Summary Sheet
Flow rates (m^3/2)
Estimation Method
10
Rational Method 1 - Use depth-duration frequiency diagram for point rainfall
Rational Method 2 - Use Modified Hershfield & TR102 for point rainfall
Rational Method 3 - Use design rainfall software for point rainfall
Standard Design Flood Method - Probabilistic
SCS-SA Method
Emperical: Midgley & Pitman
Unit Hydrograph Method
Flood Frequiency Analysis - Statistical Method
RMF - Flood Envelopes Method (Kovacs)
,20 50 100
, Rational Method 1 - Use depth-duration frequiency diagram
Description of catchment
River detail
Calculated by
Physical characteristics
Size of catchment A
4.72 km^2
Longest watercourse (L) 1.25 km
Average Slope (Sav) 0.000666667 m/m
Dolomite area (D%) 0 %
Mean annual precipitation (MAP) 900 mm
Run-off coefficient:
C
Rural
Surface slope % Factor Cs
Vleis and pans 20 0.05 0.01
Flat areas 80 0.11 0.088
Hilly 0 0.20 0
Steep areas 0 0.30 0
Total 100 0.098
Permeability % Factor CP
Very permeable 20 0.05 0.01
Permeable 40 0.10 0.04
Semi-permeable 20 0.20 0.04
Impermeable 20 0.30 0.06
Total 100 0.15
Vegetation % Factor CV
Thich bush and plantation 0 0.05 0
Light bush and farm-lands 40 0.15 0.06
Grass lands 50 0.25 0.125
No vegetation 10 0.30 0.03
Total 100 0.215
Return period (years), T 2 5 10
Run-off coefficient, C1 (C1 = Cs
+ Cp + Cv) 0.463 0.463 0.463
Adjusted for dolomite areas, C 1D (=
C1(1 - D%)+C1D%(∑(Dfactor x CS%)) 0.463 0.463 0.463
0.50 0.55 0.60
Adjustment factor for intial saturation, F t
Adjusted run-off coefficient, C 1T
( = C1D x Ft) 0.2315 0.25465 0.2778
Combined run-off coefficient CT (=
αC1T + βC2 + ϒC3) 0.4529 0.455215 0.45753
, Time of concentration (TC)
Overland flow Defined watercourse
𝑇𝑐=0.604(𝑟𝐿/ 𝑇𝑐=((0.87𝐿^2)/
√(𝑆_𝑎𝑣 ))^0.467 (1000𝑆_𝑎𝑣 ))^0.38
5
2.1073023411289 hours 1.315620879 hours
Rainfall
I
Return period (years), T 2 5 10
Point rainfall (mm) PT 20 40 60
Point intensity (mm/hour), PiT(= PT/TC) 15.2 30.4 45.6
Area reduction factor (%), ARF T 100 100 100
Average intensity (mm/hour), IT (=
PiT x ARFT) 15.2 30.4 45.6
Return period (years), T 2.0 5.0 10.0
Peak flow (m^3/s), 9.0 18.1 27.4
𝑸_𝑻 =(𝑪_𝑻 𝑰_𝑻 𝑨)/(𝟑.𝟔)
Flow rates (m^3/2)
Estimation Method
10
Rational Method 1 - Use depth-duration frequiency diagram for point rainfall
Rational Method 2 - Use Modified Hershfield & TR102 for point rainfall
Rational Method 3 - Use design rainfall software for point rainfall
Standard Design Flood Method - Probabilistic
SCS-SA Method
Emperical: Midgley & Pitman
Unit Hydrograph Method
Flood Frequiency Analysis - Statistical Method
RMF - Flood Envelopes Method (Kovacs)
,20 50 100
, Rational Method 1 - Use depth-duration frequiency diagram
Description of catchment
River detail
Calculated by
Physical characteristics
Size of catchment A
4.72 km^2
Longest watercourse (L) 1.25 km
Average Slope (Sav) 0.000666667 m/m
Dolomite area (D%) 0 %
Mean annual precipitation (MAP) 900 mm
Run-off coefficient:
C
Rural
Surface slope % Factor Cs
Vleis and pans 20 0.05 0.01
Flat areas 80 0.11 0.088
Hilly 0 0.20 0
Steep areas 0 0.30 0
Total 100 0.098
Permeability % Factor CP
Very permeable 20 0.05 0.01
Permeable 40 0.10 0.04
Semi-permeable 20 0.20 0.04
Impermeable 20 0.30 0.06
Total 100 0.15
Vegetation % Factor CV
Thich bush and plantation 0 0.05 0
Light bush and farm-lands 40 0.15 0.06
Grass lands 50 0.25 0.125
No vegetation 10 0.30 0.03
Total 100 0.215
Return period (years), T 2 5 10
Run-off coefficient, C1 (C1 = Cs
+ Cp + Cv) 0.463 0.463 0.463
Adjusted for dolomite areas, C 1D (=
C1(1 - D%)+C1D%(∑(Dfactor x CS%)) 0.463 0.463 0.463
0.50 0.55 0.60
Adjustment factor for intial saturation, F t
Adjusted run-off coefficient, C 1T
( = C1D x Ft) 0.2315 0.25465 0.2778
Combined run-off coefficient CT (=
αC1T + βC2 + ϒC3) 0.4529 0.455215 0.45753
, Time of concentration (TC)
Overland flow Defined watercourse
𝑇𝑐=0.604(𝑟𝐿/ 𝑇𝑐=((0.87𝐿^2)/
√(𝑆_𝑎𝑣 ))^0.467 (1000𝑆_𝑎𝑣 ))^0.38
5
2.1073023411289 hours 1.315620879 hours
Rainfall
I
Return period (years), T 2 5 10
Point rainfall (mm) PT 20 40 60
Point intensity (mm/hour), PiT(= PT/TC) 15.2 30.4 45.6
Area reduction factor (%), ARF T 100 100 100
Average intensity (mm/hour), IT (=
PiT x ARFT) 15.2 30.4 45.6
Return period (years), T 2.0 5.0 10.0
Peak flow (m^3/s), 9.0 18.1 27.4
𝑸_𝑻 =(𝑪_𝑻 𝑰_𝑻 𝑨)/(𝟑.𝟔)
