拿来混某课的第二篇论文

Sui Xin

 

Alternative designs for Flood Protection

1. Introduction:

 

Levee is and will still be one of the most important and widely adapted engineering works in dealing with flooding events. However, levee, as an infrastructure, has certain limitations; a levee failure may be catastrophic. Alternative designs for flood protection have been analyzed and practiced around the world. This paper will give an overview of limitations of traditional levee system, and provide case studies into several non-levee alternatives, and finally compare the advantage, limitation, and adaptation of these alternatives.

 

1. Limitations of Levee System in flood protection
   

    

   Man-made levee is a relatively easy, direct, low-tech, and low-cost way to deal with flooding events. However, there are several limitations of the traditional levee. Ecological problems could be generated by the construction of levee systems and channel training. In the aspect of flood protection, there still exists several challenges that the traditional levee system might not be a sustainable infrastructure and might not be adaptive enough for the future sea level rising and global climate change. These limitations including:

    

   a) Not full protection from the standard of levee design
   

       In the design process, the levee systems were designed to meet a specific standard that aims to provide a specific level of protection, for example, a protection form a 100-yr or 50-yr flooding event. However, climate change is proofed to be accelerating, and precipitation rate is rising at a rapid speed. Thus an expected 100-yr flooding event might hit the protected area at higher probability rate (for instance, at a 75-yr probability rate instead of expected 100-yr probability rate). As a result, a former levee system that was designed to protect a 100-yr flooding event might not meet the desired standard in the future.

    

   b) Require frequent maintenance
   

       Levee can decay over time and require frequent maintenance (Watson, 2010). Subsidence, cracks, erosions will be generated overtime, thus require a continuous maintenance including enlargement, enhancement etc. For example, the levees protecting New Orleans have grown higher and wider from 1717 until now. Without frequent maintenance, the levee will not be strong and high enough to protect the land.

    

   c) High probability of levee failure, catastrophe consequence if levee fails
   

       Levee systems are prone to fail in different modes; overtopping and breaking are two main modes. When levee system do breaks, or are overtopped, the result can be catastrophic (Watson, 2010). For example, in New Orleans, the levee is the only layer of protection in the whole urban area. A single break on the 350 miles levee system is bad enough to open the pathway for water to flood the whole city. Hence, Flood damage may be more significant than if the levee system had not been built. This consequence might mainly because when a levee failure takes place, large quantity of water hit the land in seconds. Compared to the scenario that no levee had been built, the force of waves will be more intense, all the damage is generated in seconds.

    

2. Stronger and larger levee: the Super Levee alternative
   

    

   As stated above, levee might not be strong enough to prevent from the high pressure generated by waves during large flooding, and could cracks, be eroded overtime. To deal with this, one concept is to build a super strong and super large structure that is impossible to break or crack. Based on this concept, the Super Levee model is designed and adopted in some areas in Japan.

   

   Figure 1. Super Levees and multipurpose retarding basins (temporary flood detention areas) are part of flood control, river enhancement, and urban reinvestment zone initatives.

   (Source: Hitomi Godou, Japan Ministry of Land, Infrastructure, Transport and Tourism. “River Basin Management in Japan: Flood Control Measures, Water Resources Management.”http://www.mlit.go.jp/river/basic_info/english/pdf/conf_10.pdf

   Diagram from: Donald Watson and Michele Adams: Design for Flooding)

    

   

   Figure 2: Super levee on the Edogawa in Tokyo

   (Source: http:// http://www.thepolisblog.org/2009/11/levee-town-super.html)

    

   a) Overview of the Super Levee in Japan
   

       A super levee is a large-scale river embankment. The main difference to a traditional levee is its width; a super levee often has a mild slope of 1:30. To ensure the levee is strong enough to prevent erosion, the toe (refers to the top and the slope which facing river) has been reinforced with a concrete slab and a steel sheet pile. The super-levee is a desirable solution in Tokyo in several reasons, firstly, earthquakes hit Japan frequently, as a large-scale earthwork, the super levee is resistance to earthquakes. Secondly, due to the mild slope of a super levee, during large flooding events, wave will lose energy when overtopping the levee, thus it will not hit the inner slope with large forces. Thirdly, as the super levee is a lot wider then a traditional levee, seepage is reduced, and erosion on the super levee will not undermine the protection significantly.

    

   b) The adaptation of a Super Levee
   

       The super levee is often built on top of existing traditional levees, and the design and planning are integrated with the development of the impacted district and community. It might be a part of the urban redevelopment, land rezoning projects or other urban planning projects. Implementing a super levee to an area with existing buildings is a lifetime project, and requires lots of efforts including dialogues with the community, compensation of land ownership, accommodation among different groups and different agencies. As building on top of the inner slope is permitted, the government agencies negotiate with landowners behind the former traditional levees. These landowners have the options either to be bought out and relocate to other districts or return to the same partial after the construction of the super levee. Thus, the ownership of the properties on which the super levee has been built might be unchanged. Different zones of the inner slope are planned to have different land uses regarding both the needs of flood protection and the desires in the aspects of urban planning which is a result of interests of different groups. For this reason, the residence welcomes the super levee even though the construction caused relocation or change of land ownership. The inner slope also has strength in the aspect of landscape, as it provides an open view towards the river smoothly, in combination with open recreational spaces.

