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TITLE:
Quantification of Bank Storage in a Southwestern Riparian System Using Vadose Zone Monitoring Techniques
INVESTIGATORS:
Martha P.L. Whitaker, Tom Maddock III, and Bob MacNish (UA)
OBJECTIVES:
1. To monitor and quantify changes in bank storage in response to diurnal, seasonal, and storm-induced riverbank groundwater-level fluctuations.
2. To model the changes in bank storage in two dimensions, i.e. for a cross-sectional area.
APPROACH:
Soil moisture, matric potential hydraulic head, soil temperature and stream stage are being (will be) monitored intensively in both time and space along a transect perpendicular to and crossing the San Pedro River, within the cottonwood/willow forest gallery. Most measurements are automatically collected using dataloggers; additional soil moisture and hydraulic head measurements have been/will be conducted at a more frequent interval using a neutron probe and water-level sounder during scheduled synoptic runs, as well as for several days following a "significant" rainfall event.
DATA COLLECTION (Variable, Units, Method, Location, Frequency):
1. Variable: volumetric soil moisture. Units: %. Method: Automated Water Content Reflectometry (i.e. frequency domain reflectometry, which is a variation of TDR; both are a function of dielectric constants). Locations: Two trenches situated on either side of the San Pedro River, approximately 30 m North of the southern-most piezometers. The probes are installed 4-6' below the ground surface. Frequency: every 15 minutes.
2. Variable: Volumetric soil moisture. Units: %. Method: neutron probe. Locations: 12 Neutron Probe Access Tubes (NPATs) total. 6 at a downstream location, 6 at an upstream location. For each down/upstream location, three NPATs are on either side of the river. Frequency: One full "round" of data collected during each synoptic run, and once every 1-2 weeks. Also, constant data collection for 48 hrs following a significant rainfall event, as well as 96, and 144 hours following a "significant" rainfall event.
3. Variable: Soil Matric potential. Units: cm H2O. Method: tensiometers automated with pressure transducers. Location: Three nests of four tensiometers near the WCR trench on the West side of the Vadose Zone monitoring transect, and four nests of four tensiometers near the WCR trench and NPATs on the East side of the transect. Frequency: 15 minute intervals
4. Variable: soil temperature. Units: degrees C. Method: automated thermocouples. Location: adjacent to 8 WCR probes on either side of the Vadose Zone Monitoring transect. Frequency: 15 minute intervals.
5. Variable hydraulic head. Units: m AMSL. Method: manual-read piezometers using sounder and/or chalked steel tape. Intend to eventually automate the piezometers. Locations: Identical to those of the NPATS. Frequency: Once during each synoptic run, when soil moisture is measured using the neutron probes, and at 15 minute intervals when automated.
6. Variable: stream stage. Units: m AMSL. Method: To be determined, but definitely automated. Possibly an in-stream stage recorder that uses a pressure transducer to detect stage fluctuations.
DATA REQUIRED FROM OTHER INVESTIGATORS:
1. Maddock et al.: Stream stage and stream discharge, groundwater potentiometric surface.
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