i

Prepared in cooperation with the National Park Service 

Decision Support System for Evaluation of Gunnison 

River Flow Regimes With Respect To Resources of the 

Black Canyon of the Gunnison National Park 

By Gregor T. Auble, Mark Wondzell, and Colin Talbert 

Open-File Report 2009–1126 

U.S. Department of the Interior 

U.S. Geological Survey 
Warner Point reach of Gunnison River(1994), Jonathan Friedman, USGS
Decision Support System for Evaluation 

of Gunnison River Flow Regimes With 

Respect To Resources of the Black Canyon 

of the Gunnison National Park 

By Gregor T. Auble, Mark Wondzell, and Colin Talbert

Prepared in cooperation with the National Park Service

Open-File Report 2009–1126

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director 

U.S. Geological Survey, Reston, Virginia 2009 

For product and ordering information:

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

Telephone: 1-888-ASK-USGS

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment:

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

Telephone: 1-888-ASK-USGS

Suggested citation:

Auble, G.T., Wondzell, M., and Talbert, C., 2009, Decision support system for evaluation of 

Gunnison River flow regimes with respect to resources of the Black Canyon of the Gunnison 

National Park: U.S. Geological Survey Open-File Report 2009–1126, 24 p.

Any use of trade, product, or firm names 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 material contained within this report.
iii

Contents

Introduction ...................................................................................................................................1

Purpose......................................................................................................................................1

Study Area .................................................................................................................................2

Structure of Decision Support System ..........................................................................................4

Basic Use...................................................................................................................................4

Input ...........................................................................................................................................5

Daily Hydrologic Input .............................................................................................................7

Secondary Input......................................................................................................................7

Execution and Output.................................................................................................................8

Indicator Variables ......................................................................................................................11

Box Elder Clearing ...................................................................................................................11

Plant Communities ...................................................................................................................12

Trout Fry Habitat ......................................................................................................................14

Sediment Mobilization ..............................................................................................................14

National Park Service Water Right...........................................................................................17

Overview ...............................................................................................................................17

Minimum Flow.......................................................................................................................19

May–June Peak Flow............................................................................................................19

Shoulder Flow .......................................................................................................................20

Hydrologic Indicators................................................................................................................22

Annual Minimum Daily Discharge .........................................................................................22

Annual Mean Daily Discharge...............................................................................................22

Annual Maximum Daily Discharge ........................................................................................22

Annual 14-Day Maximum Daily Discharge............................................................................22

Ramp Rate............................................................................................................................22

Flow Constancy.....................................................................................................................22

Coefficient of Variation of Monthly Discharge within Years ...................................................23

References Cited ........................................................................................................................23
iv

Figures

1. Location map.............................................................................................................................3

2. Main Menu screen at top level of navigation ............................................................................5

3. Input Scenario Specification screen where user defines location of input data for 

scenarios6

4. Input Data Summary screen displaying summary characteristics of flow scenarios as 

read into the decision support system...........................................................................................9

5. Display Indicator Output screen for Plant Communities indicator......................................10

6. Display Indicator Output screen for Annual Minimum Daily Discharge indicator..............10

7. Display Indicator Output screen for NPS Water Right: May–June Peak Flow

indicator 11

8. Relation between community distribution and inundation duration from Auble and others 

(1995) .........................................................................................................................................13

9. Rainbow trout fry habitat as a function of discharge................................................................14

10. Brown trout fry habitat as a function of discharge ................................................................. 15

11. Annual percentages of river length mobilized for three reference particle sizes....................16

12. NPS Peak Flow water right as a function of Forecast unregulated April–July 

Blue Mesa inflow.........................................................................................................................20

13. NPS Shoulder Flow water right as a function of Forecast unregulated April–July 

Blue Mesa inflow ........................................................................................................................21
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Conversion Factors

Inch/Pound to SI 

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2) 

acre 0.004047 square kilometer (km2) 

square foot (ft2) 929.0 square centimeter (cm2) 

square foot (ft2) 0.09290 square meter (m2) 

square inch (in2) 6.452 square centimeter (cm2) 

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

cubic foot (ft3) 28.32 cubic decimeter (dm3) 

cubic foot (ft3) 0.02832 cubic meter (m3) 

cubic yard (yd3) 0.7646 cubic meter (m3) 

cubic mile (mi3) 4.168 cubic kilometer (km3) 

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

Flow rate

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

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

Mass

ounce, avoirdupois (oz) 28.35 gram (g) 

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Pressure

pound-force per square inch 

(lbf/in2

) 

6.895 kilopascal (kPa)

pound per square foot (lb/ft2) 0.04788 kilopascal (kPa) 

pound per square inch (lb/in2) 6.895 kilopascal (kPa) 

Density

pound per cubic foot (lb/ft3) 16.02 kilogram per cubic meter 

(kg/m3

) 

pound per cubic foot (lb/ft3) 0.01602 gram per cubic centimeter 

(g/cm3

) 
vi

SI to Inch/Pound 

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square meter (m2) 0.0002471 acre 

square kilometer (km2) 247.1 acre

square centimeter (cm2

) 0.001076 square foot (ft2) 

square meter (m2

) 10.76 square foot (ft2) 

square centimeter (cm2

) 0.1550 square inch (ft2) 

square kilometer (km2

) 0.3861 square mile (mi2) 

Volume

cubic decimeter (dm3) 0.03531 cubic foot (ft3) 

cubic meter (m3) 35.31 cubic foot (ft3) 

cubic meter (m3) 1.308 cubic yard (yd3) 

cubic kilometer (km3) 0.2399 cubic mile (mi3) 

cubic meter (m3

) 0.0008107 acre-foot (acre-ft) 

Flow rate

meter per second (m/s) 3.281 foot per second (ft/s) 

cubic meter per second (m3/s) 35.31 cubic foot per second, cfs (ft3/s)

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound avoirdupois (lb)

Pressure

kilopascal (kPa) 0.1450 pound-force per inch (lbf/in) 

kilopascal (kPa) 20.88 pound per square foot (lb/ft2) 

kilopascal (kPa) 0.1450 pound per square inch (lb/ft2) 

Density

kilogram per cubic meter 

(kg/m3

) 

0.06242 pound per cubic foot (lb/ft3

) 

gram per cubic centimeter 

(g/cm3

) 

62.4220 pound per cubic foot (lb/ft3

) 
1

Decision Support System for Evaluation of 

Gunnison River Flow Regimes With Respect 

To Resources of the Black Canyon of the 

Gunnison National Park

By Gregor T. Auble,

1 Mark Wondzell,2 and Colin Talbert3

Introduction

Purpose

This report describes a decision support system to inform evaluation of streamflow regimes 

of the Gunnison River with respect to resources of Black Canyon of the Gunnison National Park

(BLCA). The increasing use of sophisticated reservoir operations models has cast many watermanagement decisions as choices amongst different operating rules or policies, each of which has 

associated likely sequences of streamflow. The resulting complexity of hydrologic data is 

combined with an increasing emphasis in riverine ecology on natural flow variability and the 

importance of multiple aspects of the flow regime, which drive evaluation of environmental effects 

beyond specification of a single minimum flow or optimum flow for a target organism.

