 0.0 Unburned Unburned 8.70 8.70 100.11 78 Vermillion Creek 4.93 58 27.6 86.2 28 0.32 4.76 3.31 69.6UBB3 - Unburned basin 3ac 1.20 67 0.0 Unburned Unburned 1.20 1.20 99.62 76 Crystal Creek 5.27 59 29.1 86.2 27 0.32 5.13 3.68 71.8UBB4 - Unburned basin 4ac 0.32 56 0.0 Unburned Unburned 1.05 1.05 100.1PB 891 South Platte Reach B 11.31 63 38.6 89.1 26 0.24 10.56 5.52 52.33 74 Beaver Creek 3.54 59 33.7 88.3 29 0.27 4.84 3.35 69.24 65 Hackett Gulch 6.56 57 33.2 85.9 29 0.33 3.62 2.83 78.15A 58 Tarryall Creek 8.42 59 34.0 86.3 27 0.32 6.15 4.17 67.85B 58, 72 Tarryall upstream 3.11 57 34.0 86.4 29 0.31 3.38 2.74 81.25C - Rest of Tarryall 431.05 na 0.0 Unburned Unburned na na na Tarryall regulated in this area6 63 Longwater Gulch 2.34 57 67.6 94.2 37 0.12 3.20 2.17 67.77 53 Corral Creek 4.38 56 70.3 93.3 38 0.14 2.53 2.15 84.97.1 57 Motberry Gulch 1.60 56 80.1 95.9 40 0.09 2.43 1.67 68.67.2 47 Wildcat Creek 1.98 56 80.7 96.0 40 0.08 2.54 1.71 67.48 51 Northrup Gulch 3.84 58 58.2 92.9 35 0.15 4.15 2.73 65.78.1 44 Unnamed drainage A 1.03 56 78.0 95.7 40 0.09 1.82 1.10 60.68.2 45 Unnamed drainage B 0.72 56 81.7 96.1 40 0.08 1.35 0.87 64.5PC 892 South Platte Reach C 6.49 60 61.4 91.9 32 0.18 6.02 3.15 52.49A 37 Turkey Creek 0.61 57 98.7 97.9 41 0.04 1.84 1.00 54.29B 92 Turkey Creek 1.99 57 94.9 97.5 40 0.05 3.07 1.69 55.09C 46 Turkey Creek 8.09 59 44.4 89.0 30 0.25 6.99 4.80 68.79D 37 Turkey Creek 0.99 57 98.7 97.9 41 0.04 2.60 1.58 60.69E 40 Turkey Creek 0.97 58 100.0 98.0 40 0.04 2.95 1.77 60.19F 43 Turkey Creek 1.57 57 90.9 97.1 40 0.06 2.69 1.71 63.79G 91 Turkey Creek 6.44 61 37.3 88.1 27 0.27 9.13 5.85 64.09H 90 Turkey Creek 2.16 58 20.2 85.7 28 0.33 3.38 2.52 74.69I 54 Turkey Creek 0.27 57 23.5 87.2 30 0.29 1.73 1.24 71.89J 59 Turkey Creek 0.40 57 3.7 76.9 20 0.60 2.01 1.71 85.1
Appendix 3. Appendix Tables 3–1—3–14 69

9K 62 Turkey Creek 0.48 57 6.8 81.5 24 0.45 2.05 1.53 74.79L 67 Turkey Creek 0.88 58 42.1 89.6 32 0.23 3.43 2.18 63.59M 73 Turkey Creek 2.97 58 44.7 88.4 31 0.26 3.84 2.45 63.79N 46 (partial) Turkey Creek 0.37 58 44.4 89.0 31 0.25 1.25 0.89 70.89.1 33 Unnamed drainage C 0.87 56 95.6 97.6 41 0.05 1.75 1.11 63.39.2 34 Sand Draw 0.67 57 96.3 97.6 40 0.05 2.17 1.37 63.09.3 31 Unnamed drainage D 0.75 58 93.0 97.3 40 0.06 2.59 1.56 60.410A 26 Goose Creek 2.13 58 89.6 97.0 39 0.06 2.96 1.15 38.910B 26 Goose Creek 4.67 58 89.6 97.0 39 0.06 3.63 1.54 42.510C 25 Goose Creek 2.82 58 60.0 92.7 35 0.16 2.29 1.54 67.110D 87 Goose Creek 7.38 59 63.4 92.9 34 0.15 4.88 3.20 65.510E 30 Goose Creek 1.88 58 54.9 91.4 33 0.19 1.83 1.26 68.910F 39 Goose Creek 6.27 58 8.7 69.2 11 0.89 3.45 3.28 95.110G 32 Goose Creek 3.55 58 8.6 69.5 12 0.88 2.90 2.83 97.610H - Goose Creek 7.64 58 0.0 Unburned Unburned 4.68 4.68 100.010I - Goose Creek 4.69 58 0.0 Unburned Unburned 3.26 3.26 100.010J - Goose Creek 5.48 58 0.0 Unburned Unburned 3.19 3.19 100.110K - Goose Creek 10.95 58 0.0 Unburned Unburned 3.84 3.84 99.910L - Goose Creek 12.16 58 0.0 Unburned Unburned 5.98 5.98 100.110M - Goose Creek 13.86 58 0.0 Unburned Unburned 6.73 6.73 100.010N - Goose Creek 11.70 59 0.0 Unburned Unburned 8.04 8.04 100.0

South Platte River basins and subbasins downstream from Cheesman Dam

11 28 Schoonover 1.71 57 85.4 96.2 39 0.08 2.70 1.71 63.612A 3 Sixmile and Wigwam 18.18 60 27.8 80.6 21 0.48 8.80 7.45 84.812B 2 Sixmile and Wigwam 5.22 62 42.5 85.8 24 0.33 3.96 3.16 79.712C 6 Sixmile and Wigwam 3.43 61 51.9 88.2 27 0.27 3.74 2.96 79.112D 5 Sixmile and Wigwam 7.78 60 24.4 78.5 19 0.55 4.77 4.20 88.012E 19 Sixmile and Wigwam 0.88 60 76.2 95.5 36 0.09 1.81 1.15 63.512F 22 Sixmile and Wigwam 1.19 61 78.7 95.1 34 0.10 1.67 1.33 79.613 21 Fourmile Creek 8.22 62 59.7 90.4 29 0.21 8.22 5.51 67.1

Table 3–4. Post-burn model parameters for South Platte River basins upstream and downstream from Cheesman Reservoir used in the manual calibration method.—Continued[ID, identification number; BAER, Burned Area Emergency Rehabilitation; mi2, square miles; %, percent; RCN, runoff curve number; IA, initial abstraction; LT, lag time; BOR, Bureau of Reclamation source; na, not applicable]

Model 

basin ID

Corresponding 

BAER basin(s)

Name of basin 

or drainage

Area 

(mi2)

Unburned 

RCN

Medium 

and high 

burn %

Burned 

RCN

Change 

in RCN

Burned 

default IA

Unburned 

Taylor LT

Burned 

LT BOR

Percentage 

of unburned 

LT

Note

South Platte River basins and subbasins upstream from Cheesman Dam—Continued
70 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires 14A 11 Horse Creek 3.58 59 20.7 81.2 22 0.46 5.26 3.37 64.1 14B 23 Horse Creek 1.36 61 75.3 94.8 33 0.11 1.99 1.40 70.4 14C 24 Horse Creek 0.64 58 100.0 98.0 40 0.04 1.67 0.99 59.3 14D 20 Horse Creek 0.63 62 45.8 91.2 29 0.19 1.56 1.21 77.8 14E 11, 50, 52, 55, 61, 68, 70 Horse Creek 18.80 61 36.1 83.0 22 0.41 16.20 11.16 68.9 14F 27 Horse Creek 2.05 63 54.3 89.1 26 0.24 2.52 2.04 81.0 14G 29 Horse Creek 0.55 64 29.9 86.7 22 0.31 1.53 1.33 87.3 14H 36 Horse Creek 0.76 66 30.5 85.6 19 0.34 1.46 1.23 84.0 14I 38 Horse Creek 1.16 62 44.1 90.5 28 0.21 1.65 1.29 78.4 14J 42 Horse Creek 1.89 59 30.3 87.2 28 0.29 3.28 2.35 71.5 14K 49 Horse Creek 15.54 58 41.0 87.8 29 0.28 12.78 8.10 63.4 14L 56 Horse Creek 1.19 61 41.4 90.5 29 0.21 2.36 1.56 66.2 14M 60 Horse Creek 0.40 58 59.5 92.4 34 0.16 1.67 1.16 69.5 14N 64 Horse Creek 0.65 59 87.2 96.7 37 0.07 1.60 0.99 62.0 14O 66 Horse Creek 0.49 59 59.8 89.6 30 0.23 1.89 1.43 75.5 14P 71 Horse Creek 0.58 63 22.7 84.8 21 0.36 1.70 0.91 53.5

14Q None Horse Creek 12.29 59 3.0 Unburned Unburned 10.17 10.17 100.014R None Horse Creek 12.75 58 0.0 Unburned Unburned 9.84 9.84 100.114S 85 Horse Creek 17.42 60 4.8 66.4 6 1.01 6.62 6.36 96.114T 85 Horse Creek 8.85 60 4.8 66.4 6 1.01 7.82 7.50 95.914U 85 Horse Creek 7.39 60 4.8 66.4 6 1.01 5.84 5.63 96.414V 35 Horse Creek 2.71 59 59.2 93.3 34 0.14 3.77 2.19 58.214W 85 Horse Creek 7.20 60 4.8 66.4 6 1.01 6.09 5.85 96.214X 88 Horse Creek 15.99 59 3.2 63.5 4 1.15 6.24 6.10 97.914Y 88 Horse Creek 12.78 59 3.2 63.5 4 1.15 5.64 5.51 97.614Z 88 Horse Creek 15.54 59 3.2 63.5 4 1.15 7.48 7.30 97.614AA None Horse Creek 1.83 58 3.2 Unburned Unburned 2.86 2.86 100.114BB None Horse Creek 9.45 58 3.2 Unburned Unburned 11.90 11.90 100.014CC None Horse Creek 6.43 58 3.2 Unburned Unburned 6.36 6.36 100.0

Table 3–4. Post-burn model parameters for South Platte River basins upstream and downstream from Cheesman Reservoir used in the manual calibration method.—Continued[ID, identification number; BAER, Burned Area Emergency Rehabilitation; mi2, square miles; %, percent; RCN, runoff curve number; IA, initial abstraction; LT, lag time; BOR, Bureau of Reclamation source; na, not applicable]

Model 

basin ID

Corresponding 

BAER basin(s)

Name of basin 

or drainage

Area 

(mi2

)

Unburned 

RCN

Medium 

and high 

burn %

Burned 

RCN

Change 

in RCN

Burned 

default IA

Unburned 

Taylor LT

Burned 

LT BOR

Percentage 

of unburned 

LT

Note

South Platte River basins and subbasins downstream from Cheesman Dam—Continued
Appendix 3. Appendix Tables 3–1—3–14 71

14DD None Horse Creek 9.00 58 3.2 Unburned Unburned 5.48 5.48 100.014EE None Horse Creek 13.32 58 3.2 Unburned Unburned 7.47 7.47 100.014FF None Horse Creek 8.88 58 3.2 Unburned Unburned 8.27 8.27 100.015 8 Lazy Gulch 1.23 57 39.1 90.1 34 0.22 2.21 1.70 77.016 7 Brush Creek 2.33 58 59.3 92.2 34 0.17 3.66 2.60 71.017 9 Unnamed drainage 1.16 57 0.0 57.2 0 1.50 2.67 2.67 99.9UB1 None Unburned drainage 1bc 1.75 58 0.0 Unburned Unburned 3.24 3.24 100.118 4 Saloon Gulch 1.26 57 46.6 90.3 33 0.21 2.57 2.01 78.3UB2 None Unburned drainage 2bc 1.07 57 0.0 Unburned Unburned 2.36 2.36 99.819A 1 Gunbarrel and Kelsey 0.69 57 2.0 63.3 6 1.16 2.33 2.25 96.519B 1 Gunbarrel and Kelsey 4.72 57 2.0 63.3 6 1.16 4.23 4.13 97.619C 1 Gunbarrel and Kelsey 4.79 57 2.0 63.3 6 1.16 4.07 3.97 97.5UB3 None Unburned drainage 3bc 13.12 58 0.0 Unburned Unburned 5.50 5.50 100.1M1 893 South Platte Reach 1 3.26 58 5.8 70.8 13 0.82 4.16 3.92 94.0M2 893 South Platte Reach 2 2.57 58 5.8 70.8 13 0.82 3.77 3.06 81.1M3 93, 893 South Platte Reach 3 2.98 58 9.1 74.1 16 0.70 4.19 2.98 71.2M4 93 South Platte Reach 4 4.19 58 12.3 78.9 21 0.53 4.60 2.94 63.9

Table 3–4. Post-burn model parameters for South Platte River basins upstream and downstream from Cheesman Reservoir used in the manual calibration method.—Continued[ID, identification number; BAER, Burned Area Emergency Rehabilitation; mi2, square miles; %, percent; RCN, runoff curve number; IA, initial abstraction; LT, lag time; BOR, Bureau of Reclamation source; na, not applicable]

Model 

basin ID

Corresponding 

BAER basin(s)

Name of basin 

or drainage

Area 

(mi2)

Unburned 

RCN

Medium 

and high 

burn %

Burned 

RCN

Change 

in RCN

Burned 

default IA

Unburned 

Taylor LT

Burned 

LT BOR

Percentage 

of unburned 

LT

Note

South Platte River basins and subbasins downstream from Cheesman Dam—Continued
72 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires Table 3–5. Channel routing parameters used in the HEC-HMS model for South Platte River reaches upstream and downstream from Cheesman Reservoir used in the manual calibration method. [ft, feet; ft/ft, foot per foot; ft3/s, cubic feet per second; H:V, horizontal to vertical dimension in foot per foot; n, Manning’s dimensionless roughness coefficent; U/S, upstream] Routing method Name of cross section Reach length (ft) Chanel slope (ft/ft) Channel bottom width (ft) Side slope (H:V) Composite Manning’s 

n

Note

South Platte River reaches upstream from Cheesman Dam

Muskingum-Cunge U/S cross Section 1 26,700 0.006 173 2.0 0.054 Used average cross-section properties for entire reachMuskingum-Cunge U/S cross Section 2 52,800 0.006 173 2.0 0.054Muskingum-Cunge U/S cross Section 3 4,000 0.006 173 2.0 0.054

