I'm attempting to model a small basin (~0.2 sq mi) using a long-term simulation. I can get the model to run without errors or warnings, but some of the model results are counter-intuitive. So I'd like to verify if I've set up my model correctly and throw out a couple concerns/questions that some of you might be able to help me out with.
Some quick background about my model setup: I'm using a single rain gauge located very near the basin boundary, defined using a .gag file with hourly data for the duration of November 2009. I've compiled WES format hydrometeorological data file that also gives hourly data for November 2009. My HMET file includes no radiation data, so I'm relying on the GSSHA calculated radiation from lat/lon/time&date. Active modules are as follows: Overland flow computed by ADE with Interception; Evapotranspiration via Penman method; Infiltration via G & A with Redistribution (Soil moisture depth = 1.0 m, Top layer depth = 1.0 m); Channel routing via Diffusive wave.
My primary concern with the results is the lack of evapotranspiration calculated by the simulation. Out of ~100,000 m^3 of precipitation during the simulation period, only ~100 m^3 are evaporated. (Roughly 20% of the precip is intercepted and the other 79.9% infiltrates.) 0.1% evapotranspiration seems alarmingly low, even for a very wet month with consistent cloud cover in the Pacific Northwest. I've tried manipulating all of the parameters that feed into the Penman ET calcs (including cloud cover and wind speeds in my HMET file), and I can only increase ET by about 50 m^3. Has anyone else had such a problem? Or can anyone think of a reason that ET would be so seemingly underrepresented?
Secondarily, I'm not sure if I've understood the GAR layer depth parameters. I've read the Downer paper which explains the GAR (http://www.dtic.mil/get-tr-doc/pdf?AD=ADA473824) but still am unsure about the physical meaning of "Soil moisture depth" and "Top layer depth". Can someone clear this up?
Ultimately, my basin of interest has approx. 1 m of silty loam resting atop an impermeable siltstone bedrock. A perched water table develops above the siltstone during the rainy season and it would be nice to recreate that with the model, but until now I've been unsuccessful with any of the Infiltration options. Could I model such a configuration with Richards Eq. or multi-layer G&A?
Thanks in advance to anyone who reads! Hope it's all clear