Abstract
Abstract. In many continental databases representing rivers across Africa, information on rivers characteristics (length, width, intermittent or perennial) is often incomplete, and small streams are largely underrepresented. Fortunately, the use of topographic information from digital elevation models (DEMs) provides an opportunity to have more detailed information on rivers, particularly small streams in broad areas. A common approach to extract streams from DEM is to consider as a stream all DEM cells that drain at least a certain upstream surface, commonly known as the minimum contributing area (Amin). This parameter (Amin) is generally defined uniformly over large areas and this independently of the very variable climate and landscape conditions so that the generated streams have a rather uniform spatial distribution. To address this issue, using a 3′′ (approx. 90 m × 90 m) DEM of Burkina Faso, the relationship between Amin and the observed drainage density (Ddobs) was established with satisfactory performance (r2=0.86). In ongoing work, the functional relationship between the observed drainage densities (Ddobs) and environmental variables (lithology, climate, geology, vegetation cover) should allow for the establishment of the relationships between Amin and the environmental variables. This relationship allows for spatially variable Amin values depending on landscape characteristics. Before extracting river networks in Africa, the next step will be to validate or update these relationships in several countries.
Highlights
The accurate representation of river network recently, serves as a decision aid for land managers for efficient monitoring and exploitation of the water resource (Heine et al, 2004; Ouellet Dallaire et al, 2019)
Based on the methodology used by Schneider et al (2017), our objective is to use the accuracy of local information collected from national geographic institutes and widely available climatic, landscape, digital elevation models (DEMs) information to establish relationships between the minimum contributing area (Amin) and environmental variables to constitute a spatial model
The DEM used in this study was extracted from the HydroSHEDS database (Lehner et al, 2008), which is the most widely used database currently for hydrological applications at a resolution of 3, i.e. the smallest resolution proposed by the database
Summary
The accurate representation of river network recently, serves as a decision aid for land managers for efficient monitoring and exploitation of the water resource (Heine et al, 2004; Ouellet Dallaire et al, 2019). In many continental databases representing rivers across Africa, information on river’s characteristics is often incomplete, and small streams are largely underrepresented (Lehner et al, 2008). National hydrographic databases contain reliable hydrographic information in this sense, either localized or nationwide. Accessibility to these national hydrographic databases remains difficult in Africa because of the cost required and the reluctance of some countries to share this information. The exploitation of topographic information from digital elevation models (DEM) provides a major opportunity to obtain detailed river descriptions over large areas (Liu et al, 2005). With the aid of Geographic Information Systems (GIS), river extraction usually involves defining a threshold river pixel number (Np) which is a value from which a DEM pixel is considered a river.
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