Extent of Areal Inundation of Riverine 

Wetlands Along Five River Systems in the 

Upper Hillsborough River Watershed, 

West-Central Florida

By B.R. Lewelling

U.S. Department of the Interior

U.S. Geological Survey

In cooperation with the

Southwest Florida Water Management District

Scientific Investigations Report 2004-5133
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

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

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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: Lewelling, B.R., 2004, Extent of Areal Inundation of Riverine Wetlands Along Five River Systems in 

the Upper Hillsborough River Watershed, West-Central Florida: U.S. Geological Survey Scientific Investigations Report 

2004-5133, 49 p., plus appendixes.
 iii

CONTENTS

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

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

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

Previous Investigations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Description of the Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Methodology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Hillsborough River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

New River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Blackwater Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Itchepackesassa Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

East Canal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Selected References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Appendixes: 

Hillsborough River––

 1. Extent of inundation at cross sections along the Hillsborough River for selected percentile 

discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 2

 2. Hydraulic depth at cross sections along the Hillsborough River for selected percentile 

discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 4

 3. Acreage of areal inundation between adjacent cross sections along Hillsborough River. . . . . . . . . . . . A 6

 4. Decrease of inundated acreage resulting from a potential 10-percent discharge withdrawal at 

cross sections along Hillsborough River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 8

New River––

 5. Extent of inundation at cross sections along New River for selected percentile discharges . . . . . . . . A 10

 6. Hydraulic depth at cross sections along New River for selected percentile discharges . . . . . . . . . . . . A 11

 7. Acreage of areal inundation between adjacent cross sections along New River. . . . . . . . . . . . . . . . . . . A 12

 8. Decrease of inundated acreage resulting from a potential 10-percent discharge withdrawal at 

cross sections along New River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 13

Blackwater Creek––

 9. Extent of inundation at cross sections along Blackwater Creek for selected percentile 

discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 14

10. Hydraulic depth at cross sections along Blackwater Creek for selected percentile discharges. . . . . A 16

11. Acreage of areal inundation between adjacent cross sections along Blackwater Creek . . . . . . . . . . . A 18

12. Decrease of inundated acreage resulting from a potential 10-percent discharge withdrawal

at cross sections along Blackwater Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 20

Itchepackesassa Creek––

13. Extent of inundation at cross sections along Itchepackesassa Creek for selected percentile 

discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 22

14. Hydraulic depth at cross sections along Itchepackesassa Creek for selected percentile

discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 23

15. Acreage of areal inundation between adjacent cross sections along Itchepackesassa Creek . . . . . A 24

16. Decrease of inundated acreage resulting from a potential 10-percent discharge withdrawal at 

cross sections along Itchepackesassa Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 25

East Canal––

17. Extent of inundation at cross sections along East Canal for selected percentile discharges . . . . . . . . A 26

18. Hydraulic depth at cross sections along East Canal for selected percentile discharges . . . . . . . . . . . . A 27

19. Acreage of areal inundation between adjacent cross sections along East Canal. . . . . . . . . . . . . . . . . . . A 28

20. Decrease of inundated acreage resulting from a potential 10-percent discharge withdrawal at 

cross sections along East Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 29
iv 

FIGURES

1. Map showing location of study area including the Hillsborough and New Rivers, Blackwater

and Itchepackesassa Creeks, and East Canal, west-central Florida . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

2. Example cross section showing Manning’s n-values, subareas, and water-surface elevation. . . . . . .4

3-4. Graphs showing:

3. Duration curves of daily mean discharge at four upper Hillsborough River gaging stations 

for the concurrent period 1984-2000, the New River near Zephyrhills gaging station for the

period 1965-1974, and the Blackwater Creek near Knights gaging station for the period

1973-2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 

4. Comparison of duration curves of daily mean discharge for selected periods of record at 

the Hillsborough River near Zephyrhills gaging station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

5. Map showing location of the Hillsborough River study reach and cross sections, and the

Morris Bridge, Zephyrhills, Crystal Springs, and Withlacoochee-Hillsborough Overflow gaging

stations, west-central Florida . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

6. Graph showing Hillsborough River water-surface profiles for the selected percentile discharges

and the effects of a 10-percent discharge withdrawal, from the Morris Bridge to the Withlacoochee-Hillsborough Overflow gaging stations, based on the 17-year period 1984-2000. . . . . . . . . . 11

7. Diagram showing extent of areal inundation along reaches 1-3 of the Hillsborough River study 

channel and floodplain for selected percentile discharges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-14

8-9. Graphs showing:

8. Estimated extent and frequency of areal inundation and hydraulic depth at Hillsborough 

River cross sections 30 and 41 for each of the selected percentile discharges 

and the potential 10-percent withdrawal in discharge, based on the 17-year period 

1984-2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

9. Estimated total inundated area along Hillsborough River for existing conditions and 

for a potential 10-percent discharge withdrawal, and percentage of inundated area 

decreased by a potential 10-percent discharge withdrawal for each of the selected 

percentile discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

10. Diagram showing example of extent of areal inundation along reaches 1-3 of the Hillsborough 

River study channel and floodplain for the P95 (existing conditions) and the P95-10 (potential 

10-percent discharge withdrawal) discharges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-21

11. Map showing location of the New River study reach and cross sections, and the Zephyrhills

gaging station, west-central Florida. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22.

12. Graph showing New River water-surface profiles for six selected percentile discharges and 

the effects of a 10-percent discharge withdrawal, from the mouth to cross section 8.46, based 

on the 10-year period 1965-1974. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

13. Diagram showing extent of areal inundation along reaches 1 and 2 of the New River study

channel and floodplain for selected percentile discharges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

14-15. Graphs showing:

14. Estimated extent and frequency of areal inundation and hydraulic depth at New River 

cross section 1.17 for six of the selected percentile discharges and the potential 

10-percent withdrawal in discharge, based on the 10-year period 1965-1974 . . . . . . . . . . . . . . . . 26

15. Estimated total inundated area along New River for existing conditions and for a 

potential 10-percent discharge withdrawal, and percentage of inundated area decreased 

by a potential 10-percent discharge withdrawal for each of the selected percentile 

discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

16. Diagram showing example of extent of areal inundation along reaches 1 and 2 of the New River 

study channel and floodplain for the P99.5 (existing conditions) and the P99.5-10 (potential 

10-percent discharge withdrawal) discharges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
 v

17. Map showing location of the Blackwater Creek study reach and cross sections, and the 

Knights gaging station, west-central Florida . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

18. Graph showing Blackwater Creek water-surface profiles for selected percentile discharges and

the effects of a 10-percent discharge withdrawal, from the confluence with the Hillsborough 

River to cross section 16.6, based on the 29-year period 1973-2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

19. Diagram showing extent of areal inundation along reaches 1 and 2 of the Blackwater Creek 

study channel and floodplain for selected percentile discharges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

20-21. Graphs showing:

20. Estimated extent and frequency of areal inundation and hydraulic depth at Blackwater 

Creek, 9.0, Itchepackesassa Creek, 0.82, and East Canal, 3.03 cross sections for each 

of the selected percentile discharges and the potential 10-percent withdrawal in 

discharge, based on the period 1973-2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 

21. Estimated total inundated area along Blackwater Creek, from the confluence with the

Hillsborough River to cross section 16.6, for each of the selected percentile discharges 

and for a10-percent discharge withdrawal, based on the period 1973-2001. . . . . . . . . . . . . . . . . . 35

22. Diagram showing example of extent of areal inundation along reaches 1 and 2 of the 

Blackwater Creek study channel and floodplain for the P99.97 (existing conditions) and the 

P99.97-10 (potential 10-percent discharge withdrawal) discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

23. Map showing location of the Itchepackesassa Creek study reach and cross sections, and 

the Moriczville and Knights gaging stations, west-central Florida . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

24. Graph showing Itchepackesassa Creek water-surface profiles for the selected percentile 

discharges and the effects of a 10-percent discharge withdrawal, from the confluence with 

Blackwater Creek to Interstate 4, based on the 29-year period 1973-2001. . . . . . . . . . . . . . . . . . . . . . . . . . 39

25. Diagram showing extent of areal inundation along Itchepackesassa Creek study channel 

and floodplain for selected percentile discharges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

26. Graph showing estimated total inundated area along Itchepackesassa Creek, from the mouth 

at the confluence with Blackwater Creek to Interstate 4, for each of the selected percentile 

discharges and for a 10-percent discharge withdrawal, based on the 29-year period 1973-2001 . . . 41

27. Diagram showing example of extent of areal inundation along the Itchepackesassa Creek 

study channel and floodplain for the P99.97 (existing conditions) and the P99.97-10 (potential 

10-percent discharge withdrawal) discharges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

28. Map showing location of the East Canal study reach and cross sections, west-central Florida. . . . 43

29. Graph showing East Canal water-surface profiles for the selected percentile discharges 

and the effects of a 10-percent discharge withdrawal, from the confluence with 

Itchepackesassa Creek to Interstate 4, based on the 29-year study period 1973-2001. . . . . . . . . . . . . . 44

30. Diagram showing extent of areal inundation along East Canal study channel and floodplain 

for selected percentile discharges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

31. Graph showing estimated total inundated area along East Canal, from the mouth at the 

confluence with Itchepackesassa Creek to Interstate 4, for each of the selected percentile 

discharges and for a 10-percent discharge withdrawal, based on the 29-year period 1973-2001 . . . 47

32. Diagram showing example of extent of areal inundation along East Canal study channel 

and floodplain for the P99.5 (existing conditions) and the P99.5-10 (potential 10-percent 

discharge withdrawal) discharges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

TABLES

1. Upper Hillsborough River watershed study gaging stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

2. Cross sections, drainage area, and percentile discharges used in step-backwater analyses 

based on the concurrent period 1984-2000 at Hillsborough River gaging stations: Morris 

Bridge, Zephyrhills, Crystal Springs, and Withlacoochee-Hillsborough Overflow . . . . . . . . . . . . . . . . . . 10
vi 

3. Approximate number of days daily mean discharge equaled or exceeded the selected 

percentile discharges at the Hillsborough River near Zephyrhills gage, 1984-2000 . . . . . . . . . . . . . . . . . 17

4. Cross sections, drainage area, and percentile discharges used in step-backwater analyses 

based on the period 1965-1974 at the New River near Zephyrhills gaging station . . . . . . . . . . . . . . . . . . 24

5. Approximate number of days daily mean discharge equaled or exceeded the selected 

percentile discharges at the New River near Zephyrhills gaging station, 1965-1974 . . . . . . . . . . . . . . . . 24

6. Cross sections, drainage area, and percentile discharges used in step-backwater analyses

based on the period 1973-2001 at Blackwater Creek near Knights gaging station . . . . . . . . . . . . . . . . . . 30

7. Approximate number of days daily mean discharge equaled or exceeded the percentile 

discharges at Blackwater Creek near Knights, 1973-2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

8. Cross sections, drainage area, and percentile discharges used in the Itchepackesassa 

Creek step-backwater analyses, based on the period 1973-2001, at Blackwater Creek near 

Knights gaging station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

9. Cross sections, drainage area, and percentile discharges used in the East Canal 

step-backwater analyses, based on the period 1973-2001, at Blackwater Creek near Knights 

gaging station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Conversion Factors, Acronyms, Abbreviations, 

and Datums

Multiply By To obtain

acre 4047 square meter

foot (ft) 0.3048 meter

inch (in.) 25.4 millimeter 

mile (mi) 1.609 kilometer 

square mile (mi2) 2.59 square kilometer

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

days/yr days per year

FEMA Federal Emergency Management Agency

HEC-RAS Hydrologic Engineering Center-River Analysis System

NWI National Wetlands Inventory

SR State Road

SWFWMD Southwest Florida Water Management District

US U.S. Highway

USACOE U.S. Army Corps of Engineers

USGS U.S. Geological Survey

yr year

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

(NGVD of 1929); horizontal coordinate information is referenced to the North American Datum of 

1927 (NAD 27).
Extent of Areal Inundation of Riverine Wetlands Along 

Five River Systems in the Upper Hillsborough River

Watershed, West-Central Florida

By B.R. Lewelling

Abstract

Riverine and palustrine wetlands are a major ecological 

component of river basins in west-central Florida. Healthy 

wetlands are dependent, in part, upon the frequency and duration 

of periodic flooding or inundation. This report assesses the 

extent, area, depth, frequency, and duration of periodic flooding 

and the effects of potential surface-water withdrawals on 

wetlands along five river systems in the upper Hillsborough 

River watershed: Hillsborough and New Rivers, Blackwater and 

Itchepackesassa Creeks, and East Canal. Results of the study 

were derived from step-backwater analyses performed for each 

of the river systems using the U.S. Army Corps of Engineers 

Hydrologic Engineering Center-River Analysis System 

(HEC-RAS) one-dimensional model. Step-backwater analyses 

were performed based on daily mean discharges at the 10th, 50th, 

70th, 80th, 90th, 95th, 99.5th, and 99.97th percentiles for selected 

periods. The step-backwater analyses computed extent of inundation, area of inundation, and hydraulic depth. An assessment 

of the net reduction of areal inundation for each of the selected 

percentile discharges was computed if 10 percent of the total 

river flow were diverted for potential withdrawals.

The extent of areal inundation at a cross section is 

controlled by discharge volume, topography, and the degree to 

which the channel is incised. Areal inundation can occur in 

reaches characterized by low topographic relief in the upper 

Hillsborough watershed during most, if not all, selected 

discharge percentiles. Most river systems in the watershed, 

however, have well defined and moderately incised channels 

that generally confine discharges within the banks at the 90th

percentile. The greatest increase in inundated area along the five 

river systems generally occurred between the 95th to 99.5th

percentile discharges. The decrease in inundated area that 

would result from a potential 10-percent discharge withdrawal 

at the five river systems ranged as follows: Hillsborough River, 

7 to 940 acres (2.0 to 6.0 percent); and New River, 0.2 to 58.9 

acres (0 to 11.9 percent); Blackwater Creek, 3.3 to 148 acres 

(2.2 to 9.4 percent); Itchepackesassa Creek, 1.0 to 104 acres 

(0.9 to 10.8 percent); and East Canal 0.7 to 34.6 acres (0.5 to 7.6 

percent).

Introduction

Locating alternative sources of water supply to meet the 

demand of an increasing population is a major concern in westcentral Florida. This need is further complicated by declining 

ground-water levels in the Upper Floridan aquifer, the principal 

source of supply in the area. Surface-water withdrawals from 

area rivers have become an increasingly important alternate 

supply source. The health of riverine wetlands depends, in part, 

upon the frequency and duration of periodic flooding or inundation. The U.S. Geological Survey (USGS), in cooperation with 

the Southwest Florida Water Management District 

(SWFWMD), evaluated the extent of areal inundation in the 

upper Hillsborough River watershed, and a potential range in 

areal inundation resulting from withdrawals of 10 percent of 

average daily discharges for the upper Hillsborough River and 

the New River, Blackwater and Itchepackesassa Creeks, and 

East Canal when flows exceed regulatory minimums.
2 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

0 1 2 3 4 5 MILES

012345 KILOMETERS

New

Blackwater

Creek

Creek

East

HILLSBOROUGH COUNTY

PASCO COUNTY

SUMTER 

COUNTY 

Morris Bridge Road

River

SR 39

Knights-Griffin Road (CR 582)

River

Canal

Moriczville

Chancey Road

PASCO COUNTY

Tampa Lakeland

Plant City

Sam Allen Road

Kathleen

Zephyrhills

Crystal Springs

1

2

3

4

5

6

7

8

9

10

EXPLANATION

GAGING STATION— Location and number

1 Hillsborough River at Morris Bridge

2 Hillsborough River near Zephyrhills

3 Hillsborough River above Crystal Srpings

1

4 Withlacoochee-Hillsborough Overflow near Richland

5 New River near Zephyrhills 10 Cow House Creek

Galloway

Withlacoochee

River

Tampa Bypass Canal

82ο15′ 10′ 5′ 82ο00′

28ο15′

28ο00′

5′

10′

Knights

Richland

POLK COUNTY

 

 

 

 

 

 

 

 

 

 

 

6 Blackwater Creek near Knights

7 

 Itchepackesassa Creek near Moriczville

8 Itchepackesassa Creek near Knights

9 Lake Bonnet 

 

Itchepackesassa

Hillsborough

STUDY 

AREA

BOUNDARY

54

54

S-155

75

4

4

98

92

301

Base from U.S. Geological Survey digital data, 1:200,000, 1972

Albers Equal-Area Conic projection

Standard Parallels 29°30′, and central meridian −83°00′

Galloway Road

Study 

Area

shown

ALABAMA GEORGIA

FLORIDA

Lake Okeechobee

Purpose and Scope

The purpose of this report is to present (1) the extent of 

areal inundation in an area that includes the upper Hillsborough 

River, New River, Blackwater Creek, Itchepackesassa Creek, 

and East Canal (fig. 1) based on selected long-term discharge 

record periods, and (2) the decrease in the extent of areal 

inundation when a potential diversion of 10 percent of that 

discharge occurs. Extent of areal inundation was determined for 

the 10th, 50th, 70th, 80th, 90th, 95th, 99.5th, and 99.97th percentiles 

when hydraulic conditions permitted. Percentiles used in this 

study for the four upper Hillsborough River long-term gaging 

stations, Morris Bridge, Zephyrhills, Crystal Springs, and Withlacoochee-Hillsborough Overflow, were based on the longest 

concurrent 17-year (yr) period (1984-2000). Percentiles for 

New River were based on the available 10-yr period, 

Figure 1. Location of study area including the Hillsborough and New Rivers, Blackwater and Itchepackesassa Creeks, and 

East Canal, west-central Florida.
Introduction 3

1965-1974, at the New River near Zephyrhills gaging station. 

Percentiles for Blackwater Creek, Itchepackesassa Creek, and 

East Canal were based on the 29-yr period, 1973-2001, at the 

Blackwater Creek near Knights gaging station.

The U.S. Army Corps of Engineers (USACOE) Hydrologic Engineering Center-River Analysis System (HEC-RAS) 

one-dimensional step-backwater model (Warner and Brunner, 

1998a,b) was used to compute water-surface elevations at 

cross sections for each river. These computed water-surface 

elevations were used to generate water-surface profiles, areal 

inundation width and acreage, and hydraulic depth (the ratio 

of the cross-sectional area to the surface width).

Previous Investigations

Johnson and others (1979) presented flood profiles based 

on the USGS E431 (Shearman, 1976) and the USACOE 

(HEC-2) step-backwater analyses along a 30.8-mile (mi) reach 

of the Hillsborough River from Structure-155 to United States 

(US) 98 and a 8.5-mi reach of the New River from the confluence with Hillsborough River to 1.5 mi upstream of State Road 

(SR) 54 (fig. 1). Johnson and others (1980) computed flood 

profiles using the USGS E431 step-backwater analysis along 

three Hillsborough River tributaries that included: (1) a 10.5-mi 

reach along Blackwater Creek from SR 39 to the center of 

section 33 near Galloway; (2) a 14-mi reach along Itchepackesassa Creek from the confluence with Blackwater Creek 

to Interstate Highway 4; and (3) a 4.9-mi reach along East 

Canal from the confluence with Itchepackesassa Creek to Interstate Highway 4. Harrison and others (1983) presented flood 

profiles based on the USGS E431 step-backwater analysis 

along a 11.4-mi reach of Trout Creek. Federal Emergency 

Management Agency (FEMA) (1989) presented a flood-insurance study in unincorporated areas of Hillsborough County that 

included flood profiles of reaches along the Hillsborough River 

and Blackwater Creek.

Description of the Study Area

The study area includes five river systems located in the 

upper Hillsborough River watershed: Hillsborough River and 

New River in southeastern Pasco and northeastern Hillsborough Counties; Blackwater Creek and Itchapackesassa Creek 

in eastern Hillsborough and western Polk Counties; and East 

Canal in eastern Hillsborough County (fig. 1). Unique physiographic characteristics (shape, gradient, and basin and channel 

length) affect the hydraulic conditions of the five river systems. 

Based on map delineation by the National Wetlands Inventory 

(NWI) of the U.S. Fish and Wildlife Service (Cowardin and 

others, 1979) the channel and floodplain of the five study river 

systems have been classified as predominately lower perennial 

river bounded by inland forested wetlands or uplands.

The 28-mi-long upper Hillsborough River study reach, 

from Morris Bridge Road to the Withlacoochee-Hillsborough 

Overflow at US 98, can be characterized as a broad, hardwood 

floodplain with low topographic relief and frequent, widespread, and prolonged areal inundation. The extent of areal 

inundation of low-lying areas along the study reaches of the 

Hillsborough River can be large during relatively low-discharge 

conditions. The low-gradient channel along most of the middle 

and lower study reaches is moderately incised and slightly 

meandered. Most of the channel along the upper reach is either 

poorly defined or absent within a broad floodplain. Discharge 

along the extreme upper reach of the Hillsborough River is 

generally limited to crossover flow from the Withlacoochee 

River at the Withlacoochee-Hillsborough Overflow. Crossover 

during high-flow conditions occurs annually about 25 percent 

of the time, based on the study period 1984-2000.

New River is a major tributary to the upper Hillsborough 

River and drains an approximate 19.5-square mile (mi2) area. 

The north-south trending channel is moderately incised and 

well defined along most of the 8.5-mi-long study reach. The 

study reach begins at the confluence with the Hillsborough 

River and ends approximately 1.5 mi upstream of SR 54. New 

River drains predominately pastureland with limited areas of 

residential development.

East-west trending Blackwater Creek is the largest tributary to the upper Hillsborough River, draining approximately a 

113-mi2 area. The headwaters to Blackwater Creek begin northwest of the city of Lakeland and drain westward 17.2 mi to the 

confluence with the Hillsborough River. Unique channel characteristics can be used to define both a lower and an upper 

Blackwater Creek study reach. Most of the lower reach channel, 

from the confluence with the Hillsborough River to SR 39, 

generally is deeply incised and slightly meandered. Most of the 

channel along the lower reach is natural and unaltered by channelization. In contrast, the upper reach channel, from SR 39 to 

the center of section 33 near Galloway, has been extensively 

channelized and straightened to enhance drainage. Much of the 

length along the upper channel banks are lined with spoil berms, 

excavated during ditching and channelization. Berms can 

restrict areal inundation in places, however numerous breaches 

provide flow access to the floodplain. During low-flow conditions, the Blackwater Creek channel in Polk County generally is 

dry. The Blackwater Creek watershed is predominately agricultural with limited development. Presently, Hillsborough County 

owns a large part of the western half of the upper Blackwater 

Creek watershed, which has been proposed for future well field 

development. 

Itchepackesassa Creek is the largest tributary to Blackwater Creek and drains an approximate 57-mi2 area. Much of 

Itchepackesassa Creek has been channelized to improve drainage. The Itchepackesassa Creek headwaters form west of the 

city of Lakeland and drain in a northwest direction to the 

confluence with Blackwater Creek. Discharge from the Lake 

Bonnet outfall structure is a principal source of water to Itchepackesassa Creek during low-flow conditions. At the confluence 

of Blackwater and Itchepackesassa Creeks, Itchepackesassa 

Creek has a 37-percent larger drainage area than Blackwater 
4 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

0 500 1,000 1,500 2,000 2,500

30

35

40

45

50

55

60

65

REFERENCE DISTANCE FROM LEFT BANK, IN FEET

Channel

Manning’s n-value Subarea 1

Cross Section

Water Surface

Subarea 2

Subarea 4

Subarea 5

Subarea 3

Surveyed Land-Surface Elevation

.05 .16 .07 .16 .05

 Floodplain Floodplain

View Looking Downstream

Left Bank

Right Bank

ELEVATION, IN FEET ABOVE NGVD OF 1929

Creek, and generally is either the sole source or the greatest 

source of discharge to Blackwater Creek during low-flow 

conditions.

East Canal is a major tributary to Itchepackesassa Creek 

that has been highly channelized. The north-south trending East 

Canal channel drains an approximate 13.4-mi2 area from eastern Plant City to the confluence with Itchepackesassa Creek. 

During low-flow conditions, East Canal flow is predominantly 

treated wastewater discharged from Plant City at SR 582 

(J.T. Trommer, U.S. Geological Survey, oral commun., 2001).

Methodology 

Step-backwater analyses were performed for the Hillsborough River, New River, and Blackwater Creek river systems, 

based on specific record periods, using HEC-RAS. Analyses 

for Itchepackesassa Creek and East Canal river systems were 

performed in conjunction with the Blackwater Creek analyses. 

Step-backwater analyses were performed for each of the 

selected percentile discharges. Streamflow record periods used 

to calculate the discharge percentiles for the Hillsborough 

River, New River, and Blackwater Creek analyses were 17, 10, 

and 29 years, respectively. Discharge record for the Hillsborough River was based on a concurrent period at the four study 

gaging stations. New River and Blackwater Creek discharges 

were based on the available long-term record at their respective 

gaging stations. 

Results of the step-backwater analyses were used to 

estimate water-surface elevation, extent of areal inundation, 

and hydraulic depth at each cross section. Area of inundation 

between adjacent cross sections, in acres, also was computed 

during each step-backwater analysis. The water-surface elevation computed at each cross section was used to generate watersurface profiles along the study reach. The computed watersurface elevation also was used to calculate the extent of areal 

inundation width, in feet, at each cross section, based on channel geometry and cross-sectional topography. Study reaches in 

this report are referenced from a downstream to upstream location, consistent with the direction in which the step-backwater 

analyses was performed. 

Hydraulic properties and cross-sectional geometry data for 

the stream channels and floodplains were determined from three 

sources: (1) field surveys, (2) detailed aerial 1-foot (ft) topographic contour maps (scale 1:200), or (3) previous step-backwater analyses by Johnson and others (1979) and Johnson and 

others (1980). Cross-section geometry of the channel and floodplain are defined by coordinates of both the horizontal distance 

from the left bank (looking downstream) and the corresponding 

land-surface elevation (fig. 2). The land-surface elevations of 

the first and last horizontal coordinate were selected to contain 

the highest water-surface elevation computed at each cross 

section. Water-surface elevations computed in this study generally represent more frequently occurring discharge conditions. 

Maximum water-surface elevations rarely approached the highest estimated design elevation of previous step-backwater analyses for a 100-yr flood.

A reference distance of each cross-section location, 

measured in miles upstream from the mouth, was assigned to 

each cross section. This reference distance also served as the 

identification number for each cross section. Selection of the 

cross-section location along a reach was determined based on 

characteristics that best represented existing field conditions. 

Cross sections were divided into subareas that represented 

existing hydraulic conditions. Manning’s roughness coefficient, 

n, was used to describe the degree of flow resistance of the 

channel and floodplain. The roughness coefficient is a function 

of bed material size, depth of flow, cross-sectional geometry, 

Figure 2. Example cross section showing Manning’s n-values, subareas, and water-surface elevation.
Methodology 5

DISCHARGE, IN CUBIC FEET PER SECOND

Hillsborough River at Morris Bridge (1984-2000)

Hillsborough River near Zephyrhills (1984-2000)

Blackwater Creek near Knights (1973-2001)

WithlacoocheeHillsborough Overflow

(1984-2000)

1

10

100

1,000

10,000

99.97 90 80 70 60 50 40 30 20 10 0.01

Hillsborough River above

Crystal Springs (1984-2000)

New River near Zephyrhills (1965-1974)

PERCENT OF TIME DISCHARGE WAS LESS THAN OR EQUAL

type and density of vegetation, and degree of channel meandering. For example, Manning’s roughness coefficients for the 

Hillsborough River ranged from 0.06 to 0.15 in the channel and 

from 0.11 to 0.23 in the floodplain. Roughness coefficients at 

cross sections ranged from sandy channels clear of vegetation 

and debris (0.06) to partially obstructed channels dominated by 

extensive aquatic vegetation, tree trunks, and exposed root 

systems (0.15). 

Percentile discharges used for the Hillsborough River, 

New River, and Blackwater Creek step-backwater analyses 

were determined from duration analysis curves for the selected 

record periods. Duration analysis curves are cumulative 

frequency curves that indicate the percentage of time that the 

daily mean discharge was less than or equaled a specific period 

of time (fig. 3). Percentile discharges for the Hillsborough 

River were based on the longest available concurrent period of 

record at the Morris Bridge, Zephyrhills, Crystal Springs, and 

Withlacoochee-Hillsborough Overflow gaging stations (17-yr 

period, 1984-2000); New River on the available period of 

record at the New River near Zephyrhills gaging station (10-yr 

period, 1965-1974); and the Blackwater Creek near Knights 

gaging station on three Hillsborough River gaging stations: 

Morris Bridge, Zephyrhills, and Withlacoochee-Hillsborough 

Overflow (29-yr period, 1973-2001) (table 1). Although much 

longer record periods may exist at some gaging stations, the 

accuracy of the step-backwater analysis is improved when 

multiple gaging stations along a reach are used with concurrent 

record. The period of record used in the analysis does not necessarily represent pre- or post-developmental discharge characteristics within the watershed. The degree of climatic and/or 

anthropomorphic impacts represented in the analyses may vary 

greatly depending upon the period of record selected.

Differences in the shape of duration analysis curves reflect 

variations in precipitation, drainage, and seepage conditions for 

the selected period at a gaging station. A comparison of the 

differences in the shape of duration curves for the Hillsborough 

River near Zephyrhills gaging station for the study period, 

1984-2000, is made using three selected periods (fig. 4.) These 

three examples used for comparison are: (1) the complete 

period of record, 1940-2001; (2) the period used for the New 

River analyses, 1965-1974; and (3) the Blackwater Creek analyses, 1973-2001. The shape of the duration curve for the 29-yr 

period (1973-2001) shows discharge conditions are similar to 

that of the overlapping 17-yr study period (1984-2000). The 

shape of the duration curve for the 62-yr period of record (1940-

2001), and the 10-yr period (1965-1974) however, indicates 

consistently higher flows for most percentiles, except during 

extreme conditions. Based on a break in slope of a double-mass 

curve analysis of the long-term streamflow record at the 

Zephyrhills gaging station, a measured reduction in flow 

occurred both in 1945 and 1970 (J.T. Trommer, U.S. Geological 

Survey, written commun., 2002). 

Figure 3. Duration curves of daily mean discharge at four upper Hillsborough River gaging stations for the concurrent 

period 1984-2000, the New River near Zephyrhills gaging station for the period 1965-1974, and the Blackwater Creek near 

Knights gaging station for the period 1973-2001.
6 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida DISCHARGE, IN CUBIC FEET PER SECOND

PERCENT OF TIME DISCHARGE WAS LESS THAN OR EQUAL

99.97 90 80 70 60 50 40 30 20 10 0.01

10

100

1,000

10,000

1940-2001 (62 years)

1984-2000 (17 years)

1973-2001 (29 years)

1965-1974 (10 years)

Table 1. Upper Hillsborough River watershed study gaging stations.

[mi2, square miles; ft3/s, cubic feet per second]

Map

No.

