This spot is located in the middle of Lake Keowee and allows Duke power to control the water flow between Lake Keowee and the Keowee River that leads into Lake Hartwell. Below is and explanation gleened from Duke’s Web site as to how the Spillway works.
Dam & Lake Level Basics Our lakes provide benefits that are balanced among the individual needs of several communities, including:

Municipal water supplies
Industrial and power plant water uses
Daily release requirements and drought mitigation
Wildlife habitat and aquatic environments
Recreation (fishing, boating, skiing, docks, etc.)
Each lake directly affects other lakes on the Catawba River system. To manage the level of one lake, Duke Energy must examine the levels and requirements at each of the other lakes in the system and respond accordingly.

We move water downstream using the following methods:

Hydro generation (through the turbines)
Hydro generating units serve as Duke Energy’s primary means of moving water. Depending on the design, our generating units can usually pass two to four times the average inflow to a lake or reservoir. When heavy rain inflows exceed the normal hydro unit discharge capabilities, alternate methods must be available to pass the excess.

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