HR: 1340h
AN: H23D-1459    [Abstracts]
TI: Groundwater-Stream Interactions in a Mountain - Valley Transition: Impacts on Catchment Hydrologic Response and Stream Water Chemistry
AU: * Covino, T P
EM: tcovino@montana.edu
AF: Montana State University, 334 Leon Johnson Hall P.O. Box 173120, Bozeman, MT 59717 United States
AU: McGlynn, B
EM: bmcglynn@montana.edu
AF: Montana State University, 334 Leon Johnson Hall P.O. Box 173120, Bozeman, MT 59717 United States
AU: Sojda, R
EM: sojda@usgs.gov
AF: USGS, 212 AJM Johnson Hall, Bozeman, MT 59717
AB: As mountain headwater catchments increase in size to the meso-scale, they incorporate new landscape elements including mountain-valley transition zones. Mountain-valley transition zones form part of the mountain front, and influence groundwater (GW)-stream interactions and impact hydrologic response and stream water composition. Mountain front recharge (MFR) in mountain-valley transition zones and subsequent GW discharge to streams in the valley bottom are important hydrological processes. These GW-stream interactions are dynamic in both space and time, playing a key role in regulating the amount, timing, and chemistry of stream water exiting the mountains and reaching the valley floor. We hypothesize that mountain-valley transitions function as hydrologic and biogeochemical buffers via GW recharge and subsequent GW discharge. More specifically, we propose that streams often recharge GW near the mountain front and receive stored GW further downstream. To investigate these processes we applied physical hydrology techniques (four stream gauging stations, 19 wells, and 18 piezometers), tracer injections, and geochemical hydrograph separations in the Humphrey Creek watershed in southwestern Montana. Our intensive instrumentation network allowed us to assess the spatial and temporal variability of mountain front GW recharge and GW-stream interactions across a mountain-valley transition. Geochemical signatures were used to partition stream flow into alpine and GW sources. Tracer injections were used to quantify GW recharge/discharge over multiple reaches. We found multiple lines of evidence necessary to investigate complex GW-stream interactions - single lines of evidence would have been misleading. Our results indicate that much of the alpine stream water recharged GW at the mountain front and that stored GW of a different chemical composition sustained down-valley stream discharge. Down-valley stream discharge was dominated by GW inputs and responded to GW stage more closely than upstream reaches. A critical GW stage height was necessary for down-valley channel flow, as this was the only major input to channel flow during early and late season base flow. Conversely, GW contributed little to stream flow in the upper reaches of the study area. GW-stream water exchange served as a flow and geochemical buffer, which caused significant changes in stream water chemistry from the alpine, to the MFR zone, to the valley bottom and muted fluctuations in channel flow, both at high and low flow. Implications are that mountain front GW recharge magnitudes can control valley aquifer storage state which combined with alpine runoff magnitude and valley bottom GW discharge controls stream water quantity and geochemical composition downstream.
UR: http://landresources.montana.edu/watershed/covino/
DE: 1804 Catchment
DE: 1806 Chemistry of fresh water
DE: 1830 Groundwater/surface water interaction
DE: 1860 Streamflow
DE: 1879 Watershed
SC: Hydrology [H]
MN: Fall Meeting 2005