Large Contributing Area Model
The standard (Wallingford) runoff routing model in InfoWorks ICM was designed to be used with small sub-catchments (up to 1ha). A new runoff routing model has been developed to model runoff from large contributing areas (up to 100ha).
The modified runoff routing model takes into account the flow characteristics of the catchment and represents them using one pipe. This pipe matches the discharge hydrographs from catchments in detailed models, where each node has its own subcatchment that provides flow to the system.
To give an accurate match of flow characteristics, the modified runoff routing model contains two elements that delay and attenuate the peak discharge from the single pipes. The two elements are:
- Routing coefficient multiplier
- Runoff time shift
These are applied to the standard (DLR/Wallingford model) routing coefficient and output, respectively.
The routing coefficient multiplier is derived from the following equation:
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where K: routing factor multiplier A: subcatchment area in m2 s: slope in m/m (set to a minimum of 0.002 within the software) L: length in m ck, k1, k2 and k3 are equation coefficients. The default values are: ck = 0.030 k1 = -0.022 k2 = -0.228 k3 = 0.460 
Note
If K is less than 1.0, the multiplier is not applied to the routing factor. |
The runoff time shift is derived from the following equation:
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where T: runoff lag in s A: catchment area in m2 s: slope in m/m (set to a minimum of 0.002 within the software) L: length in m ct, t1, t2 and t3 are equation coefficients. The default values are: ct = 4.334 t1 = 0.009 t2 = -0.173 t3 = 0.462 |
The lag is rounded to the nearest major (run) timestep.
