Hydrological Impacts of Urbanization: White Rock Creek .../67531/metadc... · Storm drainage systems contribute to increased volumes of storm flow and decreased lag times. Many man-made

APPROVED: Harry F.L. Williams, Major Professor Samuel F. Atkinson, Minor Professor Miguel F. Acevedo, Committee Member Paul Hudak, Chair of the Department of

Geography Sandra L. Terrell, Dean of the Robert B.

Toulouse School of Graduate Studies

HYDROLOGICAL IMPACTS OF URBANIZATION:

WHITE ROCK CREEK, DALLAS TEXAS

Julie Anne Groening Vicars, B.A.

Thesis Prepared for the Degree of

MASTER OF SCIENCE

UNIVERSITY OF NORTH TEXAS

December 2005

Vicars, Julie Anne Groening, Hydrological Impacts of Urbanization: White Rock

Creek, Dallas Texas. Master of Science (Applied Geography), December 2005, 91 pp.,

28 tables, 55 illustrations, bibliography, 22 titles.

This research project concerns changes in hydrology resulting from urbanization

of the upper sub-basin of the White Rock Creek Watershed in Collin and Dallas

Counties, Texas. The objectives of this study are: to calculate the percent watershed

urbanized for the period of 1961 through 1968 and the period of 2000 through 2005; to

derive a 1960s average unit hydrograph and a 2000s average unit hydrograph; and, to

use the two averaged hydrographs to develop a range of hypothetical storm scenarios

to evaluate how the storm response of the watershed has changed between these two

periods. Results of this study show that stormflow occurs under lower intensity

precipitation in the post-urbanized period and that stormflow peaks and volumes are

substantially larger compared to the pre-urbanized period. It is concluded that changes

in watershed surface conditions resulting from urbanization have lowered the

precipitation-intensity threshold that must be surpassed before storm run-off is

generated.

ii

Copyright 2005

by

Julie Anne Groening Vicars

iii

ACKNOWLEDGMENTS

Sally Rodriguez, Project Coordinator; Parks and Recreation, City of Dallas, Texas

John Unruh, Data Manager; United States Geological Society, Fort Worth, Texas

Dr Harry Williams, Associate Professor; Department of Geography, University of North Texas, Denton, Texas

Dr Miguel Acevedo, Professor; Department of Geography, University of North Texas, Denton, Texas

Dr Samuel Atkinson, Professor; Department of Environmental Science, University of North Texas, Denton, Texas

iv

TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS................................................................................................iii LIST OF TABLES.......................................................................................................... v LIST OF ILLUSTRATIONS...........................................................................................vii Chapters

I. INTRODUCTION ..................................................................................... 1 II. REVIEW OF LITERATURE ..................................................................... 2

Hydrologic Cycle Impervious Surface Cover Channel Modifications Objectives Study Area

III. METHODOLOGY .................................................................................... 9

Data Collection Data Analysis

IV. RESULTS .............................................................................................. 37 V. DISCUSSION ........................................................................................ 44 VI. CONCLUSION....................................................................................... 48

APPENDIX: DATA TABLES AND GRAPHS ............................................................... 49 BIBLIOGRAPHY ......................................................................................................... 90

v

LIST OF TABLES

Page

1. Calculating Unit Hydrograph Ordinates ............................................................ 20

2. Excess Precipitation and Threshold Value Calculations................................... 22

3. Events and Threshold Values Used in Analysis ............................................... 23

4. Lag Time Values and Calculations ................................................................... 27

5. Flood Event Values for White Rock Creek Watershed ..................................... 29

6. Scenario #1: 0.5 Inches per Hour for 3 Hours .................................................. 30

7. Scenario #2: 1.0 Inch per Hour for 3 Hours ...................................................... 31





12. Scenario #1 Value Comparison........................................................................ 37






18. Lag Time Comparison: Z-Test .......................................................................... 45

19. Storm Event: November 22, 1961 .................................................................... 50

20. Storm Event: April 27, 1962.............................................................................. 54

21. Storm Event: September 7-8, 1962 .................................................................. 58

22. Storm Event: April 28, 1966.............................................................................. 62

23. Storm Event: August 13-14, 1968..................................................................... 66

vi

24. Storm Event: December 30, 2002 .................................................................... 70

25. Storm Event: April 23-24, 2003......................................................................... 74

26. Storm Event: June 11-12, 2003........................................................................ 78

27. Storm Event: December 12, 2003 .................................................................... 82

28. Storm Event: June 9, 2004 ............................................................................... 86

vii

LIST OF ILLUSTRATIONS

Page

1. The Hydrologic Cycle ......................................................................................... 2

2. Impervious Surface Cover and Its Impacts on Runoff ........................................ 4

3. Study Area: White Rock Creek Watershed......................................................... 7

4. Land Use Changes for White Rock Creek Watershed, 1962 and 2002.............. 8

5. Extract of 1960s Handwritten Data ................................................................... 11

6. Example of Bimodal Hydrograph ...................................................................... 11

7. Example of Initial Hydrograph with Precipitation, for April 28, 1966 ................. 15

8. Semi-log Plot .................................................................................................... 16

9. Y=aX+b Scatter Plot ......................................................................................... 17

10. Initial Hydrograph and Baseflow....................................................................... 18

11. Unit Hydrograph ............................................................................................... 18

12. Procession from Initial Hydrograph to Unit Hydrograph.................................... 21

13. Rainfall Hyetograph showing Excess Precipitation threshold ........................... 23

14. The S-Curve Plot .............................................................................................. 24

15. S-Curve Plots and 3 Hour Unit Hydrograph...................................................... 25

16. 1960s Unit Hydrographs and Average.............................................................. 27

17. 2000s Unit Hydrographs and Average.............................................................. 28

18. Scenario #1 Hydrograph................................................................................... 37






viii

24. Peak Flow Comparison .................................................................................... 46

25. Storm Flow Volume Comparison ...................................................................... 47

26. November 22, 1961: Procession from Initial Hydrograph to Unit Hydrograph .. 51

27. November 22, 1961: Precipitation Hyetograph................................................. 52

28. November 22, 1961: Final 3-Hour Unit Hydrograph ......................................... 53

29. April 27, 1962: Procession from Initial Hydrograph to Unit Hydrograph............ 55

30. April 27, 1962: Precipitation Hyetograph .......................................................... 56

31. April 27, 1962: Final 3-Hour Unit Hydrograph................................................... 57

32. September 7-8, 1962: Procession from Initial Hydrograph to Unit Hydrograph 59

33. September 7-8, 1962: Precipitation Hyetograph............................................... 60

34. September 7-8, 1962: Final 3-Hour Unit Hydrograph ....................................... 61

35. April 28, 1966: Procession from Initial Hydrograph to Unit Hydrograph............ 63

36. April 28, 1966: Precipitation Hyetograph .......................................................... 64

37. April 28, 1966: Final 3-Hour Unit Hydrograph................................................... 65

38. August 13-14, 1968: Procession from Initial Hydrograph to Unit Hydrograph .. 67

39. August 13-14, 1968: Precipitation Hyetograph ................................................. 68

40. August 13-14, 1968: Final 3-Hour Unit Hydrograph.......................................... 69

41. December 30, 2002: Procession from Initial Hydrograph to Unit Hydrograph .. 71

42. December 30, 2002: Precipitation Hyetograph................................................. 72

43. December 30, 2002: Final 3-Hour Unit Hydrograph ......................................... 73

44. April 23-24, 2003: Procession from Initial Hydrograph to Unit Hydrograph ...... 75

45. April 23-24, 2003: Precipitation Hyetograph ..................................................... 76

46. April 23-24, 2003: Final 3-Hour Unit Hydrograph.............................................. 77

47. June 11-12, 2003: Procession from Initial Hydrograph to Unit Hydrograph...... 79

48. June 11-12, 2003: Precipitation Hyetograph .................................................... 80

ix

49. June 11-12, 2003: Final 3-Hour Unit Hydrograph............................................. 81

50. December 12, 2003: Procession from Initial Hydrograph to Unit Hydrograph .. 83

51. December 12, 2003: Precipitation Hyetograph................................................. 84

52. December 12, 2003: Final 3-Hour Unit Hydrograph ......................................... 85

53. June 9, 2004: Procession from Initial Hydrograph to Unit Hydrograph ............. 87

54. June 9, 2004: Precipitation Hyetograph............................................................ 88

55. June 9, 2004: Final 3-Hour Unit Hydrograph .................................................... 89

1

I. INTRODUCTION

Urbanization affects the environment in numerous ways, including habitat and

wildlife loss, and disruption and alteration of various hydrological processes. Statistics

show that more then 75 percent of the United States population lives in urban areas; by

the year 2030 more then 60 percent of the world's population will live in urban areas

(UN Pop Division 2001; US Census 2001; Paul and Meyer 2001).

People have flocked towards rivers for centuries. So, following that trend, over

130,000 kilometers of streams and rivers in the United States are impacted by

urbanization (USEPA 2000). Urbanization impacts rivers in various ways; channel

control, or channelization, grading of land surfaces, building construction, use of storm

water drainage systems, removal of vegetation, and increased amounts of litter and

waste are all ways in which rivers are affected by urbanization.

In Texas, urbanization is a growing trend. Many agricultural communities are

becoming suburbanized, as the demand for 'country living’ grows. With an increase in

population, also comes the potential for an increase in flooding. Urbanization changes

watershed surfaces in such a way that natural hydrological processes are disrupted.

Elements of urbanization that affect hydrological processes include homes, landscaped

yards, businesses, concrete and asphalt streets, parking lots, and storm drainage

systems. These urban features alter natural infiltration and runoff. Along with river

modifications, changes to natural watershed surfaces pose a potential threat to the

people who live near streams or rivers due to the potential increase in storm flow.

2

II. REVIEW OF LITERATURE

To understand the dynamics of a watershed, one must first understand the

hydrologic cycle (Figure 1).

Figure 1. The Hydrologic Cycle (McCuen 1998).

Water in the environment is recycled through several stages. This process,

known as the hydrologic cycle, is based on five steps: precipitation, infiltration,

evaporation, transpiration, and runoff. Precipitation falling into a watershed occupies

specific hydrological storages or pathways. Some of this precipitation will be intercepted

by foliage, which will store it until it eventually evaporates. When the foliage storage

space reaches capacity, excess water will flow to the ground as stem flow. Precipitation,

that reaches the ground may infiltrate and add itself to soil moisture or groundwater.

Subsurface water can be transpired by plants, or it can flow down slope into nearby

3

channels, supplying stream base flow. If water reaches the ground faster than it can

infiltrate, the excess water can occupy surface depression storages. When these

storages become filled to capacity, the excess precipitation will flow down slope as

surface runoff.

