SCS-SA METHOD

CATCHMENT AND RESPONSE
================================================================================================================
Catchment area: 26.900 km²
Longest watercourse: 6.690 km
Height difference along 10–85 slope: 109.000 m
Average stream slope: 0.021724 m/m
Time of concentration: 1.252 h
Lag estimation method: Time of Concentration
Catchment lag: 0.751 h
Initial abstraction: Ia = 0.10S
Area Reduction Factor method: Alexander Area Reduction Factor

HRU PARAMETERS
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HRU 1: Area 30.00% | Soil B/C | Urban/Suburban Land Uses | 7 = Residential: lot size 1350 m² - 30% impervious | Not applicable | CN 77.0 | S 75.9 mm | Ia 7.6 mm
HRU 2: Area 30.00% | Soil B/C | Urban/Suburban Land Uses | 8 = Residential: lot size 2000 m² - 25% impervious | Not applicable | CN 76.0 | S 80.2 mm | Ia 8.0 mm
HRU 3: Area 20.00% | Soil A | Veld (range) and Pasture | 2 = Veld/pasture in fair condition | Moderate | CN 49.0 | S 264.4 mm | Ia 26.4 mm
HRU 4: Area 20.00% | Soil B/C | Veld (range) and Pasture | 2 = Veld/pasture in fair condition | Moderate | CN 75.0 | S 84.7 mm | Ia 8.5 mm

RETURN PERIOD 1:2
----------------------------------------------------------------------------------------------------------------
Point one-day rainfall: 58.66 mm
Area reduction factor: 96.01% (Alexander ARF — Rational Method 2 procedure)
Catchment one-day rainfall: 56.32 mm

HRU   Area (%)   CN       S (mm)   Ia (mm)   Stormflow (mm)   Weighted contribution (mm)
----------------------------------------------------------------------------------------------------------------
1        30.00     77.0       75.9       7.6            19.06                        5.72
2        30.00     76.0       80.2       8.0            18.15                        5.45
3        20.00     49.0      264.4      26.4             3.04                        0.61
4        20.00     75.0       84.7       8.5            17.28                        3.46
Area-weighted stormflow depth: 15.23 mm
Runoff volume: 409,640 m³
Lag: 0.751 h
Time to peak: 0.826 h
Peak discharge: 62.08 m³/s

RETURN PERIOD 1:5
----------------------------------------------------------------------------------------------------------------
Point one-day rainfall: 80.99 mm
Area reduction factor: 96.01% (Alexander ARF — Rational Method 2 procedure)
Catchment one-day rainfall: 77.76 mm

HRU   Area (%)   CN       S (mm)   Ia (mm)   Stormflow (mm)   Weighted contribution (mm)
----------------------------------------------------------------------------------------------------------------
1        30.00     77.0       75.9       7.6            33.71                       10.11
2        30.00     76.0       80.2       8.0            32.43                        9.73
3        20.00     49.0      264.4      26.4             8.34                        1.67
4        20.00     75.0       84.7       8.5            31.18                        6.24
Area-weighted stormflow depth: 27.75 mm
Runoff volume: 746,449 m³
Lag: 0.751 h
Time to peak: 0.826 h
Peak discharge: 113.11 m³/s

RETURN PERIOD 1:10
----------------------------------------------------------------------------------------------------------------
Point one-day rainfall: 97.93 mm
Area reduction factor: 96.01% (Alexander ARF — Rational Method 2 procedure)
Catchment one-day rainfall: 94.02 mm

HRU   Area (%)   CN       S (mm)   Ia (mm)   Stormflow (mm)   Weighted contribution (mm)
----------------------------------------------------------------------------------------------------------------
1        30.00     77.0       75.9       7.6            46.03                       13.81
2        30.00     76.0       80.2       8.0            44.49                       13.35
3        20.00     49.0      264.4      26.4            13.76                        2.75
4        20.00     75.0       84.7       8.5            43.00                        8.60
Area-weighted stormflow depth: 38.51 mm
Runoff volume: 1,035,853 m³
Lag: 0.751 h
Time to peak: 0.826 h
Peak discharge: 156.97 m³/s

RETURN PERIOD 1:20
----------------------------------------------------------------------------------------------------------------
Point one-day rainfall: 115.90 mm
Area reduction factor: 96.01% (Alexander ARF — Rational Method 2 procedure)
Catchment one-day rainfall: 111.28 mm

