Hong Kong's sea-level record
By Ir Prof Wyss YIM

Hong Kong has extensive urbanised low-lying coastal land reclamations threatened by short-term typhoon-induced storm surges and long-term future sea level rise. It is therefore important to study past records in order to obtain information for the evaluation of future risks.

Chart datum, the lowest tide, is 0.146 m below the Hong Kong Principal Datum used in surveying. Local mean sea level is approximately 1.23 m above Principal Datum.

Based on tide gauge records in Victoria Harbour from 1954 to 2015, sea level rising at an average rate of 30 mm per decade was claimed by the Hong Kong Observatory. The projected rate of 25.5 cm by the year 2100 falls below the lower end of the fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC) predictions for four carbon dioxide scenarios with mean sea level rise ranging from 28 cm to 98 cm.

Solar variability including Earth's orbital changes and major volcanic eruptions are largely responsible for the Earth's 'long-term' natural temperature variation. This controls ice balance and the thermal expansion and contraction of seawater. Additionally human activities including water usage, fossil fuel consumption, heat generation and land utilisation have altered the natural water cycle causing sea level changes.

In coastal regions like Hong Kong other possible factors include crustal stability; geoidal changes; meteorological conditions such as pressure changes, wind directions and the passage of typhoons; and ground movement both natural like deltaic sedimentation, and man-made like construction, groundwater extraction and mining. These reasons help to account for both short and long-term sea level variability.

For measuring sea levels, tide gauges became available in Hong Kong in 1954 and satellite remote sensing in 1993.

The oldest Hong Kong tide gauge was established on the North Point coastal reclamation. In 1987, it was relocated to the Quarry Bay coastal reclamation for fear of the constructional impact of the East Island Corridor. Neither tide gauge was founded on bedrock so uncertainties exist on the influence of post-constructional or residual ground settlement.

A 1993 study (Yim 1993) of the 1962-1986 record of the North Point tide gauge revealed an average rate of sea level rise of about 0.3 mm/year. Based on a positive correlation between sea level and rainfall, river discharge was identified as an important factor. The rate was a maximum rate because coastal reclamations are prone to ground settlement.

In spite of uncertainties, the Victoria Harbour 1954-2015 sea level record show:

- A pause in the average rate of sea level rise from 1959-1993.
- An abrupt 29 cm rise in sea level during 1987-1999.
- A post-1999 pause in the average rate of sea level rise.
- The average rate of sea level rise of 30 mm/decade from 1954-2013 in Victoria Harbour claimed by the Hong Kong Observatory is likely to be an overestimation because ground settlement of the North Point and Quarry Bay tide gauge stations has not been taken into account.
- The sea level trend observed over the South China Sea through satellite remote sensing since 1993 is too short to distinguish the trend from the noise. Nevertheless, an analysis of the South China Sea (Cheng and Qi 2007) showed sea level rose at an average rate of 11.3 mm/year during 1993-2000 and fell at an average rate of 11.8 mm/year during 2001-2005.
- River discharge is an important 'noise'. For example, the low annual mean sea level in 1963 coincided with one of the most severe regional drought year on record triggered by the Agung volcanic eruption in Indonesia.
- Another 'noise' affecting tide gauges within Hong Kong is the Pacific Decadal Oscillation.
- Storm surge generated by the passage of typhoons is an immediate enemy, particularly when associated with heavy rainfall and high tide.
- Tide gauges used for the study of long-term sea level changes should be located on bedrock instead of reclaimed land in order to eliminate the possibility of ground settlement.
- Both tide gauge and satellite remote sensing records are too short for drawing reliable conclusions on projected sea level rise. Another 50 years may be needed.

To reduce risk it is important to study the stability of existing tide gauges on bedrock and on reclaimed land in Hong Kong using state-of-the-art surveying methods including interferometric synthetic aperture radar (INSAR).

1. Cheng, X and Qi, Y: "Trends of sea level variations in the South China Sea from merged altimetry data". Global and Planetary Change 57, pp 371-382, 2007.
2. Hong Kong Observatory website http://www.hko.gov.hk.
3. Yim, W W S: (1993). Chapter 22, "Future sea level rise in Hong Kong and possible environmental effects"; in Warrick, R A, Barrow, E M and Wigley, T M L, ed: Climate and Sea Level Change: Observations, Projections and Implications, Cambridge University Press, Cambridge, pp 349-376, 1993.

About the author: Ir Prof Wyss Yim was president of the Western Pacific Sub-commission on Quaternary Shorelines, International Union for Quaternary Research 1995-1999.

The North Point tide gauge

Sea-level record based on tide gauges in Victoria Harbour 1954-2015 (Source: Hong Kong Observatory website http://www.hko.gov.hk)

President's Protégé Scheme

Laying the ground work for the Protégés to come

Another crop of young engineers have 'graduated' from the President's Protégés Scheme (PPS) having spent a year shadowing President Ir C C Chan and enjoying camaraderie within a group of dynamic young people. In addition to attending a variety of HKIE events, including the 40th Anniversary Cocktail Reception, HKIE 41st Annual Dinner and 40th Anniversary Sports and Family Fun Day; the Protégés also organised a number of activities themselves, to arouse the interest of young people in engineering.

