|Goodrich, David - Dave|
|MADDOCK III, T.|
Submitted to: American Meteorological Society
Publication Type: Proceedings
Publication Acceptance Date: 1/21/1998
Publication Date: N/A
Interpretive Summary: This paper presents preliminary findings on stream-aquifer interaction along a 425-meter long reach of the San Pedro River in Cochise County, Arizona. The study was part of the Semi-Arid Land-Surface-Atmosphere (SALSA) global change research program led by the USDA Agricultural Research Service. Groundwater level and streamflow data were collected at the study site at different times during the 1997 growing season. Contour maps of groundwater elevation showed that water levels in the floodplain aquifer decreased between April and June, most likely due to the seasonal increase in transpiration by cottonwood and willow trees along the river. Daily fluctuations in groundwater levels appeared to correspond to daily transpiration activity. More conclusive analysis will be possible when these data are combined with tree sap flow and moisture flux (transpiration) data collected during the experiment.
Technical Abstract: The effect of transpiration stress on stream-aquifer water flux was examined along a 425-meter reach of the San Pedro River in Cochise County, Arizona. Piezometric head of groundwater in the floodplain and regional aquifers, and stream stage and discharge, were monitored during several intensive measurement periods at different times in the growing season. Groundwater data were collected continuously at 6 wells and one streambank piezometer, and hourly from 25 piezometers during the April and June 1997 measurement periods. Hourly measurements of stream stage and discharge (dye tracer technique) were also measured at these times at 5 cross-sections within the study reach. Contour maps constructed from these data show a reduction in piezometric head (and water table elevation) between April and June, corresponding with increased transpiration by riparian phreatophytes. Diurnal changes in piezometric head reflected transpiration activity during gboth measurement periods. Spatial variation in groundwater flow paths and water levels in the floodplain aquifer, may be due to differences in hydraulic conductivity and level of phreatophyte activity. More conclusive analysis will be possible when these data are combined with concurrent sap flow and moisture flux data collected during the experiment.