The decision support system described here is intended to help fill the gap between large 

data sets of simulated flow alternatives and judgments about the relative desirability of those 

alternatives with respect to natural resources. The intent of this work is not to evaluate alternatives, 

but rather to provide a tool for informing the evaluation of alternatives. The basic approach is to 

array differences among alternative flow regimes by calculating values of indicator variables 

representing different valued characteristics or processes of the riverine ecosystem.

There are multiple types of uncertainty in the comparison of alternatives. The 

characterization of an alternative as one or more flow sequences may imperfectly represent the flow 

sequences that might be produced by the alternative. The scientific understanding and quantitative 

relations between flow and the physical and biological responses of riverine systems are complex 

and may be imperfectly represented by indicator variables or calculations. Indicator variables may 

incompletely capture the underlying natural resource concerns. There is also room for disagreement 

about the relative importance or weighting of multiple resource concerns. Thus, a decision support 

system requires a balancing between simplifying assumptions—necessary to achieve the benefits of 

reduced complexity—and oversimplification into a highly synthetic result that cannot be 

understood or decomposed into constituent variables and calculations. This decision support system 

addresses the balancing by producing a set of indicators grouped into several areas of natural 

resource concern. The indicators are explicit and replicable calculations that reflect conditions or 

 1 U.S. Geological Survey, Fort Collins, Colorado. 2 National Park Service, Fort Collins, Colorado.

3 ASRC Management Services, Fort Collins, Colorado.
2

processes within each area of concern. Alternatives are compared directly in terms of these 

indicators, each of which can be individually understood and challenged in terms of the 

assumptions involved in the calculations. Different users could make different decisions using this 

system as they might weight the importance of multiple indicators differently or value different 

aspects of the system. Thus, the goal of the decision support system is not to make a decision, but 

rather to reduce the complexity of information and focus attention on tradeoffs involved in the 

decision.

Study Area

Black Canyon of the Gunnison National Park is located along the Gunnison River in 

western Colorado (fig. 1). The Black Canyon of the Gunnison National Monument was established 

“for the preservation of the spectacular gorges and additional features of scenic, scientific, and 

educational interest” on March 2, 1933, by Presidential Proclamation No. 2033 (47 Stat. 2558) 

pursuant to the Antiquities Act of June 8, 1906 (16 U.S.C. 431). Boundary changes occurred in 

1938, 1939, 1958, 1960, 1976, 1984, and 1999. In 1976, a portion of the park was designated as 

wilderness (90 Stat. 2692). In 1999, Black Canyon of the Gunnison National Monument was 

designated Black Canyon of the Gunnison National Park with the addition of nearly 10,000 acres of 

previously held BLM lands, including roughly 4 miles of the Gunnison Gorge and Gunnison River 

(113 Stat. 1126).

The Black Canyon is one of the steepest, narrowest canyons in the country. Elevations 

within the BLCA, which encompasses 12 miles of the 53-mile Black Canyon, exceed 8,000 feet, 

and canyon walls, which in places are only 1,300 feet apart, plunge 2,200 vertical feet to the river 

below. Access through the canyon is extremely difficult and arduous; rock piles, scree slopes, and 

boulders litter the canyon floor and make travel by foot or watercraft nearly impossible. Early 

explorers considered the canyon inaccessible.

Immediately upstream from BLCA are the three Curecanti Unit dams (Blue Mesa, Morrow 

Point, and Crystal, constructed in 1966, 1970, and 1976, respectively), known today as the Aspinall 

Unit. These dams regulate flow through the Black Canyon, effectively attenuating spring peak 

flows and augmenting late summer low flows. Flows are further modified by diversion of water 

through the 6-mile-long Uncompahgre Valley Water Users Association Gunnison Tunnel.

Completed in 1909 and used to irrigate lands in the neighboring Uncompahgre Valley, the 

Gunnison Tunnel carries a 1902 water right priority date and can divert as much as 1,300 cubic feet 

per second (ft3/s). Immediately downstream of BLCA is the Gunnison Gorge National Resource 

Conservation Area, administered by the Bureau of Land Management (BLM). 

Stream discharge is measured immediately below the inlet (East Portal) of the Gunnison 

Tunnel (U.S. Geological Survey gage 0912800), at the upstream boundary of BLCA. Discharge 

records began in 1906; the highest recorded instantaneous peak discharge is 19,000 ft3

/s, which 

occurred on June 15, 1921, and the lowest recorded daily mean flow is 0 ft3

/s, which occurred 

seven times between 1911 and 2000.

Warner and Walker (1972) provide a detailed description of a U.S. Geological Survey 

topographic surveying expedition in the Black Canyon in 1934 that includes photographs 

illustrating the sparse vegetation of the canyon bottom. The geology of the Black Canyon is 

summarized in Hansen (1965), reprinted as Hansen (1987), with additional detail described in 

Hansen (1964) and Hansen and Peterman (1968). The hydrology of the Gunnison River and its 

modification by upstream reservoirs and diversions is summarized by Diaz and others (1996).

Auble and others (1994) conducted plot-based vegetation sampling at the Warner Point 

reach in the Black Canyon and developed both a community classification and relations between 
3

 Figure 1. Location map.
4

hydrology and community distribution. Friedman and Auble (1999), also focusing on the Warner 

Point reach, quantified a model relating annual mortality of box elder to streamflow (shear stress 

and extended inundation).

Several investigators have examined sediment transport in the channel and bottom land of 

the Black Canyon. Chase (1992) estimated streamflow thresholds for gravel and cobble motion.

Elliott and Hammack (1999, 2000) examined entrainment of riparian gravel and cobbles in the 

Warner Point reach and estimated streamflows required to mobilize geomorphic features. Liquori 

(1995) inventoried talus and debris-flow deposits in the BLCA bottom land and described both 

their delivery mechanisms and transport by the Gunnison River. Dubinski (2005) and Dubinski and 

Wohl (2007) estimated a historical sediment budget for the Gunnison River in BLCA and 

developed a model relating streamflow to channel mobilization for different sediment particle sizes 

throughout BLCA.

