The Influence of Soil Characteristics in Low Flows Regionalization

Vezza Vezza

doi:10.3844/ajessp.2009.536.546

Abstract

Problem statement: For the purpose of low flows regionalization, relevant issue for water resources management like environmental flows requirements definition, this study focused on the controls on the seasonal and spatial variability of q95 (i.e., the specific discharge that was exceeded on 95% of all the time) with particular reference to the role of soil characteristics, that, like soil infiltration rate, aquifers recharge, evapotranspiration and topography, usually play a relevant role in low flows seasonality and occurrence within a river. Approach: Piemonte and Valle d'Aosta Regions (North-Western Italy) were the investigated study area (30,027 km2) where 41 catchments were analyzed with the aim of robust regression models enabling the transfer of hydrological information from gauged to un-gauged sites. Results: The regionalization method consisted of multiple regression models between low flows and catchment characteristics. Twenty-five catchment descriptors were used, checking their relative influence with the multi-regressive procedure and a special attention was devoted to the selection of significant soil characteristics in the regionalization process. Seasonality indices were used to classify catchments into two sub-regions and separate multiple regressions was performed by checking the prediction performance with cross-validation. Also a global regression was fitted out but it yielded a lower performance. In the study domain land use, topography and Thornthwaite moisture index demonstrated to be the most significant variables in order to represent relationships between catchment soil characteristics and low flows regime. Conclusion/Recommendations: Results obtained in this study were comparable with other regionalization studies carried out in Austria and Switzerland. The interpretation of the identified regression models provided, at local scale, new tools for water management and environmental flows requirements and, from a wider point of view, useful insights into the general comprehension of low flows processes.

Highlights

An accurate estimate of low flows is needed in many branches of water resources management, including environmental flows requirements
For each sub-region this method relates specific low flows indices (e.g., q95 that is the specific discharge that is exceeded on 95% of all the time) to catchment characteristics through linear or non-linear relationships
Smakhtin[9] and Demuth and Young[2] give extensive lists of references for regionalizing low flows. In most of these methods, the study domain is divided into sub-regions in which the low flows behavior is assumed to be homogeneous

Summary

Introduction

An accurate estimate of low flows is needed in many branches of water resources management, including environmental flows requirements. The literature has many references to techniques for estimating low flows regimes at un-gauged sites. Smakhtin[9] and Demuth and Young[2] give extensive lists of references for regionalizing low flows. In most of these methods, the study domain is divided into sub-regions in which the low flows behavior is assumed to be homogeneous. The identification of these regions is performed by grouping the gauged sites according to a classification criterion and checking the performance of prediction of low flows with crossvalidation.

Objectives

Results

Conclusion