Temperature signatures in the hyporheic zone of a perennial, northern New Mexico stream suggest a complex and dynamic system of interactions on a diurnal time scale. Fourteen shallow wells were instrumented with temperature data loggers and installed along four transects across a 40 ft reach of a proposed, channel-modifying restoration structure on the Rio de las Vacas. Temperature signatures in the banks and the floodplain of the reach suggest a parallel flow system while the instream wells suggest a losing reach within 15 to 30 in. of the stream bed. The thermal signatures of a losing reach that appear at the shallow depths dissipate at greater depths below the stream. Hydraulic head measurements alone, do not adequately describe the subsurface dynamics. This study suggests that the subsurface flow regime includes discrete flow paths that have minimal interaction and their discharge characteristics are temperature dependant. As a result of the temperature data, the overall estimated ground water exchange currently decreases from 0.43 cubic feet per second (cfs) to 0.40 cfs at bankfull and 0.21 cfs to 0.20 cfs at baseflow. The estimated increase in exchange from adding 7 feet of stream length with the proposed structure decreases from 0.49 cfs to 0.45 cfs at bankfull and 0.24 cfs to 0.23 cfs at baseflow conditions. The restricted loss of stream water to the subsurface reduces the residence time in the subsurface. Therefore gains in thermal stability by adding surface area over which the exchange could occur, would likely not counter the increase in stream temperatures from increased exposure to solar radiation.
Rio de Las Vacas Watershed, Wetlands Restoration Project, Freshwater ecosystems, Temperature studies, River restoration
Robertson, Andrew. "Surface Water and Ground Water Interactions of the Rio de las Vacas, NM; Characterizing Exchange and Predicting Response Using Thermal Data." (2008). http://digitalrepository.unm.edu/wr_sp/103