SYNTHETIC UNIT HYDROGRAPH METHOD
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CATCHMENT CHARACTERISTICS
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Catchment area, A                 = 26.900 km²
Longest watercourse, L            = 6.690 km
Distance to catchment centroid    = 3.350 km
Veld-type zone                    = 8 — Bushveld

UNIT HYDROGRAPH PARAMETERS
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Average stream slope, S           = 0.021724 m/m
Catchment index, Ic               = 152.055
Lag coefficient, Ct               = 0.432
Basin lag, TL                     = 1.163 h
Coefficient, Ku                   = 0.367
One-millimetre one-hour UH peak   = 8.487 m³/s/mm

DESIGN RAINFALL SOURCE
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Extraction method: 3. Area-weighted grid rainfall
Catchment file: Catchment.gpkg
Contributing grid cells: 18
Average MAP: 724.7 mm

CRITICAL-DURATION RESULTS
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Return     Duration    Point rain   Intensity    ARF       Average rain  Runoff     Effective    UH peak      Peak flow    
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1:2        15 min      17.4         69.48        93.4%     16.23         7.3%       1.18         28.23        33.42        
1:5        15 min      24.0         95.92        90.9%     21.80         8.9%       1.95         28.23        54.97        
1:10       15 min      29.0         115.98       89.0%     25.81         10.0%      2.57         28.23        72.60        
1:20       15 min      34.3         137.27       87.0%     29.86         10.9%      3.26         28.23        92.06        
1:25       15 min      36.2         144.83       86.3%     31.24         11.2%      3.51         28.23        99.08        
1:50       15 min      42.1         168.32       84.1%     35.37         12.1%      4.29         28.23        121.09       
1:100      20 min      54.2         162.49       84.6%     45.83         14.2%      6.50         22.52        146.38       
1:200      20 min      62.2         186.46       82.3%     51.18         15.2%      7.76         22.52        174.64       

CALCULATION PROCEDURE
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1. Point rainfall was logarithmically interpolated by storm duration.
2. Point intensity was calculated as point rainfall divided by duration.
3. The Rational Method 1 area-reduction-factor engine was applied.
4. Average catchment rainfall was calculated from point rainfall and ARF.
5. Flood runoff percentage was interpolated from the published rural expected-runoff relationship.
6. Effective rainfall was calculated as average rainfall multiplied by runoff percentage.
7. The one-hour regional hydrograph was dimensionalised using TL and Qp.
8. An S-curve was compiled at five-minute intervals.
9. The S-curve was lagged by each trial duration, subtracted and scaled by 1/D.
10. The duration UH peak was multiplied by effective rainfall.
11. The maximum value for each return period was selected as the design flood peak.

Software: GHI HydroSuite Version 4.0D5
Engineering Reference Library: Version 2.0.0
Method: Synthetic Unit Hydrograph Method
Date analysed: 

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