Planning for Urban Flooding by Revathi Roopini

Planning for Urban Flooding: A Review of Case Studies and Guidelines

INTRODUCTION Causes of urban flooding Classification: types of flood

Introduction Floods are a part of natureâ&#x20AC;&#x2122;s cycle. Civilizations, since time immemorial, have defended settlements from floods. Although, in todayâ&#x20AC;&#x2122;s context flooding is associated with a negative connotation, in the past civilizations depended upon floods for agriculture productivity. Seasonal floods replenished soil nutrients and increased yields.. In trying to harness and shape natural forces we have, at present, done much harm. Although most floods can be predicted, they can cause massive destruction. They impact various scales of urban development ranging from houses and neighborhoods to entire regions. However, not all floods are alike. They may be caused by different factors and behave differently. While some floods develop slowly, flash floods occur quickly- in a matter of minutes. Certain floods may occur on a regular basis or be very rare. Cities are very vulnerable to floods. This is because there is a high concentration of people, wealth and economic activity focused in urban areas and hence potential for high losses. Rapid rate of global urbanizations and expanding economies have increased areas of high risk and potential scale of devastation.

But not all cities are equally prepared to face these challenges. Cities in poorer countries are especially vulnerable since proper defense means are yet to be developed and they do not have the economic means to do so swiftly. In the decades to come, global warming is projected to further intensify the hydrological cycle. Such unpredictability will only increase the scale of impact.

Urban aggromerations with greater than 750,000 inhabitants, 2010.

Flood events between 1970 and 2011

Flood management focuses on improving four adaptation strategies of a city. The first is to improve threshold capacity. This is to build defenses and infrastructure so that the threshold to withstand or prevent damage from even extreme weather events. (e.g. a 200 year storm). The second is coping capacity. This is the capacity of a city to reduce or absorb damage in case of a disturbance that exceeds the damage threshold the cityâ&#x20AC;&#x2122;s defenses were designed to face. This capacity is determined by the presence of effective emergency and evacuation plans, effective communication and a clear organizational structure. The third is recovery capacity. This refers to the capacity of a city to recover to the same or an equivalent state as before the emergency. The fourth is adaptive capacity, this is the ability of a city to cope with future uncertainties. Even if a system is functioning well in the present, human and environmental changes may burden the system in the future.

The absolute prevention of flooding is an impossible task. Flood management is about building resilience. It is about looking for opportunities and solutions that add to the welfare of society and enhance urban life so that social and economic benefits outweigh potential costs.

Average recurrence interval: What intensity and quantity of rainfall should a sewer system be prepared to handle? Where is the line between engineered and built systems and nonstructural responses (such as early warning systems)? The average recurrence interval refers to the chances for a particular intensity of rainfall to occur in a given year (e.g. 1in 10, 1in 50, 1 in 100, 1in 500 year storm). Although a 1 in 100 year storms are rare, they cause considerable damage. Climate change is further aggravating this situation. 1 in 10 or 1in 20 year storms now occur in increasing frequency. The United Kingdom apply a four domain approach to prepare for different recurrence intervals. The four domains are based on the level of preparedness of the city to handle the rain event. Domain 1: Everyday rainfall. Here the drainage system manages everyday rainfall of low intensity and volume. Provided systems are effectively maintained hazards are rare (e.g. blockages) and likelihood of flooding is low. In this domain, the benefits of capturing and storing rainwater for purposes such as irrigating landscape predominate. Domain 2: Design rainfall. This is what drainage systems (sewers and green infrastructure) are designed to achieve. New sewer lines are designed to accommodate a 1 in 30 chance of rainfall that may occur in

any given year and highway drainages are designed to accommodate 1 in 5 chance of rainfall that may occur in any given year. With periodic maintenance, the system will function successfully to its designed limit.

Domain 4: Extreme rainfall. Coping with extreme rainfall relies upon urban resilience, spatial planning and emergency planning. Domain 3 and 4 share similar approaches but the magnitude of impact will be greater in domain 4.

Domain 3: Exceedance rainfall. In case of rain events that the system is not designed to handle, the excess runoff is detained using a range of interventions and multi-functional land uses. Flood control in this domain is using both structural (physical measures) and nonstructural responses as well (e.g. emergency planning)

The four domain approach for design to manage rainfall.

Classification: Types of Floods Urban areas are found in a wide range of geographical locations and because of this they are subject to all conceivable forms of flooding. Broadly there are two major types inland flooding and coastal flooding. Both types have further sub categories. Inland flooding is driven by rainfall whereas coastal flooding is driven by a combination of sea surge and rainfall but only occurs at times of extremely elevated sea levels. Although there are different categories of flooding, they can all occur within the same area and one can aggravate the other. (illustrated in the diagram below) for example overland flooding can worsen flooding due to minor system failure.

Or storm surges and tidal flooding can worsen ground water flooding and fluvial flooding. In the same way solutions that address one type can help mitigate impact due to other categories. An integrated portfolio of responses that encompasses land use policy, risk awareness and effective communication, urban design and water engineering systems in required to tackle the situation in totality. Inland flooding has five subcategories. These are ○ Overland ○ Fluvial ○ Groundwater, ○ Failure of minor systems ○ and failure of major systems

Several factors can cause flooding in the same area. Hence, an integrated portfolio of responses are required.

Inland Flooding Overland flooding refers to flooding caused by surface water runoff from impervious surfaces. Surface runoff from natural or agrarian ground cover is only 10% whereas it increase to 55% in urban areas with impervious surfaces between 75 to 100%. Increase in impervious areas is caused by rapid transformation in land use especially in dense urban areas. Runoff from expressways and highways is another factor. Poor management of surface run off upstream, in rural or peri-urban areas can increase surface runoff volumes in urban areas. Groundwater flooding refers to saturation of top soil from raising ground water table after a rain event. After a rain event, the infiltrated water causes the ground water level to raise. And in turn, through capillary effect this causes dampness to enter into building structures. This type of flooding can last for several days to months. It is characteristic in places with high aquifer and groundwater level, rocky soil and buildings built by casing over lakes or wetlands. Fluvial floods are caused by the exceedance or overflow of a stream or rivers designated water carrying capacity. Where defenses are developed, excess water breaches the channel walls and overflows onto land. Where defenses are not built, this refers to the flooding of the natural flood plain. In poorer countries, these flood plains are occupied by squatter settlements.

Overland 1)Developed urban surface 2)Impervious roadways 3)Rural or peri-urban land use

Groundwater 1)Saturation of top soil (former wetland/pond) 2)High aquifer level (relatively low depth of rock aquifers

Fluvial 1)Exceedance of stream or river capacity 2)Exceedance of lake capacity

Minor System Incidence 1) Exceedance of sewer capacity 2)Exceedance of SUDSâ&#x20AC;&#x2122; capacity

Major System Incidences 1) Breach or collapse of dams and embankment 2) Failure of land drainage system/discontinuation of ground water pumping.

