Historic Trends in the Sediment Flow Regime of the Mississippi River

Abstract

Prior to cultural development in the Mississippi River Basin, the main stem was a heavy sediment carrier due to the character of the climate and soils in the basin. The placement of flood control structures and other channel improvement features and the implementation of improved land management practices have significantly changed the suspended‐sediment flow regime of the main stem. The estimated annual sediment yield of the basin is 900 million (817 million metric) tons. That portion of the yield passing into the Gulf of Mexico, as monitored at suspended‐sediment sample collection stations near the mouths of the Mississippi and Atchafalaya rivers, totaled 434 million (394 million metric) tons prior to 1963; however, this value has now declined to 225 million (204 million metric) tons. Long‐term trends in the bed material gradation of the Lower Mississippi downstream from the mouth of the Arkansas River have remained relatively constant; however, from Donaldsonville, Louisiana, downstream to Head of Passes, there has been a pronounced shift from the sand to silt fraction.