Finding Potential Sites for Small-Scale Hydro Power in Uganda: a ...

Sinks are a reoccurring problem when performing interpolations. ANUDEM with itsdrainage enforcement algorithm is designed to remove all sink points in the DEM.Despite the use of ANUDEM in our interpolation, there are sinks occurring in theoutput data. We believe this is due to that the rivers used as input data in theinterpolation were incorrectly digitalized. In order for ANUDEM to work properly, therivers must be digitalized downstream, that is that the every arc’s “from-node” in theriver layer must be at a higher elevation than the “to-node”. The interpolation strives toalways let the rivers flow in downstream direction, which sometimes forces the terrain tolift up in an unnatural way. The sinks tend to arise along the sides of these elevated areas.The area containing sinks in Figure 5.4 is an example of this, where the valley bottomshould be a flat area but has been elevated to a low ridge where the river flows. Weassumed that the watercourse data we used was digitized in a correct way, but whendetecting the sinks we realized that this was not the case.6.3 AlgorithmThe algorithm produced a generally satisfying result, but we have discovered someoccurrence of noise, as can be seen in Figure 6.2. The noise consists of one up to fiveconnecting pixels where the accumulated height difference reaches only a few meters,instead of the criteria of 20 meters.Figure 6.2 Showing an example of the inexplicableoccurrence of noise in the algorithm output. Grey linesrepresent contours and red lines the potential sites.Throughout the development phase of the algorithm we used a smaller training area,which produced a noise free result, but when the algorithm was completed and we usedthe whole study area as input data, we discovered the noise. After weeks of searching foran explanation with support from competent personnel, the phenomenon is still60