CHARACTERIZING HYPORHEIC EXTENT USING ELECTRICAL RESISTIVITY AND CONCENTRATION BREAKTHROUGH CURVES

Stream-water systems provide complexity and diversity to ecosystems. Logjam-dense reaches of a stream have been shown to increase stream complexity, therefore, increasing biodiversity potential. The flow of water through slower-moving segments of a stream increases potential for nutrient exchange and pollutant transformation. Many of these processes occur in the hyporheic zone, an area of saturated porous media around streams which provides an interface for stream-water and groundwater interaction. Characterizing hyporheic exchange helps further understand the geochemical and geophysical processes that improve water quality. The goal of this research is to further understand and characterize activity in the hyporheic zone. Traditionally, methods to quantify hyporheic activity were cumbersome and insufficient. We utilized geophysical methods including electrical resistivity (ER), to observe subsurface flow, and in-stream electrical conductivity (EC) to monitor a tracer test. We then created breakthrough curves (BTC) which were used as a proxy for hyporheic and instream transport behavior in two complex reaches of Little Beaver Creek in northern Colorado. Within the ER BTC, asymmetry describes the skewness and the tailing behavior indicates solute retention, therefore, indicating hyporheic activity. The ER BTC displayed stronger tailing behavior than instream measurements which indicate that hyporheic behavior is related to longer residence times during solute transport. This study supplies data that demonstrates that ER methods coupled with tracer tests effectively characterize hyporheic activity in complex reaches of a stream, provides insight into stream systems, and can be used as a comparison with any modelling or research that involves remediation and/or sustainability efforts that are concerned with water quality.

Keywords: Hyporheic, water quality, electrical resistivity