The Atchafalaya became a free-flowing river system in the mid-nineteenth century. It progressively increased its diversion of waters from the Mississippi until, by the mid-twentieth century, it threatened to capture the total flow of the main river. The installation of control structures has, temporarily at least, prevented total diversion, limiting the flows to 30% of the Mississippi; water discharge and sediment transport into the Atchafalaya have led to deposition throughout the basin. A major system of lakes and bayous has become largely filled with deltaic sands and layered silts, so that the waters currently drain almost directly into the Atchafalaya Bay. The natural outlet and one artificially created outlet each carry waters from the system. As a result of major flooding in 1973, sediment was flushed from the Atchafalaya Basin and began the sub-aerial emergence of deltas, which had been slowly building below the bay water surface since the 1950s. The two deltas have provided, parallel growth one largely in natural form, and the other substantially modified by the dredging needed to maintain a navigable routeway to Morgan City and the interior of the basin. The sub-aerial deltas initially grew rapidly, a process apparently slowing, but the sediment transported to the depositional areas has not diminished, rather the area of deposition within the receptor basin is increasing, so that apparent growth inevitably slows. By 1994 the two deltas occupied an area of more than 153 km2 above the −0.6 m measuring datum, created in approximately 30 years. In each
Figures & Tables
There is an increasing trend in the Earth sciences towards the integration of many subdisciplines. The sedimendatry basin, is a fundamental focal point of many studies, which as a consequence often neglects the complimentary drainage basin or catchment. Sedimentary basins provide a record of Earth history, reflecting the geographical, lithological, oceanographic and ecological development through the rock record. Drainage basins in comparison record ephemeral landscape evolution, where topography is eroded and provides the flux of sediment to the basin. The basin fill reflects the sediment flux from the hinterland and provides evidence of the dynamic geomorphic processes. In context the drainage system and sedimentary basin can be regarded as a ‘production line’ with sedimentary record giving valuable insight into long-term landscape evolution and geomorphological processes illuminating the evolution of sedimentary basins.
This volume assesses the current position of understanding sediment supply to basins with the integration of the many sub-disciplines in the Earth sciences. It documents a mix of hinterland and sedimentary basin studies with a gradation from orogenic belts to the deep marine. The authors represent a wide spectrum of Earth scientist, with leaders in the science providing review papers and new-directive papers in their field of specialization.