f MONITORING A NOVEL APPROACH TO MONITOR ENHANCED RECHARGE WITH TIME LAPSE GRAVITY

We present work conducted in cooperation with the Bureau of Reclamation as part of their Enhanced Recharge Demonstration Project. The purpose of this project was to monitor the performance of a novel recharge enhancement approach based on diverting water from a main channel through a secondary channel within the floodplain. We located gravity stations along a 75 m transect that was perpendicular to the channels and extended from the midpoint between the main and excavated channels. We monitored over a period of 75 days. During this period, seepage loss measurements and streambed hydraulic conductivity measurements showed decreasing infiltration capacity with time. This response may be due to deposition of fine sediments and/or biological activity. Gravity responses mirrored these changes, showing rapid increases in water mass at early time, followed by a slow, steady decrease in stored mass. In addition, the gravity measurements gave a unique perspective on the extent of lateral movement of infiltrated water. Based on these results, we suggest that gravity monitoring could be a key component of monitoring of water movement adjacent to natural and engineered channels.