The Newaygo Dam on the Muskegon River was removed before spring run-off to limit the negative impact of stored sediments flowing downstream. Examples from other rivers can also help inform decision making. Since this storm hit much later in the growing season, the aquatic vegetation was largely left intact after the storm, in contrast to the aftermath following Hurricane Agnes when vegetation was still young and less resilient (Brainard 2011). The Chesapeake was inundated with sediment, and the water remained turbid until November. In 2011, Tropical Storm Lee hit in September. In the years following Agnes, oysters and underwater grasses died off (67% decline in underwater vegetation) (Brainard 2011). After Hurricane Agnes in June 1972, ~ 30 million tons of high nutrient sediment flushed into the Bay settling out in thick deposits. The Susquehanna releases ~1.5 million tons of sediment in a normal year. This means that the stream flow from the Conowingo generally has low turbidity and suspended sediment with short periods of very high suspended sediment during storm events, shocking the downstream ecosystems temporarily. During large storm events, the “pollution gates” are opened and suspended sediment flows out of the reservoir downstream to the Chesapeake Bay. During periods of low flow between large storms, sediments accumulate behind the dam. About 174 million tons of sediment is trapped in the Conowingo impoundment at any given time with about 3 million tons fluctuating in and out of the system every year. The Conowingo Dam functions as a “pollution gate” (LSWRA.FAQ, 2015), resulting in the buildup of sediment over time to a current state of static equilibrium.
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