South Platte River reaches downstream from Cheesman Dam Routed peak outflow over spillway = 11.400 ft3/s

Muskingum-Cunge Cross section 1 16,770 0.002 160 1.5 0.066 Above Wigwam Creek confluenceMuskingum-Cunge Cross section 2 12,010 0.003 150 4.0 0.063 Below Wigwam Creek confluence Muskingum-Cunge Cross section 3 Below Fourmile Creek confluenceMuskingum-Cunge Cross section 4 12,340 0.004 110 2.5 0.060 Above Deckers and Horse Creek confluence Muskingum-Cunge Cross section 4.5 Trumbull stream gageMuskingum-Cunge Cross section 5

19,140 0.003 210 20.0 0.058 Muskingum-Cunge Cross section 6 Wide, flat flood plain through this reach

Muskingum-Cunge Cross section 7
Appendix 3. Appendix Tables 3–1—3–14 73

Model 

basin ID

Name of basin 

or drainage

Basin 

area 

(mi2)

Percentage 

of mediumhigh burned 

area

Mediumhigh 

burned 

area 

(mi2)

Regression 

derived 

discharge 

(ft3/s)

Pre-burn 

discharge 

(ft3/s)

Correlation 

between PreQ 

and RegrQ 

(%)

Post-burn 

discharge 

(ft3/s)

Sediment 

bulked 

discharge 

(ft3/s)

Ratio 

BulkQ 

to PreQ 

(BulkQ/PreQ)

Remarks

South Platte River basins and subbasins upstream from Cheesman Dam

South Platte base flow 9400.1 Unnamed 0.60 19.6 0.119 9.4 9.2 98.4 77 81 8.8PA South Platte Reach A 3.87 4.5 0.174 43.3 43.9 101.5 399 403 9.2UBB1 Unburned basin 1ac 19.82 0.0 0.000 166.0 164 98.8 Unburned Unburned UnburnedUBB2 Unburned basin 2ac 8.70 0.0 0.000 84.3 84.4 100.1 Unburned Unburned Unburned1 Vermillion Creek 4.93 27.6 1.360 52.8 52.6 99.6 665 711 13.5UBB3 Unburned basin 3ac 1.20 0.0 0.000 16.5 16.3 98.7 Unburned Unburned Unburned2 Crystal Creek 5.27 29.1 1.531 55.8 55.5 99.5 663 711 12.8UBB4 Unburned basin 4ac 0.32 0.0 0.000 5.6 5.5 99.6 Unburned Unburned UnburnedPB South Platte Reach B 11.31 38.6 4.364 104.6 104 99.7 1,230 1,349 12.93 Beaver Creek 3.54 33.7 1.194 40.2 40.3 100.1 531 576 14.34 Hackett Gulch 6.56 33.2 2.177 66.8 66.4 99.5 954 1,033 15.65 Mouth of Tarryall Creek 443 0.89 3.922 na na na 2,160 2,165 na Total Q = Qreg + (Q100

for burned subbasins)

5A Tarryall Creek 8.42 34.0 2.865 82.1 81.4 99.2 975 1,058 13.0 Pre-burn Q only for 

unregulated subbasins

5B Tarryall Creek 3.11 34.0 1.057 36.1 35.9 99.4 477 518 14.4 Pre-burn Q only for 

unregulated subbasins

5C Tarryall upstream 431 0.0 0.000 na 715 na 715 715 1.0 Unburned, regulated6 Longwater Gulch 2.34 67.6 1.583 28.6 28.8 100.8 641 749 26.07 Corral Creek 4.38 70.3 3.080 47.9 47.6 99.3 1,150 1,352 28.47.1 Motberry Gulch 1.60 80.1 1.282 20.9 20.8 99.4 569 683 32.8

Cross Section UXS1 85.97 24.2 20.784 9,210 9,667

7.2 Wildcat Creek 1.98 80.7 1.593 24.9 24.9 100.1 694 834 33.58 Northrup Gulch 3.84 58.2 2.234 43.0 43.5 101.2 844 967 22.2

Cross Section UXS2 91.78 26.8 24.611 9,710 10,361

Table 3–6. HEC-HMS model results for South Platte River basins and subbasins upstream and downstream from Cheesman Reservoir used in the manual calibration method.[mi2, square miles; ft3/s, cubic feet per second; %, percent; PreQ, pre-burn discharge; RegrQ, regression-derived discharge; BulkQ, sediment-bulked discharge; na, not applicable]

Single basins Composite basins Subbasins of composite basins
74 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires 8.1 Unnamed drainage A 1.03 78.0 0.803 14.6 14.6 100.3 470 562 38.5 Peak discharge due to sediment bulking Cross Section UXS3 92.81 26.8 25.414 9,720 10,372 652 8.2 Unnamed drainage B 0.72 81.7 0.591 10.9 10.8 98.9 391 471 43.7 80 PC South Platte Reach C 6.49 61.4 3.987 66.2 66.4 100.2 1,230 1,419 21.4 189

9 Mouth of Turkey Creek 28.2 50.6 14.253 221.7 222 100.1 3,390 3,819 17.2 4299A Turkey Creek 0.61 98.7 0.599 9.4 10.1 na 330 411 40.79B Turkey Creek 1.99 94.9 1.889 25.0 25.2 na 766 948 37.59C Turkey Creek 8.09 44.4 3.588 79.4 72.3 na 975 1,083 15.09D Turkey Creek 0.99 98.7 0.980 14.1 13.8 na 406 506 36.79E Turkey Creek 0.97 100.0 0.968 13.8 13.9 na 370 463 33.39F Turkey Creek 1.57 90.9 1.425 20.6 21.3 na 584 717 33.79G Turkey Creek 6.44 37.3 2.400 65.8 55.8 na 631 690 12.49H Turkey Creek 2.16 20.2 0.435 26.7 27.4 na 333 350 12.89I Turkey Creek 0.27 23.5 0.063 4.8 4.6 na 68 72 15.89J Turkey Creek 0.40 3.7 0.015 6.7 6.4 na 42 43 6.79K Turkey Creek 0.48 6.8 0.032 7.7 7.6 na 74 75 9.99L Turkey Creek 0.88 42.1 0.369 12.7 12.2 na 184 203 16.69M Turkey Creek 2.97 44.7 1.327 34.8 35.1 na 544 605 17.29N Turkey Creek 0.37 44.4 0.164 6.3 7.9 na 129 143 18.29.1 Unnamed drainage C 0.87 95.6 0.831 12.7 12.6 99.4 435 539 42.8 103.99.2 Sand Draw 0.67 96.3 0.641 10.2 10.2 100.6 294 365 35.7 70.89.3 Unnamed drainage D 0.75 93.0 0.698 11.2 11.3 100.4 300 370 32.8 69.810 Mouth of Goose Creek 95.2 15.1 14.335 603.9 607 100.5 4,120 4,275 7.0 155

Table 3–6. HEC-HMS model results for South Platte River basins and subbasins upstream and downstream from Cheesman Reservoir used in the manual calibration method.—Continued[mi2, square miles; ft3/s, cubic feet per second; %, percent; PreQ, pre-burn discharge; RegrQ, regression-derived discharge; BulkQ, sediment-bulked discharge; na, not applicable]

Single basins Composite basins Subbasins of composite basins

Model 

basin ID

Name of basin 

or drainage

Basin 

area 

(mi2

)

Percentage 

of mediumhigh burned 

area

Mediumhigh 

burned 

area 

(mi2

)

Regression 

derived 

discharge 

(ft3/s)

Pre-burn 

discharge 

(ft3/s)

Correlation 

between PreQ 

and RegrQ 

(%)

Post-burn 

discharge 

(ft3/s)

Sediment 

bulked 

discharge 

(ft3/s)

Ratio 

BulkQ 

to PreQ 

(BulkQ/PreQ)

Remarks

South Platte River basins and subbasins upstream from Cheesman Dam—Continued
Appendix 3. Appendix Tables 3–1—3–14 75

10A Goose Creek 2.13 89.6 1.909 26.5 30.0 na 1,020 1,249 41.610B Goose Creek 4.67 89.6 4.181 50.5 56.4 na 1,860 2,277 40.410C Goose Creek 2.82 60.0 1.690 33.3 46.4 na 881 1,013 21.810D Goose Creek 7.38 63.4 4.677 73.6 78.7 na 1,470 1,703 21.610E Goose Creek 1.88 54.9 1.030 23.8 35.1 na 610 694 19.810F Goose Creek 6.27 8.7 0.544 64.4 81.2 na 278 284 3.510G Goose Creek 3.55 8.6 0.304 40.3 50.6 na 174 178 3.510H Goose Creek 7.64 0.0 0.000 75.8 80.8 na Unburned Unburned Unburned10I Goose Creek 4.69 0.0 0.000 50.7 63.1 na Unburned Unburned Unburned10J Goose Creek 5.48 0.0 0.000 57.7 73.3 na Unburned Unburned Unburned10K Goose Creek 10.95 0.0 0.000 101.8 129 na Unburned Unburned Unburned10L Goose Creek 12.16 0.0 0.000 111.1 98.8 na Unburned Unburned Unburned Peak sediment discharge 

(bulking) into Cheesman (ft3/s)

10M Goose Creek 13.86 0.0 0.000 123.7 97.9 na Unburned Unburned Unburned 174910N Goose Creek 11.70 0.0 0.000 107.6 79.8 na Unburned Unburned Unburned Total flood volume (bulked) 

into Cheesman (acre-feet)

South Platte River basins and subbasins downstream from Cheesman Dam 19400

11 Schoonover 1.71 85.4 1.461 22.1 22.0 99.5 607 737 33.5

Cross section DXS1 33.2 1.649 11,952 12,943

12 Mouth of Sixmile and 

Wigwam

36.7 34.2 12.555 275.4 274 99.5 2,510 2,725 9.9

12A Sixmile and Wigwam 18.2 27.8 5.053 154.6 102 na 940 1,005 9.9 Mainly a stream reach12B Sixmile and Wigwam 5.222 42.5 2.219 55.4 80.6 na 709 784 9.712C Sixmile and Wigwam 3.425 51.9 1.778 39.1 48.2 na 552 624 12.9 Burn of 34.15% for 

composite basin

Table 3–6. HEC-HMS model results for South Platte River basins and subbasins upstream and downstream from Cheesman Reservoir used in the manual calibration method.—Continued[mi2, square miles; ft3/s, cubic feet per second; %, percent; PreQ, pre-burn discharge; RegrQ, regression-derived discharge; BulkQ, sediment-bulked discharge; na, not applicable]

Single basins Composite basins Subbasins of composite basins

Model 

basin ID

Name of basin 

or drainage

Basin 

area 

(mi2)

Percentage 

of mediumhigh burned 

area

Mediumhigh 

burned 

area 

(mi2)

Regression 

derived 

discharge 

(ft3/s)

Pre-burn 

discharge 

(ft3/s)

Correlation 

between PreQ 

and RegrQ 

(%)

Post-burn 

discharge 

(ft3/s)

Sediment 

bulked 

discharge 

(ft3/s)

Ratio 

BulkQ 

to PreQ 

(BulkQ/PreQ)

Remarks

South Platte River basins and subbasins upstream from Cheesman Dam—Continued
76 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires 12D Sixmile and Wigwam 7.776 24.4 1.897 76.9 77.1 na 565 599 7.8 12E Sixmile and Wigwam 0.879 76.2 0.670 12.8 16.6 na 388 462 27.8 12F Sixmile and Wigwam 1.192 78.7 0.938 16.4 26.3 na 466 558 21.2 Cross section DXS2 34.6 14.391 13,560 14,732 13 Fourmile Creek 8.22 59.7 4.906 80.4 80.8 100.5 958 1,101 13.6 Cross section DXS3 37.1 19.445 14,449 15,789 Cross section DXS4 37.1 19.925 14,609 15,965 14 Mouth of Horse Creek 212 12.8 27.048 1,168 1,154 98.8 4,010 4,138 3.6 14A Horse Creek 3.576 20.7 0.738 40.6 39.9 na 358 376 9.4 Mainly a stream reach 14B Horse Creek 1.356 75.3 1.021 18.3 36.6 na 507 602 16.5 Burn of 11.91% for composite basin 14C Horse Creek 0.641 100.0 0.641 9.9 13.2 na 353 441 33.4

14D Horse Creek 0.633 45.8 0.290 9.8 20.4 na 209 233 11.414E Horse Creek 18.802 36.1 6.788 159.0 93.6 na 768 837 8.9 Mainly a stream reach14F Horse Creek 2.045 54.3 1.110 25.6 62.1 na 436 495 8.014G Horse Creek 0.547 29.9 0.164 8.6 21.2 na 128 138 6.514H Horse Creek 0.764 30.5 0.233 11.4 35.9 na 480 517 14.414I Horse Creek 1.155 44.1 0.509 16.0 36.6 na 353 392 10.714J Horse Creek 1.887 30.3 0.572 24.0 30.7 na 330 355 11.614K Horse Creek 15.536 41.0 6.370 135.9 65.7 na 1,120 1,235 18.8 Mainly a stream reach14L Horse Creek 1.193 41.4 0.494 16.4 30.0 na 323 356 11.914M Horse Creek 0.399 59.5 0.237 6.7 8.2 na 146 168 20.514N Horse Creek 0.653 87.2 0.569 10.0 15.2 na 337 410 27.014O Horse Creek 0.492 59.8 0.294 7.9 10.8 na 133 153 14.2

Table 3–6. HEC-HMS model results for South Platte River basins and subbasins upstream and downstream from Cheesman Reservoir used in the manual calibration method.—Continued[mi2, square miles; ft3/s, cubic feet per second; %, percent; PreQ, pre-burn discharge; RegrQ, regression-derived discharge; BulkQ, sediment-bulked discharge; na, not applicable]

Single basins Composite basins Subbasins of composite basins

Model 

basin ID

Name of basin 

or drainage

Basin 

area 

(mi2

)

Percentage 

of mediumhigh burned 

area

Mediumhigh 

burned 

area 

(mi2

)

Regression 

derived 

discharge 

(ft3/s)

Pre-burn 

discharge 

(ft3/s)

Correlation 

between PreQ 

and RegrQ 

(%)

Post-burn 

discharge 

(ft3/s)

Sediment 

bulked 

discharge 

(ft3/s)

Ratio 

BulkQ 

to PreQ 

(BulkQ/PreQ)

Remarks

South Platte River basins and subbasins downstream from Cheesman Dam—Continued
Appendix 3. Appendix Tables 3–1—3–14 77

