Optimal Allocation Of Water Resources And Calculation Of Flow And Sediment Transport Through River Network In Coastal Plain

Coastal plain areas always possess of large population and developed economy but lack for local water resources, which has becoming a bottleneck of economic and social development. To meet the needs of sustainable development of local economy sociaty, besides for reasonably exploiting and optimally allocating water resources in the region, transporting water from outside region is necessary to solve fundamentally the problem of lacking for water.Taking economic benefit, cost of water transport and equilibrium distribution into account synthetically, a new nonlinear objective function organically integrating three objectives is proposed. A new model for optimal allocation of water resources is developed under restricts with water supply and demand. The model can provide an optimal solution of water resources allocation, which overcomes the disadvantages of multiple optimal solutions in previous multi-objective programming, and effectively solve the problem of optimal allocation in complex water resources system.Using GIS technology to digitalize river network and section topography in the basin, the river network is divided into mainstream and lateral distributary as "reservoirs". A calculation method of time-dependent lateral outflow is proposed, which is adopted to compute water discharge from mainstream to reservoirs in water transport and proves the lateral outflow in Saint-Venant equation from previous constant to time-dependent process. Water level change at outlet boundary in the mathematical model is also considered as time-dependent process, which makes the calculation of unsteady flow in river network more reasonable. As a result a new method is proposed for calculation of water transport capacity in river network.As artesian flow from tidal estuary to river network is affected by tide inevitably, the sediment transport capacity of flow changes with it synchronously, but the actual sediment concentration lags behind it. So a new concept that the time-dependent sediment transport capacity is proposed, which means sediment transport capacity varies with tidal velocity and water level in half tide cycle and it is a function of time. Based on the dimensional analysis, the relationship between sediment transport capacity and time-dependent Froude number is constructed, and then the hydraulic parameters and concentrations in equilibrium points are chosen to determine the coefficients in the formulation, so a general formula for time-dependent sediment transport capacity is developed.When water flows through the river network in the coastal plain, besides tidal flow at the entrance with time-dependent sediment transport capacity, sediment alorg with water enters the river network and destroys the equilibrium state of sediment transport, which leads to non-uniform cohesive sediment deposition throughout the river network. Considering time-dependent sediment transport capacity and incipient probability of cohesive non-uniform sediment and integrating numerical calculation of unsteady flow, a calculation method of nonequilibrium sediment transport and deposition through the river network in coastal plain is established. The method is applied to calculate sediment concentration and deposition along the river network in a water transport project, the temporal and spatial distribution of sediment deposition is analyzed, and the countermeasures for decreasing deposition in river network are proposed, which provide scientific reasons for the decision of water transport project.