    

   c) Limitations of a super levee system
   

       A super levee and the construction process have certain features that limit its application. Firstly, overtopping is still possible, even though the super levee is often built under a higher standard. Addressing the overtopping problem, a dedicated zone witch designed to be temporary detention basins during peek floods could be introduced. Secondly, similar to a traditional levee, the subsidence problem still existed. Considering the super levee is much heavier, the subsidence rate is higher, and sea level rising accelerated the net level difference between sea level and inland level. Thus more earthworks should be put on top of existing super levee over time. Thirdly, as the existing houses must be removed, the process of adapting a super levee to an existing district requires long period of time and agreements among a larger number of groups and land owners, which involve great efforts. Finally, huge among of suitable earth is required in order to build a super levee; the transportation of earth might be a costly large-scale project and might not be ecologically sound.

    

3. Living with flooding: non-levee alternative
   

    

   Super levee might be one of the only possible solutions for Tokyo that has a high density, frequently hit by typhoons and earthquakes. However, in other places of the world, opposite to the concept of enhancing levee, building even stronger, larger levees, via removing levee entirely and utilize a decentralized protection system is another concept that was explored and experienced all over the world.

    

   a) Elevated house
   

       One possible way in the level on individual houses, is to elevate an existing building, or build a new one with an elevated first floor. The area under the elevated building may be used for storage, parking or building access and stairs. However, lifting an existing building is a challenging task in terms of both technically and aesthetically (Watson 2010).

   

   Figure 3: A section of a typical elevated house

   (Source: Design for Flooding, by Donald Watson and Michele Adams)

   

   Figure 4: Coastal community on Bolivar Peninsula, Texas.

   (Source: Photo by Jocelyn Augustino FEMA Photo Library, http://www.hurricanescience.org/society/impacts/)

    

   b) Floating house:
   

       Many designs of floating house have been developed; some of them were materialized. The Floating House in Lake Huron, Ontario Canada (2005) by MOS LCC Architects is one example. Lake Huron’s water level varies drastically from month-to-month, year-to-year. Adapting to this constant, dynamic change, the house floats atop a structure of steel pontoons, allowing it to fluctuate along with the lake.

   

   

   Figure 5,6: Floating House by MOS Architects.

   (Source: http://www.archdaily.com/10842/floating-house-mos/)

    

 

c) HafenCity in Germany, a city planning for flooding

HafenCity is a quarter in the borough Hamburg-Mitte of Hamburg, Germany. The new water city is under development in the old harbor of Hamburg. The HafenCity Project is one of the largest inner-city rebuilding projects in Europe, a blueprint for European city-center development at the water’s edge. The project has been in development for over ten years, it’s expected to accomplish around 2020-2030.

 

The whole of HafenCity is located outside Hamburg’s levee protection line. The land is 4 to 5.5 meters above sea level, lower than the inside areas in Hamburg’s levee. This means that it is subject to occasional flooding and that extra protection is required. Flood protection has always been an important precondition for the planning of HafenCity. The project does not propose to surround the city with levees. Instead, they decentralized the protection into individual buildings and streets. New buildings and new streets are built on elevated mounds: these foundations are 8 meters above mean sea level. Flood-secure parking garages are proposed inside these foundations. At the same time, open spaces and certain plazas will remain at an unchanged elevation of about 4.5 to 5.5 meters above sea level, therefore preserving their close links and accessibilities to the waterfront. Almost all new roads have been laid at a flood-secure level of 7.5 to 8 meters; in addition, new bridges will be built to be flood-proof, while old bridges will be renovated or raised.

Some existing streets are renovated to be able to endure flooding. The buildings along these streets generally have two vertical parts. The higher levels (7 to 8 meters above see level) are mostly residential or commercial uses. These spaces are not expected to be flooded. The lower levels are mainly parking garages. These spaces can be sealed temporarily by mechanical “flood gates” during flooding. During these periods, street parking is not permitted, thus vehicle owners are responsible to park their vehicles at safety garages. A lifted secondary pedestrian network is used as a backup of primary on-ground transportation networks during flooding.

 

Figure 7,8: Dry condition and flooded condition of Am Sandtorkai street.

(Source: Figure 7: HafenCity Hamburg Projects March 2010: Insights into Current Developments

Figure 8: HafenCity Hamburg © ELBE&FLUT)

 

Figure 5: Am Sandtorkai Street during flooding. The “flood gates” can be found at the base of each building.

