[Hong Kong] Mudflats Vs Mangroves - Pearl Report TVB

Mudflats Vs Mangroves - Pearl Report TVB

This Sunday's Pearl Report (18:50) is about the loss of inter-tidal mudflat in Deep Bay. Its titled "Mudflats Vs Mangroves". TVB will upload it to their archive several days later.

An alarming point made in the report is that 37% of the Ramsar Site mudflat was lost to mangroves between 2000 and 2007, an average annual loss of ~20 ha per annum. The intertidal mudflat is the most critical habitat for waterbirds in the Ramsar Site and if this rate is sustained the mudflat within the Ramsar boundary could disappear by 2020!

[ Last edited by WWF Mai Po at 5/05/2010 17:00 ]


Interesting topic!!!
Some day ago I discussed this topic with Chairman HF Cheung and brainstormed an idea of removing mangrove for recovering mudflat or gei wai habitat. HF Cheung said they have proposed similar idea few years ago but any action involving removal of mangrove was strongly objected by mangrove expert and also WWF staff (Please correct me if I am wrong).
So, I think the key point of this program/campaign is not educating public but to compromise with the experts about balancing the ecosystem of Inner Deep Bay mudflat and ecological value of mangrove.



Deep Bay's rising mudflats

A while ago - maybe 2004 - I did an article for S China Morning Post, about problems facing Deep Bay, especially the rising mudflats. (Which it seemed AFCD couldn't or wouldn't see; I remain sceptical of their measurements using GPS - not at all sure re accuracy; random errors might explain why they took various random looking readings]).
Article's at: Deep Bay wetland threatened

This followed the evident startling rise in level of the mud, most obviously in front of boardwalk hides (most obvious as so many observations from there; back in the day, a 1.8m tide brought tideline to the original boardwalk hide! This was constant for a few years, then a relatively sudden change; I believe as tidal regime in Deep Bay shifted thanks to projects including straightening the Shenzhen River)

So, mangroves not really the main issue, perhaps. I believe they are following the movement of the zone that suits them (tidal, but not covered for too long during day).
Was told of algae growing on top of the mud that likewise can't be covered for too long in a day: this used to be behind original boardwalk hide, and has surged out - beyond even the new hide.
Even outside the new hide, can nowadays seem more like you have patch of brackish, almost freshwater marsh in front: algae, grass, yellow wagtails and little ringed plovers and so forth happily feeding.
Again back in the day: I remember being in original hide, having avocets pushed up by tide, feeding right in front; so too shoveler. Now, barely anything for them to feed on here it seems.

SO while I believe mangroves should be chopped down in various places, inc Tsim Bei Tsui; and kept clear in front of boardwalk hides (where the expanse of mud is highly artificial), key issue is surely the rising mudflats.
Plus the fact the flats are rising, leading to steep channels; not just a migration of mudflats out into the Deep Bay (this info from a Dutch mudflat expert who was at Mai Po as I did the article).
So yes, the intertidal birds are being squeezed.

Mind you, thanks to projects like Saemangeum in S Korea, there aren't so many birds to pack into the bay as a few years back! [albeit avocets are doing well]
Hong Kong Outdoors enjoying and protecting wild Hong Kong. DocMartin includes H5N1 and wild birds info


Mangroves and Mudflats

Dear all

Mudflats and mangroves are natural products of nature on a tropical/subtropical river mouth.
They expands with the esturary as time passes. Just imagine the state of the Deep Bay area before man started claiming the land and water for his own use. It's a haven for land birds as well as for waterbirds.

Now the river mouth stops to fan out. In its stead comes urbanization. One outcome in recent years
is the rising of the level of mudflats. More of them become exposed most of the day and night, becoming
favourable soil for mangroves. All birdwatchers of more than ten years of experience will remember
best high tides in the old days were between 1.7 and 1.9 meters (figures probably not exact).
Now they are 2.2 and 2.4 metres!

So the main cause of the loss of mudflats is man-made. The suitable or sensible solution must again
be in the hand of man. Make the central part of the river deeper, and mudflats will be lower by
sliding down towards the centre. It is costly, but to protect the Ramsar site, it is a must.

Cutting the mangroves down is just like applying restraints to a growing child. The child still grows,
but it grows now into a strange being. This is what we call maltreatment of mother nature.

S L Tai


Illustration of how the Bay has changed in the last 30 years.



"An alarming point made in the report is that 37% of the Ramsar Site mudflat was lost to mangroves between 2000 and 2007, an average annual loss of ~20 ha per annum. The intertidal mudflat is the most critical habitat for waterbirds in the Ramsar Site and if this rate is sustained the mudflat within the Ramsar boundary could disappear by 2020!"

I am not sure if I understand this correctly but the above states that the mudflats could disappear by 2020 but to most visitors to the floating hides the mudflats seem to be extending out further and further. In the "old" days the hides used to float with a tide of 1.9M but now that doesn't happen unless the tide is well over 2M.

It was suggested to me, by an Ecologist, years ago that a possible solution to the rising mudflats would be to dredge "sink holes" in the middle of Deep Bay and possibly the mud would recede back into these sink holes.

The map showing the change over the past 30 years (Grey Color) doesn't state if that area lost was to Mangroves or mudflats


Hi Bob,

The statement says the mudflat inside the Ramsar Site could disappear by 2020. If this happens then no intertidal mudflat on the HK side would be under protected status because AFCD said they will not extend the Ramsar boundary despite calls by WWF and others to do so.

The map shows changes due to mangrove extension and reclamation. It is to support some of the points made by SL Tai and Wmartin.

Bena Smith

[ Last edited by WWF Mai Po at 5/05/2010 13:21 ]


In 2020, if the mudflat inside the Ramsar Site disappear, I GUESS:
>>> then Mai Po will not be protected area anymore!
>>> then Mai Po can built many many "Grand Housing" (豪宅)! (Wow! Govn't can earn mcuh money!)
>>> then Govn't no need to pay anymore Mai Po maintenance fee to WWF! (Wow! Govn't can save much money!)
>>> then WWF lost a job!  
>>> then workload of AFCD and other related Govn't Dept will be a big reduction! (Wow! Sound Great!)
>>> then we lose our only Ramsar site in Hong Kong!

[ Last edited by Sze at 5/05/2010 23:00 ]


Dear all

The map does indicate significant and threatening changes:

Firstly, the mudflats are rising at an alarming rate and innner areas are drying up, like all
natural river esturaries in its wild days. But in Deep Bay the mud seems to stay more and not
flowing out with the water quickening the rising level of the former.

The reclamation on the opposite side of MPNR which I mean Shenzhen looks set to urbanize within its
own Ramsar site. Overall possible effect seems to be slowing down the water outflow rate further and
the mud the water carries as well(or the Shenzhen river is also drying up itself).

Unless the governments on both sides see the geographical development as a serious threat to regional
environment no less than air and water pollution we are suffering now, the future looks stark unless
we start setting off the alarm loud and clear on everybody's ears.

S L Tai