Chief among them is their flagship activity, "Your School, Dream Green" competition, which was targeted at secondary school students, who were encouraged to innovate and implement green measures at their campuses through the application of engineering. Aware of young people's interest in social media, the Protégés also revamped the HKIE's social media platform, using Facebook and Instagram to introduce engineering facts to students and the public at large. Below are the Protégés thoughts on their eventful year.

It has been an enjoyable and fruitful year with President Ir Chan and my fellow Protégés. Not only have I gained professional insight through shadowing the President, I have also developed cordial friendships with the other eight Protégés. Being able to attend senior meetings deepens my understanding on the importance of interdisciplinary collaboration and broadens my industry horizon. Being part of the family of Protégés, I have numerous opportunities to reach out to the general public, especially the younger generations, through functions like "Your School, Dream Green" Competition and social media promotion. All these add to my determination to becoming a professional engineer who would work for the betterment of society.

Julia Mengpei CHEN
Being one of the President's Protégés over the past year has been a cornerstone of my professional and personal development. There were many experiences that were firsts for all of us. Apart from shadowing President Ir C C Chan and realising our ambitious year plan, we were also offered the chance to assist various HKIE Divisions and Boards in promoting the engineering profession. The scheme allowed us to take initiatives and embrace challenges at a higher level. I am truly grateful for the opportunities to learn from the professional elite and share with my talented peers the aspiration to excel and serve our society.

Jason King Wai CHEUNG
Being one of the Protégés has been a fruitful and rewarding experience. Responding to the President's commitment to foster the interest of young people in engineering, we organised a series of activities with this in mind. It feels amazing when I see what we have done over the past year. Under the supervision of the President Ir C C Chan and with the hard work of my fellow Protégés, we successfully launched the "Your School, Dream Green" competition, which encouraged students not only to design but also to implement engineering solutions on their school campus. Through shadowing the President, I also had an invaluable opportunity to learn from senior figures and gain an insight into the operations of HKIE. In short, I am grateful for the President's guidance and the invaluable exposure throughout the past year.

Stanley Yu Tang CHEUNG
I am honoured to be one of the Protégés. It is a wonderful scheme that provides me with many great opportunities to explore the world of engineering; that is, organising the "Engineering a Green Campus" competition for secondary school students, site visits for our members, the Australia delegation trip for our President and other Protégés, attending HKIE Council/Board meetings, etc.

"To serve, to inspire and to cultivate� are the core objectives of the Protégés this year. It is my great pleasure to achieve these objectives with my eight fellow Protégés. We have succeeded in serving the public and our members, inspiring the young and talented as well as cultivating the image and public awareness of professional engineers in Hong Kong.

Samantha Wing Man KONG
Being part of the President's Protégé Scheme this year has been truly rewarding, especially participating in various activities that were part of the HKIE 40th Anniversary with President Ir C C Chan and the eight other Protégés. Working with a group of elite from different disciplines and all walks of life, we have many remarkable memories of engagement through various social activities and site visits. We were also given a chance to learn more about the HKIE by taking part in Board and Council meetings and other institutional events, which have broadened my social network in the engineering industry. I am truly thankful to the President for equipping us to become all-round engineers.

Sebastian Sai Kit KONG
I still vividly remember the scene when we brainstormed our year plan on a blank piece of paper in a café one year ago. It is hard to conceive that, within half a year, we had launched the "Your School, Dream Green" competition with the support of the Environment & Conservation Fund along with many other initiatives. We turned ideas into plans and concepts into reality. For me, the President's Protégés Scheme reflects the Institution's unique strength in bringing together engineers from different disciplines. It is my greatest pleasure to have worked so closely with the President and my fellow Protégés in serving the Institution.

Bertha Wing Yin HUI
It has been an amazing and fruitful year for me as one of the President's Protégés. The precious opportunity to participate in various engineering activities has given me exposure and insight into the world of engineering. I was able to meet and learn from senior figures, at the same time broadening my social network by making new friends within the engineering field. I am especially grateful to have met my fellow Protégés. We have worked seamlessly together to organise various activities throughout the year. Here, I would like to express my deepest gratitude to our President, Ir C C Chan, for his guidance and support, and my fellow Protégés for being such a wonderful team. This invaluable experience will always remind me to stay hungry and passionate on my engineering journey.

Mandy Lai Man LAI
I would like to express my sincere gratitude to our President, Ir C C Chan, who selected me to join the Protégés' family and led us through the special occasion of the Institution's 40th Anniversary. Participating in the series of celebratory events, I realised the power of cohesion among engineers from different disciplines. It offered us valuable opportunities to widen our social network. In this landmark year, I am so delighted and proud to work with my fellow passionate and resourceful Protégés, who offered me incalculable support and guidance. Our marvellous flagship activity, a student-oriented green campus competition, was successfully held through our great effort! Together we grow with the Institution and society into the future!

Stephanie Yuen Ting LEUNG
Being one of the Protégés was a really fruitful and rewarding journey. Throughout the year, we were given the opportunity to meet senior figures and participate in important events. We also organised activities and competitions to promote engineering and inspire the young. The scheme has definitely broadened my horizon. It provided us with a platform for gaining insight into the engineering profession by shadowing President Ir C C Chan and also expanded my network with industrial leaders and young engineers from different disciplines. I would like to express my sincere gratitude to the President and my fellow Protégés for this great year and for inspiring me to better serve the engineering industry in the future.

The Protégés with President Ir C C Chan

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