Surface characteristics serve as one of the factors that affect rainfall infiltration

and runoff. Surface conditions determine whether rainfall infiltrates the ground and flows

along relatively slow subsurface hydrological pathways, or if it fails to infiltrate and

instead flows along relatively fast surface pathways (Williams Earth Science Lab). For

example, soil texture influences the rate at which surface water enters the soil profile, or

the infiltration capacity. The infiltration capacity affects the amount of water that enters

streams and rivers as direct or surface runoff (McCuen 1998). Surface runoff is

generated in two ways: infiltration-excess overland flow, which occurs when the rainfall

intensity exceeds the infiltration capacity, the excess rain becomes overland flow; and

saturation overland flow, which occurs when the soil is completely saturated, due to a

combination of precipitation and subsurface flows, the base of slopes and hill-slope

concavities are prone to this type of surface runoff, especially during prolonged

precipitation.

Surface cover significantly affects the runoff characteristics of a watershed. For

example, lag time, storm flow volume, and peak flow may all be affected by a change in

surface cover. Peak flows increase with increased urbanization in a watershed. Along

with this increase, storm flow volume also increases. Lag time – the time between

precipitation and resulting stormflow - may also be changed by changes in surface

conditions.

4

Impervious Surface Cover

Land cover greatly affects surface properties and runoff characteristics of a

watershed. Urbanization changes the natural surface of the land, often impeding natural

infiltration and promoting increased runoff (Figure 2). Rainfall that settles on to areas of

impervious surface cover will automatically become runoff, causing streets to become

urban channels; rain that falls on to areas of pervious surface will infiltrate into the

ground, pool and infiltrate slowly over time, or be intercepted by vegetation, therefore

decreasing runoff.

Figure 2. Impervious Surface Cover Impacts on Runoff.

Storm drainage systems contribute to increased volumes of storm flow and

decreased lag times. Many man-made drainage systems were built to the specifications

of a 10-year storm, but with increased impervious cover a 10-year storm can produce

the same amount of runoff as a 25-year storm, thereby overloading the drainage system

(NFIP 1994). These systems can increase flooding, leading to increased property

damage. Storm drainage systems divert the majority of surface runoff, which eventually

injects large volumes of storm water into one area of the stream. This increases storm

5

flow in the channel, promoting flooding and erosion, which will negatively affect the

stability of the stream’s channel (NFIP 1994).

Channel Modification

Rivers and streams naturally migrate over their lifespan, changing their course

over time. Due to this migration, people have seen the need to keep rivers and streams

from moving, thereby channeling them within concrete channels. Examples of

channeled rivers can be seen in most of the urban areas surrounding Dallas, one

example is White Rock Creek at Greenville Avenue. Though channeling a river does

control the issues of boundaries, it also changes the natural movement of the water. In

the past many channels built along riverbanks were created using narrower, straighter

channels then were previously (and naturally) there, thus, causing water to flow down

those channels at a higher velocity (Paul et al 2001). For a river to flow through a

narrow channel, it must push its capacity with more force, thus increasing the velocity,

and possibly overflowing the channel downstream.

Along with channelization come culverts and bridges. Culverts, especially, can be

hazardous due to debris build-up. If proper maintenance is not used, bridges and

culverts can back up flood waters to a point, that once the debris gives way, it can

produce flash flooding downstream. Upstream flooding can also occur because of this

back up (NFIP 1994).

Objectives

In this research project I will study the effects of urbanization on the upper sub-

basin of the White Rock Creek Watershed in Collin and Dallas Counties, Texas. My

objectives are:

6

1. Calculate the percent watershed urbanized for the period 1961 through 1968

(little urbanization) and the period 2000 through 2005 (substantial urbanization).

2. Derive a 1960s average unit hydrograph and a 2000s average unit

hydrograph.

3. Compare the two averaged hydrographs to evaluate how the storm response

of the watershed has changed between these two periods of contrasting urbanization.

Study Area

Headwaters for White Rock Creek are located in Frisco and Plano. The rest of

the watershed can be found in Addison, Richardson, and Dallas (Figure 3).

Presently, hydrologic instruments located on White Rock Creek include two

stream gauging stations, located at Greenville Avenue and Keller Springs Road. The

closest rain gage to White Rock Creek, operated by NOAA, is found at Dallas Love

Field Airport (approximately 4 miles away).

7

Figure 3. Study Area: White Rock Creek Watershed

Urbanization in White Rock Creek

Hydrologic instruments on White Rock Creek, in the 1960s, consisted of 14

recording rain gauges, 4 stream gauging stations, 5 crest stage partial recording

stations, and 39 flood profile partial record stations. There were 12 weighing rain

gauges throughout the watershed area above Greenville Avenue, spaced to sample 5.5

square miles.

Upper White Rock Creek, with a total area of 66.4 square miles, was 87 percent

rural in 1961 (Ollman 1969). With the decline in farming in 1967, large apartment

complexes, shopping centers, and industrial parks began being constructed in the

watershed. By 1990, the watershed was becoming much more urbanized; a trend which

8

has continued into the 2000s (Figure 4). Overall, development within the watershed has

increased from 13 percent urbanization in 1961, to approximately 95 percent today.

Figure 4. Land Use Change for White Rock Creek Watershed, 1960s and 2000s

9

III. METHODOLOGY

DATA COLLECTION Data for this study will include:

• 1960s and 2000s Stream Discharge data in cubic feet per second.

• 1960s and 2000s Hourly Rainfall data in inches per hour.

Gauging Stations

1960s and 2000s Stream flow Data: White Rock Creek at Greenville Avenue,

USGS Stream discharge gage 08057200. This gage was chosen for its completeness of

1960s data, as well as 2000s data and for its location. Gage 08057200 is located on the

intersection of White Rock Creek and Greenville Avenue, which is also the border

between the upper and the lower sub-basins of White Rock Creek. This gauge records

discharge from a 66.4 square mile drainage area.

Precipitation data was obtained from the two gauges listed below:

• 1960s Precipitation data: Rain Gauge 9-W, on White Rock Creek, near the

Greenville Avenue streamflow gauging station (Figure 3).

• 2000s Precipitation data: NOAA Rain Gauge, located at Dallas Love Field

(Figure 3).

Precipitation and stream discharge data, for the 1960s, was collected from the

report, “Hydrology Data for Urban Studies in Dallas, Texas”, published by the United

States Geological Society Water Resources Division (1961-1972). These annual reports

record major storm events that occurred each year. Storms recorded in these books are

the highest recorded stream discharge peaks of the year. For the ‘White Rock Creek at

Greenville Avenue’ stream flow gauging station, there are at least three major storm

10

events per year. For each of these storms, the data was handwritten (Figure 5). Fields

and values that were used include:

• Time and Date (time = 1 hour increments),

• Stream discharge in cubic feet per second, and

• Rainfall in inches.

Events for the 1960s were selected based on the completeness of the data, whether

or not precipitation data existed for a particular event, and visual evaluation of the initial

hydrograph. For a storm to be used the initial hydrograph must continually recede on

the recession limb side; there can be no increase from one point to the next in stream

discharge after peak discharge (i.e. bimodal hydrograph; Figure 6). Bimodal

hydrographs represent storms that were influenced by another separate period of

rainfall. Peak flow, for an event to be used, must be 900 cubic feet per second or

greater, so that only those storms that have a significant amount of rainfall are used.

Although fifteen storms were recorded for the 1960s, these were reduced to 5 storms

that met the above criteria.

11

Figure 5. Extract of 1960s handwritten data.

October 18- 19,2002: Bimodal Hydrograph

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Figure 6. Example of Bimodal Hydrograph.

12

2000s stream discharge data was downloaded from the USGS Real-Time hydrology

website. This data is updated frequently and is in 15-minute increments. Precipitation

data was downloaded from the NOAA rain gauge site. This data covers an entire month

and is recorded in 1-hour increments. Stream discharge and precipitation data was

entered into an Excel spreadsheet, using 1-hour increments.

Criteria for selecting the 2000s storm events were the same as the criteria for the

1960s. Data for twenty storms was obtained for this analysis, but due to the criteria

mentioned above, only 5 were used for analysis.

Assumptions and Potential Sources of Error

Different storm characteristics and watershed conditions can produce variations

in unit hydrographs. Hydrographs for this project were averaged for each time period,

because many watershed characteristics were not accounted for in the study. One

important factor not considered was antecedent moisture conditions. Antecedent

moisture, which refers to the moisture content of the soil immediately preceding a

rainfall event, can affect lag times and stormflow volumes and peaks. For example, a

soil already saturated at the onset of a storm may act like an impervious surface and

generate larger amounts of stormflow more quickly than under lower antecedent

moisture conditions.

Other factors include the season of the year, and in relation to that temperature

and vegetation. Season of the year affects the wetness or dryness of the watershed. In

the hot summer months the ground will be drier, therefore more accommodating to large

amounts of infiltration from precipitation. If there is a rainy season, the ground will be

wetter, thus not allowing as much infiltration. Vegetation type and the amount of cover

13

also influence the runoff in a watershed. Vegetation not only intercepts precipitation as it

falls, it can also impede runoff flowing along surface pathways and promote infiltration,

thus slowing and decreasing stormflow.

For this project, one rain gauge was used for each time period and precipitation

was assumed uniform for the entire watershed. The gauge for the 1960s was located

near the USGS White Rock Creek at Greenville Avenue stream discharge gauging

station, while the 2000s rain gauge was located 4 miles from the site at Dallas Love

Field Airport (Figure 7).

Data records (1960s) for this project came from handwritten books; which raises

the possibility of some human error during data recording. Data, in the 2000s, was

recorded using automated monitors, which may be prone to mechanical errors.

Sources of possible error within the analysis are the placement of the baseflow

separation line and the calculation of duration of excess precipitation. With the

placement of the baseflow line, finding the inflection point on the receding limb is

somewhat subjective. The calculation of the duration of excess precipitation is also

somewhat subjective, due to the fact that some precipitation outliers above the

threshold line are ignored as part of the technique employed, when in fact these

‘outliers’ may have contributed to the storm flow.

These potential sources of error are partly addressed by the averaging of the unit

hydrographs. It is assumed that averaging provides a closer approximation of the

response of the watershed to a storm.

14

DATA ANALYSIS

Data for this project was analyzed and compared using unit hydrographs. A unit

hydrograph results from one inch of excess precipitation (or runoff) spread uniformly in

space and time over a watershed for a given duration (Fielder 1999). “Excess

precipitation” means precipitation that generates stormflow and is in excess of

precipitation that fills depression storages, infiltrates the ground, etc.

Deriving a Unit Hydrograph (UHG) from a Storm Event

To derive a unit hydrograph for a particular storm event, the data was entered

into an Excel spreadsheet. Initial hydrographs of the raw data were created to begin the

analysis. These graphs included precipitation amounts and stream discharge records,

plotted on 2 axes. The bar graph, plotted on the primary Y axis, represents precipitation

amounts by time, and the line graph, plotted on the secondary Y axis, represents

stream discharge by time (Figure 6).