Nehring and Miller (1987), Nehring (1988), and Nehring and Anderson (1993) reported on

extensive studies of brown and rainbow trout at two sites in the Gunnison Gorge downstream from 

BLCA. This work included quantification of physical habitat simulation models (PHABSIM, 

Bovee and Milhous, 1978; Bovee, 1982) combining hydraulic simulation and empirical suitability 

curves to estimate weighted usable area of suitable habitat for different species and life stages, and 

multiple years of fish census data that suggest fry habitat is most limiting for trout in this part of the 

Gunnison River. The endangered fish (Colorado pikeminnow, razorback sucker, and humpback 

chub) live in the Gunnison and Colorado Rivers downstream from BLCA. Concern about these 

species (McAda, 2003) has motivated a number of studies and analyses of downstream sections of 

the Gunnison River and is a consideration in water-management decisions upstream from BLCA 

that influence Gunnison River streamflow through BLCA (for example, operation of Aspinall Unit

as described in Bureau of Reclamation, 2009).

Structure of Decision Support System

Basic Use

The system is implemented as a Microsoft Office EXCEL workbook, with embedded 

macros, entitled BCG_DSS.xls. It currently runs within either Microsoft Office EXCEL 2003 or 

2007. The workbook, a set of input data files, and supporting descriptions can be downloaded from 

http://www.fort.usgs.gov/Products/Software/. Macros must be enabled when opening 

BCG_DSS.xls, which may require setting a general security level and perhaps enabling macros 

when opening the workbook. Immediately upon opening the workbook, a title window appears that 

is cleared by clicking Ok, which then activates a Main Menu window (fig. 2), which contains a 

Display General Instructions button for the first-time user.

Navigation among worksheets and the execution of the calculations for alternatives are

performed through a user interface of clicking buttons and selecting from drop-down menus. The 

EXCEL toolbars and spreadsheet display structures remain visible and functional. They can be 

used as an alternative means of navigation among worksheets, as well as for EXCEL operations 

such as cut-and-paste, resizing, altering graph symbols, and data entry.

The basic steps to use the decision support system are listed below.

1. Specify inputs of alternative flow regimes to be evaluated (Specify Inputs button).

2. Execute the calculation of indicators associated with these regimes (red Execute button).

3. Examine the input data as it has been read into the decision support system (Display Input 

Data drop-down menu).
5

Figure 2. Screen capture depicting Main Menu at top level of navigation.

4. Display output as graphs (Display Indicator Output drop-down menu) and tables

(Tabular Output button on graph pages).

5. View descriptions of the indicators (Display Indicator Descriptions drop-down menu).

6. View and potentially alter the parameters being used in the calculations (Display 

Parameters drop-down menu).

Some of the navigation among worksheets is contextual in the sense that the navigation 

options depend on the worksheet being displayed—tabular output for an indicator is accessed from 

the sheet displaying the graph of the respective indicator and display of parameters or descriptions 

default to the particular indicator being displayed when accessed from graph or tabular output 

sheets. The Main Menu sheet also contains buttons to Save and Exit. Both of these functions can 

also be performed as direct EXCEL commands.

Input

The Input Scenario Specification worksheet (fig. 3) is where the user defines the input 

data associated with each scenario. Input data are provided as worksheets within EXCEL workbook

files. The user defines the flow alternatives on the Input Scenario Specification worksheet by 

entering a scenario name and the location (full path name of file, worksheet, and columns) for the 

different types of input data. The View Instructions button on this worksheet displays basic 

instructions for input data. Example input data files are provided with the decision support system 

program in an InputDataFiles directory. There are two basic types of input data: daily hydrologic 

data and secondary data for National Park Service (NPS) water-right calculations. Only daily 
6

Figure 3. Screen capture depicting Input Scenario Specification where user defines 

location of input data for scenarios.

hydrologic data are required. However, evaluation of indicators of NPS water rights will be limited 

to the extent that secondary data required for these calculations are not provided.

In our testing of the system, errors in the specification or structure of the input data caused 

by far the most difficulty. We have tried to trap some common errors, but if things are not working,

carefully check the input data specifications and contents of the data files themselves, comparing 

them to the example files provided. In general, input data files should start with data on the second 

line of the file below a first line containing column headings and should contain contiguous blocks 

of data without embedded empty cells or rows. Additional formatting details are provided below 

for the different types of input data.
7

Daily Hydrologic Input

The decision support system was developed to evaluate daily streamflow from a stream 

gage at the upstream boundary of the park (U.S. Geological Survey gage 0912800) and daily output 

(model slot Crystal_to_GunnisonTunnelOutflow) corresponding to this gage from the 

RIVERWARE model being used by the Bureau of Reclamation (Bureau of Reclamation, 2009).

However, daily streamflow values could come from any source, including arbitrary sequences, as 

long as they are specified as daily values in an input data worksheet.

The decision support system is structured to compare as many as eight alternative flow 

regimes, where each alternative is represented by a daily sequence of at least 20 calendar years of

streamflow occurring between 1901 and 2050. The daily flow record must start on a January 1 and 

end on a December 31 and be complete for all the calendar years included; missing values must be 

estimated by the user in the input data file. Daily streamflows are entered in cubic feet per second 

(ft3/s), abbreviated as cfs, formatted in EXCEL general or numeric format. Date values should be 

in EXCEL date or date-time format. Although there is no necessary correspondence between the 

calendar years of a flow alternative and actual historical years, any secondary data provided for 

NPS water-right calculations must appropriately correspond to the daily streamflow data for a 

given alternative. Furthermore, comparisons of specific yearly output across scenarios representing 

alternative water-management operations are potentially confusing if a specific year represents 

very different climatic conditions in the different flow alternatives (for example, 2020 is a Dry year 

in one flow alternative, whereas 2020 is a Wet year in a different flow alternative). This decision 

support system is not structured to directly analyze water-management options in terms of multiple, 

stochastically generated flow sequences.

Secondary Input

The National Park Service (NPS) water right for the instream flow of the Gunnison River in 

BLCA varies in relation to interannual variability in basin water supply (Colorado District Court 

Water Division 4, 2009). Secondary data on water supply is thus required in order to calculate 

some components of the NPS water right. If these data are not available for a particular flow 

alternative, all calculations will proceed and be displayed except some of the NPS water-right 

indicators.

Two kinds of secondary input are required. The first concerns unregulated annual April 1–

July 31 inflow to Blue Mesa reservoir in acre-feet. This quantity well expresses interannual 

variability in water supply, is used in simulation and operation of the Aspinall Unit facilities, is 

subject to real-time forecasting using snowpack conditions, and is used in the formal specification 

of the NPS water right. Both actual and May 1 forecast values of unregulated April 1–July 31 

inflow to Blue Mesa are required. The Forecast Inflow in the NPS water right (Colorado District 

Court Water Division 4, 2009) is defined as:

Forecasted Inflow means the May 1 forecast for the Gunnison River Basin, issued by the 

Colorado River Basin River Forecast Center or successor agency and used by the Bureau of 

Reclamation for forecasts, of the most probable (50 percent chance of exceedance) 

unregulated April 1 through July 31 inflow to Blue Mesa Reservoir. 

