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Contributions of riparian and hillslope waters to storm runoff across multiple catchments and storm events in a glaciated forested watershed

Inamdar, Shreeram P., Mitchell, Myron J.
Journal of hydrology 2007 v.341 no.1-2 pp. 116-130
forested watersheds, forest hydrology, watershed hydrology, hills, runoff, storms, stormwater, groundwater flow, springs (water), base flow, New York
The contributions of hillslope and riparian sources of runoff to streamflow were determined for four catchments (1.6-696 ha) in the Point Peter Brook watershed, a glaciated, forested, watershed in Western New York, USA. Investigations were performed for 10 storm events of varying size, intensity, and antecedent moisture conditions. Hydrometric, geochemical, and landscape analysis procedures were used to characterize the sources of runoff and the influence of topography on hydrologic response. Using end member mixing analysis (EMMA), throughfall, groundwater discharged at hillslope seeps, and valley-bottom riparian water were identified as the controlling end-members for storm-event runoff. Contribution from seep groundwater was highest during baseflow, contributions from throughfall increased through the rising limb of the hydrograph, while riparian water amounts were highest at or after the peak in discharge. The delayed response of riparian water was attributed to displacement by hillslope interflow. The relative contributions of the end-members varied with catchment size and storm event conditions. Riparian water contributions were greater at the large catchment size (696 ha) while seep groundwater was important for the small headwater catchments. Steep hillslope gradients and moist valley-bottoms allowed for a greater expression of hillslope seep water in runoff during baseflow conditions. Percent contributions of riparian water to streamflow were higher for larger storm events while small events and wet antecedent conditions increased the expression of seep groundwater. This study underscored the need for three-dimensional or volume-based assessments to characterize the contributions of valley-bottom riparian and wetland areas to streamflow.