14P Horse Creek 0.582 22.7 0.132 9.1 20.4 na 148 156 7.7 Mainly a stream reach14Q Horse Creek 12.287 3.0 0.369 112.0 72.8 na Unburned Unburned Unburned Mainly a stream reach14R Horse Creek 12.753 0.0 0.000 115.5 70.0 na Unburned Unburned Unburned14S Horse Creek 17.419 4.8 0.831 149.3 181 na 362 366 2.0 Mainly a stream reach14T Horse Creek 8.854 4.8 0.422 85.5 79.0 na 159 161 2.0 Mainly a stream reach14U Horse Creek 7.391 4.8 0.353 73.7 86.3 na 171 173 2.014V Horse Creek 2.706 59.2 1.603 32.2 39.7 na 703 807 20.314W Horse Creek 7.199 4.8 0.343 72.1 80.9 na 161 163 2.014X Horse Creek 15.993 3.2 0.509 139.1 137 na 241 243 1.8 Mainly a stream reach14Y Horse Creek 12.778 3.2 0.406 115.7 134 na 225 227 1.7 Mainly a stream reach14Z Horse Creek 15.538 3.2 0.494 135.9 125 na 213 215 1.7 Mainly a stream reach14AA Horse Creek 1.83 3.2 0.058 23.4 28.6 na Unburned Unburned Unburned14BB Horse Creek 9.447 3.2 0.300 90.2 42.0 na Unburned Unburned Unburned14CC Horse Creek 6.426 3.2 0.204 65.7 52.1 na Unburned Unburned Unburned Mainly a stream reach14DD Horse Creek 8.996 3.2 0.286 86.7 83.5 na Unburned Unburned Unburned Mainly a stream reach14EE Horse Creek 13.315 3.2 0.423 119.7 92.9 na Unburned Unburned Unburned14FF Horse Creek 8.88 3.2 0.282 85.7 56.2 na Unburned Unburned Unburned15 Lazy Gulch 1.23 39.1 0.480 16.8 17.0 101.0 309 339 20.016 Brush Creek 2.33 59.3 1.380 28.5 28.7 100.8 507 582 20.3

Cross section DXS4.5 18.0 48.352 17,828 18,632Cross section DXS5 18.4 50.001 17,874 18,698

17 Unnamed drainage 1.16 0.0 0.000 16.1 15.8 98.6 Unburned Unburned Unburned

Cross section DXS6 18.4 50.001 18,056 18,885

UB1 Unburned drainage 1bc 1.75 0.0 0.000 22.6 22.5 99.8 Unburned Unburned Unburned18 Saloon Gulch 1.26 46.6 0.588 17.2 17.2 99.9 290 324 18.9

Table 3–6. HEC-HMS model results for South Platte River basins and subbasins upstream and downstream from Cheesman Reservoir used in the manual calibration method.—Continued[mi2, square miles; ft3/s, cubic feet per second; %, percent; PreQ, pre-burn discharge; RegrQ, regression-derived discharge; BulkQ, sediment-bulked discharge; na, not applicable]

Single basins Composite basins Subbasins of composite basins

Model 

basin ID

Name of basin 

or drainage

Basin 

area 

(mi2)

Percentage 

of mediumhigh burned 

area

Mediumhigh 

burned 

area 

(mi2)

Regression 

derived 

discharge 

(ft3/s)

Pre-burn 

discharge 

(ft3/s)

Correlation 

between PreQ 

and RegrQ 

(%)

Post-burn 

discharge 

(ft3/s)

Sediment 

bulked 

discharge 

(ft3/s)

Ratio 

BulkQ 

to PreQ 

(BulkQ/PreQ)

Remarks

South Platte River basins and subbasins downstream from Cheesman Dam—Continued
78 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires UB2 Unburned drainage 2bc 1.07 0.0 0.000 15.1 0.0 Unburned Unburned Unburned 19 Mouth of Gunbarrel and Kelsey 10.2 2.0 0.204 96.1 96.8 100.8 220 221 2.3 19A Gunbarrel and Kelsey 0.686 2.0 0.014 10.4 10.2 97.9 22 22 2.1 Burn of 2% for composite basin 19B Gunbarrel and Kelsey 4.719 2.0 0.094 51.0 45.4 89.1 103 104 2.3 19C Gunbarrel and Kelsey 4.791 2.0 0.096 51.6 47.6 92.3 108 109 2.3 UB3 Unburned drainage 3bc 13.12 0.0 0.000 118.2 118 99.8 Unburned Unburned Unburned

Cross section DXS7 16.9 51.309 18,163 18,930

M1 South Platte Reach 1 3.258 5.8 0.188 37.6 37.2 99.0 147 149 4.0 Mainly a stream reachM2 South Platte Reach 2 2.568 5.8 0.148 30.9 31.0 100.4 135 137 4.4 Mainly a stream reachM3 South Platte Reach 3 2.977 9.1 0.269 34.9 35.4 101.5 201 206 5.8 Mainly a stream reachM4 South Platte Reach 4 4.187 12.3 0.516 46.2 46.0 99.6 395 407 8.9 Mainly a stream reach

Notes

Correlation percentages for subbasins are not meaningful, as subbasin discharge values were adjusted during calibration of the larger watershed to the regression equation by uniformly adjusting pre-burn 

runoff-curve number values for the individual basins to match the routed peak at the basin mouth. Therefore, the subbasin discharge values do not necessarily match the regression equation.

Table 3–6. HEC-HMS model results for South Platte River basins and subbasins upstream and downstream from Cheesman Reservoir used in the manual calibration method.—Continued[mi2, square miles; ft3/s, cubic feet per second; %, percent; PreQ, pre-burn discharge; RegrQ, regression-derived discharge; BulkQ, sediment-bulked discharge; na, not applicable]

Single basins Composite basins Subbasins of composite basins

Model 

basin ID

Name of basin 

or drainage

Basin 

area 

(mi2

)

Percentage 

of mediumhigh burned 

area

Mediumhigh 

burned 

area 

(mi2

)

Regression 

derived 

discharge 

(ft3/s)

Pre-burn 

discharge 

(ft3/s)

Correlation 

between PreQ 

and RegrQ 

(%)

Post-burn 

discharge 

(ft3/s)

Sediment 

bulked 

discharge 

(ft3/s)

Ratio 

BulkQ 

to PreQ 

(BulkQ/PreQ)

Remarks

South Platte River basins and subbasins downstream from Cheesman Dam—Continued
Appendix 3. Appendix Tables 3–1—3–14 79

Table 3–7. Peak flows and recovered model parameters for South Platte River subbasins upstream and downstream from 

Cheesman Reservoir.

[mi2, square miles; ft3/s, cubic feet per second; SCS, Soil Conservation Service]

HEC-HMS model 

basin identificatin number

Drainage 

area 

(mi2)

Peak-flow from 6-hour storm 

recurrence interval

Recovery SCS method 

watershed parameters 

10-year 

storm 

peak flow 

(ft3/s)

50-year 

storm 

peak flow 

(ft3/s)

100-year 

storm 

peak flow 

(ft3/s)

500-year 

storm 

peak flow 

(ft3/s)

Runoff 

curve 

number

Initial 

abstraction 

(inches)

SCS 

lag time 

(minutes)

South Platte River basins upstream from Cheesman Dam

9N 0.37 6 19 25 53 68.40 0.93 38

9C 8.09 97 281 358 626 69.70 0.87 210

9L 0.88 15 40 52 96 68.90 0.90 84

9M 2.97 41 119 151 272 68.60 0.92 127

9K 0.48 5 16 21 43 64.70 1.09 52

9J 0.40 3 11 15 30 62.80 1.18 53

9I 0.27 4 13 17 34 68.20 0.93 50

9H 2.16 25 78 101 191 66.50 1.01 89

9G 6.44 68 191 242 418 70.60 0.83 291

9F 1.57 41 109 141 255 72.60 0.76 62

9E 0.97 28 75 96 171 73.40 0.72 60

9D 0.99 28 75 97 174 73.10 0.74 57

9B 1.99 54 135 171 298 73.10 0.73 82

9A Turkey Creek 0.61 17 50 65 119 73.00 0.74 45

6 Longwater Gulch 2.34 43 115 147 267 70.00 0.86 92

3 Beaver 3.54 47 137 176 314 68.60 0.92 138

7 Corral 4.38 83 227 295 556 69.80 0.87 67

4 Hackett Gulch 6.56 69 224 290 536 66.50 1.01 115

1 Vermillion Creek 4.93 52 166 214 388 67.70 0.96 159

2 Crystal Creek 5.27 55 175 227 411 67.50 0.96 160

0.1 0.60 946 960 966 989 65.20 1.07 87

UBB1 19.82 16 114 164 353 61.60 1.25 592

UBB2 9.28 8 59 84 183 61.40 1.26 522

UBB3 0.31 4 13 16 31 67.40 0.97 72

UBB4 Unburned basin 4ac 0.32 0 4 6 13 56.10 1.56 63

PA 3.87 27 74 93 160 71.50 0.80 519

5B 3.11 36 111 144 265 66.90 0.99 111

5A Tarryall Creek 8.42 795 962 1034 1285 68.40 0.92 228

7.1 Motberry Creek 1.60 39 105 137 252 71.80 0.79 58

8 Northrup Gulch 3.84 72 189 238 413 70.90 0.82 125

7.2 Wildcat Creek 1.98 48 124 159 282 72.10 0.77 78

8.1 Unnamed drainage A 1.03 26 71 93 171 71.90 0.78 53

PB 11.31 106 273 341 572 72.60 0.75 450

8.2 Unnamed drainage B 0.72 18 57 77 149 71.80 0.79 32

10N Goose Creek 11.70 4 65 99 238 58.90 1.41 385

10M 13.86 3 74 115 279 58.50 1.43 374

10L 12.16 3 66 102 251 58.40 1.44 358

10K 10.95 0 48 88 258 55.10 1.66 187

10J 5.48 0 26 48 141 55.10 1.68 155

10I 4.69 0 23 42 123 55.10 1.68 150

10H 7.64 0 40 68 183 56.40 1.57 227
80 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

10F 6.27 5 76 114 256 58.70 1.41 143

10G 3.55 3 49 72 159 58.50 1.42 106

10C 2.82 54 144 184 336 70.10 0.85 85

10E 1.88 34 92 120 227 69.20 0.89 68

10D 7.38 129 340 428 733 71.10 0.81 157

10B 4.67 111 269 333 553 73.60 0.72 147

10A Goose Creek 2.13 55 134 167 283 73.40 0.72 112

9.1 Unnamed drainage C 0.87 24 68 89 164 72.60 0.75 46

9.2 Sand Draw 0.67 19 54 70 129 72.90 0.74 45

9.3 Unnamed drainage D 0.75 21 57 73 131 72.90 0.74 57

PC South 6.49 92 240 299 504 72.30 0.77 262

Cheesman 225.34 1739 2814 3352 5535 -- -- --

Outlet (end of upper model reach) 225.34 1739 2814 3352 5535 -- -- --

South Platte River basins downstream from Cheesman Dam

19C 4.79 1 42 66 161 57.20 1.50 159

19B 4.72 1 41 65 160 57.00 1.51 151

19A Gunbarrel and Kelsey 0.69 0 8 13 28 57.40 1.48 99

UB3 13.12 0 62 105 290 56.30 1.58 248

18 Saloon Gulch 1.26 22 60 78 149 68.90 0.90 68

UB1 1.75 0 10 18 51 55.30 1.69 119

14EE Horse Creek 13.31 7 87 131 304 59.30 1.37 361

14DD 9.00 2 62 96 236 58.00 1.45 262

14CC 6.43 2 47 72 171 58.60 1.42 274

14FF 8.88 7 62 91 204 60.30 1.32 395

14BB 9.45 9 65 94 202 61.40 1.26 477

14AA 1.83 0 16 26 64 55.70 1.59 100

14Z 15.54 7 101 154 362 59.00 1.39 340

14Y 12.78 3 86 134 329 58.00 1.45 268

14X 15.99 4 105 164 406 57.70 1.46 265

14W 7.20 4 63 95 222 58.90 1.40 237

14U 7.39 3 64 98 231 58.60 1.42 223

14V 2.71 54 139 176 309 71.00 0.82 109

14T 8.85 7 74 110 251 59.70 1.35 293

14R 12.75 4 70 106 253 59.10 1.40 403

14Q 12.29 8 81 119 270 60.00 1.33 407

14P 0.58 7 21 27 50 66.70 1.00 101

14O 0.49 8 24 32 66 68.20 0.93 42

14N 0.65 18 55 72 137 72.40 0.76 35

14M 0.40 8 25 34 69 70.30 0.85 36

14L 1.19 21 58 75 146 68.90 0.90 63

14K 15.54 132 364 460 789 71.10 0.81 404

Table 3–7. Peak flows and recovered model parameters for South Platte River subbasins upstream and downstream from 

Cheesman Reservoir.—Continued

[mi2, square miles; ft3/s, cubic feet per second; SCS, Soil Conservation Service]

HEC-HMS model 

basin identificatin number

Drainage 

area 

(mi2)

Peak-flow from 6-hour storm 

recurrence interval

Recovery SCS method 

watershed parameters 

10-year 

storm 

peak flow 

(ft3/s)

50-year 

storm 

peak flow 

(ft3/s)

100-year 

storm 

peak flow 

(ft3/s)

500-year 

storm 

peak flow 

(ft3/s)

Runoff 

curve 

number

Initial 

abstraction 

(inches)

SCS 

lag time 

(minutes)

South Platte River basins upstream from Cheesman Dam—Continued
Appendix 3. Appendix Tables 3–1—3–14 81

14J 1.89 25 73 94 169 68.00 0.94 121

14I 1.16 20 56 74 148 68.60 0.92 51

14H 0.76 9 27 36 76 65.40 1.06 47

14G 0.55 8 22 30 63 66.80 1.00 44

14F 2.05 23 72 94 179 66.00 1.03 83

14E 18.80 127 344 432 737 71.70 0.79 557

14S 17.42 11 132 197 452 59.50 1.36 318

14C 0.64 18 53 69 128 73.00 0.74 43

14B 1.36 30 85 112 211 71.00 0.82 52

14D 0.63 12 35 47 95 69.40 0.88 42

14A Horse Creek 3.58 23 78 101 186 67.40 0.97 294

17 Unnamed drainage 1.16 0 7 12 35 55.30 1.72 98

16 Brush Creek 2.33 44 117 149 269 70.20 0.85 92

15 Lazy Gulch 1.23 21 59 77 151 68.60 0.91 59

12B Sixmile and Wigwam 5.22 52 168 219 401 66.80 0.99 148

12C 3.43 44 132 169 305 68.10 0.94 125

12D 7.78 33 155 211 417 63.50 1.15 188

12E 0.88 22 62 82 155 71.70 0.79 45

12F 1.19 27 79 106 204 71.00 0.82 42

12A Sixmile and Wigwam 18.17 85 317 420 791 66.20 1.02 331

11 Schoonover 1.71 42 111 144 261 72.00 0.78 65

M1 3.26 5 49 70 151 59.60 1.36 127

Cheesman out (spillway) -- 1,739 2,814 3,352 4,867 -- -- --

Cheesman outlet gates -- 1,400 1,400 1,400 1,400 -- -- --

13 Fourmile Creek 8.22 105 288 364 625 70.80 0.82 240

M2 South Platte Reach 2 2.57 8 34 47 91 64.50 1.10 361

M3 South Platte Reach 3 2.98 12 48 64 123 65.70 1.05 335

M4 South Platte Reach 4 4.19 22 75 98 180 67.40 0.97 369

UB6 0.58 0 6 9 22 57.40 1.48 135

Outlet (end of model reach) 0.00 3,394 6,151 7,526 10,954 -- -- --

Table 3–7. Peak flows and recovered model parameters for South Platte River subbasins upstream and downstream from 

Cheesman Reservoir.—Continued

[mi2, square miles; ft3/s, cubic feet per second; SCS, Soil Conservation Service]

HEC-HMS model 

basin identificatin number

Drainage 

area 

(mi2)

Peak-flow from 6-hour storm 

recurrence interval

Recovery SCS method 

watershed parameters 

10-year 

storm 

peak flow 

(ft3/s)

50-year 

storm 

peak flow 

(ft3/s)

100-year 

storm 

peak flow 

(ft3/s)

500-year 

storm 

peak flow 

(ft3/s)

Runoff 

curve 

number

Initial 

abstraction 

(inches)

SCS 

lag time 

(minutes)

South Platte River basins downstream from Cheesman Dam—Continued
82 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Table 3–8. South Platte River Basin rainfall distribution.