Forecast and actual inflow should be generally available for simulations of Aspinall Unit 

operations (RIVERWARE model) as well as actual future years. Reconstruction of what the 

forecast would have been before forecasts were made or for periods for which input data for the 

forecasting algorithms are not available—including estimation of what the forecast would be for an 
8

arbitrary daily flow sequence—are problematic. In the example input data directory 

InputDataFiles, we provide and describe estimates of actual and forecast Blue Mesa inflow that 

may be suitable for use with scenarios based on historical hydrologic patterns.

Both the May 1 forecast and actual values are required, as well as values for the two 

preceding years (in order to assess a longer-term drought condition). Annual values for forecast and 

actual April–July Blue Mesa inflow are entered as acre-feet in cells with EXCEL general or 

numeric formatting. Cells containing corresponding years should be in EXCEL general or numeric

format.

The other type of secondary input data concerns the live storage in acre-feet in Blue Mesa 

Reservoir on December 31 of the previous year. This information is used only to suspend the 

application of a drought-provision reduction of the NPS Peak Flow right when low basin water 

supply is mitigated by the availability of substantial reservoir storage. The threshold value of Blue 

Mesa live storage volume is 550,000 acre-feet. If drought conditions exist, as determined from 

Blue Mesa inflow data, drought provisions in the NPS water right are not implemented if the 

reservoir storage on December 31 of the previous year exceeds 550,000 acre-feet. Thus, the effects 

of Blue Mesa Reservoir storage can be disabled by input values of storage less than 550,000 acrefeet, as would be appropriate when evaluating historical conditions before the dam was built.

The location of Blue Mesa live storage input data is entered on the Input Scenario 

Specification screen (fig. 3). Although only one value for a year (December 31) is needed, input is 

specified as a sequence of daily, rather than yearly, values to facilitate direct use of output from the 

Bureau of Reclamation RIVERWARE model (slot BlueMesaStorage). Live storage is provided in 

acre-feet (EXCEL general or numeric format) and date is provided in EXCEL date or date-time 

formatted cells. A complete input data set is not required. If no input file is identified for a flow 

alternative, then the effect of Blue Mesa storage is disabled by assuming values of less than 

550,000 acre-feet. If the value for December 31 of a specific year is missing from the input data 

set, it is estimated as the January 1 value for the next year if that value is provided. If this 

estimation is not possible (January 1 of the next year is also missing), then a value of less than 

550,000 acre-feet is assumed.

Execution and Output

The system is implemented as a VBA (Visual Basic for Applications) macro within a 

Microsoft Office EXCEL workbook in order to (1) utilize widely available software, (2) allow

direct examination of the underlying code by multiple users, and (3) support convenient input of 

multiple sources of alternative flow regimes as workbook files. Invoking the VBA editor within 

EXCEL allows examination of all the VBA code and objects. Values of parameters, as well as 

fonts, graphics elements, cell formulas, named ranges, and VBA code, can be modified by the user, 

although some of the cells are initially protected to limit inadvertent changes. A button control in 

the WorkbookLookups worksheet containing program parameters can be used to turn this 

protection off to allow editing of all cells. 

The code performs some limited error trapping such as checking that file paths are valid and 

that input data are complete. However, we have not explored all possible situations that might 

produce errors, and the program should be viewed as a working tool to be improved by the user if 

necessary. Serious errors may send the workbook into a Debug mode within VBA from which the 

application can either be terminated or the source of the error can be further investigated by the 

user. The most likely sources of execution errors are problems with the specification or contents of

input data files. Some execution errors may stem from having other workbooks open within the 

same instance of EXCEL running the decision support system. Thus, it is desirable to open EXCEL 
9

in a second instance to concurrently examine other workbooks. Refer to the site 

http://www.fort.usgs.gov/Products/Software/ to communicate suspected program bugs and to check 

for revised versions of the code.

No special interfaces have been developed for saving or printing output. EXCEL output 

menu controls and cut-and-paste operations can be used to export desired graphs or tables from 

BCG_DSS.xls to other locations.

Both the decision support system and this document use mixed units, which reflects a 

compromise between a scientific preference for metric or S.I. units and the desirability of limiting 

unit conversions both from the original results of the studies used to define relationships and by the 

user in preparing input data and interpreting results in the context of water-management decisions.

Tables of conversion factors are provided at the beginning of this document. 

Selecting the red Execute button from the Main Menu invokes the main processing VBA 

macro, which controls the processing of input data and updating of worksheets. A status box tracks 

execution. When calculations are completed, an Input Data Summary sheet is displayed 

providing summary information about each flow alternative (fig. 4). The user then navigates to the 

Main Menu to examine output in more detail. 

Several types of graphs are used to display output. These can generally be manipulated 

using standard EXCEL commands to rescale axes, move labels, and change symbols, line widths, 

and colors. Pie charts are used to depict plant community composition (fig. 5). Many of the 

indicators are graphed using box plots portraying distributions of values associated with each flow 

alternative (fig. 6). These box plots depict the range of indicator values (most often a collection of 

annual values) as the tops and bottoms of a whisker line, the 10th and 90th percentiles as the tops 

and bottoms of the box, and the median value as a line within the box. Thus, they are slightly 

different from a common form of box plots where the tops and bottoms of the box depict the 

percentiles and the whiskers are some function of the inter-quartile range. Percentiles are calculated 

with EXCEL conventions for interpolation.

Figure 4. Screen capture depicting Input Data Summary displaying summary 

characteristics of flow scenarios as read into the decision support system.
10

Figure 5. Screen capture depicting Display Indicator Output for Plant Communities 

indicator.

Figure 6. Screen capture depicting Display Indicator Output for Annual Minimum Daily 

Discharge indicator.
11

Some indicators are also portrayed with alternative-selectable, time-series plots. These have 

two forms. In the form used in figure 6, multiple alternatives can be selected for overlay on the 

same time-series graph, and the time axis can be rescaled to focus on either long or short intervals 

with adjustable starting times. The other form of time-series graph compares values of the NPS 

water right to observed flow values over time for a single, selectable flow alternative (fig. 7).

Figure 7 also illustrates the final type of summary graph in which alternatives are compared with 

bar charts of the percentage of years in which a condition is satisfied. Tabular output of each 

indicator is also available from the Tabular Output button on the respective graph sheets. 

