Technology Related to the Leo Kong Channel

      -some issues and some solutions

Water Quality of the Leo Kong Channel

One of the main problems with opening up the Leo Kong channel is that the water flowing through the rivers of Taipei is polluted. The channel starts form the orange X in the picture below and the channel is marked blue. The light blue markers show four bridges that are measuring points for the Environmental Protection Administration in Taiwan.

The water quality values for the four sites on the map can be found in the tables below including the water quality standards set by Environmental Protection Administration.

The orange cells of the table above shows which values exceed the water quality standards for class A waters, which means that suspended solids, biochemical oxygen demand, nutrients (nitrogen and phosphorus) and bacteria need to be reduced for the water to be advisable for people to swim in. Some of the values measured are not even sufficient for public water before sufficient cleaning by Taiwanese standards. If the water is not treated, it can still be used for raising trout, sweetfish, perch, carp, grass carp and mollusks. The lower quality water is also allowed in manufacturing and as cooling water. 

The next table below shows the values for metals in the water and the standards for protection of human health. The levels are all below the limit for human health, which means that the water can be used for agriculture in terms of toxicology.

The Kaoping River Rail Bridge Constructed Wetland

A similar project has been done in Kaoshiung City, the second biggest city in Taiwan. The wetland was commisioned in 2004.

The wetland has two systems, one with incoming water from a paper mill and the other from local drainage systems containing untreated domestic, agricultural, and industrial wastewaters. Below is an overview of the constructed wetland, and the lower system (B1-7) is the one that is interesting for the Leo Kong channel project. The system consists of a series of meandering bits of river and ponds for nutrient and suspended solids retention. The red and blue arrows indicate flow directions within the systems.

This table shows some water quality values for the wetland, system B is marked. These data can give an indication of what would happen with the Leo Kong channel values after a similar treatment. The values show that the wetland works very well for reducing coliform bacteria and phosphorus when considering the efficiency expressed in percent. This means that there is hope for treating the Leo Kong channel water relatively successfully. The water in the Kaoping wetland however, does not meet the stringent water reuse standrads, even if the water quality is significantly improved.

Design of a Constructed Wetland

One very important part of nutrient retention as well as treatment of bacteria is the flora that is put into the system. These are some examples of plant species that are commonly used in constructed wetlands.

For the Leo Kong channel however, we are mainly interested in native plants to Taiwan to enhance and support the native flora and fauna and to prevent introduction of species that can be dangerous to the existing ecosystem.

There are several ways of integrating plants in wetlands, ponds, rivers and streams. Here are a couple of examples of how plants can be integrated in innovative ways.

 

Other techniques involve collection of sediment in the water, like a sub surface sediment trap shown below. It can be designed so that all water has to pass through it or so that some of the water is still allowed to pass over the top and into a waterfall. 

Waterfalls are not just pretty, but they also help aeration of the water, which increases the amount of dissolved oxygen in the water. 

The sketch below shows two versions of a weir. This system helps for flood control and stream regulation. The weir can be designed after preference, for example so that is always lets through a certain amount of water at low flows but a higher amount at larger flows or the other way around.

A good way of improving the habitat of fish and other fauna is to place boulders in the bottom of a stream for example in a bend, which breaks up the flow of the stream. A cluster of boulders or small islands can also be beneficial in a pond or a wetland.

 

The Leo Kong channel will pass through some more populated areas with shops etc, where the streets must get enough space and where the river should still be visible. Designs similar to the ones below allow contact and closeness to the water without compromising safety. With foil underneath the channel, the water cannot go anywhere but downstream and concrete and other materials suitable to the area can assure that there will be no erosion so that the streets and the traffic is protected.