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July 25, 2020

Digital simulation study on the proposed Macau flood barrier

he Macau SAR Under Secretary for Transportation and Public Works, Dr Raimundo Rosario, said after attending a recent Legislative Council meeting,  that the government is having some questions on the proposed Inner Harbour Thames River Style Flood Barrier Scheme’s effectiveness, and will perform a real-time digital simulation study to further looking into the project’s feasibility.  
      Raimundo also said that the study is mainly to investigate the potential impacts on nearby sea water level when the barriers are closed. The project was expected to commence at the end of this year, or early next year.  If the simulation results indicate adverse effects on nearby sea level rise during storms, there is a possibility that the project may be suspended.

Alternative proposal
Dr Harris Lee Hay Ip,  a senior civil engineer and Chairman of the Association of Macau Engineering Consultant Companies, said he had made significant comments on the flood barrier scheme over the past two years, including two articles being published in major news media --  "The Flood Barriers May Not be the Only Suitable Solutions”and“A Proposal to Raise the  Flood Barrier Height to 4.5 meter " etc.   He awares that the feasibility of a long term project could change from the time when it was first studied several years ago, due to changes such as regional geography and climate etc. He urges that the new study be completed as soon as possible and the government should also commence a parallel study on a modified scheme, in case it is found to be infeasible from the simulation study.  
     Dr Lee suggested that the direction of the modified scheme should adopt the “resilient city” concept as much as possible, similar to what has been done in other places (such as in the Netherlands, Japan and mainland China, etc) as water management, rather than fighting against water flooding, which the proposed water barrier scheme suggests. That is, the ideal scheme should aim to co-exist with water, while increasing the city’s capacity to accommodate flooding.
     In this regard, one of the ideas is to construct an approximately 2 km long steel flood prevention wall structure along the Inner Harbour River in Macau, which would form a new Inner Harbor Lake between the flood prevention wall and the current shore (Figure 1). Essentially, the concept is to relocate the government's proposed flood barrier wall, along the shoreline from Ma Kok Temple to Fai Chi Kei, to approximately 100m to 150m offshore and employ the Thames River style flood barriers as the ship gates in and out of the lake. The modified scheme could be considered a combined inland flood prevention wall (moving offshore) and the Thames flood barriers (rotating) about 90 degrees to 100 degrees from the current alignment (Figure 1). Preliminary analysis of this modification may have the following main advantages:

  1. The construction of the flood prevention wall offshore can avoid the impacts on land traffic;
  2. The Inner Harbour Lake would serve as a temporary flood storage area , a buffer, in case there is a slight overflow. If necessary, the overflow can also be discharged through a new drainage culvert and several large pumps into the Sai Wan or Nam Van lakes, forming a multiple lines of defense and a circulatory system; 
  3. Geology and geotechnical considerations are more suitable for the wall construction. In addition, there would be no underground utilities at the proposed offshore wall locations;
  4. The offshore wall would have much less impact on the landscape than the coastal walls and could be constructed at a greater height of above +5.0m (Macau Mean Sea Level). This would preserve Macau’s historic land-to-sea character;
  5. The flood barriers would be closed, when necessary, to temporary control the Inner Lake water level (probably around +1.8m during storm surges or high tides). This feature can effectively tackle the most challenging problem of sea water infiltration during high tides and facilitate rainwater drainage conditions into the lake;
  6. From an engineering standpoint, the modified scheme could replace the current Thames flood barriers and the onland flood walls together;
  7. Other mobile flood barrier schemes, such as the Venice MOSE, the New York Rockaways Flood Barriers, etc, can be considered as part of the offshore wall ship gates; depending on further evaluation studies;
  8. The Inner Harbour Lake area should be sufficient to maintain navigation and , more importantly, the operation of the existing terminals would not be interrupted (Figure 2). The final location of the new wall would also depend on the future urban planning of the terminals and the hydraulic system design.

(Figure 1) The proposed Inner Harbour OffShore Flood Wall with the New Inner Harbor Lake Concept 

(Figure 2) Bird's eyes view of the proposed Macau Inner Harbour Offshore Flood Wall and the Inner Harbour Lake

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Dr Harris Lee Hay Ip


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