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New Field Method to Determine Streamflow Timing Using Electrical Resistance Sensors

^a U.S. Geological Survey, 520 North Park Ave., Suite 221, Tucson, AZ 85719, and Dep. of Hydrology and Water Resources, J.W. Harshbarger 122, 1133 East North Campus Drive, P.O. Box 210011, Univ. of Arizona, Tucson, AZ 85721
^b Dep. of Hydrology and Water Resources, J.W. Harshbarger 122, 1133 East North Campus Drive, P.O. Box 210011, Univ. of Arizona, Tucson, AZ 85721
^c U.S. Geological Survey, 5735 Kearny Villa Road, San Diego, CA 92123
^d U.S. Geological Survey, 520 North Park Ave., Suite 221, Tucson, AZ 85719

View larger version (51K): [in a new window]   Fig. 1. Schematic presentation of bulk electrical and contact resistances of a sediment medium. Dotted lines surrounding the wire leads denote the critical region for determining contact resistance. The remaining regions outside the dotted lines are important for determining the bulk electrical resistance. A measurement of electrical resistance is a combined measure of the bulk electrical resistance of the medium and contact resistance.

View larger version (40K): [in a new window]   Fig. 2. Simulated infiltration of water into fine-grained sand and coarse-grained alluvium during a 2-h streamflow event. The shaded areas in both A and B denote the period of streamflow. Measured contact resistance thresholds (dotted lines) and conductivity–saturation relationships were used to calculate saturation and normalized total electrical conductivity measurements at 0.2 m. (A) The saturation response (light solid line) and electrical resistance sensor response (dark solid lines) within the coarse-grained alluvium to the infiltration event and redistribution. (B) The simulated saturation and electrical resistance response for a sensor in fine-grained sand. The onset timing error is defined as the difference in time between the onset of a streamflow event and the activation of the electrical-resistance sensor. The cessation timing error is defined as the difference in time between the end of the streamflow event and the deactivation of the sensor. Both types of error are shown in A and B.

View larger version (20K): [in a new window]   Fig. 3. Schematic diagram of a temperature sensor: (A) before modification; (B) after conversion to an electrical-resistance sensor through removal of the thermistor.

View larger version (79K): [in a new window]   Fig. 4. Photograph and schematic diagram of the sensor locations within the laboratory column used to measure the contact-resistance threshold for the fine-grained sand and the coarse-grained alluvium.

View larger version (97K): [in a new window]   Fig. 5. Sensor locations deployed in Rillito Creek, Tucson, AZ.

View larger version (15K): [in a new window]   Fig. 6. Total electrical conductivity in relation to saturation as determined in column experiments for one of the sensors. (A) Fine-grained sand. (B) Coarse-grained alluvium. Note the higher contact-resistance threshold for the coarse-grained alluvium.

View larger version (52K): [in a new window]   Fig. 7. (A) Electrical conductivity as measured by an electrical-resistance sensor positioned 0.15 m below the ground surface and temperature responses measured at depths of 0.05 m and 1.0 m. The subsurface electrical-resistance sensor was installed 28 July 2001, after the first two streamflow events. (B) Electrical conductivity as measured by an electrical-resistance sensor positioned 0.15 m below the ground surface and saturation as measured by the water content sensors. The shaded areas denote periods of streamflow as inferred using measured soil water content data.

View larger version (17K): [in a new window]   Fig. 8. Electrical conductivity as measured by an electrical-resistance sensor positioned at the surface. The shaded areas denote periods of streamflow as measured by a U.S. Geological Survey streamflow gauge.