surface water flux

[smultsch]

Hello,

I am interested in balancing surface water runoff for a single cell. For this, I have prepared a brief example consisting of only one cell with a surface water storage and other storage which collects the water from the sw-storage. The input parameters are Manning's roughness coefficient, the flowwidth and slope between storages. When comparing different parameter setups the impact of Manning's coefficient seems to be reasonable. But I wonder why the topographic slope has almost no impact on runoff generation. The slope needs to be greater than zero to have runoff, but then no further impact can be found.

As I understood CMF makes use of the St. Vernant equation, i.e. the root of the topographic gradient is divided by the Manning's roughness coefficient in the underlying equation. So, the impact of the slope might be very low on the resulting runoff. But is this feasible?

Cheers,
Sebastian

cmf_balance_surfacerunoff.zip

[Philipp Kraft]

The sample project uses hours as timestep to observe an effect happening in minutes.
Runoff R is the precipitation (P) that does not infiltrate (I) under steady state and therefore not in the first place a function of slope:

 R = P - I_akt

If P > I_pot = Ksat * A --> R = P - Ksat * A

The slope and roughness determine how much water is stored in the surface storage to gain steady state conditions. Please avoid to attach .zip files, unless they refer to large and / or many files.

[smultsch]

Thanks for your comment. Just some notes:

• the example uses hours as time step, that's true. The storage named by 'bucket' is used in the example to collect all water from runoff in order to balance the runoff over the time step. It is not important when the runoff event does take place (at the beginning or end of the hour), because all water will finally reach the 'bucket' storage at the end of the time step. could you confirm that this a solution to balance the runoff of a single field?
• maybe add your explanation to the surface water tutorial, because the topics surface runoff and infiltration are closely related.
• I used a .zip-file because I was prevented by GitHub to upload the sole .py-file.