In waterworks and sewer systems, ‘minor systems’ refers to pipes and other infrastructure that is beneath the ground. Flooding due to minor system incidences refers to flooding due to exceedance or overflow of underground sewer capacity or exceedance of green infrastructure capacity. This normally occurs in cities which developed at a rapid pace. Older systems would not have been designed to accommodate such large loads. Failure of minor systems also occurs when there are rain events with frequency and intensity that the system was not anticipated to handle. Excess water inundate urban areas or run off into natural water bodies nearby. This leads to fluvial floods and deterioration of water quality. Major systems refers to large scale flood defense structures and mechanisms such as embankments, levees, dams, water drainage pumps etc. A failure of this kind can lead to floods at massive scale. Coastal Flooding . The three sub categories are large scale incidences, flooding in estuaries or deltas and flooding caused by the open sea. Large scale incidences refers to collapse of manmade defenses such as sea walls or natural disasters like tsunamis. Both flooding due to open seas and flooding in estuaries or deltas are caused by three factorssea level rise, tidal action and weather driven surges (typhoons or hurricanes).

Open Sea 1)Sea level rise 2)Tide – astronomically driven 3)Surge- Weather driven (typhoon

Estuaries/ Delta 1)Sea level drive 2)Tide – astronomically driven 3)Surge- Weather driven

Incidents 1)Tsunami 2)Defense Collapse

Storm surge and flood plain.

OVERLAND FLOODING Guidelines for existing urban areas Copenhagen Rotterdam Guidelines for new development Singapore United Kingdom

Overview Overland flooding and flooding due to minor system exceedance are closely related as one aggravates the other. A wide range of strategies are covered in the section below. The guidelines in Copenhagen and Rotterdam are directed towards urban areas that are already built whereas the guidelines for Singapore and United Kingdom are directed towards new development, urban renewal projects and large scale renovations. Existing urban areas have multiple challenges such as lack of space, high property and real estate value, high percentage of impervious surfaces and usually where the consequences are most disastrous. In the case of Copenhagen, the sewer system is capable of handling rainfall within the domain 1 and 2 range. When there is an exceedance of rainfall, (domain 3 and 4 events), surface flooding is managed in a controlled and predetermined manner. The cloud burst roads act as pathways to guide exceedance into the nearest water bodies. To avoid collection of water, all at the same time, the four strategies delay the rate at which the water leads into the cloud burst road. The detention and delay is in the form of green strips, plazas and parks. By this method, large volumes of runoff are broken down into smaller volumes and their released into natural water

bodies or engineered structural systems (sewers or LIDS) are staggered and delayed to avoid overload In Rotterdam the guidelines have a holistic approach. The guidelines are tailored to suit different land uses and take into consideration its typical characteristic. For example high plinths and building adaptations are recommended for buildings outside the dike protection. In the post war housing areas where there is less congestion and more space available measures which require larger space (such as wetlands) are recommended. New developments are an opportunity to make the most difference since decisions on site can have positive impact on the entire city. The aim for on surface water management in the SuDS (United Kingdom) guidelines is very straight forward. The same run off volume that previously existed on site, before development must be maintained post development. The strategies are organized into a â&#x20AC;&#x2DC;management trainâ&#x20AC;&#x2122; that delays, reuses and treats water at its source, site and region. The ABC Waters guideline in Singapore has a similar approach. The objective is to integrate ecological benefits and public amenities (such as parks and greenways) into surface water management.

Cloudburst Mitigation Plan (2012), Copenhagen Copenhagen is the capital city of Denmark and has a population of 1.3 million people. Cloudburst (mentioned in the title) refers to very intense rain over a short period of time. When this occurs, the conventional sewer system cannot handle the sudden influx of water leading to urban flooding. The Danish Meteorological Institute defines precipitation of 15mm over the course of 30 minutes as an intense rainfall occurrence. In 2014, the rains were as intense as 100mm in 30 minutes. In the Copenhagen climate adaption plan (2011), the Danish Meteorological Institute (DMI) predicts that in 2100 there will be 25-55% more precipitation in winter, precipitation in summer months will fall by 0-40% and the intensity of the heavy downpour is expected to rise by 20-50%. The cloudburst plan was framed to prepare for this scenario. The plan has three main objectives. Major part of the precipitation from an intense rain event must be routed to the sea. Only a small (quantity that can be handled by the system) should be routed towards the fresh water infiltration basins and lakes. The volume that cannot be handled by the sewerage system must be temporarily detained and released at a slower pace either through percolation or into the conventional sewerage system.

Since a large portion of public funds will be allocated towards these projects, it is vital that they serve a dual purpose of being vibrant public spaces as well.

A hydrology study was undertaken and areas in risk of flooding were identified. (Red: High Risk, Yellow: Medium Risk, Green: Low Risk)

The area with the highest risk of flooding was selected as a pilot study area.

Areas that are at risk of flooding.

Design proposal incorporates five stratergies

○ Detention streets are streets that are typically located slightly upstream of vulnerable low points. ○ These streets are designed to detain runoff, before it reaches vulnerable points downstream.

Roads for stormwater or Cloudburst roads: o These roads are specifically designed to lead surface runoff directly into the nearest water body (sea or river) o These streets can be formed with a unique V-shaped profile and raised curbs to ensure water will flow in the middle of the road, away from the buildings – contrary to standard engineering practice. o Or channels and swales are established along road edges so that water runs through these green strips.

o Pipes for stormwater or Cloudburst Pipe: These pipes also lead surface runoff towards the closest water body (river or sea) o This is placed just below street level to ensure connection to other surface solutions. o This solution is recommended only if there is no useable space for aboveground solutions. o Most expensive and time consuming to implement

○ Roads for delaying rain or Green Street: These roads are designed to store and delay the water resulting from heavy cloudbursts. ○ Green streets are proposed as upstream connections to all Cloudburst roads. ○ The green streets should be established with a combination of small scale channels and storm water planters or permeable paving. Cloudburst roads with v-shape profile.

o Spaces for delaying the rain: These spaces are meant to store large quantities of water. o Central retention areas are proposed in the squares and parks where it is possible to delay stormwater. o The central retention elements can be, for example, open depressions in the parkland or lowered seating areas. o Alternatively, they can be established as underground storage such as soak-away crates or rain gardens. o Central retention elements will typically be placed in connection with adjacent Cloudburst roads

Cloudburst roads with side strips.

