A methodology for the pre-selection of suitable sites for surface and underground small dams in arid areas: A case study in the region of Kidal, Mali

A cost-effective project design in developing countries requires that a detailed preliminary territorial analysis is conducted in order to select the optimal sites for intervention and adequately plan the fieldwork. In most cases only large-scale cartography is available, which does not provide adequate information on environmental and morphological parameters. For this purpose, remote sensing techniques can supply large amount of data with high spatial and temporal resolution, and are therefore a very useful mapping tool especially in areas where very little information is available such as most developing countries. In this work, we present a methodology for the assessment of the suitability of sites for the installation of small dams (barrages), a technology widely used for water harvesting in arid climates. The selection criteria are defined both in a qualitative and quantitative way, and are based on a territorial analysis using satellite data (images, digital elevation models) and hydrological and climatological information that are easily and freely available. Qualitative criteria imply the identification of suitable valleys, wadi beds and rock formations, based on visual interpretation of satellite images and large-scale available cartography; other qualitative selection criteria concern the distance from settlements and infrastructures, faults localisation. Quantitative criteria are expressed in terms of indexes that synthesise the effectiveness and feasibility of the possible interventions: the alluvial plan index (α), calculated as a benefit/cost ratio in terms of volume of water that can be stored versus volume of the dam; the hydrologic index (P), based on the analysis of the contributing watersheds to each site and the pluviometric patterns in the area; the combined coefficient (β), concern both morphologic and hydrologic aspects; the soil water holding capacity, estimated from the analysis of vegetation patterns using satellite indices. The methodology, applied to the region of Kidal in Mali, allowed the individuation of 66 sites, whose only 17 sites passed the proposed selection criteria. The 17 sites are classified in ground of values of β coefficient. The results served to organize the subsequent field surveys, which was conducted on the three sites that had obtained the highest scores of β, thus considerably reducing the time and cost of the survey. In one of this three sites, most effective considered, a project design of small dam is elaborated. © 2007 Elsevier Ltd. All rights reserved.