Minutes from 

beginning of storm

Percentage

of total 

rainfall

Cumulative rainfall amount each minute of storm distribution

10-year, 

6-hour storm 

(1.60-inch total)

50-year, 

6-hour storm 

(2.20-inch total)

100-year, 

6-hour storm 

(2.40-inch total)

500-year, 

6-hour storm 

(3.00-inch total)

0005 0.010 0.016 0.022 0.024 0.030

0010 0.015 0.024 0.033 0.036 0.045

0015 0.020 0.032 0.044 0.048 0.060

0020 0.027 0.043 0.060 0.065 0.081

0025 0.032 0.051 0.071 0.077 0.096

0030 0.040 0.064 0.088 0.096 0.120

0035 0.046 0.073 0.101 0.110 0.138

0040 0.053 0.085 0.116 0.127 0.159

0045 0.060 0.096 0.132 0.144 0.180

0050 0.068 0.109 0.149 0.163 0.204

0055 0.077 0.123 0.170 0.185 0.231

0100 0.085 0.136 0.187 0.204 0.255

0105 0.093 0.149 0.204 0.223 0.279

0110 0.102 0.163 0.225 0.245 0.306

0115 0.112 0.179 0.247 0.269 0.336

0120 0.122 0.195 0.269 0.293 0.366

0125 0.132 0.211 0.291 0.317 0.396

0130 0.144 0.231 0.317 0.346 0.433

0135 0.157 0.251 0.346 0.377 0.471

0140 0.169 0.271 0.372 0.406 0.508

0145 0.188 0.301 0.413 0.451 0.564

0150 0.204 0.327 0.449 0.490 0.613

0155 0.240 0.384 0.528 0.576 0.720

0200 0.290 0.464 0.638 0.696 0.870

0205 0.360 0.576 0.792 0.864 1.080

0210 0.423 0.677 0.930 1.015 1.269

0215 0.490 0.784 1.078 1.176 1.470

0220 0.552 0.883 1.215 1.325 1.656

0225 0.606 0.969 1.333 1.454 1.818

0230 0.627 1.003 1.380 1.505 1.881

0235 0.648 1.037 1.425 1.555 1.944

0240 0.662 1.059 1.457 1.589 1.986

0245 0.680 1.088 1.496 1.632 2.040

0250 0.698 1.117 1.535 1.675 2.094

0255 0.710 1.136 1.562 1.704 2.130

0300 0.724 1.159 1.593 1.738 2.173

0305 0.738 1.181 1.623 1.771 2.214

0310 0.751 1.201 1.652 1.802 2.253

0315 0.761 1.217 1.674 1.826 2.283

0320 0.772 1.235 1.699 1.853 2.316

0325 0.783 1.253 1.722 1.879 2.349

0330 0.794 1.271 1.747 1.906 2.383

0335 0.805 1.288 1.771 1.932 2.415

0340 0.815 1.304 1.793 1.956 2.445

0345 0.823 1.317 1.810 1.975 2.469

0350 0.832 1.331 1.831 1.997 2.496
Appendix 3. Appendix Tables 3–1—3–14 83

0355 0.841 1.345 1.850 2.018 2.523

0400 0.850 1.360 1.870 2.040 2.550

0405 0.860 1.376 1.892 2.064 2.580

0410 0.869 1.391 1.912 2.086 2.608

0415 0.878 1.405 1.931 2.107 2.634

0420 0.883 1.413 1.942 2.119 2.649

0425 0.892 1.427 1.963 2.141 2.676

0430 0.901 1.441 1.982 2.162 2.703

0435 0.907 1.451 1.996 2.177 2.721

0440 0.914 1.463 2.011 2.194 2.743

0445 0.920 1.472 2.024 2.208 2.760

0450 0.927 1.483 2.040 2.225 2.781

0455 0.934 1.495 2.055 2.242 2.803

0500 0.941 1.505 2.070 2.258 2.823

0505 0.948 1.517 2.085 2.275 2.844

0510 0.954 1.527 2.099 2.290 2.863

0515 0.960 1.536 2.112 2.304 2.880

0520 0.967 1.547 2.128 2.321 2.901

0525 0.973 1.557 2.140 2.335 2.919

0530 0.979 1.567 2.154 2.350 2.938

0535 0.985 1.576 2.167 2.364 2.955

0540 0.990 1.584 2.178 2.376 2.970

0545 0.994 1.591 2.187 2.386 2.983

0550 0.998 1.597 2.195 2.395 2.994

0555 1.000 1.600 2.200 2.400 3.000

0600 1.000 1.600 2.200 2.400 3.000

0605 1.000 1.600 2.200 2.400 3.000

Table 3–8. South Platte River Basin rainfall distribution.—Continued

Minutes from 

beginning of storm

Percentage

of total 

rainfall

Cumulative rainfall amount each minute of storm distribution

10-year, 

6-hour storm 

(1.60-inch total)

50-year, 

6-hour storm 

(2.20-inch total)

100-year, 

6-hour storm 

(2.40-inch total)

500-year, 

6-hour storm 

(3.00-inch total)
84 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Table 3–9. Flood peak flows through the Deckers-to-Trumbull reach, South Platte River.

[ft3/s, cubic feet per second]

Cross 

section

River 

station

Recurrence interval discharges, 

6-hour-storm

10-year 

(ft3/s)

50-year 

(ft3/s)

100-year 

(ft3/s)

500-year 

(ft3/s)

V 13 3,139 4,211 4,909 7,424

U 11 3,139 4,211 4,909 7,424

T 10 3,139 4,211 4,909 7,424

S 9.5 3,139 4,211 4,909 7,424

R 9 3,160 4,270 4,986 7,575

Q 8 3,160 4,270 4,986 7,575

P 7 3,160 4,270 4,986 7,575

O 6 3,486 5,860 7,212 12,244

N 5 3,486 5,860 7,212 12,244

M 4 3,486 5,860 7,212 12,244

L 3 3,486 5,860 7,212 12,244

K 2 3,486 5,867 7,225 12,279

J 1 3,490 5,883 7,246 12,320

I 0.5 3,538 6,016 7,417 12,630

H 0 3,538 6,016 7,417 12,630

G –1 3,538 6,016 7,417 12,630

F –2 3,538 6,016 7,417 12,630

E –3 3,538 6,016 7,417 12,630

D –4 3,538 6,016 7,417 12,630

C –5 3,538 6,016 7,417 12,630

B –6 3,538 6,016 7,417 12,630

A –7 3,538 6,016 7,417 12,630
Appendix 3. Appendix Tables 3–1—3–14 85

Table 3–10. Summary of Manning’s n values for roughness and downstream reach lengths.

[Manning’s n values are dimensionless; downstream reach lengths are the distance from the cross section downstream to the next cross 

section; ft, feet; *, interpolated in HEC-RAS]

Cross 

section

River 

station

Manning’s n values Downstream reach lengths

Left 

overbank Channel Right overbank

Left 

(ft)

Channel 

(ft)

Right 

(ft)

V 13 0.080 0.035 0.060 675 675 675

U 11.5 0.080 0.035 0.060 1,925 1,925 1,925

T 11 0.080 0.035 0.060 600 600 600

S 10 0.120 0.040 0.080 130 130 130

R 9.5 0.120 0.040 0.080 770 770 770

Q 9 0.120 0.040 0.080 830 830 830

P 8 0.120 0.040 0.080 27 27 27

7.9* 0.120 0.040 0.080 27 27 27

7.7* 0.120 0.040 0.080 27 27 27

O 7.6 0.120 0.040 0.080 208 208 208

7.5 Bridge Bridge

N 7 0.070 0.045 0.080 332 332 332

M 5 0.070 0.045 0.100 350 350 350

L 4 0.070 0.045 0.080 654 654 654

K 3 0.100 0.045 0.080 196 196 196

2.5 Bridge Bridge

J 2 0.100 0.045 0.080 800 800 800

I 1 0.100 0.045 0.080 2,120 2,120 2,120

H 0.5 0.100 0.045 0.080 1,160 1,160 1,160

G 0 0.054 0.038 0.054 525 525 525

F –1 0.054 0.038 0.054 250 250 250

E –2 0.054 0.038 0.054 525 525 525

D –3 0.054 0.038 0.054 185 185 185

C –4 0.054 0.038 0.054 200 200 200

–5 Bridge Bridge

B –6 0.054 0.038 0.054 2,380 2,380 2,380

A –7 0.054 0.038 0.054 0 0 0
86 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires Table 3–11. Results of step-backwater computations using HEC-RAS program. [ft3/s, cubic feet per second; ft, feet; ft/s, feet per second; hr, hour; datum is National Geodetic Vertical Datum of 1929 in feet; -- no data] Cross section River station Profile Discharge total (ft3/s) Discharge left overbank (ft3/s) Discharge channel (ft3/s) Discharge right overbank (ft3/s) Water surface elevation (ft) Critical water surface (ft) Velocity channel (ft/s) Flow area (ft2

)

Top 

width 

(ft)

Froude 

number 

channel

V 13 10-year, 6-hour storm 3,140 13 2,949 177 6,415.90 -- 5.40 687 178 0.40V 13 50-year, 6-hour storm 4,210 24 3,820 365 6,416.86 -- 5.97 870 198 0.41V 13 100-year, 6-hour storm 4,910 32 4,361 517 6,417.42 -- 6.27 982 204 0.42V 13 500-year, 6-hour storm 7,420 65 6,225 1,130 6,419.12 -- 7.19 1,333 209 0.43U 11.5 10-year, 6-hour storm 3,140 12 3,125 2 6,412.58 6,412.39 9.61 333 106 0.92U 11.5 50-year, 6-hour storm 4,210 25 4,170 15 6,413.33 6,413.10 10.52 416 114 0.91U 11.5 100-year, 6-hour storm 4,910 35 4,842 32 6,413.80 6,413.55 10.98 470 118 0.90U 11.5 500-year, 6-hour storm 7,420 85 7,193 142 6,415.34 6,414.90 12.23 657 124 0.87

T 11 10-year, 6-hour storm 3,140 14 3,107 19 6,408.88 -- 4.14 782 155 0.32T 11 50-year, 6-hour storm 4,210 25 4,150 35 6,409.93 -- 4.63 947 159 0.32T 11 100-year, 6-hour storm 4,910 34 4,829 47 6,410.55 -- 4.91 1,047 162 0.33T 11 500-year, 6-hour storm 7,420 74 7,243 102 6,412.58 -- 5.71 1,382 169 0.33

S 10 10-year, 6-hour storm 3,140 0 3,140 0 6,405.67 6,405.67 10.66 295 86 1.01S 10 50-year, 6-hour storm 4,210 1 4,207 3 6,406.42 6,406.42 11.74 361 92 1.01S 10 100-year, 6-hour storm 4,910 3 4,900 7 6,406.91 6,406.91 12.25 407 95 1.00S 10 500-year, 6-hour storm 7,420 29 7,355 36 6,408.40 6,408.40 13.97 557 106 0.99

R 9.5 10-year, 6-hour storm 3,140 41 3,070 30 6,402.90 6,402.39 10.04 348 97 0.82R 9.5 50-year, 6-hour storm 4,210 74 4,089 46 6,403.31 6,403.31 12.28 389 100 0.96R 9.5 100-year, 6-hour storm 4,910 117 4,731 63 6,403.84 6,403.84 12.88 441 102 0.96R 9.5 500-year, 6-hour storm 7,420 304 6,974 142 6,405.62 6,405.62 14.39 644 126 0.94

Q 9 10-year, 6-hour storm 3,160 50 3,082 28 6,398.12 -- 7.14 485 130 0.61Q 9 50-year, 6-hour storm 4,270 133 4,066 71 6,400.76 -- 5.84 858 152 0.39Q 9 100-year, 6-hour storm 4,990 178 4,717 95 6,401.57 -- 6.07 985 159 0.38Q 9 500-year, 6-hour storm 7,580 369 7,022 189 6,403.62 -- 7.15 1,326 172 0.40

P 8 10-year, 6-hour storm 3,160 125 2,938 97 6,396.69 -- 5.27 738 100 0.31P 8 50-year, 6-hour storm 4,270 212 3,890 168 6,399.98 -- 5.13 1,210 202 0.26P 8 100-year, 6-hour storm 4,990 305 4,481 204 6,400.75 -- 5.57 1,377 230 0.27P 8 500-year, 6-hour storm 7,580 720 6,615 246 6,402.53 -- 7.24 1,856 317 0.33
Appendix 3. Appendix Tables 3–1—3–14 87

