Experimental river diversion for marsh enhancement

Abstract

The Nueces River is the primary source of freshwater inflow to Corpus Christi Bay and virtually the only source of freshwater inflow to the Nueces Delta. In association with reservoir development and operation within the Nueces Basin, the magnitude of freshwater inflow has been greatly reduced since 1958. Continually increasing salt concentrations in the soil and water have compromised the function of the delta as a viable component of the estuarine ecosystem. In 1993, the U.S. Bureau of Reclamation began a 5-yr diversion project to increase the opportunity for freshwater flow into the delta. With the excavation of two overflow channels, the minimum flooding threshold for the upper delta was significantly lowered, and more frequent diversions of freshwater from the Nueces River were enabled. During the 50-mo diversion period, the amount of freshwater diverted into the upper Nueces Delta was increased seven- fold. The average salinity gradient in the upper delta reverted to a more natural pattern, with average salinity concen- trations decreasing from the lower (bay) to upper (riverine) delta, and a corresponding improvement in abundance and diversity of both intertidal vegetation and benthic communities.