Development of Integrated Surface-Subsurface Flow Model Considering Evapotranspiration and its Application to Small Forest Catchment

Wednesday, 26 July 2017: 11:15 AM
Paul Brest West (Munger Conference Center)
Kazuaki Yorozu, Aulia Febianda Anwar Tinumbang, Yutaka Ichikawa, Yasuto Tachikawa and Sunmin Kim, Kyoto University, Civil and Earth Resources Engineering, Kyoto, Japan
In this study, we developed a three dimentional physically-based surface-subsurface flow model considering evapotranspiration. Developing such model is important to predict hydrologic processes on the land. We applied the developed model to 3 slopes in small forest catchment in Japan as a testing place by utilizing the observed data at the site, and we compared the simulated result with the observed value of volumetric water content of soil.

We combined two models of surface-subsurface flow model and evapotranspiration model. The surface-subsurface flow model was developed by An and Yu (2014). For subsurface flow component, Richards equation is used as governing equation, while Saint Venant Equation is utilized for surface flow component. Both combined systems employed backward Euler time discretization and Newton iteration. As for evapotranspiration model, we adapted the governing equation used in Simple Biosphere Model.

Teseted forest catchment is located in Koga City, Shiga Prefecture in Japan, with total area about 24.6 hectare. In our testing site, an observation tower with height about 45 meter was installed to monitor some meteorological phenomena such as rainfall amount, temperature, ground surface temperature, humidity, solar radiation amount, wind speed and so on. Those observed data were utilized for input data of our model. We used sandy loam soil type in all soil layers for two weeks simulation.In this simulation, 1 m holizontal spatial interval and 20cm vertical interval are utilized, respectively.

We compared the calculated result to the observed value of soil moisture content from 7 observation points located at 3 slopes in the forest. Three of the results from each slope were shown in the figure. In figure (a), which showed the result of slope A in point 2, we can see quite big gap between our calculated result and observed data. However, during the rainfall event, the calculated water content was responded as the observed value was. Figure (b) showed the result of point 4. Our calculated result obtained excellent result which was similar to the observed value. In figure C for point 6, we can see good comparison for simulated result and observed value especially in the initial period. One of the reasons of the gap between our result and observation is assumed to set inappropriate soil parameters.