2017 Excellence in Environmental Engineering and Science® Awards Competition Winner

Honor Award - Environmental Sustainability

A Biophilic MyWaterway@Punggol - Innovative Floating Wetlands and Freshwater-Tolerant Mangroves

Entrant: Housing & Development Board (HDB) Singapore
Engineer in Charge: Mr. Lim Han, Vincent
Location: Punggol Eco-Town, Singapore
Media Contact: Mr. Lim Han, Vincent

Entrant Profile

The Housing & Development Board (HDB) is Singapore's public housing authority. We plan and develop Singapore's housing estates; building homes and transforming towns to create a quality living environment for all. We provide various commercial, recreational, and social amenities in our towns for our residents' convenience. As the public housing agency that houses over 80% of Singapore's population, HDB has a key role in supporting Singapore's commitment to sustainable development.

Punggol, as the first Eco-Town of Singapore, thus provides HDB the opportunity to drive innovation and experimentation of initiatives that are in support of Singapore's efforts to become a liveable and sustainable city.

Central to Punggol's Eco-Town's development is HDB's Punggol Waterway, a 4.2km long man-made Waterway which was opened in Oct 2011. This is the first and longest man-made Waterway in Singapore. In line with the vision to develop Punggol as the first eco-town of Singapore, HDB's architects and engineers took great effort to ensure that the Waterway was constructed in an environmentally- sustainable manner, and that the area's biodiversity would be preserved and enhanced as much as possible.

Greenery and nature are key elements in the design of the Waterway. The aim is to create an environment with abundant nature that encourages residents to foster deeper connections with the natural world and provide a picturesque backdrop for the residents who have made Punggol their home. To intensify greenery and bring nature close to residents' door step, HDB piloted first-of-its-kind solutions: Floating Wetlands System and Freshwater-Tolerant Mangroves, in the Waterway.

Project Description

Executive Summary

MyWaterway@Punggol, completed in 2011, serves to reinforce Punggol's vision as a waterfront town and creates opportunities for Housing & Development Board (HDB) to provide a waterfront residential living environment under the theme of "Green Living by the Waters".

A holistic and comprehensive Sustainable Development (SD) framework covering social, economic and environmental considerations was devised to steer the development of Punggol Eco-Town. One of the desired SD outcomes was "Enhanced Greenery and Biodiversity". As an Eco-Town, Punggol was also positioned as a living laboratory to test bed new urban solutions. To achieve this outcome, the team explored innovative ways to intensify greenery for the waterway through:

Cultivation of Freshwater-Tolerant Mangroves

With rapid urbanisation, Singapore has lost substantial green spaces for infrastructural development. Over the years, Singapore has lost about 90% of mangroves coverage. This drastic reduction has led to the rapid decline of biodiversity count and significant reduction of our natural heritage. The cultivation of Freshwater-Tolerant Mangroves along the Waterway aims to restore coverage of rare mangrove species, and stablise the slope along the embankments through natural means and slow down the surface runoff of sediments into the waterway from the embankment. In addition, the benefits of mangroves include carbon sink and sequestration. The mangrove ecosystem also allows for carbon capture from the atmosphere, and improve the water quality.

Development of Floating Wetlands System

One key concern for water bodies is accidental leaching of nitrogen and phosphorus from soil, resulting in eutrophication in waterbodies. Hence, there is a need to develop innovative and biological floating wetlands system best suited for our tropical environment, and to create aesthetically pleasing and lively ecological habitats. Floating Wetlands placed in the water bodies can help to improve the water quality in the immediate vicinity through absorption of nutrients via roots of the plants, and soften the hardscape such as columns of footbridge and concrete structures along the waterway.

Positive Impacts to the Living Environment

Today, more than 35 species of freshwater-tolerant mangroves and 15 species of floating wetlands were implemented along the waterway. Besides enhancing the theme of "Green Living by the Waters", the team has:

Developed, patented and implemented an innovative floating wetlands
Adopted planting as a natural means to stablise embankments
Enhanced water quality through natural means - 20% reduction of Total Nitrates and Total Phosphates, and 30% improvement in turbidity levels
Sustained and increased the biodiversity from 100 to 114 (90 birds, 10 butterflies and 14 dragonflies species)

Advancement of knowledge with practical applications of science to solve existing challenges and potential beneficial impact to society

Applying unsaturated soil mechanics principles to track the extent of improvements which mangroves can make on slope stability of embankments

Slope failures can lead to socio – economic problems caused by damages and destructions to nearby infrastructures. In the field of geotechnical engineering and design, the team had stretched the conventional design approach to adopt unsaturated soil conditions for slope analysis stability. We took an integrated design approach that incorporated both soil engineering principles and organic growth effects of vegetation roots. The mangroves not only strengthen embankments and control slope erosion, but it also improve the overall aesthetics of the waterway. In addition, it reduces the flow of sediments from the embankments into the waterway. We have also strategically located mangroves (planted across the entire slope face) to improve slope stability in a gradual and cost effective manner as these plants enhance and maintain soil suction within the soil vicinity of their roots. Under certain soil characteristics and slope profile, this methodology replaces the need for construction of geotextile bags and/or reinforced concrete walls for the embankments.