(fig. 1)

Station Station

No.1

Drainage

area

(mi2)

Continuous

period of

record

(water year2)

Instantaneous peak Minimum

flow

(ft3 (ft /s) 3/s) Date

1 Hillsborough River at Morris Bridge 02303330 375 1973-current year 5,200 12-15-1997 21

2 Hillsborough River near Zephyrhills 02303000 220 1940-current year 12,600 03-18-1960 27

3 Hillsborough River above Crystal Springs 02301990 82 1984-current year 2,700 12-13-1997 3.4

4 Withlacoochee-Hillsborough Overflow near 

Richland

02311000 314.2 1960-current year 1,880 03-19-1960 0

5 New River near Zephyrhills4 02303100 15 1965-1974 269 09-12-1964 0

6 Blackwater Creek near Knights 02302500 101.6 1951-current year 5,400 03-18-1960 0

7 Itchepackesassa Creek near Moriczville 02302280 48.5 2000-2002 673 09-16-2001 0

8 Itchepackesassa Creek near Knights5 02302260 34 1982-1998 660 09-07-1988 0

1USGS downstream station order identification number.

2Water year is a 12-month period from October 1 through September 30.

3Drainage area is variable at high flow based on stage of Withlacoochee and Hillsborough River.

4Gaging station discontinued after 1974.

5Crest-stage gage.

Figure 4. Comparison of duration curves of daily mean discharge for selected periods of record at the Hillsborough 

River near Zephyrhills gaging station.
Hillsborough River 7

Step-backwater analyses were performed for each of the 

selected percentile discharges, 10th, 50th, 70th, 80th, 90th, 95th, 

99.5th, and 99.97th, when hydraulic conditions permitted. 

Percentile is a value on a scale of 0 to 100 that indicates the 

percentage of a streamflow distribution that is equal to or less 

than a specific discharge. For example, based on a selected 

streamflow record period, the 90th percentile discharge indicates that 90 percent of the flows are equal to or less than a 

specific discharge and 10 percent of the flows are greater. The 

10th percentile discharge was omitted from the New River and 

Blackwater Creek analyses because flows were not sufficient to 

perform step-backwater analysis. The 99.97th percentile 

discharge was omitted from the New River analyses because of 

limited peak streamflow events during the record period (1965-

1974).

A second step-backwater analysis was performed using 10 

percent less discharge to estimate the effects on area of inundation that would result from a potential 10-percent surface-water 

withdrawal at each of the five river systems. A 10-percent 

reduction was applied to each of the selected percentile 

discharges. The analysis performed using 100 percent of the 

discharge was identified as the existing step-backwater analysis 

and the analysis performed using 10 percent less discharge was 

identified as the potential step-backwater analysis. Results of 

the existing and potential analyses were then compared to evaluate the effects of potential withdrawal. During the step-backwater analysis, the 10-percent reduction was implemented 

equally along each river reach. In actual practice, however, 

withdrawals from the river would not occur uniformly along 

the reaches, but at a specific location. The 10-percent reduction 

simulates flow conditions for the selected record period, which 

are in addition to any existing natural or anthropomorphic 

impacts.

Terminology used to simplify representation of results for 

this study was applied to all percentiles. The 10th percentile of 

daily mean discharge is identified as P10 discharge. The potential 10-percent withdrawal of the P10 discharge is identified as 

P10-10 discharge. Computation of the P10 and P10-10 discharges 

were omitted in the step-backwater analyses of New River, 

Blackwater Creek, Itchepackesassa Creek, and East Canal 

because of insufficient discharge to perform the analyses. 

Water-surface profiles were computed from one cross 

section to the next by solving the energy equation with an iterative procedure called the standard step method (Warner and 

Brunner, 1998b). The energy equation is written as follows:

Y2 + Z2 + (α2V2

2)/2g = Y1 + Z1 + (α1V12)/2g + he (1)

where: 

Y1, Y2 = depth of water at cross sections,

Z1, Z2 = elevation of the main channel inverts,

V1, V2 = average velocities (total discharge/total area flow), 

α1 , α2 = velocity weighting coefficients,

g = gravitational acceleration, and

he = energy head loss.

,

Energy losses were evaluated by friction and contraction/ 

expansion. Computation of the step-backwater analyses began 

at the most downstream cross section (initial cross section) of 

the study reach. At the initial cross section, the known watersurface elevation (gage height) was determined for each of the 

selected percentile discharges, based on the established stagedischarge relation at the gage. During the step-backwater analysis computation, once the energy balance between the first and 

second cross sections was achieved, the analysis "steps" to the 

next upstream cross section and computes an energy balance 

between the second cross section and the next upstream cross 

section. This process continues in an upstream direction until 

the energy balance between the final two cross sections has 

been achieved. 

Accuracy of the step-backwater analyses for the upper 

Hillsborough River was determined by comparing the rated 

(stage-discharge relation established at the gaging station) 

water-surface elevation with the computed (HEC-RAS) watersurface elevations at the three upstream gaged cross sections: 

Zephyrhills, Crystal Springs, and Withlacoochee-Hillsborough 

Overflow. The determination of accuracy was reduced, 

however, because of the limited number or absence of upstream 

gaged cross sections for New River, Blackwater and Itchepackesassa Creeks, and East Canal. Gaging stations with established 

stage-discharge relations used in this report are presented in 

table 1. Results of the step-backwater analyses were judged to 

be good when the computed water-surface elevation converges 

successfully within plus or minus 0.5 ft of the established stagedischarge relation at upstream gaged cross sections. The error 

range, plus or minus 0.5 ft, is based on the potential error range 

using the 1-ft aerial contour maps. 

Hillsborough River

The upper Hillsborough River study watershed covers 

parts of southeastern Pasco, western Polk, and northeastern 

Hillsborough Counties, and drains about 375 mi2 at the Morris 

Bridge gaging station (fig. 5). The 28-mi-long upper Hillsborough River study reach, from Morris Bridge Road to the 

Withlacoochee-Hillsborough Overflow at US 98, can be characterized as a broad, hardwood floodplain with low topographic 

relief and frequent, widespread, and prolonged areal inundation. 

The low-gradient channel along most of the middle and lower 

study reaches is moderately incised and slightly meandering. 

Most of the channel along the upper reach is either poorly 

defined or absent within a broad floodplain. Much of the channel is defined and controlled by karst outcropping. During high 

flows, an exchange of discharge may occur between the Hillsborough and Withlacoochee River watersheds at the Withlacoochee-Hillsborough Overflow. The contribution of flow from 

the Withlacoochee River is the primary source of water to the 

uppermost part of the Hillsborough River watershed during 

high-flow events. Overflow occurs about 25 percent of the time.
8 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

 

 

 

 

 

Chancey Road

HILLSBOROUGH COUNTY

PASCO COUNTY

PASCO COUNTYPOLK COUNTY

Morris Bridge Road (CR 579)

Central Ave

SR 39

Knights-Griffin Road (CR 582)

32.1

39.2

38.7

38.2

37.62

37.30

36.7

36.4

35.9

35.3

34.9

34.5

34.1

33.7 33

33

.4

3

.0

2.6

32.3

3

31.

1.8

4

30.9 30.6

30.3

30.0

29.6

29.1

32.8

29.49

28.9

43.3 43

42.7

42.5

42.4

41.9

41.6

41.2

41

40.7 40.4

4

3

0.2

9.8 39.5

41.64

42.35

46.41

46

45.7

45

45

.4

.1

44.9

44

44

.6

.3 44.1

43.6

43.8

46.2

46.3

46.6

48.4

48.2

48.18

48.1

48.0

47.86

47

4

.6

7.3

47.1

46.46

46.9

47.8

47.9

41.5

47.84

50.9

50.6

50.4

50.1

49.7

49.4

49.2

48.9

48.7

49.9 50.2

53

52.8

52.5 52.3 52.1

5

5

1.9

1.6 51.2

53.3 53.44

56.9

56.6

56.1

55.8

55.61

55.5

55.1

54.8

54.4

54.1

53.7 53.5

55.53

55.6

56.5

01234 5

012345

MILES

KILOMETERS

GAGING STATION With site number

30.6 CROSS SECTION With number

Tampa

Zephyrhills

Crystal

Springs

EXPLANATION

1

1 Hillsborough River at Morris Bridge (02303330)

2 Hillsborough River near Zephyrhills (02303000)

3 Hillsborough River above Crystal Srpings (02301990)

4 Withlacoochee-Hillsborough Overflow near Richland (02311000)

82ο15′ 82ο

10′

28ο

15′

28ο 05′

1

2

3

4

River

River

Hillsborough

Hillsborough

Cow House

Creek

54

54

98

301

301

Creek

Creek

Blackwater Itchepackesassa

East Canal

New

River

⎯ 

⎯ 

Base from U.S. Geological Survey digital data, 1:200,000, 1972

Albers Equal-Area Conic projection

Standard Parallels 29°30′, and central meridian −83°00′

42.38

Figure 5. Location of the Hillsborough River study reach and cross sections, and the Morris Bridge, Zephyrhills, Crystal 

Springs, and Withlacoochee-Hillsborough Overflow gaging stations, west-central Florida. (Location of the study area 

shown in figure 1).
Hillsborough River 9

The extent of areal inundation along the upper Hillsborough 

River can be large during relatively low discharges because 

of the low topographic relief. Four long-term USGS gaging 

stations were used in the step-backwater analyses of the 

upper Hillsborough River: (1) Morris Bridge at SR 579, 

(2) Zephyrhills at Hillsborough River State Park, (3) Crystal 

Springs at Crystal Springs Road and (4) WithlacoocheeHillsborough Overflow at US 98 (fig. 5 and table 1). 

Ground-water seepage discharging directly from numerous 

large and small spring vents and diffusely through channelbed 

sediments is a large source of flow in the river. In the upper Hillsborough River watershed, a substantial contribution of groundwater discharge is from the Upper Floridan aquifer, in addition to 

discharge contributions from both major and minor tributaries. 

Discharge from Crystal Springs, located about 2 mi west of the 

town of Crystal Springs, averaged 53.9 cubic feet per second 

(ft3/s), based on 467 measurements made since 1923.

The upper Hillsborough River channel and floodplain were 

delineated by the NWI and are classified predominately as lower 

perennial river and inland forested wetlands, respectively 

(Cowardin and others, 1979). The inland forested wetlands that 

are present along the broad Hillsborough River floodplain are 

predominately mixed cypress and hardwoods. The length of the 

study floodplain corridor, from Morris Bridge Road to the Withlacoochee-Hillsborough Overflow, is bounded by uplands.

The shape of the discharge duration curves for three of the 

Hillsborough River gages: Morris Bridge, Zephyrhills, and 

Crystal Springs, indicate similar flow characteristics (fig. 3). 

The absence of zero flow at these sites can be attributed to the 

(1) large size of the gaged drainage areas, (2) depth of the 

incised channel, and (3) ground-water discharge that provides a 

sustained baseflow. The steeply shaped discharge duration 

curve for the Withlacoochee-Hillsborough Overflow, however, 

indicates high variability in flow, in which zero-flow days 

occur approximately 75 percent of the time. Although the 

drainage area at the Morris Bridge (375 mi2) gaging station is 

155 mi2 larger than that at the Zephyrhills gaging station 

(220 mi2), duration curves show that discharge at Morris 

Bridge for the concurrent period (1984-2000) is similar or less 

during both moderate- to low-flow and extreme high-flow 

conditions. Both the P10 and the P99.97 percentile discharges 

calculated at the Morris Bridge gage were less than those calculated at the Zephyrhills gage. Three possible factors may 

account for a reduction in discharges at the Morris Bridge gage. 

First, diffuse and direct recharge losses occur from the channel 

and floodplain to the underlying aquifer. Additional recharge 

losses may also be the result of induced effects from groundwater pumping at area wellfields. Second, during high flows, 

discharge is naturally diverted from the Hillsborough River 

channel to the Cow House Creek distributary. This diversion 

allows water to discharge into the Tampa Bypass Canal or 

return to the Hillsborough River downstream from the Morris 

Bridge gage by way of a control structure. Third, losses from 

the large storage capacity of the broad floodplain along the 

reach between the Morris Bridge and Zephyrhills gages may 

effectively reduce discharge reaching the Morris Bridge gage. 

The step-backwater analyses were adjusted to correct for these 

losses by setting the initial discharges at the Morris Bridge gage 

and for all cross sections upstream to the Zephyrhills gaging 

station constant for the P10 and the P99.97 percentiles. This 

adjustment was done for the following two reasons. First, 

computation during the step-backwater analysis requires that 

the channel maintains or decreases discharge to achieve an 

energy balance between downstream and upstream cross 

sections. Second, the extent of areal inundation at the Morris 

Bridge gaging station, based on the water-surface elevation at 

the P10 and P99.97 percentile discharges, generally reflects the 

actual conditions at the gage.

Step-backwater analyses were performed using 122 cross 

sections along the 28-mi-long Hillsborough River study reach. 

The analyses began at the Morris Bridge gaging station 

(02303330) and terminated upstream of the WithlacoocheeHillsborough Overflow gaging station (02311000) (fig. 5). 

Initial water-surface elevations, based on the selected percentile 

discharges, were determined from the stage-discharge relation 

developed at the Morris Bridge gage. Hillsborough River 

reaches downstream of the Morris Bridge gage were not 

included in the study because of variable backwater effects 

from the Tampa Reservoir and high-flow diversion at S-155 to 

the Tampa Bypass Canal. 

During computation of the step-backwater analyses, 

discharges were proportionally reduced at selected upstream 

cross sections to adjust for the decrease in contributing drainage 

area (table 2). Water-surface profiles generated, for each 

percentile discharge, were based on the computed water-surface 

elevations at each of the 122 cross sections (fig. 6). Results of 

the step-backwater analyses were considered acceptable if the 

computed water-surface elevation converged within plus or 

minus 0.5 ft of the established stage-discharge relation (rated 

water-surface elevation) at the Zephyrhills, Crystal Springs, and 

Withlacoochee-Hillsborough Overflow gaging stations. The 

difference between the computed and the rated water-surface 

elevation for both the P99.5 and P99.97 discharges exceeded the 

0.5 ft accuracy criterion at the Zephyrhills gage. This difference 

was likely the result of uncertainty (effects of the diversion to 

Cow House Creek between the Morris Bridge and Zephyrhills 

gages) associated with percentile discharges and water-surface 

elevations at the Morris Bridge gage during high flows, which 

were previously discussed.

Topographic relief, channel gradient and depth, and 

discharge control the extent of areal inundation along the Hillsborough River. Many areas along the Hillsborough River have 

low topographic relief that result in widespread areal inundation 

for percentile discharges greater than P70. For example, the 

extent of inundation at the Withlacoochee-Hillsborough Overflow (cross section 56.9) can range from more than 5,000 ft at 

the P90 discharge (26.9 ft3/s) to about 6,700 ft at the P99.97

discharge (970 ft3/s) (fig. 7 and app. 1). The comparison of the 

maximum extent of areal inundation for each of the percentile 

discharges shown in figure 7 represents the maximum extent of 

left and right bank inundation, but does not show elevated areas 

along the cross section that may not be inundated. Therefore, 
10 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Table 2. Cross sections, drainage area, and percentile discharges used in step-backwater analyses 

based on the concurrent period 1984-2000 at Hillsborough River gaging stations: Morris Bridge, 

Zephyrhills, Crystal Springs, and Withlacoochee-Hillsborough Overflow.

[mi2, square miles; --, undetermined]

Cross section 

No.

Drainage 

area

(mi2)

Discharge (cubic feet per second)

P10 P50 P70 P80 P90 P95 P99.5 P99.97

128.9-32.8 375 59.0 121 200 300 535 881 2,950 5,840

33-34.9 371 59.0 121 199 298 531 875 2,946 5,840

35.3-36.7 321 58.9 115 184 273 483 803 2,898 5,840

37.3-37.62 -- 58.9 110 169 248 436 730 2,849 5,840

38.2 -- 58.9 110 169 238 418 703 2,831 5,840

239.2-340.4 234 58.9 110 169 229 400 676 2,814 5,840

40.7-42.38 220 58.8 105 154 222 387 656 2,800 5,840

442.4 218 58.3 104 153 220 383 650 2,775 5,787

42.5-44.9 105 13.3 26.8 43.5 64.2 183 374 1,537 3,419

45.1-45.4 95 12.0 24.2 39.4 58.0 166 338 1,390 3,093

45.7-46.0 88 11.2 22.6 36.7 54.1 154 315 1,295 2,882

546.2-48.4 82 10.4 20.9 34.0 50.1 143 292 1,200 2,670

48.7-50.6 69 8.8 17.6 28.6 42.2 120 246 1,010 2,247

50.9-52.1 56 7.1 14.3 23.2 34.2 97.7 199 820 1,823

52.3-53.5 49 6.2 12.6 20.4 30.1 85.6 175 755 1,604

53.7-54.4 42.5 5.0 11.0 18.0 26.0 74.0 151 690 1,384

54.8-55.53 29.6 3.2 6 9.4 14.3 52.6 141 680 1,206

55.6-55.8 16.8 0 0 1.3 2.6 31.4 129 670 1,028

56.1 15.5 0 0 1.2 2.5 30.5 126 660 999

656.5-56.9 14.2 0 0 1.2 2.5 26.9 122 660 970

1Hillsborough River at Morris Bridge gaging station.

2New River confluence.

3Hillsborough River near Zephyrhills gaging station.

4Blackwater Creek confluence.

5Hillsborough River above Crystal Springs gaging station.

6Withlacoochee-Hillsborough Overflow gaging station.
28.9

29.49

30.0

30.6

31.4

31.8

32.1

32.6

33.0

33.4

33.7

34.1

34.5

34.9

35.3

35.9

36.4

36.7

48.9

49.4

49.9

50.2

50.6

50.9

51.2

51.6

51.9

52.3

52.8

53.3

28 30 35 40 45 50 

2030405060708014

84

ELEVATION, IN FEET ABOVE NGVD OF 1929

DISTANCE, IN MILES ABOVE MOUTH

New River Confluence

Zephyrhills Gaging Station

Blackwater Creek Confluence

Big Ditch Confluence

Morris Bridge Gaging Station

Crystal Springs Gaging Station

US 301 Bridge

Bridge

Crystal Springs

SR 39 Bridge

Railroad Bridge

Rock Quarry

Bridge

Channel Bed

Cro

Maximum Elevationof Bridge Opening

HILLSBOROUGH RIVER-Morris Bridge to Withlachoochee-Hillsborough Overflow

Solid lidischaDashed discha

P99

P99

P9P9P8P7P5P1

37.30

37.62

38.2

38.7

39.2

39.5

40.2

40.7

41.2

41.5

41.9

42.4

42.7

43.3

43.8

44.1

44.6

45.1

45.7

46

46.3

46.9

47.3

47.7

48.0

48.4

40.4

41

Figure 6. Hillsborough River water-surface profiles for the selected percentile discharges and the effects of a 10-percent discharge withdrBridge to the Withlacoochee-Hillsborough Overflow gaging stations, based on the 17-year period 1984-2000.
12 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

32.1

39.2

38.7

38.2

37.62

37.30

36.7

36.4

35.9

35.3

34.9

34.5

34.1

33.7

33.4

33.0

32.6

32.3

31.8

31.4

30.9

30.6

30.3

30.0

29.6

29.1

32.8

CROSS SECTION

Hillsborough River Channel

Hillsborough River-Reach 1

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

Morris Bridge Gaging

Station (02303330)

Confluence with New River

P99.97

P99.5

P95

P90

P80

P70

P50

EXPLANATION

P10

Percentile

Discharges Flow

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

0 10,000 20,000 5,000 15,000 FEET

Figure 7. Extent of areal inundation along reaches 1-3 of the Hillsborough River study channel and 

floodplain for selected percentile discharge. 
Hillsborough River 13

CROSS SECTION

Hillsborough River Channel

Flow

Hillsborough River-Reach 2

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

46.6

46.41

46

45.7

45.4

45.1

44.9

44.6

44.3

44.1

43.6

43.3

43

42.7

42.5

42.4

42.38

41.9

41.6

41.2

41

40.7

40.4

40.2

39.8

39.5

39.2

41.64

42.35

43.8

46.2

46.3

48.4

48.2

48.18

48.1 48.0

47.86

47.6

47.3

47.1

46.46

46.9

47.8

47.9

US 301 Bridge

Zephyrhills Gaging

Station (02300000)

Crystal Springs Bridge

Gaging Station (02301990) 

SR 39 Bridge

Railroad Bridge

P99.97

P99.5

P95

P90

P80

P70

P50

EXPLANATION

P10

Percentile

Discharges

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

0 2,000 FEET 4,000 6,000 

Figure 7. Extent of areal inundation along reaches 1-3 of the Hillsborough River study channel and 

floodplain for selected percentile discharge. (Continued)
14 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

CROSS SECTION

Hillsborough River Channel Flow

Hillsborough River-Reach 3

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

US Highway 98 WithlacoocheeHillsborough River Overflow

Gaging station (02311000)

SR 54 Bridge

Railroad Bridge

Rock Quarry Crossing

Withlacoochee River Watershed 56.9

56.6

56.1

55.8

55.61

55.5

55.1

54.8

54.4

54.1

53.7

53.5

53

52.8

52.5

52.3

52.1

51.9

51.6

51.2

50.9

50.6

50.4

50.1

49.7

49.4

49.2

48.9

48.7

48.4

49.9

50.2

53.3

53.44

55.53 55.6

56.5

P99.97

P99.5

P95

P90

P80

P70

P50

EXPLANATION

P10

Percentile

Discharges

0 4,000 8,000 FEET

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

Figure 7. Extent of areal inundation along reaches 1-3 of the Hillsborough River study channel and 

floodplain for selected percentile discharge. (Continued)
New River 15

because of this difference, the actual calculated extent of areal 

inundation of the 122 cross sections presented in appendix 1 

may not agree with the width shown in figure 7. This difference 

is illustrated by the cross sections shown in figure 8a and 8b.

The actual P99.97 discharge inundation width for cross section 

30 is 14,730 ft (app. 1), however, the width of inundation 

between left and right bank is about 18,000 ft (fig. 7). Because 

no non-inundated areas exist within the cross section in figure 

8b, both the actual inundation width and the inundation width 

between left and right banks are the same. All figures in this 

report showing extent of areal inundation conform to this 

convention, and the appendices present the actual calculated 

width of inundation. 

During the 17-yr study period, areal inundation along the 

Hillsborough River for the selected percentile discharges was 

highly variable from year to year (table 3). The number of days 

at the P50 discharge ranged from a minimum of 42 days (2000) 

to a maximum of 320 days (1984), with an average of 195 days 

per year (days/yr). The P99.97 discharge, however, occurred for 

2 days and only during 1998. During the study period, the P10, 

P50, P70, and P80 discharges occurred annually, with frequencies 

ranging from 1 to 366 days/yr. Whereas, the P90 and P95 

discharges occurred during 15 and 13 yrs of the 17-yr study 

period, for an average of 37 and 16 days/yr, respectively. The 

P99.5 discharge occurred in less than one-half of the effected 

study years for an average of 2 days/yr. 

The extent of areal inundation and an estimated mean 

number of days per year that selected percentile discharges will 

occur at two example Hillsborough River cross sections are 

compared in figure 8. The inundation width at cross section 30 

(fig. 8a) can exceed 3,800 ft during the P90 discharge, which 

occurs on average 37 days/yr. In contrast, the inundation width 

at cross section 41 (fig. 8b) for the P90 discharge is less than 400 ft 

during that same period. Limited floodplain inundation along 

low-lying areas of the Hillsborough River study reach occurs 

during the P80 percentile discharge. During the study period, 

inundation at the P80 discharge occurs an average of 72 days/yr. 

Extensive inundation of the floodplain occurs at both the P99.5

and P99.97 percentile discharges; however, those discharges 

occurred in only 7 years and 1 year, respectively, in the 17-yr 

study period for an average of 2.2 and 0.1 days. 

During the step-backwater analyses of the eight percentile 

discharges, hydraulic depths were computed at each cross 

section (app. 2). In areas where the upper Hillsborough River 

study reach channel is not well defined or incised, hydraulic 

depths can be considered an estimate of the floodplain depth 

only. Hydraulic depths generally are greatest at locations where 

reaches contract due to bridges, culverts, control structures, or 

natural topography. Comparisons of hydraulic depths are 

shown in example cross sections 30 and 41 (fig. 8a,b). Differences in hydraulic depths at the example cross sections may be 

attributed to the effect of topography, channel configuration, or 

slope. Mean hydraulic depths along the Hillsborough River 

study reach channel and floodplain ranged from approximately 

1.4 (P10) to 3.1 (P99.97) ft (app. 2).

Inundated acreage along the Hillsborough River channel 

and floodplain was determined by summing the computed 

water-surface area between adjacent cross sections (app. 3). 

Area of inundation ranged from approximately 277 (P10) to 

16,350 (P99.97) acres (fig. 9). The inundated area at the P90

discharge (about 2,800 acres) generally is confined to within the 

channel banks. Limited floodplain inundation, however, can 

occur for low-lying areas at the extreme lower and upper ends 

of the study reach during the P90 discharge. The inundated area 

at the P95, P99.5, and P99.97 discharges predominately include the 

floodplain at 4,600, 12,000, and 16,350 acres, respectively.

Loss of inundated area by a potential 10-percent discharge 

withdrawal from the Hillsborough River was estimated for each 

of the eight percentile discharges by comparing the difference 

between the existing step-backwater analyses (100 percent of 

the discharge) and the potential step-backwater analyses 

(discharges reduced by 10 percent). Except for differences in 

discharge and beginning water-surface elevations, identical 

hydraulic and geometric data were used for both step-backwater 

analyses. Accuracy of the potential step-backwater analyses, 

based on the difference between rated and computed watersurface elevations at the three upstream gages, were similar to 

the existing step-backwater analyses. All profiles converged 

successfully, except the P99.5 and P99.97 discharges at the 

Zephyrhills gage. The difference in water-surface profiles from 

the effects of a 10-percent discharge withdrawal are compared 

in figure 6. The water-surface elevation computed in the potential step-backwater analyses is lower at each cross section, thus 

limiting the extent of areal inundation. Based on the difference 

between the existing and potential step-backwater analyses, the 

estimated non-inundated area affected by surface-water withdrawals ranged from 7.0 (P10) to 940 (P99.5) acres (fig. 10 and 

app. 4). The largest percentage loss (16 percent) of inundated 

area (99 acres), however, occurred at the P70 discharge (fig. 9). 

An example of inundated area loss is compared in figure 10

between the P95 and P95-10 discharge analyses. The greatest 

losses between the P95 and P95-10 discharges were limited to a 

few topographically low-lying cross sections. Most of the losses 

occur uniformly at cross sections along much of the floodplain. 

Areas within the cross section having higher topographic relief 

may not be inundated. Cross section 30 in figure 8a shows an 

example of a non-inundated areas. Based on the record period 

(1984-2000), the P95 discharge occurred at least once a year 

during 13 yrs of the 17-yr study period for an average of 16 days 

(table 3).

New River

New River, a major tributary to the Hillsborough River, 

drains about 19.5 mi2 in eastern Pasco and Hillsborough Counties (figs. 1 and 11). The 8.46-mi-long north-south trending 

study reach begins at the confluence with the Hillsborough 

River and ends approximately 1.5 mi upstream of SR 54. The 

study channel generally is well defined and moderately incised. 
2,000 2,500 3,000 3,500 4,000 4,500 

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET ABOVE NGVD OF 1929 HILLSBOROUGH RIVER-Cross section 41 

P99.97, 5.2

P99.5, 3.3

P95, 2.4

P90, 2.1

P80, 2.1

P70, 2.3

P50, 2.8

P10, 2.1

Hillsborough River Channel

Water Surface

Floodplain

HILLSBOROUGH RIVER-Cross section 30

P99.97, 3.4

P99.5, 2.3

P95, 1.6

P90, 1.2

P80, 1.0

P70, 0.8

P50, 0.9

P10, 3.0

Water Surface

Floodplain

Island at or above P90

Island above P95

P70, 0.83 Percentile Discharge, H

P70-10 10-Percent Discharge R

EXPLANATION

P70, 2.3 Percentile Discharge, Hydraulic Depth

P70-10 10-Percent Discharge Reduction

30

35

40

45

50

55

20

25

30

35

40

45

500 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 

DISTANCE FROM LEFT BANK, IN FEET

Hillsborough River Channel

EXPLANATION

P10 322 P50 195 P70 103 P80 72 P90 37 P95 16 P99.5 2.2 P99.97 0.1 

(a)

(b)

Percentiledischarge

Mean num

days/y

HILLSBOROUG

NEAR ZEPHYRHILLS G

BASED ON 17 YE

Figure 8. Estimated extent and frequency of areal inundation and hydraulic depth at Hillsborough River cross sections (a) 30 and (b) 41 for 

the selected percentile discharges and the potential 10-percent withdrawal in discharge, based on the 17-year period 1984-2000.
New River 17

The shape of the watershed is elongated. Land use is predominately mixed agricultural and rural residential. The New River 

channel is delineated on maps by the NWI as predominately 

bounded by either inland forested wetlands or uplands 

(Cowardin and others, 1979). 

Percentile discharges used for the step-backwater analyses at New River were based on the continuous 10-yr (1965-

1974) period at the New River near Zephyrhills gaging station 

(02303100) (table 1). The stage-discharge relation developed at 

the Zephyrhills gaging station was used to compare the 

computed water-surface elevations with the rated water-surface 

elevations at the gaged cross section. Extremes in daily mean 

discharge during the 10-yr period, ranged from zero (many 

years) to 269 ft3/s (1964). Step-backwater analyses were 

performed using 66 cross sections along the 8.46-mi length of 

the New River study reach. The analyses were based on six of 

the percentile discharges (P50, P70, P80, P 90, P95, and P99.5). The 

P10 discharge was omitted because of insufficient discharge to 

perform the analysis, and the P99.97 discharge was not used 

because of insufficient high-flow record to calculate percentile. 

Water-surface profiles for the six selected percentile discharges 

were generated from the computed water-surface elevations at 

each of the 66 cross sections (fig. 12). The initial water-surface 

elevations at the mouth of New River were derived from the 

water-surface elevations computed at the confluence from a 

step-backwater analysis of the Hillsborough River for the same 

10-yr period. Initial discharges at the mouth and at selected 

cross sections along the New River study reach were estimated 

based on the proportionality of drainage area with the 

Zephyrhills gaging station (table 4). 

Table 3. Approximate number of days daily mean discharge equaled or 

exceeded the selected percentile discharges at the Hillsborough River 

near Zephyrhills gage, 1984-2000.