15

April 28, 1966

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

0

5000

10000

15000

20000

25000

Stre

am d

isch

arge

(cfs

) .

Precipitation Stream discharge

Figure 7. Example Initial Hydrograph with Precipitation, for April 28, 1966

Separation of Baseflow

The next step in the process was to separate the baseflow of the stream from the

storm flow. Baseflow must be taken out because it is the part of the stream discharge

that is not attributable to direct runoff from precipitation (AMS 2000). Baseflow is

considered to be “a straight line connecting that point at which the hydrograph begins to

rise rapidly and the inflection point on the recession side of the hydrograph” (Fielder

1999).

Baseflow was found using two methods: visual inspection of the hydrograph and

using a semi-log plot of the stream flow in cubic feet per second. Visual inspection of

the hydrograph involved printing out the initial hydrograph and marking the point were

16

storm flow began, the point where the hydrograph begins to rise rapidly, and then

estimating the location of the inflection point on the recession limb side, which

represents the end of stormflow. For the semi-log plot (Figure 8), stream flow values

were plotted on the log scale against time, and the hour was noted when the recession

side fit an approximate straight line. These two techniques were used in combination to

separate the baseflow for each storm.

April 28, 1966: Semi-log Plot

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

4.500

5.000

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Time (hours)

Log

of C

FS .

Figure 8. Semi-log Plot

Once the beginning and end of baseflow were found, I used a scatter plot and

the formula y=ax+b, to find an equation to separate baseflow from stream flow; where

‘x’ equals time and ‘y’ equals cubic feet per second. Once the ‘x, y’ coordinates for both

the beginning and the end of baseflow were plotted, a trendline was fit to the points,

Hour when recession limb becomes straight line.

17

displaying the equation (Figure 9). The equation shown on the graph was used to plot

the baseflow on the hydrograph (Figure 10), Baseflow was then subtracted from the

initial stream flow records, the product of this calculation provided new ordinates which

represent storm flow (Figure 11).

Baseflow Separation: Scatter Plot

y = 55.833x + 518.33

0

200

400

600

800

1000

1200

1400

0 2 4 6 8 10 12 14 16

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Figure 9. Y=aX+b Scatter Plot

18

April 28, 1966: Baseflow and Hydrograph

0

5000

10000

15000

20000

25000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Figure 10. Initial Hydrograph and Baseflow

April 28, 1966: Unit Hydrograph Ordinates

0

2000

4000

6000

8000

10000

12000

2 3 4 5 6 7 8 9 10 11 12 13 14

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Figure 11. Unit Hydrograph

19

The next step in the process involved calculating the depth of direct runoff. The

value found through these calculations was later used in conjunction with the

precipitation values to find duration of excess precipitation. Calculations for direct runoff

are as follows:

1. Storm flow ordinates were summed and then multiplied by 3600 seconds to

create a value that represents storm flow volume in cubic feet. April 28, 1966

Example: Sum of Ordinates = 92475.08 cubic feet second * 3600 seconds =

332910280.80 cubic feet (storm flow volume).

2. Storm flow volume was then converted into acre-feet by dividing by 43,560

square feet per acre. April 28, 1966 Example: 332910280.80 cubic feet / 43560

ft2/acre = 7642.57 acre-feet.

3. The depth of direct runoff in feet was found by dividing the total volume of excess

precipitation by the watershed area. April 28, 1966 Example: 7642.57 acre-feet /

(66.4 square miles * 640 acres) = 0.179842066 feet.

4. The depth of direct runoff, for April 28, 1966, in inches, was 0.179842066 feet *

12 inches = 2.15810479 inches.

Obtaining UHG Ordinates

To obtain the unit hydrograph ordinates, each flow was divided by the depth of

direct runoff/excess precipitation (Table 1; Figure 12). Units for the unit hydrograph in

this analysis are cubic feet per second per inch of excess precipitation.

20

Table 1. Calculating Unit Hydrograph Ordinates. Stream Discharge Without Baseflow

(cfs) Depth of Direct Runoff

(inches) Unit Hydrograph

(cfs/inch)

0 2.158104790 0

7704.2 2.158104790 3569.9

21358.3 2.158104790 9896.8

16102.5 2.158104790 7461.4

12946.7 2.158104790 5999.1

10290.8 2.158104790 4768.5

8235.0 2.158104790 3815.9

6179.2 2.158104790 2863.2

4423.3 2.158104790 2049.6

3067.5 2.158104790 1421.4

1611.7 2.158104790 746.8

555.8 2.158104790 257.6

0 2.158104790 0

21

April 28, 1966: Procession from Initial Hydrograph to Unit Hydrograph

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

0

5000

10000

15000

20000

25000

Stre

am d

isch

arge

(cfs

) .

Precipitation Initial Hydrograph Without Baseflow Unit Hydrograph

Figure 12. Procession from Initial Hydrograph to Unit Hydrograph.

Determining UHG Duration

The duration of the derived unit hydrograph is found by examining the

precipitation for the event and determining that precipitation which is in excess (Fielder

1999). Excess precipitation is considered that precipitation which becomes storm flow.

To find the excess precipitation for a particularly storm event, I graphed the

precipitation for the storm in hyetograph form. I then had to find the threshold value for

the storm event. Using the depth of direct runoff value, which was calculated

previously, I estimated different threshold values to find which one would create an

amount of excess precipitation that equaled the direct runoff (Table 2). Once the correct

22

value was found and the sum of the new precipitation values equaled the direct runoff,

the threshold value was plotted as a horizontal line across the precipitation hyetograph.

Table 2. Excess Precipitation and Threshold Value Calculations Time

(hours) Precipitation

(inches) Threshold Value

(inches)

New Precipitation

(inches)

Sum of New Precipitation: 2.158

1 1.1 2.242 0 Direct Runoff: 2.158104790

2 4.4 2.242 2.158 Threshold Value: 2.242

3 0.58 2.242 0 Duration of Excess Precipitation: 1 hour

4 0.02 2.242 0

5 0.05 2.242 0

6 0.05 2.242 0

Everything above the threshold value line on the hyetograph is considered excess

precipitation (Figure 11). The duration, in hours, of excess precipitation, equals the

duration of the unit hydrograph for this storm.

23

April 28, 1966: Precipitation Hyetograph

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 2 3 4 5 6 7

Time (hours)

Prec

ipita

tion

(inch

es)

.

Precipitation Threshold Value

Figure 13. Rainfall Hyetograph showing excess precipitation threshold.

Table 3. Events and Threshold Values Used in Analysis

Time Period Storm Events Threshold Values

(inches) Average

November 22, 1961 0.997 April 27, 1962 0.151 September 8-9, 1962 0.565 April 28, 1966 2.242

1960s

August 13-14, 1968 1.324

1960s Threshold Average:

1.056 inches

December 30, 2002 0.671 April 23-25, 2003 0.913 June 11-12, 2003 0.039 December 12, 2003 0.146

2000s

June 9-10, 2004 0.410

2000s Threshold Average:

0.436 inches

Precipitation above this line is considered excess precipitation.

24

Table 3 shows the 10 events that were used for analysis and their threshold

values. The threshold values were averaged in preparation for the scenario analysis.

Changing the Duration of the Storm Event

To average and compare the unit hydrographs, each unit hydrograph must be of

equal duration. The average duration of all ten storm events was calculated and

rounded up to the nearest whole hour – 3 hours. Then the S-Curve method was used to

change the duration of all unit hydrographs to the average duration. The S-curve

method involves continually lagging the unit hydrographs by their duration and adding

the ordinates (Fielder 1999). Theoretically, the S-curve is a representation of what

would happen if it rained continually, the top of the curve flattens due to equilibrium

between input and output of precipitation (Figure 12).

S-Curve Plot

0.0

5000.0

10000.0

15000.0

20000.0

25000.0

30000.0

35000.0

40000.0

45000.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Figure 14. The S-Curve Plot

25

To change the duration of a 1-hour unit hydrograph to a 3-hour duration unit

hydrograph, s-curve ordinates were lagged by 3-hours, and the difference between the

two curves equals a 3-hour unit hydrograph (Figure 13; Fielder 1999). Because the

original unit hydrograph was of 1-hour-duration; the new 3-hour-duration unit

hydrograph will represent 3 inches of rain (instead of the required one inch). Therefore

the new hydrograph ordinates must be multiplied by 1/3, in order to show a true

representation of a 3-hour-duration hydrograph.

April 28,1966: S-Curve Plots and 3-Hour Unit Hydrograph

0.0

5000.0

10000.0

15000.0

20000.0

25000.0

30000.0

35000.0

40000.0

45000.0

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Time (hours)

Stre

am d

isha

rge

(cfs

) .

S-Curve S-Curve 3-Hour Unit Hydrograph

Figure15. S-Curve Plots and 3-Hour Unit Hydrograph

Average Hydrographs and Threshold Values

Once the S-Curve plots were completed for all storms, the ordinates for each

event were copied into the same Excel file. These storms’ ordinates were then

26

averaged to find an average unit hydrograph for the 1960s and the 2000s (Figure 14,

Figure 15). A unit hydrograph represents a combination of watershed characteristics

and watershed conditions as it reacts to excess precipitation (McCuen 1998). Therefore,

any characteristics or conditions that were not uniform through time will be reflected in

the shape of the hydrograph. The April 27, 1962 hydrograph is different from the other 4

hydrographs in its shape and time to peak. Its differences cannot be explained, but

removing this graph does not significantly change the averaged unit hydrograph

ordinates or the lag time. Since the data meets the criteria listed for data usage,

completely removing the event from the analysis would disregard those criteria.

Lag times for the storm events were calculated using the raw data from each of

the 10 storm events using the following steps:

1. Find the center of mass of precipitation. Calculate to fraction of the hour.

2. Find the hour of peak flow. It is assumed that peak flow occurs in the middle

of the hour. Therefore, if peak flow occurs in Hour 15, I will record this has

Hour 15.5.

3. The center of mass of precipitation hour is subtracted from the hour of peak

flow.