Park space: central retention area.

Climate Change Adaption Strategy (2014), Rotterdam Rotterdam is a port city in Netherlands with around 1.2 million inhabitants. Since more than 50% of the city is below sea level, the Dutch have adapted to living with water in various ways. In the Shanghai World Expo (2010), Rotterdamâ&#x20AC;&#x2122;s water management systems were displayed in the water city pavilion in the urban best practices area. Although the city has a robust defense system, climate change has increasingly impacted the city with unpredictable weather events. In order to prepare for challenges posed by raising sea levels and climate change, the city adopted a climate change adaptation strategy in 2014. The strategy has a holistic approach and tries to incorporate all possible measures: Robust and resilient: To increase sewer capacities and incorporate green infrastructure(LID) Protect and live with water: To protect the city from storm surges and rising sea level by reinforcing dikes and levees but also experiment with adaptive and floating buildings. Delta work and small scale: To mange water at all scales ranging from permeable pavers for infiltration to surge barriers. Technology and nature: To incorporate technology for smarter mange water but also harness the capabilities of natural systems.

Guidelines for climate adaptations are based on land use and six distinct land uses were identified. Anticipated consequences of climate change include increase in rainfall, storms, rise in sea level, and heat waves. Guidelines for the port area are discussed in the next page. (The other land uses are described in appendix 3)

Existing flood defenses and water management system.

Objectives.

Flooding of areas outside the dike in 2100. (green line: dike)

Legend:

Port â&#x2014;&#x2039; The port area stretches out over forty km and encompasses one third of the total land area in Rotterdam. â&#x2014;&#x2039; The Port of Rotterdam has considerable economic value and directly provides many jobs for the people in the Rotterdam region. (largest in Europe) 1. Safe terp (elevated platforms):Protection of goods at safe collection points. 2. Wet-proof Construction (resistant to water):Floodable ground floor and internal moving of goods to higher floors. 3. Small compartment dike: Outer to inner protection and vice versa 4. Elevated infrastructure (roadways/ trains):Guarantees accessibility of the port/ safe evacuation routes. 5. Ecological structure: Local cooling/biodiversity 6. Dry proof construction/ flood wall: Protection of essential functions whose continual operation must be guaranteed.

Sustainable Urban Drainage System (SuDS), United Kingdom Sustainable drainage systems (SuDS) are designed to maximize the opportunities and benefits from surface water management. Since the 1970â&#x20AC;&#x2122;s, cities and towns in UK have been implementing these systems to minimize overland flooding, in place of traditional grey infrastructure. Today, the SuDS are implemented in all new development. The objective is very simple, the new development must maintain the same runoff quantity as before (runoff in its undeveloped state).

Objectives of SuDS Design.

SUDS devices are most effective when arranged in a series which mimics natural catchment processes, in the form of a â&#x20AC;&#x2DC;management trainâ&#x20AC;&#x2122;. In this way, the passage of water through the urban environment is slowed, maximizing the opportunity for infiltration and pollution control before the release into artificial channels or watercourses. In planning a management train, progressive stages in the management of runoff can be identified: inlet control, source control, site control and regional control. Inlet control refers to the point at which rain water reaches land. In the build environment this refers to building roofs, car parks etc. Source control is retention/ treatment of water as close to the inlet as possible. Conveyance is the pathway by which water which can cannot be

SuDS management train

retained or treated by source control is transported to larger site control measures such as parks or other open spaces. Excess water which cannot be treated or stored in the site control measure is similarly conveyed to regional control measures (wetlands, lakes). As shown in the figure, rapid urbanization results in increase surface runoff. By incorporating various elements of SuDS in the development, runoff can be significantly reduced.

Impact of urbanisation on catchment area

Commonly employed SuDS for different types on development

Conceptual design process: ○ Set strategic storm water management goals(quantity of runoff reduction, standard of water quality, biodiversity and addition amenities) ○ Identify feasible points of discharge ○ Define surface water subcatchments and flow routes ○ Select SuDS components for Management Train ○ Outline design

Planning for phased development is a challenge since the system becomes more cost effective with larger density. And it may not be justifiable or viable to construct large ponds or parks that are necessary for the system to function but increase the upfront cost for the developer.

3. Define parks, open spaces and corridors

4. Define road network 1. Flow routes and discharge points

2. Defining surface water sub-catchments

5. Define exceedance routes. These are flow or retention routes in case of extreme rain event.

ABC Waters Guideline (2009), Singapore Singapore is an island country with a population of 5.5 million people. Being an island, the city depends heavily upon water depends heavily upon water imported from Malaysia for its every day use. In order to reduce dependency and promote sustainability the city built 15 reservoirs to store and reuse surface runoff. In 2006, the water board adopted a new approach towards surface water management. The goal was to transition from being a ‘city in a garden’ to ‘city of garden and water’. As part of this initiative, a masterplan was framed. It identified 120 potential projects. In 2009, the ABC (Active, Beautiful and Clean) Waters guideline was released by the government to promote and incentivize an ecological approach to surface water management in new or renovating private and public development. The guidelines are summarized here.

Stormwater Canals remain dry and underused throughout the year except during rain events where water levels reach short and extreme peaks.

With the new approach, rainwater is stored and treated closer to its source and is slowly released into water bodies. This approach will improve water quality and enhance urban ecology.

Based upon the storm water passage, the guidelines describe in detail the following: ○ Catchment elements ○ Treatment elements ○ Collection and storage

Steps of a typical stormwater passage.

Catchment Elements: Rain water is relatively clean but it becomes contaminated as it moves through urban surfaces. The surfaces in our urban environment can be categorized into structures (buildings, plazas, parking lots), circulation infrastructure (roads and bikeways), softscape (parks, gardens, playfields), waterbodies (lakes, ponds) and waterways: (streams, rivers) Categories of surfaces in urban areas

Water can be captured, stored, treated and reused on softscapes like plazas and parks

Source control: on site collection and treatment or conveyance can be accommodated into any size or footprint of buildings.

Within a building elements can be incorporated into rooftops, sky garden ,balcony Planter boxes and ground floor

Treatment elements Treatment elements can be applied to urban components to slow down or retain surface runoff while simultaneously cleaning it.. They are cost effective when compared to conventional grey infrastructure solutions and provide multiple other benefits. It is difficult to greatly reduce contamination and improve quality with a single element but a series of elements can achieve the required quality. For example, sedimentation basins remove large particles, and cleansing biotopes remove nutrients.

