A Global Challenge
International Water Power & Dam Construction
12 October, 2017
Photo courtesy of Getty
College of Environmental Design (CED) Professor of Landscape Architecture and Environmental Planning Matt Kondolf recently co-authored a research paper with visiting scholar Rafael Schmitt on geomorphic impacts of hydropower dams, dam sediment trapping, network scale planning of hydropower cascades, geomorphology and sediment transport in many large rivers (mainly in Southeast Asia). Titled “A Global Challenge,” the research is a product of Riverlab, a research group based at CED and led by Kondolf, which strives to inform project planning and water resources use with a catchment-scale perspective on natural processes.
According to the paper, since 2000 reservoir storage space per capita has been in consistent decline. In the current state of climate change, reservoir storage is of the utmost importance. The diminished storage is due not only to rising populations but is also because storage space in existing projects is continuously lost to sedimentation. Thus, for the purpose of this research, reservoir storage was considered a nonrenewable, scarce, and finite resource.
Sedimentation in reservoir storage is problematic for a number of reasons. Firstly, sedimentation requires major, costly maintenance and when the sediment is not maintained, the buildup can compromise safety. Sediment can also lead to the creation of delta-like deposits which reduce the operational capacity of the reservoir storage leading to diminished energy returns and flood buffer. Lastly, sediment trapping in dams has adverse effects for downstream rivers. Riverbeds, banks, bars, and deltas are all formed through the natural flow of sediment and when that flow is disrupted by dams, ecosystems, and infrastructures within the rivers can be degraded.
To quantify sediment trapping on the scale of the entire river, Kondolf and Schmitt suggest employing a network-scale sediment assessment known as CASCADE (CAtchment Sediment Connectivity And DElivery). CASCADE is a notable model as it provides a “flexible, numerically efficient, and spatially distributed screening tool for modeling sediment connectivity and transport in large river networks.”
The researchers applied the CASCADE model to a trans-boundary river in Southeast Asia. The Se San, Se Kong, and Sre Pok Rivers join before flowing into the Mekong River, thus forming one of the river’s largest tributary basins. The construction of 41 reservoirs in the basin created concerns over the impact of sediment trapping on Mekong’s sediment budget.
With the model, Kondolf and Schmitt discovered that most of the total sand load likely originates from the Sre Pok River. They also used the model to determine which reservoirs pose the greatest threats of losing significant amounts of storage over a 40-year period. Finally, the researchers used the basin as a case study to determine how different dam sites can result in variable sediment trapping, despite yielding similar economic benefits.
The case study of the basin supported new modeling approaches and demonstrated that there is a potential to reduce economic and ecological impacts derived from sediment trapping. Kondolf and Schmitt have future aspirations to carry out sediment modeling on a more multi-faceted network scale so as to minimize dam sediment trapping, preserve storage space, and reduce downstream impacts.
To read Kondolf and Schmitt’s full research paper, click here.