Challenges of Reservoir Sedimentation and Public Policy: What the sedimentary record can teach us and how to communicate the findings to the public and stakeholders.

Abstract

Dams are historically essential for supplying drinking water, energy, and flood mitigation on the global, regional, and local levels and therefore are useful, however, they have a finite life span. Sedimentation rates in reservoirs around the world appear to be increasing with climate change. Increased sedimentation limits the dams from being used effectively as designed. The loss of efficiency causes a decrease in water storage and floodplain levels rising leading to higher needs for flood mitigation. Governments have reacted differently to the problems, deploying a variety of methods. In this study, we use one of the 173 documented dams in Otsego County, NY found in the City of Oneonta's watershed. The focus is on the sustainability of the city drinking water source, sedimentation rates, and communicating the problems and results to the stakeholders. While the reservoir was draining sediment cores were collected using manual and Vibracors techniques, and sediment profiling. Coring produced 101 cm of a useable section which bottomed out in a coarse gravel layer while the Vibrasors had a recovery rate of 68%. These cores were augmented by a 1.5 m sediment core collected from a stream bank downcutting through the lake sediments. The cores document a sequence of alternating layers of clay, silty clay, silty clay rich in organics, and gravel. The sequence of lake sediments is interpreted to show sedimentation is driven by high precipitation, and snow melt flows events during fall and spring. Also, organics appear to be concentrated towards the top of most sections, possibly showing an increase in organics during flooding events. The local dams are insignificant compared to dams worldwide but may yet pose significant problems locally and downstream. Finally, we summarize lessons learned from current and past research so the information can be incorporated into a more informed decision-making process and effectively communicated to the public and stakeholders.