[P10, 10th percentile discharge]

Year

Number of days per year

P10 P50 P70 P80 P90 P95 P99.5 P99.97

1984 366 320 188 121 42500

1985 287 79 68 59 41 17 2 0

1986 365 276 144 88 36900

1987 365 293 103 65 29 15 4 0

1988 366 216 111 83 46 17 6 0

1989 344 264 78 49 24 10 0 0

1990 356 129 47 19 0000

1991 237 127 85 61 45 14 0 0

1992 295 107 70 50 16000

1993 328 193 117 72 34200

1994 305 157 93 76 48 27 1 0

1995 365 302 163 123 76 44 1 0

1996 362 290 175 112 56 19 0 0

1997 292 80 46 35 13630

1998 365 303 212 182 146 96 20 2

1999 319 141 41 23 5000

2000 164 42 7 1 0000

Mean 322 195 103 72 37 16 2.2 0.1

Maximum 366 320 212 123 146 96 20 2

Minimum 164 42 7 1 0 0 0 0
18 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

10th 50th 70th 80th 90th 95th 99.5th 99.97th

PERCENTILE DISCHARGE

TOTAL INUNDATED AREA, IN ACRES

Hillsborough River

Area Inundated Area Inundated After a 10-Percent

Reduction in Discharge

Lines Indicated Interpolated Area

Percent Inundated

Area Decreased

2 % 6 % 16 % 13 %

11 %

10 %

8 %

5 %

The approximate number of days a percentile discharge 

occurred at the New River near Zephyrhills gaging station 

during the study period is shown in table 5. Based on the New 

River near Zephyrhills gage, most percentile discharges at or 

below the P90 discharge occur annually. The P99.5 discharge 

occurred during 3 yrs of the 10-yr study period, for an average 

of 0.8 days.

The New River channel generally confines most 

discharges within its banks at or below the P90 discharge. 

Calculated maximum floodplain inundation can exceed 2,900 ft 

(cross section 1.83) during the P99.5 discharge (fig. 13 and 

app. 5). Mean inundation width for the 66 cross sections along 

the reach ranged from about 17 (P50) to 563 P99.5) ft. Mean 

inundation at the P90 discharge (67 ft) was considered the width 

for a bankfull channel. An approximate twofold increase in 

mean inundation occurs from the P80 (31.9 ft) to the P90 (67 ft) 

discharge, and more than a three-fold increase from P95 (132 ft) 

to the P99.5 (563 ft).

Hydraulic depths were computed at each cross section 

during the step-backwater analyses for each of the percentile 

discharges. Computed hydraulic depths for example cross 

section 1.17 are shown in figure 14. The mean hydraulic depth 

along the New River study reach channel and floodplain ranged 

from approximately 0.2 (P50) to 1.6 (P99.5) ft (app. 6). 

Area of inundation along New River was computed for 

each percentile discharge (app. 7). Total acreage of inundated 

area along the New River channel and floodplain was calculated 

by summing the computed water-surface area between adjacent 

cross sections for each percentile discharge. Area of areal 

inundation ranged from 17.3 (P50) to 489 (P99.5) acres (fig. 15).

The inundated area at the P95 discharges was 98.2 acres, which 

generally includes the bankfull channel and a limited number 

of low-lying cross sections. The inundated area at the P99.5 

discharge, however, predominately includes the floodplain at 

489 acres.

Potential loss of inundated area was estimated for each 

percentile discharge by comparing the difference between the 

existing step-backwater analyses (100 percent of the discharge) 

and the potential step-backwater analyses (discharges reduced 

by 10 percent). Except for differences in discharge and beginning water-surface elevations, identical hydraulic and geometric data were used for both step-backwater analyses. The 

difference in water-surface profiles from the effects of a 10-

percent discharge withdrawal are compared in figure 12. Based 

on the difference between the two step-backwater analyses, the 

estimated non-inundated area affected by surface-water withdrawals ranged from 0.2 (P50) to 58.9 (P99.5) acres (app. 8). The 

greatest effect of surface-water withdrawals to inundated area 

occurs between the P99.5 and P99.5-10 discharges, with a loss of 

58.9 acres or 12 percent (fig. 15). An example of inundated area 

Figure 9. Estimated total inundated area along Hillsborough River for existing conditions and for a potential 10-percent 

discharge withdrawal, and percentage of inundated area decreased by a potential 10-percent discharge withdrawal for 

each of the selected percentile discharges.
New River 19

32.1

39.2

38.7

38.2

37.62

37.30

36.7

36.4

35.9

35.3

34.9

34.5

34.1

33.7

33.4

33.0

32.6

32.3

31.8

31.4

30.9

30.6

30.3

30.0

29.6

29.1

32.8

CROSS SECTION

Flow

Hillsborough River Channel

Hillsborough River-Reach 1

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

Morris Bridge Gaging

Station (02303330)

Confluence with New River

P95

P95-10

EXPLANATION

 Percentile

Discharges

Abandoned roadbed crossing

875-788 730-657 803-723 703-633 881-793

DISCHARGE, IN CUBIC FEET PER SECOND P95 - P95-10

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

P95

P95-10

676-608

0 10,000 20,000 FEET 5,000 15,000

Figure 10. Example of extent of areal inundation along reaches 1-3 of the Hillsborough River study 

channel and floodplain for the P95 (existing conditions) and the P95-10 (potential 10-percent discharge 

withdrawal) discharges.
20 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

CROSS SECTION

Hillsborough River Channel Flow

Hillsborough River-Reach 2

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

Railroad Bridge

P95

P95-10

EXPLANATION

Percentile

Discharges

SR 39 Bridge

0 5,000 10,000 FEET

46.6

46.41

46

45.7

45.4

45.1

44.9

44.6

44.3

43.6

43.3

43

42.7

42.5

42.4

42.38

41.9

41.6

41.2

41

40.7

40.4

40.2

39.8

39.5

39.2

41.64

42.35

46.2

46.3

48.4

48.2 48.18

48.1

48.0

47.86

47.6

47.3

47.1

46.46

46.9

47.8

47.9

US 301 Bridge

Zephyrhills Gaging

Station (02300000)

Cyrstal Springs Bridge

Gaging Station (02301990) 

656-590

315-284 338-304 676-608

DISCHARGE, IN CUBIC FEET PER SECOND P95 - P95-10 650-585

374-337 292-263

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

P95

P95-10

Figure 10. Example of extent of areal inundation along reaches 1-3 of the Hillsborough River study 

channel and floodplain for the P95 (existing conditions) and the P95-10 (potential 10-percent discharge 

withdrawal) discharges. (Continued)
New River 21

CROSS SECTION

Hillsborough River Channel Flow

Hillsborough River-Reach 3

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

US Highway 98 WithlacoocheeHillsborough River Overflow

Gaging station (02311000)

SR 54 Bridge

Railroad Bridge

Rock Quarry Crossing

Withlacoochee River Watershed

56.9

56.6

56.1

55.8

55.61

55.5

55.1

54.8

54.4

54.1

53.7

53.5

53

52.8

52.5

52.3

52.1

51.9

51.6

51.2

50.9

50.6

50.4

50.1

49.7

49.4

49.2

48.9

48.7

48.4

49.9

50.2

53.3

53.44

55.53 55.6

56.5

P95

P95-10

EXPLANATION

Percentile

Discharges

151-136 175-158 141-127

DISCHARGE, IN CUBIC FEET PER SECOND P95 - P95-10

199-179 246-221

129-116 126-113 122-110

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

P95

P95-10

0 4,000 8,000 FEET

Figure 10. Example of extent of areal inundation along reaches 1-3 of the Hillsborough River study channel 

and floodplain for the P95 (existing conditions) and the P95-10 (potential 10-percent discharge withdrawal) 

discharges. (Continued)
22 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

 

0 1 MILE

0 1 KILOMETER

Chancey Road

PASCO COUNTY

HILLSBOROUGH COUNTY

Morris Bridge Road (CR 579)

New River

3.85

3.83

3.51

3.27

2.84

2.43

2.10

1.99

1.92

1.88 1.81

1.62

1.49

1.39

1.29

1.22

1.17 0.98

0.91

0.77

0.72

0.58

0.46

0.36

0.16

0.02

1.12

2.21

6.41

6.92

6.39

5.89

5.87

4.53

4.55

4.52

4.21

4.02

3.22

8.46

8.17

8.05

7.87

7.68

7.58

7.44

7.27

6.96

6.81

6.43

6.29

6.15

5.92

5.60

5.36

5.07

4.87

7.98

3.82

6.94

Zephyrhills Gaging

Station (02303100)

EXPLANATION

GAGING STATION— With site number

CROSS SECTION— With number

2.84

Branchton

82ο 82 15′ ο

17′

28ο

14′

28ο09′

Creek

 Road

 

Hillsborough River

54

301

Base from U.S. Geological Survey digital data, 1:200,000, 1972

Albers Equal-Area Conic projection

Standard Parallels 29°30′, and central meridian −83°00′

Figure 11. Location of the New River study reach and cross sections, and 

the Zephyrhills gaging station, west-central Florida. (Location of the study 

area shown on figure 1).
0123 45 6 7 

304050607080

90

P99.5 

P95 P90 P80 P70 P50 

ELEVATION, IN FEET ABOVE NGVD OF 1929

NEW RIVER

DISTANCE, IN MILES ABOVE MOUTH

Morris Bridge Road

Gaging Station

Culvert

Creek Road

Chancy Road

Channel Bed

Cross 

Maximum Elevationof Bridge Opening

Solid lines inddischarge proDashed lines discharge wit

 Cr

Mouth, Confluence with Hillsborough River

0.02

0.36

0.46

0.58

0.72

0.91

1.12

1.22

1.39

1.49

1.62

1.81

1.92

2.10

2.21

2.43

2.84

3.22

3.51

3.82

4.02

4.21

4.52

4.87

5.07

5.36

5.60

5.87

6.15

6.29

6.39

6.81

6.92

0.16

Farm Bridge

Bridge

Destroyed

EXPLA

SR 54

Culvert

Figure 12. New River water-surface profiles for six selected percentile discharges and the effects of a 10-percent discharge withdrawal, fro

section 8.46, based on the 10-year period 1965-1974. 
24 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Table 4. Cross sections, drainage area, and percentile discharges used in stepbackwater analyses based on the period 1965-1974 at the New River near 

Zephyrhills gaging station.

[mi2, square miles]

Cross section 

No.

Drainage 

area

(mi2)

Discharge (cubic feet per second)

P50 P70 P80 P90 P95 P99.5

10.02-0.46 19.5 0.7 5.1 12.6 26.3 53.0 269

0.58-1.83 17.5 0.6 4.5 11 23 46.4 241

21.85-1.83 15 0.5 3.8 9.4 19.7 39.8 207

5.36-6.96 13 0.4 3.3 8.2 17.1 34.5 179

7.27-8.46 6 0.2 1.5 3.8 7.9 15.9 82.6

1Confluence of Hillsborough River and New River.

2New River near Zephyrhills gaging station (02303100) at Morris Bridge Road.

Table 5. Approximate number of days daily mean discharge equaled or 

exceeded the selected percentile discharges at the New River near 

Zephyrhills gaging station, 1965-1974.

[P50, 50th percentile discharge]

Year

Number of days per year

P50 P70 P80 P90 P95 P99.5

1965 71 31 21 17 15 6

1966 189 63 35 19 8 0

1967 62 29 18 13 7 1

1968 115 55 38 27 12 0

1969 107 47 33 22 12 0

1970 153 61 37 22 12 1

1971 41 7 0 0 0 0

1972 24 0 0 0 0 0

1973 87 21 9 3 0 0

1974 86 28 18 12 5 0

Mean 94 34 21 14 7.1 0.8

Maximum 189 63 38 27 15 6

Minimum 21 0 0 0 0 0
New River 25

P99.5

P95

P90

P80

P70

P50

EXPLANATION

Percentile

Discharges

0 1,000 2,000 FEET

CROSS SECTION

New River Channel

New River

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

Confluence with Hillsborough River

Flow

Reach 1 Reach 2

3.85

3.83

3.51

3.27

2.84

2.43

2.10

1.99

1.92 1.88

1.81

1.62

1.49

1.39

1.29

1.22

1.17

0.98

0.91

0.77

0.72

0.58

0.46

0.36

0.16

0.02

1.12

2.21

6.41

6.92

6.39

5.89

5.87

4.53

4.55

4.52

4.21

4.02

4.52

3.22

8.46

8.17

8.05

7.87

7.68

7.58

7.44

7.27

6.96

6.81

6.43

6.29

6.15

5.92

5.60

5.36

5.07

4.87

7.98

Morris Bridge Gaging

Station (02303100)

Creek Road

Bridge

Bridge

Chancy Road Bridge

SR 54

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

Figure 13. Extent of areal inundation along reaches 1 and 2 of the New River study channel and floodplain for 

selected percentile discharges.
1,000 2,000 3,000 

46

48

50

52

54

56

58

DISTANCE FROM LEFT BANK, IN FEET

NEW RIVER-Cross Section 1.17 Lookin

P90, 0.9

P80, 0.8 P70, 0.5 P50, 0.2

New River Channel

P95, 1.1 Percentile Discharge, Hyd

P95-10 10-Percent Discharge Red

EXPLANATION

P99.5, 0.7 Water Surface

P95, 1.1

Land-Surface Elevation

 Percentile Mean number Occurrence  discharge days/yr (no. years) 

P50 94 10P70 34 9 P80 21 8 P90 14 8P95 7.1 7P99.5 0.8 3

NEW RIVER NEAR ZEPHYRHILLS GAGING STATION

BASED ON 10-YEARS RECORD

ELEVATION, IN FEET ABOVE NGVD OF 1929

Figure 14. Estimated extent and frequency of areal inundation and hydraulic depth at New River cross section 1.17 for six of the selec

discharges and the potential 10-percent withdrawal in discharge, based on the 10-year period 1965-1974.
Blackwater Creek 27

New River

1.2 %

2.8 %

4.6 %

2.2 %

9.9 %

Area Inundated

Area inundated after a 10-percent reduction in discharge

Lines indicated interpolated area

Percent Inundated

Area Decreased

12.0 %

TOTAL INUNDATED AREA, IN ACRES

PERCENTILE DISCHARGE

50th 70th 80th 90th 95th 99.5th

0

50

100

150

200

250

300

350

400

450

500

loss was compared between the P99.5 and P99.5-10 discharges 

(fig. 16). Losses between the P99.5 and P99.5-10 discharges generally are uniform along the reaches, except at a limited number 

of low-lying cross sections. Areas within the cross section 

having higher topographic relief may not be inundated. Cross 

section 1.17 in figure 14 shows an example of a non-inundated 

areas. Based on the record period (1965-1974), the P99.5

discharge occurred during 3 yrs of the 10-yr study period, for 

an average of 0.8 days/yr (table 5).

Blackwater Creek

Blackwater Creek, the largest tributary to the Hillsborough River, drains about 113 mi2 in northwestern Polk and 

northeastern Hillsborough Counties (figs. 1 and 17). Blackwater Creek generally flows in a westerly direction for 17.2 mi, 

from the headwaters northwest of the city of Lakeland to its 

confluence with the Hillsborough River. Approximately the 

upper two-thirds of the Blackwater Creek study reach has been 

channelized to improve drainage. The channel along the lower 

one-third of the study reach is predominately natural, from the 

mouth to an area directly downstream of SR 39. Much of the 

channel is moderately incised and well defined, containing 

most low to moderate discharges within the banks. The width 

of the floodplain is relatively narrow and generally uniform in 

width along the length of the channel. Much of the Blackwater 

study reach is delineated on NWI maps as inland forested 

wetlands, except for the upper one-quarter, which is delineated 

as upland (Cowardin and others, 1979). The Blackwater Creek 

watershed has a drainage area of approximately 101.6 mi2 at the 

Blackwater Creek near Knights gaging station (02302500), 

located 0.2 mi upstream of SR 39. Discharge data have been 

collected by the USGS continuously at the Knights gage since 

1951. Extremes in daily mean discharge at the gaging station for 

the record period (1951-2002) ranged from zero (many days) to 

5,400 ft3/s (1960). 

Step-backwater analyses were performed using 114 cross 

sections along the Blackwater Creek study reach, from the 

confluence with the Hillsborough River to cross section 16.6 

(0.5 mi west of Galloway Road) (fig. 17). The analyses for 

Blackwater Creek included the P50, P70, P80, P 90, P95, P99.5, and 

P99.97 percentile discharges, based on the 29-yr period, 1973-

2001, at the Knights gaging station. The analysis for the P10 

percentile discharge was not performed because of insufficient 

discharge at the Knights gaging station (fig. 3). Discharges used 

in the analyses were reduced at selected cross sections, based on 

proportionality of contributing drainage area with that of the 

Knights gaging station (table 6). Initial water-surface elevations 

at the mouth of Blackwater Creek were estimated from the 

water-surface elevations computed at the confluence with 

Blackwater Creek during a Hillsborough River analysis (cross 

section 42.4), based on the same 29-yr period. 

Figure 15. Estimated total inundated area along New River for existing conditions and for a potential 10-percent 

discharge withdrawal, and percentage of inundated area decreased by a potential 10-percent discharge withdrawal for 

each of the selected percentile discharges.
28 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

0 1,000 2,000 FEET

CROSS SECTION

New River Channel

New River

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

Confluence with Hillsborough River

Flow

Reach 1 Reach 2

3.85

3.83

3.51

3.27

2.84

2.43

2.10

1.99

1.92

1.88

1.81

1.62

1.49

1.39

1.29

1.22

1.17

0.98

0.91

0.77

0.72

0.58

0.46

0.36

0.16

0.02

1.12

2.21

4.52

4.21

4.02

3.22

6.41

6.92

6.39

5.89

5.87

4.53

4.55

4.52

8.46

8.17

8.05

7.87

7.68

7.58

7.44

7.27

6.96

6.81

6.43

6.29

6.15

5.92

5.60

5.36

5.07

4.87

7.98

Morris Bridge Gaging

Station (02303100)

Creek Road

Bridge

Bridge

Chancy Road Bridge

SR 54

P99.5

P99.5-10

EXPLANATION

Percentile

Discharges

53-47.7 39.8-35.8

DISCHARGE, IN CUBIC FEET PER SECOND P95 - P95-10

46.4-41.8

15.9-14.3

DISCHARGE, IN CUBIC FEET PER SECOND P95 - P95-10

34.5--31 39.8-35.8

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections. P99.5-10

P99.5

Figure 16. Example of extent of areal inundation along reaches 1 and 2 of the New River study channel and floodplain for 

the P99.5 (existing conditions) and the P99.5-10 (potential 10-percent discharge withdrawal) discharges.
 

Hillsborough

Creek

East Canal

HILLSBOROUGH COUNTY

POLK COUNTY

River

Central Ave

012 3

0123

MILES

KILOMETERS

PASCO COUNTYHILLSBOROUGH COUNTY

Knights GagingStation (02302500)

Knights-Griffin Road (CR 582)

6.44

6.06

5

5

.90

.82

5.49 5.34

5.19

4.85

4.65

4.36

3

4.14

.95

3.78

3.59

3.27

3.02

2.82

2.37

2.04

1.80

1.55

1.34

1.14

0.93

.68

.43 .28

.01

.15

.59

0.90

0.91

5.76

5.93

7.92

7.71

7.45

6.97

7.69

9.00 8.84

8.59

8.34

8.07

8.74

8.80

11.89

11.63

11.07

10.79

10.48

10.25

9.87

9.52

9.27

10.41

11.54 11.44

13.28

13.21

12.98

12.72

12.50

12.31 12.39

12.55

12.90

13.02

14.33

14.08

13.94

13.67

13.58

13.74

13.77

13.91

14.23

15.45

15.22

14.80

14.64

15.65

15.70

15.03 15.15

Walker Road

EXPLANATION

GAGING STATION

—

 With site numberCROSS SECTION

—

 With number

3.02

Plant City

Crystal Springs

82ο10′ 

28ο10′

28ο03′

Itch epacke sassa

Blackwater Creek

39

301

Base from U.S. Geological Survey digital data, 1:200,000, 1972Albers Equal-Area Conic projectionStandard Parallels 29°30′, and central meridian −83°00′

Figure 17. Location of the Blackwater Creek study reach and cross sections, and the Knights gaging station, west-central Florida. (Location of 

figure 1).
30 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Water-surface profiles were generated during the stepbackwater analyses from the computed water-surface elevation 

at each of the 114 cross sections (fig. 18). In addition to the 

water-surface profiles, results of the computed water-surface 

elevations were used to determine the extent of areal inundation, acreage of inundation, and hydraulic depth at each cross 

section.

The number of days per year a percentile discharge 

occurred at the Knights gaging station was variable. The P50, 

P70, P80, and P 90 discharges occurred every year, and ranged 

from 1 (P 90) to 305 (P50) days (table 7). The P99.5, and P 99.97 

discharges were rare during the 29-yr period, occurring during 

only 8 yrs and 1 yr, respectively, with mean durations of 1.1 and 

less than 0.1 days, respectively. 

Maximum floodplain inundation can exceed 5,900 ft 

(cross section 5.89) during the P99.97 discharge (fig. 19 and 

app. 9). Mean inundation width for the 114 cross sections range 

from 36 (P50) to 833 (P99.97) ft. The incised channel generally 

confined most discharges at or below the P95 discharge. Mean 

inundation width along the study channel at the P95 discharge 

(105 ft) may approximate the bankfull channel width. The 

largest increase in extent of mean inundation occurs during the 

transition from channel to floodplain at the P99.5 (364 ft) to the 

P99.97 (833 ft) discharge. 

Percentile discharges at or below the P95 discharge were 

confined within the channel and those above inundate the floodplain (cross section 9.0, fig. 20a). At cross section 9.0, the P95 

discharge was confined within the channel at a width of approximately 44 ft. The P95 discharge occurred during 27 yrs of the 

29-yr study period, for an average of 20 days/yr (table 7). The 

moderately incised channel contains flow for most percentile 

discharges. At the P99.5 discharge, however, widespread inundation occurs in the study reach floodplain during 8 yrs of the 

29-yr study period, for an average of approximately 1.1 days/yr.

Maximum hydraulic depths for Blackwater Creek ranged 

from 2.5 (P50) to 9.6 (P99.97) ft , and a mean depth of 1.5 (P95

discharge) ft , which generally was confined to the channel 

(app. 10). Hydraulic depths along Blackwater Creek typically 

are deepest in the reach above the mouth, because the channel 

is more incised, has a steeper gradient, and greater contributing 

drainage area in this part of the study reach. Conversely, the 

upper reaches are generally poorly incised within an area of low 

relief. 

Table 6. Cross sections, drainage area, and percentile discharges used in step-backwater analyses based on 

the period 1973-2001 at Blackwater Creek near Knights gaging station.

[mi2, square miles]

Cross section 

No.

Drainage 

area 

(mi2)

Discharge, in cubic feet per second

P50 P70 P80 P90 P95 P99.5 P99.97

10.01-0.91 113.0 23.4 47.5 82.7 178 334 1,270 3,003

0.93-1.55 112.7 23.3 47.4 82.5 177 333 1,267 2,995

1.80-2.04 111.5 23.1 46.9 81.8 176 330 1,255 2,967

2.37-3.02 110.6 22.9 46.5 81 174 327 1,243 2,939

3.27-4.14 107.4 22.3 45.3 78.9 170 317 1,188 2,854

4.36-4.85 105.0 21.7 44.1 76.9 165 310 1,180 2,790

5.19-5.93 103.2 21.4 43.4 75.6 163 305 1,161 2,745

26.06-6.44 101.6 21 42.7 74.4 160 300 1,124 2,700

6.97-7.71 97.2 20.1 40.9 71.3 153 287 1,094 2,586

37.92-7.92 93 19.2 39.1 68.1 146 275 1,045 2,471

8.07-9.00 36 7.4 16.1 26.4 56.7 106 405 957

9.27-10.41 29 6 12.2 21.3 45.7 85.8 321 772

10.45-11.62 22.1 4.6 9.3 16.2 34.8 65.3 248 587

11.63-12.90 14.7 3 6.1 10.7 22.9 43 164 387

12.98-14.64 7 1.4 2.9 5.1 11 20.7 78.7 186

14.8-16.5 4.1 0.9 1.7 3 6.5 12.3. 46.6 110

16.6-16.6 1.3 0.3 0.5 1 2 3.8 14.6 34.5

1Mouth Blackwater Creek.

2Blackwater Creek near Knights gaging station.

3Confluence of Blackwater Creek and Itchepackesassa Creek.
01234567 8 9 10 11 12 13 14 

30405060708090

100110120130

.28

.59

.90

1.14

1.34

1.55

1.80

2.04

2.37

2.82

3.02

3.27

3.59

3.78

3.95

4.14

4.36

4.65

4.85

5.19

5.49

5.76

5.93

6.44

6.97

7.45

7.69

7.92

8.34

8.59

8.79

9.00

9.27

9.52

9.87

10.25

10.41

10.79

11.07

11.44

11.61

11.89

12.31

12.49

12.72

12.90

13.21

13.28

13.58

13.741

13.917

14.23

P99.97 P9

P99.5 P

P95 P

P90 PP80 PP70 PP50 P

ELEVATION, IN FEET ABOVE NGVD OF 1929

BLACKWATER CREEK

DISTANCE, IN MILES ABOVE MOUTH

Channel Bed

Cross Se

Maximum Elevationof Bridge Opening

Solid lines indicate pdischarge profile.Dashed lines indicatdischarge withdraw

 Cross Section

Mouth, Confluence Hillsborough River

Ranch Bridge

Two Rivers

SR 39 Bridge

Railroad Bridge Blackwater Creek Gaging Station

Old Sheet-Pile Dam

Itchepackesassa Creek Confluence

Farm Road Bridge

Farm Road Bridge

Farm Road Bridge

Logging Road Bridge

Culvert

Water Oak Dr Culvert

Foot Bridge

y 

EXPLANATI

Figure 18. Blackwater Creek water-surface profiles for selected percentile discharges and the effects of a 10-percent discharge withdraw

confluence with the Hillsborough River to cross section 16.6, based on the 29-year period 1973-2001.
32 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Table 7. Approximate number of days daily mean discharge equaled or exceeded 

the percentile discharges at Blackwater Creek near Knights, 1973-2001.

[P50, 50-percentile discharge; <, less than]

Year

Number of days per year

P50 P70 P80 P90 P95 P99.5 P99.97

1973 237 124 59 25 16 0 0

1974 209 90 40 22 16 0 0

1975 119 76 46 23 17 0 0

1976 205 131 71 39 25 0 0

1977 148 44 20 8 4 0 0

1978 198 96 51 23 16 0 0

1979 200 133 83 59 42 2 0

1980 228 95 28 10 5 0 0

1981 107 51 25 6 1 0 0

1982 182 129 77 28 18 0 0

1983 253 191 128 74 54 0 0

1984 288 182 83 24 16 0 0

1985 80 65 40 18 12 1 0

1986 186 89 43 21 15 0 0

1987 223 110 52 22 15 3 0

1988 213 125 70 33 18 6 2

1989 175 77 34 20 12 0 0

1990 138 82 32 5 0 0 0

1991 140 96 68 32 19 0 0

1992 134 92 62 31 17 0 0

1993 202 142 87 42 24 0 0

1994 204 130 85 52 34 2 0

1995 305 181 111 65 49 0 0

1996 254 167 83 36 21 0 0

1997 122 71 43 16 9 4 0

1998 301 241 175 105 78 14 0

1999 182 84 27 7 1 0 0

2000 100 41 17 1 0 0 0

2001 87 72 47 22 14 1 0

Mean 187 111 62 30 20 1.1 <0.1

Maximum 305 241 175 105 78 14 2

Minimum 80 41 17 1 0 0 0
Blackwater Creek 33

 Confluence Itchepackesassa Creek 16.6

16.4

15.99

15.79

15.45

15.22

14.80

14.33

14.08

13.94

13.67

13.28

13.21

12.98

12.72

12.50

12.31

11.89

11.63

11.07

10.79

10.48

10.25

9.87

9.52

9.27

9.00

8.84

8.59

8.34

8.07

8.74

8.80

10.41

11.54

11.44

12.39

12.49

12.55

12.90

13.02

13.58

13.74

13.77

13.91

14.26

14.23

14.64

16.5

15.75

15.65

15.70

 Confluence Itchepackesassa

 Creek

Ranch Bridge

Ranch Bridge

Ranch Bridge

Bethel Road

Culvert

Greenbriar Road

Water Oak Drive

Shady Oak Drive West

Shady Oak Drive East

Simms Road Bridge

15.03

15.15

Harrelson Road Bridge

Timberwood Road

Blackwater Creek Channel

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

Reach 2

7.92

7.71

7.45

6.97

6.44

6.06

5.89

5.82

5.49

5.34

5.19

4.85

4.65

4.36

4.14

3.95

3.78

3.59

3.27

3.02

2.82

2.37

2.04

1.80

1.55

1.34

1.14

0.93

.68

.43

.28

.01

.15

.59

0.91

0.90

5.76

5.93

7.69

7.70

Confluence Hillsborough River

Two River Ranch Bridge

SR 39 Bridge

Railroad Bridge

Gaging Station (02302500)

 Dam

Blackwater Creek

Flow

Reach 1

CROSS SECTION

P99.97

P99.5

P95

P90

P80

P70

P50

EXPLANATION

Percentile

Discharges

0 1,000 2,000 FEET

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

Figure 19. Extent of areal inundation along reaches 1 and 2 of the Blackwater Creek study channel and floodplain 

for selected percentile discharges.
34 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

400 600 800 1,000 1,200

82

84

86

88

90

92

94

96

1,300

Looking Downstream

Looking Downstream

1,500 2,000 2,500 3,000

96

98

100

102

104

106

108

1,200

Blackwater Creek-Cross Section 9.0

700 800 900 1,000 1,100 1,200 1,300 1,400 1,500

82

84

86

88

90

92

94

96

P99.97, 1.92

P99.5, 1.38

P95, 2.15

P90, 1.54

P80, 1.09

P70, 0.85

P50, 0.58

Itchepackesassa Creek-Cross Section 0.82

ELEVATION, IN FEET ABOVE NGVD OF 1929

DISTANCE FROM LEFT BANK, IN FEET

Itchepackasassa Creek Channel

Water Surface

Floodplain

Berm

 Land-Surface Elevation

Blackwater Creek Channel

Water Surface

Floodplain

Berm

Land-Surface Elevation

(b)

(a)

P99.97, 1.49

P99.5, 1.79

P95, 2.50

P90, 1.83

P80, 1.09

P70, 0.75

P50, 0.40

EXPLANATION

P70, 0.85 Percentile Discharge, Hydraulic Depth

P70-10 10-Percent Discharge Withdrawal

EXPLANATION

P70, 0.75 Percentile Discharge, Hydraulic Depth

P70-10 10-Percent Discharge Withdrawal

East Canal-Cross Section 3.03 Looking Downstream

East Canal Channel

Water Surface

Floodplain

Berm

 Land-Surface Elevation

 (c ) 

P99.97, 1.56

P99.5, 1.01

P95, 1.74

P90, 1.18

P80, 0.73 P70, 0.51 P50, 0.31 EXPLANATION

P70, 0.51 Percentile Discharge, Hydraulic Depth

P70-10 10-Percent Discharge Withdrawal

 Blackwater Creek near Knights Gaging Station

 Based on 29-years record 

Percentile Mean number Occurrence 

discharge days/yr (no. years) 

P50 187 29

P70 111 29 

P80 62 29 

P90 30 29

P95 20 27

P99.5 1 8

P99.97 <0.1 1

Figure 20. Estimated extent and frequency of areal inundation and hydraulic depth at (a) Blackwater Creek, 

9.0, (b) Itchepackesassa Creek, 0.82, and (c) East Canal, 3.03 cross sections for each of the selected 

percentile discharges and the potential 10-percent withdrawal in discharge, based on the period 1973-2001.
Itchepackesassa Creek 35

PERCENTILE DISCHARGE

TOTAL INUNDATED AREA, IN ACRES

Blackwater Creek Area Inundated

Area inundated after a 

10-percent reduction in

discharge

Lines indicate interpolated area

4.2 % 4.1 % 5.4 % 5.7 %

7.4 %

7.5 %

9.0 %

Percent Inundated

Area Decreased

0

200

400

600

800

1,000

1,200

1,400

1,600

50 70 80 90 95 99.5 99.97

Total inundated area within the channel and floodplain 

ranged from approximately 80 (P50) to 1,500 (P99.97) acres for 

the selected percentile discharges (fig. 21 and app. 11). Inundated 

area at and below the P95 discharge generally was confined to 

within the channel (figs. 19 and 20a). A total of 228 acres at the 

P95 discharge were inundated, generally consisting of that area 

confined to within the bankfull channel. Inundation at both the 

P99.5 and P99.97 discharges predominately includes the floodplain area at 744 and 1,552 acres, respectively. 