Collection and Storage Elements: Ultimately, the excess water after treatment and storage is led into the water ways or water bodies. Singaporeâ&#x20AC;&#x2122;s water catchment area, is divided into three regions (central, western and eastern), and it constitutes 32 major rivers, 15 reservoirs and more than 7,000 km of canals and drains. Two strategies are recommended to enhance the existing grey infrastructure system. Naturalization of concrete channels and bioengineering techniques for new or reconstructed canals Both these strategies enhance ecology, improve water quality and improve aesthetics and visual appeal.

Naturalization of concrete channels using gabions.

Section illustrating bioengineering techniques

FLUVIAL FLOODING Defensive Flood Management: Super Levees, Tokyo Multifulctional Dykes, Rotterdam Non-Defensive Flood Management Flood Plain design- UK Balancing Lakes- UK

Overview In the past fluvial floods were a necessity for the food and economic success of a settlement. The process replenished soil nutrients, making the banks fertile for agriculture. Two strategies emerge as solutions to safe guard settlements from fluvial floods. One is to integrate other is to defend. The defend model encompasses large scale structures such as dams, levees and embankments that keep water away from habitable areas. The integrate model, on the other hand, incorporate as waterways into the settlement in the form of smaller streams and waterbodies such as canals and lakes. At the regional scale, the SuDS system in UK has two approaches to integrate. The balancing lakes are a system of connected lakes along the flood plain of a river. Flooding after a heavy rainfall is avoided as water is temporarily detained in these lakes. The other non-defensive flood management strategy is by controlling the land use on the flood plains. By designing open spaces such as parks and parking areas along the flood plain, the areas can conveniently flood during heavy rain events and serve its original purpose other times of the year. A non- defensive or integrate strategy has lesser costs associated with construction and maintenance and the risk of damage if it fails is lower.

The defense systems in the form of levees and dikes in Tokyo and Rotterdam are examples of the defend strategy. In Tokyo the threat of breach and water seepage is addressed by building super levees. In Rotterdam space within a levee is designed for multiple functions such as residences, offices and shops. The integration of multiple uses into its structure, reduces costs for the city as it can be undertaken as a public-privatepartnership.(manipulating market demand for water front properties)

Super Levees, Tokyo Tokyo, is the capital city of Japan. Most parts of Tokyo are spread below the designed (designated) high water levels. This is the maximum carrying capacity of the channelized river during a flood event. The levees, hence are important defense structures since even a small breach will cause serious inundation. .

Advantages of super levee over a conventional levee.

The diagram below illustrates the relatively low land level when compared to the designated high water level in Tokyo in comparison to New York city where the land is considerably higher than the designated high water level

High standard levees or a super levees are gentle slope levees that are able to withstand large scale earthquakes and contribute to safer and better environment. It is an especially wide embankment built in collaboration with urban redevelopment projects. They enable effective utilization of land, reinforcement of flood control, are more resilient to earthquakes and enhance urban environments.

Super levee along the Arakawa River constructed in alliance with urban renewal.

Length of embankment area around 30 times the height of the levee Advantages of a super levee over a conventional levee during a flood or earthquake.

Multifunctional Dykes, Rotterdam Rotterdam is a city in the Netherlands, located within the Rhineâ&#x20AC;&#x201C; Meuseâ&#x20AC;&#x201C;Scheldt river delta at the North Sea. 70 % of its area is on reclaimed land or beneath mean sea level. Hence the dike that surrounds the city is an important flood defense especially during storm surges. The dikes incorporate multiple functions within them. This strategy encourages the best utilization of limited land resource, enhances urban areas and reduces cost of construction through possible private public partnerships. Three examples are illustrated below:

The green line indicates the existing dike

Dakpark Dakpark is a multi functional dike structure that has been designed to accommodate shops, offices, and a parking garage on the ground floor and first floors. The rooftop is a park, accessible from the road. The structure was constructed in 2010, as part of a urban renewal effort to raise dyke heights to protect the city against the projected rise in sea levels in 2100.

Views of the park. Retaining wall Old dike Water level in 2100

Hilledijk The new construction is to not integrated in the actual flood defense (orange line), but will be constructed just outside the theoretical profile of the new flood defense. This implies that when the buildings are removed or demolished, the operation of the flood defense structure remains intact. Although the new buildings are not legally a part of the flood defense, structurally they will contribute to the strength of the embankment.

Noordendijk Dordrecht Single family housing units area integrated into the dike design. It adds to the structural stability. The resulting space (below the orange line) functions as a private parking garage. The roof slab of the parking garage is used as a public space, side walk and bike path.

Flood Plain Design, UK Conventional flood defense methods are becoming increasingly expensive to construct and maintain and face a potentially high risk to safety if they fail. Moreover, channelizing rivers in one place defers the problems onto another. The non-defensive flood risk management strategies on the other hand incorporate water onto the site in a controlled and predetermined manner. This may not be appropriate if the floodwater is deep or fast flowing but where it is possible this approach may create opportunity for other benefits on site.

The different components are explained in the diagram below: ○ Safe haven: Resilient buildings (community center and schools) in the highest point on site. These places can act as refuges in case of emergency situations. ○ Flood gardens: Small scale raingardens in front of houses to collect water and prevent any structural damage. ○ Canal paths: planted channels that collect and convey rain water away from buildings ○ Village blue: small ponds designed to expand during a flood and used for recreational activities rest of the time. ○ Village green: Play areas designed to flood during big floods.

Balancing Lakes, UK A non- defensive flood management strategy (part of a sustainable urban drainage system SuDS) is to create a system of balancing lakes along the flood plain. A balancing lakes are lakes adjacent to a river along its flood plains. It is used to control flooding by temporarily detaining surface runoff and rain water during storm events. The rest of the time the lake functions as a natural habitat and recreational facility. A case study of this Willen Lake in Milton Keynes. Willen Lake is one of the largest purpose-built storm water balancing lake in the UK, with a surface area of 400,000 mÂ˛. It was constructed between 1972-78.

The area in purple is the Ouzel river flood plain. Caldecotte Lake, Walton Lake and Willen Lake (marked with a red dot) together form the balancing lake system.

The lake has two basins, North and South. It has been designed so that throughout the year water levels in the South Basin maintains a depth of 2 m and the North Basin a depth of 1.5 m; a series of deeper hollows (normal depth 2.2 m) were also incorporated into the design to provide refuges for fish during periods of dry weather. In addition, the lake has the capacity to accommodate up to a further 1.3m depth of stormwater (equivalent to a 1in 200 year storm).

Layout of Lake Willen.

