Wallingford Runoff Routing Model
The overland routing transforms the net resulting rainfall for each sub-catchment into an inflow hydrograph at each node, using two notional linear reservoirs in a series to represent the storage which is available on the ground and in minor drains, and the delay induced between the peak rainfall and peak runoff. In this way, a reduced peak runoff is generated with a lag after the peak rainfall. The flow routing coefficient depends on the rainfall intensity, contributing area and slope. For these reasons overland flow in the Wallingford procedure models are modelled using reservoir-routing concepts. Initially a Non-linear reservoir (NLR) model was used; however a Double Linear Reservoir (Wallingford) Model has now superseded this.
The storage routing model is based on the use of a double quasi-linear reservoir model. Two reservoirs are applied in series for each surface type with an equivalent storage-output relationship for each reservoir. This relationship is given by:
|
|
where
where
where i10 - running ten minute average of rainfall intensity |
Combination of the two storage relationships with the continuity equation leads to a second-order ordinary differential equation of the form:
|
|
|
Sarginson and Nussey in fact first proposed this form of model for use in the UK.
For each of the small catchments described in Table 1 the value of C has been derived by optimisation. An overall relationship relating this value to catchment characteristics was then developed and included in the software; the final relationship is:
|
|
where S - slope (m/m) A - the area (m2) of the surface, for example the area of the paved surface |
Within the software limits are placed on the parameters as described below:
If (S<0.002), S = 0.002
If (A<1000), A = 1000
If (A>10000), A = 10000
| Subcatchment Name | Location | Events | Total Area to Gulley (m2) | |||
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | |||
|
Ennerdale Two |
Bracknell, UK |
15 |
118 |
358 |
90 |
|
|
Bishopdale |
Bracknell, UK |
11 |
167 |
591 |
|
|
|
Hyde Green North |
Stevenage, UK |
9 |
485 |
844 |
|
|
|
School Close |
Stevenage, UK |
13 |
459 |
717 |
|
|
|
Hawthorn Close |
Wallingford, UK |
11 |
215 |
145 |
176 |
206 |
|
Hyde Green North (78) |
Stevenage, UK |
12 |
1329 |
|
|
|
|
School Close (78) |
Stevenage, UK |
17 |
500 |
802 |
|
|
|
Twyford Gardens |
Nottingham, UK |
3 |
475 |
|
|
|
|
Lelystad Housing Area |
Lelystad, Netherlands |
10 |
20000 |
|
|
|
|
Lelystad Parking Lot |
Lelystad, Netherlands |
10 |
7000 |
|
|
|
|
Lund 1:75 |
Lund, Sweden |
11 |
291 |
|
|
|
|
Klostergarden 1:76 |
Lund, Sweden |
11 |
326 |
|
|
|
|
Klostergarden 1:77 |
Lund, Sweden |
13 |
335 |
|
|
|
|
Klostergarden 2:76 |
Lund, Sweden |
11 |
82 |
|
|
|
|
Klostergarden 2:77 |
Lund, Sweden |
12 |
78 |
|
|
|
|
Klostergarden 3:76 |
Lund, Sweden |
11 |
306 |
|
|
|
|
Klostergarden 3:77 |
Lund, Sweden |
13 |
413 |
|
|
|
|
Klostergarden 4:76 |
Lund, Sweden |
10 |
277 |
|
|
|
|
Klostergarden 4:77 |
Lund, Sweden |
13 |
279 |
|
|
|
|
Lab Catchment |
Imperial College, UK |
102 |
Various |
|
|
|
Table 1: Measurements of the inlet flows into the drainage system