Inundation losses resulting from the effects of a 10-

percent reduction in discharge were assessed along Blackwater 

Creek. The difference in inundated area, between existing and 

potential step-backwater analyses using discharges reduced by 

10 percent, ranged from 3.3 (P50) to 148 (P99.97) acres (app. 12). 

Inundated area losses based on the difference between the P95

and the P95-10 discharges, which are generally confined within 

the channel, totaled 16.8 acres. The greatest loss of inundated 

area occurred for the difference between the P99.97 and the 

P99.97-10 discharges at 148 acres. An example of the effects from 

a 10-percent discharge withdrawal during the P99.97 and the 

P99.97-10 discharges is shown in figure 22. Areas within the 

cross section having higher topographic relief may not be 

inundated. Cross section 9 in figure 20a shows an example of 

non-inundated areas. 

Itchepackesassa Creek

Itchepackesassa Creek, the largest tributary to Blackwater 

Creek, drains about 57 mi2 in northeastern Hillsborough and 

northwestern Polk Counties. The approximate 11.6-mi-long 

creek generally flows in a northwesterly direction, from Lake 

Bonnet, at the west side of the city of Lakeland, to the confluence with Blackwater Creek (figs. 1 and 23). Itchepackesassa 

Creek and many of its tributaries have been extensively channelized to improve drainage. Most of the channel along the 

study reach is moderately incised and typically well defined, 

confining all but the highest discharges within the banks. 

Step-backwater analyses for the Itchepackesassa Creek 

study reach were based on seven percentile discharges, P50, P70, 

P80, P 90, P95, P99.5, and P99.97. The step-backwater analyses used 

49 cross sections along the 11.6-mi-long study reach, from the 

confluence with Blackwater Creek to Interstate Highway 4. 

Discharges used in the analyses were calculated based on the 

proportionality of drainage area with that of the Blackwater 

Creek near Knights gaging station for the 29-yr period, 1973-

2001 (table 8). Water-surface profiles were generated from 

water-surface elevations computed at each of the 49 cross 

sections during the step-backwater analyses (fig. 24). Extent of 

areal inundation and hydraulic depth at the cross sections also 

Figure 21. Estimated total inundated area along Blackwater Creek, from the confluence with the 

Hillsborough River to cross section 16.6, for each of the selected percentile discharges and for a 10-

percent discharge withdrawal, based on the period 1973-2001.
36 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

 Confluence Itchepackesassa Creek

Blackwater Creek Channel

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

Confluence Hillsborough River

Two River Ranch Bridge

SR 39 Bridge

Railroad Bridge

Gaging Station (02302500)

 Dam

Blackwater Creek

Flow

Reach 1

CROSS SECTION

7.92

7.71

7.45

6.97

6.44

6.06

5.90

5.82

5.49

5.34

5.19

4.85

4.65

4.36

4.14

3.95

3.78

3.59

3.27

3.02

2.82

2.37

2.04

1.80

1.55

1.34

1.14

.93

.68

.43

.28

.01

.15

.59

.91

.90

5.76

5.93

7.69

7.70

0 1,000 2,000 FEET

P99.97

P99.97-10

EXPLANATION

Percentile

Discharges

3,003-2,703

Ranch Bridge

Ranch Bridge

Ranch Bridge

Bethel Road

Culvert

Greenbriar Road

Water Oak Drive

Shady Oak Drive West

Shady Oak Drive East

Simms Road Bridge

Harrelson Road Bridge

Timberwood Road

Reach 2

16.6

16.4

15.99

15.79

15.45

15.22

14.80

14.33

14.08

13.94

13.67

13.28

13.21

12.98

12.72

12.50

12.31

11.89

11.63

11.07

10.79

10.48

10.25

9.87

9.52

9.27

9.00

8.84

8.59

8.34

8.07

8.74

8.80

10.41

11.54

11.44

12.39

12.49

12.55

12.90

13.02

13.58

13.74

13.77

13.91

14.26

14.23

14.64

16.5

15.75

15.65

15.70

15.03

15.15

957-861

2,995-2,696 2,586-2,327 2,700-2,430 2,745-2,471 2,790-2,511 2,854-2,579 2,939-2,645 2,967-2,670

2,471-2,224

DISCHARGE, IN CUBIC FEET PER SECOND P99.97 - P99.97-10

772-695

34.5-31.1110-99 186-167 387-348 587-528

DISCHARGE, IN CUBIC FEET PER SECOND P99.97 - P99.97-10

Confluence

 Itchepackesassa 

Creek

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

P99.97-10

P99.97

Figure 22. Example of extent of areal inundation along reaches 1 and 2 of the Blackwater Creek study channel and 

floodplain for the P99.97 (existing conditions) and the P99.97-10 (potential 10-percent discharge withdrawal) discharges.
Itchepackesassa Creek 37

 

 

 

012 3

0123

MILES

KILOMETERS

Sam Allen Road

Knights-Griffin Road

Walker Road

Harrelson Road

Gallowaly Road

CR 35A

Duff Road

HILLSBOROUGH COUNTYPOLK COUNTY

2.72

2.45

2.08

1.71

1.39

1.30

1.07

0.82

0.55

0.20

0.15

3.48

3.16

2.94

5.28

4.97

4.88

4.66

4.31 4.14

3.86

11.64

11.40

11.15

10.94

10.71

10.52

10.16

10.07

9.84

9.63

9.40

9.26

9.24

9.11

8.849.08.53

7.88

8.22

7.59

7.24

6.95

6.58

6.30

6.12

5.68

5.62 5.45

6.25

1.36

10.96

Plant City Lakeland

Kathleen

EXPLANATION

GAGING STATION— With site number

CROSS SECTION— With number

6.58

Knights Gaging

Station (02302260)

Moriczville Gaging

Station (02302280)

Knights

Knights Gaging

Station (02302500)

82ο05′ 82ο00′

28ο

08′

28ο03′

Blackwater

Creek

East Canal

Creek

Itch epacke sassa

4

39 4

Base from U.S. Geological Survey digital data, 1:200,000, 1972

Albers Equal-Area Conic projection

Standard Parallels 29°30′, and central meridian −83°00′

Lake 

Bonnet

were based on the computed water-surface elevations for the 

selected percentile discharges. Accuracy of the step-backwater 

analyses were determined by comparing results of the 

computed water-surface elevations with rated water-surface 

elevations at the Itchepackesassa Creek near Moriczville 

(02302280) and the Itchepackesassa Creek near Knights 

(02302260) gaging stations. The computed water-surface 

elevations for percentile discharges converged successfully 

within plus or minus 0.5 ft of the established stage-discharge 

relation at the Moriczville and Knights gaging stations.

Estimated floodplain inundation can exceed 4,700 ft 

(cross section 9.26) during P99.97 discharges (app. 13). Mean 

inundation width for the 49 cross sections along the study reach 

ranged from 28 (P50) to 793 (P99.97) ft. The moderately incised 

channel of the study reach generally confines most flows below 

the P99.5 discharge, except for a limited number of low-lying 

cross sections (figs. 20b and 25). Mean width at the P95

discharge (64 ft) was considered the mean width of the bankfull 

channel. The increase in the extent of mean areal inundation 

from the P95 to the P95.5 discharge and from the P95.5 to the P99.97 

discharge are similar. In example cross section 0.82, discharges 

below P99.5 generally were confined within the channel, and 

those above can inundate the floodplain (fig. 20b). The approximate mean number of days that inundation of the floodplain 

occurred at the P99.5 discharge was 1.1 days, which occurred 

during 8 yrs of the 29-yr period, based on the frequency at the 

downstream Blackwater Creek near Knights gaging station 

(table 7).

Figure 23. Location of the Itchepackesassa Creek study reach and cross sections, and the Moriczville and Knights 

gaging stations, west-central Florida. (Location of the study area shown in figure 1).
38 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Hydraulic depths below the P99.5 discharge generally were 

confined within the channel. Mean hydraulic depths along the 

reach ranged from 0.5 to 3.0 ft, and maximum depths ranged 

from 1.6 to 8.0 ft (app. 14). Because of the increase in crosssectional area at the transition from the channel to floodplain in 

example cross section 0.82, the hydraulic depth of 2.5 ft at the 

P95 discharge is greater than the 1.79 ft at the P99.5 discharge 

(fig. 20b).

Total inundated area within the channel and floodplain 

ranged from 33.5 (P50) to 966 (P99.97) acres (fig. 26, app. 15). 

Inundated acreage at or below the P95 discharge generally was 

confined within the channel, except at two adjacent cross 

sections in a low-lying area near the mouth (fig. 25). The inundated acreage at the P95 discharges, which largely included the 

area within the channel, was approximately 86 acres. The inundated area at both the P99.5 and P99.97 discharges predominately 

include the floodplain at 339 and 966 acres, respectively.

The difference in inundated area, between the existing and 

the potential step-backwater analyses, ranged from 1.0 (P50) to 

104 (P99.97) acres (app. 16). Loss of inundated area at or below 

the P95-10 discharge generally occurred within the channel and 

ranged from approximately 1.0 to 6.0 acres. The greatest loss 

occurred at the P99.97-10 discharge with 104 acres (fig. 27).

East Canal

East Canal drains about 13.4 mi2 from south of Plant City 

to its confluence with Itchepackesassa Creek (fig. 1 and 28).

The 4.9-mi-long north-south trending study reach starts at the 

confluence with Itchepackesassa Creek and ends at Interstate 

Highway 4. The East Canal study reach is highly channelized, 

generally deeply incised, and well defined. 

Step-backwater analyses were performed based on seven 

percentile discharges, P50, P70, P80, P 90, P95, P99.5, and P99.97. 

Water-surface profiles were generated from water-surface elevations computed at the 46 cross sections during the step-backwater 

analyses (fig. 29). Water-surface elevations also were used to 

compute the extent of areal inundation and hydraulic depth at 

each of the 46 cross sections. The proportionality of drainage area 

to discharge at the Blackwater near Knights gaging station for the 

period, 1973-2001, was used to determine the percentile 

discharges used in the East Canal analyses (table 9). 

Estimated maximum floodplain inundation can exceed 

2,200 ft (cross section 2.44) during P99.97 discharges (app. 17). 

Mean inundation width for the 46 cross sections along the 

reach ranged from 21 (P50) to 451 (P99.97) ft. The incised 

channel generally confines most flows within the banks at 

or below the P95 discharge, except at the low-lying cross 

section 3.03 (figs. 20c and 30). The mean inundation width at 

the P95 discharge (43 ft) was considered the bankfull channel. 

The greatest increase in extent of mean areal inundation 

occurred between the P95 (43 ft) to the P99.5 (177 ft) discharges 

(app. 17). This increase in mean areal inundation may reflect the 

transition from channel to floodplain. Example cross section 

3.03 shows that discharges below P95 are confined to the channel, and those above may inundate the floodplain (fig. 20c). 

Based on the Blackwater near Knights gaging station (table 7), 

the approximate mean number of days that inundation of the 

floodplain occurs at the P95 discharge is 20 days. The P95

discharge occurred during 27 yrs of the 29-yr study period.

Table 8. Cross sections, drainage area, and percentile discharges used in the Itchepackesassa Creek step-backwater analyses, based on the period 1973-2001, at Blackwater 

Creek near Knights gaging station.

[mi2, square miles; --, not determined]

Cross section 

No.

Drainage 

area 

(mi2)

Discharge, in cubic feet per second

P50 P70 P80 P90 P95 P99.5 P99.97

0.15-2.45 57 11.8 24 41.7 90 168 641 1,515

2.72 39.8 8.2 16.7 29.1 63 118 447 1,058

2.94-3.48 -- 8.0 16.3 28.4 61.1 115 436 1,031

3.86-4.14 37.8 7.8 15.9 27.7 60 112 425 1,005

4.31-4.88 -- 7.3 14.9 25.9 55.7 105 398 941

4.97-6.63 33 6.8 13.9 24.2 52 97.4 371 877

5.64-7.59 -- 5.7 11.7 20.3 43.7 82 312 737

7.88-9.25 22.5 4.7 9.5 16.5 35.4 66.4 253 598

9.26-10.52 -- 4 8.2 14.3 30.7 57.6 219 518

10.71-11.64 16.5 3.4 6.9 12.1 26 49 185 438
01234567 8 9 10 

8090

100110120

P99.97 P99.

P99.5 P99

P95 P95P90 P90P80 P80P70 P70P50 P50

125

75

0.15

0.20

0.55

0.82

1.07

1.30

1.71

2.08

2.45

2.72

2.94

3.16

3.48

3.86

4.14

4.31

4.66

4.88

5.28

5.45

5.62

6.12

6.25

6.58

6.95

7.24

7.59

7.88

8.22

8.53

8.84

9.0

9.11

9.24

9.40

9.63

9.84

10.07

1.36

Itchepackesassa Creek

Mouth, Confluence Blackwater Creek

Cone Ranch Bridge

Gaging Station

Confluence East Canal

Wooden Bridge

Knights-Griffin Road Bridge

Crest-Stage Gage

Bridge

Walker Road

WATER-SURFACE ELEVATION, IN FEET ABOVE NGVD 1929

DISTANCE, IN MILES ABOVE MOUTH

Channel Bed

Cross Section Number

Maximum Elevationof Bridge Opening

Solid lines indicate pedischarge profile.Dashed lines indicate discharge withdrawal

EXPLANATION

Figure 24. Itchepackesassa Creek water-surface profiles for the selected percentile discharges and the effects of a 10-percent discharge confluence with Blackwater Creek to Interstate 4, based on the 29-year period 1973-2001.
40 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

3.48

3.16

2.94

2.72

2.45

2.08

1.71

1.39

1.30

1.07

0.82

0.55

0.20

0.15

7.59

7.24

6.95

6.58

6.30

6.12

5.68

5.62

5.45

5.28

4.97

4.88

4.66

4.31

4.14

3.86

11.64

11.40

11.15

10.97

10.96

10.71

10.52

10.16

10.07

9.84

9.63

9.40

9.27 9.26

9.24

9.11

9.0

8.84

8.53

8.22

7.88

6.25

CROSS SECTION

Itchepackesassa Creek Channel

Itchepackesassa Creek

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

Ranch Bridge and Gaging Station (02302280)

800 feet above Confluence

with Blackwater Creek

P99.97

P99.5

P95

P90

P80

P70

P50

EXPLANATION

Percentile

Discharges

Flow

Confluence with East Canal

Knights-Griffin Road Bridge

and gaging station (02302260)

Walker Road Bridge

Bridge

Swindel Road Bridge

Interstate 4

0 4,000 8,000 FEET

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

Figure 25. Extent of areal inundation along Itchepackesassa Creek study channel and floodplain 

for selected percentile discharges.
Summary 41

PERCENTILE DISCHARGE

TOTAL INUNDATED AREA, IN ACRES

Itchepackesassa Creek

Area Inundated

Area inundated after a 

10-percent reduction in

discharge

Lines indicated interpolated area

3.0 % 3.6 % 2.8 % 7.6 %

7.0 %

11.2 %

10.8 %

Percent Inundated

Area Decreased 0

100

200

300

400

500

600

700

800

900

1,000

50th 70th 80th 90th 95th 99.5th 99.97th

Hydraulic depths at or below the P95 discharge generally 

were confined within the channel. Mean hydraulic depths 

ranged from approximately 0.3 to 2.2 ft, and maximum depths 

ranged from 0.8 (P50) to 4.8 (P99.97) ft (app. 18). In example 

cross section 3.03, the hydraulic depths at the P95 discharge 

were confined to the channel. The P95 discharge occurs on average for about 20 days during 27 yrs of the 29-yr period, based 

on conditions at the Blackwater near Knights gaging station 

(table 7 and fig. 20c). 

Total inundated area within the channel and floodplain 

ranged from 12.4 (P50) to 378 (P99.97) acres (fig. 31 app. 19).

The inundated acreage at the P95 discharges was approximately 

35 acres, which predominantly includes that area confined 

within the bankfull channel. Whereas, the P99.5 and P99.97 

discharges generally include inundated areas along the floodplain at 153 and 378 acres, respectively.

Loss of inundated area, between the existing and the 

potential step-backwater analyses ranged from 0.7 (P50) to 34.6 

(P99.97) acres (app. 20). Loss of inundated area at or below the 

P95-10 discharge generally occurred within the channel and 

ranged from 0.7 to 2.4 acres. An example of the effects of a 

potential 10-percent discharge withdrawal (16.5 acres) for the 

P99.5 discharge is shown in figure 32.

Summary

Inland forested wetlands are a major ecological component 

of river basins in west-central Florida. Healthy wetlands are 

dependent, in part, upon the frequency and duration of periodic 

inundation. This report assesses the extent, area, depth, 

frequency, and duration of periodic inundation and the effects 

of potential consumptive surface-water withdrawals on the 

Hillsborough and New Rivers, Blackwater and Itchepackesassa 

Creeks, and East Canal. Results of the study were based on stepbackwater analyses performed for each of the river systems 

using the U.S. Army Corps of Engineers HEC-RAS (Hydrologic Engineering Center-River Analysis System) one-dimensional model. Step-backwater analyses of mean daily 

discharges for the 10th, 50th, 70th, 80th, 90th, 95th, 99.5th, and 

99.97th percentiles were used to compute lateral extent of areal 

inundation, area of inundation, and hydraulic depth. The 10th

and 99.97th percentile discharges were omitted for selected 

analyses because of limiting hydrologic conditions. Percentile 

discharges selected for the Hillsborough River study reach were 

determined based on the longest concurrent daily mean 

discharge record (17-yr period, 1984-2000) at the four longterm steamflow gaging stations: Morris Bridge, Zephyrhills, 

Crystal Springs, and Withlacoochee-Hillsborough Overflow. 

Figure 26. Estimated total inundated area along Itchepackesassa Creek, from the mouth at the confluence 

with Blackwater Creek to Interstate 4, for each of the selected percentile discharges and for a 10-percent 

discharge withdrawal, based on the 29-year period 1973-2001.
42 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

3.48

3.16

2.94

2.72

2.45

2.08

1.71

1.39

1.30

1.07

0.82

0.55

0.20

0.15

7.59

7.24

6.95

6.58

6.30

6.12

5.68

5.62

5.45

5.28

4.97

4.88

4.66

4.31

4.14

3.86

11.64

11.40

11.15

10.97

10.96

10.71

10.52

10.16

10.07

9.84

9.63

9.40

9.27

9.24

9.11

9.0

8.84

8.53

8.22

7.88

6.25

CROSS SECTION

Itchepackesassa Creek Channel

Itchepackesassa Creek

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

CROSS SECTION NUMBER

Ranch Bridge and Gaging Station (02302280)

800 feet above Confluence

with Blackwater Creek

Flow

Confluence with East Canal

Knights-Griffin Road Bridge

and gaging station (02302260)

Walker Road Bridge

Bridge

Swindel Road Bridge

Interstate 4

0 2,000 4,000 FEET

P99.97

P99.97-10

EXPLANATION

Percentile

Discharges

9.26

1,058-952 1,515-1,364 438-394 518-466 598-538 737-663 877-789 941-847 1,005-905 1,031-928

DISCHARGE, IN CUBIC FEET PER SECOND P99.97 - P99.97-10

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

P99.97-10

P99.97

Figure 27. Example of extent of areal inundation along the Itchepackesassa Creek study channel and 

floodplain for the P99.97 (existing conditions) and the P99.97-10 (potential 10-percent discharge withdrawal) 

discharges.
Summary 43

0 1

0 1

MILE

KILOMETER

East Canal

Sam Allen Road

Knights-Griffin Road

SR 39

Plant City

EXPLANATION

CROSS SECTION—

 With number

1.13

1.65

1.38

1.13

0.96

0.84

0.78

0.70

0.61

0.44

0.29

0.22

0.15

0.20

4.89

4.79

4.72

4.65

4.58

4.54

4.49

4.44

4.38

4.52

2.09

1.96

1.94

1.83

1.99

4.34

4.23 4.18

4.13

4.05

3.96

3.67

3.40

3.23

3.03

2.82

2.55

2.44

4.16

0.19

82ο07′30 82ο06′

28ο

05′

28ο

02′

Itchepackesassa

Creek

4

Base from U.S. Geological Survey digital data, 1:200,000, 1972

Albers Equal-Area Conic projection

Standard Parallels 29°30′, and central meridian −83°00′

Figure 28. Location of the East Canal study reach and cross 

sections, west-central Florida. (Location of the study area 

shown in figure 1).
1 2 3 4 

85

90

95

100

105

110

115

0

.15

0.19

0.29

0.44

0.61

0.70

0.78

0.84

0.96

1.13

1.38

1.65

1.83

1.94

2.00

2.09

2.44

2.55

2.82 3.03

3.23

3.40 3.67 3.96

4.05

4.13

4.18

P99.97 

P99.5 

P95 P90 P80 P70 P50 

East Canal

WATER-SURFACE ELEVATION, IN FEET ABOVE NGVD OF 1929

DISTANCE, IN MILES ABOVE MOUTH

Cross Section Number

Maximum Elevationof Bridge Opening

Mouth, Confluence Itchepackesassa Creek

Knights-Griffin Road Culvert

Allen Road Culvert

Solid lines inddischarge proDashed lines discharge wi

EXPLA

Figure 29. East Canal water-surface profiles for the selected percentile discharges and the effects of a 10-percent discharge withdrawal, 

with Itchepackesassa Creek to Interstate 4, based on the 29-year study period 1973-2001.
Summary 45

Percentile discharges for New River were based on the available 

10-yr period, 1965-1974, at the New River near Zephyrhills 

gaging station. Percentile discharges for Blackwater Creek, 

Itchepackesassa Creek, and East Canal were based on the 29-yr 

period, 1973-2001, at the Blackwater Creek near Knights 

gaging station. Discharges at the 99.5th and 99.97th percentiles 

generally occur once every 5 to 10 yrs. Assessment of the net 

reduction of areal inundation was compared between existing 

and potential step-backwater analysis (10 percent of the total 

river flow was diverted for potential withdrawals). 

The Hillsborough River watershed drains a 375-mi2 area

in southeastern Pasco, western Polk, and northeastern Hillsborough Counties. The low-gradient channel generally is poorly 

incised and not well defined. Widespread inundation of the 

inland forested wetlands, which dominate the length of the 

Hillsborough floodplain, occurs at discharges associated with 

the 80th percentile. Discharges at the 80th percentile generally 

occur about 72 days annually for the Hillsborough River. 

During the study period, the maximum extent of inundation 

was about 15,600 ft in width, and the mean inundation width 

along the channel ranged from approximately 98 to 4,800 ft. 

The inundated area along the Hillsborough River study reach 

ranged from about 280 to 16,300 acres. The mean hydraulic 

depth ranged from 1.4 to 3.1 ft, with a maximum depth of 8.9 ft. 

Loss of inundated area from a potential 10-percent reduction in 

discharge ranged from 7 to 940 acres.

New River drains 19.5 mi2 in eastern Pasco and Hillsborough Counties. The New River channel is generally well 

defined and moderately incised. Most discharges at or below 

the 90th percentile are contained within the banks of the channel. 

Discharges at the 50th percentile occur about 94 days annually 

and discharges at the 90th percentile occur most years for about 

14 days annually. The maximum extent of areal inundation 

along New River was approximately 2,900 ft in width, and the 

mean inundation width ranged from approximately 17 to 560 ft. 

Total inundated area ranged from about 17 to 490 acres. Mean 

hydraulic depth ranged from 0.2 to 1.6 ft, with a maximum 

depth of 4.6 ft. Losses of inundated area from a potential 

10-percent reduction in discharge ranged from 0.2 to 59 acres.

Blackwater Creek, the largest tributary to the Hillsborough 

River, drains about 113 mi2 in northwestern Polk and northeastern Hillsborough Counties. The channel along the lower onethird of the study reach is predominately natural, from the 

mouth to directly downstream of SR 39. Most of the channel is 

moderately incised and well defined, confining most discharge 

within the banks at or below the 95th percentile. Step-backwater 

analyses were performed at 114 cross sections. Maximum areal 

inundation width was about 6,000 ft, and the mean inundation 

width along the channel ranged from approximately 36 to 800 ft. 

Inundation along the Blackwater Creek study reach ranged from 

about 80 to 1,500 acres. The mean hydraulic depth ranged from 

0.5 to 2.8 ft, with a maximum depth of 9.6 ft. Loss of inundated 

area from a 10-percent reduction in discharge ranged from 3.3 

to 148 acres. 

Itchepackesassa Creek, the largest tributary to Blackwater 

Creek, drains about 57 mi2 in northeastern Hillsborough and 

northwestern Polk Counties. The 11.6-mi-long creek generally 

flows in a northwesterly direction, from its headwaters at Lake 

Bonnet, to its confluence with Blackwater Creek. Itchepackesassa 

Table 9. Cross sections, drainage area, and percentile discharges used in the East Canal 

step-backwater analyses, based on the period 1973-2001, at Blackwater Creek near Knights 

gaging station.

[mi2, square miles; --, not determined]

Cross section 

No.

Drainage 

area (mi2)

Discharge, in cubic feet per second

P50 P70 P80 P90 P95 P99.5 P99.97

0.15 13.4 2.8 5.6 9.8 21 40 151 356

0.19-0.96 -- 2.4 5 8.7 18.7 35 133 315

1.13-1.96 10.3 2.1 4.3 7.5 16 30 116 274

1.99-2.44 -- 1.9 4 6.9 14.8 27.8 106 250

2.55-3.03 8.5 1.8 3.6 6.2 13 25 96 226

3.23-3.96 -- 1.4 2.8 4.8 10.3 19.3 73.6 174

4.05-4.79 4.6 1 1.9 3.4 7.2 13.6 52 122
46 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

CROSS SECTION

East Canal

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

Confluence Itchepackesassa Creek

P99.97

P99.5

P95

P90

P80

P70

P50

EXPLANATION

Percentile

Discharges

Flow

Knights-Griffin Road Culvert

Interstate 4

Abandoned Wooden Bridge

2.09

2.00

1.96 1.94

1.83

1.65

1.38

1.13

0.96

0.84

0.78

0.70

0.61

0.44

0.29

0.22

.15

.20

1.99

4.89

4.79

4.72

4.65

4.58 4.54

4.49

4.44

4.38

4.34

4.23

4.18

4.13

4.05

3.96

3.67

3.40

3.23

3.03

2.82

2.55

2.44

4.52

4.16

Bailey Road

Allen Road Culvert

Terrace Road Bridge

East Canal Channel

0 2,000 4,000 FEET

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

Figure 30. Extent of areal inundation along East Canal study channel and floodplain for selected 

percentile discharges.
Selected References 47

PERCENTILE DISCHARGE

East Canal

Area Inundated

Percent Inundated

Area Decreased

Area inundated after a 10-percent reduction in discharge

Lines indicated interpolated area

TOTAL INUNDATED AREA, IN ACRES

0

25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

400

50 70 80 90 95 99.5 99.97

8.3 %

5.6 %

4.9 % 7.8 % 6.8 %

10.8 %

9.2 %

Creek and many of its tributaries have been extensively channelized to improve drainage. The channel along the study reach 

typically is moderately incised and well defined, confining all 

but the highest discharges within the banks. Discharges at or 

below the 99.5th percentile generally are contained within the 

banks of the channel. Discharges at the 50th percentile occur 

about 190 days annually, and discharges at the 95th percentile 

occur during most years for about 20 days. Maximum areal 

inundation along Itchepackesassa Creek was about 4,700 ft in 

width, and the mean inundation width along the channel ranged 

from approximately 30 to 800 ft. Total inundated area ranged 

from about 34 to 970 acres. Mean hydraulic depth ranged from 

0.5 to 3.0 ft, with a maximum depth of 8.0 ft. Loss of inundated 

area from a 10-percent reduction in discharge ranged from 1.0 

to 104 acres.

East Canal drains about 13.4 mi2 from south of Plant City 

to the confluence with Itchepackesassa Creek. The 4.9-mi-long 

study reach begins at the confluence with Itchepackesassa 

Creek and ends at Interstate 4. The East Canal study reach 

generally is highly channelized, deeply incised, and well 

defined. Maximum areal inundation width was about 2,200 ft, 

and the mean inundation width along the channel ranged from 

approximately 21 to 450 ft. Total inundated area along the 

Blackwater Creek study reach ranged from about 12 to 400 

acres. The mean hydraulic depth ranged from 0.3 to 2.2 ft, with 

a maximum depth of 4.8 ft. Loss of inundated area from a 

10-percent reduction in discharge ranged from 0.7 to 34.6 acres.

Selected References

Cowardin, L.M., Carter, Virginia, Golet, F.C., and LaRoe, E.T., 

1979, Classification of wetlands and deepwater habitats of 

the United States: U.S. Fish and Wildlife Service, 

FWS/OBS-79/31, 103 p.

Federal Emergency Management Agency, 1989, Flood insurance study, Hillsborough County, unincorporated areas: 

Federal Insurance Administration, 56 p.

Harrison, Thomas, Arnold, David, and Brass, N.B., Jr., 1983, 

Floodplain information on Trout Creek: Brooksville, Fla., 

Southwest Florida Water Management District, 18 p.

Johnson, Malcolm, Hubbell, Peter, and Brass, N.B., Jr., 1979, 

Flood plain information on the Hillsborough River watershed, Hillsborough River and New River: Brooksville, Fla., 

Southwest Florida Water Management District, 25 p.

