METHODOLOGY FOR CONVEYANCE ESTIMATION IN TWO-STAGE STRAIGHT, SKEWED AND MEANDERING CHANNELS

摘要

Reliable estimates of discharge capacity are essential for the design, operation and maintenance of open channels, and more importantly, the prediction of flood levels. The conveyance estimation methods that are employed in commercially available river modelling software are principally based on historic hand-calculation formulae, with little or no account taken of the more recent advances in knowledge and understanding. A scoping study, commissioned by the British Environment Agency, identified the need to reduce the uncertainty associated with flood level prediction through incorporating this recent research into a Conveyance Estimation System (called the "CES"). The development of the CES is now underway, involving a partnership between academic researchers, experts and users. This paper describes the calculation methodology that has been adopted, which is applicable to all river and floodplain morphologies, considers all the physical flow processes that are present and where necessary, includes empirical or calibration coefficients that are based on previous research and expert advice. The approach uses a depth-integration of the Reynolds Averaged Navier-Stokes equations for flow in the streamwise direction, and generates a numerical solution using the finite element method. Emphasis is given to the secondary flow energy loss mechanisms and their effect on the lateral velocity distribution. The depth-averaged velocity predictions are compared with measured data from the Flood Channel Facility at HR Wallingford, the University of Bristol 1:5 scale model of the River Blackwater and the River Seven at Shrewsbury.