Suitability of open-access elevation models for micro-scale watershed planning

Watershed planning is a major issue in Turkey and other parts of the world. Surrounded by seawater on almost three-quarters of its international borders and by sheer mountains along the coastal regions and throughout the country, Turkey experiences a range of climatic changes, which constantly shape its topography. Recently, the occurrences of floods, landslides, and torrents have increased, forcing decision-makers to come up with solutions to manage and rehabilitate the upper watersheds in order to stop or limit the impact of disasters on downstream areas. Possible solutions should reduce flow coefficients, erosion, and sedimentation and increase reservoir capacities. It is expected that torrent volumes will decrease, drainage regimes on slopes will be better organized and adjusted, thawing snow will be better deposited and delayed, evapotranspiration will increase, surface runoffs will be delayed, and water regimes will be better managed, meaning that flood and torrent control will be achieved. For the reasons mentioned above, watershed parameters need to be firmly set. In the scope of this study, the elevation, slope acreage, and reservoir capacity of a small watershed, as extracted from open-access elevation models, were compared to a real-time kinematic (RTK) global positioning system (GPS)-generated point cloud and the resulting elevation model through various geospatial and analytical means. The Shuttle Radar Topography Mission (SRTM) C-band digital elevation model (DEM) (version 3) proved to be a satisfactory method in making residual, correlation, mean, and reservoir capacity comparisons. An L-band Advanced Land Observing Satellite (ALOS) phased-array-type synthetic aperture radar (PALSAR) and an X-band DLR_SRTM ASTER were slightly superior methods in terms of defining a greater number of slope categories than the other models. Finally, DLR_SRTM and SRTMv3 could match a greater number of slope façades than the other models. Seventeen years after its acquisition, SRTM and its derivatives have continued leading the topographic definition of the Earth.