Figure 31. Estimated total inundated area along East Canal, from the mouth at the confluence with Itchepackesassa 

Creek to Interstate 4, for each of the selected percentile discharges and for a 10-percent discharge withdrawal, based 

on the 29-year period 1973-2001. 
48 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

CROSS SECTION

CROSS SECTION NUMBER

LIMIT OF STUDY

FLOODPLAIN BOUNDARY

Knights-Griffin Road Culvert

Interstate 4

2.09

2.00

1.96

1.94

1.83

1.99

4.89

4.79

4.72

4.65

4.58 4.54

4.49

4.44

4.38

4.34

4.23

4.18

4.13

4.05

3.96

3.67

3.40

3.23

3.03

2.82

2.55

2.44

4.52

4.16 Allen Road Culvert

Terrace Road Bridge

Confluence Itchepackesassa Creek

Flow

Abandoned Wooden Bridge

1.65

1.38

1.13

0.96

0.84

0.78

0.70

0.61

0.44

0.29

0.22

.15

.20

Bailey Road

East Canal Channel

0 2,000 4,000 FEET

East Canal

P99.5

P99.5-10

EXPLANATION

Percentile

Discharges

133-120 52-46.8 73.6-66.2 96-86.4 106-95 116-104

DISCHARGE, IN CUBIC FEET PER SECOND P99.97 - P99.97-10

151-136

Shaded areas represent maximum extent

of inundated area within the cross section

that occurs between banks. Non-inundated

areas having higher relief may occur within

each of the cross sections.

P99.5-10

P99.5

Figure 32. Example of extent of areal inundation along East Canal study channel and floodplain for the 

P99.5 (existing conditions) and the P99.5-10 (potential 10-percent discharge withdrawal) discharges.
Selected References 49

Johnson, Malcolm, Hubbell, Peter, McCallister, Scott, and 

Brass, N.B., Jr., 1980, Flood plain information on the Blackwater Creek watershed, Blackwater Creek, East Canal, and 

Itchepackesassa Creek: Brooksville, Fla., Southwest Florida 

Water Management District, 19 p.

Murphy, W.R., Jr., 1978, Flood profiles for Cypress Creek, 

west-central Florida: U.S. Geological Survey WaterResources Investigations Report 78-8, 29 p.

Murphy, W.R., Jr., Hammett, K.M., and Reeter, C.V., 1978, 

Flood profiles for Peace River, south-central Florida: U.S. 

Geological Survey Water-Resources Investigations Report 

78-57, 35 p.

Robertson, A.F., 1978, Flood profiles of the Alafia River, westcentral Florida: U.S. Geological Survey Water-Resources 

Investigations Report 77-74, 21 p.

Shearman, J.O., 1976, Computer program E431 user’s manual: 

U.S. Geological Survey Open-File Report 76-499, 175 p.

Stamey, T.C., 1985, Frequency and duration of flooding of 

Grove Creek near Kenansville, North Carolina, for present 

and proposed restored channel conditions: U.S. Geological 

Survey Water-Resources Investigations Report 85-4298, 

52 p.

Warner, J.C., and Brunner, G.W., 1998a, HEC-RAS River 

Analysis System: U.S. Army Corps of Engineers Hydrologic 

Engineering Center, Hydraulic Application Guide, version 

2.2, CPD-70, 283 p.

Warner, J.C., and Brunner, G.W., 1998b, HEC-RAS River 

Analysis System: U.S. Army Corps of Engineers Hydrologic 

Engineering Center, Hydraulic Reference Manual, version 

2.2, CPD-69, 251 p.

White, W.A., 1970, The geomorphology of the Florida Peninsula: Tallahassee, Florida Bureau of Geology Bulletin 

No. 51, 164 p.

Appendixes 1-20
A 2 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Appendix 1. Extent of inundation at cross sections along the 

Hillsborough River for selected percentile discharges. 

[--, no flow]

Cross 

section 

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Feet

28.9 241 264 275 287 307 327 3,822 7,189

128.99 153 161 165 172 184 196 3,155 7,267

29 Morris Bridge

29.01 153 161 165 173 185 196 3,197 7,312

29.1 156 173 246 315 429 525 4,116 8,628

29.49 64 295 1,088 1,352 2,728 4,543 10,393 15,434

29.5 19 19 21 29 45 1,540 7,014 13,717

29.6 50 54 321 1,042 2,156 5,195 10,819 15,323

30.0 71 572 1,366 2,069 3,820 4,983 10,913 14,730

30.3 79 1,175 1,847 2,261 4,144 5,062 10,870 14,633

30.6 98 100 151 236 3,825 4,694 10,526 14,542

30.9 97 100 132 320 3,133 3,691 9,463 13,341

31.4 91 93 95 774 1,820 2,294 8,336 12,001

31.8 61 64 255 2,366 3,076 3,398 9,813 12,850

32.1 64 69 1,275 2,277 3,086 3,558 10,364 13,150

32.3 79 85 343 1,390 3,502 4,596 11,576 13,944

32.6 96 100 275 2,295 3,913 5,493 11,794 13,588

32.8 92 95 331 1,832 4,462 5,702 12,229 13,888

33.0 81 83 359 2,549 4,067 6,407 10,341 15,359

33.4 68 69 690 1,972 4,257 5,712 9,920 14,720

33.7 81 84 146 296 3,428 4,738 11,143 15,635

34.1 76 79 319 645 1,269 4,504 11,689 15,253

34.5 111 115 119 193 418 6,364 11,347 14,149

34.9 88 89 89 90 887 3,566 8,710 11,739

35.3 58 63 66 69 1,153 4,677 8,073 10,846

35.9 74 76 77 79 236 1,525 5,516 7,167

36.4 63 65 66 68 123 923 3,360 7,057

36.7 63 64 66 67 69 70 6,577 8,436

37.30 87 89 91 92 95 198 5,147 6,543

37.62 87 89 90 92 94 178 5,261 6,099

38.2 83 84 86 87 89 126 4,338 6,090

38.7 92 94 95 97 99 140 3,929 5,353

39.2 107 110 113 116 121 221 1,223 1,676

39.5 114 115 117 120 127 212 596 1,467

39.8 89 91 93 96 103 365 938 2,148

40.2 75 77 78 80 181 350 1,114 3,008

240.4 78 82 85 92 320 645 1,347 2,116

40.7 82 84 109 156 349 481 1,179 1,996

 41 97 100 151 222 395 611 2,029 2,485

41.2 95 96 97 99 265 467 1,440 2,000

41.5 106 108 109 134 214 327 1,591 3,269

41.55 106 131 150 171 293 342 832 3,173

41.57 US 301 Bridge

41.6 108 132 152 173 295 345 863 3,182

41.64 85 86 88 89 110 148 1,127 1,898

41.9 99 101 102 103 105 140 1,813 2,160

42.35 138 142 145 149 365 450 1,299 1,785

42.38 67 70 73 76 96 188 1,623 2,005

42.4 87 90 93 96 185 452 2,739 3,425

42.5 77 80 83 86 119 190 686 1,829

42.7 83 86 89 92 99 299 871 1,400

43 47 47 48 48 51 54 123 1,120

43.3 56 57 58 58 60 63 813 1,225

43.6 56 56 57 57 58 60 863 1,266

43.8 47 47 48 48 50 57 913 1,250

44.1 61 62 62 63 64 78 777 1,312

44.3 94 94 94 95 96 109 942 1,461

44.6 39 40 40 41 55 491 1,016 1,360

44.9 72 74 75 76 161 676 1,516 1,708

45.1 70 73 76 79 106 206 1,000 1,449

45.4 65 69 73 77 130 743 1,286 1,557

45.7 46 48 51 57 86 349 1,374 1,657

46 107 156 191 236 657 1,129 1,376 1,735

46.2 65 67 86 154 956 1,133 1,460 1,678

46.3 63 65 66 68 69 232 1,546 1,814

346.4 66 68 69 88 1,126 1,561 1,964 2,172

46.405 Crystal Springs Bridge

46.41 67 69 89 503 1,227 1,827 2,025 2,497

46.46 43 45 47 48 422 1,269 1,628 2,745

46.6 67 69 71 89 699 1,112 1,379 1,740

46.9 45 47 49 82 395 1,134 1,554 1,694

47.1 58 60 61 63 181 694 2,151 2,973

47.3 54 56 57 59 128 302 901 1,814

47.6 34 36 38 40 128 357 1,063 1,313

47.7 50 53 56 58 182 410 1,152 1,350

47.8 41 42 43 44 157 378 865 1,134

47.84 28 30 31 33 55 80 312 541

47.85 SR 39 Bridge

47.86 28 30 32 33 58 83 379 626

47.9 47 48 48 49 78 129 724 1,163

48.0 54 58 63 67 241 329 1,192 1,934

48.1 44 45 47 49 171 277 711 879

48.16 25 31 36 42 61 77 655 818

48.17 Railroad Bridge

48.18 26 32 37 42 62 78 659 832

48.2 49 68 101 134 218 280 586 1,095

48.4 38 40 42 44 50 199 781 1,092

48.7 53 54 55 56 66 224 725 1,278

48.9 46 47 47 47 48 50 695 1,110

49.2 46 46 47 47 48 68 781 1,309

49.4 45 45 46 46 48 94 900 1,653

49.7 46 46 47 47 48 48 337 867

49.9 46 47 47 47 48 49 1,046 1,193

50.1 45 46 46 46 48 50 1,864 1,963

50.2 42 42 43 44 47 1,028 1,371 1,460

50.3 31 32 32 33 35 38 912 996

50.4 34 42 49 55 58 60 1,153 1,389

50.6 43 44 45 46 75 1,035 1,213 1,369

50.9 44 46 47 49 71 86 171 2,046

51.2 32 34 37 45 72 92 2,760 3,042

51.6 28 29 31 32 44 64 4,596 5,012

51.9 44 52 60 69 269 531 1,814 1,898

52.1 39 43 47 108 259 999 1,784 1,844

52.3 45 52 59 65 402 507 790 1,543

Appendix 1. Extent of inundation at cross sections along the 

Hillsborough River for selected percentile discharges. 

[--, no flow]

Cross 

section 

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Feet
Hillsborough River A 3

52.5 90 186 273 355 632 830 1,416 1,871

52.8 38 47 54 60 84 576 1,683 2,090

53 55 69 80 101 915 1,386 1,815 1,998

53.3 49 61 71 80 396 743 1,674 1,794

53.4 24 36 59 80 155 241 510 1,075

53.42 Railroad Bridge

53.44 68 87 102 116 175 298 548 1,159

53.5 146 190 226 259 451 626 1,506 1,909

53.7 66 68 70 71 77 299 3,720 5,481

54.1 44 65 258 422 1,275 2,247 5,409 6,010

54.4 42 49 330 649 1,439 2,144 4,862 6,014

54.8 511 740 953 1,140 1,586 1,787 3,214 5,548

55.1 830 1,184 1,515 1,816 2,066 2,179 3,358 3,986

55.5 627 875 1,121 1,339 1,575 1,716 3,409 4,522

55.53 1,520 1,548 1,578 1,604 1,702 1,802 3,608 4,245

55.55 SR 54 Bridge

55.6 -- -- -- 1,608 1,706 1,809 4,037 4,391

55.61 -- -- -- 49 1,055 1,846 3,767 4,620

55.8 -- -- -- 1,643 1,802 1,936 6,261 7,748

56.1 -- -- -- 2,318 2,645 2,872 6,810 7,173

56.5 -- -- -- 47 49 925 6,494 7,234

456.52 -- -- -- 1,506 1,640 1,832 5,299 6,476

56.54 US 98 Bridge

56.56 -- -- -- 1,528 1,678 2,640 6,217 6,593

56.6 -- -- -- 2,057 2,254 2,519 6,573 8,716

56.9 -- -- -- 5,329 5,484 5,679 6,094 6,729

Mean 97.7 127 196 455 833 1,322 3,475 4,782

Maximum 1,520 1,548 1,848 5,329 5,484 6,407 12,229 15,635

Minimum 19 19 21 29 35 38 123 541

1Hillsborough River at Morris Bridge gaging station. 

2Hillsborough River near Zephyrhills gaging station.

3Hillsborough River above Crystal Springs gaging station.

4Withlacoochee-Hillsborough River Overflow gaging station.

Appendix 1. Extent of inundation at cross sections along the 

Hillsborough River for selected percentile discharges. 

[--, no flow]

Cross 

section 

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Feet
A 4 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Appendix 2. Hydraulic depth at cross sections along the 

Hilsborough River for selected percentile discharges.

[--, no flow}

Cross 

section 

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Feet

28.9 3.5 4.3 4.7 5.0 5.4 5.9 1.8 2.4

128.99 4.3 5.2 5.7 5.9 6.3 6.7 1.2 1.8

29 Morris Bridge

29.01 4.3 5.2 5.7 5.9 6.3 6.7 1.2 2.0

29.1 4.2 4.9 3.9 3.5 3.2 3.4 2.1 2.5

29.49 4.3 1.3 0.8 1.1 1.2 1.4 2.2 3.1

29.5 5.4 6.5 6.5 5.1 3.9 0.7 1.3 2.2

29.6 4.9 5.7 1.1 0.7 1.0 1.0 2.1 3.2

30.0 3.0 0.9 0.8 1.0 1.2 1.6 2.3 3.4

30.3 3.6 0.6 0.9 1.3 1.3 1.8 2.4 3.5

30.6 3.6 4.8 3.7 2.8 0.6 1.1 2.0 3.1

30.9 2.7 3.9 3.6 1.8 0.7 1.2 1.9 3.0

31.4 1.8 3.0 3.8 0.7 1.0 1.3 1.6 2.7

31.8 2.4 3.5 1.2 0.6 1.1 1.6 2.0 3.0

32.1 2.7 3.7 0.5 0.7 1.1 1.6 1.9 3.0

32.3 3.0 4.1 1.4 0.7 0.8 1.1 1.9 3.1

32.6 4.8 5.9 2.8 0.5 0.9 1.1 2.0 3.3

32.8 4.1 5.3 2.1 0.6 0.8 1.2 2.0 3.3

33.0 3.5 4.8 1.4 0.5 0.9 1.1 2.3 2.9

33.4 2.7 4.0 0.6 0.7 0.8 1.1 2.2 2.8

33.7 2.8 4.0 3.0 2.0 0.6 0.9 1.9 2.6

34.1 2.4 3.7 1.4 1.2 1.2 0.6 1.6 2.5

34.5 3.1 4.4 5.3 3.8 2.3 0.5 1.7 2.6

34.9 3.1 4.5 5.6 6.3 0.9 0.8 1.6 2.4

35.3 2.3 3.5 4.4 5.1 0.6 0.5 1.6 2.4

35.9 2.7 3.9 5.0 5.8 2.6 0.8 1.3 2.0

36.4 2.0 3.3 4.3 5.2 3.8 1.1 1.6 1.7

36.7 3.0 4.2 5.3 6.2 7.7 8.9 1.0 1.8

37.30 3.2 4.4 5.5 6.5 8.1 4.7 2.1 2.8

37.62 1.6 2.8 4.0 5.0 6.7 4.5 1.9 2.9

38.2 2.5 3.7 4.7 5.8 7.5 6.8 1.4 2.2

38.7 1.8 2.9 4.0 5.0 6.8 6.3 1.1 2.2

39.2 0.7 1.4 2.4 3.3 5.0 4.0 3.3 4.1

39.5 1.1 1.4 1.9 2.7 4.3 3.9 4.3 3.1

39.8 0.8 1.2 1.6 2.0 3.3 1.9 4.0 3.3

40.2 1.5 2.0 2.5 3.0 2.0 2.1 3.2 2.8

240.4 1.8 2.3 2.8 3.1 1.5 1.7 4.2 4.7

40.7 1.8 2.4 2.4 2.2 1.8 2.4 3.4 4.2

41 2.1 2.8 2.3 2.1 2.1 2.4 3.3 5.2

41.2 2.4 3.1 3.6 4.2 2.2 2.3 3.4 4.8

41.5 2.3 3.1 3.7 3.6 3.2 3.2 3.1 3.3

41.55 1.7 2.1 2.4 2.8 2.5 3.4 6.3 8.2

41.57 US 301 Bridge

41.6 1.7 2.1 2.4 2.8 2.6 3.4 6.4 8.3

41.64 2.3 3.1 3.7 4.3 4.6 4.5 2.6 3.8

41.9 2.5 3.3 3.9 4.6 5.8 5.6 2.9 5.0

42.35 1.5 2.3 2.9 3.5 2.3 3.2 4.2 5.4

42.38 1.8 2.5 3.0 3.6 4.0 3.2 2.5 4.7

42.4 1.6 2.3 2.9 3.5 2.6 2.1 3.0 4.9

42.5 1.4 2.1 2.7 3.3 3.5 3.4 4.2 3.6

42.7 0.6 1.3 1.9 2.5 3.8 2.2 3.8 4.6

43 0.2 0.2 0.3 0.4 2.0 3.4 4.2 2.0

43.3 0.8 1.1 1.5 1.8 2.9 4.3 1.5 3.2

43.6 0.9 1.3 1.7 2.1 3.5 5.1 1.7 3.1

43.8 0.1 0.4 0.7 1.1 2.5 3.7 1.8 3.3

44.1 0.1 0.8 0.9 1.1 1.9 2.5 2.1 3.0

44.3 0.5 0.5 0.8 1.0 1.9 2.7 2.1 3.1

44.6 0.7 1.2 1.5 1.7 2.3 0.7 2.4 3.6

44.9 0.7 1.1 1.4 1.8 1.6 1.1 2.3 3.9

45.1 0.7 1.1 1.4 1.7 2.5 2.2 2.0 3.0

45.4 0.5 0.8 1.1 1.4 1.8 1.1 2.7 4.0

45.7 0.5 0.7 0.9 1.1 1.8 1.0 2.1 3.5

46 0.4 0.5 0.6 0.7 0.8 1.4 3.4 4.4

46.2 0.3 0.4 0.4 0.4 0.6 1.3 3.2 4.6

46.3 0.3 0.5 0.6 0.7 0.9 0.4 1.8 3.4

346.4 0.3 0.4 0.5 0.6 0.7 1.2 2.5 4.3

46.405 Crystal Springs Bridge

46.41 0.4 0.5 0.6 0.4 0.9 1.5 3.0 5.1

46.46 0.4 0.6 0.8 1.0 0.2 0.5 1.8 2.7

46.6 0.6 0.9 1.1 1.1 0.5 0.7 1.8 3.0

46.9 0.8 1.1 1.3 1.0 0.6 0.6 1.7 3.1

47.1 0.8 1.2 1.5 1.8 1.2 0.7 1.3 2.1

47.3 0.9 1.3 1.6 1.9 1.7 1.4 1.6 1.7

47.6 0.9 1.3 1.6 1.9 1.3 1.2 1.9 2.9

47.7 0.9 1.3 1.6 2.0 1.4 1.4 2.1 3.2

47.8 0.8 1.2 1.6 2.0 1.3 1.3 2.3 3.2

47.84 0.8 1.2 1.6 1.9 2.3 2.6 1.9 3.4

47.85 SR 39 Bridge

47.86 0.9 1.3 1.6 2.0 2.3 2.7 2.1 4.0

47.9 0.9 1.3 1.8 2.2 2.6 2.6 2.1 2.9

48.0 0.8 1.2 1.5 1.9 1.5 2.2 2.2 3.0

48.1 0.8 1.2 1.6 2.0 1.6 2.0 2.9 4.2

48.16 0.7 1.0 1.2 1.5 2.4 3.1 3.0 3.9

48.17 Railroad Bridge

48.18 0.8 1.0 1.3 1.5 2.4 3.1 3.1 4.1

48.2 1.1 1.2 1.1 1.3 2.1 2.8 3.7 3.7

48.4 0.9 1.3 1.7 2.1 3.4 1.7 2.4 3.7

48.7 0.7 1.2 1.6 2.1 3.4 1.9 2.6 3.3

48.9 0.6 1.0 1.4 1.8 3.6 5.2 2.0 3.1

49.2 0.3 0.5 0.7 1.0 2.6 3.1 2.5 3.2

49.4 0.5 0.7 0.9 1.1 2.0 1.8 2.3 3.0

49.7 0.4 0.7 0.9 1.2 2.3 3.6 1.1 2.1

49.9 0.6 0.8 1.1 1.4 2.5 3.9 1.8 3.2

50.1 0.3 0.5 0.8 1.0 2.2 3.5 2.0 3.5

50.2 0.5 0.7 0.9 1.1 2.0 0.3 2.0 3.4

50.3 0.6 0.9 1.1 1.4 2.4 3.4 0.9 2.3

50.4 0.4 0.5 0.7 0.9 2.0 3.0 0.9 1.9

50.6 0.8 1.1 1.4 1.7 1.8 0.8 2.4 3.4

50.9 0.7 1.1 1.4 1.7 2.3 2.8 2.8 1.1

51.2 0.7 1.1 1.4 1.5 2.1 2.7 0.8 1.8

51.6 0.6 1.0 1.3 1.6 2.5 2.9 1.1 1.9

51.9 0.4 0.6 0.8 0.9 0.9 1.3 1.9 2.8

52.1 0.4 0.6 0.7 0.4 0.6 0.6 1.9 2.9

52.3 0.4 0.6 0.8 0.9 0.4 0.8 1.5 1.6

Appendix 2. Hydraulic depth at cross sections along the 

Hilsborough River for selected percentile discharges. (Continued)

[--, no flow}

Cross 

section 

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Feet
Hillsborough River A 5

52.5 0.6 0.5 0.5 0.6 0.9 1.2 1.9 2.5

52.8 0.2 0.5 0.6 0.8 1.2 0.5 1.4 2.2

53 0.5 0.7 0.8 0.8 0.5 0.7 1.8 2.7

53.3 0.4 0.7 0.8 1.0 0.5 0.6 1.3 2.2

53.4 0.1 0.2 0.3 0.3 0.7 0.8 1.4 2.2

53.42 Railroad Bridge

53.44 0.3 0.4 0.4 0.5 0.8 0.8 1.4 2.3

53.5 0.3 0.4 0.5 0.5 0.7 0.9 1.3 1.9

53.7 0.6 0.8 1.0 1.1 1.6 0.6 0.7 1.1

54.1 0.6 0.6 0.3 0.4 0.5 0.8 1.2 1.7

54.4 0.5 0.7 0.2 0.2 0.6 0.9 1.3 1.7

54.8 0.2 0.3 0.4 0.5 0.9 1.4 1.8 1.6

55.1 0.2 0.3 0.4 0.5 1.0 1.5 2.1 2.5

55.5 0.2 0.3 0.4 0.5 1.0 1.5 2.2 2.3

55.53 0.5 0.7 0.8 1.0 1.6 2.3 3.8 4.5

55.55 SR 54 Bridge

55.6 -- -- -- 1.0 1.6 2.3 4.0 4.9

55.61 -- -- -- 0.8 0.3 0.8 2.1 2.5

55.8 -- -- -- 0.1 0.7 1.4 1.4 1.9

56.1 -- -- -- 0.1 0.7 1.3 2.3 3.0

56.5 -- -- -- 0.0 0.2 0.3 0.9 1.6

456.52 -- -- -- 0.1 0.6 1.1 2.3 3.1

56.54 US 98 Bridge

56.56 -- -- -- 0.2 0.7 1.4 2.9 3.7

56.6 -- -- -- 0.2 0.6 1.2 1.6 1.9

56.9 -- -- -- 0.2 0.7 1.3 2.8 3.2

Mean 1.4 1.91 1.92 1.9 2.1 2.2 2.2 3.1

Maximum 5.4 6.5 6.5 6.5 8.1 8.9 6.4 8.3

Minimum 0 0 0 0 0.2 0.3 0.7 1.1

1Hillsborough River at Morris Bridge gaging station. 

2Hillsborough River near Zephyrhills gaging station.

3Hillsborough River above Crystal Springs gaging station.

4Withlacoochee-Hillsborough River Overflow gaging station.

Appendix 2. Hydraulic depth at cross sections along the 

Hilsborough River for selected percentile discharges. (Continued)

[--, no flow}

Cross 

section 

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Feet
A 6 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Appendix 3. Acreage of areal inundation between adjacent

cross sections along Hillsborough River.

[--, no flow}

Cross 

section

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Acres

28.9 Initial Cross Section

28.99 0.9 1.0 1.0 1.1 1.1 1.2 16.0 33.2

29 Morris Bridge

29.01 0.3 0.3 0.3 0.3 0.3 0.4 1.9 4.1

29.1 0.7 0.8 0.9 1.1 1.4 1.7 16.8 36.6

29.49 6.7 13.5 36.9 46.1 87.7 142.4 412.8 684.2

29.5 0.0 0.2 0.6 0.8 1.6 3.5 10.0 16.7

29.6 0.0 0.0 0.2 0.6 1.3 3.9 10.2 16.7

30.0 3.4 17.1 45.3 83.9 155.6 259.0 539.7 741.0

30.3 2.4 24.8 46.1 62.6 118.4 150.1 331.3 448.6

30.6 3.7 23.6 36.3 44.7 133.1 162.3 350.0 475.9

30.9 2.9 3.0 4.3 7.8 81.8 98.9 233.4 326.8

31.4 5.6 5.8 6.6 28.6 126.1 152.3 451.1 642.1

31.8 3.5 3.6 7.6 65.3 101.7 118.3 376.0 514.8

32.1 2.3 2.4 23.4 70.0 92.9 104.9 302.7 389.8

32.3 2.0 2.1 23.0 52.1 93.0 115.2 312.5 386.1

32.6 2.8 3.0 9.3 54.2 108.2 147.7 345.1 406.9

32.8 2.4 2.5 7.6 51.7 105.0 140.4 300.6 343.9

33.0 2.8 2.9 9.6 57.5 110.7 156.1 289.2 373.6

33.4 3.4 3.4 18.2 74.6 134.9 194.3 320.5 472.7

33.7 2.7 2.8 14.8 39.9 130.9 176.0 349.2 498.8

34.1 3.8 3.9 10.7 21.3 104.9 203.6 499.7 671.1

34.5 4.7 4.9 9.9 18.2 35.6 228.5 496.5 642.3

34.9 4.1 4.2 4.3 5.4 20.2 150.2 281.5 356.4

35.3 4.0 4.2 4.3 4.4 45.4 180.7 367.0 493.5

35.9 4.5 4.8 4.9 5.1 45.5 200.8 435.7 576.8

36.4 3.8 3.9 4.0 4.0 9.7 65.4 236.8 379.3

36.7 2.9 3.0 3.0 3.1 4.2 20.1 197.3 307.6

37.30 5.3 5.4 5.4 5.6 5.7 9.2 388.6 497.9

37.62 3.4 3.5 3.5 3.6 3.7 7.1 191.4 232.4

38.2 5.4 5.5 5.6 5.7 5.8 8.2 191.6 242.9

38.7 6.2 6.3 6.4 6.5 6.7 9.0 213.6 295.0

39.2 Confluence of Hillsborugh River and New River

39.5 3.9 4.0 4.1 4.2 4.4 7.4 29.4 50.2

39.8 3.5 3.6 3.6 3.7 4.0 8.1 19.2 41.6

40.2 4.2 4.2 4.3 4.4 6.3 13.0 33.9 85.5

40.4 2.5 2.6 2.7 2.8 7.6 14.8 36.1 75.3

40.7 2.7 2.8 3.1 3.9 9.5 15.6 34.2 55.0

41 2.9 3.0 4.0 5.6 10.6 15.4 44.2 61.6

41.2 2.0 2.0 2.5 3.2 6.6 10.7 35.1 45.9

41.5 3.9 4.0 4.0 4.4 7.3 11.0 38.4 66.3

41.55 0.8 0.9 1.0 1.2 1.9 2.4 7.0 17.4

41.57 US 301 Bridge

41.6 0.6 0.7 0.8 1.0 1.7 1.9 3.4 9.3

41.64 0.4 0.5 0.6 0.6 0.9 1.1 4.6 11.7

41.9 2.5 2.6 2.6 2.7 2.9 3.8 30.1 41.5

42.35 2.2 2.2 2.3 2.3 4.0 4.9 26.2 32.4

42.38 1.4 1.5 1.5 1.5 3.0 4.0 16.4 22.1

42.4 1.1 1.1 1.1 1.2 2.0 4.8 28.6 36.1

42.5 1.3 1.4 1.4 1.5 2.2 4.0 19.7 29.7

42.7 2.0 2.1 2.2 2.3 2.6 4.7 13.4 27.6

43 2.2 2.2 2.3 2.3 2.5 5.3 13.5 33.5

43.3 1.7 1.7 1.7 1.7 1.8 1.9 8.8 20.8

43.6 2.1 2.1 2.1 2.1 2.2 2.2 15.1 21.9

43.8 1.2 1.2 1.2 1.2 1.3 1.3 22.6 30.6

44.1 2.1 2.1 2.2 2.2 2.2 2.5 21.5 32.3

44.3 2.1 2.2 2.2 2.2 2.2 2.6 21.1 34.2

44.6 2.4 2.5 2.5 2.5 2.8 8.5 25.7 36.6

44.9 1.9 1.9 1.9 2.0 3.2 13.6 28.2 33.9

45.1 2.3 2.4 2.4 2.5 4.0 12.1 33.7 42.1

45.4 2.3 2.4 2.5 2.6 3.7 13.3 30.6 40.0

45.7 2.0 2.2 2.3 2.5 3.9 19.5 44.3 53.2

46 2.8 3.6 4.2 5.0 12.1 23.8 43.5 53.6

46.2 2.0 2.5 3.0 4.1 17.4 24.3 30.1 36.1

46.3 1.0 1.1 1.2 1.8 8.2 10.7 22.2 25.8

46.4 0.3 0.4 0.3 0.4 2.7 4.5 9.0 10.3

46.405 Crystal Springs Bridge

46.41 0.1 0.1 0.2 0.5 1.3 1.8 2.0 2.3

46.46 0.3 0.3 0.4 2.0 5.2 8.9 10.7 14.9

46.6 1.1 1.2 1.2 1.4 12.2 25.0 30.7 45.9

46.9 1.7 1.7 1.8 2.5 14.9 30.8 40.4 47.7

47.1 1.4 1.4 1.5 1.9 6.8 21.4 43.6 54.3

47.3 1.7 1.8 1.8 1.9 4.3 13.8 42.1 65.0

47.6 1.3 1.3 1.4 1.4 3.7 9.5 28.2 44.9

47.7 0.6 0.7 0.7 0.8 2.3 5.8 16.7 20.1

47.8 0.4 0.4 0.5 0.5 1.6 3.6 9.1 11.1

47.84 0.2 0.3 0.3 0.3 0.7 1.5 3.8 5.4

47.85 SR 39 Bridge

47.86 0.1 0.1 0.1 0.1 0.1 0.2 0.7 0.9

47.9 0.3 0.3 0.3 0.3 0.5 0.7 3.6 5.8

48.0 0.6 0.6 0.6 0.7 1.9 2.7 11.3 18.3

48.1 0.6 0.6 0.6 0.7 2.4 3.6 11.1 16.4

48.16 0.2 0.3 0.3 0.3 0.7 1.2 4.7 5.6

48.17 Railroad Bridge

48.18 0.0 0.1 0.1 0.1 0.1 0.2 1.2 1.5

48.2 0.3 0.3 0.4 0.5 0.7 0.8 2.6 4.0

48.4 1.1 1.3 1.6 2.0 2.9 5.1 14.5 22.8

48.7 1.3 1.4 1.4 1.4 1.7 6.4 21.6 34.4

48.9 1.2 1.2 1.2 1.3 1.4 3.1 15.5 26.1

49.2 1.6 1.6 1.6 1.6 1.7 2.0 23.5 38.8

49.4 1.4 1.4 1.4 1.4 1.4 2.3 22.3 36.4

49.7 1.5 1.5 1.5 1.5 1.5 2.2 17.3 34.9

49.9 1.6 1.6 1.6 1.6 1.6 1.7 23.2 34.6

50.1 0.7 0.7 0.8 0.8 0.8 0.8 19.1 20.6

50.2 1.1 1.1 1.1 1.1 1.2 11.9 35.7 37.8

50.3 0.3 0.3 0.3 0.3 0.4 2.7 5.5 6.0

50.4 0.1 0.1 0.1 0.1 0.1 0.1 2.9 3.2

50.6 1.2 1.3 1.5 1.6 2.1 17.4 37.5 43.4

50.9 1.6 1.6 1.7 1.8 2.5 17.3 20.7 51.8

51.2 1.5 1.6 1.6 1.8 2.5 3.0 43.9 75.6

51.6 1.1 1.1 1.2 1.4 2.0 2.5 99.7 110.0

51.9 1.4 1.5 1.7 1.9 5.6 10.4 108.6 117.4

52.1 1.1 1.3 1.5 2.4 6.9 20.0 47.1 49.0

52.3 1.1 1.2 1.3 2.1 8.0 17.5 29.7 38.9

Appendix 3. Acreage of areal inundation between adjacent

cross sections along Hillsborough River. (Continued)

[--, no flow}

Cross 

section

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Acres
Hillsborough River A 7

52.5 1.9 3.4 4.8 6.0 14.8 19.2 31.6 49.0

52.8 1.9 3.3 4.6 5.8 9.9 19.4 42.7 54.6

53 1.4 1.7 2.0 2.4 14.9 29.5 53.6 63.1

53.3 1.9 2.4 2.8 3.3 23.7 38.4 62.6 67.9

53.4 0.4 0.6 0.7 0.9 3.1 5.6 12.4 16.7

53.42 Railroad Bridge

53.44 0.1 0.1 0.2 0.2 0.3 0.5 0.9 1.3

53.5 0.4 0.5 0.6 0.6 1.1 1.6 3.5 5.3

53.7 2.7 3.2 3.6 4.0 6.0 11.3 61.0 82.9

54.1 2.5 3.0 6.7 9.9 27.0 50.8 187.0 236.5

54.4 1.7 2.1 8.4 14.8 36.5 58.6 136.2 159.4

54.8 13.6 19.3 31.1 43.1 73.1 95.2 193.6 277.6

55.1 21.6 30.8 39.4 47.2 58.3 63.3 103.9 150.4

55.5 27.4 38.6 49.4 59.0 68.0 72.6 123.9 155.8

55.53 4.9 5.6 6.2 6.8 7.5 8.1 16.1 20.1

55.55 SR 54 Bridge

55.6 -- -- -- 3.6 3.8 3.9 7.7 8.7

55.61 -- -- -- 4.9 8.2 10.8 24.1 28.0

55.8 -- -- -- 22.0 36.9 48.6 133.6 165.6

56.1 -- -- -- 72.1 81.0 87.6 232.9 265.5

56.5 -- -- -- 52.1 59.3 83.6 296.1 320.6

56.52 -- -- -- 1.8 1.9 3.2 13.5 15.7

56.54 US 98 Bridge

56.56 -- -- -- 2.3 2.5 3.1 7.6 8.6

56.6 -- -- -- 16.0 17.5 22.9 56.3 67.3

56.9 -- -- -- 127.0 133.1 141.1 216.3 262.6

Total 277 379 624 1,454 2,812 4,621 12,126 16,350

Appendix 3. Acreage of areal inundation between adjacent

cross sections along Hillsborough River. (Continued)

[--, no flow}

Cross 

section

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Acres
A 8 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Appendix 4. Decrease of inundated acreage resulting from a

potential 10-percent discharge withdrawal at cross sections along 

Hillsborough River. 

