SEEPAGE FLUX ESTIMATION USING FLOOD FRONT VELOCITIES COUPLED WITH SURFACE AND GROUND-WATER DATA

Determining the spatial variability of seepage fluxes along ephemeral channels can be important to assess the controls on groundwater recharge in arid and semi-arid regions. The longitudinal variability in seepage flux along a 1.4 km reach of an artificial channel was estimated using measurements of flood front velocity, surface water stage and groundwater level. A numerical model that combines the diffusion wave approximation of the Saint-Vénant equations for streamflow routing, with Phillips’ infiltration and the groundwater flow equation was used to quantify seepage flux. The model was implemented to simulate a controlled flow event which took place from 19 May - 2 June 2011 along the study reach. Estimates of seepage flux were obtained for the upstream segments, where streambed hydraulic conductivity (K_s) was ~10² m d^-1 and seepage flux was on the order of 10^-2 m³ d^-1 m^-2. In the downstream segments, streambed hydraulic conductivity was highly variable (~10^-2 – 10^-5 m d^-1), and seepage flux was more difficult to accurately quantify due to insensitivity of K_s to the constraining observations during calibration. Higher seepage fluxes generally coincided with high sensitivity of K_s to the constraining observations allowing more reliable estimation of fluxes. The availability of groundwater levels and surface water depths in addition to flood front timings provided valuable constraints to reduce the error in the estimated seepage flux.