The USGS Water Science School
In this picture, sediment-laden water from a inflow tributary stream is entering a much clearer river, the Chattahoochee River in Atlanta, Georgia, USA. Just like all rivers, the Chattahoochee River has a main stem with tributaries coming into it at various points along its path. These tributaries contribute water to the main-stem flow. The watersheds of the tributaries may drain landscape that is very different in nature, and espeically in land use, than the basin of the main-stem river, and thus, water from tributaries can alter the water characteristics and water quality of the main river as it flows towards the oceans. As this picture shows, a tributary can contribute large amounts of sediment to a larger river.
I don't know the exact circumstances of the sediment-heavy inflow from this tributary into the Chattahoochee River here, but this could be a case of suburban construction occuring in the watershed surrounding the tributary along with occurrence of a large rainstorm. If proper sediment-trapping systems were not used, then rainfall runoff could wash large amounts of sediment into the tributary, where it eventually will flow into the main stem of the Chattahoochee River. These events could occur many miles away and affect the water quality far downstream.
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