Temperature based estimates of streamflow patterns and seepage losses in ephemeral channels.

摘要

In arid environments, seepage losses from ephemeral streams make up a significant portion of potential recharge to ground water. Currently, information is limited regarding stream flow frequency or duration along ephemeral channels. The placement of instrumentation in these flashy and erosive environments is difficult and often costly. Traditional stream-gaging methods do not function reliably and are not practical in ephemeral stream channels due to non-stationary channel geometry. Temperature-based methods hold promise as a simple, yet robust, alternative technique for detecting the presence or absence of ephemeral streamflow and for determining potential recharge.; Heat is used to track the timing, frequency and duration of ephemeral streamflow. Disruptions in the subsurface thermal patterns due to surface flows in the channel are found to be more pronounced than disruptions due to localized meteorological events. Channel geometry and volumes of flow will also influence the temperature patterns recorded by buried probes. The timing, frequency, and duration of stream flow events will affect the change in subsurface energy. Therefore, one-time vertical thermal profiles beneath ephemeral channels may be compared with vertical profiles in a benchmark bank location to qualitatively determine if the channel has experienced surface flows.; Three ephemeral channels were selected as study sites. Two primary sites, Abo Arroyo, NM and the Amargosa River, NV, were extensive, multiyear studies. The Isleta Arroyo, NM, was a short-term study utilizing aquifer pump test outflow as the contrived ephemeral stream.; Thermal measurements were collected longitudinally in each channel. Thermal records were used in the development of analysis tools to determine temporal and spatial patterns of ephemeral streamflow. A variety of analysis techniques were investigated, including comparison of channel temperatures with benchmarks and calculation of thermal standard deviations.; Subsurface temperatures may also be used to estimate the vertical movement of water in systems where the predominant means of heat-transport is advection. Percolation rates during ephemeral flow events were computed by calibrating simulated temperatures to measured thermal profiles.