Fluvial and sedimentological processes, Owens Lake Delta, CA

Braided channel systems in rivers commonly are associated with abundant sediment load, gradients steeper than meandering and straight channels, and mobile banks owing to poor sediment cohesion. The Owens River flows through the Owens Valley in eastern California and over most of its ~295 km course it is a low gradient meandering system actively entrenching in its own floodplain. However, the final 8 km of the Owens River are characterized by a rapidly shifting braided system. In order to understand the nature of the braided section and the geomorphic change it experiences, two field surveys were conducted (June 2009 and June 2010). These surveys allowed for calculation of sinuosity ( 1.0934 in 2009 and 1.1956 in 201 0), gradient (0.00213 in 2009 and 0.00211 in 2010), percent slope (0.2103 in 2009 and 0.2078 in 2010), and unit stream power (2.8125 Wm2 in 2009 and 7.5942 Wm2 in 2010). In addition to the surveys 32 sediment samples were collected for grain size analysis. Statistical analysis of the samples showed the river system is dominated by moderately-sorted medium sand. Flow in the lower Owens River is completely controlled by the Los Angeles Department of Water and Power. Over the finalS km, discharge is reduced to -1.13 m3s-1 with the rest of the water being diverted from the lower Owens River to the Los Angeles aqueduct for use by the city of Los Angeles. Comparison of the data with data from other braided streams reveals that the Owens River behaves more like a meandering or straight channel, in terms of gradient, percent slope, and unit stream power. Ultimately, it appears the reason for braiding over the last 8 km is a result of an abundant sediment load and a dramatic loss of discharge. An increase of discharge in this section would result in a larger unit stream power and increase the ability to carry suspended sediment, possibly resulting in the channel reverting to a meandering system similar to its upstream reaches.