Influence of Saturated Wedge Hydrodynamics on Hillslope-Stream Connectivity

Publication Date

12-2006

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Hydrologic Sciences

Department

Geosciences

Supervisory Committee Chair

James P. McNamara

Abstract

More and more research is being conducted to investigate the water flowpaths in a watershed from the time water falls as precipitation to the time it becomes streamflow. Understanding the flow of water in the subsurface is a prerequisite to understanding the quality and quantity of water in streams because subsurface pathways define the earth materials that waters will come in contact with, and these pathways set transit times, which dictate the time available for chemical reactions (Anderson et al., 1997). Recent research has identified the need to combine hydrometric and chemical (tracer) studies to advance the understanding of watershed flow mechanisms (Freer et al., 2002, Joerin et al., 2005, and McDonnell et al., 1999).

The research presented provides actual hydrometric and artificial tracer data to test the "hydrological connectivity" hypothesis proposed by McNamara et al. (2005). This goal was achieved by addressing two main objectives: 1) testing the growth of the saturation wedge in and around the near-stream zone, and 2) testing if, and when, the hillslope becomes hydrologically connected to the stream. These objectives were accomplished by analyzing hydrometric and geochemical field data to describe the vertical and lateral flow evolution on the hillslopes and the crucial role that the saturated wedge plays in connecting the hillslopes to the stream.

Hydrometric and geochemical data provide evidence of the hillslope connection to the stream via the saturated wedge. The connectivity of the hillslope to the stream is hinged on the soils reaching their specific retention moisture content during the wet spring high flux period. Once the specific retention is satisfied, lateral flow in the shallow soils commences, followed by deep soil-bedrock interface flow. Solute recharge in the stream is primarily due to bedrock flow and the saturated wedge development in the near-stream environment. The saturated wedge lateral extent is further extenuated by the presence of clay lenses in the hillslopes. Finally, data presented in this work indicates stream water and solute loss in the middle and lower portions of the watershed to the underlying fractured granite bedrock.

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