STANDARD DESIGN FLOOD METHOD
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PROJECT INFORMATION
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Project name                 = Floods estimation example
Project number               = 2026-001
Client                       = City of Tshwane
Designer                     = Marco van Dijk
Date                         = 2026-09-16
Description of catchment     = Moretele Spruit Catchment
River / stream               = Moretele Spruit
Latitude                     = -25.80
Longitude                    = 28.30
Project notes                = Example flood estimation project for a culvert upgrade

CATCHMENT CHARACTERISTICS
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Catchment area               = 26.900 km²
Longest watercourse          = 6.690 km
Height difference (10–85)    = 109.000 m
Average slope                = 0.02172 m/m
Time of concentration        = 1.25 h (75.1 min)
SDF drainage basin           = 1

REPRESENTATIVE BASIN AND RAINFALL DATA
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SAWS station                 = 546204 - STRUAN
Coordinates                  = 25°24’ & 26°07’
Mean annual daily maximum M  = 56.0 mm
Days of thunder per year R   = 30.0 days/year
Basin MAP                    = 550.0 mm
Basin MAE                    = 1800.0 mm
Basin evaporation index MAE/MAP = 3.27
Area reduction factor        = 96.01 %

DESIGN RAINFALL (mm)
Duration            1:2        1:5       1:10       1:20      1:25*       1:50      1:100      1:200
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0.25 h             15.0       25.3       33.2       41.0       43.5       51.3       59.1       66.9
0.5 h              19.6       33.0       43.1       53.3       56.6       66.7       76.9       87.1
1 h                24.1       40.6       53.1       65.7       69.7       82.2       94.7      107.2
2 h                28.6       48.3       63.1       78.0       82.8       97.6      112.5      127.4
4 h                33.1       55.9       73.1       90.3       95.9      113.1      130.3      147.5
1 day              56.0       80.0       99.0      119.0      126.5      150.0      177.0      206.0
2 day              71.0      105.0      132.0      161.0      171.7      205.0      243.0      286.0
3 day              80.0      117.0      146.0      177.0      188.4      224.0      263.0      308.0
7 day             102.0      154.0      196.0      242.0      258.6      310.0      369.0      435.0

Calibrated runoff coefficient C2   = 10 %
Calibrated runoff coefficient C100 = 40 %

STANDARD DESIGN FLOOD RESULTS
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Return             Point      ARF      Catchment      Average        Runoff         Peak
period     precipitation           precipitation    intensity   coefficient         flow
(years)             (mm)      (%)           (mm)       (mm/h)           (%)       (m³/s)
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1:2                 25.5     96.0           24.5         19.6          10.0         14.7
1:5                 43.1     96.0           41.4         33.1          20.8           51
1:10                56.4     96.0           54.1         43.2          26.5           86
1:20                69.7     96.0           66.9         53.4          31.1          124
1:25                73.9     96.0           71.0         56.7          32.4          137
1:50                87.2     96.0           83.7         66.9          36.4          182
1:100              100.5     96.0           96.5         77.1          40.0          231
1:200              113.8     96.0          109.2         87.2          43.2          282

Rainfall calculation method = Modified Hershfield equation
