Submitted to: United States Committee of Irrigation and Drainage Engineering Conference
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2002
Publication Date: 7/13/2002
Citation: Robinson, P., Clemmens, A.J., Carman, D.K., Dalmut, Z., Fortner, T. 2002. Irrigation development in eastern arkansas: water supplies, uses, and efficiencies. United States Committee of Irrigation and Drainage Engineering Conference. p. 283-292. Interpretive Summary: Even in humid regions of the United States, irrigation is needed in most years to provide sufficient yields for economic viability of farms. Poor timing of rainfall causes this need for irrigation, even when annual rainfall is sufficient. Lack of shallow groundwater aquifers has prompted farmers to drill deep wells to irrigate crops, causing groundwater overdraft. The U.S. Army Corp of Engineers is planning surface water diversions to replace groundwater pumping. Several irrigation districts have formed in Central Arkansas to receive this water. The Corp has also provided funds for on-farm improvements, including surface water reservoirs and tailwater pits to capture rainfall and irrigation water runoff. In this paper, we analyze the effectiveness of these reservoirs and pits at reducing the amount of groundwater and/or surface water needed to irrigate crops in central Arkansas. It is also shown that the field application efficiency has little influence on irrigation water diversions/pumping when irrigation water runoff is captured in these pits and pumped to a supply reservoir. These results should be of use to irrigation districts, consultants, and the Bureau of Reclamation. Ultimately better management of irrigation water supplies will conserve water and benefit the environment.
Technical Abstract: Irrigation has expanded rapidly in Eastern Arkansas over the last four decades. Arkansas currently ranks fourth in the United States in irrigated acreage, with more than four million irrigated acres. This area receives more than 40 inches in annual rainfall, but extended periods without summer rain make irrigation necessary in most years. Much of the irrigation development over the last several decades has relied on deep groundwater. However, rapidly declining groundwater levels over much of the area has prompted the State of Arkansas to examine surface water sources as a replacement to groundwater. Ten irrigation projects have been identified that rely on surface water diversions, covering nearly 2 million acres. Progress on these projects range from a completed small demonstration, to initial planning. This paper focuses on the Grand Prairie Project, which is currently under construction. In addition to the major diversion works and canals, these project have a significant on-farm component, with water supply reservoirs and tailwater recovery systems that are used to capture and store rainfall runoff prior to the irrigation season and irrigation runoff during the irrigation season. The capture of rainfall runoff allow the size of the canals, delivery pipelines, and diversion works to be reduced. It also provides storage during the irrigation season to allow a low continuous flow supply to be used effectively on farm. Tailwater recapture and pumpback systems are used to reduce the amount of runoff that leaves the irrigated area. A water balance for a small sub-watershed is used to describe and compare these systems and their performance under groundwater pumping only and under post-project conditions.