Application of a two-dimensional model to calculate water balance of an agricultural hillslope

The objective was to simulate runoff production on an agricultural hillslope in Southern Finland. Water balance was calculated using a quasi-two-dimensional model describing vertical soil moisture distribution and horizontal water movement along a hillslope strip. The model accounted for the production of saturated overland flow on the exfiltration part of the hillslope. The model results were assessed against measurements of surface runoff, subsurface drainage flow, and water table level, which were available at individual field sections for years 199-96. Intensive runoff events during summer and autumn rainfalls were the primary focus in the modeling application. The model performed well during wet periods when water table remained close to the soil surface, but the results were less satisfactory during dry periods.

The objective of this study was to model the hydrological response of a cultivated hillslope of heavy clay to summer and autumn rainfalls. At the study site, a fastly increasing subdrain flow after a rainfall event indicated that preferential flow paths existed down to drain depth. Cracks and macropores in the surface layers of the soil were observed especially after a dry period. The macropore flow was modeled by assuming three mechanisms that enhance a fast ground water table response to rainfall: The soil moisture profile in the unsaturated zone was assumed to reach immediate steady state during one time step. The maximum infiltration capacity at the soil surface was taken as the air volume in the unsaturated soil. The subsurface drainage flow was calculated through the soil domain and the macropores.