Dam Impact Assessment

Fragmentation and flow regulation of global rivers systems

We developed a global scale framework to model the main impacts of dams, in particular their effect as a barrier and changes to the natural flow regime as a result of dam operations. For these impacts, we developed indicators of river connectivity and river regulation to assess the state of the world’s river basins today, but also estimate future impacts based on a comprehensive, global scale set of large hydropower projects that are planned in the near future. We combined state-of-the-art global scale hydrographic data (HydroSHEDS) and hydrological datasets (WaterGAP) with a river routing model (HydroROUT). Our results show that the majority of river basins are heavily to severely impacted from fragmentation effects and changes due to flow regulation, but on the other hand, several basins and tributaries of important rivers are relatively little affected, suggesting the possibility of further assessments as a conservation target. However, some of these areas are threatened by nearly 4000 hydroelectric dam schemes currently planned worldwide. In the worst-case scenario, if all of these dams were built, we can expect significant impacts on fragmentation and natural flow in several basins, particularly little impacted basins such as the Amazon, as well as numerous important rivers in South Asia, would be severely affected in the future.



We developed two new indicators: the River Regulation Index (RRI) and the River Connectivity Index (RCI). This figure shows a preliminary assessment of the combined effect of river regulation and fragmentation from current and future dams (future dams based on list of hydropower projects under construction).

Related Publications

Grill, G., Lehner, B., Lumsdon, A.E., MacDonald, G.K., Zarfl, C., Reidy Liermann, C. (2015): An index-based framework for assessing patterns and trends in river fragmentation and flow regulation by global dams at multiple scales. Environmental Research Letters 10 015001. doi:10.1088/1748-9326/10/1/015001 (Open Access)

Opperman, J., Grill, G. and Hartmann, J. (2015): The Power of Rivers – Finding balance between energy and conservation in hydropower development (Washington, DC: The Nature Conservancy). Download key findings herefull white paper here.

Grill, G., Ouellet Dallaire, C., Fluet-Chouinard, E., Sindorf, N., Lehner, B. (2014): Development of new indicators to evaluate river fragmentation and flow regulation at large scales: a case study for the Mekong River BasinEcological Indicators 45: 148-159doi: 10.1016/j.ecolind.2014.03.026

Lehner, B. & Grill, G. (2013): “Global river hydrography and network routing: baseline data and new approaches to study the world’s large river systems”. Hydrological Processes 27 (15), 2171-2186. doi: 10.1002/hyp.9740