Flood and Runoff estimation methods
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Flood and Runoff estimation Flood and Runoff estimation methods methods Direct Methods ( measurement s ) Indirect Methods ( Equations )
description
Flood and Runoff estimation methods. Indirect Methods (Equations). Direct Methods (measurements). Talbot’s. CN (SCS). Rational. Indirect Methods. Unit Hydrograph. Manning ’ s Formula. Equation Creager ’ s. Direct Methods. Current meter. Staff gauge. Crest stage gauge. - PowerPoint PPT Presentation
Transcript of Flood and Runoff estimation methods
Flood and Runoff estimationFlood and Runoff estimationmethodsmethods
Direct Methods
(measurements)
Indirect Methods
(Equations)
Indirect Methods
Rational
Unit Hydrograph
Equation Creager’s
CN )SCS(
Manning’s Formula
Talbot’s
Direct Methods Staff gauge
Crest stage gauge
Current meter
SCS MethodSCS Method• SCS Method
• In this method the runoff volume (Q) resulting from a given rainfall storm (P) is calculated using the following formula.
SPSPQ
8.0)2.0( 2
25425400
CNS
Talbot MethodTalbot Method
• Talbot Method
• Design flood can be related to morphological properties of the catchment. Design flood discharge (Q), in m3 /sec, can be calculated using the following formula
naCAQ
Talbot MethodTalbot Method
• Talbot Method
Catchments characteristics C
C1 = Terrain conditionMountainsSemi-mountainsLow lands
0.300.200.10
C2 = Slope of drainage areaabove 15%10 – 15 %5 – 10 %2- 5 %1 – 2 %
0.50.40.230.250.2
C3 = Shape of drainage areaWhen width equals lengthWhen width equals 0.4 of lengthWhen width equals 0.2 of length
0.300.200.10
Runoff coefficients according to catchments characteristics
Estimation of Design FloodEstimation of Design Flood
• Rational Method
• The rational method uses existing rainfall data and land use in estimating peak runoff from small drainage areas that are less than 15 km2.
CiAQ 278.0
Estimation of Design FloodEstimation of Design Flood
• Rational Method
Type Of Drainage Area Runoff Coefficient, C
Steep, bare rock Rock, steep but wooded
Plateaus lightly covered, ordinary ground bare Densely built up areas of cities with metal led roads & paths
Residential areas not densely built up, with metal led roadsResidential areas not densely built up, with unmetalled roads
Clayey soils, stiff and bare Clayey soils lightly covered
Loam, lightly cultivated or covered Loam, lightly, largely cultivated
Suburbs with gardens, lawns and macadamized roads Sandy soil, light growth
0.900.800.70
0.70-0.900.50-0.700.20-0.50
0.600.500.400.300.300.20
Runoff Coefficients for the Rational Method
Estimation of Design FloodEstimation of Design Flood
• Rational Method
• The rainfall intensity (i) in millimeters per hour for duration corresponding to the time of concentration for the catchment area and having a recurrence period appropriate to the site conditions, is read from IDF curves.
Estimation of Design FloodEstimation of Design Flood
• Rational Method
• Time of concentration is defined as the interval time in minutes from the beginning of rainfall to the time when water from the most remote position of the catchment reaches the outlet.
• Kirkpich formula
385.0155.1 /)52/1( HLTc
Estimation of Design FloodEstimation of Design Flood
• Rational Method
R a in fa ll I D F C urv e s a t H a jja h ; Y e m e n
1
1 0
1 0 0
1 0 0 0
1 1 0 1 0 0 1 0 0 0 1 0 0 0 0
D ur a tio n )m inu te (
Inte
nsi
ty )
mm
/hr(
2 - Y e a rs 5 - Y e a rs 1 0 -Y e a r s 2 5 -Y e a r s 5 0 -Y e a r s1 0 0 -Y e ar s
Estimation of Design FloodEstimation of Design Flood
• SCS Method
• In this method the runoff volume (Q) resulting from a given rainfall storm (P) is calculated using the following formula.
SPSPQ
8.0)2.0( 2
25425400
CNS
Estimation of Design FloodEstimation of Design Flood
• Talbot Method
• Design flood can be related to morphological properties of the catchment. Design flood discharge (Q), in m3 /sec, can be calculated using the following formula
naCAQ
Estimation of Design FloodEstimation of Design Flood
• Talbot Method
Catchments characteristics C
C1 = Terrain conditionMountainsSemi-mountainsLow lands
0.300.200.10
C2 = Slope of drainage areaabove 15%10 – 15 %5 – 10 %2- 5 %1 – 2 %
0.50.40.230.250.2
C3 = Shape of drainage areaWhen width equals lengthWhen width equals 0.4 of lengthWhen width equals 0.2 of length
0.300.200.10
Runoff coefficients according to catchments characteristics
Estimation of Design FloodEstimation of Design Flood
• Talbot Method
Formulas according to catchment properties
Catchments area (sq. km) Q25 (m3 /sec) Notes
<5 Qbasic * SFQbasic = basic flows derived from standards figures;SF = Slope factor for Catchment area
5 – 12.6 0.837 * C * A0.75 C = C1 + C2 + C3
12.6 - 36 4.985 * C * A0.5 C = C1 + C2 + C3
>36 14.232 C A0.4 C = C1 + C2 + C3
Q5 = 0.6 Q25; Q10 = 0.8Q25; Q50 = 1.2Q25; Q100 = 1.4Q25
CREAGER’S METHODCREAGER’S METHOD048.0)*386.0(*894.0
1 )*386.0(*
Am ACQ
048.0)*386.0(*894.01 )*386.0(*
Am ACQ
048.0)*386.0(*894.01 )*386.0(*
Am ACQ
Where:Qm = Maximum or peak flow for a given return period.A = Catchment area )Sq. Km(.C1 = Greagers number )max. 130(.
Theoretical eq. for runoff est. for YemenTheoretical eq. for runoff est. for Yemen
السطحي • الجريان الحتساب النظرية (المعادالت :لليمن )• Jac A.M. van der Gun and others 1995.
R. O.= 0.055*P )mm(.P= precipitation (mm)
• Arnon 1972 R. O.= 0.6*P*S )mm(.
S=Slop• Runoff Coefficient Method
V=103C.P.A )m3(.C=Runoff Coefficient
• Flood EstimationQ=C.I.A/3.6 )m3/s(.I=Rainfall Intensity (mm/hr)
• SCS Curve Number MethodF/S = Q/PeF=Actual water retention (Pe-Q)
S=Potential Maximum RetentionQ=Actual Runoff
• Pe=Potential runoff
Flow measurementsFlow measurements
Flow measurementsFlow measurements
Flow measurementsFlow measurementscurrent meterscurrent meters
Current metersCurrent meters