4. Values for each of the time periods are averaged and compared (Table 4).

27

Table 4. Lag Time Values and Calculations

Storm Event Center of Mass of Precipitation

(hours)

Peak Flow (hours)

Lag Time

(hours)

Average (hours)

Nov 22, 1961 6.59 9.5 2.91 Apr 27, 1962 5.3 10.5 5.2 Sept 7-9, 1962 23.19 27.5 4.31 Apr 28, 1966 2.45 4.5 2.05 Aug 13-14, 1968 19.59 21.5 1.91

3.276

Dec 30, 2002 15.5 16.5 1 Apr 23-25, 2003 21.5 24.5 3 Jun 11-12, 2003 16.54 20.5 3.96 Dec 12, 2003 18.06 22.5 4.44 Jun 9-10, 2004 25.63 25.5 -0.13

2.454

Unit Hydrographs and Average, 1960s

0

2000

4000

6000

8000

10000

12000

14000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Nov 22, 1961 Apr 27, 1962 Sept 7-9, 1962Apr 28, 1966 Aug 13-14, 1968 Average Unit Hydrograph

Figure 16. 1960s Unit Hydrographs and Average

28

Unit Hydrographs and Average, 2000s

0

2000

4000

6000

8000

10000

12000

14000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Dec 30, 2002 Apr 23-25, 2003 Jun 11-13, 2003Dec 12, 2003 Jun 8-11, 2004 Average Unit Hydrograph

Figure 17. 2000s Unit Hydrographs and Average

Scenario Analysis

To compare the response of the watershed to storms between the two time

periods, a range of scenarios using hypothetical storms of varying precipitation intensity

were developed. The limit of these scenarios was set at the 500-year flood event,

which, for White Rock Creek Watershed, equals 56,500 cubic feet per second (FIS

2004; Table 4).

A total of 6 scenarios were used:

0.5 inch per hour for 3 hours

1.0 inch per hour for 3 hours

1.5 inches per hour for 3 hours

29




Table 5: Flood Event Values for White Rock Creek Watershed, 2004

Cubic Feet per Second Flood Event Percent Chance of Occurrence

25,000 10-year 10

37,200 50-year 2

42,800 100-year 1

56,500 500-year 0.2

Scenario calculations were as follows (Tables 6-11):

1. Subtract the threshold value from the precipitation values and sum the total

amount of excess precipitation.

2. To find the storm flow ordinates, multiply the unit hydrograph ordinates by the

total amount of excess precipitation.

30

Table 6. Scenario #1: 0.5 inches of rain per hour for 3 hours 1960s Time Precipitation Threshold Value Excess

Precipitation 1960s UHG Total Excess Precipitation New Ordinates

1 0.5 1.056 -0.556 0 2 0.5 1.056 -0.556 2790 3 0.5 1.056 -0.556 6424 8673 8255

Total Excess Precipitation: -1.668

5659 Threshold Value Larger then Precipitation: No Storm Flow. 4415 3001 1914 829 388 162 67 17 0

2000s Time Precipitation Threshold Value Excess Precipitation 2000s UHG Total Excess

Precipitation New Ordinates Peak Flow (cubic feet per second): 1,519

1 0.5 0.43576 0.064 0 0.193 0 2 0.5 0.43576 0.064 1994 0.193 384 3 0.5 0.43576 0.064 5806 0.193 1119

Volume of Storm flow (cubic feet): 29,729,080

7569 0.193 1459 7881 0.193 1519

Total Excess Precipitation: 0.193

6624 0.193 1277 4900 0.193 944 3295 0.193 635 2088 0.193 402 1254 0.193 242 730 0.193 141 400 0.193 77 228 0.193 44 82 0.193 16 0 0.193 0

31

Table 7. Scenario #2: 1.0 inch of rain per hour for 3 hours 1960s Time Precipitation Threshold Value Excess

Precipitation 1960s UHG Total Excess Precipitation New Ordinates

1 1.0 1.056 -0.056 0 2 1.0 1.056 -0.056 2790 3 1.0 1.056 -0.056 6424 8673 8255

Total Excess Precipitation: -0.168

5659 Threshold Value Larger then Precipitation: No Storm Flow. 4415 3001 1914 829 388 162 67 17 0

2000s Time Precipitation Threshold Value Excess Precipitation 2000s UHG Total Excess


1 1.0 0.43576 0.564 0 1.693 0 2 1.0 0.43576 0.564 1994 1.693 3375 3 1.0 0.43576 0.564 5806 1.693 9827


7569 1.693 12812 7881 1.693 13340


6624 1.693 11213 4900 1.693 8294 3295 1.693 5577 2088 1.693 3535 1254 1.693 2122 730 1.693 1235 400 1.693 678 228 1.693 386 82 1.693 140 0 1.693 0

32

Table 8. Scenario #3: 1.5 inch of rain per hour for 3 hours 1960s Time Precipitation Threshold Value Excess Precipitation 1960s UHG Total Excess


1 1.5 1.056 0.444 0 1.332 0 2 1.5 1.056 0.444 2790 1.332 3717 3 1.5 1.056 0.444 6424 1.332 8557


8673 1.332 11552 8255 1.332 10995


5659 1.332 7538 4415 1.332 5880 3001 1.332 3998 1914 1.332 2550 829 1.332 1105 388 1.332 516 162 1.332 215 67 1.332 89 17 1.332 23 0 1.332 0

2000s Time Precipitation Threshold Value Excess Precipitation 2000s UHG Total Excess Precipitation New Ordinates Peak Flow (cubic feet

per second): 25,161

1 1.5 0.43576 1.064 0 3.193 0 2 1.5 0.43576 1.064 1994 3.193 6365 3 1.5 0.43576 1.064 5806 3.193 18536


7569 3.193 24166 7881 3.193 25161


6624 3.193 21149 4900 3.193 15643 3295 3.193 10519 2088 3.193 6667 1254 3.193 4002 730 3.193 2330 400 3.193 1278 228 3.193 728 82 3.193 263 0 3.193 0

33



1 2.0 1.056 0.9440 0 2.832 0 2 2.0 1.056 0.9440 2790 2.832 7903 3 2.0 1.056 0.9440 6424 2.832 18192


8673 2.832 24562 8255 2.832 23377 5659 2.832 16027


4415 2.832 12502 3001 2.832 8499 1914 2.832 5421 829 2.832 2348 388 2.832 1098 162 2.832 458 67 2.832 190 17 2.832 49 0 2.832 0


per second): 36,981

1 2.0 0.43576 1.564 0 4.693 0 2 2.0 0.43576 1.564 1994 4.693 9356 3 2.0 0.43576 1.564 5806 4.693 27244


7569 4.693 35520 7881 4.693 36981


6624 4.693 31085 4900 4.693 22993 3295 4.693 15461 2088 4.693 9799 1254 4.693 5882 730 4.693 3425 400 4.693 1878 228 4.693 1071 82 4.693 387 0 4.693 0

34


Precipitation New Ordinates Peak Flow (cubic feet

per second): 37,571

1 2.5 1.056 1.4440 0 4.332 0 2 2.5 1.056 1.4440 2790 4.332 12088 3 2.5 1.056 1.4440 6424 4.332 27828


8673 4.332 37571 8255 4.332 35759


5659 4.332 24515 4415 4.332 19124 3001 4.332 13001 1914 4.332 8292 829 4.332 3592 388 4.332 1679 162 4.332 701 67 4.332 290 17 4.332 74 0 4.332 0

2000s Time Precipitation Threshold Value Excess Precipitation 2000s UHG Total Excess Precipitation

New Ordinates Peak Flow (cubic feet per second): 48,802

1 2.5 0.43576 2.064 0 6.193 0 2 2.5 0.43576 2.064 1994 6.193 12346 3 2.5 0.43576 2.064 5806 6.193 35953


7569 6.193 46874 7881 6.193 48802


6624 6.193 41021 4900 6.193 30342 3295 6.193 20404 2088 6.193 12932 1254 6.193 7763 730 6.193 4520 400 6.193 2479 228 6.193 1413 82 6.193 511 0 6.193 0

35

Table 11. Scenario #6: 3.0 inch of rain per hour for 3 hours


per second): 50,580

1 3.0 1.056 1.9440 0 5.832 0 2 3.0 1.056 1.9440 2790 5.832 16274 3 3.0 1.056 1.9440 6424 5.832 37464


8673 5.832 50580 8255 5.832 48141


5659 5.832 33004 4415 5.832 25745 3001 5.832 17503 1914 5.832 11163 829 5.832 4836 388 5.832 2260 162 5.832 943 67 5.832 390 17 5.832 100 0 5.832 0


per second): 60,623

1 3.0 0.43576 2.564 0 7.693 0 2 3.0 0.43576 2.564 1994 7.693 15337 3 3.0 0.43576 2.564 5806 7.693 44662

Volume of Storm flow (cubic feet): 1,186,682,680

7569 7.693 58228 7881 7.693 60623


6624 7.693 50957 4900 7.693 37692 3295 7.693 25346 2088 7.693 16064 1254 7.693 9643 730 7.693 5614 400 7.693 3079 228 7.693 1755 82 7.693 634 0 7.693 0

36

Once this process was completed for each scenario, I plotted the ordinates created

and compared the responses of the watershed, in terms of peak flow and volume of

storm flow.

Calculating Comparison Values

Areas of comparison for this analysis included, peak flow, lag time, and volume

of storm flow.

Peak flow: the highest discharge value, in cubic feet per second (cfs).

Lag time: the time between the center of rainfall to the peak rate of flow (to the

nearest hour), (Viessman 1977).

Volume of storm flow: in cubic feet.

37

IV. RESULTS

Due to the size of precipitation and the threshold value for the first and second

scenarios, there was no storm flow for the 1960s. For the 2000s, 3 hours of 0.5 inches

of rainfall, produced a peak flow of approximately 1,519 cubic feet per second, and a

storm runoff volume of 29,729,080 cubic feet (Table 12; Figure 18).

Table 12. Scenario # 1: 0.5 inches per Hour for 3 Hours

1960s Peak Flow (cfs): 0.0

Volume of Storm Runoff (cubic

feet): 0.0

2000s Peak Flow (cfs): 1,519


feet): 29,729,080

Scenario #1: 0.5 Inches per Hour for 3 Hours

0

200

400

600

800

1000

1200

1400

1600

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Time (hours)

Stre

am d

isch

arge

(cf

s)

2000's OrdinatesNo Stormflow 1960's Ordinates

38

Figure 18. Scenario #1 Storm Hydrograph: 0.5 Inches per Hour for 3 Hours

In Scenario #2, the 2000s produced a peak flow of 13,340 cubic feet per second,

and a storm flow volume of 261,119,800 cubic feet (Table 13).


0

2000

4000

6000

8000

10000

12000

14000

16000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Time (hours)

Stre

am d

isch

arge

(cfs

) .

2000's OrdinatesNo Stormflow 1960's Ordinates

Figure 19. Scenario #2 Storm Hydrograph: 1.0 Inch per Hour for 3 Hours

Table 13. Scenario #2: 1.0 inch per Hour for 3 Hours

1960s Peak Flow (cfs): 0.0


feet): 0.0



feet): 261,119,800

39

Both averaged unit hydrographs generated storm flow in Scenario #3. The 2000s

values are much larger then the 1960s, with a peak flow of 25,161 cfs. The 1960s peak

flow value is 11,552 cfs, with a storm flow volume of 204,243,935 cubic feet. Storm flow

volume for the 2000s is 492,510,520 cubic feet (Table 14; Figure 20).