HRU   Area (%)   CN       S (mm)   Ia (mm)   Stormflow (mm)   Weighted contribution (mm)
----------------------------------------------------------------------------------------------------------------
1        30.00     77.0       75.9       7.6            59.88                       17.96
2        30.00     76.0       80.2       8.0            58.11                       17.43
3        20.00     49.0      264.4      26.4            20.61                        4.12
4        20.00     75.0       84.7       8.5            56.38                       11.28
Area-weighted stormflow depth: 50.79 mm
Runoff volume: 1,366,366 m³
Lag: 0.751 h
Time to peak: 0.826 h
Peak discharge: 207.05 m³/s

RETURN PERIOD 1:25
----------------------------------------------------------------------------------------------------------------
Point one-day rainfall: 122.29 mm
Area reduction factor: 96.01% (Alexander ARF — Rational Method 2 procedure)
Catchment one-day rainfall: 117.41 mm

HRU   Area (%)   CN       S (mm)   Ia (mm)   Stormflow (mm)   Weighted contribution (mm)
----------------------------------------------------------------------------------------------------------------
1        30.00     77.0       75.9       7.6            64.95                       19.48
2        30.00     76.0       80.2       8.0            63.11                       18.93
3        20.00     49.0      264.4      26.4            23.29                        4.66
4        20.00     75.0       84.7       8.5            61.30                       12.26
Area-weighted stormflow depth: 55.33 mm
Runoff volume: 1,488,481 m³
Lag: 0.751 h
Time to peak: 0.826 h
Peak discharge: 225.56 m³/s

RETURN PERIOD 1:50
----------------------------------------------------------------------------------------------------------------
Point one-day rainfall: 142.12 mm
Area reduction factor: 96.01% (Alexander ARF — Rational Method 2 procedure)
Catchment one-day rainfall: 136.45 mm

HRU   Area (%)   CN       S (mm)   Ia (mm)   Stormflow (mm)   Weighted contribution (mm)
----------------------------------------------------------------------------------------------------------------
1        30.00     77.0       75.9       7.6            81.11                       24.33
2        30.00     76.0       80.2       8.0            79.05                       23.72
3        20.00     49.0      264.4      26.4            32.33                        6.47
4        20.00     75.0       84.7       8.5            77.02                       15.40
Area-weighted stormflow depth: 69.92 mm
Runoff volume: 1,880,768 m³
Lag: 0.751 h
Time to peak: 0.826 h
Peak discharge: 285.00 m³/s

RETURN PERIOD 1:100
----------------------------------------------------------------------------------------------------------------
Point one-day rainfall: 164.12 mm
Area reduction factor: 96.01% (Alexander ARF — Rational Method 2 procedure)
Catchment one-day rainfall: 157.57 mm

HRU   Area (%)   CN       S (mm)   Ia (mm)   Stormflow (mm)   Weighted contribution (mm)
----------------------------------------------------------------------------------------------------------------
1        30.00     77.0       75.9       7.6            99.60                       29.88
2        30.00     76.0       80.2       8.0            97.34                       29.20
3        20.00     49.0      264.4      26.4            43.48                        8.70
4        20.00     75.0       84.7       8.5            95.10                       19.02
Area-weighted stormflow depth: 86.80 mm
Runoff volume: 2,334,807 m³
Lag: 0.751 h
Time to peak: 0.826 h
Peak discharge: 353.81 m³/s

RETURN PERIOD 1:200
----------------------------------------------------------------------------------------------------------------
Point one-day rainfall: 188.32 mm
Area reduction factor: 96.01% (Alexander ARF — Rational Method 2 procedure)
Catchment one-day rainfall: 180.81 mm

HRU   Area (%)   CN       S (mm)   Ia (mm)   Stormflow (mm)   Weighted contribution (mm)
----------------------------------------------------------------------------------------------------------------
1        30.00     77.0       75.9       7.6           120.46                       36.14
2        30.00     76.0       80.2       8.0           118.01                       35.40
3        20.00     49.0      264.4      26.4            56.91                       11.38
4        20.00     75.0       84.7       8.5           115.57                       23.11
Area-weighted stormflow depth: 106.03 mm
Runoff volume: 2,852,319 m³
Lag: 0.751 h
Time to peak: 0.826 h
Peak discharge: 432.23 m³/s

IDENTIFICATION
----------------------------------------------------------------------------------------------------------------
Software: GHI HydroSuite Version 1.1
Engineering Reference Library: Version 2.2.0
Method: SCS-SA Method
Date analysed: 2026-09-16 13:58:30

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Copyright © 2026 Green Hippo Innovations. All rights reserved.
Copyright © 2026 Green Hippo Innovations. All rights reserved.