Specific sediment yield evaluation in the drainage basin of the Puente Alta reservoir (Segovia) through direct and indirect methods

Abstract

Reservoirs act as sediment stores, so that a survey of the deposits accumulated within them is a common approach to evaluate the sediment yield of their drainage basins. Such is the case with the Puente Alta reservoir (Guadarrama Mountains, Segovia Province, Spain), described in this paper. Repair work conducted on the dam face in the summer of 1995 allowed for an analysis of the reservoir’s sediment, which yielded and estimate of the rate of accumulation that had occurred over the forty years since the reservoir’s establishment in 1955. This information was used to directly calculate rates of sediment yield in its drainage basin, and also to validate an empirical method for obtaining sediment yield which blends the Sediment Delivery Ratio concept with the Universal Soil Loss Equation. In order to achieve this second aim, a Geographical Information System was built with each of these factors needed for the evaluation; eventually these were integrated in the Idrisi 32 software. In both cases, the resulting values for specific sediment yield were very close to 70 t/km2 · year, which could be considered low in comparison with values obtained from other Spanish drainage basins in which similar evaluations have been carried out. On the other hand, the results of the comparison between both methods show a very good correlation (less than 3 % deviation), which could be interpreted as support for the validity of this empirical procedure in physiographic settings similar to the study area.