Table 14. Scenario #3: 1.5 Inches per Hour for 3 Hours



feet): 204,243,935



feet): 492,510,520


0

5000

10000

15000

20000

25000

30000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Time (hours)

Stre

am d

isch

arge

(cfs

) .

1960's Ordinates 2000's Ordinates


40

The fourth scenario, 2.0 inches per hour for 3 hours, almost produces a10-year

flood event for the 1960s. Peak flow for the 1960s is 24,562 cfs; a 10-year event

requires 25,000 cfs. The 2000s peak flow is 36,981 cfs (Table 15; Figure 21).




feet): 434,248,367



feet): 955,291,960


0

5000

10000

15000

20000

25000

30000

35000

40000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Time (hours)

Stre

am d

isch

arge

(cfs

) .



41

In Scenario #5, the 2000s unit hydrograph produced enough storm flow to

produce a 100-year flood event (Table 16; Figure 22). The 1960s unit hydrograph

generated a peak flow of 37,571 cfs, which is just over the requirements for a 50-year

event. Total volume of storm flow for the 2000s equaled 955,291,960 cubic feet; the

1960s, 664,252,798 cubic feet.

Table 16. Scenario #5: 2.5 inches per Hour for 3 Hours



feet): 664,252,798



feet): 955,291,960


0

10000

20000

30000

40000

50000

60000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Time (hours)

Stre

am d

isch

arge

(cfs

) .


42

Figure 22. Scenario #5 Storm Hydrograph: 2.5 inches per Hour for 3 Hours

The last scenario, Scenario #6, each time period created a significant amount of

stormflow. The 1960s unit hydrograph generated a peak flow of 50,580 cfs, with a storm

flow volume of 894,257,229 cubic feet. With a peak flow of 60,623 cfs, the 2000s unit

hydrograph generated an event that has a 0.2 percent chance of occurring in any given

year, a 500-year storm event (Table 17; Figure 23).




feet): 894,257,229



feet): 1,186,682,680

43


0

10000

20000

30000

40000

50000

60000

70000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Time (hours)

Stre

am d

isch

arge

(cfs

) .



44

V. DISCUSSION

Threshold values were a key component to this analysis and were found during

the excess precipitation calculations. These values are of great importance because

they make possible the comparison of the two time periods. When looking at the

individual threshold values for the 10 storms used in the analysis, there is a large range

of variability between them. This could be due to antecedent moisture conditions, for

example, a saturated 1960s pervious watershed may display the same hydrologic

characteristics as the 2000s urbanized watershed.

The crucial difference between the two time periods is the averaged threshold

values. The higher 1960s value indicates greater precipitation intensity is necessary to

surpass the infiltration-excess threshold and create overland flow, whereas the lower

2000s value indicates less precipitation intensity is needed to produce surface runoff

(and stormflow). The decreased threshold value for the 2000s illustrates a change in the

surface characteristics of the watershed (i.e. urbanization). Higher values of storm flow

volume and peak flow are seen in correlation to the lower threshold value

Lag times for the two time periods, when compared using a z-test, showed no

significant difference (Table 18). The results suggest that the difference in lag times is

relatively small (on the order of one hour or less) and the coarse resolution of the

precipitation and streamflow data (1-hour increments) can not be used to confidently

resolve this difference. Farther research into the issue of lag time changes is required

using higher resolution data (e.g. 15-minute increments) and a larger dataset.

45

Table 18. Lag Time Comparison: Z-Test

1960s Lag Time (hours) 2000s Lag Time (hours)

Mean 3.276 2.454

Known Variance 2.06848 3.8254

Observations 5 5

z 0.75710639

In Figure 20, a comparison of peak flow between the 1960s and the 2000s shows

a substantial difference at lower precipitation intensities. For example, from Scenario #2

to Scenario #3, peak flow values, as well as storm flow volumes, nearly doubled. But, as

the precipitation intensity increases (e.g. scenarios 4, 5 and 6), the 1960s peak flows

gradually increase and become closer to the 2000s peak flows. A reasonable

explanation for these close values is that so much rain is falling; the 1960s soil has

become completely saturated and has begun to behave like the 2000s impervious

surface. Figure 21 shows a comparison between 1960s and 2000s storm flow volume

calculated during the scenario analysis. The 2000s values are approximately

300,000,000 cubic feet higher then the1960s, starting in Scenario #2. From Scenarios

#3 to #6, the 1960s and 2000s values stay an equal distance apart.

46

Peak Flow Comparison

0

10000

20000

30000

40000

50000

60000

70000

0.5 1.0 1.5 2.0 2.5 3.0

Precipitation (Inches/3 Hours)

Pea

k flo

w (c

fs)

.

1960s 2000s

Figure 24. Peak Flow Comparison

47

Stormflow Volume Comparison

0

200000000

400000000

600000000

800000000

1000000000

1200000000

1400000000

0.5 1.0 1.5 2.0 2.5 3.0

Precipitation (Inches/3 Hours)

Sto

rmflo

w (c

f) .

1960s 2000s

Figure 25. 1960s and 2000s Storm Flow Volume Comparison

48

VI. CONCLUSIONS

Results of the study support the hypothesis that increased urbanization in White

Rock Creek watershed has altered the creek’s hydrological response to storms. The

findings suggest that threshold values (precipitation intensity that must be surpassed

before the onset of infiltration-excess overland flow) have been lowered by the

proliferation of impervious surfaces that accompanies urbanization.

The impact of this change is reflected in higher peak flows and storm flow volume

values. In this analysis, the 2000s exhibit much larger volumes as well as much larger

peak flows, resulting in flooding events that would not have occurred, under the same

conditions, in the 1960s. Peak flows and volumes at lower precipitation intensities, such

as between Scenarios #1 and #2, increased as much as 8 times the Scenario #1 value.

These large increases, in the bottom three scenarios, are seen in the 2000s values

only. The 1960s shows no generated storm flow until Scenario #3.

An increase in peak flow and storm flow volume can negatively impact a river

channel. Increased erosion, channel and bank cutting, and eventual deposition can lead

to sizeable changes in the hydraulics and hydrology of a watershed. Watersheds that

are located in and around areas of large population growth, such as the greater Dallas-

Fort Worth area, are susceptible to these negative impacts.

Changes in lag times between the two time periods could not be resolved in this

study, probably because resolution of the precipitation and streamflow data is too

coarse. It is recommended that farther study of lag times be made using higher

resolution data (e.g. 15-minute increment) and a larger dataset.

49

APPENDIX

DATA TABLES AND GRAPHS

Table 19: November 22, 1961

Date Time CFS Precip LogCFS Baseflow WithoutBaseflow DirectRunoff UnitHydrograph Depth of Direct Runoff: Excess Precip Time Precip Threshold Value NewPrecip S-Curve Time Sum Flow NewFlow22-Nov 4 25 0.05 1.39794 Sum of CFS: 8739.03 4 0.05 0.997 0 7 0 0 0

5 25 0.05 1.39794 *3600 31460508.00 5 0.05 0.997 0 8 4470.7 4470.7 1490.26 38 1.2 1.57978 in AcreFeet: 722.23 6 1.2 0.997 0.203 9 18251.8 18251.8 6083.97 107 0.14 2.02938 107.0 0 0.203944056 0 DepthinFeet: 0.016995338 7 0.14 0.997 0 10 27662.9 0 27662.9 9221.08 1040 0.14 3.01703 128.2 911.8 0.203944056 4470.7 DepthinInches: 0.203944056 8 0.14 0.997 0 11 33537.6 4470.7 29066.8 9688.99 2960 0.04 3.47129 149.4 2810.6 0.203944056 13781.0 9 0.04 0.997 0 12 37788.2 18251.8 19536.4 6512.1

10 2090 0 3.32015 170.7 1919.3 0.203944056 9411.1 Sum of Final: 42850.13 13 40493.2 27662.9 12830.4 4276.811 1390 3.14301 191.9 1198.1 0.203944056 5874.7 *3600: 154260480.00 Sum: 0.203 14 42064.5 33537.6 8526.9 2842.312 1080 3.03342 213.1 866.9 0.203944056 4250.6 Direct Runoff: 0.203944056 15 42850.1 37788.2 5061.9 1687.313 786 2.89542 234.3 551.7 0.203944056 2705.0 Threshold Value: 0.997 16 42850.1 40493.2 2356.9 785.614 576 2.76042 255.6 320.4 0.203944056 1571.3 Duration: 1 hour 17 42850.1 42064.5 785.7 261.915 437 2.64048 276.8 160.2 0.203944056 785.6 18 42850.1 42850.1 0 016 298 2.47422 298.0 0 0.203944056 0 19 42850.1 42850.1

20 42850.1 42850.121 38379.4 42850.122 24598.4 42850.123 15187.3 42850.124 9312.6 38379.425 5061.9 24598.426 2356.9 15187.327 785.7 9312.628 0 5061.929 2356.930 785.731 0

Sum of Flow: 42850.13*3600: 154260480.00

50

51

Figure 26November 22, 1961: Procession from Initial Hydrograph to Unit Hydrograph

0

0.2

0.4

0.6

0.8

1

1.2

1.4

4 5 6 7 8 9 10 11 12 13 14 15 16

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

0

2000

4000

6000

8000

10000

12000

14000

16000

Stre

am d

isch

arge

(cfs

) .


52

Figure 27November 22, 1961: Precipitation Hyetograph

0

0.2

0.4

0.6

0.8

1

1.2

1.4

4 5 6 7 8 9

Time (hours)

Pre

cipi

tatio

n (in

ches

) .


