Sediment Modeling of the Middle Rio Grande with and without the Temporary Channel: San Antonio to Elephant Butte Reservoir

The Elephant Butte Temporary Channel (Temp Channel) on the Middle Rio Grande in New Mexico was excavated from 2000 to 2004 and is being maintained to increase water and sediment delivery to Elephant Butte Reservoir. At the same time, the drought in the 2000s resulted in the lowing Elephant Butte Reservoir pool. Significant degradation has been observed in the reach from the Bosque del Apache National Wildlife Refuge (BDANWR). This study provides an estimate of the impact of the Temp Channel on the upstream degradation in the BDANWR. A one-dimensional (1D) sediment transport model was used to simulate the future channel bed response to river geometry with and without the Temp Channel. Three river geometry configurations were simulated in this study: 1). The current channel geometry with the Temp Channel, 2). The current channel geometry without the Temp Channel in which water flows in the lowest portion of a cross section, and 3). SRH-2D predicted channel at the end of 2009 had the Temp Channel not been excavated. The model utilized a 10-year hydrology scenario for the period of 2010 to 2020, namely the 50% non-exceedance (most probable) hydrology. The Elephant Butte Reservoir pool elevations, obtained from a separate river operation model, were used as the downstream boundary condition. Conclusions regarding the impact of the Temp Channel were drawn from the model results.