1. Runoff Generation and Routing in the TOPMODEL
Venkatesh Merwade

2. Recap R E Overland Flow Gravity Zone Saturated Zone P Root Zone
Soil Moisture Deficit

3. Key Points
Zi (The distance between the land surface and the groundwater table)
Topographic Index
Drainage Area (Contributing area)

4. Topographic Index What is Topographic Index ? Index Curve
x = ln(a/tanb)
a = A/(nL)
Index Curve
It defines the percentage of the total drainage area that contributes to the surface runoff.

5. Index Curve
Area
Ln(a/tanb)

6. Run off Generation Contributing Area Still No Runoff! Ground SurfaceZi
Water Table Z
To Outlet Channel
Datum

7. Runoff Generation Cont’d

8. Routing The transfer component is divided into two phase
Overland flow within the contributing area which is routed at a velocity proportional to the local gradient with overland flow velocity constant.
Flow to the outlet

9. Channel (Linear Routing)
Routing cont’d
The saturation excess and the overland flow is routed through a routing model to get the resulting run-off.
Saturation excess and Overland flow
Channel (Linear Routing)
Runoff