53

Figure 28November 22, 1961: Final 3-Hour Unit Hydrograph

0

2000

4000

6000

8000

10000

12000

7 8 9 10 11 12 13 14 15 16 17 18

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Table 20: April 27, 1962

Date Time CFS Precip LogCFS Baseflow WithoutBaseflow DirectRunoff UnitHydrograph Depth of Direct Runoff: Excess Precip Time Precip Threshold Value NewPrecip S-Curve Time Sum Flow NewFlow27-Apr 1 39 Sum of CFS: 11794.97 1 0 0.1513 0 4 0 0 0

2 39 * 3600 seconds: 42461874.00 2 0 0.1513 0 5 1212.6 1212.6 2020.93 39 0.33 1.59106 into Acrefeet: 974.79 3 0.33 0.1513 0.1787 6 1818.4 1818.4 3030.74 97 0.19 1.98677 97.0 0 0.27526087 0 DirectRunoff(ft): 0.022938406 4 0.19 0.1513 0.0387 7 3038.2 0 3038.2 5063.75 450 0.15 2.65321 116.2 333.8 0.27526087 1212.6 DirectRunoff(in): 0.275260870 5 0.15 0.1513 0 8 4781.2 1212.6 3568.6 5947.76 636 0.2 2.80346 135.5 500.5 0.27526087 1818.4 6 0.2 0.1513 0.0487 9 6019.2 1818.4 4200.8 7001.37 991 0.16 2.99607 154.7 836.3 0.27526087 3038.2 Sum of Final: 42850.13 7 0.16 0.1513 0.0087 10 7888.4 3038.2 4850.2 8083.78 1490 0.02 3.17319 173.9 1316.1 0.27526087 4781.2 *3600: 154260480.00 8 0.02 0.1513 0 11 8206.5 4781.2 3425.3 5708.89 1850 0.08 3.26717 193.2 1656.8 0.27526087 6019.2 9 0.08 0.1513 0 12 8230.2 6019.2 2211.0 3685.1

10 2050 0 3.31175 212.4 1837.6 0.27526087 6675.9 10 0 0.1513 0 13 8341.2 7888.4 452.7 754.511 1990 3.29885 231.6 1758.4 0.27526087 6388.1 14 8368.5 8206.5 162.1 270.112 1680 3.22531 250.8 1429.2 0.27526087 5192.0 Sum: 0.275 15 9263.4 8230.2 0 013 1250 3.09691 270.1 979.9 0.27526087 3560.0 Direct Runoff: 0.275260870 16 8646.9 8341.214 936 2.97128 289.3 646.7 0.27526087 2349.4 Threshold Value: 0.1513 17 8230.2 8368.515 687 2.83696 308.5 378.5 0.27526087 1374.9 Duration: 5 hours 18 8341.2 9263.416 449 2.65225 327.8 121.2 0.27526087 440.4 19 8368.5 8646.917 347 2.54033 347.0 0 0.27526087 0 20 9263.4 8230.218 295 2.46982 21 8646.9 8341.2

22 8230.2 8368.523 8341.2 9263.4

Sum of Flow: 41566.53*3600: 149639518.08

54

55

Figure 29April 27, 1962: Procession from Initial Hydrograph to Unit Hydrograph

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

0

1000

2000

3000

4000

5000

6000

7000

8000

Stre

am d

isch

arge

(cfs

) .

Precipitation Hydrograph Without Baseflow Unit Hydrograph

56

Figure 30April 27, 1962: Precipitation Hyetograph

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

1 2 3 4 5 6 7 8 9 10

Time (hours)

Pre

cipi

tatio

n (in

ches

) .


57

Figure 31April 27, 1962: Final 3-Hour Unit Hydrograph

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

4 5 6 7 8 9 10 11 12 13 14 15

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Table 21: September 7-8, 1962

Date Time CFS Precip LogCFS Baseflow WithoutBaseflow DirectRunoff UnitHydrograph Depth of direct runoff: Excess Precip Time Precip Threshold Value NewPrecip S-Curves Time Sum Flow NewFlow7-Sep 21 286 0.08 Sum of CFS: 18841.50 21 0.08 0.565 0 24 0 0 0

22 238 0.95 2.37658 *3600 67829400.00 22 0.95 0.565 0.385 25 5337.4 5337.4 5337.423 348 0.47 2.54158 in AcreFeet: 1557.15 23 0.47 0.565 0 26 8368.8 8368.8 8368.824 746 0.62 2.87274 746.0 0 0.439706917 0 DepthinFeet: 0.036642243 24 0.62 0.565 0.055 27 9421.5 0 9421.5 9421.525 3070 0.12 3.48714 723.1 2346.9 0.439706917 5337.4 DepthinInches: 0.439706917 25 0.12 0.565 0 28 13264.5 5337.4 7927.1 7927.126 4380 0 3.64147 700.2 3679.8 0.439706917 8368.8 26 0 0.565 0 29 13118.5 8368.8 4749.8 4749.8

8-Sep 27 4820 3.68305 677.3 4142.7 0.439706917 9421.5 Sum of Final: 42850.1 27 0 0.565 0 30 12722.3 9421.5 3300.8 3300.828 4140 3.61700 654.4 3485.6 0.439706917 7927.1 *3600: 154260480.0 31 15457.6 13264.5 2193.1 2193.129 2720 3.43457 631.5 2088.5 0.439706917 4749.8 Sum: 0.440 32 14226.5 13118.5 1108.0 1108.030 2060 3.31387 608.6 1451.4 0.439706917 3300.8 Runoff: 0.439706917 33 13166.0 12722.3 443.7 443.731 1550 3.19033 585.7 964.3 0.439706917 2193.1 Threshold Value: 0.565 34 15457.6 15457.6 0 032 1050 3.02119 562.8 487.2 0.439706917 1108.0 Duration: 3 hours 35 14226.5 14226.533 735 2.86629 539.9 195.1 0.439706917 443.7 36 13166.0 13166.034 517 2.71349 517.0 0 0.439706917 0 37 15457.6 15457.635 401 2.60314 38 14226.5 14226.536 342 2.53403 39 13166.0 13166.037 342 2.53403 40 15457.6 15457.638 273 2.43616 41 14226.5 14226.539 273 2.43616 42 13166.0 13166.040 229 2.35984 43 15457.6 15457.641 229 2.35984 44 14226.5 14226.542 198 2.29667 45 13166.0 13166.0

46 15457.6 15457.647 14226.5 14226.548 13166.0 13166.049 15457.6 15457.650 14226.5 14226.551 13166.0 13166.0

Sum of Flows: 42850.1*3600: 154260480.0

58

59

Figure 32September 7 - 8, 1962: Procession from Initial Hydrograph to Unit Hydrograph

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Stre

am d

isch

arge

(cfs

) .


60

Figure 33September 7 - 8, 1962: Precipitation Hyetograph

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

21 22 23 24 25 26 27

Time (hours)

Pre

cipi

tatio

n (in

ches

) .


61

Figure 34September 7-8, 1962: Final 3-Hour Unit Hydrograph

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

24 25 26 27 28 29 30 31 32 33 34

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Table 22: April 28, 1966

Date Time CFS Precip LogCFS Baseflow WithoutBaseflow DirectRunoff UnitHydrograph Depth of Direct Runoff: Excess Precip Time Precip Threshold Value NewPrecip S-Curves Time Sum Flow NewFlow

28-Apr 1 104 1.1 Sum of CFS: 92475 1 1.1 2.242 0 2 0.0 0 0

2 630 4.4 2.79934 630.0 0 2.158104790 0 *3600: 332910280.8 2 4.4 2.242 2.158 3 3569.9 3569.9 1190.0

3 8390 0.58 3.92376 685.8 7704.2 2.158104790 3569.9 inAcreFeet: 7642.56843 3 0.58 2.242 0 4 13466.7 13466.7 4488.9

4 22100 0.02 4.34439 741.7 21358.3 2.158104790 9896.8 DepthinFeet: 0.179842066 4 0.02 2.242 0 5 20928.1 0.0 20928.1 6976.0

5 16900 0.05 4.22789 797.5 16102.5 2.158104790 7461.4 DepthinInches: 2.15810479 5 0.05 2.242 0 6 26927.2 3569.9 23357.3 7785.8

6 13800 0.05 4.13988 853.3 12946.7 2.158104790 5999.1 6 0.05 2.242 0 7 31695.6 13466.7 18229.0 6076.3

7 11200 0 4.04922 909.2 10290.8 2.158104790 4768.5 Sum of Final 42850.13 7 0 2.242 0 8 35511.5 20928.1 14583.4 4861.1

8 9200 3.96379 965.0 8235.0 2.158104790 3815.9 *3600 154260480.00 9 38374.7 26927.2 11447.6 3815.9

9 7200 3.85733 1020.8 6179.2 2.158104790 2863.2 Sum: 2.158 10 40424.4 31695.6 8728.7 2909.6

10 5500 3.74036 1076.7 4423.3 2.158104790 2049.6 Direct Runoff: 2.15810479 11 41845.8 35511.5 6334.3 2111.4

11 4200 3.62325 1132.5 3067.5 2.158104790 1421.4 Threshold Value: 2.242 12 42592.6 38374.7 4217.8 1405.9

12 2800 3.44716 1188.3 1611.7 2.158104790 746.8 Duration: 1 hour 13 42850.1 40424.4 2425.7 808.6

13 1800 3.25527 1244.2 555.8 2.158104790 257.6 14 42850.1 41845.8 1004.4 334.8

14 1300 3.11394 1300.0 0 2.158104790 0 15 42850.1 42592.6 257.6 85.9

15 1100 3.04139 16 42850.1 42850.1 0 0

16 1000 3.00000 17 42850.1 42850.1

17 900 2.95424 18 42850.1 42850.1

18 800 2.90309 19 42850.1 42850.1

19 700 2.84510 20 42850.1 42850.1

20 600 2.77815 Sum of Flow: 42850.1

21 500 2.69897 *3600: 154260480.0

62

63

Figure 35April 28, 1966: Procession from Initial Hydrograph to Unit Hydrograph

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

0

5000

10000

15000

20000

25000

Stre

am d

isch

arge

(cfs

) .


64

Figure 36April 28, 1966: Precipitation Hyetograph

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 2 3 4 5 6 7

Time (hours)

Pre

cipi

tatio

n (in

ches

) .


65

Figure 37April 28, 1966: Final 3-Hour Unit Hydrograph

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Table 23: August 13-14, 1968

Date Time CFS Precip LogCFS Baseflow WithoutBaseflow DirectRunoff UnitHydrograph Depth of Direct Runoff: Excess Precip Time Precip Threshold Value NewPrecip S-Curve Time Sum Flow NewFlow13-Aug 17 Sum: 19111.55 18 0 1.324 0 19 0 0 0

18 2.4 0.38021 * 3600: 68801562.00 19 1.77 1.324 0.446 20 11741.7 11741.7 3913.919 16 1.77 1.20412 16.0 0 0.446008997 0 into AcreFeet: 1579.47 20 0.05 1.324 0 21 30440.3 30440.3 10146.820 5270 0.05 3.72181 33.1 5236.9 0.446008997 11741.6 DirectRunoff(ft): 0.037167416 21 0.03 1.324 0 22 38046.9 0 38046.9 12682.321 8390 0.03 3.92376 50.2 8339.8 0.446008997 18698.6 DirectRunoff(in): 0.446008997 22 0.02 1.324 0 23 41512.1 11741.7 29770.5 9923.522 3460 0.02 3.53908 67.4 3392.6 0.446008997 7606.6 23 0.08 1.324 0 24 42308.9 30440.3 11868.6 3956.223 1630 0.08 3.21219 84.5 1545.5 0.446008997 3465.2 Sum of Final: 42850.1 24 0.01 1.324 0 25 42697.4 38046.9 4650.4 1550.124 457 0.01 2.65992 101.6 355.4 0.446008997 796.8 *3600: 154260480 25 0.02 1.324 0 26 42850.1 41512.1 1338.0 446.025 292 0.02 2.46538 118.7 173.3 0.446008997 388.5 26 0.1 1.324 0 27 42850.1 42308.9 541.2 180.426 204 0.1 2.30963 135.9 68.1 0.446008997 152.8 27 0.02 1.324 0 28 42850.1 42697.4 152.8 50.9

14-Aug 27 153 0.02 2.18469 153.0 0 0.446008997 0 29 42850.1 42850.1 0 028 138 0 2.13988 Sum: 0.446 30 42850.1 42850.1

Direct Runoff: 0.446008997 31 42850.1 42850.1Threshold Value: 1.324 32 42850.1 42850.1Duration: 1 hour 33 42850.1 42850.1

34 42850.1 42850.135 42850.1 42850.136 31108.5 42850.137 12409.9 42850.138 4803.2 42850.139 1338.0 31108.540 541.2 12409.941 152.8 4803.242 0 1338.043 541.244 152.845 0

Sum of Flows: 42850.13*3600: 154260480.00

66

67

Figure 38August 13 - 14, 1968: Procession from Initial Hydrograph to Unit Hydrograph

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

18 19 20 21 22 23 24 25 26 27 28

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

Stre

am d

isch

arge

(cfs

) .

