Morphometric parameters of Santa Cruz and Umari Reservoirs, Rio Grande do Norte semiarid, Brazil

Abstract

This study aimed to describe the morphology of Santa Cruz and Umari reservoirs, in the semi-arid region of Rio Grande do Norte. The survey was conducted in December 2012, with aid of an echo-sounder coupled to DGPS. The navigation went in lines perpendicular to the coast of the reservoirs. The bathymetry in Santa Cruz was based on a total of 35,971 pairs of points and in Umari, 26,575. The Santa Cruz reservoir had 15,984 m in length, 13 m average depth and maximum depth of 38 m. Umari presented for these same parameters 14,227 m, 8 m and 28 m respectively. The total water volume recorded for Santa Cruz was 295,858,761 m³ and for Umari, 114,866,034 m³. Although with lower volume, Umari showed greater perimeter 110,887 m. The hipsometric curves show that in Umari there is an increased volume of water at low depths, facilitating the entry of light and providing greater support to the biological productivity, compared with Santa Cruz. The highest values of Fetch and the smallest depth were found in Umari, which possibly leads to increased sediment resuspension in this reservoir, and then, causing higher loads of nutrients. A higher proportion of coastline in Umari favors the colonization of the margins by plant communities. The reservoirs, in particular Umari, showed low relative depths, a possible factor that increases thermal instability and hence greater mixing of the water masses, facilitated by the wind.