Associations between changes in agriculture and hydrology in the Cache River basin, Arkansas, USA

Abstract

Impacts to the hydrology of the Cache River, a major river system in the Mississippi Alluvial Valley, were assessed by integrating hydrologic analyses with a review of historical land use changes. Extreme low flows have become more frequent in recent years, coincident with a dramatic increase in rice farming in the basin and its associated irrigation. Annual drawdowns in the alluvial aquifer were positively correlated with the annual area of rice crops. There is no evidence that a change in climatic conditions accounts for the increase in extreme low flow frequency. In fact, multiple regression analyses indicate the relationship between climate and flow is weakest in more recent decades when extreme low flows were more prevalent. Low flows in the summer (when rice irrigation occurs) were least associated with climate in most recent decades. Average monthly flows for August and September have increased, which is also an impact consistent with rice agriculture practices. Water is drained from rice fields to surface-water drainages at the end of the summer and may eventually reach the Cache River, thus increasing late summer flows. The timing and nature of changes in agricultural practices within the Cache River basin suggest agricultural impacts have contributed to the observed changes in hydrology.