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TITLE:
Quantification and Simulation of Groundwater - Surface Water Interactions in a Southwestern Riparian System
INVESTIGATORS:
Dave Goodrich and Bruce Goff (ARS), Bob MacNish and Tom Maddock III (UA), Don Pool (USGS)
OBJECTIVES:
1. To quantify groundwater (GW) and surface water (SW) fluxes into and out of a riparian "control volume" in order to develop a more robust algorithm for simulating these processes in groundwater models.
2. To model the GW-SW interaction at the stream-aquifer interface under conditions of regional pumping and seasonally varying streamflow.
APPROACH:
An experimental control volume has been established along the San Pedro riparian corridor at Lewis Springs, Arizona. The study site is instrumented with devices that continuously measure and record well water levels and stream stage. Additional variables will be manually measured during several 48-hour intensive measurement periods ("synoptic runs") scheduled for 1997 and in response to flood events. These measurements will include groundwater levels in paired-piezometers, and stream stage and discharge at several cross-sections along the control reach. Ground surveys will be carried out to establish horizontal and vertical positions of all wells, piezometers, and staff gages to enable accurate computation of GW and SW gradients.
Simulation of GW-SW interactions will require development of a robust algorithm for adjusting stream conductance with variation in discharge. This will require the characterization of base flow on a seasonal basis through analysis of both historical measurements and those carried out during the 1997 riparian campaign. In addition, a stream width/discharge rating curve will be developed for the stream reaches within the Lewis Springs corridor. Stream width estimation over large parts of the San Pedro river corridor using aircraft radar (SAR) data will also be examined in coordination with the Remote Sensing Group if that data becomes available via the AMPS aircraft.
DATA COLLECTION (Variable, Units, Method, Location, Frequency):
1. Variable: stream discharge. Units: m3/s. Method: current meter, tracer dye dilution techniques. Location: current meter stations at cross-sections (XS) 1, 3, 5; tracer sampling stations at XS 1-5. Frequency: current meter measurements taken periodically during synoptic runs and flood events; tracer samples collected hourly during synoptic runs.
2. Variable: stream stage. Units: m. Method: staff gages (SG), bubble-gages (BG), instream stage recorder. Location: SG and/or BG at XS 1-5; instream stage recorder at XS 3. Frequency: SG measurements taken hourly during synoptic runs and flood events; BG measurements taken continuously during synoptic runs; instream stage recorder measurements taken continuously.
3. Variable: stream channel geometry (cross-section area, wetted perimeter). Units: m and m2. Method: standard survey methods and (possibly) aircraft imagery. Location: upstream end, middle, and downstream end of the control reach (XS 1, 3, 5). Frequency: during synoptic runs and intermittently throughout season.
4. Variable: groundwater potentiometric surface. Unit: m AMSL. Method: monitoring wells equipped with pressure transducers/data logger and piezometers measured manually with electronic sounder. Location: 6 monitoring wells along a transect running perpendicular to the river on the west side, 24 piezometers arranged in rectangular array (about 200 m x 300 m) overlaying control reach. Frequency: wells monitored continuously; piezometers measured hourly during synoptic runs and flood events.
DATA REQUIRED FROM OTHER INVESTIGATORS:
1. USGS - data on aquifer characteristics from pumping tests; stream temperature data; intermittent channel seepage measurements at several locations within the Lewis Springs area.
2. Whitaker - groundwater level measurements from neutron probe access tubes/piezometers.
3. Moran - SAR data for San Pedro riparian corridor.
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