Determining the hydraulic conductivity of river beds using slug test techniques

Protecting, remediating and restoring endangered fish habitat in the northern Rocky Mountains requires knowledge of how water in a stream channel and regional groundwater interface at the bed of gravel dominated rivers. Ground water and stream water interactions are important for nutrient levels and the temperature of fish spawning sites. Field methods to determine the overall transmission properties of spawning bed material often rely on grain size characterization and the use of in-channel slug tests and temperature techniques. Unfortunately, applying standard hydraulic slug tests to determine bed hydraulic conductivity is believed to yield poor representations of bed transmission properties. This work attempts to use a laboratory approach to testing the applicability of standard testing techniques as applied to small diameter piezometers often used in field studies. Lab tests used three different kinds of perforations in sand, gravel and water in a 68.5 cm tall and 25.1 cm radius barrel. Slugs of air with an air compressor were used and slugs of water were used in some tests as well. Water over the sediments in the sand and gravel barrels aimed to simulate a stream bed. Oscillatory responses that have been observed during testing have been noted in the literature. These responses need additional analyses to determine hydraulic conductivity, especially when derived from small diameter wells. Lab tanks containing a gravel of about 5 mm radius were used to examine how well diameter, well design, stream water depth and the magnitude of slug displacement impact estimates of shallow riverbed sediment hydraulic conductivity. Study results will be used to modify standard slug test techniques so that more representative hydraulic conductivities of river bed sediments can be obtained