Modeling runoff dynamics from zero-order basins: implications for hydrological pathways

Although zero-order basins (geomorphic hollows) are important components of headwater catchments, their hydrologic regime has not been thoroughly investigated. A multi-tank model approach is used to simulate flow from zero-order basins in Hitachi Ohta Experimental Watershed, Japan, and simulations are compared with six months of wet season flows. A three-tank model accurately simulated runoff for the 6-month period from basin (FA) with two zero-order basins and deep soils, whereas a two-tank model performed satisfactorily in a zero-order basin with shallower soils (ZB). Characteristics of flow paths were evaluated and the concept of threshold response was assessed in simulations. In FA, preferential flow from the upper outlet of Tank 1 only occurred during the two largest storms; no overland flow was simulated. Less rapid subsurface flow emitted from the side outlet of Tank 2 during large and several moderate-size storms. During small storms, no overland, preferential, or subsurface flows occurred. Water depth in Tank 3, which indicates shallow groundwater storage in FA, is highly correlated with 30-day antecedent rainfall. The concept of threshold response is evidenced by intermittent quick and moderate flows from Tanks 1 and 2, respectively.