Applying Finite Element Analysis using ABAQUS Software for design of innovative Floating Wetlands System

Beyond conventional design, the team collaborated with the National University of Singapore (NUS) to apply numerical analysis in the development of an innovative floating wetlands system. This system is able to overcome current limitations for existing floating wetlands systems such as buoyancy, system modularity and loading capacity. We have also achieved better designs in terms of enhanced safety, flexibility in design and increased applications. Both static and hydroelastic analyses were performed to determine whether the floating module was able to meet the minimum freeboard, strength and serviceability requirements. Hydroelastic analysis was also carried out to assess the degree of flexibility of the floating wetland action. A well thought out and designed floating wetlands will not only provide water cleansing treatment but also enable a wider variety of plants to be planted on the system. This first of its kind modular floating wetlands system also address the safety of maintenance workers by ensuring stability when it is subjected to wind and/or wave action from passing boats. Currently, the floating wetlands have attracted a number of wildlife such as waterhens and otters, and these floating wetlands are expected to continue to draw different wildlife species e.g. birds, insects and fishes, as the plants mature.

Enhancing Engineering Capabilities

This is a complex and trans-disciplinary project that requires different disciplines to jointly create new methodological and translational innovations. For example, expertise in landscape design is required in the selection of suitable and resilient plant species with minimal maintenance for tropical condition. The application of unsaturated soil mechanics principles, together with landscaping knowledge in freshwater- tolerant mangroves has advanced our engineering capabilities to study effect of these mangroves in slope stability with the inclusion of unsaturated soil properties in the slope stabilities analysis. This has allowed us to move towards a more sustainable design and lower carbon footprint solution for strengthening embankments and resulted in a more cost effective method to improve slope stability.

The other area is the application of finite element technique in the development of floating wetlands. It is a software widely used in mechanical, aerospace and civil engineering fields to solve traditional implicit finite element analyses, static, dynamics, thermal, all powered with the widest range of conduct and nonlinear material options. HDB collaborated with NUS to utilise this finite element software to carry out static and hydrostatic analysis for the design of its unique and innovative modular system.

An Accurate and Efficient Approach

Freshwater-Tolerant Mangroves - The usage of Geostudio software such as Slope/W computes factor of safety for slopes in relation to the mangroves, and enables simple and complex analyses for a variety of slip surface shapes under different pore-water pressure conditions, soil properties, analysis methods and loading conditions. Seep/W software is also used to analyse groundwater seepage for different types of conditions from simple saturated steady-state to sophisticated saturated/unsaturated time-dependent analyses for slope. This saves Engineers significant time performing conventional method of calculations.

Floating Wetlands System - The computational time in performing the static analysis using the ABAQUS is much more efficient as compared to manual calculations. Moreover, this software enables symmetrical and anti-symmetrical properties of the floating wetlands configurations to be exploited, and this modelling method further reduced the computational time by half and saved the need to model all ten floating wetlands at the waterway.

Contribution to general public, society & nation building with considerations of the commercial and social impact

Freshwater-Tolerant Mangroves - Once established, the roots of mangroves gradually stabilise the slope of the waterway, and cleanse the water naturally. The foliage from mangroves has provided some green shade from the tropical weather, reduced ambient temperature and enhanced thermal comfort for the residents to stroll leisurely during daytime. They have transformed the waterway into an attractive relief corridor within a high density urban living environment. Such corridor provides opportunity for outdoor education on the characteristics of mangroves which is integral of Singapore's natural heritage. At the same time, it also builds up our landscape industry for diversity of plants, and expand the application of these mangroves to stabilize the slopes in our reservoirs.

Floating Wetlands System – The floating wetlands system create additional green spaces within water bodies in land-scarce Singapore. The floating wetlands will improve water quality in fresh water bodies e.g. lakes, ponds and dams. The emergent plants soak up excessive nutrients from the water body as part of their feed and consequently reduce the concentration of dissolved pollutants. Floating wetlands can also inhibit excessive algae growth through shading and reducing tidal erosion of lake banks. With this development, we see the potential towards launching large floating structure to accommodate strategic amenities. We are also commercializing this modular system and we are working on other forms of applications such as floating solar, maintenance walkway and etc. We are also working on other floating wetlands projects currently. Recently, these modules were used by another government agency to plant young tree saplings.

Technological innovation with Originality and Creativity

This is a multi-award winning project that won Association of South East Asian Nations (ASEAN) Outstanding Engineering Achievement Award, The Institution of Engineers, Singapore (IES) Prestigious Engineering Award, The Institution of Structural Engineers (IStructE) Award for Sustainability and The Singapore Concrete Institute Award for Innovators Category in 2016 for its outstanding engineering achievement in innovation. This is the first of its kind freshwater-tolerant mangroves arboretum, which can be found at MyWaterway@Punggol. It has over 35 species, and it includes rare species such as Lumnitzera littorea, Bruiguiera gymnorrhiza, Nypa fruiticans and etc. This is one of the few places in Singapore where visitors can see freshwater- tolerant mangroves in man-made waterway. One of the key challenges is to cultivate native mangroves in freshwater condition. With the development of Singapore's first floating wetlands system with in-built maintenance platform, HDB has also filed for patent on the innovative interlocking mechanism for its floating module, and this build up its intellectual property. A technical paper that discusses about the unique and innovative interlocking design and numerical analyses in IES journal Part A: Civil & Structural Engineering was also publicised.

Click images to enlarge in separate window.


Team Members standing on the floating wetlands at MyWaterway@Punggol.	The floating wetlands at MyWaterway@Punggol, where residents and visitors are able to see and enjoy the lush greenery closer.

The freshwater-tolerant mangroves planted along the embankments of MyWaterway@Punggol that brings our national heritage to the doorsteps of public housing developments.