A KARST HYDROLOGIC INVESTIGATION OF THE NORTH RIVER AND ITS TRIBUTARIES, SHENANDOAH VALLEY, VIRGINIA

Within the Valley and Ridge Province of Virginia there are numerous sinking, or dry streams, and springs as a result of karst development. This research has examined examples of these karst features on the North River of the Shenandoah Valley, Virginia, and its tributaries, Briery Branch and Dry River, which are all ephemeral in nature. Field and lab methods have been used to investigate the extent to which structural geology, karst development, water chemistry, and deposition of sediment have influenced both surface and groundwater flow.

Physical evidence of karst geology exists throughout the alluvial plain and the Valley as evidenced by numerous springs, sinkholes, and three major ephemeral streams in the areas underlain by carbonates. The three ephemeral streams are braided river systems that have deposited approximately 20-30 feet of siliclastic dominated alluvium on top of carbonate bedrock. Chemical analysis of waters in the area shows that recharge is originating in the mountains to the west where acidic and chemically aggressive, juvenile waters are undersaturated with respect to the carbonates in the Valley. Waters typically become more basic, mature, and saturated with respect to carbonate as it flows into the Valley to the east.

Despite the seasonal disappearance of water within the ephemeral stream channels, hydrologic connection has been established between them and several springs in the study area through dye trace studies. Additionally, a resistivity survey suggests a possible water layer 15-30 feet below the surface of the North River during a period of no flow in the stream channel. Due to the seasonal loss of foliage these ephemeral streams begin to flow in late fall.

We continue to develop a conceptual model based on this data that links both the surface and subsurface hydrology of these three ephemeral streams. These findings are useful for understanding the origins and fate of both surface- and ground-water, especially as it pertains to land use, planning, and potential environmental impacts.