Precipitation Hydrograph Direct Runoff Unit Hydrograph

68

Figure 39August 13 - 14, 1968: Precipitation Hyetograph

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

18 19 20 21 22 23 24 25 26 27

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

Precipiation Threshold Value

69

Figure 40August 13 -14, 1968: Final 3-Hour Unit Hydrograph

0

2000

4000

6000

8000

10000

12000

14000

19 20 21 22 23 24 25 26 27 28 29

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Table 24: December 30, 2002

Date Time CFS Precip LogCFS Baseflow WithoutBaseflow DirectRunoff UnitHydrograph Depth of Direct Runoff: Excess Precip Time Precip Threshold Value NewPrecip S-Curves Time Sum Ordinates NewOrdinates30-Dec 10 102 0.01 Sum of CFS: 48823 10 0.01 0.671 0 14 0 0 0

11 108 0 *3600: 175764186 11 0 0.671 0 15 4205.1 4205.1 1401.712 104 0.03 in AcreFeet: 4034.990496 12 0.03 0.671 0 16 17374.1 17374.1 5791.413 106 0.21 2.02495 DepthinFeet: 0.094949889 13 0.21 0.671 0 17 28183.6 0 28183.6 9394.514 180 0.03 2.25587 180.2 0 1.139398672 0 DepthinInches: 1.139398672 14 0.03 0.671 0 18 35935.9 4205.1 31730.8 10576.915 5035 1.81 3.70199 243.6 4791.3 1.139398672 4205.1 15 1.81 0.671 1.139 19 39918.6 17374.1 22544.5 7514.816 15312 0.15 4.18502 307.0 15004.7 1.139398672 13169.0 16 0.15 0.671 0 20 41600.1 28183.6 13416.5 4472.217 12687 0.14 4.10335 370.3 12316.3 1.139398672 10809.5 17 0.14 0.671 0 21 42511.3 35935.9 6575.4 2191.818 9267 3.96693 433.7 8833.0 1.139398672 7752.4 Sum of Final: 42850.1 22 42850.1 39918.6 2931.5 977.219 5035 3.70199 497.1 4537.8 1.139398672 3982.7 *3600: 154260480.0 Sum: 1.139 23 42850.1 41600.1 1250.0 416.720 2476 3.39381 560.5 1915.9 1.139398672 1681.5 Direct Runoff: 1.139398672 24 42850.1 42511.3 338.8 112.921 1662 3.22064 623.8 1038.2 1.139398672 911.2 Threshold Value: 0.671 25 42850.1 42850.1 0 022 1073 3.03070 687.2 386.1 1.139398672 338.8 Duration: 1 hour 26 42850.1 42850.123 751 2.87538 750.6 0 1.139398672 0 27 42850.1 42850.124 544 2.73531 28 42850.1 42850.1

29 42850.1 42850.130 42850.1 42850.131 42850.1 42850.132 42850.1 42850.133 42850.1 42850.134 38645.0 42850.135 25476.0 42850.136 14666.5 42850.137 6914.2 38645.038 2931.5 25476.039 1250.0 14666.540 338.8 6914.241 0 2931.542 1250.043 338.844 0

Sum of Flow: 42850.1*3600: 154260480.0

70

71

Figure 41December 30, 2002: Procession from Initial Hydrograph to Unit Hydrograph

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Stre

am d

sich

arge

(cfs

) .


72

Figure 42December 30, 2002: Precipitation Hyetograph

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

10 11 12 13 14 15 16 17

Time (hours)

Pre

cipi

tatio

n (in

ches

) .


73

Figure 43December 30, 2002: Final 3-Hour Unit Hydrograph

0

2000

4000

6000

8000

10000

12000

14 15 16 17 18 19 20 21 22 23 24 25

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Table 25: April 23 - 24, 2003

Date Time CFS Precip LogCFS Baseflow WithoutBaseflow DirectRunoff UnitHydrograph Depth of Direct Runoff: Excess Precip Time Precip Threshold Value NewPrecip S-Curve Time Sum Flow NewFlow23-Apr 21 180 1.01 2.25587 180.2 0 0.097345793 0 Sum: 4171.28 21 1.01 0.913 0.097 21 0 0 0

22 483 0.01 2.68436 191.5 292.0 0.097345793 2999.3 *3600: 15016608.72 22 0.01 0.913 0 22 2999.3 2999.3 999.823 1222 0 3.08691 202.7 1018.8 0.097345793 10465.8 inAcreFeet: 344.73 23 13465.2 13465.2 4488.424 1360 3.13343 214.0 1145.7 0.097345793 11769.1 DepthinFeet: 0.008112149 Sum: 0.097 24 25234.2 0 25234.2 8411.4

24-Apr 25 942 2.97421 225.2 717.1 0.097345793 7366.6 DepthinInches: 0.097345793 Direct Runoff: 0.097345793 25 32600.8 2999.3 29601.5 9867.226 651 2.81346 236.5 414.3 0.097345793 4256.3 Threshold Value: 0.913 26 36857.1 13465.2 23391.9 7797.327 493 2.69242 247.7 244.8 0.097345793 2514.5 Sum of Final: 42850.13 Duration: 1 hour 27 39371.6 25234.2 14137.4 4712.528 437 2.64045 259.0 178.0 0.097345793 1828.4 *3600: 154260480.00 28 41200.0 32600.8 8599.1 2866.429 370 2.56797 270.2 99.6 0.097345793 1022.8 29 42222.7 36857.1 5365.6 1788.530 328 2.51626 281.5 46.8 0.097345793 480.8 30 42703.5 39371.6 3331.9 1110.631 307 2.48714 292.7 14.3 0.097345793 146.5 31 42850.0 41200.0 1650.1 550.032 304 2.48287 304.0 0 0.097345793 0 32 42850.1 42222.7 627.4 209.133 282 2.44989 33 42850.1 42703.5 146.6 48.934 293 2.46704 34 42850.1 42850.0 0 035 282 2.44989 35 42850.1 42850.136 279 2.44557 36 42850.1 42850.137 262 2.41750 37 42850.1 42850.138 265 2.42282 38 39850.8 42850.139 252 2.40140 39 29385.0 42850.140 246 2.39126 40 17615.9 42850.141 235 2.37076 41 10249.3 39850.842 232 2.36559 42 5993.0 29385.043 246 2.39126 43 3478.5 17615.944 240 2.38105 44 1650.2 10249.345 235 2.37076 45 627.4 5993.046 211 2.32356 46 146.6 3478.547 206 2.31286 47 0 1650.248 203 2.30748 48 627.4

49 146.650 0

Sum of Flow: 42850.13*3600: 154260480.00

74

75

Figure 44April 23-24, 2003: Procession from Initial Hydrograph to Unit Hydrograph

0

0.2

0.4

0.6

0.8

1

1.2

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

0

2000

4000

6000

8000

10000

12000

14000

Stre

am d

isch

arge

(cfs

) .


76

Figure 45April 23-24, 2003: Precipitation Hyetograph

0

0.2

0.4

0.6

0.8

1

1.2

21 22

Time (hours)

Pre

cipi

tatio

n (in

ches

) .


77

Figure 46April 23-24, 2003: Final 3-Hour Unit Hydrograph

0

2000

4000

6000

8000

10000

12000

21 22 23 24 25 26 27 28 29 30 31 32 33 34

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Table 26: June 11-12, 2003

Date Time CFS Precip Baseflow WithoutBaseflow DirectRunoff UnitHydrograph Depth of Direct Runoff: Excess Precip Time Precip Threshold Value NewPrecip S-Curve Time Sum Flow NewFlow11-Jun 23 37 0.09 37.4 0 0.072875548 0 Sum: 3122.73 23 0.09 0.039 0.051 23 0 0 0

24 460 0.06 48.8 410.9 0.072875548 5637.9 *3600: 11241816.98 24 0.06 0.039 0.021 24 5637.9 5637.9 5637.912-Jun 25 999 0.04 60.2 938.6 0.072875548 12879.8 inAcreFeet: 258.08 25 0.04 0.039 0.001 25 12879.8 12879.8 12879.8

26 869 0.03 71.6 796.9 0.072875548 10934.8 DepthinFeet: 0.006072962 26 0.03 0.039 0 26 10934.7 0 10934.8 10934.827 582 0.02 83.0 499.1 0.072875548 6849.3 DepthinInches: 0.072875548 27 0.02 0.039 0 27 12487.2 5637.9 6849.3 6849.328 334 0.02 94.4 239.5 0.072875548 3285.9 28 0.02 0.039 0 28 16165.7 12879.8 3285.9 3285.929 246 0.02 105.8 140.4 0.072875548 1926.1 Sum of Final: 42850.13 29 0.02 0.039 0 29 12860.9 10934.7 1926.1 1926.130 185 0.01 117.2 68.0 0.072875548 932.9 *3600: 154260480.00 30 0.01 0.039 0 30 13420.2 12487.2 932.9 932.931 158 0.02 128.6 29.4 0.072875548 403.4 31 0.02 0.039 0 31 16569.1 16165.7 403 40332 140 0.01 140.0 0 0.072875548 0 32 0.01 0.039 0 32 12860.9 12860.9 0 033 123 0.01 151.4 33 0.01 0.039 0 33 13420.2 13420.234 112 0 162.8 34 0 0.039 0 34 16569.1 16569.135 102 174.2 35 12860.9 12860.936 98 185.6 Sum: 0.073 36 13420.2 13420.237 97 Direct Runoff: 0.072875548 37 16569.1 16569.138 92 Threshold Value: 0.039 38 12860.9 12860.939 89 Duration: 3 hours 39 13420.2 13420.2

40 16569.1 16569.141 12860.9 12860.9

Sum of Flow: 42850.13*3600: 154260480.00

78

79

Figure 47June 11-12, 2003: Procession from Initial Hydrograph to Unit Hydrograph

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

0

2000

4000

6000

8000

10000

12000

14000

Stre

am d

isch

arge

(cfs

) .


