Dirk Pretorius from SMC Synergy assisted officials from the United Nations Development Programme (UNDP) to evaluate the use of low cost sonar equipment and existing digital terrain data in a GIS environment (Global Mapper) to estimate the storage capacity of the Macubeni dam in the Eastern Cape. The excellent DEM processing and analysis tools of Global Mapper again proved to be indispensable. Although the outcomes of the research were very promising it was highlighted that more accurate results can be obtained by incorporating a more recent DEM of the dam area - the DEM can be generated from LiDAR as well as drone generated point cloud data. It would be ideal to capture this information at the date of the dam sonar survey. Other means to create an improved DEM can also be investigated (e.g. WorldDEM).