On predicting of some consequences of planned dam construction in a pristine sand-gravel river large catchment: Rio San Pedro, Nayarit, Northwest Mexico

Abstract

The pressure on water and energy resources is increasing globally, particularly in emerging countries. Some of them use their rivers for electric power generation, paying little or no attention to the hydromorphological changes generated in the rivers due to the infrastructure associated. One case is the St. Pedro River in the Northwest of Mexico (Rio San Pedro), where it is planned to build a hydroelectric dam. The importance is due to its flow discharges directly to a marsh system called Marismas Nacionales, considered a Biosphere Reserve that includes approximately 20% of all mangroves in Mexico. The alteration of its natural conditions is a critical issue for the ecosystem. There are many studies about the effects of dams on rivers after their construction, but only a few related to the river characterization before intervention within its channel. In this work, we highlight the relevance of the latter. We conducted extensive fieldwork, including morphological survey, sediment transport measurement, hydrodynamics, and bathymetry over 80 km of the river. We establish a baseline with the hydromorphological parameters in the river and run a numerical simulation with 2-D HEC-RAS 6.1 model to compare natural and controlled runoff. The goal of our study was to discuss possible scenarios and some consequences that could be generated with the dam construction—alterations in the lower basin— and suggest actions that can help to minimize the detrimental consequences. The novelty of our work is the scope of fieldwork, the wide range of the data, careful modeling based on detailed field data, and finally, the possible way one might use our results in the future to minimize the adverse consequences of dam construction. The methodology presented can be used as a guide to other dam projects worldwide, which face all these issues and need to redesign the dam and consider modern techniques to preserve the riverine conditions close to the more natural possible.