Impacts of agricultural development on ephemeral channel planform: using GIS to evaluate change of the Cuyama River, CA - 1938-2011

Humans have impacted river systems for millennia in order to support agricultural activities. Deliberate modifications are made to river systems to provide irrigation or flood control, and include activities such as damming river courses and channelization or diversion of flow. Additionally, river systems are also impacted by many non-deliberate effects of agricultural land use, especially since the implementation of modern, collectivized, and industrial-scale farming in the 20th century. The purpose of this study is to investigate the effects of agricultural land use growth on the channel planform of the Cuyama River in California. GIS was used to register aerial photographs, digitize channel boundaries, and then measure various characteristics of river channel form from 1938 to 2011. Channel planform characteristics measured in this study are: channel width, lateral meander migration, and sinuosity. Subsequent measurements to meander wavelength and amplitude were taken for a portion of the study reach in order to gain additional understanding of the initial three characteristics. The results of this study show that during this period, the river experienced significant geomorphologic activity, which was exacerbated by the growth of agriculture in the surrounding valley. Specifically, a deliberate channelization and straightening of the river caused lasting effects downstream. The discussion that follows examines the numerous challenges which make it difficult to link non-deliberate effects of agriculture to change in river form; however, there is evidence that there are more influences affecting channel pattern than changes in climate and discharge. This study shows the effectiveness of GIS to measure changes to river form over time, and offers a unique case study examining the effects of agriculture on a dryland river.