|Cady, Ralph - US NUC REGULATORY COMM|
|Nicholson, Thomas - US NRC|
Submitted to: American Society of Agronomy Meetings
Publication Type: Proceedings
Publication Acceptance Date: February 15, 2000
Publication Date: N/A
Technical Abstract: Annual estimates of ground-water recharge using water balance methods fail to capture significant episodic recharge events that may occur over short time periods (e.g., hourly or daily) in shallow ground-water systems. We investigated uncertainties in estimating ground-water recharge using data recorded from real-time, near-continuous piezometers for measuring shallow ground-water and multi-sensor capacitance probes (MCP) for measuring soil water content. The data were recorded at 10-minute intervals. Analytical and numerical methods were used to compare ground-water recharge estimates. These methods included: (1) time-series analyses of hydrographs and soil water contents, (2) steady-state estimates using meteorological data only, and (3) a water budget model. Higher estimates of ground-water recharge were obtained using real-time, near-continuous piezometer and MCP data than estimates derived strictly from meteorological data. Taking into account errors introduced by estimating the recession coefficients, the sum of positive changes in head is the most appropriate approach for estimating recharge at this site using piezometer data. The piezometer and MCP data showed a very rapid response (i.e., < 20 minutes) in the shallow water table to rainfall events over short time intervals, and verified the occurence of significant episodic recharge.