Most of the time the lake receives its water from the two surface water sewers that carry runoff from Milton Keynes, and discharge, via diffusing channels that trap grit and oil, into the South Basin. However, when the flow in the River Ouzel reaches a critical level, a computer controlled, adjustable weir is activated which diverts the majority of water into the lake. As the system is finely tuned, it is only the more severe storms that tend to activate it. As soon as river levels start to subside, the excess water is drained from the lake back into the River Ouzel. The operation is carried out as quickly as possible in order to restore the stormwater capacity; under favorable conditions the lake returns to its normal level within 24 hours of being flooded. Although the lake's principal function is to prevent floods, its design was strongly influenced by the potential to fulfil other purposes. The South Basin, provides the main water sports facility in Milton Keynes and attracts more than a million users each year. The North Basin, by contrast, has been zoned for nature conservation and low key recreation. The bond dividing the basins not only prevents boats from straying into the conservation area, but also allows water within the latter to be artificially lowered without adversely affecting boating activities.

View of North and South basin

View of the bird island during construction

Bird habitat in the North basin

Recreation and water sports facility in the South basin.

COASTAL FLOODING Science first approach: Copenhagen Climate Adaptation Plan Context based approach Ho Chi Minh City Climate Adaptation Plan Integrating Adaptive Strategies into Urban Redevelopment- UK

Coastal Flooding The major challenge in planning for climate change is uncertainty. Although global leaders are now in talks to curb greenhouse gas emissions, the future of sea level rise and other related phenomena are unknown. This poises a difficult question for cities and urban planners. Should plans, under a broad umbrella, take into account the worst possible outcomes which require high amounts of initial investments and may not be required in the long run? Or should plans be periodically assessed and implemented? Building flexibility into adaptive measures increases its cost. (Example: If a sea wall is built with a bigger foundation, in case the wall needs to be expanded in the future.) Two approaches have been used in forming plans for climate change adaptation, these are the science first approach and context first approach. Science First Approach: The science first approach is based on stimulations and complex climate models. Future scenarios are mapped based on these findings and adaptation plans are made based upon these. There are several short comes to this method: The projections and predictions may not be accurate, as several unknown factors are involved. There may be catastrophic outcomes if the model under predicts and a waste of resources and investment if the model over predicts.

The city of Copenhagenâ&#x20AC;&#x2122;s climate adaptation plan is an example of the science first approach: The plan uses models based on the A2 scenario recommended by IPCC (International Panel for Climate Change). IPCC has 4 major themes or story lines of future possibilities. Each storyline is basically a short "history" of a possible future development expressed as a combination of key scenarios. The storylines identify particular dynamics, visible in the world today, which might have important influences on future GHG emissions. The A2 scenario is at the higher end of the four scenarios, this was preferred because, from an impacts and adaptation point of view, if one can adapt to a larger climate change, then the smaller climate changes of the lower end scenarios can also be adapted to. (See Appendix: 1) Using the A2 emission scenario as the probable future at the end of this century, the city of Copenhagen, using various climate simulations, projections and modelling techniques, came to the conclusions summarized below:

Science First Approach

Appropriate recommendations based on inferences

Deduce possible future scenarios

Climate Models and Simulations

Changes due to climate change in 2100. Predictions based on A2 scenario. Parameter Precipitation

Prediction 



Impact

25-55% more precipitation  in the winter months in 2100, while precipitation in the summer months is  expected to fall by 0-40%. The intensity of the heavy downpours is expected to rise by 20-50%. The sea level will raise up to  1m.

Increase surface run off and increase load on sewer systems and water courses. Increase overland flooding and risk of infrastructure damage.

Frequent flooding of inland areas during storms and during high tide.

Rise in sea level



Storm Surge



Maximum tidal surge of 226  m (in combination with a sea level raise of 1m)

Groundwater



Drop in ground water between 25 to 50 cm



Other parameters

 



Increase in urban heat island effect Increase in spread of diseases and Public health concerns Decrease in urban biodiversity. Increase in heat strokes.



Flood areas (periodically or permanently) along the coast line, making it uninhabitable.

Combined with storm surge, the salt content in the water will increase. May lead to water shortage as useable ground water decreases. Impact on citizens health and well being

Geospatial analysis based on predictions

Areas at risk of flooding due to sea level rise and storm surge in 2100

Change in depth of groundwater in 2100

Areas at risk of flooding due to rain in 2100

As the final step in the â&#x20AC;&#x2DC;science first approachâ&#x20AC;&#x2122;, adaptation measures are recommended based on this analysis.

Level 1 Level 2 Level 3

The city acknowledges that, due to practical constraints, it may not be possible to retrofit the entire city to be resistant to floods. Hence places are classified into three levels. The goal of the measures is to reduce likelihood of flooding in level 1 areas, reduce the scale of impact on Level 2 areas, and reduce vulnerability or prepare areas for convenient cleanup post flood.

Hospitals, electrical services, residences Businesses, industries, schools Parks and playgrounds, parking lots

The measures are further broken down into geographical scales such as region, municipality, district, street and building to mitigate impact at different levels. An example of this is illustrated in the table below

The table summarizes the maximum extra water Level 3 areas can be designed to retain during an extreme rain event. These areas are designed to detain water during heavy rainfall ( to avoid overloading the sewer system) and for easy clean up after a heavy rainfall.

Context based approach: This approach is less data driven and accommodates flexibility into adaptations. The science behind climate change is still largely unpredictable. The context based approach is an incremental planning process. It centers the focus on the community and present day issues. The strategies are flexible and implemented in a step wise manner. Implementation of different measures are sequenced over time so that the system can adapt to climate over time. Hence options are left open to deal with a range of possible different climates. Strategies can also be incorporated such that there are cobenefits with other policy areas. The method is summarized in the diagram on the right. As indicated, the process is repeated periodically. The table (to the right) is an example of incorporating flexibility into strategies. The Thames barrier is a storm surge gate in the Thames estuary in London, United Kingdom. The infrastructure has a key role to play in protecting the mainland against storm surges especially when sea level raises. If the barrier needs to be replaced, it is an expensive investment for the government and may prove to be redundant if sea levels do not rise as predicted. Hence, an adaptive path way or route map was outlined. The requirements for different scenarios (1m rise, 2m rise, 3m rise and 4m rise)

Context based approach.

Adaptive pathways for the Thames barrier

View of the Thames barrier

are presented in the table. The city then identified key time thresholds (the first one being in 2050). The city will review the situation then and choose a course of action most suited. And continue to monitor periodically. For example, the blue line indicates the course of action if climate change start to accelerate at an unanticipated rate after the first 1m rise. Althoughperformance standards might dip, as measures become redundant with time, with better understanding and knowledge regarding climate change effective measures can be implemented incrementally. The adaptation plan for the city of Ho Chi Minh City (HCMC) in Vietnam is an example of context based approach. With 10 million inhabitants, the city is rapidly industrializing and growing. Through the planning process, the city incorporated strategies into its master plan. These are â&#x20AC;&#x2DC;no regretâ&#x20AC;&#x2122; strategies i.e. they have multiple benefits and in no future scenario will the city regret making the investment. The challenge the city faces is uncertainty

Schematic diagram of thresholds, lead time (time for construction and implementation) and decision points.