[Blanks indicate no decrease in inundated acreage; --, no flow]

Cross 

section

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Acres

28.9 Initial Cross Section

28.99 0.01 0.01 0.01 0.02 0.02 0.02 1.26 0.71

29 Morris Bridge

29.01 0.11 0.05

29.1 0.01 0.01 0.15 0.05 0.06 0.03 1.53 0.99

29.49 0.07 6.17 3.73 2.60 16.74 9.53 33.07 19.66

29.5 0.13 0.05 0.05 0.33 0.29 0.99 0.47

29.6 0.09 0.11 0.35 0.20 1.02 0.47

30 0.18 3.44 9.45 10.72 26.42 10.11 44.39 17.69

30.3 0.08 3.37 5.07 4.35 14.17 4.91 32.65 10.97

30.6 0.01 1.99 3.29 2.39 14.10 4.71 32.78 12.76

30.9 0.01 0.01 0.36 2.30 7.72 3.31 22.67 10.03

31.4 0.02 0.23 20.52 9.45 4.44 35.71 19.00

31.8 0.02 0.02 2.08 19.48 4.85 2.21 22.00 14.59

32.1 0.02 0.02 8.76 6.52 3.92 4.05 21.96 10.39

32.3 0.01 0.03 9.35 5.24 4.10 8.26 24.08 9.67

32.6 0.02 0.02 3.04 28.42 6.66 10.82 20.25 9.19

32.8 0.01 0.02 1.11 33.08 10.91 6.57 12.79 7.18

33 0.01 0.02 4.37 13.48 12.38 4.49 9.39 27.95

33.4 14.77 4.28 22.74 7.78 11.66 59.82

33.7 0.01 0.02 11.63 2.83 21.05 10.48 22.32 34.68

34.1 0.02 0.02 3.35 2.45 8.61 61.78 37.21 9.42

34.5 0.02 0.04 2.29 2.30 4.26 63.78 44.59 8.00

34.9 0.01 0.01 0.01 0.59 6.66 8.81 16.66 3.25

35.3 0.01 0.03 0.04 0.01 21.12 46.08 8.44 4.55

35.9 0.03 0.03 0.04 0.04 21.03 75.81 9.73 23.71

36.4 0.01 0.02 0.01 0.02 3.38 16.57 9.73 31.64

36.7 0.02 0.02 0.02 0.02 1.06 3.74 12.57 17.25

37.3 0.01 0.02 0.02 0.02 0.03 3.21 16.26 18.35

37.62 0.01 0.00 0.02 0.02 0.02 3.11 5.03 7.07

38.2 0.01 0.03 0.02 0.02 0.02 1.68 8.38 9.64

38.7 2.28 2.38 2.48 2.56 2.72 5.03 209.62 291.06

39.2 Confluence of Hillsborugh River and New River

39.5 0.01 0.01 0.03 0.04 0.05 1.20 1.72 6.03

39.8 0.02 0.01 0.02 0.05 1.19 1.21 7.93

40.2 0.02 0.01 0.02 0.04 0.47 1.70 2.61 13.98

40.4 0.01 0.02 0.03 0.04 1.23 1.54 2.61 8.57

40.7 0.02 0.03 0.18 0.23 1.29 1.25 3.73 5.62

41 0.01 0.01 0.40 0.55 1.02 0.99 4.15 3.27

41.2 0.01 0.15 0.25 0.75 0.89 2.11 0.86

41.5 0.02 0.02 0.03 0.15 0.67 0.80 2.31 6.02

41.55 0.02 0.02 0.02 0.07 0.14 0.12 0.55 1.23

41.57 US 301 Bridge

41.6 0.01 0.02 0.02 0.03 0.09 0.06 0.30 0.18

41.64 0.01 0.01 0.02 0.01 0.04 0.04 0.57 0.50

41.9 0.01 0.01 0.01 0.02 0.08 0.18 2.24 2.22

42.35 0.02 0.01 0.01 0.34 0.18 1.03 1.14

42.38 0.02 0.01 0.01 0.01 0.36 0.13 1.13 1.04

42.4 0.00 0.01 0.01 0.59 0.43 2.18 0.79

42.5 0.01 0.01 0.02 0.02 0.41 0.32 0.97 0.93

42.7 0.01 0.02 0.02 0.03 0.12 0.42 0.60 1.34

43 0.01 0.01 0.01 0.03 0.54 0.97 3.14

43.3 0.01 0.01 0.01 0.01 0.01 1.45 1.52

43.6 0.01 0.01 0.01 1.96 0.54

43.8 0.01 0.08 2.35 0.94

44.1 0.01 0.01 0.01 0.13 2.10 1.57

44.3 0.01 0.20 1.67 1.77

44.6 0.01 0.07 1.60 1.30 1.43

44.9 0.01 0.01 0.69 2.38 0.63 0.77

45.1 0.01 0.01 0.01 0.01 0.77 1.62 0.97 0.95

45.4 0.01 0.02 0.03 0.03 0.45 1.10 1.20 1.07

45.7 0.01 0.03 0.04 0.06 0.62 2.27 1.14 1.69

46 0.02 0.08 0.19 0.21 4.36 1.52 0.87 1.71

46.2 0.03 0.06 0.21 0.33 3.20 0.42 0.42 0.99

46.3 0.09 0.18 0.15 1.18 0.49 0.44

46.40 0.01 0.01 0.02 0.11 0.71 0.16 0.15

46.405 Crystal Springs Bridge

46.41 0.01 0.18 0.04 0.10 0.01 0.11

46.46 0.80 0.72 0.28 0.23 0.87

46.6 0.01 0.02 0.05 4.36 0.31 0.55 0.99

46.9 0.03 0.28 2.90 1.69 0.41 1.35

47.1 0.01 0.02 0.01 0.18 1.75 3.55 0.78 1.56

47.3 0.02 0.01 0.47 3.14 1.59 3.36

47.6 0.00 0.02 0.01 0.01 0.56 0.94 2.06 2.47

47.7 0.01 0.00 0.01 0.02 0.42 0.57 0.83 0.41

47.8 0.01 0.24 0.31 0.34 0.26

47.84 0.01 0.01 0.00 0.08 0.14 0.28 0.21

47.85 SR 39 Bridge

47.86 0.01 0.01 0.04 0.03

47.9 0.01 0.04 0.04 0.27 0.25

48 0.01 0.10 0.13 1.22 0.67

48.1 0.01 0.01 0.16 0.19 1.10 0.51

48.16 0.05 0.07 0.14 0.29

48.17 Railroad Bridge

48.18 0.01 0.01 0.01 0.01 0.12

48.2 0.01 0.01 0.02 0.02 0.02 0.02 0.11 0.08

48.4 0.01 0.06 0.09 0.09 0.08 0.41 1.16 0.50

48.7 0.01 0.01 0.01 0.01 0.08 0.98 1.95 1.46

48.9 0.04 0.37 1.50 1.58

49.2 0.01 0.01 0.01 0.29 1.06 3.37

49.4 0.01 0.81 0.79 1.68

49.7 0.01 0.60 2.53 0.44

49.9 -0.01 0.01 2.98 0.57

50.1 0.01 0.00 0.21 0.22

50.2 0.01 0.01 4.53 0.25 0.27

50.3 0.97 0.18 0.10

50.4 0.09 0.05

50.6 0.01 0.02 0.04 0.02 0.41 0.24 0.35 0.66

50.9 0.02 0.01 0.01 0.02 0.43 0.23 0.35 1.12

51.2 0.02 0.04 0.04 0.07 0.07 2.00 1.47

51.6 0.01 0.00 0.03 0.05 0.06 0.14 3.33 1.12

51.9 0.02 0.04 0.05 0.05 0.63 2.35 2.08 0.55

Appendix 4. Decrease of inundated acreage resulting from a

potential 10-percent discharge withdrawal at cross sections along 

Hillsborough River. (Continued)

[Blanks indicate no decrease in inundated acreage; --, no flow]

Cross 

section

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Acres
Hillsborough River A 9

52.1 0.01 0.03 0.03 0.80 0.75 4.53 0.21 0.29

52.3 0.02 0.03 0.04 0.68 0.47 2.51 0.42 1.57

52.5 0.02 0.26 0.31 0.37 0.62 0.62 1.23 2.82

52.8 0.03 0.25 0.30 0.36 0.44 1.99 1.57 1.17

53 0.03 0.05 0.06 0.22 1.34 2.11 1.59 0.45

53.3 0.04 0.07 0.09 0.31 2.50 1.31 0.95 0.59

53.4 0.02 0.04 0.04 0.04 0.33 0.45 0.16 0.81

53.42 Railroad Bridge

53.44 0.01 0.02 0.01 0.04 0.03 0.08

53.5 0.02 0.02 0.02 0.03 0.12 0.17 0.24

53.7 0.07 0.08 0.09 0.09 0.14 2.19 3.08 3.00

54.1 0.02 0.31 0.83 0.89 3.40 3.80 30.59 7.71

54.4 0.03 0.24 1.65 1.66 2.98 3.08 18.49 4.87

54.8 0.70 1.01 3.08 2.89 2.00 4.09 6.90 8.70

55.1 1.15 1.66 1.90 1.73 0.47 0.68 3.05 2.37

55.5 1.42 2.05 2.36 2.18 0.42 0.62 2.94 4.49

55.53 0.09 0.12 0.13 0.12 0.06 0.05 0.30 0.57

55.55 SR 54 Bridge

55.6 -- -- -- 0.01 0.02 0.01 0.28 0.11

55.61 -- -- -- 0.02 0.34 0.06 1.44 0.74

55.8 -- -- -- 1.89 1.55 0.23 17.28 5.19

56.1 -- -- -- 2.63 0.80 0.29 19.40 5.29

56.5 -- -- -- 0.03 0.65 3.20 15.15 2.95

56.52 -- -- -- 0.01 0.21 0.95 0.36

56.54 US 98 Bridge

56.56 -- -- -- 0.01 0.14 0.27 0.20

56.6 -- -- -- 0.05 0.08 0.95 1.84 1.19

Total 7.0 24.9 98.8 186 297 464 940 860

Appendix 4. Decrease of inundated acreage resulting from a

potential 10-percent discharge withdrawal at cross sections along 

Hillsborough River. (Continued)

[Blanks indicate no decrease in inundated acreage; --, no flow]

Cross 

section

No.

Percentiles

P10 P50 P70 P80 P90 P95 P99.5 P99.97

Acres
Appendix 5. Extent of inundation at cross sections along 

New River for selected percentile discharges.

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5

Feet

Mean

Maximum

Minimum

A 10 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

0.02 6 15 22 27 30 1,727

0.16 4 28 36 128 517 1,491

0.36 13 18 25 32 40 500

0.46 6 28 39 61 152 453

0.58 6 11 17 22 28 59

0.72 8 13 14 15 37 171

0.77 19 33 34 34 35 131

0.91 2 5 7 9 17 138

0.98 4 9 17 29 45 130

1.12 8 22 34 54 89 1,099

1.17 16 24 28 44 68 1,309

1.22 39 40 55 97 147 572

1.29 8 22 27 29 70 396

1.39 10 19 25 34 231 1,270

1.49 20 44 60 80 106 880

1.62 22 22 22 23 23 52

1.81 30 32 33 35 38 97

1.83 6 9 11 13 1,334 2,932

1.84 Morris Bridge

1.85 9 11 13 1,415 1,889 2,880

1.88 13 26 28 30 33 44

1.92 9 9 11 21 28 206

1.99 9 16 17 18 20 581

2.10 6 17 21 22 23 102

2.21 18 28 34 40 50 219

2.43 9 23 30 31 33 74

2.84 29 35 39 45 60 142

3.22 31 35 39 44 56 101

3.24 53 59 65 83 134 511

3.245 Camp Road Culvert

3.25 53 59 65 85 137 553

3.27 28 31 33 42 58 410

3.51 45 154 67 200 229 446

3.82 21 36 53 39 44 176

3.83 37 49 66 69 82 168

3.85 45 47 51 53 57 550

4.02 7 12 17 201 262 1,428

4.21 18 22 25 27 30 1,488

4.52 8 18 23 29 151 1,873

4.53 10 20 22 25 27 1,094

4.55 28 30 34 44 267 1,807

4.87 25 35 47 64 83 1,162

5.07 18 22 24 36 61 619

5.36 17 23 31 44 61 635

5.60 34 40 44 50 58 82

5.87 14 34 55 61 62 65

5.88 4 8 13 21 30 40

5.889 Chancy Road Bridge

5.89 7 13 18 23 31 61

5.92 2 5 7 9 11 79

6.15 5 10 15 25 88 388

6.29 8 20 23 26 29 75

6.39 10 23 31 35 41 186

6.41 19 26 27 30 36 59

6.43 6 14 16 18 25 59

6.81 14 29 99 171 244 501

6.92 28 35 38 41 50 426

6.925 43 71 82 93 162 525

6.93 SR 54 Culvert

6.94 43 71 82 93 163 533

6.96 22 31 40 49 57 121

7.27 17 12 22 27 261 1,123

7.44 14 16 17 18 105 190

7.58 11 12 13 14 16 105

7.68 10 11 12 13 16 213

7.87 14 15 17 19 23 302

7.98 9 9 12 17 34 267

8.05 12 14 18 24 78 293

8.17 11 14 17 22 136 476

8.46 16 19 24 52 92 291

17.4 26.7 31.9 67.0 132 563

53 154 99 1,415 1,889 2,932

2 5 7 9 11 40

Appendix 5. Extent of inundation at cross sections along 

New River for selected percentile discharges. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5

Feet
Appendix 6. Hydraulic depth at cross sections along 

New River for selected percentile discharges. 

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5

Feet

New River A 11

0.02 0.06 0.2 0.2 0.3 0.5 1.5

0.16 0.09 0.6 0.8 0.4 0.3 0.9

0.36 0.32 0.5 0.7 0.9 1.3 0.5

0.46 0.08 0.4 0.5 0.6 0.6 1.1

0.58 0.41 0.7 0.9 1.1 1.4 1.4

0.72 0.25 0.8 1.5 2.2 1.4 1.7

0.77 0.23 0.7 1.4 2.1 3.1 2.3

0.91 0.13 0.3 0.4 0.6 1.2 1.6

0.98 0.45 0.9 0.9 1.0 1.2 1.7

1.12 0.13 0.4 0.6 0.8 1.0 0.8

1.17 0.24 0.5 0.8 0.9 1.1 0.7

1.22 0.34 0.8 0.9 0.9 1.1 1.3

1.29 0.16 0.4 0.8 1.2 0.9 1.2

1.39 0.25 0.5 0.6 0.9 0.3 1.0

1.49 0.14 0.4 0.5 0.7 1.0 0.8

1.62 0.10 0.2 0.3 0.5 0.9 1.1

1.81 0.17 0.6 0.9 1.4 1.9 2.4

1.83 0.09 0.4 0.7 1.1 1.5 1.8

1.84 Morris Bridge

1.85 0.31 0.7 1.0 1.6 1.7 1.8

1.88 0.05 0.4 0.8 1.5 2.2 2.6

1.92 0.21 0.2 0.3 0.5 1.1 0.7

1.99 0.30 0.7 1.1 1.5 2.0 0.5

2.10 0.07 0.2 0.5 1.0 1.7 1.6

2.21 0.22 0.5 0.7 0.9 1.2 1.3

2.43 0.15 0.4 0.6 1.0 1.5 2.0

2.84 0.12 0.3 0.5 0.6 0.8 1.6

3.22 0.10 0.4 0.6 0.9 1.1 1.8

3.24 0.15 0.4 0.7 1.1 1.6 3.2

3.245 Camp Road Culvert

3.25 0.16 0.5 0.8 1.1 1.6 3.3

3.27 0.02 0.1 0.1 0.3 0.6 1.0

3.51 0.02 0.3 0.1 0.6 0.9 1.6

3.82 0.03 0.1 0.6 0.2 0.4 0.8

3.83 0.13 0.3 0.6 0.6 0.7 1.1

3.85 0.03 0.2 0.4 0.6 0.8 0.5

4.02 0.57 1.0 1.0 0.3 0.5 0.6

4.21 0.68 1.4 1.8 2.3 2.6 0.8

4.52 0.04 0.7 1.2 1.6 0.8 0.6

4.53 0.21 0.4 1.0 1.6 2.2 0.4

4.55 0.17 0.6 1.1 1.5 0.7 0.7

4.87 0.24 0.6 0.9 1.2 1.7 0.9

5.07 0.22 0.7 1.1 1.3 1.4 0.6

5.36 0.25 0.7 1.0 1.2 1.6 0.6

5.60 0.19 0.7 1.1 1.6 2.2 3.8

5.87 0.15 0.4 0.6 1.1 1.9 4.6

5.88 0.15 0.3 0.5 0.8 1.2 3.4

5.889 Chancy Road Bridge

5.89 0.26 0.5 0.7 0.9 1.3 3.4

5.92 0.30 0.6 0.8 1.1 1.3 1.1

6.15 0.58 1.1 1.5 1.5 0.8 1.7

6.29 0.35 0.9 1.6 2.2 2.8 2.4

6.39 0.03 0.1 0.4 1.1 1.8 1.4

6.41 0.13 0.3 0.5 0.8 1.5 2.8

6.43 0.13 0.3 0.6 0.8 1.1 2.1

6.81 0.36 0.7 0.5 0.6 0.9 1.9

6.92 0.12 0.7 1.1 1.5 1.7 0.9

6.925 0.08 0.7 1.1 1.5 2.0 3.9

6.93 SR 54 Culvert

6.94 0.08 0.7 1.1 1.5 2.0 3.9

6.96 0.12 0.5 0.8 1.1 1.4 2.1

7.27 0.12 0.1 0.2 0.5 0.2 1.2

7.44 0.12 0.5 0.8 1.1 0.4 0.8

7.58 0.28 0.7 1.1 1.5 1.8 0.8

7.68 0.06 0.5 1.0 1.4 1.7 0.9

7.87 0.17 0.4 0.7 1.1 1.6 0.8

7.98 0.41 0.8 1.1 1.2 1.1 1.2

8.05 0.24 0.7 1.0 1.2 0.8 1.6

8.17 0.18 0.6 1.0 1.2 0.6 1.4

8.46 0.12 0.4 0.7 0.7 0.8 1.5

Mean 0.2 0.5 0.8 1.1 1.3 1.6

Maximum 0.7 1.4 1.8 2.3 3.1 4.6

Minimum 0.02 0.1 0.1 0.2 0.2 0.4

Appendix 6. Hydraulic depth at cross sections along 

New River for selected percentile discharges. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5

Feet
Appendix 7. Acreage of areal inundation between 

adjacent cross sections along New River. 

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5

Acres

Initial cross section above confluence with Hillsborough River

Morris Bridge

Camp Road Culvert

Chancy Road Bridge

SR 54 Culvert

Total

A 12 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

0.02

0.16 0.09 0.37 0.50 1.3 4.43 25.42

0.36 0.21 0.56 0.73 1.87 6.72 24.36

0.46 0.11 0.29 0.4 0.59 1.21 6.01

0.58 0.09 0.27 0.38 0.57 1.24 3.65

0.72 0.11 0.19 0.25 0.3 0.51 1.76

0.77 0.07 0.12 0.12 0.13 0.19 0.8

0.91 0.19 0.33 0.35 0.37 0.44 2.31

0.98 0.03 0.07 0.13 0.2 0.31 1.33

1.12 0.1 0.26 0.43 0.69 1.12 10.23

1.17 0.07 0.13 0.17 0.28 0.45 6.91

1.22 0.19 0.22 0.29 0.49 0.74 6.48

1.29 0.19 0.25 0.33 0.51 0.88 4.03

1.39 0.1 0.23 0.3 0.37 1.74 9.59

1.49 0.18 0.39 0.52 0.69 2.07 13.01

1.62 0.27 0.41 0.52 0.64 0.81 5.82

1.81 0.59 0.62 0.63 0.66 0.7 1.6

1.83 0.05 0.05 0.06 0.06 1.65 3.66

1.84

1.85 0.01 0.02 0.02 0.67 1.12 4.65

1.88 0.04 0.07 0.07 3.29 4.38 6.64

1.92 0.05 0.08 0.09 0.12 0.14 0.62

1.99 0.08 0.11 0.13 0.18 0.22 2.81

2.10 0.1 0.21 0.25 0.27 0.29 4.37

2.21 0.16 0.32 0.38 0.43 0.51 2.18

2.43 0.38 0.73 0.92 1.02 1.18 3.8

2.84 0.74 1.12 1.35 1.48 1.81 3.81

3.22 1.42 1.63 1.83 2.09 2.62 4.92

3.24 0.08 0.1 0.11 0.13 0.19 0.6

3.245

3.25 0.06 0.06 0.07 0.09 0.15 0.61

3.27 0.06 0.07 0.07 0.1 0.15 0.71

3.51 1.09 2.75 1.49 3.52 4.1 11.49

3.82 1.21 3.48 2.19 4.26 4.79 9.95

3.83 0.07 0.1 0.14 0.12 0.15 0.4

3.85 0.09 0.11 0.14 0.14 0.15 0.82

4.02 0.6 0.68 0.78 3.17 4.01 23.27

4.21 0.2 0.27 0.33 1.73 2.21 23.31

4.52 0.49 0.72 0.83 0.97 2.88 47.47

4.53 0.02 0.04 0.06 0.06 0.21 3.4

4.55 0.07 0.09 0.09 0.12 0.51 5

4.87 1.04 1.26 1.56 2.05 6.87 55.15

5.07 0.49 0.65 0.79 1.1 1.56 18.72

5.36 0.61 0.79 0.96 1.31 1.88 18.64

5.60 0.75 0.93 1.07 1.26 1.5 7.29

5.87 0.77 1.18 1.6 1.78 1.92 2.33

5.88 0.01 0.04 0.06 0.08 0.08 0.1

5.889

5.89 0.01 0.01 0.02 0.02 0.03 0.04

5.92 0.01 0.02 0.02 0.04 0.05 0.15

6.15 0.11 0.21 0.3 0.44 1.19 5.4

6.29 0.11 0.27 0.33 0.44 0.97 3.75

6.39 0.11 0.27 0.35 0.39 0.44 1.48

6.41 0.03 0.06 0.06 0.07 0.09 0.28

6.43 0.03 0.04 0.05 0.06 0.07 0.15

6.81 0.47 0.99 2.17 3.36 4.61 9.23

6.92 0.29 0.44 0.88 1.34 1.87 6.02

6.925 0.04 0.06 0.07 0.08 0.12 0.54

6.93

6.94 0.13 0.2 0.24 0.26 0.47 1.52

6.96 0.07 0.12 0.15 0.18 0.28 0.91

7.27 0.71 0.77 1.14 1.42 5.49 21.16

7.44 0.32 0.28 0.41 0.46 3.82 14.03

7.58 0.21 0.24 0.25 0.28 0.94 2.3

7.68 0.13 0.14 0.15 0.16 0.19 1.83

7.87 0.28 0.3 0.33 0.36 0.45 5.59

7.98 0.15 0.17 0.2 0.26 0.39 3.92

8.05 0.08 0.09 0.12 0.16 0.45 2.25

8.17 0.18 0.21 0.26 0.33 1.49 5.32

8.46 0.47 0.58 0.69 1.29 4.02 13.3

17.3 27.8 31.7 52.7 98.2 489

Appendix 7. Acreage of areal inundation between 

adjacent cross sections along New River. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5

Acres
Appendix 8. Decrease of inundated acreage resulting

from a potential 10-percent discharge withdrawal at

cross sections along New River. 

[Blanks indicate no decrease in inundated acreage]

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5

Acres

Morris Bridge

Camp Road Culvert

Chancy Road Bridge

SR 54 Culvert

Total

New River A 13

0.02 Initial cross section above confluence at 

Hillsborough River

0.16 0.01 0.02 0.21 0.9 1.7

0.36 0.03 0.02 0.28 1.4 0.4

0.46 0.01 0.02 0.09 0.1 0.0

0.58 0.01 0.01 0.08 0.1 0.2

0.72 0.01 0.01 0.01 0.0 0.1

0.77 0.1

0.91 0.01 0.01 0.2

0.98 0.01 0.01 0.1

1.12 0.02 0.03 0.06 0.1 0.8

1.17 0.01 0.02 1.0

1.22 0.01 0.03 0.04 1.0

1.29 0.00 0.01 0.02 0.03 0.1 0.2

1.39 0.01 0.4 0.5

1.49 0.01 0.02 0.03 0.03 0.4 0.6

1.62 0.03 0.01 0.01 0.02 0.0 0.2

1.81 0.2

1.83 0.01 0.00 0.01 0.00 0.1 0.1

1.84

1.85 0.03 0.1 1.2

1.88 0.01 0.14 0.2 0.2

1.92 0.01 0.01 0.1

1.99 0.01 0.3

2.10 0.01 0.01 0.4

2.21 0.01 0.01 0.01 0.3

2.43 0.02 0.01 0.02 0.5

2.84 0.03 0.01 0.01 0.1 0.1

3.22 0.02 0.05 0.1 0.3

3.24 0.01 0.01 0.01 0.1

3.245

3.25 0.1

3.27 0.01 0.02 0.1

3.51 0.07 0.07 0.1 0.7

3.82 0.10 0.06 0.1 0.6

3.83 0.03

3.85 0.02 0.1

4.02 0.01 0.10 0.3 1.8

4.21 0.05 0.2 2.7

4.52 0.01 0.01 0.02 0.3 8.0

4.53 0.01 0.7

4.55 0.01 0.01 0.1 1.2

4.87 0.01 0.05 0.07 0.8 8.4

5.07 0.01 0.02 0.02 0.06 0.1 2.0

5.36 0.01 0.02 0.07 0.1 9.7

5.60 0.01 0.02 0.03 5.0

5.87 0.01 0.03 0.06 0.01

5.88 0.01

5.889

5.89 0.01

5.92 0.01

6.15 0.01 0.02 0.01 0.3 0.3

6.29 0.02 0.01 0.03 0.2 0.1

6.39 0.01 0.01 0.1

6.41

6.43 0.01

6.81 0.01 0.04 0.17 0.19 0.2 0.9

6.92 0.05 0.07 0.1 0.6

6.925

6.93

6.94 0.01 0.01 0.1

6.96 0.01 0.01 0.01 0.1

7.27 0.01 0.03 0.04 1.1 0.8

7.44 0.01 0.01 0.7 0.5

7.58 0.01 0.4

7.68 0.01 0.01 0.4

7.87 1.0

7.98 0.01 0.01 0.5

8.05 0.01 0.01 0.1 0.1

8.17 0.01 0.01 0.01 0.02 0.2 0.2

8.46 0.01 0.01 0.15 0.4 0.7

0.2 0.6 0.9 2.4 9.7 58.9

Appendix 8. Decrease of inundated acreage resulting

from a potential 10-percent discharge withdrawal at

cross sections along New River. (Continued)

[Blanks indicate no decrease in inundated acreage]

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5

Acres
A 14 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Appendix 9. Extent of inundation at cross sections along

Blackwater Creek for selected percentile discharges. 

