Hi everyone,

I’m a civil engineering student calibrating a WEAP model for a South African catchment (Zwartkopjes gauge, 2013 data).

I recently switched to the Soil Moisture Method, but my modeled flow has crashed to near zero, resulting in a PBIAS of -85% and NSE of -0.16. The observed flow is ~7 to 14 CMS, but the model is producing almost nothing.

Parameters already adjusted:

RRF: 0.5

Preferred Flow Direction: 0.8

Soil Water Capacity: 300

Total Catchment Area: 15,000 ha

Questions:

Is a catchment area of 15,000 ha too small to generate ~10 CMS flow?

Why did the model volume drop to zero after switching from the Simplified Method to Soil Moisture?

What is the best parameter to adjust to fix this massive underestimation?

Any advice would be greatly appreciated. Thank you!

Hello Mulinda,

I would first recommend to check your Soil Moisture results of your catchment. If the soil moisture results stay at or near 0% or shift suddenly, then you will have to adjust your calibration. You want smooth soil moisture levels that do not stay right near 0% nor 100%. See the Calibration chapter in the WEAP Tutorial, where it contains a guide on how to adjust your parameters if you flow is too low: https://www.weap21.org/Tutorial/

-Doug