CVEEN 4410 Hydrology Homework 5 - University of Utahco2.coe.utah.edu/CVEEN4410b/pdf/HW5_SOLN.pdf ·...

CVEEN4410HydrologyHomework5

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Problem1:UnitHydrographA 56 acre watershed experiences the following storm (hyetograph) and has the resulting flow measured by a stream gage. Construct the unit hydrograph given the provided information. Assume infiltration follows the Phi Index model and is a fifth inch per hour.

SOLUTION Remember the steps:


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1.

2.

33 ∗3600

4356012 1

560.58

3.

0.58 ; 0.55; 0.55 ≅ 0.58; Close enough use 0.55 for the rest of the calculations.

Time (hr)

Q (cfs)

Baseflow (cfs)

DRO (cfs)

0 3 3 0

1 3 3 0

2 3 3 0

3 4.8 3 1.8

4 6.4 3 3.4

5 9.6 3 6.6

6 8.8 3 5.8

7 8.2 3 5.2

8 7.2 3 4.2

9 6 3 3

10 5 3 2

11 4 3 1

12 3 3 0

sum: 33

Time (hr) Hyetograph

(in/hr) Phi Index (in/hr)

Excess Rain (in/hr)

Excess Volume (in)

0.25 0.4 0.2 0.2 0.05

0.5 0.6 0.2 0.4 0.1

0.75 0.7 0.2 0.5 0.125

1 0.3 0.2 0.1 0.025

1.25 0.8 0.2 0.6 0.15

1.5 0.5 0.2 0.3 0.075

1.75 0.3 0.2 0.1 0.025

2 0.1 0.2 0 0

sum: 0.55


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4.

U = DRO/0.55

5. 60 ∗

1.06 ≅ 1

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12

Flow (cfs)

Time (hr)

Hydrograph

Q (cfs)

Baseflow (cfs)

DRO (cfs)

U (cfs)

Time (hr)

Q (cfs)

Baseflow (cfs)

DRO (cfs)

U (cfs)

0 3 3 0 0.0

1 3 3 0 0.0

2 3 3 0 0.0

3 4.8 3 1.8 3.3

4 6.4 3 3.4 6.2

5 9.6 3 6.6 12.0

6 8.8 3 5.8 10.5

7 8.2 3 5.2 9.5

8 7.2 3 4.2 7.6

9 6 3 3 5.5

10 5 3 2 3.6

11 4 3 1 1.8

12 3 3 0 0.0

sum: 33 60.0


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Problem2:UnitHydrographConvolution Create a storm hydrograph using the provided unit hydrograph and rainfall event. Be sure to print out your spreadsheet showing the offset of calculations and hand in.

SOLUTION Notice that the precip values need to be converted to depth before multiplying by the unit hydrograph. Multiply by the time (1/2 hour).

Time (hr) P (in/hr) P (in) 0 0.3 0.15

0.5 0.8 0.40 1 1.1 0.55

1.5 1.3 0.65 2 0.8 0.40

2.5 0.3 0.15 See the spreadsheet for the calculations


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Time (hr) P1*U P2*U P3*U P4*U P5*U P6*U SUM

0 0 REMEMBER TO OFFSET!! 0 0.5 15 0 REMEMBER TO OFFSET!! 15 1 48 40 0 REMEMBER TO OFFSET!! 88

1.5 67.5 128 55 0 OFFSET!! 250.5 2 55.5 180 176 65 0 OFFSET!! 476.5

2.5 37.5 148 247.5 208 40 0 681 3 24 100 203.5 292.5 128 15 763

3.5 13.5 64 137.5 240.5 180 48 683.5 4 6 36 88 162.5 148 67.5 508

4.5 0 16 49.5 104 100 55.5 325 5 0 22 58.5 64 37.5 182

5.5 0 26 36 24 86 6 0 16 13.5 29.5

6.5 0 6 6 7 0 0


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Problem3:CurveNumbertoCalculateRunoffDetermine the 10 year, 25 year, and 100 year storm runoff (ac-ft) for the basin with the following soil characteristics. The Basin is in Brigham City. Use the Brigham City (42-0924) weather station.

