Determining Spatial and Temporal Variability of Percolation Rates from a River-Side Recharge Basin Using Fiber Optic Distributed Temperature Sensing

Percolation rates in Managed Aquifer Recharge (MAR) facilities, such as recharge basins and stream channels, can vary widely through both time and space. Natural variations in sediment hydraulic conductivity can create "dead zones" in which percolation rates are negligible. Clogging is a constant problem, leading to decays in facility percolation rates. Measuring percolation rate variations is important for management, maintenance, and remediation of surface MAR facilities.;We have used Fiber Optic Distributed Temperature Sensing (FODTS) to monitor percolation in a long narrow river channel separated from an active river by a levee. The alluvial sediment in the river channel varies widely in texture and water balance is difficult to monitor independently. The off-river channel was monitored by installing a fiber optic cable in the subsurface and measuring the propagation rate of the diurnal temperature oscillations carried downward with infiltrating water. In this way, heat was used as a tracer of percolation rates along the section defined by the 1800 meters of buried cable. We were able to confirm the FODTS measurements of percolation in the Off River Channel and demonstrate its wide applicability. Results from the measurements have been used to understand both the hydraulic behavior of percolation in the facilities and to make management decisions regarding facility operations and the potential need for additional surface sediment remediation.