Indicator Variables

Box Elder Clearing

Photographs and reports from visits indicate that there was little riparian vegetation on the 

canyon bottom in many areas of the Black Canyon of the Gunnison prior to flow regulation 

(Warner and Walker, 1972). Currently, many bottom-land surfaces are vegetated with a 

combination of herbaceous and woody plant species. Friedman and Auble (1999) developed a box 

elder clearing model for the Warner Point reach of the Gunnison River (fig. 1). Their model relates

Figure 7. Screen capture depicting Display Indicator Output for NPS Water Right: 

May–June Peak Flow indicator.
12

streamflow to an annual fraction of the bottom land cleared. A step-backwater hydraulic model 

relates discharge to water-surface elevations, which are then used to estimate inundation durations 

and shear stresses at plots. Estimates of sediment particle sizes at plots are used to estimate critical 

shear stress at plots. Friedman and Auble (1999) proposed a two-part clearing function: a plot was 

cleared in a year if the shear stress exceeded the critical shear stress for mobilizing sediment at that 

plot, and a plot was cleared if it was inundated for more than 85 days in the growing season. They 

quantified this relation by (a) aging existing trees and retrospectively estimating the worst 

conditions those trees had survived and by (b) directly observing mortality over a year with 

extended inundation.

Work of Friedman and Auble (1999) is applied here to estimate two indicators: Percentage 

of Bottomland Cleared and Percentage of Bottomland Cleared by Scour. Parameter tables of 

the bottom-land plots used by Friedman and Auble define the inundating discharge (discharge 

required to inundate the plot) and the discharge producing greater than critical shear stress at 

the plot.

Shear stress, or the force per unit area applied by the water at the boundary surface, is 

calculated at the plot level as

  = gRS (1)

where τ is shear stress,  is the density of water, g is the acceleration of gravity, R is the hydraulic 

radius (assumed to be approximated by water depth over a plot), and S is the energy gradient at the 

cross section. Critical shear stress necessary to mobilize sediment is related to the sediment particle 

size through Shields equation (1936) as

( ) *

cr cr s 50    = − g d (2)

where τcr is critical shear stress, *

cr  is critical dimensionless shear stress, g is the acceleration of 

gravity, s is the density of sediment,  is the density of water, and d50 is the diameter of the 50th 

percentile or median particle. Particle sizes were assigned to plots based on pebble count 

measurements on all distinct fluvial surfaces at the Warner Point reach, and a value of 0.031 was 

used for *

cr  following Andrews’ (1984) work on gravel-bed rivers in Colorado.

Values of discharge at which critical shear stress is exceeded were not estimated for 

discharges above 20,000 ft3/s, and the relation is assumed to reach a plateau above this discharge.

Percentages of the bottom land are then calculated as percentages of these plots. Note that the total 

Percentage of Bottomland Cleared does not simply separate into Percentage of Bottomland 

Cleared by Scour (presented as an indicator) and a percentage cleared by inundation (not 

presented) because some plots can be cleared by both scour and inundation in a given year.

Following Friedman and Auble (1999), (a) the bottom land is limited to plots above the 300-ft3/s 

flow line, (b) the relationships are quantified for the Warner Point reach, (c) shear stress uses the 

depth of water over the plot-specific ground surface, and (d) dimensionless critical shear stress is 

assumed to be 0.031 for the plot-based estimated D50 particle size. Here, we substitute maximum 

daily discharge for the peak instantaneous discharge used by Friedman and Auble (1999). For both 

indicators, box plots (line at median, box at 10th and 90th percentiles, whiskers to range of data) 

depict distributions of annual values associated with alternative flow regimes.

Plant Communities

Auble and others (1994) developed a riparian vegetation community model for the bottom

land at the Warner Point reach (fig. 1) based on a direct gradient relation between community 

occurrence and long-term inundation duration. They based community definitions on a 

TWINSPAN classification of species occurrences at randomly selected plots; they used a step-
13

backwater hydraulic model to estimate the inundating discharge of each plot and a 17-year flow 

history to calculate inundation duration for each plot. The distribution of communities in different 

classes of inundation duration (fig. 8) was then used to predict distribution across the plots under 

alternative flow regimes that would result in different inundation durations for the plots.

The indicator Percentage of Bottomland in Community Types estimates the percentage

of bottom land in the four community types of (a) Aquatic, (b) Hydric, (c) Mesic, and (d) Xeric 

following Auble and others (1994) with respect to (a) definitions of communities; (b) a calibration

table relating inundation duration to the probability of being in a given community; and (c) the set 

of plots of different inundating discharges in the Warner Point reach representing the bottom land 

above the 300-ft3/s flow line. Here we substitute a daily flow duration curve for the full period of 

input record specified for a flow alternative for the 17-year interval used by Auble and others 

(1994) in order to produce a single result for percentages of the bottom land in different riparian 

vegetation community types for each flow alternative. These distributions are depicted in a pie 

chart for each flow alternative (fig. 5).

Figure 8. Screen capture depicting Display Parameters for relation between community 

distribution and inundation duration from Auble and others (1995). This relation is used in 

the calculation of the Plant Communities indicator.
14

Trout Fry Habitat

Estimates of suitable fry habitat (Rainbow Trout Fry Habitat and Brown Trout Fry 

Habitat) are calculated by applying published relations between discharge and weighted useable 

habitat area to average daily flow within critical time intervals for each year (June 15 through July 

15 for rainbow trout fry and May 1 through June 15 for brown trout fry). These relations are 

depicted in figures 9 and 10. They were derived from tables of mean monthly discharge and 

associated weighted useable areas in Nehring and Miller (1987) and Nehring (1988) based on work

at two sites in the Gunnison Gorge downstream from the Park (fig. 1). The published relations are 

used with extrapolation assuming no change in weighted useable area with discharge below the low 

end of the curves and no change in weighted useable area with discharge at the high end of the 

curves. Original calculations were based on hydraulic models and species preferences for depth, 

velocity, and substrate conditions derived from a combination of literature and site-based fish 

observations.

Both indicators are presented as box plots (line at median, box at 10th and 90th percentiles, 

whiskers to range of data) depicting the distributions of annual values of weighted useable area.

Other indicators relevant to fish habitat include Annual Minimum Daily Discharge and Ramp 

Rate.

Sediment Mobilization

Sediment dynamics and the consequent bottom-land disturbance regimes and maintenance 

of channel form are complex functions of sediment sources, the composition and particle-size 

distribution of bottom-land sediment, existing channel geometry and gradient, the magnitude and 

duration of streamflows with different capabilities of dislodging and transporting sediment of 

different sizes, and the stabilizing effects of vegetation. Several of the general hydrologic indicators 

calculated by the decision support system are thus relevant to sediment dynamics, including 

Figure 9. Screen capture depicting Display Parameters for rainbow trout fry habitat as a 

function of discharge. Relation is based on values reported in Nehring and Miller (1987) 

and Nehring (1988). It is used in the fish habitat indicator Rainbow Trout Fry Habitat.
15

Figure 10. Screen capture depicting Display Parameters for brown trout fry habitat as a 

function of discharge. Relation is based on values reported in Nehring and Miller (1987) 

and Nehring (1988). It is used in the fish habitat indicator Brown Trout Fry Habitat. 

Annual Mean Daily Discharge (Mean Daily Q), Annual Maximum Daily Discharge (Max Daily 

Q), and 14-Day Maximum Daily Discharge (14-Day Max Q).

