Impacto do desassoreamento nos recursos hídricos de reservatório de importância socioturística em Fernandópolis-SP

Abstract

Desilting is an important work in reservoir’s recovery, however, even if temporary, it disturbs the environment and can become a process of potential pollution in water resources. The objective was to evaluate the silt excavation operation impact in an important sociotouristic reservoir in Fernandópolis-SP. For this purpose, qualitative water variables were monitored, and the evolution of the service was accompanied. Completely randomized experimental design in 2 x 3 x 4 factorial scheme was used, and the main effects were runoff periods (with and without runoff), the level of second were excavation periods (before, during and after) and the level of third were monitoring points (points upstream E1, E2 and E3 and point S downstream, in relation to the reservoir). 100 water samples were collected, in a total of 25 biweekly/monthly sampling campaigns, and 13 aerial drone surveys were carried out between July 2020 and March 2022. To evaluate the qualitative water variables, analysis of variance was performed for the analyzed effects, followed by the mean comparison test. To evaluate the excavation progress effect, the Pearson correlation test was performed, followed by regression analysis. It was observed that the dynamics of sediment removal presented two distinct periods, which terrain instability, associated with precipitated rainfall, reduced the operational yield by 59.6%. During the desilting work, there was negative impact in the ammonium and ammonia concentration, increasing the averages by 154.1% and 151.9%, respectively. The excavation dynamics correlated only with water conductivity, resulting in an expected average increment of 1 µScm-1 for every 175 m3 removed. Considering those results and the reservoir historical, landscape, cultural and tourist importance, the desilting operation was adequate. However, it is necessary to carry out restoration and maintenance works in the reservoir contribution basin to minimize future problems with siltation.