Yuen Long Bypass Floodway

Investigators:

• Prof. Joseph Hun-wei Lee
• Dr. H.W. Tang
• Dr. C. P. Kuang

Introduction

Results

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Introduction

The Yuen Long Bypass Floodway is proposed to divert flood flows from the Sham Chung River, the San Hui River, and part of the flow from the Yuen Long Main Nullah into the Kam Tin Floodway. A 1:50 undistorted Froude scale model and numerical model are designed and constructed to study water levels and flow characteristics in the model flood way, and to investigate optimal design arrangements at channel junctions and transitions. Special emphasis is placed on the complicated flow interactions at channel junctions, which cannot be resolved by mathematical models of unsteady flow in commercial use.
　

 Fig.1 Yuen Long Bypass Floodway model

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Results

Five schemes were compared, the results indicate that :

• The use of a diversion channel with appropriate length and width is successful in diverting the required flow from a supercritical flood stream into the Floodway;

• The use of a hydraulic structure to create a local constriction and nearly critical flow conditions at the San Hui junction has the effect of significantly bringing down the stage in the Floodway upstream while still allowing the passage of the required flood flow;

• The best choice can enhance the flood control capacity from that of a one in 10-year to a one in 200-year flood.

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