Coral communities threatened by development in Hoi Ha

Introduction

This is a comment on Draft Hoi Ha Outline Zoning (OZP) Plan No. S/NE-HH/1.

Objections

When the Draft Hoi Ha OZP was being drafted it failed to consider three key issues:

1. The presence of coral communities in Hoi Ha Wan;

2. The threat to these coral communities from pollution, because the underlying geology will not support the use of on-site septic tanks and soakaway (STS) systems; and

3. The threat to these coral communities from sedimentation resulting from clearing land for development.

Coral communities

The coral communities in Hoi Ha Wan are the dominant feature of conservation and ecological significance in the area, yet the Draft OZP doesn’t mention this. You cannot consider the ecology, conservation or development of Hoi Ha without discussing the coral communities. Moreover, when the Hoi Ha Wan Site of Special Scientific Interest (SSSI) and Marine Park were being established, only two threats significant enough to cause irreparable damage to the coral communities were identified. These are pollution and sediment runoff from future development in the area.

Hoi Ha Wan Site of Special Scientific Interest designation document

Comments made at the opening of Hoi Ha Wan Marine Park

Threat to coral communities from pollution

The underlying geology in Hoi Ha village will not support the use of on-site septic tanks and soakaway (STS) systems to disperse untreated wastewater into the surrounding soil. The underlying surface sediment in Hoi Ha village comprises a mixture of alluvium, beach deposits and debris flow deposits. Such deposits are porous and highly permeable, allowing for rapid drainage.

Because of this, pollution will not be filtered, which will result in nutrient rich wastewater flowing into Hoi Ha Wan, leading to irreparable damage being caused to the coral communities there. It is important to note, two of the worst nutrient threats to coral communities are excess nitrogen and phosphorous, whilst two of the main nutrient products of STS systems are nitrogen and phosphorous.

Threat to coral communities from sediment runoff

At the same time, excavations undertaken during development will expose soil and sediment to the elements, which will disrupt the geologic continuum in the area. Because Hong Kong is naturally subject to heavy downpours of rain and extreme weather events, such exposure could lead to a massive single discharge of sediment or prolonged discharges of sediment into Hoi Ha Wan, smothering the coral communities. Hoi Ha Wan has a documented history of this. In the 1980’s, the loss of a coral community was recorded on the eastern shore of Hoi Ha Wan because of soil and sand runoff when trees and rocks were removed from the surrounding hills for reclamation of land at the Ma On Shan new town.

Comment

Because none of these issues has been considered in the Draft Hoi Ha OZP, appropriate assessments have not been made and no development should be allowed in Hoi Ha village until these issues have been properly considered and evaluated.

Petition 

If you want to object to the proposed development in Hoi Ha, please sign the petition here:

http://www.change.org/en-GB/petitions/town-planning-board-hong-kong-residents-only-please

Coral communities were not considered in the Draft Hoi Ha Outline Zoning Plan.

Introduction

This is a comment on Draft Hoi Ha Outline Zoning (OZP) Plan No. S/NE-HH/1.

The Draft Hoi Ha OZP was drawn up in recognition of the need to conserve areas of conservation value and protect the ecological significance of the area, yet only terrestrial species are considered as Species of Ecological Significance in the Draft OZP. No mention is made of the coral communities in Hoi Ha Wan, despite the fact it is an internationally recognized marine biodiversity hotspot.

The coral communities are the dominant feature of conservation and ecological significance in the area, yet the Draft OZP has been drafted as if the coral communities aren’t relevant or don’t exist. You cannot consider the ecology, conservation or development of Hoi Ha without discussing the coral communities.

See what was included in the Draft Hoi Ha Outline Zoning Plan and what was left out in the diagrams below.

Background

Hoi Ha Wan is one of the best sea areas in Hong Kong with good water quality and diverse marine life. It was designated a Site of Special Scientific Interest in 1989 in recognition of its coral communities and critically, because it was not affected by pollution. In 1996 it was designated a Marine Park.

