Study of three subsurface hydrologic systems based on spectral and cross-spectral analysis of time series

Estimating the major hydrological processes and their characteristic time s cale is important when studying the hydrology of a catchment. However, in g eneral, only limited data are available, namely climatic data and stream di scharge. In this paper, the catchment is viewed as a system that converts t he rainfall to the stream discharge through a transfer function (TF). The o bserved TF calculated hom the rainfall and the specific stream discharge de pends on the hydrological processes operating in the catchment, By comparin g the observed TF to simulated TF, these processes and their time scale are identified. The simulated TF are developed from the Dupuit and linear repr esentations of the aquifer. The identification of the TF is based on the st ochastic method using a spectral representation of the rainfall and stream- discharge time series. The novelty of this work is to extend the stochastic approach to the one-order catchment hydrology and to develop a model, whic h takes into consideration both the aquifer discharge and the rapid flows. The method was applied to three first-order agricultural catchments. For ea ch site, the theoretical results are in accordance with reality. These resu lts show that the stream discharge is dominated by the aquifer flow, the fa st transfer accounting for 3-8% of the total discharge depending on the cat chment. The stochastic approach based on spectral analysis of the temporal variation of global observations appears useful to extract significant info rmation about dominant processes occurring in the catchment and their chara cteristic time scale. (C) 1999 Elsevier Science B.V. All rights reserved.