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        Discussion Area 討論區 >> Conservation 自然保育 >>  Mai Po works update
        
(Message started by: Lew on Sep 11^th, 2003, 10:31am)

Title: Mai Po works update
Post by Lew on Sep 11^th, 2003, 10:31am

MAI PO WORKS UPDATE – SEPTEMBER 2003

Earthmoving in gei wai 16/17
Gei wai 16/17 is managed as one of the main roosting sites for the waterbirds that use Mai Po Nature Reserve. This is done by carefully adjusting the water level inside the gei wai over the course of the year, so that the ponds has a range of water depths, from deep to shallow, for the different birds to roost and feed in, depending on their requirement.

However, the floor of the gei wai has been silting up over the past decades because of mud that is brought into the pond each month when water exchange takes place. As a result, some parts of the floor of the pond has slowly been rising and are now difficult to cover with water. These drier areas can become quickly invaded by tall grasses and so are not used by roosting birds. One such area is the floor of the pond in front of Birdwatching Hide #3.

As a result, gei wai 16/17 will be drained down from September to December 2003 so that earthmoving works can be carried out to lower this part of the pond floor. A bulldozer and backhoe will be used to carry out the works, and the silt that is removed will be placed along the side of the pond. The aim is to complete the work by December 2003 but Mai Po staff will try their best to finish the work as soon as possible so that the pond can be refolded and the wintering waterbirds can once again use it for roosting and feeding.

To further minimise disturbance to the wintering waterbirds, we have lowered the water levels in a number of other gei wai (e.g. gei wai 6 and 11), so that these waterbirds can use other ponds in the reserve in the meantime.

Dredging channels in gei wai 7
The problem of siltation is common amongst all the gei wai, and was even recognised by the fishermen who used to manage the Mai Po gei wai before WWF Hong Kong arrived. Silt that comes with the water that is flushed into the gei wai, particularly settles on the floor of the perimeter channels and it has been estimated that these channels are silting up by around 1.3 cm per year!. These channels provide a deeper area of water for the shrimps and fish in the gei wai, where they can avoid the heat of the summer and the cold of water but if they were to become increasingly shallow, then this will affect the survival of these shrimps and fish.

As a result, a dredger on pontoon is used to dredge out the silt that has built up in the channels on a periodic basis. In the case of gei wai 7, the perimeter channels have not been dredged for a long time even before WWF Hong Kong took over management of the pond. As a result, the water channels in the pond have silted up and are now covered with reeds. As a result, Mai Po staff will be using a dredger on floating pontoons to dredge this channel over the coming 12-months. However, work will temporarily stop from November to April in order to reduce disturbance to the migratory waterbirds.

The silt from the bottom of the channel that has been dredged up, is usually placed on the side bunds of the pond. In the case of gei wai 7, the bunds are now heavily overgrown with trees and so trimming of some branches will have to be carried out.

Grasscutting in Pond 20 and 24
From 1998 when earthmoving works began to turn Ponds 20 and 24 into rain-fed freshwater ponds, they have slowly become popular as roosting sites for wintering ducks that visit Deep Bay. These ducks prefer to roost on the bunds with short grass or mud, and in the open areas of water. As a result, each year in autumn before the ducks return to Deep Bay, the tall dense grasses that have grown up along the bunds over the summer have to be cut and removed. Over the coming weeks and until the end of October therefore, these grasses will be cut and removed. That way, Mai Po can continue to provide a good habitat for our feathered visitors in winter!

If you have any questions or comments about these works, then please contact Lew Young at Mai Po on 2471-6306 (O) or by e-mail <lyoung@wwf.org.hk>. Thank you very much!