Interpolated 7.9* 10-year, 6-hour storm 3,160 65 2,966 129 6,396.70 -- 4.93 787 134 0.29Interpolated 7.9* 50-year, 6-hour storm 4,270 161 3,771 339 6,400.02 -- 4.54 1,401 258 0.23Interpolated 7.9* 100-year, 6-hour storm 4,990 246 4,310 434 6,400.81 -- 4.87 1,619 294 0.24Interpolated 7.9* 500-year, 6-hour storm 7,580 644 6,307 629 6,402.65 -- 6.24 2,283 437 0.29Interpolated 7.7* 10-year, 6-hour storm 3,490 12 3,466 12 6,396.52 -- 5.59 667 142 0.35Interpolated 7.7* 50-year, 6-hour storm 5,860 131 5,429 300 6,399.68 -- 6.30 1,297 288 0.33Interpolated 7.7* 100-year, 6-hour storm 7,210 228 6,526 456 6,400.34 -- 7.16 1,501 329 0.36Interpolated 7.7* 500-year, 6-hour storm 12,200 618 10,687 896 6,401.42 -- 10.75 1,903 430 0.52O 7.6 10-year, 6-hour storm 3,490 3,490 6,396.48 6,392.70 5.50 634 84 0.35O 7.6 50-year, 6-hour storm 5,860 58 5,773 29 6,399.57 6,394.24 6.46 1,064 296 0.35O 7.6 100-year, 6-hour storm 7,210 132 6,976 102 6,400.19 6,395.05 7.38 1,272 374 0.39O 7.6 500-year, 6-hour storm 12,200 414 11,361 425 6,401.09 6,397.59 11.12 1,660 486 0.56Upstream bridge 7.5 10-year, 6-hour storm 3,490 0 3,490 0 6,393.98 6,392.72 8.39 -- -- --Upstream bridge 7.5 50-year, 6-hour storm 5,860 522 4,883 456 6,399.57 6,393.84 9.97 -- 296 --Upstream bridge 7.5 100-year, 6-hour storm 7,210 1,211 4,856 1,143 6,400.19 6,393.87 8.96 -- 374 --Upstream bridge 7.5 500-year, 6-hour storm 12,172 3,650 4,773 3,749 6,401.09 6,402.06 7.73 -- 486 --Downstream bridge 7.5 10-year, 6-hour storm 3,490 89 3,233 168 6,394.05 6,390.92 5.74 -- -- --Downstream bridge 7.5 50-year, 6-hour storm 5,860 626 4,604 630 6,399.57 6,392.42 7.24 -- 227 --Downstream bridge 7.5 100-year, 6-hour storm 7,210 1,256 4,717 1,237 6,400.19 6,393.11 6.87 -- 277 --Downstream bridge 7.5 500-year, 6-hour storm 12,172 3,614 4,814 3,744 6,401.09 6,401.15 6.32 -- 346 --N 7 10-year, 6-hour storm 3,490 107 3,170 213 6,395.25 -- 4.70 916 264 0.29N 7 50-year, 6-hour storm 5,860 189 4,926 745 6,397.13 -- 5.93 1,486 325 0.33N 7 100-year, 6-hour storm 7,210 254 5,729 1,227 6,398.04 -- 6.32 1,787 336 0.34N 7 500-year, 6-hour storm 12,200 641 8,308 3,251 6,400.93 -- 7.25 2,810 369 0.34M 5 10-year, 6-hour storm 3,490 31 3,459 1 6,392.85 6,392.85 9.93 358 122 1.00M 5 50-year, 6-hour storm 5,860 84 5,773 4 6,394.11 6,394.11 11.75 514 128 1.00M 5 100-year, 6-hour storm 7,210 123 7,077 10 6,394.75 6,394.75 12.55 596 132 0.99M 5 500-year, 6-hour storm 12,200 317 11,820 63 6,396.80 6,396.80 14.81 879 144 0.99

Table 3–11. Results of step-backwater computations using HEC-RAS program.—Continued[ft3/s, cubic feet per second; ft, feet; ft/s, feet per second; hr, hour; datum is National Geodetic Vertical Datum of 1929 in feet; -- no data]

Cross 

section

River 

station Profile

Discharge 

total 

(ft3/s)

Discharge 

left 

overbank 

(ft3/s)

Discharge 

channel 

(ft3/s)

Discharge 

right 

overbank 

(ft3/s)

Water 

surface 

elevation 

(ft)

Critical 

water 

surface 

(ft)

Velocity 

channel 

(ft/s)

Flow 

area 

(ft2)

Top 

width 

(ft)

Froude 

number 

channel
88 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

L 4 10-year, 6-hour storm 3,490 0 3,490 0 6,388.20 -- 8.06 433 109 0.71L 4 50-year, 6-hour storm 5,860 0 5,838 22 6,390.35 -- 8.74 680 119 0.63L 4 100-year, 6-hour storm 7,210 0 7,164 46 6,391.26 -- 9.32 790 123 0.63L 4 500-year, 6-hour storm 12,200 0 11,934 266 6,393.91 -- 11.16 1,186 195 0.64K 3 10-year, 6-hour storm 3,490 84 3,192 213 6,385.82 6,382.29 6.20 703 132 0.38K 3 50-year, 6-hour storm 5,860 205 5,104 551 6,388.03 6,384.02 7.78 1,059 192 0.43K 3 100-year, 6-hour storm 7,210 278 6,075 857 6,388.83 6,384.97 8.58 1,216 199 0.45K 3 500-year, 6-hour storm 12,200 585 9,497 2,118 6,391.00 6,388.32 11.22 1,665 216 0.54Upstream bridge 2.5 10-year, 6-hour storm 3,490 72 3,280 138 6,383.20 6,382.80 10.90 -- -- --Upstream bridge 2.5 50-year, 6-hour storm 5,859 363 4,294 1,202 6,388.03 6,388.11 10.31 -- 192 --Upstream bridge 2.5 100-year, 6-hour storm 7,210 547 4,722 1,941 6,388.83 6,388.67 10.09 -- 199 --Upstream bridge 2.5 500-year, 6-hour storm 12,187 1,261 6,542 4,384 6,391.00 6,390.24 10.79 -- 216 --Downstream bridge 2.5 10-year, 6-hour storm 3,490 216 2,908 365 6,383.20 6,380.58 8.11 -- -- --Downstream bridge 2.5 50-year, 6-hour storm 5,859 705 3,985 1,168 6,388.02 6,382.73 8.81 -- 230 --Downstream bridge 2.5 100-year, 6-hour storm 7,210 1,003 4,500 1,707 6,388.62 6,387.69 9.30 -- 238 --Downstream bridge 2.5 500-year, 6-hour storm 12,187 2,006 6,385 3,796 6,390.39 6,389.66 11.08 -- 253 --J 2 10-year, 6-hour storm 3,490 186 3,024 280 6,384.13 -- 6.43 726 120 0.38J 2 50-year, 6-hour storm 5,870 414 4,912 544 6,385.88 -- 8.75 953 139 0.47J 2 100-year, 6-hour storm 7,220 489 6,011 719 6,386.66 -- 9.98 1,078 199 0.52J 2 500-year, 6-hour storm 12,300 1,470 9,519 1,311 6,389.01 -- 13.13 1,613 243 0.62I 1 10-year, 6-hour storm 3,490 5 3,302 183 6,380.11 6,379.87 8.62 454 173 0.85I 1 50-year, 6-hour storm 5,880 22 5,322 536 6,381.72 6,380.99 9.24 748 191 0.74I 1 100-year, 6-hour storm 7,250 37 6,439 774 6,382.60 6,381.53 9.48 919 200 0.70I 1 500-year, 6-hour storm 12,300 118 10,354 1,828 6,385.65 9.92 1,582 234 0.59H 0.5 10-year, 6-hour storm 3,540 51 3,444 45 6,368.40 -- 6.26 610 110 0.44H 0.5 50-year, 6-hour storm 6,020 135 5,773 111 6,370.34 -- 8.05 831 117 0.49H 0.5 100-year, 6-hour storm 7,420 190 7,076 154 6,371.15 -- 9.00 927 120 0.52H 0.5 500-year, 6-hour storm 12,600 408 11,867 326 6,373.00 -- 12.55 1,155 127 0.67

Table 3–11. Results of step-backwater computations using HEC-RAS program.—Continued[ft3/s, cubic feet per second; ft, feet; ft/s, feet per second; hr, hour; datum is National Geodetic Vertical Datum of 1929 in feet; -- no data]

Cross 

section

River 

station Profile

Discharge 

total 

(ft3/s)

Discharge 

left 

overbank 

(ft3/s)

Discharge 

channel 

(ft3/s)

Discharge 

right 

overbank 

(ft3/s)

Water 

surface 

elevation 

(ft)

Critical 

water 

surface 

(ft)

Velocity 

channel 

(ft/s)

Flow 

area 

(ft2

)

Top 

width 

(ft)

Froude 

number 

channel
Appendix 3. Appendix Tables 3–1—3–14 89

G 0 10-year, 6-hour storm 3,540 62 3,391 86 6,364.41 -- 6.80 581 193 0.54G 0 50-year, 6-hour storm 6,020 282 5,423 316 6,365.68 -- 8.64 905 346 0.61G 0 100-year, 6-hour storm 7,420 495 6,390 534 6,366.20 -- 9.39 1,113 430 0.64G 0 500-year, 6-hour storm 12,600 1,821 8,904 1,875 6,367.85 -- 10.52 1,905 502 0.64F –1 10-year, 6-hour storm 3,540 85 3,146 308 6,362.96 -- 5.44 805 314 0.45F –1 50-year, 6-hour storm 6,020 466 4,806 747 6,364.34 -- 6.34 1,350 458 0.46F –1 100-year, 6-hour storm 7,420 707 5,525 1,188 6,364.98 -- 6.58 1,645 476 0.46F –1 500-year, 6-hour storm 12,600 1,590 7,973 3,037 6,366.73 -- 7.47 2,494 489 0.46E –2 10-year, 6-hour storm 3,540 0 2,596 944 6,362.60 -- 4.64 1,103 342 0.34E –2 50-year, 6-hour storm 6,020 0 3,827 2,193 6,363.99 -- 5.51 1,586 355 0.37E –2 100-year, 6-hour storm 7,420 0 4,506 2,914 6,364.58 -- 5.98 1,800 363 0.38E –2 500-year, 6-hour storm 12,600 0 6,997 5,603 6,366.19 -- 7.64 2,407 395 0.45D –3 10-year, 6-hour storm 3,540 486 3,024 30 6,361.42 -- 5.84 762 259 0.45D –3 50-year, 6-hour storm 6,020 973 4,906 140 6,362.02 -- 8.51 986 567 0.62D –3 100-year, 6-hour storm 7,420 1,246 5,769 405 6,362.33 -- 9.52 1,162 571 0.67D –3 500-year, 6-hour storm 12,600 2,220 8,269 2,111 6,363.39 6,363.39 11.66 1,774 584 0.76C –4 10-year, 6-hour storm 3,540 290 2,854 396 6,361.11 6,359.04 5.19 1,153 877 0.39C –4 50-year, 6-hour storm 6,020 519 4,102 1,399 6,361.70 6,361.15 6.74 1,733 1,025 0.48C –4 100-year, 6-hour storm 7,420 661 4,310 2,449 6,362.23 6,361.62 6.51 2,278 1,036 0.45C –4 500-year, 6-hour storm 12,600 1,147 5,767 5,686 6,363.20 6,362.40 7.58 3,291 1,050 0.49Upstream bridge –5 10-year, 6-hour storm 3,518 0 1,854 1,664 6,361.11 6,361.52 6.30 -- 528 --Upstream bridge –5 50-year, 6-hour storm 5,994 0 1,368 4,626 6,361.70 6,361.93 4.65 -- 707 --Upstream bridge –5 100-year, 6-hour storm 7,405 72 839 6,493 6,362.23 6,362.04 2.57 -- 963 --Upstream bridge –5 500-year, 6-hour storm 12,568 335 967 11,267 6,363.20 6,362.60 2.28 -- 997 --Downstream bridge –5 10-year, 6-hour storm 3,518 23 2,016 1,479 6,361.11 6,358.44 6.18 -- 528 --Downstream bridge –5 50-year, 6-hour storm 6,011 36 1,672 4,303 6,361.70 6,361.95 5.12 -- 736 --Downstream bridge –5 100-year, 6-hour storm 7,405 80 1,033 6,291 6,362.22 6,362.22 2.99 -- 950 --Downstream bridge –5 500-year, 6-hour storm 12,568 323 1,142 11,102 6,362.69 6,362.69 3.05 -- 953 --

Table 3–11. Results of step-backwater computations using HEC-RAS program.—Continued[ft3/s, cubic feet per second; ft, feet; ft/s, feet per second; hr, hour; datum is National Geodetic Vertical Datum of 1929 in feet; -- no data]

Cross 

section

River 

station Profile

Discharge 

total 

(ft3/s)

Discharge 

left 

overbank 

(ft3/s)

Discharge 

channel 

(ft3/s)

Discharge 

right 

overbank 

(ft3/s)

Water 

surface 

elevation 

(ft)

Critical 

water 

surface 

(ft)

Velocity 

channel 

(ft/s)

Flow 

area 

(ft2)

Top 

width 

(ft)

Froude 

number 

channel
90 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

B –6 10-year, 6-hour storm 3,540 26 3,283 231 6,358.52 6,358.52 10.26 426 187 0.80B –6 50-year, 6-hour storm 6,020 70 4,781 1,169 6,360.02 6,360.02 11.54 749 232 0.79B –6 100-year, 6-hour storm 7,420 101 5,119 2,200 6,361.08 6,361.08 10.64 1,210 773 0.68B -6 500-year, 6-hour storm 12,600 171 6,335 6,095 6,362.56 6,362.56 11.03 2,579 952 0.64

A –7 10-year, 6-hour storm 3,540 2 3,513 26 6,347.58 6,345.89 4.59 806 365 0.44A –7 50-year, 6-hour storm 6,020 28 5,558 435 6,348.67 6,346.98 5.51 1,314 510 0.46A –7 100-year, 6-hour storm 7,420 55 6,612 754 6,349.16 6,347.50 5.90 1,572 550 0.47A –7 500-year, 6-hour storm 12,600 206 10,028 2,366 6,350.58 6,348.89 6.97 2,366 574 0.49

Table 3–11. Results of step-backwater computations using HEC-RAS program.—Continued[ft3/s, cubic feet per second; ft, feet; ft/s, feet per second; hr, hour; datum is National Geodetic Vertical Datum of 1929 in feet; -- no data]

Cross 

section

River 

station Profile

Discharge 

total 

(ft3/s)

Discharge 

left 

overbank 

(ft3/s)

Discharge 

channel 

(ft3/s)

Discharge 

right 

overbank 

(ft3/s)

Water 

surface 

elevation 

(ft)

Critical 

water 

surface 

(ft)

Velocity 

channel 

(ft/s)

Flow 

area 

(ft2

)

Top 

width 

(ft)

Froude 

number 

channel
Appendix 3. Appendix Tables 3–1—3–14 91

Table 3–12. Floodway data for the Deckers to Trumbull reach, South Platte River, computed in HEC-RAS.