80

Figure 48June 11-12, 2003: Precipitation Hyetograph

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

23 24 25 26 27 28 29 30 31 32 33 34

Time (hours)

Pre

cipi

tatio

n (in

ches

) .


81

Figure 49June 11-12, 2003: Final 3-Hour Unit Hydrograph

0

2000

4000

6000

8000

10000

12000

14000

23 24 25 26 27 28 29 30 31 32

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Table 27: December 12, 2003

Date Time CFS Precip LogCFS Baseflow WithoutBaseflow DirectRunoff UnitHydrograph Depth of Direct Runoff: Excess Precip Time Precip Threshold Value NewPrecip S-Curves Time Sum Ordinates NewOrdinates12-Dec 13 27 0.09 1.43136 Sum of CFS: 8568.0 13 0.09 0.1458 0 15 0 0 0

14 58 0.04 1.76343 *3600: 30844800.0 14 0.04 0.1458 0 16 1217.78799 1217.8 1217.815 102 0.22 2.00860 102.0 0 0.199952703 0 inAcreFeet: 708.1 15 0.22 0.1458 0.0742 17 4115.47324 4115.5 4115.516 354 0.24 2.54900 110.5 244 0.199952703 1218 DepthinFeet: 0.016662725 16 0.24 0.1458 0.0942 18 6263.48121 0 6263.5 6263.517 942 0.16 2.97405 119.1 823 0.199952703 4115 DepthinInches: 0.199952703 17 0.16 0.1458 0.0142 19 8288.46008 1217.788 7070.7 7070.718 1380 0.1 3.13988 127.6 1252 0.199952703 6263 18 0.1 0.1458 0 20 11293.6708 4115.473 7178.2 7178.219 1550 0.08 3.19033 136.2 1414 0.199952703 7071 Sum of Final: 42850.13 19 0.08 0.1458 0 21 12098.8612 6263.481 5835.4 5835.420 1580 0.03 3.19866 144.7 1435 0.199952703 7178 *3600: 154260480.00 20 0.03 0.1458 0 22 12475.4502 8288.46 4187.0 4187.021 1320 0 3.12057 153.2 1167 0.199952703 5835 21 0 0.1458 0 23 14332.8895 11293.67 3039.2 3039.222 999 2.99957 161.8 837 0.199952703 4187 24 14130.3416 12098.86 2031.5 2031.523 778 2.89098 170.3 608 0.199952703 3039 Sum: 0.183 25 13563.7076 12475.45 1088.3 1088.324 585 2.76716 178.8 406 0.199952703 2031 Direct Runoff: 0.183153316 26 14888.5209 14332.89 555.6 555.625 405 2.60746 187.4 218 0.199952703 1088 Threshold Value: 0.1458 27 14397.9049 14130.34 267.6 267.626 307 2.48714 195.9 111 0.199952703 556 Duration: 3 hours 28 13563.7076 13563.71 0 027 258 2.41162 204.5 54 0.199952703 268 29 14888.5209 14888.5228 213 2.32838 213.0 0 0.199952703 0 30 14397.9049 14397.9

31 13563.7076 13563.7132 14888.5209 14888.5233 14397.9049 14397.934 13563.7076 13563.7135 14888.5209 14888.5236 14397.9049 14397.937 13563.7076 13563.7138 14888.5209 14888.5239 14397.9049 14397.940 13563.7076 13563.71

Sum of Flows: 42850.1*3600: 154260480.0

82

83

Figure 50December 12, 2003: Procession from Initial Hydrograph to Unit Hydrograph

0

0.05

0.1

0.15

0.2

0.25

0.3

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Time (hours)

Pre

cipi

tatio

n (in

ches

) .

0

1000

2000

3000

4000

5000

6000

7000

8000

Stre

am d

isch

arge

(cfs

) .

Precipitation Hydrograph Without Baseflow Unit hydrograph

84

Figure 51December 12, 2003: Precipitation Hyetograph

0

0.05

0.1

0.15

0.2

0.25

0.3

13 14 15 16 17 18 19 20 21

Time (hours)

Pre

cipi

tatio

n (in

ches

) .


85

Figure 52December 12, 2003: Final 3-Hour Unit Hydrograph

0

1000

2000

3000

4000

5000

6000

7000

8000

15 16 17 18 19 20 21 22 23 24 25 26 27 28

Time (hours)

Stre

am d

isch

arge

(cfs

) .

Table 28: June 9-10, 2004

Date Time CFS Precip LogCFS Baseflow WithoutBaseflow DirectRunoff UnitHydrograph Depth of Direct Runoff: Excess Precip Time Precip Threshold Value NewPrecip S-Curves Time Sum Flow NewFlow9-Jun 16 167 0.61 2.2223 166.9 0 0.200683719 0 Sum of CFS: 8599.32 16 0.61 0.41 0.200 16 0 0 0

17 317 0.04 2.5015 174.6 142.7 0.200683719 711.1 *3600: 30957566.76 17 0.04 0.41 0 17 711.1 711.1 711.118 534 0.45 2.7277 182.3 351.9 0.200683719 1753.4 inAcreFeet: 710.69 18 0.45 0.41 0.040 18 1753.4 1753.4 1753.419 760 0.05 2.8810 190.0 570.3 0.200683719 2841.7 DepthinFeet: 0.016723643 19 0.05 0.41 0 19 2841.7 0 2841.7 2841.720 1209 0 3.0824 197.8 1011.2 0.200683719 5038.9 DepthinInches: 0.200683719 20 0 0.41 0 20 5750.0 711.1 5038.9 5038.921 1679 0 3.2251 205.5 1473.8 0.200683719 7344.0 21 0 0.41 0 21 9097.4 1753.4 7344.0 7344.022 1729 0.02 3.2378 213.2 1515.6 0.200683719 7552.3 Sum of Final: 42850.1 22 0.02 0.41 0 22 10394.0 2841.7 7552.3 7552.323 1484 0.01 3.1716 220.9 1263.5 0.200683719 6295.9 *3600: 154260480 23 0.01 0.41 0 23 12045.8 5750.0 6295.9 6295.924 1078 0.1 3.0327 228.7 849.4 0.200683719 4232.8 24 0.1 0.41 0 24 13330.2 9097.4 4232.8 4232.8

10-Jun 25 780 0.07 2.8921 236.4 543.6 0.200683719 2708.8 25 0.07 0.41 0 25 13102.8 10394.0 2708.8 2708.826 625 0 2.7959 244.1 380.9 0.200683719 1898.0 26 13943.8 12045.8 1898.0 1898.027 500 2.6990 251.8 248.2 0.200683719 1236.6 Sum: 0.200 27 14566.8 13330.2 1236.6 1236.628 425 2.6284 259.6 165.4 0.200683719 824.4 Direct Runoff: 0.200683719 28 13927.3 13102.8 824.4 824.429 350 2.5441 267.3 82.7 0.200683719 412.2 Threshold Value: 0.41 29 14356.1 13943.8 412.2 412.230 275 2.4393 275.0 0 0.200683719 0 Duration: 3 hours 30 14566.8 14566.8 0 031 250 2.3979 31 13927.3 13927.332 225 2.3522 32 14356.1 14356.1

33 14566.8 14566.834 13927.3 13927.335 14356.1 14356.136 14566.8 14566.837 13927.3 13927.338 14356.1 14356.139 14566.8 14566.840 13927.3 13927.341 14356.1 14356.142 14566.8 14566.843 13927.3 13927.3

Sum of Flow: 42850.1*3600: 154260480.0

86

87

Figure 53June 9, 2004: Procession from Initial Hydrograph to Unit Hydrograph

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Time (hours)

Pre

cipi

tatio

n (in

ches

)

0

1000

2000

3000

4000

5000

6000

7000

8000

Stre

am d

isch

arge

(cfs

)


88

Figure 54June 9, 2004: Precipitation Hyetograph

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

16 17 18 19 20 21 22 23 24 25

Time (hours)

Pre

cipi

tatio

n (in

ches

)


89

Figure 55June 9, 2004: Final 3-Hour Unit Hydrograph

0

1000

2000

3000

4000

5000

6000

7000

8000

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Time (hours)

Stre

am d

isch

arge

(cfs

) .

90

BIBLIOGRAPHY

Arnold, CL and Gibbons, CJ 1996. Impervious Surface Coverage: The Emergence of a

Key Environmental Indicator. America Planners Assoc J. 62:243-58.

Chorley, Richard 1969. Introduction to Physical Hydrology. Methuen and Company, Ltd,

Great Britain.

Dunne, T and Leopold, LB 1978. Water in Environmental Planning. New York:

Freeman. 818 pp.

Fielder, F 1999. “Unit Hydrograph Theory.” PowerPoint on the Web.

FIS 2004. Flood Insurance Study for Dallas County Unincorporated Areas, Texas.

FEMA, Revised August 2004.

Konrad, Christopher and Booth, Derek 2002. “Hydrologic Trends Associated with Urban

Development for Selected Streams in the Puget Sound Basin, Western

Washington.” Washington Department of Ecology.

McCuen, Richard 1998. Hydrologic Analysis and Design. Prentice Hall, New Jersey.

NFIP 1999. Floodplain Mangement Requirements: A Study Guide and Desk Reference

for Local Officials.

Ollman, Ralph 1969. “Impervious Surface Area in the Upper White Rock Creek

Watershed, Dallas and Collin Counties, Texas, 1969.” USGS Open file report.

Paul, Michael and Meyer, Judy 2001. “Streams in the Urban Landscape.” Annual

Review Ecological System. 32:333-65.

Steuer, JJ and Hunt, RJ 2001. “Use of Watershed-Modeling Approach to Assess

Hydrologic Effects of Urbanization, North Fork Pheasant Branch Basin near

91

Middleton, Wisconsin.” City of Middleton, Wisconsin Department of Natural Resources.

USGS.

Sultana, Selima and Chaney, Philip 2003. “Impacts of Urban Sprawl on Travel

Behaviors and Local Watersheds in the Auburn-Opelika Metropolitan Area:

A Case Study on a Small MSA.”

US Census Bureau 2001. www.census.gov

US Environmental Protection Agency, 2000. The quality of our nation’s waters. EPA

841-S-00-001.

USGS 1961-1967, Basic Data for Urban Hydrology Studies, Dallas Texas.

UN Population Division 1997. Urban and Rural Areas, 1950-2030 (The 1996

Revision). New York: United Nations.

Viessman, Warren, et al 1977. Introduction to Hydrology. 2nd Edition; Harper & Row,

New York.

Documents

Hydrological Impacts of Urbanization: White Rock Creek .../67531/metadc... · Storm drainage systems contribute to increased volumes of storm flow and decreased lag times. Many man-made