Analysis of flooding in basin number 9529319-6 (Río Seco) of the pacific of Nicaragua, using the HEC-RAS model

Abstract

Nicaragua’s vulnerability to disasters was exposed with the passage of Hurricane Mitch in October 1998, which led the Nicaraguan State to establish in March 2000 a comprehensive system for Disaster Risk Reduction (DRR) called the “National System for Disaster Prevention, Mitigation and Response (SINAPRED) (IFRC, Disaster Risk Reduction). 2013, p. 5). The municipality of Nagarote is exposed to both natural and man-made threats; mainly associated with hydrometeorological phenomena. In a risk level classification carried out in 151 municipalities in Nicaragua, Nagarote ranks 14th, where position 1 represents the highest risk. The main threats in the area are drought, rated at the highest level, followed by the risk of floods and seismic activity (ENACAL, 2019, p.60). In addition, the lack of detailed mapping prevents the precise identification of the affected areas and the extent of the surface water surface. Against this background, this study carries out an analysis of flooding in the basin, with the aim of spatially identifying the most vulnerable areas and the level of the surface water surface. To this end, hydrological modelling was used using geographic information systems and the HEC-GeoRAS tool, simulating scenarios for return periods of 10 and 25 years. The main results indicate that the areas with the highest exposure to flooding correspond to the most populated areas of the municipality. Similarly, most of the dry river is unable to channel the waters, which causes flooding on both banks of the river where water velocities range from 01 to 39 m/s, while the surface water varies between 1 and 3 meters in height in some areas of the watershed. That is why the identification of flood zones in the event of an extreme event is of great importance in territorial planning and risk management, especially in highly exposed municipalities in Nicaragua.