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet

0.01 42 45 52 399 513 1,515 2,092

.15 150 154 159 206 285 658 1,113

.28 76 81 87 108 142 204 386

.43 50 52 53 60 78 130 246

.59 73 77 86 143 168 296 702

.68 123 127 133 156 266 533 788

.90 69 79 88 104 116 272 869

.904 Two Rivers Ranch Bridge

.91 56 71 80 92 100 128 543

.93 64 66 68 75 87 199 1,267

1.14 43 66 91 138 195 771 1,526

1.34 122 175 233 350 394 832 1,394

1.55 60 69 167 328 411 764 1,144

1.80 96 136 187 310 538 1,041 1,417

2.04 58 78 100 117 136 198 857

2.37 77 93 100 113 130 265 459

2.82 58 70 81 106 162 380 1,029

3.02 181 241 269 312 397 1,084 1,609

3.27 93 133 169 297 456 1,148 1,711

3.59 92 150 226 340 461 975 1,167

3.78 60 87 132 261 355 638 752

3.95 39 57 79 103 135 287 835

4.14 13 16 23 49 83 246 2,351

4.36 27 29 30 33 46 1,210 2,796

4.65 26 43 53 85 240 1,059 1,713

4.85 46 48 70 149 252 764 1,093

5.19 34 35 36 38 88 518 1,111

5.34 53 54 56 60 100 749 1,218

5.49 27 31 35 58 90 729 1,234

5.76 30 35 41 50 60 992 1,565

5.82 22 29 38 54 73 644 1,996

5.86 29 35 54 91 131 566 3,717

5.875 SR 39 Bridge

5.88 27 36 56 93 134 1,628 4,257

5.89 28 37 56 93 134 2,114 5,932

5.894 Railroad Bridge

5.90 29 39 58 96 137 1,057 5,530

5.93 32 33 35 38 46 1,311 1,758

6.06 36 38 40 45 55 978 2,756

6.44 33 34 36 39 48 1,177 1,740

6.97 11 17 35 85 139 706 2,162

7.45 41 ,46 64 227 435 1,216 2,457

7.69 49 53 55 60 107 780 2,054

7.70 35 53 75 108 147 842 2,099

7.71 110 126 140 173 216 1,104 2,129

7.92 314 379 455 628 855 1,805 2,375

8.07 44 45 78 180 317 866 1,220

8.34 23 27 32 42 63 354 953

8.59 49 51 104 209 412 985 1,293

8.74 23 24 24 25 27 65 152

8.79 31 34 37 42 44 50 56

8.796 Ranch Bridge

8.80 32 34 38 42 44 50 56

8.84 21 22 23 25 27 81 347

9.00 26 30 34 41 44 209 575

9.27 45 48 64 138 209 392 766

9.52 5 7 10 15 19 43 551

9.87 44 47 51 57 66 96 335

10.25 10 14 17 23 24 30 249

10.41 45 51 57 66 75 91 805

10.45 24 25 26 27 29 39 294

10.454 Bridge

10.46 25 25 26 27 29 50 401

10.48 25 25 26 28 29 37 399

10.79 35 36 37 39 41 49 361

11.07 15 16 17 20 23 40 304

11.44 13 17 21 26 29 32 84

11.48 26 28 29 31 32 33 33

11.484 Ranch Bridge

11.49 27 28 30 31 32 33 33

11.54 13 14 15 18 21 33 56

11.61 29 31 32 35 40 53 104

11.62 Logging Road Bridge

11.63 29 31 33 36 40 56 470

11.89 12 14 16 19 23 36 114

12.31 17 20 24 33 44 87 126

12.39 31 32 32 34 35 46 164

12.42 5 6 8 17 25 38 167

12.49 21 21 22 23 24 29 57

12.497 Culvert

12.50 21 22 22 23 25 30 211

12.55 25 26 26 27 29 35 247

12.72 12 11 11 12 14 27 37

12.90 17 19 21 24 29 60 125

12.98 14 14 18 24 32 61 103

13.02 18 18 19 19 20 22 58

13.21 30 30 31 31 32 35 40

13.28 7 7 7 8 8 10 13

13.58 20 20 21 22 24 30 445

13.67 20 21 21 24 27 41 282

13.74 20 20 21 21 22 25 28

13.741 Water Oak Drive Culvert

13.75 20 21 21 21 22 25 28

13.77 3 4 4 6 8 17 39

13.91 16 16 17 17 18 245 756

13.917 Shady Oak Drive West Culvert

13.92 16 16 17 17 17 19 639

13.93 15 15 15 16 16 19 110

Appendix 9. Extent of inundation at cross sections along

Blackwater Creek for selected percentile discharges. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet
Blackwater Creek A 15

13.937 Culvert

13.94 15 15 15 16 16 19 473

14.08 14 15 18 22 27 511 912

14.23 9 9 10 11 12 28 158

14.24 16 17 18 21 23 31 51

14.249 Shady Oak Drive East Culvert

14.25 16 17 18 21 24 32 56

14.26 16 17 18 21 24 32 57

14.33 6 8 10 10 12 17 43

14.64 13 15 17 22 27 327 486

14.80 15 15 16 18 21 210 358

15.03 12 13 13 15 16 23 27

15.12 31 31 31 31 32 33 34

15.14 15 9 20 31 31 32 33

15.149 Sims Road Bridge

15.15 20 23 29 31 31 32 33

15.17 10 10 10 10 10 13 14

15.22 4 4 4 5 7 7 20

15.45 6 8 10 12 14 18 24

15.65 14 14 14 15 16 21 40

15.70 20 20 21 22 25 88 305

15.72 24 25 27 30 47 307 651

15.725 Harrelson Road Bridge

15.73 24 26 28 31 52 313 655

15.75 13 14 16 19 22 35 445

15.79 6 8 9 12 20 35 403

15.99 12 14 14 15 15 15 19

16.4 26 26 27 28 30 36 43

16.5 9 13 14 14 14 17 18

16.6 18 18 18 18 19 19 20

Mean 36 42 52 76 105 364 833

Maximum 314 379 455 628 855 2,114 5,932

Minimum 3 4 4 5 7 7 13

Appendix 9. Extent of inundation at cross sections along

Blackwater Creek for selected percentile discharges. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet
A 16 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Appendix 10. Hydraulic depth at cross sections along 

Blackwater Creek for selected percentile discharges. 

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet

0.01 1.05 1.64 2.1 1.1 2.2 3.6 5.5

.15 0.78 1.37 2.0 2.7 3.3 4.1 5.1

.28 0.14 0.55 1.2 2.2 2.9 6.0 5.6

.43 0.96 1.22 1.4 1.9 2.6 5.2 5.3

.59 1.14 1.50 1.7 1.8 2.6 4.8 4.2

.68 1.22 1.62 2.0 2.5 2.4 4.6 6.1

.90 0.41 0.82 1.2 1.9 2.8 5.8 9.6

.904 Two Rivers Ranch Bridge

.91 0.48 0.70 1.0 1.8 2.8 6.0 8.1

.93 0.82 1.17 1.5 2.2 3.0 3.8 2.5

1.14 0.43 0.60 0.8 1.1 1.6 2.3 4.0

1.34 0.50 0.55 0.6 0.8 1.3 2.7 4.1

1.55 0.89 1.13 0.7 0.8 1.2 2.6 4.1

1.80 0.60 0.80 1.0 1.2 1.2 2.4 4.1

2.04 0.75 0.91 1.1 1.7 2.3 3.5 2.2

2.37 0.43 0.65 0.9 1.4 2.0 3.2 3.9

2.82 0.64 0.80 1.0 1.2 1.2 2.0 2.2

3.02 0.45 0.60 0.8 1.2 1.4 1.9 3.3

3.27 0.52 0.63 0.7 0.8 1.0 1.8 3.1

3.59 0.92 0.92 1.0 1.3 1.6 2.3 3.6

3.78 0.58 0.82 0.9 1.1 1.5 2.6 4.0

3.95 1.10 1.15 1.3 1.7 2.1 2.7 2.3

4.14 0.44 0.62 0.9 1.1 1.6 2.4 1.0

4.36 1.33 1.89 2.4 3.3 3.4 1.3 1.9

4.65 0.33 0.60 1.0 1.4 1.1 1.5 2.0

4.85 1.04 1.44 1.3 1.2 1.4 1.9 2.7

5.19 0.79 1.31 1.9 2.9 1.8 1.8 1.9

5.34 0.78 1.20 1.7 2.7 2.5 1.2 2.1

5.49 0.65 0.93 1.2 1.5 1.8 1.6 2.0

5.76 1.77 2.11 2.5 3.1 3.7 1.3 2.0

5.82 0.99 1.36 1.6 2.2 2.8 1.3 1.3

5.86 1.17 1.59 1.6 1.9 2.4 3.4 4.8

5.875 SR 39 Bridge

5.88 0.95 1.27 1.4 1.8 2.4 3.5 5.2

5.89 1.21 1.48 1.5 1.9 2.4 2.6 4.4

5.894 Railroad Bridge

5.90 1.58 1.74 1.7 2.0 2.5 2.7 4.5

5.93 0.67 1.31 1.9 2.9 3.6 1.2 2.5

6.06 0.94 1.37 1.9 2.8 3.6 1.3 1.5

6.44 1.43 2.08 2.8 4.0 4.8 1.8 2.3

6.97 0.46 0.70 1.0 1.4 2.0 1.8 1.7

7.45 1.24 1.70 1.7 1.1 1.3 2.4 2.6

7.69 0.78 1.31 1.8 2.7 2.3 1.5 2.0

7.70 0.21 0.26 0.3 0.4 0.5 1.2 1.9

7.71 2.23 2.12 2.1 1.9 1.9 1.3 2.1

7.92 0.94 0.95 1.0 1.0 1.1 2.2 3.3

8.07 2.46 2.62 1.6 1.0 1.0 1.9 2.9

8.34 0.57 0.68 0.8 1.1 1.3 1.0 1.5

8.59 1.42 1.58 1.0 0.9 1.0 1.9 3.1

8.74 0.68 0.91 1.2 1.7 2.3 2.6 2.0

8.79 0.33 0.56 0.8 1.3 1.9 3.8 5.3

8.796 Ranch Bridge

8.80 0.37 0.58 0.8 1.3 1.9 3.8 5.3

8.84 0.48 0.69 0.9 1.4 1.9 1.8 1.4

9.00 0.56 0.81 1.1 1.5 2.1 1.4 1.9

9.27 0.73 1.10 1.2 1.1 1.4 2.7 2.9

9.52 0.31 0.47 0.7 1.1 1.5 2.1 1.5

9.87 0.33 0.48 0.6 0.9 1.3 2.6 1.6

10.25 0.18 0.24 0.3 0.4 0.6 1.7 0.7

10.41 0.51 0.67 0.8 1.1 1.4 2.7 0.9

10.45 0.40 0.62 0.9 1.2 1.6 2.5 3.4

10.454 Bridge

10.46 0.46 0.69 0.9 1.3 1.7 2.3 3.6

10.48 0.48 0.70 0.9 1.3 1.8 3.0 1.0

10.79 0.12 0.30 0.5 1.0 1.5 3.3 1.0

11.07 0.49 0.59 0.7 0.9 1.1 2.3 0.9

11.44 0.27 0.47 0.7 1.0 1.4 3.1 2.4

11.48 0.21 0.31 0.5 0.9 1.4 3.2 5.2

11.484 Ranch Bridge

11.49 0.25 0.35 0.5 0.9 1.4 3.2 5.2

11.54 0.43 0.57 0.7 1.0 1.3 2.3 2.8

11.61 0.63 0.87 1.1 1.6 2.1 3.9 5.8

11.62 Logging Road Bridge

11.63 0.64 0.88 1.1 1.6 2.2 4.3 1.1

11.89 0.37 0.63 0.9 1.3 1.8 3.2 2.3

12.31 0.32 0.45 0.6 0.9 1.2 2.5 3.9

12.39 0.41 0.62 0.9 1.4 1.9 3.5 2.3

12.42 0.16 0.20 0.3 0.6 0.9 2.7 1.6

12.49 0.45 0.65 0.8 1.3 1.9 4.2 6.8

12.497 Culvert

12.50 0.52 0.74 1.0 1.5 2.1 4.5 1.2

12.55 0.11 0.31 0.5 1.0 1.6 3.5 1.2

12.72 0.27 0.13 0.2 0.3 0.4 1.9 3.8

12.90 0.23 0.39 0.5 0.7 0.9 1.4 2.5

12.98 0.14 0.17 0.3 0.4 0.6 1.3 2.5

13.02 0.16 0.26 0.4 0.5 0.8 1.8 1.7

13.21 0.12 0.17 0.3 0.5 0.7 1.8 3.5

13.28 0.33 0.46 0.6 0.8 1.0 1.9 3.0

13.58 0.12 0.20 0.3 0.6 0.9 2.1 0.4

13.67 0.15 0.21 0.3 0.5 0.7 1.7 0.8

13.74 0.17 0.25 0.4 0.6 0.9 2.2 3.8

13.741 Water Oak Drive Culvert

13.75 0.18 0.27 0.4 0.6 0.9 2.2 3.9

13.77 0.23 0.30 0.4 0.5 0.7 1.3 1.6

13.91 0.22 0.33 0.5 0.8 1.1 2.4 4.0

13.917 Shady Oak Drive West Culvert

13.92 0.24 0.36 0.5 0.8 1.1 2.5 4.2

13.93 0.26 0.38 0.5 0.8 1.1 2.5 4.1

13.937 Culvert

13.94 0.32 0.43 0.6 0.9 1.2 2.6 4.4

14.08 0.24 0.34 0.5 0.7 0.9 0.6 1.6

14.23 0.33 0.47 0.6 0.9 1.2 1.3 0.7

14.24 0.26 0.39 0.6 0.8 1.2 2.3 3.6

14.249 Shady Oak Drive East Culvert

14.25 0.32 0.44 0.6 0.9 1.3 2.4 3.8

14.26 0.33 0.45 0.6 0.9 1.2 2.0 2.2

Appendix 10. Hydraulic depth at cross sections along 

Blackwater Creek for selected percentile discharges. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet
Blackwater Creek A 17

14.33 0.09 0.12 0.1 0.2 0.6 1.5 1.5

14.64 0.36 0.51 0.7 1.0 1.2 0.2 0.7

14.80 0.05 0.07 0.2 0.5 0.9 0.7 0.9

15.03 0.30 0.43 0.6 0.7 1.0 1.7 2.3

15.12 0.05 0.16 0.3 0.5 0.8 2.0 2.9

15.14 0.07 0.05 0.1 0.3 0.6 1.8 2.7

15.149 Sims Road Bridge

15.15 0.10 0.11 0.1 0.3 0.6 1.8 2.7

15.17 0.03 0.04 0.1 0.1 0.2 1.2 2.0

15.22 0.26 0.34 0.5 0.7 0.9 1.0 1.2

15.45 0.21 0.27 0.4 0.5 0.8 1.6 2.4

15.65 0.16 0.23 0.4 0.6 0.9 1.8 1.9

15.70 0.03 0.03 0.1 0.2 0.5 0.7 1.1

15.72 0.13 0.17 0.2 0.3 0.4 1.3 2.6

15.725 Harrelson Road Bridge

15.73 0.14 0.18 0.2 0.3 0.4 1.3 2.6

15.75 0.15 0.19 0.3 0.3 0.5 1.2 0.5

15.79 0.04 0.06 0.1 0.1 0.2 0.9 0.5

15.99 0.13 0.16 0.2 0.4 0.5 0.5 1.1

16.4 0.10 0.14 0.2 0.3 0.5 0.9 1.4

16.5 0.03 0.05 0.1 0.1 0.2 0.6 1.2

16.6 0.24 0.30 0.4 0.5 0.7 1.3 2.1

Mean 0.5 0.7 0.9 1.2 1.5 2.3 2.8

Maximum 2.5 2.6 2.8 4.0 4.8 6.0 9.6

Minimum 0.03 0.03 0.1 0.1 0.2 0.2 0.4

Appendix 10. Hydraulic depth at cross sections along 

Blackwater Creek for selected percentile discharges. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet
A 18 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Appendix 11. Acreage of areal inundation between

adjacent cross sections along Blackwater Creek. 

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Acres

0.01 Initial cross section above confluence with Hillsborough River

.15 1.8 1.8 1.9 3.9 4.8 10.9 16.6

.28 1.8 1.9 2 2.5 3.3 6.5 11.4

.43 1.1 1.1 1.2 1.4 1.8 2.7 5.1

.59 1.2 1.3 1.3 1.8 2.1 3.2 6.6

.68 1.1 1.2 1.3 1.6 2.1 3.7 6.8

.90 2.5 2.7 2.8 3.3 4.4 8.2 16

.904 Two Rivers Ranch Bridge

.91 0.1 0.1 0.1 0.1 0.1 0.2 0.4

0.93 0.1 0.1 0.2 0.2 0.2 0.4 2.6

1.14 1.5 1.8 2 2.5 3.3 10 28.8

1.34 2.1 2.8 3.6 5 5.9 15.1 27

1.55 2 2.6 4 6.7 7.7 15 23.7

1.80 2.3 2.8 4.6 8 11.7 21.9 31.2

2.04 2.2 3.1 4.1 6 9.8 17.7 28.9

2.37 2.6 3.2 3.7 4.2 4.7 8 21.7

2.82 3.8 4.5 4.9 5.7 7.1 13.3 28.4

3.02 2.4 3.1 3.4 4.1 5.2 12.9 22.1

3.27 3.3 4.3 5 6.4 8.9 23.8 33.5

3.59 3.3 4.9 6.6 10.6 15.1 34.4 46.5

3.78 1.7 2.5 3.6 5.9 8 15.6 18.5

3.95 0.9 1.3 1.9 3.1 4.1 7.7 13

4.14 0.6 0.8 1.1 1.6 2.2 5.3 30

4.36 0.5 0.6 0.7 1 1.5 16 56.2

4.65 1 1.2 1.5 2.1 4.9 36.5 72.3

4.85 0.8 1.1 1.4 2.6 5.4 19.5 30

5.19 1.8 1.9 2.2 3.5 6 22.1 37.1

5.34 0.8 0.8 0.9 0.9 1.3 6.2 11

5.49 0.7 0.8 0.8 1.1 1.7 12 19.8

5.76 0.9 1 1.2 1.6 2.2 26.7 41.9

5.82 0.2 0.3 0.3 0.4 0.6 6.6 14.3

5.86 0.2 0.1 0.2 0.4 0.5 2.7 13.1

5.875 SR 39 Bridge

5.88 0 0.1 0.2 0.2 0.3 3.1 11

5.89 0.1 0 0 0.1 0.1 1 2.9

5.894 Railroad Bridge

5.90 0 0.1 0.1 0.1 0.2 1.7 4.7

5.93 0.1 0.1 0.2 0.2 0.3 3.1 9.3

6.06 0.5 0.6 0.5 0.7 0.8 17.4 34.4

6.44 1.6 1.6 1.8 1.9 2.3 49.7 104.6

6.97 1.4 1.7 2.3 3.9 5.9 55.4 113.8

7.45 1.5 1.8 2.7 8.1 14.5 47.9 114.5

7.69 1.4 1.5 1.8 4.3 8.1 29.6 66.3

7.70 0.1 0.1 0.1 0.1 0.2 1.9 4.7

7.71 0.1 0.2 0.3 0.4 0.5 2.2 4.9

7.92 5.4 6.4 7.5 10.1 13.5 36.8 57.1

8.07 Ranch Bridge

8.34

8.59 1 1.2 2 3.7 7.1 20 33.5

8.74 0.7 0.7 1.2 2.2 4 9.7 13.3

8.79 0.2 0.2 0.2 0.2 0.3 0.4 0.7

8.796 Confluence with Itchepackesassa Creek

8.80 0 0 0 0.1 0 0 0.1

8.84 0.1 0.2 0.1 0.1 0.2 0.3 0.9

9.00 0.5 0.5 0.6 0.7 0.7 2.9 9.2

9.27 1.1 1.2 1.6 2.8 4 9.5 21

9.52 1.2 1.3 1.7 3.5 5.2 10 30.3

9.87 1 1.2 1.3 1.6 1.8 3 18.8

10.25 1.3 1.4 1.5 1.8 2.1 2.9 12.7

10.41 0.6 0.6 0.8 0.9 1 1.2 10.8

10.45 0.1 0.2 0.1 0.2 0.2 0.2 2.3

10.454 Bridge

10.46 0 0 0.1 0 0.1 0.1 0.2

10.48 0.1 0.1 0 0.1 0 0.1 0.9

10.79 0.9 0.9 1 1 1.1 1.3 11.6

11.07 1 1.1 1.1 1.2 1.3 1.9 13.5

11.44 0.7 0.7 0.9 1 1.2 1.6 8.9

11.48 0.1 0.1 0.1 0.2 0.2 0.2 0.2

11.484 Ranch Bridge

11.49 0 0.1 0 0 0 0 0.1

11.54 0.1 0.1 0.2 0.2 0.2 0.2 0.3

11.61 0.2 0.2 0.2 0.2 0.2 0.4 0.6

11.62 Logging Road Bridge

11.63 0 0 0 0 0.1 0 0.2

11.89 0.7 0.8 0.8 0.9 1 1.6 9.8

12.31 0.7 0.8 1 1.3 1.7 3.1 6.1

12.39 0.3 0.3 0.3 0.4 0.4 0.7 1.5

12.42 0 0 0.1 0.1 0.1 0.1 0.6

12.49 0.2 0.2 0.1 0.2 0.2 0.3 1

12.497 Culvert

12.50 0.1 0.1 0.2 0.2 0.3 0.3 1.2

12.55 0.2 0.2 0.1 0.1 0.1 0.1 1.3

12.72 0.4 0.4 0.4 0.4 0.5 0.7 2.8

12.90 0.3 0.3 0.4 0.4 0.4 0.9 1.7

12.98 0.1 0.2 0.2 0.3 0.3 0.6 1.1

13.02 0.1 0 0.1 0.1 0.1 0.2 0.4

13.21 0.6 0.6 0.5 0.5 0.6 0.7 1.1

13.28 0.3 0.4 0.4 0.4 0.4 0.4 0.6

13.58 0.5 0.5 0.5 0.6 0.6 0.8 9.2

13.67 0.2 0.2 0.3 0.2 0.3 0.3 4

13.74 0.2 0.2 0.1 0.2 0.2 0.3 8.7

13.741 Water Oak Drive Culvert

13.75 0 0 0 0 0 0 0

13.77 0.1 0 0.1 0.1 0.1 0.1 0.2

13.91 0.1 0.2 0.2 0.2 0.2 2.3 6.8

13.917 Shady Oak Drive West Culvert

13.92 0 0 0 0 0 0.2 0.8

13.93 0.1 0 0 0 0 0 0.6

13.937 Culvert

13.94 0 0.1 0 0 0 0 0.2

14.08 0.2 0.2 0.3 0.3 0.4 4.2 10.9

14.23 0.2 0.2 0.2 0.3 0.4 5 9.9

14.24 0.1 0.1 0.1 0.1 0 0.1 0.2

14.249 Shady Oak Drive East Culvert

14.25 0 0 0 0 0 0.1 0.1

14.26 0 0 0 0 0.1 0 0

Appendix 11. Acreage of areal inundation between

adjacent cross sections along Blackwater Creek. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Acres
Blackwater Creek A 19

14.33 0.1 0.1 0.1 0.2 0.1 0.2 0.4

14.64 0.3 0.4 0.5 0.5 0.7 6.1 9.5

14.80 0.3 0.3 0.4 0.4 0.5 5.4 8.4

15.03 0.4 0.4 0.4 0.5 0.5 2.8 4.9

15.12 0.2 0.2 0.2 0.2 0.3 0.3 0.3

15.14 0.1 0.1 0.1 0.1 0.1 0.1 0.1

15.149 Sims Road Bridge

15.15 0 0 0 0.1 0 0.1 0

15.17 0.1 0.1 0.1 0 0.1 0 0.1

15.22 0 0 0 0.1 0 0.1 0.1

15.45 0.1 0.2 0.2 0.2 0.3 0.4 0.7

15.65 0.3 0.3 0.3 0.4 0.4 0.5 0.7

15.70 0.1 0.1 0.1 0.1 0.1 0.3 1.1

15.72 0 0 0.1 0 0.1 0.5 1.1

15.725 Harrelson Road Bridge

15.73 0.1 0.1 0 0.1 0 0.2 0.4

15.75 0 0 0.1 0 0.1 0.4 1.3

15.79 0.1 0 0 0.1 0.1 0.1 1.9

15.99 0.2 0.3 0.3 0.3 0.5 0.6 4.9

16.4 0.9 0.9 1 1 1 1.2 1.4

16.5 0.2 0.3 0.3 0.3 0.3 0.4 0.4

16.6 0.2 0.2 0.2 0.2 0.2 0.2 0.3

Total 77.8 91.9 112 162 228 744 1,552

Appendix 11. Acreage of areal inundation between

adjacent cross sections along Blackwater Creek. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Acres
A 20 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

Appendix 12. Decrease of inundated acreage resulting

from a potential 10-percent discharge withdrawal at

cross sections along Blackwater Creek. 

[Blanks indicate no decrease in inundated acreage]

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Acres

0.01 Initial cross section above confluence with Hillsborough River

.15 0.1 0.2 0.1 0.8 0.5

.28 0.1 0.2 0.2 0.7 0.6

.43 0.1 0.1 0.4

.59 0.1 0.1 0.1 0.1 0.2 1.3

.68 0.1 0.1 0.1 1.5

.90 0.2 0.2 0.6 1.5

.904 Two Rivers Ranch Bridge

.91 0.1 0.1 0.2

0.93 0.9

1.14 0.1 0.1 0.1 0.2 1.3 4.1

1.34 0.2 0.1 0.2 0.2 0.2 1.5 1.2

1.55 0.1 0.3 0.5 0.2 0.9 1.4

1.80 0.1 0.4 0.5 0.7 1 2.1

2.04 0.2 0.3 0.2 0.7 0.7 1.9

2.37 0.1 0.1 0.1 0.1 0.6 2.4

2.82 0.3 0.1 0.1 0.1 0.3 0.5 3.5

3.02 0 0.1 0.2 0.2 0.7 1.4

3.27 0.1 0.2 0.2 0.2 0.6 1.4 0.5

3.59 0.2 0.3 0.3 0.6 1.0 1.7 0.9

3.78 0.1 0.2 0.3 0.4 0.5 0.6 0.3

3.95 0.2 0.1 0.1 0.4 0.5

4.14 0.1 0.1 0.1 0.2 0.2 0.6 11.7

4.36 0.1 1.4 15.7

4.65 0.1 0.1 0.1 0.6 2.1 4.1

4.85 0.1 0.2 0.7 0.8 1.9

5.19 0.1 0.1 0.1 0.2 1.1 1.1 2.4

5.34 0.1 0.3 0.6 0.5

5.49 0.1 0.2 1.2 0.8

5.76 0.1 1.1 2.2

5.82 0.1 0.3 0.8

5.86 0.1 1.0

5.875 SR 39 Bridge

5.88 0.1 0.4 1.0

5.89 0.1 0.1 0.2

5.894 Railroad Bridge

5.90 0.2 0.3

5.93 0.1 0.1 0.1 0.8

6.06 0.1 0.1 0.7 1.7

6.44 0.1 0.2 2.6 6.5

6.97 0.1 0.2 0.3 0.7 2.9 7.1

7.45 0.1 0.3 0.8 1.9 2.5 6.3

7.69 0.1 0.1 0.3 0.5 1.2 1.8 2.5

7.70 0.2 0.2

7.71 0.1 0.1 0.1 0.4 0.2

7.92 0.1 0.1 0.2 0.4 0.7 4.2 1.4

8.07 Ranch Bridge

8.34 Confluence with Itchepackesassa Creek

8.59 0.2 0.3 0.6 1.6 1.5

8.74 0.1 0.1 0.2 0.4 0.5 0.7

8.79 0.1 0.1 0.2

8.796

8.80 0.1

8.84 0.1 0.1

9.00 0.1 0.6 1.0

9.27 0.1 0.2 0.3 1.4 1.5

9.52 0.1 0.3 0.3 0.2 0.9 2.1

9.87 0.1 0.1 0.2 1.7

10.25 0.1 0.2 3.4

10.41 0.1 0.1 1.4

10.45 0.2

10.454 Bridge

10.46 0.1 0.1

10.48 0.1 0.1 0.1

10.79 0.1 4.1

11.07 0.1 6.0

11.44 0.1 0.1 2.6

11.48 0.1

11.484 Ranch Bridge

11.49 0.1 0.1

11.54 0.1 0.1

11.61 0.2

11.62 Logging Road Bridge

11.63 0.1

11.89 0.1 0.1 0.8

12.31 0.1 1.0

12.39 0.1 0.1 0.1 0.1 0.1

12.42 0.1

12.49 0.1 0.1 0.1 0.2

12.497 Culvert

12.50 0.1 0.1 0.7

12.55 0.1 0.1 1.0

12.72 0.1 1.9

12.90 0.1

12.98 0.1 0.1

13.02 0.1 0.1 0.1

13.21 0.1 0.3

13.28 0.1

13.58 0.1 0.1 3.8

13.67 0.1 1.4

13.74 0.1 2.4

13.741 Water Oak Drive Culvert

13.75

13.77 0.1 0.1 0.1

13.91 0.1 0.1 0.4 0.6

13.917 Culvert

13.92

13.93 0.1 0.1

13.937 Shady Oak Drive West Culvert

13.94 0.1 0.1

14.08 0.4 3.8

14.23 0.1 0.5 1.6

Appendix 12. Decrease of inundated acreage resulting

from a potential 10-percent discharge withdrawal at

cross sections along Blackwater Creek. (Continued)

[Blanks indicate no decrease in inundated acreage]

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Acres
Blackwater Creek A 21

14.24 0.1 0.1 0.1 0.1

14.249 Shady Oak Drive East Culvert

14.25 0.1

14.26 0.1

14.33 0.1

14.64 0.1 5.1 0.6

14.80 0.1 0.1 3.1 0.5

15.03 0.1 0.2 0.6

15.12 0.1

15.14 0.1

15.149 Sims Road Bridge

15.15 0.1

15.17 0.1 0.1

15.22 0.1

15.45

15.65 0.1 0.1 0.1

15.70 0.1

15.72 0.1 0.1 0.1

15.725 Harrelson Road Bridge

15.73 0.1

15.75 0.2

15.79 0.1 0.5

15.99 0.1 0.1 1.1

16.4 0.1

16.5 0.1

16.6

Total 3.3 3.8 6.1 9.3 16.8 55.9 148

Appendix 12. Decrease of inundated acreage resulting

from a potential 10-percent discharge withdrawal at

cross sections along Blackwater Creek. (Continued)

[Blanks indicate no decrease in inundated acreage]

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Acres
Appendix 13. Extent of inundation at cross sections

along Itchepackesassa Creek for selected percentile

discharges. 

