GIS MULTITEMPORAL ANALYSIS OF REMOTE SENSING IMAGES TO ASSESS THE SILTING OF ANTHROPOGENIC DAM LAKES IN THE OUTER SUBCARPATHIAN AREA. CASE STUDY: PUCIOASA ACCUMULATION LAKE, ROMANIA

Abstract

On Romania's territory, after the major floods that took place during the 70s, the hydrotechnical setup of the large rivers that drain the peri-Carpathian areas was made. The purpose of building these anthropogenic dam lakes is complex, given that extreme hydrological phenomena occurred in late spring and early summer, caused by a significant rainwater supply (about 70%), the difference being made up by the underground supply. Such a hydrotechnical setup was made in the Subcarpathian areas, on large rivers, to mitigate flood waves, but also to create water resources to supply local communities. The main problem facing these lakes is the massive silting due on the one hand to the geological and geomorphological characteristics of the Subcarpathians and, on the other hand, to the high degree of anthropization. The Subcarpathians are, from a geological point of view, made up of friable deposits (marls, clays, marl-clays, gypsums, conglomerates), which trigger a series of geomorphological processes of slope erosion (areal streaming, ravine creation, runoffs, torrential rainfall, and landslides), all of which are involved in the hydrological drainage regime. The Subcarpathians also make up a geographical area with a high density of population and, implicitly, of anthropogenic activities, which under certain conditions favour the erosion and degradation of land. These factors ensure that the solid flow recorded on the Subcarpathian Rivers is between 5-25 million tons/ha per annum. All this leads to the intense silting of anthropogenic lakes, which causes the volume of water stored in the tank to sometimes decrease to 1/3 of its initial volume. Under these conditions, in the extremity of basins, lacustrine plains were formed, and within the dam area, the pelitic sedimentary deposits exceeded 7-10 m in thickness. The aim of this study is to perform a multitemporal analysis of lake silting in the Subcarpathian area by using GIS and integrating the suite of bathymetric elevations and the series of satellite images existing from the time of the lake's construction to present-day.