Experimental Study on Hydraulic Transients Caused by Drainage Gate Operation in the Drainage Canal of a Reclamation Area

Abstract

Numerical unsteady flow analysis is one of the important factors for determining the dimensions and locations of drainage facilities for land reclamation areas. This paper describes the experimental results of hydraulic transients which flow through the sluice gate, so as to set up suitable boundary conditions for a hydraulic simulation model. The experimental results of hydraulic transients in the laboratory flume are as follows.
1. Water level drop down in speed, just after the gate was suddenly opened at the upstream, is not negligible with acceleration of gravity within 0.2 s and water surface shape became the upward curved line (convex) for the rapidly varied unsteady flow.
2. The vertical pressure distribution in the laboratory flume, just after sluice gate was suddenly opened, became hydrostatic pressure at the ponit of 2 times the distance of the initial depth from the gate site to upstream and this distance is coincident with the Pohle solution. Also hydrostatic pressure is preserved continuously during transient flow.
3. The horizontal velocity of rapidly varied unsteady flow is delayed in comparison with the theoretical velocity of shallow water wave, that is u=2√g (√h₀+η-√h₀) (u<0).
If the delay time is considered, the horizontal velocity can be expressed by the delay of the first degree that is u= (1-e^-t/T) ×2√g (√h₀+η-√h₀) T is time constant.
4. When the sluice gate is opened partially, the steady water level after hydraulic transients can be expressed by Eq.(21) and the H. R. Henry coefficient of discharge under the condition of free and submerged flow.
5. The falling speed of water level under the condition of submerged flow is slower than the speed given by Eq.(23). The speed under the condition of this experiment is 0.30-0.49 times of the gate opening speed.
6. Eq.(32) is applicable, as a boundary treatment, to the numerical model of unsteady flow analysis for rapidly varied unsteady flow.