IWRA Proceedings

Abstract1. INTRODUCTION The following document represents a summary of the core considerations of the hidrological study, which was carried out to determine the impact on the strategic hidric resources of the northern zone of El Salvador, as a result of the planned construction of the hidroelectric dam “El Cimarrón” on the River Lempa, the country´s principal. Said investigation has been carried out as an environmental impact study under the auspices of the Hidroelectric Commision for the River Lempa, (CEL) the company charged with the electric energy production for the country, and of the Ministry for the Environment and Natural Resources (MARN), with the aim of assessing the viability or environmental inconvenience of the project. 2. OBJECTIVE a) To present the hidrological evaluation and the biophysical characteristics of the hydrographic system which represents the ambit of hidroelectric project.; b) To define the levels of water flow or environmental flows required for the preservation of the natural ecosystem and the required hydric usage. c) To outline the recommendatations derived from the study regarding the hydric viability of the project. 3. METHODOLOGY The hydrological analysis was carried out based on equations of regionalization and areales relations of precipitation-draining, taking into account the predefined homogenous hydrologic regions of the state. In the same way hidrograms were drawn in order to ascertain the behavior of the mean flows, on the basis of which were defined the estimates of the environmental flows, by way of the hydrological index, and estimates of the percentile range of the average flow as an indicative of a required environmental quality. Additionally, the analysis was carried out using hydrologic models of generation and simulation of flows. 3. RESULTS Quantitative and qualitative aspects of the local state of hydric resources; determination of environmental flows; present and future demand of the hydric resource. 4. CONCLUSION The implementation of the hydroelectric project will directly affect the principal source for the supply of drinking water for the metropolitan area of San Salvador, the nation´s capital, which comes directly from the River Lempa, whose channel will be interrupted by the realisation of the energy project in an area located 81kms above the point at which the water supply is taken for San Salvador. The population directly affected represents 28% of the overall population of the country. The water flows which will be interfered, with are of vital importance for the natural dilution of other water effluents, which contain a considerable level of contamination, and which form an integral part of the volumes or flows which come together at the point where the water supply is taken for San Salvador. The maintenance of a fluvial dynamic which will permit the environmental preservation of acuatica and riverside ecosystems, and in particular the hydric availablity, require, at the least the maintenance of the ambient water flows established for the winter and the summer (between 3.05m3/s and 29m3/s) which are insufficent to permit the predicted generation capacity of 242Mw, in particular during the six months of the dry season.