Quantitative hydrology REPORT.pptx

8/12/2019 Quantitative hydrology REPORT.pptx

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QU NTIT TIVEHYDROLOGYChapter 3

3.1 Basin Recharge and Runoff

3.2 Hydrograph Analysis

Estimating Volume of Runoff

3.3 Runoff Coefficients

3.4 Infiltration

3.5 Infiltration Indices

3.6 Rainfall-runoff Correlations

3.7 Moisture-accounting Procedures

3.8 Long-period runoff relations

Runoff from Snow

3.9 Physics of Snowmelt

3.10 Snowmelt Computation


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3.1BAS

IN

RECHAR

GE

AND

RU

NOFF

Basin Recharge

Interception together with depression

storage and soil moisture

Direct Runoff

Overland flow and interflow

Influent Streams Intermittent streams (can go dry

because of time elapses between rain)

Effluent Streams

Groundwater


3/18

THREEPATHSTO

A

STREAM

FORWATERNOTWITHHELDASBASIN

RECHARGE

RainOverland

Flow

Nearest

Channel

Rain InterflowNearest

Channel

Rain Percolation Groundwater/SoilMoisture


4/18


5/18

HYDROGRAPHANALYSIS

N = Ad0.2

N = Number of days

for recovery after

the peak

Ad= drainage area

in square miles
http://localhost/var/www/apps/conversion/tmp/scratch_4/PPT/Hydrograph_Analysis.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_4/PPT/Hydrograph_Analysis.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_4/PPT/Hydrograph_Analysis.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_4/PPT/Hydrograph_Analysis.ppt


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E

STIMATIN

GVOLUME

OF

RU

NOFF

Theoretical Formula

R = P L G

Where:R -Runoff

P - Precipitation

L - Basin Recharge

G - Groundwater Accretion


7/18

In the design of storm drains and water-control projects, runoff volume iscommonly assumed to be a percentage of rainfall

R = kP

Where:

R Runof

k runoff coefficient

P - Precipitation

Table 3.1 Values of Runoff Coefficients k for

various surfaces

Urban Residential

Simple Houses

Garden ApartmentsCommercial and Industrial

Parks

Asphalt or concretepavement

0.20

0.300.90

0.05-0.30

0.85-1.0


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Table 1: Runoff Coefficients

Soil Groups A and B are sandier and Soil Groups C and D are

more clayey. These soil classifications would be found in a county

soil survey available at any Soil and Water Conservation District

office or North Carolina Cooperative Extension center.


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EX

A

MP

L

E

Step 1:Assess SiteConditions

In this example we will use a 200 ft2 patio

Step 2:ObtainRunoff

Coefficient

Using the provided table (Table 1), look up the runoffcoefficient that most closely resembles your site. In this caseit is 0.98

Step 3: Dothe Math

Volume Runoff = Surface Area x Runoff Coefficient xRainfall Depth

Volume Runoff = 200ft2 x 0.98 x 0.083ft = 16.3ft3

Note: Make sure that Surface Area and Rainfall Depth are in the sameunits. It doesnt matter what you use, just stay consistent measurements infeet or meters are generally easiest.

Step 4:Convert ifNecessary

Most people have trouble thinking about water volume incubic feet so we will convert to gallons multiplying by7.48gal/ft3. Volume Runoff = 16.3ft3 x 7.48 gal/ft3 =121.gallons


10/18

INFILTR TIONPPT\Infiltration.ppt
http://localhost/var/www/apps/conversion/tmp/scratch_4/PPT/Infiltration.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_4/PPT/Infiltration.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_4/PPT/Infiltration.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_4/PPT/Infiltration.ppt


11/18

3.6 Rainfall-Runoff Correlation

Plot of average rainfall versus resulting runoff

PaN = bPaN-1+ PN

PaN Atecedent-Precipitation Index

at the end of Nth day

PaN-1Precipitation index on

previous day

b ranges from 0.85-0.95

When there is no rain for t days,

PaN-1= PaNbt


12/18

RUNOFFFROM

SNOW

3.9 Physics of SnowmeltFactors Affecting Snowmelt

Solar Radiation

Depends on Reflectivity orAlbedo

Heat from warm Air

Turbulence resulting to

speedy wind bringing large

quantities of warm air

Rainfall


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Heat from warm Air

Heat ofFusion of Ice

Heat ofCondensation

of Water

Therefore,

1073/144=7.5 units

Thus, in 1

unit ofmoisture

on snow,

7.5 of

water will

melt


14/18

Rainfall

Where:

Ms amount of melt in inches or millimeter

P - Rainfall or precipitationTw Wet-bulb temperature


15/18

SNOWMELTINBASINSWITHLITTLE

RANGEINELEVATION

Degree-day factors

defined as a departure of 1 degree in mean dailytemperature above 32F.

Depth of water melted from the snow in inches or

millimeter per degree-day

may be determined by dividing the volume of stream flow

produced by melting snow within a given time period by thetotal degree days for the period.

Usually ranging from 0.05-0.15in/degree-F with an

average value of 0.08in/degree-F

Ranges from 2-7mm/degree-C day.


16/18

E

xa

m

p

l

e

The area-elevation distribution in a basin on the board. The average

snow line is at 5000 ft and the temperature index station is at 6000

ft. Assume a temperature decrease of 3F per 1000ft increase in

elevation and a degree-day factor of 0.10. Compute the snowmelt in

second-foot days for a day when the mean daily temperature at the

index station is 44F

Solution: With a temperature of 44F at 6000 ft the freezing level is at

6000 + {[(44-32)/3]*1000} = 10,000 ft

The area between the snowline (5000 ft) and the freezing level is 305 sq.mi.

from the figure, the average temperature over this area is:

0.5(47+32) = 39.5F

And the average degree days above 32F is

39.5 32 = 7.5 degree days

The total melt therefore: 7.5*0.10*305 = 229 sq.mi. inches

26.9*229 = 6150 sfd


17/18

Did I make myself clear?


18/18

Maraming Salamat!

Kristian Carlo M. BolaBS IN CIVIL ENGINEERING VA

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Quantitative hydrology REPORT.pptx