Numerical Modeling Of Mississippi River Sediment Transport Courses In The Gulf Of Mexico

The deltaic coast of the Mississippi River,which is the largest river in USA,and the fourth longest river in the world,has been undergoing severe erosion,for example,at the rate of 62km2/a from 1932 to 2010 due to(a)regulation works such as reservoirs in the upper basin,river dikes,and soil conservation,cut-off of the distributaries,dredging of the coastal canals,(b)sea level rising,deltaic subsidence,wind,waves,and storms.The coast also is a risky area where,for example,1600 people died and property loss of100 billions USD was caused due to a storm in 2005.Besides,the sediment of coarse particles released from the river mouth will accumulate at the shelf foreset until a critical condition,beyond which the deposits will rush down the foreset in the forms of debris current or slide,forming a new submerged sediment-transport-intensive river network on the deep flat floor of the gulf.The new type of sediment transport,also called mass transport,will damage cables,pipelines,oil-drilling rigs and ecological environments along its course.There are two fundamental issues among the American researchers in the field coastal protection and restoration.(1)About which of the ocean driving factors is the most significant driving flow and sediment transport in the Gulf of Mexico(GoM),there are four answers,(a)the southeast wind,which are thought to drive the flow and sediment transport in the direction of west along the northern coast of GoM,with divergence of sediment transport rate leading to deposition or erosion,(b)sea level rising,which is thought to erode the coast due to the ravinement effect,(c)storms,which are thought to erode the coast due to surging effect and waves impact,and(d)combined winds and storms.(2)So far there is no tool forecast available for a possible course the mass transportwould take once it starts to move.The thesis is focused on the modelings of the traveling courses of both the fine sediment sediment released from the passes orientating westward,southward and east and the courses of the mass transport in the deep water of GoM,using Mike21.1.The modeling of the traveling course of both the fine sediment sediment released from the passes orientating west,south and east.The results of the modeling of the hydrodynamics and fine sediment in the area covering GoM,and partial Caribbean Sea and western Atlantic Ocean show that the flow and the fine sediment tend to move westwards due to pure tides,no matters the orientations of the passes are,which are proven by the observations,meanwhile good agreements are found between the modeled and observed tidal level processes.2.Course taken by the mass transport on the shelf foreset and deep floor.Considering the facts that there is nearly no exchange between mass transport and its ambient water due to the stagnating tidal current and that no wave particles can reach the deep floor,and that mass transport is driven by gravity,bottom friction and pressure,which are included in Mike21 HD and sediment module,Mike21 is used to simulate the debris flow on the shelf foreset and deep floor of the GoM assuming the initial water depths at all the meshes in GoM to be zeros and upper boundary at the intlet to the shelf canyon.It is found from the modeling that the bebris will continue to follow the same path as the observed.Conclusions:(a)westward movement of fine particles released from the Mississippi river mouth along the northern coast of GoM can be driven by pure tides,which is a break through to the popular point of view about southeast wind effect;(b)debris flow along the shelf foreset and deep floor of the GoM follow the travel path which can be simulated with Mode21.