The Marine Park has lush coral communities and is one of the best coral sites in Hong Kong. 64 out of 84 stony coral species recorded in Hong Kong can be found in the Marine Park, with some of the best coral sites recording over 50 species of stony corals. Studies have identified more than 120 species of coral associated fish, as well as diverse marine invertebrates and a new fish species has recently been discovered in the park.

Threats from pollution and sedimentation

When the SSSI and Marine Park were being established, only two threats significant enough to cause irreparable damage to the coral communities in Hoi Ha Wan were identified. These are pollution and sediment runoff from future development in the area, yet neither of these threats, nor the conservation value or ecological significance of the coral communities has been discussed in the Draft OZP.

Comment

If the General Planning Intent is to conserve the areas of conservation value and protect the ecological significance of the area, then no development in Hoi Ha can be undertaken without first specifically considering the needs of the coral communities.

What was included in the Draft Hoi Ha Outline Zoning Plan as Species of Conservation Interest

What was left out of the Draft Hoi Ha Outline Zoning Plan

Corals in Hoi Ha Wan Marine Park

Other marine biodiversity in Hoi Ha Wan Marine Park

Petition

If you want to object to the proposed development in Hoi Ha, please sign the petition here:

http://www.change.org/en-GB/petitions/town-planning-board-hong-kong-residents-only-please

Underlying geology will not support the use of on-site septic tanks and soakaway (STS) systems in Hoi Ha, posing a threat to the coral communities in Hoi Ha Wan Marine Park

Introduction

This is a comment on Draft Hoi Ha Outline Zoning (OZP) Plan No. S/NE-HH/1.

Proposals in Draft OZP for treatment of sewage and wastewater.

According to the Draft OZP, there is no existing sewer or planned public sewer for the area, and at present, each house is typically served with its own on-site septic tanks and soakaway (STS) system. Any increase in residential developments would require additional facilities, including their own individual STS system, which need to comply with relevant standards and regulations, such as EPD’s Practice Note for Professional Person (ProPECC) 5/93.

EPD standards and regulations

According to the relevant EPD standards and regulations, this involves dispersing untreated wastewater into the surrounding soil and relying on the soil to remove the polluting material from the wastewater and adequate purification can only be achieved after the wastewater has travelled a fairly long distance through the ground. The relevant standards and regulations also note, pollution would result if a STS is located too near to a beach or a stream.

Underlying geology of Hoi Ha Village

The problem with this is the underlying surface sediment in Hoi Ha village comprises porous and highly permeable sedimentary deposits, which are a mixture of alluvium (Qa), beach deposits (Qb) and debris flow deposits (Qd). Such deposits allow for rapid drainage, so no matter how far the distance, interstices in these deposits means adequate purification cannot be achieved before the wastewater reaches the sea, and because Hoi Ha village is at the mouth of a watershed, this means all of the pollutants in the wastewater will ultimately be deposited in Hoi Ha Wan.

See the maps at the bottom of the page..

Threat to coral communities in Hoi Ha Wan

Coral communities are sensitive receivers and the coral communities in Hoi Ha Wan lie downstream from Hoi Ha village. The watershed feeds into these communities. Coral communities thrive in nutrient-poor habitats by containing many species whose complex food chains recycle essential nutrients with great efficiency, making them especially sensitive to any process that disrupts recycling. For example, if wastewater is not properly treated nutrients such as nitrogen and phosphorous in the waste can stimulate prolific growth of algae, which overgrows corals, or form algal mats which prevents new polyps from settling and establishing themselves. Worst still, some chemicals in the wastewater could simply kill the more sensitive species of coral in the bay.

Threats to coral communities in Hoi Ha Wan from pollution and sediment specifically highlighted

Hoi Ha Wan is an enclosed bay. When it was designated as an SSSI, one of the stated reasons was because critically the bay was not affected by pollution and the only identified hazard to the reef was that future changes to land use may cause water pollution or sedimentation.  When the Marine Park was designated, pollution was specifically identified as a threat to the coral communities, but water quality in the park was good because there was no large water disposal nearby. It was also noted, the government’s approach to water treatment was not treatment, but disposal, yet this is what is now being planned.