[ft, feet; ft2, square feet; ft/s, feet per second; NGVD ft, National Geodetic Vertical Datum of 1929 in feet; *, interpolated cross section in HEC-RAS; Cross 

section A is equivalent to cross section DXS5 in figure 9; u.s., upstream; d.s., downstream]

Flooding source Floodway 100-year base flood water-surface elevation

Cross 

section

River 

station

Distance 

above 

XS-A 

(ft)

Width 

(ft)

Section 

area 

(ft2)

Mean 

velocity 

(ft/s)

Regulatory Without 

floodway

With 

floodway Increase

(NGVD ft)

V 13 14,895 100 714 6.87 6,417.42 6,417.42 6,417.61 0.19

U 11.5 14,220 95 476 10.32 6,413.80 6,413.80 6,414.16 0.37

T 11 12,295 140 1,002 4.90 6,410.55 6,410.55 6,410.68 0.13

S 10 11,695 85 400 12.28 6,406.91 6,406.91 6,406.91 0.00

R 9.5 11,565 66 366 13.43 6,403.84 6,403.84 6,403.81 –0.03

Q 9 10,795 120 1,000 4.99 6,401.57 6,401.57 6,402.53 0.96

P 8 9,965 75 1,016 4.91 6,400.75 6,400.75 6,401.63 0.88

7.9* 9,938 86 1,099 4.54 6,400.81 6,400.81 6,401.67 0.85

7.7* 9,912 76 967 7.45 6,400.34 6,400.34 6,401.12 0.78

O 7.6 9,885 153 1,198 6.02 6,400.19 6,400.19 6,401.19 1.00

7.5 u.s. side 

of bridge

9,855 159 802 8.99 6,400.19 6,400.19 6,401.19 1.00

7.5 d.s. side 

of bridge

9,807 140 843 8.56 6,400.19 6,400.19 6,400.98 0.79

N 7 9,677 83 944 7.64 6,398.04 6,398.04 6,398.49 0.45

M 5 9,345 114 573 12.58 6,394.75 6,394.75 6,394.83 0.08

L 4 8,995 125 911 7.91 6,391.26 6,391.26 6,392.24 0.97

K 3 8,341 97 884 8.16 6,388.83 6,388.83 6,389.31 0.48

2.5 u.s. side 

of bridge

8,251 125 726 9.93 6,388.83 6,388.83 6,389.31 0.48

2.5 d.s. side 

of bridge

8,225 174 951 7.58 6,388.62 6,388.62 6,388.72 0.10

J 2 8,145 53 632 11.43 6,386.66 6,386.66 6,387.05 0.39

I 1 7,345 154 835 8.68 6,382.60 6,382.60 6,382.69 0.10

H 0.5 5,225 95 930 7.98 6,371.15 6,371.15 6,372.08 0.93

G 0 4,065 101 780 9.51 6,366.20 6,366.20 6,367.20 0.99

F –1 3,540 161 1,118 6.64 6,364.98 6,364.98 6,365.98 1.00

E –2 3,290 136 998 7.43 6,364.58 6,364.58 6,365.08 0.49

D –3 2,765 177 1,025 7.24 6,362.33 6,362.33 6,363.31 0.97

C –4 2,580 256 1,061 7.00 6,362.23 6,362.23 6,362.49 0.26

–5 u.s. side of 

bridge

2,480 454 834 8.90 6,362.23 6,362.23 6,362.49 0.26

–5 d.s. side of 

bridge

2,455 443 876 8.47 6,362.22 6,362.22 6,362.49 0.27

B –6 2,380 144 697 10.65 6,361.08 6,361.08 6,360.69 –0.39

A –7 0 225 1,209 6.14 6,349.16 6,349.16 6,349.56 0.40
92 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Table 3–13. Comparison of 1978 study 100-year flood elevations at selected cross sections 

to 2004 study 100-year flood elevations at the same cross sections.

[1978 data from Federal Emergency Management Agency (1978). All elevations in National Geodetic Vertical 

Datum of 1929, in feet]

Cross section 100-year flood elevation Difference 

(2004 minus 1978) 1978 USGS 2004 1978 USGS 2004

1 I 6,381 6,383 2

2 J 6,386 6,387 1

3 K 6,388 6,389 1

4 L 6,393 6,391 –2

5 M 6,395 6,395 0

6 N 6,398 6,398 0

7 O 6,400 6,400 0

8 P 6,403 6,401 –2

9 Q 6,405 6,402 –3

10 S 6,408 6,407 –1

11 T 6,410 6,414 4

13 V 6,417 6,417 0
Appendix 3. Appendix Tables 3–1—3–14 93

Table 3–14. Pre- and post-burn model parameters for South Platte River subbasins upstream and downstream from Cheesman Reservoir used in the objective calibration method.[ID, identification number; BAER, Burned Area Emergency Rehabilitation; mi2, square miles; RCN, runoff curve number; IA, initial abstraction; LT, lag time; *, Tarryall basin 5C is regulated]

Model 

basin ID

Corresponding 

BAER Basin(s)

Name of basin 

or drainage

Drainage 

area 

(mi2)

Percentage of 

medium-high 

burned area

Preburn 

RCN 

Preburn 

IA

Preburn 

LT

Postburn 

RCN

Postburn 

IA

Postburn 

LT

Recovered 

RCN

Recovered 

IA

Recovered 

LT

South Platte River subbasins upstream from Cheesman Dam

0.1 84 Unnamed 0.60 19.6 55.7 1.59 110.84 82.4 0.43 53.17 65.2 1.07 87.09PA 80, 77, 75 South Platte Reach A 3.87 4.5 64.3 1.11 627.79 84.2 0.38 353 71.5 0.80 518.8UBB1 - Unburned basin 1ac 19.82 0 60.3 1.32 529.45 60.3 1.32 529.45 –999 –2.20 –999UBB2 - Unburned basin 2ac 8.70 0 59.7 1.35 406.38 59.7 1.35 406.38 –999 –2.20 –9991 78 Vermillion Creek 4.93 27.6 56.6 1.53 211.62 86.4 0.31 90.59 67.7 0.95 159.3UBB3 - Unburned basin 3ac 1.20 0 54 1.70 57.71 54.0 1.70 57.71 –999 –2.20 –9992 76 Crystal Creek 5.27 29.1 56.5 1.54 212.3 86.3 0.32 91.02 67.5 0.96 160.26UBB4 - Unburned basin 4ac 0.32 0 56.7 1.53 40.45 56.7 1.53 40.45 –999 –2.20 –999PB 891 South Platte Reach B 11.31 38.6 62.2 1.22 592.93 89.4 0.24 260.99 72.6 0.75 450.233 74 Beaver Creek 3.54 33.7 56.3 1.55 188.49 88.5 0.26 73.97 68.6 0.92 137.534 65 Hackett Gulch 6.56 33.2 54.9 1.64 153.55 86.0 0.33 63.72 66.4 1.01 114.545A 58 Tarryall Creek 8.42 34 57.8 1.46 299.64 86.5 0.31 131.56 68.4 0.92 227.995B 58, 72 Tarryall Creek 3.11 34 55.5 1.60 148.16 86.3 0.32 61.88 66.9 0.99 110.855C - Tarryall upstream 431.056 63 Longwater Gulch 2.34 67.6 53.4 1.75 140.8 94.4 0.12 39.62 70 0.86 91.957 53 Corral Creek 4.38 70.3 54 1.70 101.2 93.5 0.14 30.16 69.8 0.87 67.347.1 57 Motberry Gulch 1.60 80.1 54.8 1.65 90.7 96.2 0.08 24.04 71.8 0.79 58.37.2 47 Wildcat Creek 1.98 80.7 55.3 1.62 119.99 96.2 0.08 32.21 72.1 0.77 77.488 51 Northrup Gulch 3.84 58.2 56.1 1.57 182.75 93.2 0.15 58.5 70.9 0.82 124.68.1 44 Unnamed drainage A 1.03 78 55.1 1.63 81.87 96.0 0.08 22.21 71.9 0.78 52.988.2 45 Unnamed drainage B 0.72 81.7 54.7 1.66 50.05 96.4 0.07 13.16 71.8 0.79 32.12PC 892 South Platte Reach C 6.49 61.4 59.4 1.37 367.24 92.1 0.17 133.88 72.3 0.77 261.69A 37 Turkey Creek 0.61 98.7 55 1.64 71.58 98.1 0.04 17.12 73 0.74 44.749B 92 Turkey Creek 1.99 94.9 55.6 1.60 129.6 97.8 0.05 32.19 73.1 0.74 82.079C 46 Turkey Creek 8.09 44.4 57.6 1.47 286.48 89.2 0.24 113.15 69.7 0.87 209.729D 37 Turkey Creek 0.99 98.7 55.2 1.62 90.37 98.1 0.04 21.75 73.1 0.74 56.679E 40 Turkey Creek 0.97 100 55.5 1.60 95.04 98.3 0.03 22.86 73.4 0.72 59.629F 43 Turkey Creek 1.57 90.9 55 1.64 98.38 97.3 0.06 24.7 72.6 0.75 62.299G 91 Turkey Creek 6.44 37.3 59.7 1.35 385.56 88.3 0.27 165.81 70.6 0.83 290.339H 90 Turkey Creek 2.16 20.2 55.2 1.62 118.51 85.8 0.33 49.95 66.5 1.01 88.829I 54 Turkey Creek 0.27 23.5 56.7 1.53 67.09 87.3 0.29 27.77 68.2 0.93 49.95
94 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires 9J 59 Turkey Creek 0.40 3.7 56.1 1.57 62.32 76.6 0.61 36.18 62.8 1.18 52.62 9K 62 Turkey Creek 0.48 6.8 55.6 1.60 65.9 81.6 0.45 32.4 64.7 1.09 52.24 9L 67 Turkey Creek 0.88 42.1 55.9 1.58 116.97 89.7 0.23 43.25 68.9 0.90 83.67 9M 73 Turkey Creek 2.97 44.7 56.3 1.55 174.29 88.6 0.26 68.07 68.6 0.92 127.11 9N 46 (partial) Turkey Creek 0.37 44.4 55.6 1.60 52.96 89.0 0.25 20.04 68.4 0.92 38.16 9.1 33 Unnamed drainage C 0.87 95.6 54.7 1.66 72.58 97.8 0.05 17.58 72.6 0.75 45.54 9.2 34 Sand Draw 0.67 96.3 55.1 1.63 71.41 97.9 0.04 17.32 72.9 0.74 44.88 9.3 31 Unnamed drainage D 0.75 93 55.4 1.61 89.24 97.6 0.05 22.29 72.9 0.74 56.54 10A 26 Goose Creek 2.13 89.6 56.6 1.53 174.67 97.2 0.06 46 73.4 0.72 112.48 10B 26 Goose Creek 4.67 89.6 57 1.51 227.01 97.2 0.06 60.39 73.6 0.72 146.84 10C 25 Goose Creek 2.82 60 55 1.64 125.63 93.0 0.15 39.49 70.1 0.85 85.21 10D 87 Goose Creek 7.38 63.4 56.6 1.53 229.22 93.1 0.15 74.41 71.1 0.81 157.2 10E 30 Goose Creek 1.88 54.9 54.7 1.66 98.27 91.6 0.18 32.66 69.2 0.89 67.72 10F 39 Goose Creek 6.27 8.7 55 1.64 156.84 67.8 0.95 113.16 58.7 1.41 143.05 10G 32 Goose Creek 3.55 8.6 54.6 1.66 117.02 68.2 0.93 82.59 58.5 1.42 106.03 10H - Goose Creek 7.64 0 56.4 1.55 224.83 56.4 1.55 224.83 –999 -2.20 -999 10I - Goose Creek 4.69 0 55.1 1.63 147.39 55.1 1.63 147.39 –999 -2.20 -999 10J - Goose Creek 5.48 0 55.1 1.63 151.85 55.1 1.63 151.85 –999 -2.20 -999

10K - Goose Creek 10.95 0 55.1 1.63 184.17 55.1 1.63 184.17 –999 -2.20 -99910L - Goose Creek 12.16 0 58.4 1.42 355.84 58.4 1.42 355.84 –999 -2.20 -99910M - Goose Creek 13.86 0 58.5 1.42 372.64 58.5 1.42 372.64 –999 -2.20 -99910N - Goose Creek 11.70 0 58.9 1.40 383.27 58.9 1.40 383.27 –999 -2.20 -999

South Platte River subbasins downstream Cheesman Dam

11 28 Schoonover 1.71 85.4 55 1.64 100.72 96.5 0.07 26.5 72 0.78 64.7212A 3 Sixmile and Wigwam 18.18 27.8 58.6 1.41 402 80.5 0.48 220.45 66.2 1.02 331.0112B 2 Sixmile and Wigwam 5.22 42.5 56.2 1.56 194.2 85.2 0.35 85.58 66.8 0.99 147.9412C 6 Sixmile and Wigwam 3.43 51.9 56 1.57 169.98 87.9 0.28 67.59 68.1 0.94 124.6512D 5 Sixmile and Wigwam 7.78 24.4 56.4 1.55 224.89 77.7 0.57 127.16 63.5 1.15 187.8412E 19 Sixmile and Wigwam 0.88 76.2 54.9 1.64 69.08 95.8 0.09 18.81 71.7 0.79 44.7312F 22 Sixmile and Wigwam 1.19 78.7 54.4 1.68 64.1 95.3 0.10 17.75 71 0.82 41.7813 21 Fourmile Creek 8.22 59.7 58.4 1.42 331.39 90.5 0.21 126.58 70.8 0.82 240.114A 11 Horse Creek 3.58 20.7 59.9 1.34 356 81.4 0.46 196.45 67.4 0.97 293.39

Table 3–14. Pre- and post-burn model parameters for South Platte River subbasins upstream and downstream from Cheesman Reservoir used in the objective calibration method.—Continued[ID, identification number; BAER, Burned Area Emergency Rehabilitation; mi2, square miles; RCN, runoff curve number; IA, initial abstraction; LT, lag time; *, Tarryall basin 5C is regulated]

