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SHC 410: Design Flood Estimation Excel Sheet

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Course
SHC 410 - Hydraulics (SHC410)

Institution
University Of Pretoria (UP)

This Excel file contains some of the more important design flood estimation methods used in South Africa in excel format. The formulas have already been entered but please be sure to check each formula as the conditions might change. These design flood estimation methods are based on the Drainage M...

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Uploaded on May 30, 2021
Number of pages 88
Written in 2020/2021
Type Other
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shc410
shc 410
410
shc
hydraulic
hydraulics
design flood estimation
flood
engineering
civil
tuks
water
rain
flood
up

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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)

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