Will industrial output and economic growth continue? Will it be necessary to invest in expensive defense mechanisms such as storm surge gates? Or will economic growth decline and population will dwindle as people move back to their rural existence? In which case expensive flood barriers will be unnecessary.

The planning process took into consideration all of these uncertainties. A charrette was held with all the key public officials present. The extreme scenarios for key parameters were discussed as follows. The situation in reality will be somewhere in between the extremes

Indicator

Best case scenario

Worst case scenario

Economic growth

If global economy is strong, and foreign direct investment (FDA) increases, the city will see a 7% to 8% average annual growth. Fastest being tourism followed by construction. Currently the main focus has been on exports and light industry.

If FDA decreases and the export market becomes more competitive due to global competition, the growth rate could fall to 2-3%

Population and In 2025 the population may be as high Migration as 10 million (it is already 10million) and (30 million in 2100). In high growth rate, the jobs and growing income in the city will attract low-educated people from rural areas. Coupled with high fertility rates, population could explode.

If economic growth is low, moving to cities will become less attractive At first the population will slowly rise and then decline as people emigrate, towards their former rural existence.

Urban development and infrastructure

Haphazard development: Private entities control growth and land value No equitable distribution Since population is dwindling the status quo will be maintained

Power of the government to orchestrate development: Growth can be dominated by market forces leaving the people and companies with the highest purchasing power with the best locations, forcing social housing along forcing social housing along Services will be centralized in such nodes and large investments in highways and public transportation will be made to connect the new centers.

Urban development and infrastructure

More space will be kept open for green and blue projects. When market forces dominate spatial Development, there is a high risk that public needs will not be prioritized. If orchestrated, predominantly low income immigrants will be housed concentrated in low cost residential areas along new nodes. In long term, when development pressure decreases, and there is redevelopment these areas will have to potential to become green spaces.

PortShifting the location of the port.

Strong economic activity will Industries and activities related to support in expansion and shifting the port will continue to remain in of the port. the inner city area. Full development will lead to complete outplacement of current harbor related activities

Agriculture and rural

Industrialized, large scale farming dominates. Existing small farms in the outskirts are used as used as garden communities, recreation areas golf courses, parks etc.

Nature and ecology

Network of green spaces, Without coordination only high conserved areas, green belts and value areas (mangrove in the greenways. south will be conserved).

Loss of all green spaces within the city limits. Small scale farms continue to dominate at the periphery. Remigration can be scattered or ordered centralized around villages.

Six key strategies emerged as solutions, these measures can better quality of life for residents and are multiple functional. Adaptive pathways or route maps were outlined to accompany them so that the city can periodically assess the necessity of each strategy at key thresholds. The question still remains if the cityâ&#x20AC;&#x2122;s adaptation measures can be implemented on time to avoid large scale impact.

Integrating Adaptive Strategies into Urban Redevelopment: â&#x20AC;&#x2DC;Facing up to rising sea levels: The future of our coastal and estuarine citiesâ&#x20AC;&#x2122; is a joint publication and exhibition by two UK based organizations, Institute of Civil Engineers and Building Futures. The length of UK coastline is around 12,429km. Around 10 million people, in 5.5 million, live in flood risk areas with 2.6 of these properties at direct risk of flooding from rivers or the sea. The publication looks at the major challenges in adapting to rising sea level rise and illustrates possible strategies through two case studies.

Major challenges towards better planning preparation include coordination amongst different agencies (government and private), limited resources (financial and material), short term political will and effective communication

Key strategy

Strength

Retreat

Defend

Attack

•

Managed Retreat or Managed Realignment is the process by which critical infrastructure and housing is relocated to safer areas inland, and allows for tidal sea waters to flood areas previously occupied.

•

To follow conventional flood defense mechanism by building dikes/ embankments/ levees along the coast.

•

Money is saved by significantly decreased investment in flood defense infrastructure Through the process, much needed intertidal habitat (such as mud flats and saltmarsh) are created.

•

The method has proven to be successful in the past especially against fluvial flooding. The defenses could serve multiple purposes (parks, housing etc.) and be incorporated into urban renewal plans.

•

• • •

•

Build out into the water by utilizing: Land reclamation Stilts Floating structuresboats to platoons

This method can create unique places for the city. It can be successful by taping into the increasing demand for water front properties

Weakness

•

In retreating investments made in the existing structures and infrastructure is lost.

•

Not a sustainable approach. It destroys the coastal ecosystem and may limit access to the water front.

•

Although there are precedents set by cities like Venice, the method is still not widely practiced and embraced.

Challenges

•

The process is very difficult to implement in densely populated urban areas.

•

Flood defense is usually implemented in a piece meal fashion. Is it possible to defend the entire coastal periphery of a city ?

•

Developing guidelines to build into the water sustainably.

The city of Porthmouth has 1.5 million inhabitants and is located in the south of England. Retreat strategy: In the case of city of Portsmouth, in the retreat strategy the land use in the vulnerable areas will be re zoned and the city will continue to grow into the hilly terrain. The now vacant land will be designed to become parks, agriculture areas and natural habitats. The port alone will be re developed using adaptive measures to continue operations.

Defend In the defend strategy, the coast is protected by a multi-functional dyke and the other two side of the island are protected by storm surge barriers. The dikes can be developed in tandem with urban redevelopment plans so that its cost can be reduced through public private partnerships as the they can be designed to incorporate residences, shops, offices and other profitable uses.

Advance In the advance/ attack strategy, the city develops into the water using land reclamation, floating buildings and stilted development. The city can invest in building out elevated piers and bridges and private development in the form of floating structures and stilted buildings can be concentrated along these. Ideally the final plan will be a combination of all these strategies.

