Why are the bottoms of many long gulfs covered with silt?

The bottoms of many long gulfs are typically covered with silt because these environments often feature limited water circulation and reduced wave energy, which allow fine-grained particles to settle out of the water column.1

In long gulfs, or those restricted by a sill, the isolation from the open ocean prevents the strong currents necessary to keep fine sediments in suspension or to erode the seafloor. Because silt is easily transported by moving water but settles readily in relatively still conditions, it accumulates across the bottom, even in shallow areas.12

Furthermore, the sediment composition in a gulf is often a direct reflection of the load transported by rivers entering the system. As river discharge enters the gulf, the velocity of the water diminishes, causing the suspended inorganic and organic particles to drop out of the water and accumulate on the floor. Only in areas where tidal currents are sufficiently strong can this siltation be prevented or reversed through bottom erosion.13