DSD R&D Forum 2013 – Session 1 (20 Nov 2013) Sustainable Drainage Session Keynote Address by Permanent Secretary for Development (Works) CC, distinguished guests, ladies and gentlemen, good afternoon. It is my pleasure joining with you at the DSD R&D Forum 2013 today. First of all, may I ask you a question? Does anyone know who in the Bible is frequently paired with water? The answer is Moses. Moses’s association with water started when he was still an infant. In the Bible, he was set adrift on the Nile by his mother, who was discovered in the rushes by the daughter of Pharaoh and was raised to become a prince of Egypt. Moses’s association with water continues throughout his life. The first plague of Egypt involves Moses turning the Nile blood red. On his way out of town with the Israelites, he parted the Red Sea. When they were withering away in the desert and Moses asked God for assistance, he was instructed to bring forth water from a rock. Some 3,400 years later, another “Moses”, who is also associated with water, has born in Venice, Italy in recent years. Does anyone here know who this “Moses” is? The new Moses was born after a severe flooding hit Venice in 1966. In that incident, the flood level in the city reached almost 2 meters and 80 percent of the city was submerged in water, which left more than 5,000 people homeless and caused extensive damage to historic buildings and cultural monuments in this historic city. After the flooding incident, the City of Venice has determined to solve the flooding problem that has been troubling Venice for over 1,000 years. As many of you may know, the flooding threat troubled by Venice is mainly due to the rising sea levels induced by the climate change over the past centuries or so. What the Italian Government has done to solve this flooding threat is to construct 78 giant steel gates across the three inlets to the Venice's lagoon. These steel gates will be raised whenever a dangerously high tide is predicted, which will form as a barrier to the incoming waves. The acronym of the project’s italian name is “MOSES”. The name also alludes to the Old Testament story of how Moses parted the waves of the Red Sea during the Israelite exodus from Egypt. Of course, Venice is not the only place troubled by the climate change. Rising sea levels and more extreme rainfalls induced by climate change have become an emerging threat to the mankind, particularly to those living in the coastal cities around the world. This is a real challenge that we need to tackle today and for tomorrow. The impact of climate change on
sea level rise has been increasing at an alarming rate. In the past 20 years or so, the annual rate of sea level rise is 3.2 millimeters a year, which is roughly twice the average speed of the preceding 80 years. Looking ahead, scientists have predicted that the sea level may rise faster as oceans continue to warm and land ice melts more rapidly. It is predicted that the sea level will rise between 800 millimeters and 2 meter by 2100, which will be enough to swamp many coastal cities. But how the rising sea level will affect our city here? To illustrate, DSD has completed a study recently which reveals that, if we are not going to do anything, the rising sea level may cause some 3% increase in flooded area in Yuen Long if a 200 year storm hits us in 2050, or some 6% increase in flooded area for a five years storm, which may not sound too alarming, but the threat still deserves our serious attention. But remember rising sea level is not the only threat we are facing, as climate change will also lead to the occurrence of more extreme rainfalls. As you all know, serious flooding caused by extreme rainfalls happens in Hong Kong from time to time. The highest hourly rainfall ever recorded in Hong Kong occurred on the 7 th of June 2008. On that day, some 145mm rains fell within an hour causing 622 flooding in the territory. Two years later on the 22 nd of July 2010, another extreme rainfall hit the territory causing 2 deaths and 44 flooding across the territory. When we look at the past rainfall records over a long time span, we can see a mild increasing trend of annual rainfall and the more frequent occurrence of heavy rainfalls in Hong Kong. Looking ahead, it is projected that not only the increasing trend of annual rainfall will continue, but we are also expecting the occurrence of more extreme rainfall events, which means less days with rains, but more rains concentrated on the rainy days. According to a recent study, a 1 in 20 years event nowadays may become a 1 in 12 years event by 2050, which will be further changed to a 1 in 7 years event by the end of this century. There are bound to be a lot of challenges ahead of us in response to the impact of climate change on our drainage systems. However, it also provides good opportunities for us to rethink on how best our flood prevention strategies could be enhanced to meet with present day expectation of our society. Traditionally, our solutions to address flooding problem have been to widen, train or deepen the existing rivers in the rural areas, and install stormwater drains under the ground in the urban areas. More recent approach to avoid extensive pipe laying works in urban areas includes the construction of drainage tunnels to intercept rain water from hillside catchments, and the construction of underground stormwater storage tank schemes to temporarily store the rain water during heavy rainstorms, before the rain water enters the existing under-capacity drainage systems in the urbanised areas. However, the drainage tunnels and underground storage tanks which were once considered
as innovative and creative means to solve the flooding problem a few years ago, may not be able to fully meet the present day expectation of our society on “sustainability”. What we need is a drainage system that will not be limited to protecting people from flooding, but should also be able to enhance the quality of the life of people living there as well as increase the biodiversity in the community. This is the concept of “Sustainable Drainage”. A successful example of urban sustainable drainage is the 清溪川 in Korea which has demonstrated aptly how urban drainage design can be integrated seamlessly with heritage conservation, environmental protection and other social considerations. The Government is well aware that we need to realize the “sustainable drainage” concept in our city. The strategy that we are going to pursue is to adopt the blue-green infrastructure concept in planning our drainage system in new town developments, with special focus directed on blue, which means “river”, and green, which means “vegetation”, infrastructures. Our emphasis will be on upstream interception or at source control, together with good land use planning that will facilitate gradual seepage of water into the ground, slow water flows, and provide temporary or permanent on-site storage in the event of extreme heavy rainfalls. Another feature of blue-green infrastructure is retention lake to be included in river improvement works, which will serve to increase the ecological and aesthetic values of the surrounding environment while increasing the flood protection level of the river. Other features that will be pursued as part of our overall sustainable drainage approach include green roof, porous pavement, rain water reuse, and opening the rivers to the public. This sustainable drainage design concept is not new to Hong Kong. In fact, this concept has already been embedded in some of our drainage projects. For example, DSD has just completed the first rain water harvesting system under the Kowloon City Sewage Pumping Station. The system involves the collection of rain water and groundwater for irrigation of the sports field and vegetation, as well as for toilet flushing etc. Apart from rain water harvesting, we have also included many ecological enhancement features in some of our river training projects. For example, we have included such features as fish shelters, plantation within rivers, fish deflector, riffles and pools, etc in the Ho Chung River project to preserve the existing habitats while increasing the flood protection capacity of this river. Admittedly, there bound to be many challenges and problems that we will need to overcome in our pursuit of sustainable drainage in Hong Kong. In this regard, I am pleased to note that DSD has commissioned a number of research and development projects to support this sustainable drainage movement, which include the design of porous pavement, bioswale [ 生 態截流系統 ], biodiversity and rain garden. I am sure that more will still need to be done. But I must say that the Government could not do all the work alone. You are the experts in this field. We are prepared to listen to you and learn from your professional knowledge and
experience on this important topic on sustainable drainage. Before I conclude my speech, I would like to put forward my three aspirations for everyone of you today. I aspire that with our d edication and determination to s trive for excellence we will build a world-class d rainage system for our tomorrow. The acronym of these three aspirations is DSD. And to this, I would like to dedicate my three aspirations especially to the colleagues of DSD. Thank you very much. Ir WAI Chi Sing PS for Dev (Works) Development Bureau 20 November 2013
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