Controls on flow conveyance losses in the San Acacia reach of the Middle Rio Grande

Abstract

The San Acacia reach of the Middle Rio Grande experiences high conveyance losses throughout the year that vary greatly based on local features, seasonal flow variability, and regional influences. Variability in loss rates are driven by hydrogeological differences, topographical differences, and vegetative differences throughout the region, with some sub-reaches occasionally gaining flow and some sub reaches frequently losing 100% of flow. Summer drying events provide insight into the most critical reaches, and close analysis of water table trends within these areas can provide further indications of the controlling local features. In addition to these local controls, there is a larger climate-related control on the entire region. During poor water years, flows have higher percentage losses than good water years, minimizing effective conveyances. It becomes difficult to counteract the effects that poor flows have on the water table, which raise hydraulic gradients and increase conveyance losses for extended periods of time. Conveyance losses are controlled by several scales of influence, but outlining them and understanding the interactions between them is a critical challenge for maximizing flow transmission in the future.