In addition, we calculate a set of indicators estimating annual sediment mobilization. Three 

indicators are based on Dubinski’s (2005) model for fraction of the river’s length having 

mobilization of three different sediment-size classes. 

Dubinski (2005) and Dubinski and Wohl (2007) developed models of the fractions of the 

river in the park that are mobilized for the D16, D50, and D84 particle sizes by using generalized 

hydraulic models and particle-size compositions partitioned across the length of river. Dubinski 

(2005) used Komar’s (1987) equation for critical shear stress 

( ) * 0.6 0.4

cr, cr s 50 i i    = − g dd (3) 

where τcr,i is critical shear stress for the ith diameter particle size,  *

cr is critical dimensionless shear 

stress, g is the acceleration of gravity, s is the density of sediment,  is the density of water, and 

d50 is the diameter of the 50th percentile or median particle, and di is the diameter of the ith particle 

size for which critical shear stress is being estimated. This (Komar’s equation 3 above) reduces to 

the Shields equation (equation 1 above) used by Friedman and Auble (1999) for the median, d50, 

particle size. Dubinski (2005) conducted sensitivity analyses of variation in both dimensionless 

critical shear stress and the roughness parameter of Manning’s n used in his hydraulic model and 

judged values of 0.045 for dimensionless critical shear stress and 0.05 for Manning’s n to be the 

most appropriate single values for application to all park reaches. We used these results of 

Dubinski (2005) to derive summary relationships (fig. 11) for fraction of the river length mobilized 

for each size fraction as a function of the maximum daily discharge of the year. Dubinski’s (2005) 

hydraulic simulations were conducted between 300 and 10,000 ft3/s. We developed simple 

extrapolations of these relationships using a logit-transform regression (in which fraction mobilized 

is asymptotically bounded by 0 and 1.0) to estimate several points between 10,000 and 20,000 ft3/s

(fig. 11). We then constructed a linear interpolation of fractions of river length assuming 0.0 

mobilized at 0 ft3/s discharge, using points reported by Dubinski (2005) between 300 and 10,000 

ft3/s, and the regression-estimated points between 10,000 and 20,000 ft3/s. The relationship was 
16 

Figure 11. Screen capture depicting Display Parameters for annual percentages of river 

length mobilized for three reference particle sizes. Relations are derived from Dubinski 

(2005) with extrapolation beyond range of simulated discharges as indicated in the figure. 

These relations are used in the sediment mobilization indicators Annual Percentage of 

River Length Mobilized-D16, Annual Percentage of River Length Mobilized-D50, and 

Annual Percentage of River Length Mobilized-D84. 

assumed to plateau above 20,000 ft3

/s. Thus, the overall relationship is most reliable between 300 

and 10,000 ft3

/s, is considerably less reliable between 10,000 and 20,000 ft3/s, and is bounded at a 

maximum value above 20,000 ft3

/s. 

 Alternative flow regimes are compared by box plots (line at median, box at 10th and 90th 

percentiles, whiskers to range of data) of the annual percentages of river length mobilized for each 

of the three sediment particle sizes—Annual Percentage of River Length Mobilized-D16, Annual 

Percentage of River Length Mobilized-D50, and Annual Percentage of River Length 

Mobilized-D84. 
17

The box elder clearing indicator, Percentage of Bottomland Cleared by Scour, estimates

sediment mobilization for the D50 size class at the Warner Point reach based on more site-specific 

hydraulic models and sediment particle-size determinations as described in Friedman and Auble 

(1999). Friedman and Auble’s (1999) model produces somewhat lower values for mobilization of 

the D50 size class than Dubinski’s (2005). The differences are produced by a combination of 

reasons, including (a) the nature of the hydraulic models and extrapolation beyond calibrated 

discharges, (b) Friedman and Auble’s (1994) partitioning of shear stress and particle size across the 

bottom land to estimate percentage of bottom land mobilized as opposed to Dubinski’s (2005) use 

of generalized conditions at reaches to estimate percentage of river length with mobilization, and 

(c) different assumed values for dimensionless critical shear stress

National Park Service Water Right

Overview

The National Park Service (NPS) Federal reserved water right (Colorado District Court 

Water Division 4, 2009) is a direct flow right “expressed in cubic feet per second (“c.f.s.”) as 

measured at the Gunnison River below Gunnison Tunnel gage (No. 09128000).” This water right 

has three basic components: Minimum Flow, May-June Peak Flow, and Shoulder Flow. The 

specific values of the right in a given year involve some relatively complex calculations referencing 

previous and forecast hydrologic conditions expressed as unregulated inflow and referencing 

reservoir storage levels on December 31 of the previous year. For each flow alternative, we attempt 

a calculation of each element of the right in each year and then compare actual observed flows to 

the right. Details of these calculations are described under the individual indicators corresponding 

to the respective elements of the water right.

In general, specific flow values of the right depend on a secondary data set of annual 

forecast and actual inflow unregulated April 1 through July 31 inflow to Blue Mesa Reservoir.

From Colorado District Court Water Division 4 (2009), “Forecasted Inflow” means the “May 1 

forecast for the Gunnison River Basin issued by the Colorado Basin River Forecast Center or 

successor agency, and used by the Bureau of Reclamation for forecasts, of the most probable (50

percent chance of exceedance) unregulated April 1 through July 31 inflow to Blue Mesa 

Reservoir.” This inflow is further used to define year categories as:

Dry Year: A year in which the Forecasted Inflow is less than 381,000 acre-feet. 

Moderately Dry Year: A year in which the Forecasted Inflow is greater than or equal to 

381,000 acre-feet but less than 561,000 acre-feet.

Average Dry Year: A year in which the Forecasted Inflow is greater than or equal to 

561,000 acre-feet but less than 709,000 acre-feet. 

Average Wet Year: A year in which the Forecasted Inflow is greater than or equal to 

709,000 acre-feet but less than 871,000 acre-feet.

Moderately Wet Year: A year in which the Forecasted Inflow is greater than or equal to 

871,000 acre-feet but less than 1,123,000 acre-feet. 

Wet Year: A year in which the Forecasted Inflow is greater than or equal to 1,123,000 

acre-feet.