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet

Mean

Maximum

Mean

A 22 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

0.15 49 56 62 74 80 691 876

0.20 32 42 54 168 940 1,575 1,760

0.55 36 37 37 38 345 638 879

0.82 25 30 35 39 43 145 508

1.07 31 34 36 40 45 196 457

1.30 17 20 22 27 39 304 851

1.34 34 36 39 44 92 249 718

1.36 34 36 39 44 93 248 705

1.366 Cone Ranch Bridge and Gaging Station (02302280)

1.37 34 36 39 44 95 252 734

1.39 39 41 44 64 106 472 723

1.71 21 24 26 29 36 316 835

2.08 28 33 41 57 164 784 917

2.45 17 19 21 35 69 311 1,039

2.72 26 30 32 35 41 61 79

2.94 24 25 27 30 40 88 142

3.16 18 20 23 27 37 83 498

3.48 18 18 19 21 23 162 244

3.86 25 26 27 28 31 46 369

4.14 21 23 26 31 36 163 434

4.31 21 24 25 27 28 248 635

4.66 14 14 15 16 18 1,482 1,809

4.88 18 25 26 27 29 54 313

4.97 17 19 21 24 29 61 806

5.28 29 32 35 40 54 191 210

5.45 18 19 21 23 25 51 80

5.62 26 28 29 33 40 65 120

5.63 20 26 29 37 43 60 179

5.638 Cone Ranch Wooden Bridge

5.64 25 26 27 30 34 60 179

5.68 21 22 24 28 34 116 365

6.12 21 22 23 25 29 76 162

6.25 26 27 28 30 33 319 510

6.27 53 54 54 55 56 340 542

6.278 Knights-Griffin Road Bridge and Gaging Station (02302260)

6.28 53 54 54 55 56 341 543

6.30 8 11 13 17 21 51 109

6.58 30 31 31 32 34 55 284

6.95 21 22 22 25 31 59 79

7.24 24 27 30 35 41 68 174

7.59 19 22 24 30 35 56 2,729

7.88 20 20 21 27 34 62 410

8.22 21 21 22 25 28 96 1,121

8.53 39 40 43 49 58 97 250

8.84 28 28 28 29 29 59 800

9.0 22 25 26 27 29 55 124

9.11 26 26 26 27 28 35 325

9.24 33 34 34 35 36 52 438

9.25 64 65 65 66 66 356 4,694

9.259 Walker Road Bridge

9.26 64 65 65 66 66 372 4,742

9.27 43 44 44 45 47 74 1,389

9.40 36 36 37 38 39 50 2,081

9.63 26 27 27 28 29 865 2,062

9.84 17 18 19 21 24 1,500 1,819

10.07 22 22 23 25 27 139 1,982

10.16 23 24 25 28 31 53 1,027

10.52 22 24 25 28 32 43 800

10.71 23 25 27 30 35 52 190

10.94 48 52 54 60 66 85 133

10.95 49 52 55 60 66 85 134

10.958 Swindell Road Bridge

10.96 50 52 55 60 66 85 136

10.97 13 19 26 33 41 63 170

11.15 33 34 36 40 47 118 598

11.40 22 23 24 28 31 44 461

11.64 15 18 20 23 24 30 710

Interstate Highway 4

28 30 32 38 64 242 793

64 65 65 168 940 1,575 4,742

8 11 13 16 18 30 79

Appendix 13. Extent of inundation at cross sections

along Itchepackesassa Creek for selected percentile

discharges. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet
Appendix 14. Hydraulic depth at cross sections along

Itchepackesassa Creek for selected percentile

discharges. 

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet

Cone Ranch Wooden Bridge

Knights-Griffin Road Bridge and Gaging Station (02302260)

Walker Road Bridge

Swindell Road Bridge

Mean

Maximum

Minimum

Itchepackesassa Creek A 23

0.15 1.1 1.1 1.2 1.4 1.8 1.0 2.4

0.20 1.3 1.2 1.2 0.7 0.6 2.0 3.4

0.55 1.6 1.9 2.3 3.2 0.8 1.7 2.7

0.82 0.4 0.8 1.2 2.0 2.7 1.8 1.6

1.07 0.7 1.0 1.3 2.1 2.7 1.8 2.3

1.30 0.8 1.1 1.4 1.9 2.1 1.5 1.7

1.34 0.7 1.1 1.4 2.1 1.7 2.6 2.3

1.36 0.7 1.1 1.4 2.1 1.7 3.8 6.0

1.366 Cone Ranch Bridge and Gaging Station (02302280)

1.37 0.7 1.1 1.5 2.1 1.7 3.9 6.1

1.39 0.8 1.2 1.6 1.8 1.9 2.0 3.4

1.71 0.3 0.7 1.2 2.0 2.6 1.5 1.7

2.08 0.7 0.9 1.1 1.6 1.2 2.2 3.8

2.45 0.6 0.9 1.2 1.3 1.4 1.5 1.7

2.72 0.3 0.5 0.7 1.2 1.8 3.4 4.4

2.94 0.8 1.1 1.3 1.8 2.0 2.7 3.6

3.16 0.4 0.8 1.1 1.6 1.9 2.9 1.1

3.48 0.6 0.9 1.2 1.9 2.8 1.6 2.6

3.86 0.4 0.7 1.0 1.6 2.4 4.6 1.6

4.14 0.7 0.9 1.1 1.6 2.2 2.1 2.4

4.31 0.3 0.5 0.9 1.5 2.2 1.1 1.9

4.66 0.8 1.1 1.4 1.9 2.6 0.5 1.5

4.88 0.5 0.8 1.1 1.9 2.8 4.2 1.1

4.97 1.0 1.3 1.6 2.2 2.8 4.0 0.9

5.28 0.7 1.1 1.4 2.1 2.6 3.3 4.8

5.45 0.7 1.1 1.5 2.3 3.3 4.3 4.4

5.62 0.3 0.7 1.1 1.9 2.7 5.0 4.9

5.63 0.2 0.4 0.8 1.5 2.5 5.3 7.8

5.638

5.64 0.3 0.5 0.9 1.7 2.7 4.4 7.0

5.68 0.4 0.6 0.9 1.6 2.5 2.6 2.6

6.12 0.4 0.6 0.9 1.4 2.1 3.1 3.2

6.25 0.3 0.5 0.7 1.2 1.9 1.1 2.6

6.27 0.4 0.5 0.8 1.3 2.2 5.7 7.9

6.278

6.28 0.4 0.6 0.8 1.3 2.2 5.7 8.0

6.30 0.2 0.3 0.4 0.7 1.4 3.3 3.1

6.58 0.6 0.9 1.2 1.7 2.4 4.4 1.7

6.95 0.1 0.2 0.3 0.6 1.2 3.7 5.4

7.24 0.6 0.8 1.1 1.5 1.8 3.5 3.0

7.59 0.1 0.4 0.6 1.1 1.7 3.2 1.5

7.88 0.6 0.9 1.2 1.7 2.1 3.1 0.9

8.22 0.3 0.5 0.8 1.6 2.4 2.8 1.2

8.53 0.4 0.5 0.7 1.2 1.8 4.0 2.4

8.84 0.2 0.3 0.5 0.9 1.6 3.2 1.1

9.0 0.4 0.5 0.7 1.0 1.5 3.1 2.9

9.11 0.3 0.6 0.8 1.2 1.7 4.2 1.1

9.24 0.3 0.5 0.7 1.2 1.7 3.4 1.3

9.25 0.3 0.4 0.7 1.1 1.7 3.7 5.4

9.259

9.26 0.3 0.5 0.7 1.2 1.8 3.7 5.4

9.27 0.2 0.4 0.6 1.1 1.6 3.4 0.7

9.40 0.4 0.6 0.7 1.2 1.7 3.9 1.1

9.63 0.3 0.5 0.8 1.2 1.8 0.6 1.7

9.84 0.3 0.4 0.6 1.0 1.5 0.6 2.1

10.07 0.4 0.6 0.8 1.2 1.7 0.9 0.8

10.16 0.4 0.6 0.8 1.2 1.6 2.5 0.7

10.52 0.4 0.6 0.9 1.3 1.8 3.2 0.7

10.71 0.5 0.7 1.0 1.4 1.9 3.3 2.0

10.94 0.3 0.6 0.8 1.4 1.9 3.8 3.9

10.95 0.3 0.6 0.9 1.4 2.0 3.8 4.5

10.958

10.96 0.4 0.6 0.9 1.4 2.0 3.8 4.5

10.97 0.3 0.4 0.5 1.0 1.5 3.1 2.2

11.15 0.4 0.7 0.9 1.4 1.9 2.1 1.8

11.40 0.4 0.6 0.8 1.3 1.9 3.6 0.8

11.64 0.4 0.5 0.8 1.2 1.8 3.9 1.0

Interstate Highway 4

0.5 0.7 1.0 1.5 2.0 3.0 2.9

1.6 1.9 2.3 3.2 3.3 5.7 8.0

0.1 0.2 0.3 0.6 0.6 0.5 0.7

Appendix 14. Hydraulic depth at cross sections along

Itchepackesassa Creek for selected percentile

discharges. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet
Appendix 15. Acreage of areal inundation between adjacent 

cross sections along Itchepackesassa Creek. 

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet

Initial cross section above confluence with Blackwater Creek

Cone Ranch Bridge and Gaging Station (02302280)

Confluence with East Canal

Cone Ranch Wooden Bridge

Knights-Griffin Road Bridge and Gaging Station (02302260)

Walker Road Bridge

Swindell Road Bridge

Total

A 24 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

0.15

0.20 1 1.2 1.4 2.9 12.3 27.3 31.8

0.55 0.7 0.9 1 2.3 14.6 25.1 29.8

0.82 1.1 1.1 1.2 1.3 6.6 13.3 23.4

1.07 0.8 0.9 1.1 1.2 1.3 4.8 13.9

1.30 0.6 0.8 0.8 0.9 1.2 7.0 17.5

1.34 0.2 0.1 0.1 0.2 0.4 1.5 4

1.36 0 0.1 0.1 0.1 0.1 0.5 1.3

1.366

1.37 0.1 0.1 0.1 0.1 0.2 0.2 0.5

1.39 0.1 0.1 0.1 0.1 0.2 0.9 1.7

1.71 1.2 1.2 1.3 1.8 2.8 15.3 30.1

2.08 1.1 1.3 1.5 1.9 4.4 24.1 38.3

2.45 1 1.2 1.4 2.1 5.2 24.5 43.8

2.72

2.94 0.7 0.8 0.8 0.9 1.1 2.0 3

3.16 0.5 0.6 0.7 0.7 1 2.3 8.4

3.48 0.7 0.7 0.8 1 1.2 4.6 14.1

3.86 1 1 1 1.1 1.3 5.0 14.2

4.14 0.8 0.9 0.9 1 1.1 3.5 12.4

4.31 0.4 0.4 0.5 0.6 0.6 4.2 11.1

4.66 0.8 0.9 0.9 0.9 1 33.2 48.7

4.88 0.4 0.5 0.5 0.6 0.6 20.3 28

4.97 0.2 0.2 0.3 0.3 0.4 0.6 6.5

5.28 0.8 1 1 1.2 1.5 4.8 18.6

5.45 0.5 0.5 0.6 0.6 0.8 2.5 3

5.62 0.5 0.5 0.5 0.6 0.7 1.2 2.1

5.63 0 0.1 0.1 0.1 0.1 0.1 0.2

5.638

5.64 0 0 0 0 0 0.0 0.1

5.68 0.2 0.1 0.1 0.2 0.2 0.5 1.5

6.12 1.1 1.2 1.3 1.4 1.7 4.7 11.7

6.25 0.4 0.4 0.4 0.4 0.4 3.1 5.3

6.27 0.1 0.1 0.1 0.1 0.1 0.8 1.2

6.278

6.28 0 0 0 0.1 0.1 0.1 0.1

6.30 0.1 0.1 0.1 0.1 0.1 0.4 0.8

6.58 0.6 0.7 0.8 0.8 0.9 1.8 7

6.95 1.2 1.2 1.2 1.3 1.5 2.6 8.2

7.24 0.8 0.9 0.9 1 1.3 2.2 4.5

7.59 0.9 1 1.2 1.4 1.6 2.6 61.3

7.88 0.7 0.7 0.7 1 1.2 2.1 56.6

8.22 0.7 0.8 0.8 0.9 1.1 2.8 27.7

8.53 1.1 1.2 1.3 1.4 1.6 3.7 26.2

8.84 1.2 1.2 1.3 1.4 1.6 2.9 19.1

9.0 0.4 0.4 0.4 0.5 0.5 0.9 7.1

9.11 0.5 0.5 0.5 0.5 0.5 0.9 4.1

9.24 0.7 0.7 0.7 0.7 0.8 0.9 8.8

9.25 0.1 0.1 0.1 0.1 0.1 0.4 4.4

9.259

9.26 0.1 0.1 0.1 0.1 0.1 0.3 2.8

9.27 0.1 0.1 0.1 0.1 0.1 0.4 5.6

9.40 0.6 0.7 0.7 0.7 0.6 1.0 27.4

9.63 0.9 0.8 0.8 0.9 1 10.9 46.3

9.84 0.5 0.6 0.6 0.6 0.6 29.3 50.3

10.07 0.6 0.6 0.6 0.7 0.8 23.0 53.7

10.16 0.2 0.2 0.3 0.3 0.3 0.8 20.5

10.52 1 1 1.1 1.2 1.3 2.1 38.9

10.71 0.5 0.6 0.6 0.6 0.8 1.1 11.5

10.94 1 1.1 1.1 1.3 1.4 1.9 4.5

10.95 0.1 0 0.1 0.1 0.1 0.1 0.2

10.958

10.96 0 0.1 0 0.1 0.1 0.1 0.1

10.97 0.1 0 0.1 0 0 0.1 0.2

11.15 0.5 0.6 0.6 0.8 1 2.0 8.3

11.40 0.8 0.9 1 1 1.2 2.4 16

11.64 0.5 0.6 0.6 0.8 0.8 1.1 17.3

Interstate Highway 4

33.5 36.4 39.0 47.1 86.2 339 966

Appendix 15. Acreage of areal inundation between adjacent 

cross sections along Itchepackesassa Creek. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet
Appendix 16. Decrease of inundated acreage resulting

from a potential 10-percent discharge withdrawal at

cross sections along Itchepackesassa Creek.

[Blanks indicate no decrease in inundated acreage]

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet

Initial cross section above confluence with Blackwater Creek

Cone Ranch Bridge and Gaging Station (02302280)

Confluence with East Canal

Cone Ranch Wooden Bridge

Knights-Griffin Road Bridge and Gaging Station (02302260)

Walker Road Bridge

Swindell Road Bridge

Total

Itchepackesassa Creek A 25

0.15

0.20 1.1 1.1 0.7 0.8 0.4

0.55 0.9 0.1 1 0.8 0.6 0.4

0.82 0.1 1.1 0.1 0.3 1.3 1.1

1.07 0.9 1.1 1.1

1.30 0.8 0.2 1 2.2

1.34 0.1 0.1 0.2 0.5

1.36 0.1 0.1

1.366

1.37 0.1 0.1 0.1

1.39 0.1 0.1 0.2

1.71 1.2 0.1 0.4 1.1 4.7

2.08 1.2 0.1 0.1 0.9 1.4 5.4

2.45 1.2 0.2 1 3.4 4

2.72

2.94 0.8 0.1

3.16 0.5 0.1 0.1 0.2 3.5

3.48 0.8 0.1 0.1 0.3 5.3

3.86 1 0.3 1.4

4.14 0.8 0.1 0.1 0.1 0.5 1

4.31 0.5 1.1 0.9

4.66 0.1 0.8 0.1 2.7 2.6

4.88 0.5 0.6 1.1

4.97 0.3 0 0.1 0.4

5.28 0.9 0 0.1 0.1 1.1

5.45 0.6 0 0.1 0.1 0.2

5.62 0.4 0 0.1 0 0.1

5.63 0.1 0.1 0 0 0

5.638

5.64 0.1

5.68 0.1 0.1 0.1 0.1

6.12 1.2 0.1 0.8 1.3

6.25 0.1 0.4 2.1 0.3

6.27 0.1 0.4

6.278

6.28 0.1

6.30 0.1 0.1

6.58 0.7 0.1 0.2 2.9

6.95 0.1 1.2 0.1 0.1 3.3

7.24 0.8 0.1 0.1 0.9

7.59 1 0.1 0 0.1 4.3

7.88 0.8 0.1 0 0.3 4.6

8.22 0.7 0.1 0 0.3 2.7

8.53 1.2 0.1 0.3 1.3

8.84 1.2 0.1 0.2 2.6

9.0 0.1 0.5 0.1 1.1

9.11 0.5 0.1 0.7

9.24 0.7 0.1 0.1 2

9.25 0 0.2 0.2

9.259

9.26 0.2 0.2 0.1

9.27 0.1 0.2 0.7

9.40 0.6 0.1 0.1 0 0.1 6.7

9.63 0.9 0.1 3.1 3.2

9.84 0.5 6.5 0.8

10.07 0.6 0.1 4.6 2.9

10.16 0.2 0.1 0.2 2.7

10.52 1.1 10.6

10.71 0.5 0.1 4.2

10.94 1.1 0.1 0.5

10.95 0.1 0.1 0.1

10.958

10.96 0.1 0.1

10.97 0.1 0.1 0.1

11.15 0.6 0.1 0.1 0.2 0.5

11.40 0.9 0.2 2.1

11.64 0.6 0.1 2.6

Interstate Highway 4

1.0 1.3 1.1 3.6 6.0 38 104

Appendix 16. Decrease of inundated acreage resulting

from a potential 10-percent discharge withdrawal at

cross sections along Itchepackesassa Creek. (Continued) 

(Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet
Appendix 17. Extent of inundation at cross sections along East 

Canal for selected percentile discharges. 

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet

Mean

Maximum

Minimum

A 26 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

.15 4 5 6 12 22 300 794

0.19 6 10 12 17 70 303 811

0.20 23 24 24 24 25 41 60

0.22 7 10 13 18 76 306 834

0.29 20 21 22 24 28 39 149

0.44 21 22 22 24 25 34 645

0.61 21 22 23 24 27 33 830

0.70 21 23 26 30 34 285 480

0.78 32 34 36 40 46 230 277

0.84 7 8 9 11 14 23 201

0.96 8 8 9 9 40 355 922

1.13 20 22 23 26 29 36 282

1.38 27 27 28 29 625 1,076 1,264

1.65 26 27 28 29 35 52 69

1.83 28 29 31 33 49 608 759

1.94 17 17 18 19 20 22 30

1.96 48 49 50 55 65 245 524

1.98 Knights-Griffin Road Culvert

1.99 48 49 50 55 65 247 805

2.00 40 40 40 41 42 73 477

2.09 26 27 28 28 31 155 415

2.44 16 17 18 19 21 220 2,259

2.55 35 36 37 39 41 338 2,207

2.82 17 18 19 21 25 193 387

3.03 30 31 32 34 37 1,192 1,411

3.23 21 23 24 26 29 102 605

3.40 30 31 31 32 33 980 1,075

3.67 22 22 23 23 24 118 833

3.96 16 16 16 17 17 19 20

4.05 20 21 21 22 23 26 28

4.13 15 16 17 18 20 30 130

4.16 34 34 34 35 38 53 63

4.17 Allen Road Culvert

4.18 35 35 35 36 38 53 63

4.23 23 23 23 23 23 24 25

4.34 16 16 16 17 17 18 20

4.38 19 19 19 19 19 20 37

4.44 19 19 19 20 20 22 226

4.49 11 12 12 13 13 24 235

4.52 17 17 17 18 19 27 142

4.54 16 16 17 18 19 28 36

4.58 12 13 14 17 20 32 44

4.65 12 15 17 19 22 32 51

4.68 17 18 20 23 27 46 66

4.687 Terrace Road Bridge

4.69 17 18 20 23 27 46 67

4.72 9 9 9 10 12 22 39

4.79 19 19 20 21 21 24 27

4.89 7767 8 12 27

Interstate Highway 4

21 22 22 24 43 177 451

48 49 50 55 625 1,192 2,259

4 5 6 7 8 12 20

Appendix 17. Extent of inundation at cross sections along East 

Canal for selected percentile discharges. (Continued)

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet
Appendix 18. Hydraulic depth at cross sections along

 East Canal.

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet

Knights-Griffin Road Culvert

Allen Road Culvert

Terrace Road Bridge

Mean

Maximum

Minimum

East Canal A 27

.15 0.26 0.34 0.53 0.79 1.03 1.68 1.76

0.19 0.66 0.71 0.80 1.01 0.60 1.74 1.77

0.20 0.29 0.63 0.90 1.40 2.04 3.02 3.69

0.22 0.66 0.72 0.81 1.03 0.60 1.80 1.80

0.29 0.08 0.24 0.44 0.81 1.31 2.84 1.44

0.44 0.31 0.41 0.51 0.71 1.01 2.42 0.73

0.61 0.15 0.34 0.55 0.93 1.31 2.40 0.27

0.70 0.34 0.47 0.60 0.93 1.38 0.65 1.57

0.78 0.22 0.39 0.57 0.94 1.39 1.23 2.15

0.84 0.19 0.24 0.34 0.61 0.96 2.24 0.67

0.96 0.77 1.07 1.35 1.82 0.69 0.89 1.21

1.13 0.84 1.11 1.37 1.85 2.43 3.82 0.88

1.38 0.48 0.83 1.18 1.81 0.50 1.76 2.71

1.65 0.53 0.87 1.22 1.84 2.52 3.22 3.59

1.83 0.15 0.45 0.80 1.42 1.80 1.14 2.15

1.94 0.31 0.31 0.50 1.08 2.02 3.59 3.79

1.96 0.25 0.32 0.47 0.98 1.84 3.06 4.48

1.98

1.99 0.25 0.32 0.48 0.98 1.84 3.07 4.50

2.00 0.05 0.06 0.15 0.68 1.67 2.12 1.06

2.09 0.45 0.64 0.78 0.88 1.57 0.82 1.19

2.44 0.48 0.73 0.98 1.43 1.95 0.84 0.66

2.55 0.20 0.42 0.68 1.17 1.76 1.00 0.80

2.82 0.46 0.59 0.77 1.15 1.63 0.66 0.99

3.03 0.31 0.49 0.70 1.14 1.70 0.89 1.56

3.23 0.28 0.42 0.61 1.02 1.54 1.25 0.72

3.40 0.14 0.24 0.38 0.75 1.32 0.68 1.45

3.67 0.49 0.65 0.82 1.18 1.69 1.06 0.74

3.96 0.24 0.44 0.66 1.08 1.65 3.75 4.79

4.05 0.29 0.44 0.65 1.05 1.60 3.59 4.73

4.13 0.18 0.30 0.48 0.86 1.36 2.74 1.48

4.16 0.03 0.05 0.07 0.18 0.64 2.89 4.43

4.17

4.18 0.08 0.11 0.15 0.24 0.65 2.89 4.44

4.23 0.11 0.17 0.24 0.37 0.44 2.49 3.96

4.34 0.16 0.23 0.32 0.51 0.83 1.82 3.25

4.38 0.05 0.09 0.15 0.27 0.44 1.40 2.09

4.44 0.25 0.34 0.46 0.66 0.90 1.66 0.61

4.49 0.12 0.21 0.33 0.56 0.84 1.54 0.43

4.52 0.20 0.29 0.40 0.63 0.92 1.92 0.85

4.54 0.19 0.29 0.40 0.62 0.91 1.93 2.71

4.58 0.19 0.27 0.38 0.57 0.80 1.82 2.57

4.65 0.25 0.33 0.44 0.70 1.00 2.01 2.39

4.68 0.18 0.28 0.40 0.64 0.91 1.74 3.11

4.687

4.69 0.20 0.29 0.41 0.64 0.91 1.75 3.12

4.72 0.63 0.74 0.88 1.14 1.37 1.97 2.12

4.79 0.04 0.15 0.33 0.64 1.06 2.60 3.96

4.89 0.29 0.31 0.23 0.32 0.45 1.36 1.92

Interstate Highway 4

0.29 0.42 0.58 0.91 1.26 1.99 2.20

0.84 1.11 1.37 1.85 2.52 3.82 4.79

0.03 0.05 0.07 0.18 0.44 0.65 0.27
Appendix 19. Acreage of areal inundation between

adjacent cross sections along East Canal. 

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet

Initial cross section above confluence with 

Itchespackesassa Creek

Knights-Griffin Road Culvert

Allen Road Culvert

Terrace Road Bridge

Interstate Highway 4

Total

A 28 Extent of Areal Inundation in the Upper Hillsborough River Watershed, West-Central Florida

.15

0.19 0.03 0.04 0.05 0.08 0.24 1.44 4.23

0.20 0.02 0.02 0.02 0.03 0.05 0.19 0.5

0.22 0.02 0.03 0.04 0.04 0.1 0.32 0.82

0.29 0.12 0.13 0.14 0.18 0.45 1.53 4.26

0.44 0.38 0.4 0.41 0.43 0.48 0.66 6.89

0.61 0.42 0.44 0.46 0.49 0.52 0.67 15.07

0.70 0.24 0.25 0.27 0.31 0.35 1.76 8.04

0.78 0.24 0.26 0.28 0.33 0.36 2.48 3.65

0.84 0.13 0.13 0.15 0.16 0.19 0.84 1.62

0.96 0.14 0.15 0.16 0.19 0.51 3.57 10.61

1.13 0.28 0.31 0.32 0.36 0.72 4.23 12.72

1.38 0.7 0.73 0.77 0.83 10.01 17.02 23.54

1.65 0.79 0.81 0.83 0.87 10.19 17.42 20.1

1.83 0.6 0.62 0.64 0.67 0.92 7.27 9.13

1.94 0.31 0.32 0.33 0.36 0.47 4.01 5

1.96 0.12 0.11 0.12 0.12 0.14 0.51 1.06

1.98

1.99 0.11 0.12 0.12 0.13 0.15 0.56 1.52

2.00 0.1 0.1 0.1 0.11 0.13 0.37 1.47

2.09 0.32 0.32 0.33 0.33 0.35 1.07 4.12

2.44 0.93 0.96 0.99 1.03 1.12 8.09 57.7

2.55 0.35 0.37 0.37 0.4 0.44 3.84 30.75

2.82 0.84 0.86 0.9 0.97 1.06 8.54 41.69

3.03 0.61 0.63 0.66 0.72 0.8 17.96 23.32

3.23 0.62 0.65 0.67 0.72 0.79 16.3 24.96

3.40 0.53 0.55 0.57 0.6 0.65 11.17 17.37

3.67 0.83 0.85 0.85 0.88 0.92 16.47 28.56

3.96 0.57 0.57 0.58 0.6 0.62 1.98 11.86

4.05 0.3 0.3 0.3 0.31 0.32 0.36 0.38

4.13 0.18 0.19 0.2 0.2 0.21 0.28 0.82

4.16 0.1 0.11 0.11 0.12 0.13 0.18 0.41

4.17

4.18 0.08 0.08 0.08 0.08 0.08 0.12 0.15

4.23 0.14 0.14 0.14 0.14 0.16 0.19 0.21

4.34 0.27 0.27 0.27 0.27 0.27 0.29 0.31

4.38 0.09 0.09 0.1 0.1 0.1 0.1 0.15

4.44 0.13 0.13 0.12 0.13 0.13 0.14 0.85

4.49 0.1 0.1 0.11 0.11 0.11 0.16 1.59

4.52 0.04 0.04 0.04 0.04 0.05 0.07 0.52

4.54 0.04 0.05 0.04 0.05 0.05 0.08 0.24

4.58 0.07 0.07 0.08 0.09 0.1 0.15 0.21

4.65 0.11 0.13 0.15 0.16 0.19 0.28 0.42

4.68 0.05 0.05 0.06 0.07 0.08 0.14 0.21

4.687

4.69 0.02 0.02 0.02 0.02 0.03 0.03 0.03

4.72 0.04 0.04 0.04 0.05 0.06 0.1 0.17

4.79 0.13 0.13 0.14 0.15 0.15 0.21 0.3

4.89 0.14 0.15 0.15 0.15 0.17 0.21 0.31

12.4 12.8 13.3 14.2 35.1 153 378
Appendix 20. Decrease of inundated acreage resulting 

from a potential 10-percent discharge withdrawal at cross

sections along East Canal. 

[Blanks indicate no decrease in inundated acreage]

Cross 

section

No.

Percentiles

P50 P70 P80 P90 P95 P99.5 P99.97

Feet

Initial cross section above confluence with Itchepackassa Creek

Knights-Griffin Road Culvert

Allen Road Culvert

Terrace Road Bridge

Interstate Highway 4

Total

East Canal A 29

.15

0.19 0.03 0.04 0.05 0.04 0.04 0.53

0.20 0.02 0.03 0.05

0.22 0.03 0.04 0.04 0.02 0.12

0.29 0.02 0.03 0.04 0.05 0.03 0.56

0.44 0.03 0.06 2.29

0.61 0.02 0.04 0.06 0.02 10.07

0.70 0.04 0.01 0.05 0.66 5.24

0.78 0.58 0.05

0.84 0.03 0.03 0.05 0.06 0.04 0.22

0.96 0.04 0.05 0.06 0.21 0.77 1.11

1.13 0.01 0.12 0.83 1.72

1.38 0.07 0.03 0.61 0.12 2.74

1.65 0.01 0.59 0.12 0.9

1.83 0.02 0.04 0.02 0.27 0.23

1.94 0.01 0.02 0.03 0.07 0.11 0.2

1.96 0.02 0.01 0.02 0.02 0.01 0.06

1.98

1.99 0.01 0.02 0.03 0.05 0.06 0.22

2.00 0.01 0.03 0.17 0.17

2.09 0.03 0.03 0.67 0.82

2.44 0.03 0.06 0.02 3.19 2.3

2.55 0.05 0.07 0.04 0.34 0.55

2.82 0.06 0.07 2.94 1.29

3.03 0.01 0.02 0.1 2.36 0.62

3.23 0.02 0.05 0.02 0.6 0.66

3.40 0.03 0.07 0.77 0.47

3.67 0.03 0.05 0.02 1.07 0.56

3.96 0.08 0.02 0.28 0.26

4.05 0.01 0.02

4.13 0.01 0.12

4.16 0.01 0.01 0.02 0.03 0.08 0.01

4.17

4.18 0.08

4.23 0.04 0.09 0.01

4.34 0.07 0.07 0.01

4.38 0.09 0.05

4.44 0.03 0.03 0.03 0.05

4.49 0.01 0.01 0.06 0.09

4.52 0.04 0.04 0.04 0.04 0.05 0.12

4.54 0.05 0.04

4.58 0.07 0.07 0.08 0.05 0.01

4.65 0.02

4.68 0.05 0.05 0.06 0.04 0.01

4.687

4.69 0.02 0.02 0.02 0.03 0.03 0.03

4.72 0.04 0.05 0.06

4.79 0.03 0.03 0.04 0.1

4.89 0.04 0.05 0.05 0.01 0.01

0.7 1.0 1.1 0.7 2.4 16.5 34.6