Nội dung

Vietnam Journal of Mechanics, NCST of Vietnam Vol. 24, 2002, No 3 (181 - 196) ON AN ONE- AND QUASI-TWO DIMENSIONAL LINKING HYDRAULIC MODEL FOR THE COMPLEX RIVER NETWORK-VALIDATION AND APPLICATION NGUYEN VAN HANH 1 , NGO HUY CAN 2 AND NGUYEN VAN DIEP 2 1 Institute for Water Resources Research, 271 Tay son street, Hanoi, Vietnam 2 Institute of Mechanics, 264 Doi can street, Hanoi, Vietnam ABSTRACT. This paper describes an approach to construct an one- and quasi-two dimensional hydraulic model for the complex river network, including various hydraulic structures. The model is based on the numerical solution of the Saint-Venant equations for river branches, the continuity equation for storages, the equation for junction conditions of the confluences, tributaries , the equation for hydraulic structures between rivers and storage cells. Cross sections are modeled as a combination of main and flood plain parts to simulate better the flow pattern. The calculating program has been ~eveloped, validated by test cases, proposed by European big hydraulic research laboratories and then applied to build a hydraulic model for the complicated Red-Thai Binh river network. 1. Introduction Free surface flow in a river delta is complicated and is investigated extensively last years. The flow can be simulated by one- or two-dimensional mathematical models [1-3], depending on the study purpose. However, two-dimensional models are expensive for large river deltas. In this case, the main technique is to use an one- and quasi-two dimensional approach [3], which can be rather cheaper both in calculating time and cost. In the one- and quasi-two dimensional approach the research area is considered as a combination of a river network and storage cells. Storage cells can exchange flow with rivers and with each other through hydraulic structures. In this paper an approach to construct an one- and quasi-two dimensional linking hydraulic model for the complex river network is presented. The focus is an approach of verifying hydraulic program by various test cases to validate the numerical scheme. The hydraulic model for the complex Red-Thai Binh river network is constructed, followed flood protection rules of the Government , including the special operational scheme of the Van Coe sluice and the Day dam. The model then is applied to evaluate flood scenarios. 2. Equations For a general network there may exist a flow in river network, flow in- or outstorage cells. So one has to deal with three types of equations: partial differential 181 \ ~rdinary differential equations for storage cells equations for a single river branch, and equations for hydraulic structures. Apart from these it is needed to add junction conditions in some location of the network to keep the flow continuity. Equations for a single river bradch The free surface flow in a single lhranch of a river network can be described by the so-called Saint-Venant equations [1-3] under the assumption of a hydrostatic pressure and an uniform distribution of the velocity along the vertical axis. In practice, the flow in the main fhannel and the flood plain are quite different due to different frictions. So the foll0iwing type of equations are often used: &As &t &Q &t &Q _ O + &x - ' 2 & (Q ) + &x A1 (2.1) 1 &z gA1 &x + gA1 QIQI K2 = 0, (2.2) where Z is water elevation Q ,. discharge As and A 1 - wet cross sectional areas for the main and total flow K - conveyance g - gravity t - time x - space coordinate Equations for storage cells This is the continuity equation for storage cells (2.3) where V is the water volume, Q is in- and out-going discharges. Equation for hydraulic structures and junction conditions The flow must be conservative, so at confluences or tributaries the sum of all discharges must be zero. At hydraulic structures fl.ow rate is defined by the formula: Q J(Zu, Zhz, a), = (2.4) where Zu, Zhz are the upstream and downstream water levels and a is characteristic parameter of structures. A structure may be modeled by one of two types: a spillway and a sluice. The discharge, going through a spillway is calculated by [4] Q = mbj29(Zu - Z0 ) 2 Q =

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.