Formatted Title:

Sedimentation Impacts on Dam Rehabilitation and Retrofit Strategies

Background/Objectives:

Aging dams and water infrastructure pose both challenges and opportunities for the hydropower industry. In the last decade, retrofits of existing dams have accounted for roughly 75% (505 MW) of the new hydropower capacity in the US. The assessment of potential for adding generation to existing nonpowered dams has typically been limited to physical or technical potential across inventories of dams, estimating a total nominal capacity of 4.1 GW. However, actual feasibility and development strategies require deeper understanding of the limitations and constraints associated with reservoir storage and sediment accumulation. Data describing reservoir storage and accumulation rates are collected and compiled at varying levels of detail from individual facility operators to state and federal agencies. Given the potential to increase cost and impact project timelines, understanding the scope of the sediment mitigation required at these dams with high retrofit/rehabilitation potential is critical.

Approach/Activities:

A review of licensing documents, historical reservoir survey reports, and time-lapsed bathymetric/reservoir morphology data are used to quantify the range and magnitude of sedimentation problems at dams that have been recently retrofit or are currently in the process of adding generation capabilities. Additionally, we analyze land use change and soil erosion measures at the watershed scale to relate upstream development and management activities to observed sedimentation and storage capacity losses.

Results/Lessons Learned:

This review and analysis summarizes sedimentation and storage considerations at multiple scales (facility- and watershed-level) and presents the findings alongside the broader context of nationwide sedimentation and infrastructure inventories. There is a large geographic variation in sedimentation challenges that are documented at these dams that have high technical potential for retrofit. Existing hydropower dams generally have lower rates of annual storage capacity loss than other dams included in high-level assessments of generation potential. We highlight the characteristics of reservoir facilities and their watersheds that can be related to specific retrofitting or rehabilitation decisions. Additionally, we identify cases with exemplary successful sediment mitigation and nonpower benefits (e.g., habitat or recreational improvements). Our findings underscore the importance of historical and ongoing reservoir sedimentation as a key design consideration in dam retrofit, rehabilitation, and upgrade planning.

Jiyong Lee

Affiliation

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Sedimentation Impacts on Dam Rehabilitation and Retrofit Strategies