Rapid identification of transience in streambed conductance by inversion of floodwave responses

Streambed conductance controls the interaction between surface and groundwater. However,
the streambed conductance is often subject to transience. Directly measuring hydraulic properties in a river
yields only point values, is time-consuming and therefore not suited to detect transience of physical properties.
Here, we present a method to continuously monitor transience in streambed conductance. Input data
are time series of stream stage and near stream hydraulic head. The method is based on the inversion of
floodwave responses. The analytical model consists of three parameters: x, the distance between streambank
and an observation well, a, the aquifer diffusivity, and a the retardation coefficient that is inversely
proportional to the streambed conductance. Estimation of a is carried out over successive time steps in
order to identify transience in streambed conductance. The method is tested using synthetic data and is
applied to field data from the Rh^one River and its alluvial aquifer (Switzerland). The synthetic method demonstrated
the robustness of the proposed methodology. Application of the method to the field data
allowed identifying transience in streambed properties, following flood events in the Rh^one. This method
requires transience in the surface water, and the river should not change its width significantly with a rising
water level. If these conditions are fulfilled, this method allows for a rapid and effective identification of
transience in streambed conductance.