Comment

Given the short distance between Hoi Ha village and the sea and because of the porous and permeable nature of the underlying surface sediment in the area, what is certain is the STS system will not remove pollutants from the wastewater as envisaged. This untreated, nutrient rich mix will then feed into Hoi Ha Wan and over time this will result in the degradation or destruction of the coral communities.

It is important to note, two of the worst nutrient threats to coral communities are excess nitrogen and phosphorous, whilst two of the main nutrient products of STS systems are nitrogen and phosphorous.

Summary

The underlying geology will not support the use of on-site septic tanks and soakaway (STS) systems to disperse untreated wastewater into the surrounding soil in Hoi Ha. Pollution will not be filtered as proposed, and the discharge of untreated wastewater into the environment will lead to irreparable damage being caused to the coral communities in Hoi Ha Wan.

Geological Survey Map of Hoi Ha Village

                                         

Proposed development in Hoi Ha (Draft Hoi Ha Outline Zoning (OZP) Plan No. S/NE-HH/1)

Overlay of proposed development in Hoi Ha village on local geology

Petition

If you want to object to the proposed development in Hoi Ha, please sign the petition here:

http://www.change.org/en-GB/petitions/town-planning-board-hong-kong-residents-only-please

Sediment runoff from development in Hoi Ha will threaten the coral communities in Hoi Ha Wan Marine Park

Introduction

This is a comment on Draft Hoi Ha Outline Zoning (OZP) Plan No. S/NE-HH/1.

Background

When Hoi Ha Wan SSSI and Marine Park were being established, only two threats significant enough to cause irreparable damage the coral communities in Hoi Ha Wan were identified. These are pollution and sediment runoff from future development in the area, yet neither of these risks have been considered in the Draft OZP.

Geologic continuum

Hoi Ha Wan lies at the end of a geologic continuum, which starts in the hills above Hoi Ha and passes directly through Hoi Ha village into Hoi Ha Wan. This continuum comprises a simple cycle of uplift, erosion and deposition. In this continuum, Hoi Ha village is an area of deposition and the coral communities lie at its end.

Disruption of geologic continuum and threats of sedimentation

Development of village houses in the area will require excavation and exposure of the topsoil and underlying sediments, causing a disruption to this continuum. Because of the underlying geology, a landslide hazard has been identified as a Geotechnical Constraint in the area, but the Geological Constraints associated with this have not been considered.

Because Hong Kong is naturally subject to heavy downpours of rain and extreme weather events, the excavation and exposure of topsoil and sediment in the area could lead to a massive single discharge of sediment or prolonged discharges of sediment into Hoi Ha Wan, smothering the coral communities, leading to their degradation or in a worst case scenario, resulting in their total destruction.

Hoi Ha Wan has a history of this. In the 1980’s, the loss of a coral community was recorded on the eastern shore of Hoi Ha Wan because of soil and sand runoff,  when trees and rocks were removed from the surrounding hills for reclamation of land at the Ma On Shan new town¹. In fact, this incident represents a classic case study to show what can go wrong if attention is not paid to the risks associated with disrupting a geologic continuum.

Comment

If, as stated in the Draft Hoi Ha OZP there is a need to conserve the areas of conservation value and protect the ecological significance of the area, no discussion can take place without making reference to the risks associated with disrupting the geological continuum in the area, meaning that the threats posed to the coral communities from sediment inundation have not been considered or addressed.

Reference

¹ LAM, K Y, SHIN, P K S, BRADBEER, R S, KU, K K K , HODGSON, P A and CHEUNG, S G, "Baseline Data of Subtropical Coral Communities in Hoi Ha Wan Marine Park, Hong Kong, Obtained by an Underwater Remote Operated Vehicle (ROV)", Marine Pollution Bulletin, Vol 54, January 2007, pp 107-112. 

Petition

If you want to object to the proposed development in Hoi Ha, please sign the petition here:

http://www.change.org/en-GB/petitions/town-planning-board-hong-kong-residents-only-please