A sediment forebay is a pre-treatment structure designed to slow velocities of incoming stormwater runoff. When velocities slow down, sediment isn't able to remain in suspension and collects in the forebay rather than directly flow into a river or lake. After storm events, maintenance crews can vacuum or sweep the sediment out of the forebay.
If suspended sediments from stormwater are not deposited in a forebay and make it to a river or pond, they decrease the clarity of the water, which obstructs sunlight and limits the ability of aquatic plants to create there own food, reduces available oxygen levels, and raises water temperature.
This particular forebay in Roger Williams Park (Site 1F) located across the street from The Boathouse, is made of permeable interlocking concrete pavers. The small gaps between the pave stones allow some stormwater to infiltrate into the soils where pollutants can be removed.