Surface water resources assessment in scarcely gauged basins in the north of Spain

This paper describes a study developed to estimate available surface water resources in twelve basins in the north of Spain by means of numerical tools. These basins are characterized by their small surface area, short length, steep slope, and scarce hydrological gauging. The available information has conditioned the use of a lumped continuous simulation hydrological model. The HEC-HMS program with continuous soil moisture accounting (SMA) model was chosen. The model development is described in detail, focusing on the methodology used to fill the incomplete daily rainfall series and to establish the daily uniform precipitation over the sub-basins taking advantage of the results provided by a previous study with different time scale. Several techniques were used to calibrate and validate the hydrologic model, since few stream gauges were available. Comparison between observed flow data and results provided by simulation was in good agreement. The model application allowed assessment of the daily flow series at different main stream locations during a continuous time period up to thirty-three water years. These series have been used as input data for instream flows studies following the guidelines of the European Water Framework Directive. The processing of results allowed for analysis of the hydrological behaviour of the selected basins focusing in low water periods.