Summary

City/ country

Singapore

Copenhagen

Rotterdam

Ho Chi Minh City

United Kingdom

Primary issue

groundwater recharge Increase drinking water supply

Flash floods Storm surge

Flash floods Subsidence Fluvial floods Storm surge

Flash floods Fluvial floods Storm surge

Secondary issues

Climate changeincreased rainfall

Sea level rise Flooding of rivers/ canals Salinization

Sea level rise Salinization

Geography

Island

delta

Island

Economic prosperity

Developed country

Developed Country

Developed country

3rd world country

Developed country

Multifunctional flood defense strategies

Parks and public spaces Bio swales/ wetlands LID

Road ways Parks Plazas LID

Levee/Urban redevelopment Multiuse plazas Rooftop storage LID

Urban redevelopment Redirect growth LID

SuDS Storm barriers Non defensive flood defense

Conclusion Flooding is a global issue and arises due to several complexities. The solutions to control flooding are never simple. They require coordination between multiple government agencies, analysis backed by data and innovative strategies that can provide multiple benefits. Some of the common challenges and solutions are discussed below. Challenges: Climate change: Increasing emission of greenhouse gases has resulted in warmer climates and unpredictable weather patterns. In some places intensity and frequency of precipitation is increasing whereas subsidence and decrease in ground water table are the cause of concern in others. The science and theory of climate change is still not understood in great depth. Scientific research shine new light on the topic everyday unfortunately, from a cityâ&#x20AC;&#x2122;s adaptive capability perspective, action needs to be taken today. This uncertainty has led to two kinds of planning processes. One is a science based approach; to model and simulate future scenarios and develop defense mechanisms to cope towards it. The second is a context based approach where adaptive pathways are established for solutions and at different time thresholds appropriate actions are evaluated and implemented.

Density and lack of space in existing urban areas: In most cities, the poor are at most risk as rapid urbanization has pushed them into the most vulnerable neighborhoods, often in low-lying areas and along waterways prone to flooding. Unregulated development and mistakes in the past has led to encroachment on water ways and filling up of wetlands and other water bodies for development. Coupled with increased impervious areas, the impacts of flooding are felt most in highly congested urban areas. Space in such urban areas are highly contested and very expensive. In response, solutions have made innovative use of space. Detention and treatment elements have been integrated into roofs of building, balconies, facades and even street furniture. Availability of data The design of any system needs to be backed by data and analysis of soil type, hydrology, ground water table etc. for maximum benefit. Most often this data is not available or highly inaccurate, especially in developing countries. It is an expensive and high risk mistake to depend upon trial and error.

Scales of intervention and piecemeal execution of plans: As illustrated in the SuDS example a management train that acts at the scale of a household, neighborhood and the larger region is necessary for effective outcomes. But different players and agencies need to initiate and include strategies within their development at each scale. For example regional measures and conveyance on road ways by city government, parks and greenways with in housing complexes by housing associations and rain barrels and planter boxes at a house hold level. Piecemeal execution disturbs the management train and does not lead to desirable outcomes. Areas already inundated will continue to flood unless control actions are executed upstream. Although all elements need to be in place for proper functioning, key projects which make the most difference can be identified and constructed first as demonstration projects to reduce scale of damage. Emerging solutions Incorporate measures into urban redevelopment/ renewal: In existing urban areas, urban renewal projects are an opportunity to restructure and incorporate measures to create a significant difference. The key challenge lies in coordination between intergovernmental agencies and in identifying private developers for a public private partnership. Multifunctional adaptations: Increasing sewer capacity is expensive and is utilized effectively

only during intense rains. Hence, cities are seeking ways by which their investment can creates multiple benefits by incorporating ecological considerations and urban design Ecology: Mimic natural cycles (retain-store-use): The technological advancements of twentieth century aided in rapid global transformation. It became possible to utilize technology to inhabit any piece of land. Embankments keep rivers from flooding, dams upstream control water flow, and pumps drain water out of swamps. We were able to shape any piece of land into habitable spaces for development. Today in the era of sustainability, cities are moving towards integration with nature: surface water management with both technological and natural interventions. Manipulating the potential offered by natural systems within urban environments have multiple benefits. They improve water quality, increase bio diversity, better ecology, increase aesthetic value, and are proving to be more cost effective than conventional grey infrastructure. Today, several cities choose to compliment and support conventional grey infrastructure with green infrastructure.

Multiple functions: Expose value of investment.

Types of Urban Floods

Coastal

Inland

Overland Sewer system SUDS-swale/pond/etc Capture and store or allow water to infiltrate as close to its source as possible.

Fluvial Concrete channel Embankment Reservoirs Naturalize flood plain Riparian buffer Balancing lakes Protection of flood plain from development

Minor System Incidence Increase sewer capacity Increase SUDS capacity

Groundwater Sewer system Drainage of groundwater Detention pond Building regulations: water proof basement/building on stilts.

Major System Incidences Effective communication and Emergency evacuation plan

Estuaries/ Delta Dike Flood gate Mangroves/swamps Coral reefs Minimum distance regulation

Open Sea Sea wall Mangroves/swamps Artificial coral reefs Minimum distance regulation

Incidents Effective communication and Emergency evacuation plan

Conventional solutions SuDS solutions Policy or regulation reccomendations

Diagram summarises conventional grey infrastructure approach, SuDS approach and possible policies and building regulations to tackle each type of flood

Water sensitive urban design: Flooding presents an opportunity to transform impervious concrete surfaces into vibrant public spaces and softscapes (parks, gardens and playfields). It is an opportunity to showcase rain and water in the urban sphere

Water square in urban spaces- Rotterdam

Plan Defensive vs. integration Two common concepts emerge at the core of water management. These are integration and defense. Cities are moving away from the defend concept towards the integration concept. This method is more sustainable since it in less dependent upon energy driven systems it provides multiple ecological benefits since it mimics the natural hydrological cycle. The absolute prevention of flooding is an impossible taskFlood management is about building resilience; It is about looking for opportunities and solutions that add to the welfare of society and enhance urban life so that social and economic benefits outweigh potential costs.

Normal conditions

30 times a year

Once a year

In winter

â&#x20AC;&#x153; The absolute prevention of flooding is an impossible taskFlood management is about building resilience; It is about looking for opportunities and solutions that add to the welfare of society and enhance urban life so that social and economic benefits outweigh potential costs

Appendix 1. A2 scenario storyline 2. SuDS: Recommandations for diffĂ¨rent typologies 3. Rotterdam Climate Adaptation Strategy- guidelines

A2 Scenario Storyline The A2 scenario family represents a differentiated world. Compared to the A1 storyline it is characterized by lower trade flows, relatively slow capital stock turnover, and slower technological change. The A2 world "consolidates" into a series of economic regions. Selfreliance in terms of resources and less emphasis on economic, social, and cultural interactions between regions are characteristic for this future. Economic growth is uneven and the income gap between nowindustrialized and developing parts of the world does not narrow, unlike in the A1 and B1 scenario families. The A2 world has less international cooperation than the A1 or B1 worlds. People, ideas, and capital are less mobile so that technology diffuses more slowly than in the other scenario families. International disparities in productivity, and hence income per capita, are largely maintained or increased in absolute terms. With the emphasis on family and community life, fertility rates decline relatively slowly, which makes the A2 population the largest among the storylines (15 billion by 2100). Global average per capita income in A2 is low relative to other storylines (especially A1 and B1), reaching about US$7200 per capita by 2050 and US$16,000 in 2100. By 2100 the global GDP reaches about US$250 trillion.

