1. Evolution of Engineered Channels

In Hong Kong, river training works are carried out mainly to solve flooding problems. In early days, river training works in Hong Kong meant straightening and deepening of natural channels and cementing riverbeds and riverbanks in order to discharge storm water as quickly as possible, which might cause damage to the natural hydrology, ecology as well as water quality. The complex natural setting comprising sand, mud, gravels and vegetation is replaced by smooth, bare and monotonous concrete surfaces. Rivers' natural environments and hydrology were ruined by such works, leading to ecological devastation and water quality deterioration.

Now, improved designs for channel and embankment construction are adopted to retain natural riverbeds and meanders. For example, in the 1990s the natural riverbeds were retained in Shan Pui River and Kam Tin River training works to provide habitats for animals. Mangroves were planted to enhance the channels' ecological value.

Practices have been improved to include grasscrete, rip-raps (rock armour) and gabions. Grasscrete – growing grass in the concrete grids; rip-rap – rock armour for river beds; and gabions - metal mesh baskets filled with stones for embankment construction, which are currently widely used.

In front of you is the Yuen Long Bypass Floodway. The porous "grasscrete" paving of the channel allows the flow between river water and groundwater and supports plant growth. It was also designed to be meandering instead of straight, mimicking the natural alignment. This makes the channel look more natural.

However, existing river training techniques still affect natural rivers' ecology and hydrology. As technology advances, we long for more environment-friendly river training works.

You may find out other improved designs along this Trail. Are these designs bringing positive or negative impacts to flood prevention, landscape, ecology and water quality?

A concrete channel

Grasscrete

Rip-raps

Gabions

Yuen Long Bypass Floodway was designed to be meandering