(Source: Miniatur Wunderland)

Figure 6: Elevated secondary pedestrian pathway

(Source: Freie und Hansestadt Hamburg, Behörde für Stadtentwicklung und Umwelt by Amt für Bau und Betrieb Abteilung Hochwasserschutz http://www.hamburg.de/contentblob/129586/data/flutschutz-hafencity-druck.pdf)

 

d) Decentralized network of detention basins

    The detention basin is structures temporarily hold and detain runoff for several hours or days. This application has evolved from the approach of flood control. During a flooding event, water can be hold temporarily in these basins, reducing the total among of water that floods into the urban area. After flooding, water held in these basins will be released back to river channels. This method has been widely implemented from site to regional scale (Watson 2010). However, centralized large scale detention basins might not solve the flooding problem due to two main limitations. Firstly, a centralized detention basin has a large area of “service territory”, which means that the surface runoff from a large area needs to be drained into the basin, thus needs a higher runoff rate or longer time. During a flooding event, huge among of water floods inland in relatively short period of time, there might not be sufficient time to allow the runoff discharge into the detention basin. Secondly, as the large detention basin has a large “service area”, any failure (including a disconnection from the stream channel, insufficient capacity, etc.) has an impact of the whole area, thus the failure will bring about disasters.

    In dealing with these limitations, a decentralized network of smaller scale detention basins might be a solution to overcome these problems, firstly, as detention volume breaks into many connected smaller basins within the neighborhoods, surface runoff is able to drain into the adjacent basin immediately. Secondly, an individual failure of detention basin will not impact the whole network, hence, as those basins are interconnected, when one basin is full of water during flooding, other basins in the network could hold the extra runoffs.

One example is proposed by the Dutch Dialogue 2 in New Orleans neighborhood, several open spaces are designed to be flooded and serve as detention basins during flooding (Figure 7,8). Another Example is proposed by me in LAR 7010 New Orleans Studio, the concept is utilize vacant parcels and transform them into detention pools, and then connects these basins together to form a network (Figure 9,10,11).

Figure 7,8: Hoffman Triangle BW Cooper Water Plan Before and After compare

(Source: Dutch Dialogue 2 http://dutchdialogues.com/2010/05/03/dutch-dialogue-2/)

    

Figure9: Mapping of vacant parcels Figure 10: Proposed small detention pools

(Diagrams by Sui Xin) (Diagrams by Sui Xin)

Figure 11: Proposed decentralized network of detention basins in the New Orleans Mid-city area

(Diagrams by Sui Xin)

 

1. Conclusion
   

   There is not a single solution that promised to solve the flooding problem all by itself. All the proposed concepts and designs have its limitations and their best adapted preconditions. The following table tried to compare these different designs and their limits of adaptations. To achieve a suitable goal of flood protection, combinations of traditional levees with other alternative models is necessary. Top-down foresightedly regional planning and bottom-up community driven efforts should be integrated to achieve the ambitious goal of sustainable flood protection. Finally, people’s perception of living may change; a lifestyle of “living with flooding” in coastal cities will emerge overtime.
   

	Advantage	Limitations	Adaptation
Super Levee	Break-proof Seepage-proof Earthquake-proof Provide a barrier-free connection from inland to waterfront	Huge among of earthwork required Subsidence is accelerated Need great effort of negotiations among different groups, land owners High cost	High density urban core Earthquake zones
Elevated house	Existing house can be elevated Relatively low cost Engineering project can be done quickly	Limited to 1 or 2 story residence Technical and aesthetic challenges exists	Existing or newly developed low density residence zones
Floating house	Highly waterfront accessibility	Relatively higher cost Limited to 1 or 2 story residence Only new developments Technical challenges exists	New water front developments Wealthy communities
Sealed lower level of a building	Flexible in both dry conditions and wet conditions. Can be applied to high density areas. Existing buildings can be renovated to be flood-proof	Regional planning is required, need large scale engineering, all the buildings in the region should be renovated. Need an information system to alert residence.	Existed or newly developed mix-use areas with a high density
Decentralized detention basins	Provides extra volumes to hold water in a sudden flooding event Different use of open spaces in dry and wet period A single basin failure will not affect the whole area	Regional planning is required, need cooperation between land owners	Low density areas or areas that have many vacant parcels.

Table 1: Compare of different alternatives

 

 

Bibliography

 

Watson, Donald and Adams, Michele. Design for Flooding: Architecture, Landscape, and Urban Design for Resilience to Climate Change. Wiley Pub. 2010

 

Graff, R.D and Hooimeijer, F.H . Urban Water in Japan Vol. 11,
Taylor & Francis Group, 2008

 

Stiller, Eileen and Jeske, Janina Hafencity Hamburg Projects: Insights into Current Developments HafenCity Hamburg GmbH, 14^th edition, 2010