Technological change in the A2 scenario world is also more heterogeneous than that in A1. It is more rapid than average in some regions and slower in others, as industry adjusts to local resource endowments, culture, and education levels. Regions with abundant energy and mineral resources evolve more resource-intensive economies, while those poor in resources place a very high priority on minimizing import dependence through technological innovation to improve resource efficiency and make use of substitute inputs. The fuel mix in different regions is determined primarily by resource availability. High-income but resourcepoor regions shift toward advanced post-fossil technologies (renewables or nuclear), while low-income resourcerich regions generally rely on older fossil technologies. Final energy intensities in A2 decline with a pace of 0.5 to 0.7% per year. In the A2 world, social and political structures diversify; some regions move toward stronger welfare systems and reduced income inequality, while others move toward "leaner" government and more heterogeneous income distributions. With substantial food requirements, agricultural productivity in the A2 world is one of the main focus areas for innovation and research, development, and deployment (RD&D) efforts, and environmental concerns. Initial high

levels of soil erosion and water pollution are eventually eased through the local development of more sustainable high-yield agriculture. Although attention is given to potential local and regional environmental damage, it is not uniform across regions. Global environmental concerns are relatively weak, although attempts are made to bring regional and local pollution under control and to maintain environmental amenities. As in other SRES storylines, the intention in this storyline is not to imply that the underlying dynamics of A2 are either good or bad. The literature suggests that such a world could have many positive aspects from the current perspective, such as the increasing tendency toward cultural pluralism with mutual acceptance of diversity and fundamental differences.

SuDS: Recommendations for different typologies

Typology 1: Small residential infill

Typology 2: Medium residential infill

Typology 3: Mixed use

Typology 6: Elevated space

Typology 4: Destination public space

Typology 5: Transitional public space

Typology 7: Neighborhood street

Typology 9: Greenways

Rotterdam Climate Adaptation Strategy- Guidelines Legend:

Shadshavens o The area is home to new generation of port and transport companies, innovative enterprises and knowledge institutes as well as special residential environments and cultural facilities. o Located in parts outside the dike and within. 1. Adaptive development: Safe living and working environments, floating houses, dry and wet proof buildings. 2. Climate dike: Linking dike reinforcement with real estate development, extra infiltration and greening potential. 3. Dike reinforcement: Protection of the inner- dike city 4. Tidal park/ building with nature: Improving the recreational facilities/ ecology. Construction of wave breakers to protect the dike/ delta area. Creation of added value: ○ Adaptive development ○ Improved recreational facilities ○ Strengthening the relationship of the city with the river ○ Climate dike ○ Attractive environment for living and working; dike as public space ○ Increase green space ○ Dike reinforcement ○ More green spaces and cycle routes ○ Tidal park/ building with nature: ○ Better water quality and biodiversity ○ Natural dike reinforcement

Outer dike urban districts ○ The urban districts are central, lie directly on the river Meuse and are in contact with the water. ○ Since these outer-dike areas are relatively low-lying, they are vulnerable to high water levels. Restructuring and design is difficult due to the characteristic old buildings and the limited space available. Furthermore, there is a lot of paving so much heat is retained. ○ In these areas, there are two distinct types of flood protection tactics: keeping the water back or facilitating controlled flooding. 1.

2. 3.

Flood wall: Protection of neighborhood/ added green space. Water robust street/ façade garden: Natural infiltration/greening the streets Collective garden: collection, delayed drainage and recycling of rainwater, social space. Floodable quay: strengthens contact between land and water/ functional use in relationship to shipping.

Creation of added value ○ Flood wall ○ Attractive residential environment, playgrounds, increase in property value, more greenery/biodiversity ○ Water robust street/ façade garden ○ More attractive residential environment, more greenery biodiversity ○ Collective garden ○ Community building, production and sales of own grown products. ○ Floodable quay ○ Closer contact with water ○ Increase in property values.

Inner dike urban districts ○ The inner-dike city districts of Rotterdam are located around the city center and are all densely built-up. Restructuring in all these districts can only take place through small-scale interventions that maintain the character of the district. ○ Problems of flooding and heat stress occur in nearly all the pre-war districts. The wooden pile foundations commonly found here are vulnerable to droughts. 1. Collective gardens: collection, delayed drainage and recycling of rainwater/ more green in courtyards/ social binding. 2. Water robust street/ façade garden: natural infiltration/greening the streets 3. Rain barrel and green courtyard: local rainwater collection. 4. Water square: temporary storage and multi functional space. Creation of added value ○ Collective gardens ○ Community building ,production and sales of own grown products ○ Water robust street/ façade garden ○ More attractive residential streets ○ Rain barrel and green courtyard ○ Recycling of water, more green/ biodiversity ○ Water square ○ attractive residential environment, playgrounds, increase property value.

Compact City Center o The city center is compact and characterized by modern high-rise buildings. There is considerable consumer pressure. o There is a lot of paving and high road traffic, which means that flooding and heat stress are already causing significant problems. 1. Green facades and blue roofs: reduces energy consumption 2. Green Roof: water retention and recycling, cooling, insulation 3. Water storage/ smart reuse: water collection and recycling. 4. Water robust infrastructure/ bioswales: Water collection, natural infiltration, improved quality of public areas, more green. 5. Multi-functional dike reinforcement: linking dike reinforcement in with other development. Creation of added values ○ Green facades and blue ○ Community building ,production and sales of own grown products ○ Water robust street ○ More attractive residential streets ○ Rain barrel and green courtyard ○ Recycling of water, more green/ biodiversity ○ Water square ○ Attractive residential environment, playgrounds, increase property value.

Post war districts and surrounding areas ○

The post-war districts are the large areas located on the outskirts of Rotterdam. In some of these areas, heavy rainfall already causes flooding.

1. More water storage/ green framework: Increased water storage capacity 2. Wet nature (wetland): Strengthen recreational potential, infiltration. 3. Green- blue ribbon: strengthen ecological and recreational potential/ cleaner water. 4. Collective gardens: collection, delayed drainage and recycling of rainwater, co-ownership and social binding Creation of added value ○ More water storage/ green framework ○ attractive residential environment, improving recreational facilities, increase in property value, more green/ more biodiversity. ○ ○

Wet nature (wetland) recreational urban outskirts, stimulating regional food production, ecological network

○ ○

Green- blue ribbon More attractive residential and working environment, ecological network.

○ ○

Collective gardens More attractive living environment, community building, playgrounds, increase in property values