Model 

basin ID

Corresponding 

BAER Basin(s)

Name of basin 

or drainage

Drainage 

area 

(mi2

)

Percentage of 

medium-high 

burned area

Preburn 

RCN 

Preburn 

IA

Preburn 

LT

Postburn 

RCN

Postburn 

IA

Postburn 

LT

Recovered 

RCN

Recovered 

IA

Recovered 

LT

South Platte River subbasins upstream from Cheesman Dam—Continued
Appendix 3. Appendix Tables 3–1—3–14 95

14B 23 Horse Creek 1.36 75.3 54.6 1.66 78.91 94.9 0.11 22.31 71 0.82 51.6814C 24 Horse Creek 0.64 100 54.9 1.64 68.69 98.3 0.03 16.26 73 0.74 42.8814D 20 Horse Creek 0.63 45.8 55.2 1.62 59.73 91.4 0.19 20.28 69.4 0.88 41.514E 11, 50, 52, 55, 

61,68,70

Horse Creek 18.80 36.1 63.2 1.16 696.8 86.1 0.32 356.52 71.7 0.79 556.53

14F 27 Horse Creek 2.05 54.3 52.4 1.82 117.44 88.4 0.26 41.85 66 1.03 83.0514G 29 Horse Creek 0.55 29.9 55.4 1.61 58.37 86.2 0.32 24.43 66.8 0.99 43.6214H 36 Horse Creek 0.76 30.5 54.8 1.65 61.67 84.3 0.37 27.14 65.4 1.06 47.0414I 38 Horse Creek 1.16 44.1 54.6 1.66 73.56 90.6 0.21 25.35 68.6 0.92 51.3814J 42 Horse Creek 1.89 30.3 56.5 1.54 162.34 87.2 0.29 67.12 68 0.94 120.7814K 49 Horse Creek 15.54 41 60.7 1.29 531.8 88.2 0.27 234.98 71.1 0.81 404.4614L 56 Horse Creek 1.19 41.4 54.9 1.64 89.81 90.7 0.21 31.08 68.9 0.90 62.7414M 60 Horse Creek 0.40 59.5 55.7 1.59 52.04 92.6 0.16 16.91 70.3 0.85 35.6514N 64 Horse Creek 0.65 87.2 55.1 1.63 54.28 97.0 0.06 13.92 72.4 0.76 34.6214O 66 Horse Creek 0.49 59.8 55 1.64 58.86 89.4 0.24 21.54 68.2 0.93 41.9314P 71 Horse Creek 0.58 22.7 56.7 1.53 131 84.4 0.37 60.34 66.7 1.00 101.4514Q none Horse Creek 12.29 3 59.3 1.37 414.37 62.2 1.22 385.3 60 1.33 407.2914R none Horse Creek 12.75 0 59.1 1.38 401.4 59.1 1.38 401.4 –999 –2.20 –99914S 85 Horse Creek 17.42 4.8 57.6 1.47 333.76 64.6 1.10 279.07 59.5 1.36 318.1914T 85 Horse Creek 8.85 4.8 57.9 1.45 306.87 64.8 1.09 257.28 59.7 1.35 292.9214U 85 Horse Creek 7.39 4.8 56.6 1.53 234.13 64.0 1.13 194.17 58.6 1.41 222.7714V 35 Horse Creek 2.71 59.2 55.9 1.58 161.2 93.5 0.14 50.49 71 0.82 109.1414W 85 Horse Creek 7.20 4.8 57 1.51 248.77 64.2 1.12 207.23 58.9 1.40 237.1814X 88 Horse Creek 15.99 3.2 56.6 1.53 272.27 61.2 1.27 242.29 57.7 1.47 264.7514Y 88 Horse Creek 12.78 3.2 56.9 1.52 275.46 61.4 1.26 245.67 58 1.45 267.8514Z 88 Horse Creek 15.54 3.2 58 1.45 348.88 62.2 1.22 313.28 59 1.39 34014AA none Horse Creek 1.83 3.2 55 1.64 102.38 58.3 1.43 94.07 55.7 1.59 100.4914BB none Horse Creek 9.45 3.2 60.7 1.29 485.37 63.5 1.15 452.08 61.4 1.26 476.5514CC none Horse Creek 6.43 3.2 57.8 1.46 279.44 61.0 1.28 257.16 58.6 1.41 273.514DD none Horse Creek 9.00 3.2 57.1 1.50 267.98 60.5 1.31 245.89 58 1.45 262.1614EE none Horse Creek 13.32 3.2 58.5 1.42 368.07 61.7 1.24 339.71 59.3 1.37 360.7914FF none Horse Creek 8.88 3.2 59.5 1.36 403.1 62.5 1.20 373.46 60.3 1.32 395.3

Table 3–14. Pre- and post-burn model parameters for South Platte River subbasins upstream and downstream from Cheesman Reservoir used in the objective calibration method.—Continued[ID, identification number; BAER, Burned Area Emergency Rehabilitation; mi2, square miles; RCN, runoff curve number; IA, initial abstraction; LT, lag time; *, Tarryall basin 5C is regulated]

Model 

basin ID

Corresponding 

BAER Basin(s)

Name of basin 

or drainage

Drainage 

area 

(mi2)

Percentage of 

medium-high 

burned area

Preburn 

RCN 

Preburn 

IA

Preburn 

LT

Postburn 

RCN

Postburn 

IA

Postburn 

LT

Recovered 

RCN

Recovered 

IA

Recovered 

LT

South Platte River subbasins downstream Cheesman Dam—Continued
96 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires 15 8 Lazy Gulch 1.23 39.1 54.9 1.64 84.19 90.4 0.21 29.51 68.6 0.92 59.18 16 7 Brush Creek 2.33 59.3 55.5 1.60 133.72 92.5 0.16 43.58 70.2 0.85 91.62 17 9 Unnamed drainage 1.16 0 55.3 1.62 94.16 55.3 1.62 94.16 –999 –2.20 –999 UB1 none Unburned drainage 1bc 1.75 0 55.3 1.62 115.81 55.3 1.62 115.81 -999 -2.20 -999 18 4 Saloon Gulch 1.26 46.6 55.2 1.62 96.94 90.5 0.21 34.15 68.9 0.90 68.21 UB2 none Unburned drainage 2bc 1.07 0 54.9 1.64 84.32 54.9 1.64 84.32 -999 -2.20 -999 19A 1 Gunbarrel and Kelsey 0.69 2 56 1.57 102.69 61.8 1.24 88.51 57.4 1.48 99.08 19B 1 Gunbarrel and Kelsey 4.72 2 55.4 1.61 157.11 62.0 1.23 132.87 57 1.51 150.79 19C 1 Gunbarrel and Kelsey 4.79 2 55.5 1.60 165.64 62.1 1.22 140.15 57.2 1.50 158.82 UB3 none Unburned drainage 3bc 13.12 0 56.3 1.55 245.71 56.3 1.55 245.71 -999 -2.20 -999

M1 893 South Platte Reach 1 3.26 5.8 55.3 1.62 141.79 69.9 0.86 97.22 59.6 1.36 127.18M2 893 South Platte Reach 2 2.57 5.8 61.1 1.27 393.83 72.1 0.77 294.51 64.5 1.10 360.94M3 93, 893 South Platte Reach 3 2.98 9.1 60.7 1.29 380.89 76.1 0.63 251.64 65.7 1.04 334.7M4 93 South Platte Reach 4 4.19 12.33 61.1 1.27 433.57 79.6 0.51 261.27 67.4 0.97 368.66

Explanation of ParametersPre-burn RCN = RCN determined from composite and individual BAER team basins (base RCN for natural forest min. 55)Default IA = Initial Abstraction value determined by SCS method, IA = 0.2 × [(1,000/RCN) – 10].

Table 3–14. Pre- and post-burn model parameters for South Platte River subbasins upstream and downstream from Cheesman Reservoir used in the objective calibration method.—Continued[ID, identification number; BAER, Burned Area Emergency Rehabilitation; mi2, square miles; RCN, runoff curve number; IA, initial abstraction; LT, lag time; *, Tarryall basin 5C is regulated]

Model 

basin ID

Corresponding 

BAER Basin(s)

Name of basin 

or drainage

Drainage 

area 

(mi2

)

Percentage of 

medium-high 

burned area

Preburn 

RCN 

Preburn 

IA

Preburn 

LT

Postburn 

RCN

Postburn 

IA

Postburn 

LT

Recovered 

RCN

Recovered 

IA

Recovered 

LT

South Platte River subbasins downstream Cheesman Dam—Continued
Appendix 4. Appendix Tables 4–1—4–2 97

Appendix 4. Appendix Tables 4–1—4–2

Table 4–1. Global Positioning System positions for South Platte River cross sections used in post-fire hazard analysis.

[All elevations are referenced to top of aluminum cap unless noted (GRD) or (HUB); UTM, Universal Transverse Mercator; NAD 83, North American Datum 

of 1983; NAVD 88, North American Vertical Datum of 1988; ft, feet; HUB, survey instrument hub; GRD, ground surface; LB, left bank; RB, right bank; 

Gage Sta., gaging station]

Cross-section 

identification

UTM Zone 13, NAD 83 NAVD 88 elevation 

(geoid 99) 

(ft)

Remarks X coordinate 

Easting 

(ft)

Y coordinate 

Northing 

(ft)

DXS1(HUB) 477,986.253 4,343,306.038 6,500.44

DXS1LB(GRD) 477,938.505 4,343,297.499 6,525.46

DXS1RB(GRD) 478,068.958 4,343,322.911 6,497.37 Rebar 0.46 ft below hub

DXS2(HUB) 478,904.807 4,343,681.383 6,467.87

DXS2LB 478,887.125 4,343,704.940 6,489.76

DXS2RB(GRD) 478,969.329 4,343,606.025 6,480.57

DXS3(HUB) 479,614.577 4,344,700.990 6,423.47

DXS3LB 479,592.348 4,344,753.101 6,460.18

DXS3RB(GRD) 479,636.612 4,344,645.984 6,442.45

DXS4(HUB) 479,913.762 4,345,022.802 6,408.72

DXS4LB 479,948.497 4,345,060.743 6,425.05

DXS4RB 479,902.202 4,345,008.717 6,452.85

DXS4.5(HUB) 480,857.763 4,345,702.909 6,387.97

DXS4.5LB 480,864.862 4,345,728.710 6,409.11

DXS4.5RB 480,843.438 4,345,650.779 6,393.04

DXS5(HUB) 481,261.899 4,346,922.073 6,356.11

DXS5LB 481,171.726 4,347,015.987 6,369.85

DXS5RB 481,305.291 4,346,874.061 6,355.49

DXS6(HUB) 481,791.463 4,348,552.495 6,351.87

DXS6LB 481,676.268 4,348,610.702 6,346.67

DXS6RB 481,932.866 4,348,484.984 6,395.21

DXS7(HUB) 483,225.050 4,351,387.126 6,298.38

DXS7LB 483,194.958 4,351,499.095 6,312.19

DXS7RB 483,233.308 4,351,356.234 6,335.35

DXS8(HUB) 484,023.989 4,352,730.141 6,292.42

DXS8LB 483,818.698 4,352,792.488 6,305.49 Stake not found by GPS crew

DXS8RB 484,040.175 4,352,723.982 6,325.01

DXS8.5(HUB) 484,215.700 4,353,651.673 6,266.91

DXS8.5LB 484,171.349 4,353,594.817 6,284.64

DXS8.5RB 484,233.498 4,353,674.483 6,282.33

DXS9(HUB) 484,960.253 4,355,721.889 6,222.85

DXS9LB 484,908.928 4,355,792.820 6,271.67

DXS9RB 484,973.458 4,355,704.064 6,243.28

DXS10(HUB) 485,623.612 4,357,974.849 6,199.08

DXS10LB 485,547.168 4,358,007.244 6,200.66

DXS10RB 485,658.706 4,357,959.868 6,200.75

DXS11(HUB) 485,305.729 4,359,798.809 6,162.35

DXS11LB 485,253.226 4,359,820.942 6,165.95

DXS11RB 485,330.878 4,359,787.873 6,202.19
98 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

DXS12(HUB) 485,629.890 4,361,033.568 6,121.39

DXS12LB 485,572.890 4,361,022.287 6,132.44

DXS12RB 485,643.198 4,361,034.919 6,154.65

DXS13(HUB) 485,521.902 4,362,167.728 6,091.85

DXS13LB 485,526.388 4,362,181.144 6,100.79

DXS13RB 485,508.874 4,362,128.641 6,093.91

WXS2(HUB) 489,379.537 4,366,297.346 5,725.99

WXS2LB 489,328.471 4,366,306.639 5,745.33

WXS2RB 489,389.599 4,366,294.449 5,747.95

WXS3(HUB) 489,371.572 4,367,199.807 5,691.57

WXS3LB 489,324.709 4,367,196.454 5,690.53

WXS3RB 489,401.623 4,367,201.744 5,721.33

UXS1 471,751.252 4,330,513.623 7,131.68

UXS1LB 471,629.409 4,330,498.789 7,135.40

UXS1RB 471,813.445 4,330,521.141 7,144.99

UXS2 472,771.431 4,333,173.589 6,962.48

UXS2LB(HUB) 472,707.509 4,333,162.777 6,987.28 Stake not visited by GPS crew

UXS2RB 472,809.171 4,333,180.226 6,995.32

BM6854(Gage Sta.) 473,201.828 4,334,857.208 6,857.12 Control Station for CDXS3

UXS3RB 473,235.792 4,334,798.047 6,872.54

UXS3LB 473,149.827 4,334,839.811 6,873.94

BM5671 489,072.657 4,367,617.932 5,679.74 Control Station for WDXS2 & WDXS3

Table 4–1. Global Positioning System positions for South Platte River cross sections used in post-fire hazard analysis.—Continued

[All elevations are referenced to top of aluminum cap unless noted (GRD) or (HUB); UTM, Universal Transverse Mercator; NAD 83, North American Datum 

of 1983; NAVD 88, North American Vertical Datum of 1988; ft, feet; HUB, survey instrument hub; GRD, ground surface; LB, left bank; RB, right bank; 

Gage Sta., gaging station]

Cross-section 

identification

UTM Zone 13, NAD 83 NAVD 88 elevation 

(geoid 99) 

(ft)

Remarks X coordinate 

Easting 

(ft)

Y coordinate 

Northing 

(ft)
Appendix 4. Appendix Tables 4–1—4–2 99

Table 4–2. Global Positioning System positions for South Platte River cross sections used in detailed hydraulic analysis 

of recovered conditions.

