Marsh Enhancement by Freshwater Diversion

Abstract

The delta of the Nueces River, Texas, is a low‐lying coastal marsh with dendritic distributaries and flats, infrequently inundated by flood events overbanking from the river. This study examines the feasibility of improving the ecological value of the marsh by creation of diversion works to increase the frequency and duration of marsh inundation. To this end, the morphology and statistical occurrence of flood events in the Nueces were examined using longperiod gage records on the river. A canonical parameterization of flood events was used as input to a numerical hydrodynamic model of the deltaic system, which predicts the time evolution of flow and water level throughout the delta, and includes provision for simulating distributary confluence and difluence, inundation and dewatering of floodplains and flats, and activation of transient channels. The response of the marsh to specified flood events was computed for various alternative physiographies, including existing conditions and candidate combinations of weirs and diversion channels. Coupled with the statistical frequency of occurrence of the specified flood event, the potential ecological value of each diversion alternative was quantitatively established in terms of total inundation period in key segments of the marsh.