Calculations of the specific values of the Peak and Shoulder Flows are based on the value of 

Forecast Inflow in a year, with the parameters of that calculation varying according to the year 

type. For both Peak and Shoulder Flows, the water-right values may be further modified under a 

“Drought Recovery Provision.” This provision is invoked “In any year classified as Average Dry or 

Moderately Dry, which (1) follows a Dry year or two consecutive years classified as Dry and/or 
18

Moderately Dry Years, and (2) in which in the prior year Blue Mesa Reservoir live storage content 

was at or below 550,000 acre-feet on December 31....” We use forecast inflow in the current year 

and actual inflow of preceding years in this calculation. The drought recovery modification for 

Shoulder Flows is formulated as a lower-bound threshold of 300 ft3/s. The drought recovery 

modification for Peak Flows is formulated as a multiplicative reduction factor applied to the 

unadjusted Peak Flow (Colorado District Court Water Division 4, 2009). This reduction factor is 

calculated as:

( ) ( )

( )

Actual Apr. through July BM inflow in previous year May 1 Forecast for Apr. through July BM inflow in current year

Max. possible April through July BM Inflow in the previous year category Max. poss

+   

  +( ible Apr. through July BM inflow in current year category)   (4)

where “Max. possible Apr. through July BM inflow” has the following values for the possible year 

classes of:

Dry Year: 381,000 acre-feet

Moderately Dry Year: 561,000 acre-feet

Average Dry Year: 709,000 acre-feet.

Complete calculation of the NPS water right thus requires information on Forecast Inflow 

in the current year, previous and current years’ Actual Inflow (unregulated April 1 through July 31 

inflow to Blue Mesa Reservoir), and furthermore the previous year’s (December 31) live storage in 

Blue Mesa Reservoir. This considerably expands the input data required to evaluate whether the 

water right is met beyond a simple flow record at the gage site and thus restricts the applicability of 

these indicators to flow alternatives for which appropriate and consistent additional data are 

available. 

Actual and estimated historical values are available for forecast and actual April–July 

unregulated inflow. These values are provided as an input data file (in InputDataFiles directory)

and can be used for flow alternatives in which the years of the flow alternative appropriately match 

the years of the historical record. Users beware that (1) these inflow values have to be consistent 

with the hydrology described in the gage flow for the alternative (you cannot fairly evaluate 

changes in streamflow data for a given year without considering whether those changes are 

consistent with the inflow data being used for that year); and (2) the inflow values required are not 

easily obtainable from measured or published streamflow because the required data (a) refers to 

unregulated rather than actual measured inflows and (b) involves forecasted values using additional 

secondary data sets.

The legal specification of the NPS water right (Colorado District Court Water Division 4, 

2009) also identifies an unquantified flood protection provision as follows.

In order to minimize downstream flooding: (1) the United States shall continue to operate the 

Aspinall Unit to give the highest priority to flood control, subject to the need to release water 

in order to maintain the safety and integrity of the Aspinall Unit structures; and (2) this decree 

shall not be exercised to supersede flood control operations. This provision is intended to 

protect human health and safety and prevent the loss of property located along the Gunnison 

River downstream from the Park, including particularly, but without limitation, property in 

and the inhabitants of Delta County.

We calculate the NPS water right without any modification for how it might be reduced by the 

flood protection provision.
19

Minimum Flow

The Minimum Flow element of the NPS water right is fixed at 300 ft3/s for all days of all 

years. We calculate the observed minimum daily flow for each year and compare alternatives with 

two graphs. The first graph portrays the percentage of years in which the right was satisfied 

(percentage of years in which minimum flow was greater than or equal to 300 ft3

/s). The second 

graph is an alternative-selectable, time-series plot that compares annual values of the water right 

and the actual minimum flow.

Other box plots and time-series plots of actual minimum flows are provided under the 

Hydrologic Indicators section as Annual Minimum Daily Discharge.

May–June Peak Flow

The observed May–June Peak Flow is calculated for each year as the maximum daily 

discharge over the interval May 1 through June 30. Calculation of the Peak Flow (May–June) 

element of the NPS water right is a multistep process. Peak Flow here refers to maximum daily 

discharge rather than instantaneous peak (Colorado District Court Water Division 4, 2009). First, 

an unadjusted Peak Flow right for each year is calculated as follows using Forecast Input (of 

unregulated Blue Mesa inflow as described in the NPS Water Right Overview section) for the 

respective year.

If Forecasted Inflow is 372,000 acre-feet or less, the Peak Flow shall be 482.95 c.f.s. plus 

1.44 times the Forecasted Inflow number divided by 1,000, expressed as c.f.s.

If the Forecasted Inflow is more than 372,000 acre-feet but not more than 715,000 acrefeet, the Peak Flow shall be 15.24 times the Forecasted Inflow number divided by 

1,000, expressed as c.f.s., minus 4,651.66 c.f.s. 

If the Forecasted Inflow is more than 715,000 acre-feet but not more than 925,000 acrefeet, the Peak Flow shall be 5,449.13 c.f.s. plus 1.15 times the Forecasted Inflow 

number divided by 1,000, expressed as c.f.s.

If the Forecasted Inflow is more than 925,000 acre-feet but not more than 1,001,000 acrefeet, the Peak Flow shall be 14.57 times the Forecasted Inflow number divided by 

1,000, expressed as c.f.s., minus 6975.28 c.f.s. 

If the Forecasted Inflow is more than 1,001,000 acre-feet but not more than 1,050,000 acrefeet, the Peak Flow shall be 70.40 times the Forecasted Inflow number divided by 

1,000, expressed as c.f.s., minus 62886.00 c.f.s. 

If the Forecasted Inflow is more than 1,050,000 acre-feet, the Peak Flow shall be 10.68 

times the Forecasted Inflow number divided by 1,000, expressed as c.f.s., minus 

180.00 c.f.s.

This formula for unadjusted peak flow is presented graphically in figure 12.

The unadjusted Peak Flow is then subject to possible drought provision reduction. Drought 

provision is applied if the current year is classified as Average Dry or Moderately Dry and (1) 

follows a Dry year or two consecutive years classified as Dry or Moderately Dry Years, and (2) in 

which in the prior year Blue Mesa Reservoir live storage content was at or below 550,000 acre-feet 

on December 31, according to definitions of year class presented in the NPS Water Right Overview 

section. If the drought provision is in effect, the unadjusted Peak Flow value is reduced by 

multiplying the unadjusted value by the fraction defined in equation (4) of the NPS Water Rights 

Overview section. The observed May–June peak flow is calculated for each year as the maximum 

daily discharge in the interval May 1 through June 30.
20

Figure 12. Screen capture depicting Display Parameters for NPS Peak Flow water right 

as a function of Forecast unregulated April–July Blue Mesa inflow. Water right is fully 

specified in (Colorado District Court Water Division 4, 2009). Right displayed here is 

unadjusted for drought year provisions.

If the required data on Blue Mesa Inflow are not provided for one or more years of a flow 

alternative, no calculation of the Peak Flow right is made for that year and no overall calculation of 

the percentage of years the right was satisfied is attempted. Missing data for December 31 values of 

storage in Blue Mesa Reservoir are treated more generously. First we substitute the January 1 value 

(if that is provided) for a missing value for December 31 of the previous year. Second, we ignore 

the effect of Blue Mesa Reservoir storage if no actual or estimated December 31 value is available 

by assuming that Blue Mesa Reservoir storage has no effect on whether the drought provision is or 

is not in effect. This facilitates the evaluation of alternatives that do not have Blue Mesa Reservoir 

(for example, before its construction). The effect of Blue Mesa Reservoir can also be disabled 

by providing input values for Blue Mesa Reservoir storage of less than 550,000 acre-feet on 

December 31.

