Field study and simulation of diurnal temperature effects on infiltration and variably saturated flow beneath an ephemeral stream

Abstract

Abstract. Two experiments were performed to investigate flow beneath an ephemeral stream and to estimate streambed infiltration rates. Discharge and stream-area measurements were used to determine infiltration rates. Stream and subsurface temperatures were used to interpret subsurface flow through variably saturated sediments beneath the stream. Spatial variations in subsurface temperatures suggest that flow beneath the streambed is dependent on the orientation of the stream in the canyon and the layering of the sediments. Streamflow and infiltration rates vary diurnally: Streamflow is lowest in late afternoon when stream temperature is greatest and highest in early morning when stream temperature is least. The lower afternoon streamflow is attributed to increased infiltration rates; evapotranspiration is insufficient to account for the decreased streamflow. The increased infiltration rates are attributed to viscosity effects on hydraulic conductivity from increased stream temperatures. The first set of field data was used to calibrate a two-dimensional variably saturated flow model that includes heat transport. The model was calibrated to (1) temperature fluctuations in the subsurface and (2) infiltration rates determined from measured streamflow losses. The second set of field data was to evaluate the ability to predict infiltration rates on the basis of temperature measurements alone. Results indicate that the variably saturated subsurface flow depends on downcanyon layering of the sediments. They also support the field observations in indicating that diurnal changes in infiltration can be explained by temperature dependence of hydraulic conductivity. Over the range of temperatures and flows monitored, diurnal stream temperature changes can be used to estimate streambed infiltration rates. It is often impractical to maintain equipment for determining infiltration rates by traditional means; however, once a model is calibrated using both infiltration and temperature data, only relatively inexpensive temperature monitoring can later yield infiltration rates that are within the correct order of magnitude.

Relative contributions of transient and steady state infiltration during ephemeral streamflow

“…This model has been employed successfully in previous investigations to estimate stream channel infiltration [e.g., Ronan et al, 1998;Constantz, 1998;Bartolino and Niswonger, 1999]. The two longest flow events (November 2000 andApril 2001) recorded during the monitoring period were used to calibrate the thermal (sediment heat capacity and saturated thermal conductivity) and hydraulic (saturated hydraulic conductivity and porosity) parameters within the model.…”

“…Exact matches were not considered possible given the simplicity of the model and the difference between a point scale core measurement and a field parameter. On the basis of previous sensitivity analyses by Ronan et al [1998] and Bailey [2002], the saturated hydraulic conductivity was considered the most sensitive parameter for modeling coupled heat transport and water flow. The lowest model residuals were found with the parameters shown in Table 2.…”

“…Numerous infiltration and recharge investigations have been conducted to quantify the contributions of streambed recharge to the water budget for resource planning [Wilson et al, 1980;Ronan et al, 1998]. …”

“…These methods have been applied to estimate infiltration rates through saturated streambed sediments during periods of constant streamflow well after streamflow onset. To date, only one study [Ronan et al, 1998] has used temperature-profiling methods to simulate infiltration rates at the onset of streamflow. The authors evaluated their simulated infiltration rates during the transient period with seepage measurements between two flumes.…”

Evaluation of the streambed leakage concept in analytical models using data from three pumping tests

“…That study demonstrated qualitatively that the effect of temperature was the main reason for the variability in daily streamflow losses. Ronan et al (1998) also studied diurnal fluctuations in seepage rates and included numerical modeling results in their study. Bravo and Jiang (2002) applied a coupled groundwater flow and heat transport model to account for the dependence of water density and viscosity on temperature.…”