Available Irrigation Water from Small Tennessee Valley Streams

Abstract

Increased demand for irrigation water in the southeastern United States is causing increased stress on many small streams where farmers are pumping directly from the stream. As a possible method to decrease this demand during periods of low stream flow and to make more water available for irrigation, we initiated a study to evaluate the feasibility of pumping during high stream flows to off-stream storage sites. These sites could be on-farm or farmer-shared reservoirs. One objective of the study, and the subject of this discussion, was to evaluate the volume of water available for pumping when stream flows are greater than preselected minimums. These minimum stream flows were defined as a function of long-term mean stream flow and ranged from mean flow to one-fourth mean flow. Flow data for nine streams in the study area were evaluated. A method of obtaining distribution-free tolerance limits was used to develop exceedance limits for volume of water available during a four-month period (January through April) of high stream flow. For example, using this approach with data collected from Flint River we can be 95% confident that available water will be at least 3.6 ha-cm/ha of watershed area in 9 of every 10 years when mean stream flow is taken as the minimum acceptable pumping flow. Similar exceedance limits for other streams varied from a high of 8.4 to a low of 0.8 ha-cm/ha, thus, demonstrating the variability of water availability from streams in this area.