In the analysis of converting the Plover Cove Reservoir into a new town, the first key issue is its impact on the water supply. If the proposal would lead to a water shortage in Hong Kong, this should be abandoned. Is reclaiming the Plover Cove Reservoir harming water supply for our population? Let us go through this question from different angles.
Currently, Hong Kong has only two sources of water supply: Dongjiang (Eastern River) Water and rainwater. When daily water supply is interrupted, the reserve would be utilized. According to the Water Supplies Department, “The total storage capacity of Hong Kong’s impounding reservoirs, comprising two reservoirs constructed by damming the sea and 15 conventional reservoirs, is 586 million m3. When they are 100% full, the storage can meet about 6 months’ demand of Hong Kong.”
It is straight-forward that the construction of the New Town will not in any way affect the size or ecology of the water catchment. Therefore, there will be no impact on the capability of rainwater collection.
The total storage capacity of all reservoirs in HK is 586 million m³, while the average rainwater collected for the past 10 years was 246 million m³ per year. Therefore, even if we take away the 230 million m³ capacity of the Plover Cove Reservoir, there would be still enough storage capacity elsewhere to contain the entire rainwater collection.
For the year 2015/16, the total rainwater collected was 270 million m³, with the Plover Cove and High Island Reservoirs accounting for 138 million m3. Assuming these two reservoirs have a similar catchment capacity, the Plover Cove Reservoir should have collected about 70 million m³ rainwater. With 280 million m³ capacity and average water storage at 72%, the High Island Reservoir has a residual capacity of 78 million m³, thus it alone can accommodate all the rainwater collected by the Plover Cove Reservoir.
Due to the huge surface area of the Plover Cove Reservoir, every year it lost about 15 million m³ water, or about one-fifth of the rainwater collection, due to evaporation. If all rainwater is transferred to the High Island Reservoir, 15 million m³ rainwater will be saved due to its much smaller surface area.
According to the Water Supplies Department, “The total storage capacity of Hong Kong’s impounding reservoirs, comprising two reservoirs constructed by damming the sea and 15 conventional reservoirs, is 586 million m³. When they are 100% full, the storage can meet about 6 months’ demand of Hong Kong.” For the sake of risk management, we need to consider the worst scenario: assuming the three reservoirs (Plover Cove, High Island and Tai Lam Chung) receiving Dongjiang Water are also contaminated, the total water storage of the remaining 14 reservoirs has a mere 54.7 million m³ and can only last for 20 days. Under this stress test, despite claiming a total of 586 million m3 reserve, the HK water system is incredibly fragile.
In April 2015, water storage of most reservoirs dropped to the low point in 10 years’ time. Apart from the three reservoirs receiving Dongjiang Water, the other reservoirs had about 20-30% storage. That is, under the worst scenario, when the reservoirs containing Dongjiang Water are contaminated, and the storage of all other reservoirs is about 30% of 54.7 million m³ or a mere 16.4 million m³, the water reserve can last for 6 days only. In other words, we cannot afford any delay to develop new source of water!
The development of a Plover Cove New Town is tied in with the construction of two desalination plants. Taking into account the ultimate water production capacity of the Tseung Kwan O Desalination Plant, the annual production of the 3 plants can reach 300 million m³ each year, providing 30% of water usage for HK on sustainable basis. In the case of total suspension of Dongjiang Water due to contamination or water shortage in Mainland, the total 356 million m³ of all Hong Kong reservoirs (excluding Plover Cove) can last for 188 days to meet the 70% water usage; this is similar to the 6-month period mentioned above.
Under the worst scenario with two new desalting plants, when reservoirs (High Island and Tai Lam Chung) containing Dongjiang Water are also contaminated, the total storage of 54.7 million m³ of the remaining 14 reservoirs can support a longer period of 29 days to meet the 70% water usage. More importantly, the three desalination plants can continue to supply 30% of water usage during the difficult period. So this is a more secured alternative by means of risk diversification.
The development of the New Town will not lead to importing more Dongjiang Water. The New Town, aiming to house 10% of the population, will implement various environmental friendly measures, such as large-scale tree planting, grey water recycling, rainwater harvesting, etc. This will result in reducing the overall water consumption of Hong Kong as well as lowering the import of the Dongjiang Water. In addition to the desalination plant in Tseung Kwan O, the development of the Plover Cove New Town are as mentioned accompanied by the construction of 2 more desalination plants, bringing the total annual production of fresh water to 300 million m³ by these plants. The supply of water can then be diversified across three sources: Dongjiang Water (45%), desalination (30%) and rainwater (25%), which is a better strategy for long-term risk control. According to the Water Resources Group of World Economic Forum, by 2030, the Pearl River Basin will face water scarcity gap of 23% or shortage of 28 billion m³. As a coastal city, Hong Kong has obvious geographical advantages to develop desalination. As a member of the global village, Hong Kong should bear the carbon emission burden, instead of pushing this to the inland cities of the Guangdong Province.