Evaluation of transmission losses in ephemeral streams with compound channels.

The problem of analyzing and estimating transmission losses in ephemeral streams with compound channels was the focus of this research. The Kinematic Runoff and Erosion model KINEROS (Woolhiser et al., 1990) and the Soil Conservation Service SCS model (Lane, 1983) were employed in this study as they represent a range in model complexity. Initial soil moisture and channel wetness conditions were employed to modify channel infiltration capacity in the SCS model and the saturated hydraulic conductivity in KINEROS. Numerically both models have been improved to treat compound channel routing with differential over-bank and main channel infiltration. The KINEROS model was extended by coupling the over-bank and channel one-dimensional kinematic and infiltration equations through the lateral inflow terms with an assumed horizontal water surface. The SCS was extended to incorporate the Manning's equation for flow with the ordinary differential equation employed in the model. Results demonstrate that simulations by multiple trapezoidal and multiple compound cross sections further decrease computed outflow volumes and increase transmission losses as compared to using a single average trapezoidal cross section. Both models simulated observed channel losses with a comparable degree of accuracy for eight carefully checked runoff events. Over-bank losses represented 12.5% of the mean main channel loss in the case of KINEROS model and 13.4% in the SCS model. The evaluation of the performance of both models demonstrated that the best results were obtained by introducing the channel bed capacity term in the analysis to more fully treat pre-runoff channel moisture conditions