Taking advantage of a new hydraulic infrastructure to study the sediment yield in a small basin of central Spain

Abstract

Predicting the sediment yield at a catchment scale is one of the main challenges regarding fluvial geomorphology, however, it involves some difficulties. In this study, we have taken advantage of the construction of a new hydraulic infrastructure to study the sediment yield in its drainage basin between 2007 and 2010. This infrastructure is a small dam constructed in the riverine zone of the Entrepeñas Reservoir (upper Tagus catchment, central Spain), which generates a small water body, the Pareja Limno-reservoir (0.94 hm3), with a drainage area of 88 km2. It was built to mitigate the environmental and socioeconomic impacts of the construction and use of the Entrepeñas Reservoir, including the “arid band” phenomenon. Sediment yield was studied taking three sediment cores in the shallowest section, the central part and the deepest zone of the limno-reservoir. The layer of surface sediment was analized and a decreasing thickness of sediment towards the deepest zone of the limno-reservoir was observed. After assigning an area of the limno-reservoir to each core record, estimated annual sedimentation rate was 2032 Mg year-1, which supposes an annual storage capacity loss around 0.3% and a specific sediment yield in the drainage basin around 0.23 Mg ha-1 year-1. Comparing this value with previous soil loss studies performed in the basin, sediment delivery ratio in the basin varies from 2.2% to 3.8%. Both sediment yield and sediment delivery ratio showed low values for the Mediterranean context. The characteristics of the basin (small area, elongated shape with one main river channel, abundant vegetation), the absence of other erosive processes than rill and interrill erosion and the lower aggressiveness of rainfall in the center of the Iberian Peninsula may explain these results. The presence of the National Road N-204 surrounding the limno-reservoir may play a role in the low sediment delivery, especially from the adjoining hillslopes.

Keywords

• catchment sediment yield, limno-reservoir, mediterranean, reservoir siltation, sediment delivery ratio