DIURNAL GROUNDWATER FLUCTUATIONS IN RESPONSE TO RIVER STAGE AND TEMPERATURE ALONG THE BOSQUE RIPARIAN CORRIDOR, NEW MEXICO

Water allocation conflicts and interstate compact demands have motivated intense hydrologic characterization along a 50-mile section of the Bosque Riparian Corridor in central New Mexico. Hourly head measurements provide a high-resolution dataset for understanding surface and groundwater interactions between the Rio Grande and the shallow aquifer. Diurnal (24-hour), sinusoidal groundwater fluctuations vary spatially and seasonally, and commence during early- and mid-May and cease in October. Patterns in head during no-flow conditions in the Rio Grande suggest that groundwater recharge from the river is contributing to the diurnal head change in the aquifer.

Diurnal fluctuations in river water temperature have been documented previously to influence river discharge and streamflow loss. As the stream temperature changes diurnally those variations can significantly affect the fluid viscosity, and to a much lesser extent fluid density, consequently modifying the streambed hydraulic conductivity. Near Escondida, New Mexico, a diurnal water temperature change from 17 to 24 ºC would result in nearly an 18% increase in streambed hydraulic conductivity. Based on a thermal estimate for each hourly measurement, the mean conductivity for the silty sand streambed during June 2003 was 8.8 cm/d, which is in agreement with a SF₆-tracer value of 6.4 to 12.8 cm/d. While diurnal fluctuations in head are usually associated with evapotranspirative demand alone, it appears that streamflow loss recharging the aquifer may explain a significant proportion of the variation. Analysis of stream temperature and discharge should be considered during coupled simulations of hydrodynamic interactions between rivers and riparian corridors in semi-arid regions.