Land Use / Cover Hydrologic Soil

Group Area (ac)

City Park with nearly 100% grass coverage C 2.5

Roads A 0.6

Parking Lot B 1.2

1/4 acre housing lots (~38% impervious) C 35

Strip Mall B 1.8

Tree Farm in good condition B 20

0

200

400

600

800

1000

0 1 2 3 4 5 6 7 8

Q (cfs)

Time (hr)

Storm Hydrograph

0

100

200

300

400

500

600

700

800

900

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7

Q (cfs)

Hydrographs

Time (hr)

SUM

P6*U

P5*U

P4*U

P3*U

P2*U

P1*U


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SOLUTION


Group Area (ac) CN

City Park with nearly 100% grass coverage C 2.5 74

Roads A 0.6 98

Parking Lot B 1.2 98

1/4 acre housing lots (~38% impervious) C 35 83

Strip Mall B 1.8 92

Tree Farm in good condition B 20 58

61.1 2.5 74 0.6 98 1.2 98 35 83 1.8 92 20 58

61.175

100010 3.33

100.2 2

0.82.33 0.2 3.33 2

2.33 0.8 3.330.55

12∗ 61.1 2.82


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250.2 2

0.82.75 0.2 3.33

2

2.75 0.8 3.330.80

12∗ 61.1 4.08

1000.2 2

0.83.43 0.2 3.33 2

3.43 0.8 3.331.25

12∗ 61.1 6.38

Problem4:CurveNumberHydrologyUse the Curve number method to calculate the 10 year, 25 year, and 100 year storm runoff (ac-ft) for your Semester Project predevelopment watershed. Assume the whole area is hydrologic soil group C and has an area of 400 acres. Use your best judgment to decide which type of land use/cover to use, and the approximate area percentage relative to your total watershed area.


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Looks like good coverage

Looks like poor coverage


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Valley likely sagebrush with poor coverage


Group Area (%) CN

Woods good coverage C 35 70

woods poor coverage C 35 77

sagebrush poor coverage C 30 80

0.35 70 0.35 77 0.3 801

75

100010 3.33


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100.2 2

0.82.43 0.2 3.33 2

2.43 0.8 3.330.61

12∗ 400 20.4

250.2 2

0.82.83 0.2 3.33

2

2.83 0.8 3.330.85

12∗ 400 28.4

1000.2 2

0.83.47 0.2 3.33 2

3.47 0.8 3.331.28

12∗ 400 42.7

Problem5TimeofConcentrationCalculate the Time of Concentration for your project watershed. Show your work, if you use a spreadsheet; be sure to print out a copy.

SOLUTION Overland Flow: Length = 300 ft n = 0.6 from table 3-1 in TR55. Using average of Woods Light Underbrush and Dense Underbrush


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P2 = 1.79 in

∆√∆ ∆

6591 6513342 6591 6513

0.23 /


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0.007 .

. .

0.007 0.6 ∗ 300 .

1.79 . 0.23..600

Shallow Concentrated Flow (SCF) Given the huge range of different slopes, divide the rest of your watershed up into sections of similar slope. From an analysis of the mountain slopes, I have divided my SCF into 6 sections.


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Section 1

0.5 5280 2640

∆√∆ ∆

6536 61762640 6536 6176

0.14

From Figure 3-1, TR55. Using the calculated slope and unpaved, 6

36002640

3600 ∗ 60.122

Section 2


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∆√∆ ∆

6008 55001520 6008 5500

0.35

From Figure 3-1, TR55. Using the calculated slope and unpaved, 9.5

36001520

3600 ∗ 9.50.044

Section 3

∆√∆ ∆

5571 52391225 5571 5239

0.28


36001225

3600 ∗ 8.50.040

Section 4


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∆√∆ ∆

5328 50641386 5328 5064

0.19

From Figure 3-1, TR55. Using the calculated slope and unpaved, 7

36001386

3600 ∗ 70.055

Section 5


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∆√∆ ∆

5114 49411023 5114 4941

0.17


36001023

3600 ∗ 6.50.044

Section 6


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0.68 5280 3590

∆√∆ ∆

4987 47363590 4987 4736

0.07


36003590

3600 ∗ 4.20.237

0.600 0.122 0.044 0.040 0.055 0.044 0.2371.142 68.5

Problem6:Cowan’sMethodYou survey a section of stream with the following characteristics:

Earthen bottom of fine sand

Minor irregularities in the reach

Occasional section changes

Minor woody debris from beaver activity

Moderate vegetation with some seedlings

No meandering

Calculate the Manning’s roughness coefficient.


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SOURCE: http://www.ntc.blm.gov/krc/uploads/398/CowanMethod.pdf

CVEEN 4410 Hydrology Homework 5 - University of Utahco2.coe.utah.edu/CVEEN4410b/pdf/HW5_SOLN.pdf ·...

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