[All elevations are referenced to ground surface; UTM, Universal Transverse Mercator; NAD 83, North American Datum of 1983; NAVD 88, 

North American Vertical Datum of 1988; RB, right bank; LB, left bank; na, not aplicable; approximate, endpoint digitized from Flood Insurance Rate Map (FEMA, 1978)]

Cross-section 

identification

UTM Zone 13 NAD 83 NAVD 88 elevation 

(geoid 99) 

(ft)

Remarks X coordinate 

Easting 

(ft)

Y coordinate 

Northing 

(ft)

A RB 481,171.726 4,347,015.987 6,369.85

A LB 481,305.291 4,346,874.061 6,355.49

B LB 481,189.538 4,346,127.056 6,379.89

B RB 481,331.957 4,346,198.265 6,364.09

C LB 481,262.507 4,346,098.412 6,366.91

C RB 481,345.438 4,346,142.197 6,363.65

D LB 481,279.612 4,346,076.716 6,368.82

D RB 481,352.775 4,346,137.894 6,365.50

E LB 481,331.203 4,345,959.541 6,368.47

E RB 481,461.236 4,346,006.082 6,372.06

F LB 481,340.532 4,345,871.064 6,376.14

F RB 481,478.276 4,345,955.294 6,379.38

G LB 481,322.815 4,345,821.092 6,375.17

G RB 481,428.218 4,345,697.490 6,377.03

H LB 480,864.862 4,345,728.710 6,409.11

H RB 480,843.438 4,345,650.779 6,393.04

I LB approximate 480,707.233 4,345,388.538 6,407.00

I RB approximate 480,739.036 4,345,386.435 6,407.20

J LB 480,699.912 4,344,993.783 6,393.07

J RB 480,685.186 4,344,906.660 6,402.90

K LB 480,654.322 4,344,981.835 6,386.56

K RB 480,616.345 4,344,934.353 6,398.13

L LB approximate 480,433.785 4,345,266.777 6,411.10

L RB approximate 480,449.264 4,345,246.140 6,411.10

M LB approximate 480,377.032 4,345,222.406 6,420.50

M RB approximate 480,395.606 4,345,204.864 6,420.50

N LB 480,322.515 4,344,930.170 6,415.51

N RB 480,398.919 4,344,900.507 6,398.37

O LB approximate na na interpolated section

O RB approximate na na

P LB 480,324.584 4,344,853.437 6,400.93

P RB 480,331.913 4,344,810.617 6,413.36
100 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Q LB approximate 480,131.445 4,344,966.500 6,429.10

Q RB approximate 480,131.445 4,344,946.895 6,430.00

R LB 479,948.497 4,345,060.743 6,425.05

R RB 479,902.202 4,345,008.717 6,452.85

S LB approximate 479,905.465 4,345,072.783 6,431.10

S RB approximate 479,892.050 4,345,057.306 6,431.80

T approximate 479,746.555 4,345,129.538 6,441.40

T approximate 479,772.352 4,345,103.740 6,430.90

U LB 479,592.348 4,344,753.101 6,460.18

U RB 479,636.612 4,344,645.984 6,442.45

V LB approximate 479,473.108 4,344,606.375 6,444.00

V RB approximate 479,493.745 4,344,601.216 6,447.60

Table 4–2. Global Positioning System positions for South Platte River cross sections used in detailed hydraulic analysis 

of recovered conditions.—Continued

[All elevations are referenced to ground surface; UTM, Universal Transverse Mercator; NAD 83, North American Datum of 1983; NAVD 88, 

North American Vertical Datum of 1988; RB, right bank; LB, left bank; na, not aplicable; approximate, endpoint digitized from Flood Insurance Rate Map (FEMA, 1978)]

Cross-section 

identification

UTM Zone 13 NAD 83 NAVD 88 elevation 

(geoid 99) 

(ft)

Remarks X coordinate 

Easting 

(ft)

Y coordinate 

Northing 

(ft)
Appendix 5. Appendix Tables 5–1—5–4 101

Appendix 5. Appendix Tables 5–1—5–4

Table 5–1. Mitchell Creek subbasin characteristics and pre-burn model parameters.

[mi2, square miles; in, inches; ft, feet; ft/ft, foot per foot; min, minutes; hrs, hours; SCS, Soil Conservation Service]

Subbasin 

number

Subbasin 

name

Drainage 

area 

(mi2)

Pre-burn 

runoff curve 

number

Initial 

abstraction 

(in)

Subbasin 

length, L 

(ft)

Drainagebasin slope 

(ft/ft)

Storage

SCS 

lag time 

(min)

SCS 

lag time 

(hrs)

23 Storm King 1 0.201 72.5 0.759 6,708 0.535 3.80 14.9 0.248

24 Storm King 2 0.055 73.7 0.713 2,933 0.563 3.56 7.23 0.121

25 Mitchell E1 0.290 72.2 0.770 7,600 0.398 3.85 19.2 0.321

26 Mitchell E2 0.013 79.2 0.525 2,579 0.357 2.63 6.98 0.116

27 Mitchell E3 0.051 79.9 0.503 5,025 0.340 2.52 11.9 0.199

28 Mitchell E4 0.045 77.9 0.568 3,223 0.462 2.84 7.63 0.127

29 Mitchell W4-S 0.010 78.5 0.547 1,819 0.714 2.73 3.81 0.064

30 Mitchell W3 0.117 74.0 0.703 3,750 0.764 3.52 7.51 0.125

31 Mitchell W2 0.133 73.4 0.727 3,711 0.703 3.63 7.90 0.132

32 Mitchell W1 0.147 73.8 0.711 4,570 0.652 3.56 9.57 0.160

33 Mitchell W4-N 0.031 77.5 0.580 2,768 0.648 2.90 5.77 0.096

36 Upper Mitchell West 2.372 70.0 0.856 18,670 0.364 4.28 43.8 0.731

37 Upper Mitchell East 2.747 70.4 0.842 19,951 0.312 4.21 49.5 0.824

38 Fish hatchery 0.575 67.4 0.969 9,630 0.704 4.85 19.9 0.332

39 Donegan Bridge 4.418 69.5 0.879 29,604 0.412 4.39 60.4 1.007

Table 5–2. Mitchell Creek subbasin characteristics and post-burn model parameters.

[mi2, square miles; in, inches; ft, feet; ft/ft, foot per foot; min, minutes; hrs, hours; SCS, Soil Conservation Service]

Subbasin 

number 

Subbasin 

name 

Drainage 

area 

(mi2)

Post-burn 

runoff curve 

number

Initial 

abstraction 

(in)

Subbasin 

length, L 

(ft)

Drainagebasin slope 

(ft/ft)

Storage

SCS 

lag time 

(min)

SCS 

lag time 

(hrs)

23 Storm King 1 0.201 94.7 0.111 6,708 0.535 0.557 6.78 0.113

24 Storm King 2 0.055 90.5 0.210 2,933 0.563 1.05 4.13 0.069

25 Mitchell E1 0.290 90.7 0.206 7,600 0.398 1.03 10.5 0.174

26 Mitchell E2 0.013 95.1 0.103 2,579 0.357 0.515 3.79 0.063

27 Mitchell E3 0.051 97.7 0.046 5,025 0.340 0.231 5.73 0.095

28 Mitchell E4 0.045 97.0 0.062 3,223 0.462 0.309 3.59 0.060

29 Mitchell W4-S 0.010 97.2 0.057 1,819 0.714 0.284 1.81 0.030

30 Mitchell W3 0.117 95.7 0.089 3,750 0.764 0.446 3.38 0.056

31 Mitchell W2 0.133 95.2 0.102 3,711 0.703 0.510 3.60 0.060

32 Mitchell W1 0.147 89.0 0.247 4,570 0.652 1.24 5.82 0.097

33 Mitchell W4-N 0.031 96.8 0.066 2,768 0.648 0.331 2.72 0.045

36 Upper Mitchell West 2.372 75.2 0.660 18,670 0.364 3.30 38.0 0.633

37 Upper Mitchell East 2.747 77.3 0.589 19,951 0.312 2.94 40.7 0.678

38 Fish hatchery 0.575 92.6 0.161 9,630 0.704 0.803 8.75 0.146

39 Donegan Bridge 4.418 74.4 0.688 29,604 0.412 3.44 52.7 0.879
102 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

Table 5–3. Results of rainfall-runoff modeling using recurrence intervals for the 1-hour storm in the Coal Seam burned area.

[mi2, square miles; ft3/s, cubic feet per second; SCS, Soil Conservation Service; CB, composite basin of several upstream subbasins]

Model 

basin 

number

HEC-HMS model 

basin identification

Drainage 

area 

(mi2)

Flow peak from 1-hour storm recurrence interval Recovery SCS method watershed 

parameters

10-year 

storm 

peak flow 

(ft3/s)

50-year 

storm 

peak flow 

(ft3/s)

100-year 

storm 

peak flow 

(ft3/s)

500-year 

storm 

peak flow 

(ft3/s)

Runoff 

curve 

number

Initial 

abstraction 

(inches)

SCS 

lag time 

(minutes)

23 CS23 Storm King 1 0.20 91 177 266 365 84.6 0.4 10

24 CS24 Storm King 2 0.06 24 51 89 115 82.6 0.4 6

25 CS25 Mitch E1 0.29 85 173 280 372 82.1 0.4 14

26 CS26 Mitch E2 0.01 12 22 34 43 87.9 0.3 5

27 CS27 Mitch E3 0.05 46 78 109 143 89.8 0.2 8

28 CS28 Mitch E4 0.05 44 80 110 153 88.5 0.3 5

29 CS29 Mitch W4-S 0.01 14 24 37 45 88.9 0.3 3

30 CS30 Mitch W3 0.12 83 162 258 334 85.9 0.3 5

31 CS31 Mitch W2 0.13 90 178 257 372 85.4 0.3 5

32 CS32 Mitch W1 0.15 51 110 194 248 81.8 0.5 8

33 CS33 Mitch W4-N 0.03 33 60 91 115 88.2 0.3 4

36 CS36 Upper Mitchell West 2.37 122 337 701 897 72.4 0.8 41

37 CS37 Upper Mitchell East 2.75 160 413 824 1,052 73.7 0.7 45

38 CS38 Fish Hatchery 0.58 154 323 516 718 81.0 0.5 13

CB Fish Hatchery 6.23 355 746 1,517 1,937 -- -- --

39 CS39 Donegan Bridge 4.42 150 440 967 1,208 71.8 0.8 57

CB Donegan Bridge 11.21 490 1,161 2,447 3,078 -- -- --
Appendix 5. Appendix Tables 5–1—5–4 103

Table 5–4. Mitchell Creek rainfall distribution.

[in., inch]

Minutes 

from 

beginning 

of storm

Percentage 

of total 

rainfall 

Cumulative rainfall amount each minute of storm distribution

10-year, 

1-hour storm 

(1.35 in. total)

50-year, 

1-hour storm 

(1.80 in. total)

100-year, 

1-hour storm 

(2.40 in. total)

500-year, 

1-hour storm 

(2.60 in. total)

0001 0.000 0.000 0.000 0.000 0.000

0002 0.008 0.011 0.014 0.019 0.021

0003 0.016 0.022 0.029 0.039 0.042

0004 0.025 0.033 0.044 0.059 0.064

0005 0.033 0.045 0.060 0.080 0.087

0006 0.043 0.057 0.077 0.102 0.111

0007 0.052 0.071 0.094 0.126 0.136

0008 0.063 0.085 0.113 0.151 0.164

0009 0.074 0.100 0.134 0.178 0.193

0010 0.086 0.117 0.155 0.207 0.224

0011 0.099 0.134 0.178 0.238 0.257

0012 0.112 0.152 0.202 0.270 0.292

0013 0.127 0.171 0.228 0.304 0.329

0014 0.142 0.192 0.256 0.341 0.369

0015 0.160 0.215 0.287 0.383 0.415

0016 0.180 0.243 0.324 0.432 0.468

0017 0.205 0.277 0.369 0.492 0.533

0018 0.255 0.344 0.459 0.612 0.663

0019 0.345 0.466 0.621 0.828 0.897

0020 0.437 0.590 0.787 1.049 1.136

0021 0.530 0.716 0.954 1.272 1.378

0022 0.603 0.814 1.085 1.447 1.568

0023 0.633 0.855 1.139 1.519 1.646

0024 0.660 0.891 1.188 1.584 1.716

0025 0.684 0.923 1.231 1.642 1.778

0026 0.705 0.952 1.269 1.692 1.833

0027 0.724 0.977 1.303 1.738 1.882

0028 0.742 1.002 1.336 1.781 1.929

0029 0.759 1.025 1.366 1.822 1.973

0030 0.775 1.046 1.395 1.860 2.015

0031 0.790 1.067 1.422 1.896 2.054

0032 0.804 1.086 1.448 1.930 2.091

0033 0.818 1.104 1.472 1.963 2.127

0034 0.831 1.122 1.496 1.995 2.161

0035 0.844 1.139 1.519 2.025 2.194

0036 0.856 1.156 1.541 2.055 2.226

0037 0.868 1.172 1.562 2.083 2.256

0038 0.879 1.187 1.582 2.110 2.285

0039 0.890 1.201 1.602 2.136 2.313

0040 0.900 1.215 1.620 2.160 2.341

0041 0.910 1.229 1.639 2.185 2.367

0042 0.920 1.242 1.656 2.208 2.392

0043 0.930 1.255 1.673 2.231 2.417
104 Analysis and Mapping of Post-Fire Hydrologic Hazards for the 2002 Wildfires

0044 0.939 1.268 1.690 2.254 2.442

0045 0.948 1.280 1.707 2.276 2.466

0046 0.957 1.292 1.723 2.298 2.489

0047 0.966 1.304 1.739 2.319 2.512

0048 0.975 1.316 1.754 2.339 2.534

0049 0.983 1.327 1.770 2.360 2.556

0050 0.992 1.339 1.785 2.380 2.578

0051 1.000 1.350 1.800 2.400 2.600

Table 5–4. Mitchell Creek rainfall distribution.—Continued

[in., inch]

Minutes 

from 

beginning 

of storm

Percentage 

of total 

rainfall 

Cumulative rainfall amount each minute of storm distribution

10-year, 

1-hour storm 

(1.35 in. total)

50-year, 

1-hour storm 

(1.80 in. total)

100-year, 

1-hour storm 

(2.40 in. total)

500-year, 

1-hour storm 

(2.60 in. total)