Abstract
In a headwater which has no or low-order perennial streams, groundwater has been considered to be a prominent contributor to the generation of overland flow during and after a storm rainfall. Previous hydrological studies have emphasized the importance of geological and geomorphological effects on stormflow generation in headwaters. However, the study of groundwater storage and runoff processes faces many unsolved problems: in particular, the mechanism of quick response of groundwater discharge to a rainfall has not been fully understood. The present study examined the storage function and subsurface water behavior in a layered hillslope during and after storm rainfalls.
It was observed that the water table in the coarse-grained and underlying layer of a layered hillslope rises locally in response to a rainfall, in a phenomenon called the “groundwater ridge”. An understanding of this storage function of the layered hillslope is an addition to our store of knowledge. After the formation of the groundwater ridge, the groundwater body expands into a fine grained and overlying layer with another storm rainfall. Under these conditions, the pore air trapped in the underlying layer by a surrounding groundwater body is compressed by successive rainfall and dispels the water in the groundwater ridge. The quick response of the groundwater discharge to a rainfall-that is, the overland flow generation in a layered hillslope-requires the needs hydrological conditions outlined above. The pre-event (stored) water plays an important role in the rainfall runoff process.
