Several posts here have been devoted to talking about dams, the complex ways in which they change the surface processes of our planet, human relationships with them, and the controversies surrounding their construction and operation. As we read of the approval to construct the world’s third-largest dam in Brazil, the profound problems now emerging with China’s Three Gorges dam, and transnational issues around a planned series of dams on the Mekong River, I have, thanks to Science Daily, just come across an extraordinary resource. The Digital Water Atlas is one of those inspiring international collaborative projects, the results of which are available for all to access:
The Digital Water Atlas is an activity of the Global Water System Project (GWSP). The Atlas is implemented at the GWSP International Project Office (IPO) that is funded by the German Federal Ministry of Education and Research (BMBF) and the Ministry of Innovation, Science, Research and Technology of the State of North Rhine-Westphalia (NRW). The maps and datasets included in the Atlas are in-kind contributions from GWSP partners (see credits for more details). We would like to thank our funders and our partners, especially the Center for Development Research (ZEF ) at the University of Bonn as our host organisation, for their kind support.
Just click the “credits” link to see how truly international this project is. Browse the selection of dozens of maps and you will be fascinated. The data includes not only the global data base of dams (the map shown at the head of this post and the technical documentation available here - click on the image for a higher resolution), but a remarkable range of maps and data that document water issues on a global scale: “The purpose and intent of the ‘Digital Water Atlas’ is to describe the basic elements of the Global Water System, the interlinkages of the elements and changes in the state of the Global Water System by creating a consistent set of annotated maps. The project will especially promote the collection, analysis and consideration of social science data on the global basis.”
There is no need for me to say more, other than encouraging you to browse – oh, and, of course, showing this map: “Sediment Trapping by Large Dams.” The description is as follows:
A total of 236 regulated basins with 633 large reservoirs (> 0.5 km3 maximum storage capacity), which collectively represent about 70% of registered impoundment storage volume was used to estimate basinwide relative loss of suspended sediment destined for the world's oceans. For the purposes of display, the basins include both discharging and non-discharging portions of the land mass. A total of approximately 25-30% of pre-disturbance sediment flux is sequestered by modern impoundments, most built since 1950.
The residence time of water in large reservoirs and subsequent sediment trapping efficiencies is calculated as a measure of the impact of these man-made structures on the characteristics of river flow and sediment discharge to the ocean. Estimations of water removed from basins as diversions (i.e., interbasin transfers and consumptive use) also provide information on the impacts of diversions on river flow and sediment transport.
Note that this massive disruption to the global sediment budget reflects only suspended sediment – the bed load of rivers is challenging to measure (but also massive).
Dam builders and busters would do well to reflect on the data in the Digital Water Atlas.
[Maps reproduced courtesy of the "GWSP Digital Water Atlas (2008). Available online at http://atlas.gwsp.org."]