Alternatives are compared with two graphs (fig. 7). The first graph portrays the percentage 

of years in which the right was satisfied. The second graph is an alternative-selectable, time-series 

plot that compares annual values of the Peak Flow (May–June) element of the NPS water right and 

actual values of May–June Peak Flow. Other box plots and time-series plots of Actual Maximum 

Daily Discharge over all days of the year (as opposed to those restricted to May–June) are 

provided as a hydrologic indicator.

Shoulder Flow

Shoulder Flow refers to the minimum daily flow that occurs in the restricted interval of 

May 1 through July 25 (Colorado District Court Water Division 4, 2009). The observed shoulder 

flow in a year is the minimum daily flow over this interval. The shoulder flow water right for each 
21

year is calculated using Forecast Inflow for the current year and a determination of whether the 

drought recovery provision is in effect as described in National Park Service Water Rights 

Overview section herein. Treatment of missing data required to calculate the shoulder flow right is 

the same as described here for the peak flow right. Shoulder flow right in a year is calculated as 

follows (Colorado District Court Water Division 4, 2009).

If the Forecasted Inflow is 561,000 acre-feet or less, or the drought recovery provisions of 

are applicable, the flow for the period shall be 300 c.f.s.

If the Forecasted Inflow is more than 561,000 acre-feet but not more than 690,000 acrefeet, the flow for the period shall be 2.692 times the Forecasted Inflow number 

divided by 1,000, expressed as c.f.s, minus 1207.69 c.f.s.

If the Forecasted Inflow is more than 690,000 acre-feet but not more than 1,000,000 acrefeet, the flow for the period shall be 1.129 times the Forecasted Inflow number 

divided by 1,000, expressed as c.f.s, minus 129 c.f.s.

If the Forecasted Inflow is more than 1,000,000 acre-feet, the flow for the period shall be 

1000 c.f.s

This formula is presented graphically in figure 13. Alternatives are compared with two graphs. The 

first graph portrays the percentage of years that the right was satisfied. The second graph is an 

alternative-selectable, time-series plot that compares the annual values of Shoulder Flow water 

right and the actual value of Shoulder Flow (minimum daily flow in interval May 1–July 25).

Figure 13. Screen capture depicting Display Parameters for NPS Shoulder Flow water 

right as a function of Forecast unregulated April–July Blue Mesa inflow. Water right is fully 

specified in (Colorado District Court Water Division 4, 2009). Right displayed here is 

unadjusted for drought year provisions.
22

Hydrologic Indicators

Annual Minimum Daily Discharge

Annual Minimum Daily Discharge (Min Daily Q) is the minimum value of daily 

discharge for each year. This is portrayed as both box plots (line at median, box at 10th and 90th 

percentiles, whiskers to range of data) of annual values in each flow alternative and as a time-series 

graph for selectable flow alternatives (fig. 6). This indicator (Annual Minimum Daily Discharge)

is equivalent to the Minimum Flow component of the National Park Service (NPS) Water Right.

Annual Mean Daily Discharge

Annual Mean Daily Discharge (Mean Daily Q) is the mean value of daily discharge for 

each year. This is portrayed both as box plots (line at median, box at 10th and 90th percentiles, 

whiskers to range of data) of annual values in each flow regime and as a time-series graph for 

selectable flow alternatives. 

Annual Maximum Daily Discharge

Annual Maximum Daily Discharge (Max Daily Q) is the maximum value of daily 

discharge for each year. This is portrayed both as box plots (line at median, box at 10th and 90th 

percentiles, whiskers to range of data) of annual values in each flow regime and as a time-series 

graph for selectable flow alternatives. 

Annual 14-Day Maximum Daily Discharge

Annual 14-Day Maximum Daily Discharge (14-Day Max Daily Q) is the highest daily 

discharge that is equaled or exceeded for 14 consecutive days in a given year. Flow alternatives are 

compared as box plots (line at median, box at 10th and 90th percentiles, whiskers to range of data)

of values of maximum 14-day discharge for years within each flow regime and as a time-series 

graph for selectable flow alternatives.

Ramp Rate

Many aquatic organisms, including fish at multiple life stages, are sensitive to rapid 

changes in flow often referred to as ramping rates. Ramp Rate is evaluated in terms of how often 

specified thresholds of change are exceeded. It is calculated as the percentage of days in each year 

where the change in discharge exceeds these threshold values. For this calculation, threshold values 

can be defined for up to three separate flow ranges and are specified as thresholds of maximum 

absolute change in flow from one day to the next. Ranges and thresholds are disabled by setting 

table entries to extreme values or by leaving parameter table entries blank.

Flow alternatives are compared with box plots (line at median, box at 10th and 90th 

percentiles, whiskers to range of data) of percentage of days exceeding thresholds within each year.

Flow Constancy

Flow Constancy (Daily Flow Constancy) is a measure of the percentage of days in the flow 

record when the flow remains essentially constant from one day to the next. It is calculated by first 

taking the log10 of each daily flow and then converting these log10 values to discrete increments of 

0.004321 (increments of approximately 1 percent of untransformed flow). The indicator is then 

calculated as the percentage of days in the overall flow record for which the discretized daily flow 
23

does not change from that of the previous day. Flow alternatives are compared with box plots (line 

at median, box at 10th and 90th percentiles, whiskers to range of data) of the distribution of annual 

values.

Note that the source of the daily flow record should be considered when comparing values 

of Flow Constancy. Flow regimes themselves may differ in flow constancy—for example, a 

stable, spring-fed stream compared to a snowmelt hydrograph compared to a heavily managed flow 

regime dominated by a small number of desirable flows. Discretization may also be introduced in 

the measurement and reporting of flow data or in the way a flow simulation model treats short-term 

variation.

Coefficient of Variation of Monthly Discharge within Years

Coefficient of Variation of Monthly Discharge within Years (CV of Monthly Q within 

Years) is the coefficient of variation of mean monthly flows around the grand mean monthly flow 

of the year in which they occur. For each year, 12 monthly mean flows are calculated as the means 

of daily flow in the respective months. A coefficient of variation is then calculated for the 

dispersion of these monthly mean flows around the grand mean of months within that year. Thus,

the number of values for each flow alternative is equal to the number of years of record for that 

regime. Flow alternatives are compared with box plots (line at median, box at 10th and 90th 

percentiles, whiskers to range of data) of these annual values of coefficient of variation.

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techniques: U.S. Fish and Wildlife Service, FWS/OBS–78/33, Washington, DC, 130 p.

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24

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