Sediment Dynamics in Alluvial Rivers Used as a Resource for Land-Building.

摘要

There is a dire need to use sediment from alluvial rivers to sustain and create new marsh land and sustain barrier islands and ridges. Coastal Louisiana is a prime example where wetland loss rates are one of the highest nationwide. This study focuses on investigating the sediment dynamics of the Lower Mississippi River, specifically the temporal and spatial variability of the sediment concentration as well as the sediment size characteristics. The objectives of this study are: to analyze and quantify the impact of diversion design parameters on the efficiency of sediment capture, to analyze the hydrodynamic and morphological patterns at sand bar borrow areas and to quantify the infill spatial and temporal patterns of these dredged pits. The investigation was performed using a morphodynamic numerical tool (Delft3D). The Louisiana 2012 State Master Plan identified two viable mechanisms to build land: sediment diversions and dedicated dredging. The morphodynamic model was parameterized and validated using historical and recent field observations. The model was used to examine three different parameters hypothesized as key design parameters that govern the sediment capture efficiency of sediment diversions: the alignment angle, invert elevation and diversion size. Diverted sediment loads and the sediment concentration ratio were used to assess the efficiency achieved to the corresponding change in design. Implications of choosing the designs on construction and efficiency was discussed.;The model was also used to investigate the riverside morphological response to a number of parameters for dredging lateral sand bars. Detailed analyses were carried out for the hydrodynamics at the dredge pit and its implications on the morphological development. Sensitivity analysis of hydrodynamic and sediment transport parameters examined the morphological response within the dredge pit. Findings put emphasis on data collection requirements and helped form future recommendations for predictive modeling of dredged sandbar infill. The study is concluded with an economic assessment for the impact of land-building mechanisms on the riverside in correlation to waterborne economy.