Planning criteria for Water Sensitive Urban Design - WIT Press

The Sustainable City IX, Vol. 2

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Planning criteria for Water Sensitive Urban Design M. I. Rodríguez1, M. M. Cuevas1, G. Martínez2 & B. Moreno2 1

Department of Urban and Regional Planning, University of Granada, Spain 2 Department of Construction and Engineering Projects, University of Granada, Spain

Abstract The densification of cities, which occurred during the twentieth century, has caused ‘soil sealing’, leading to numerous irreversible environmental impacts such as soil degradation, reduction of biodiversity, the increase of temperature and the ‘urban heat island’ effect. Another important consequence is the increase in run-off flows and associated problems in the sanitary networks, generating spills and floods. This development is unsustainable. SUDS (Sustainable Urban Drainage Systems) have gained popularity in recent years as a way of solving this problem. They are a sequence of water management practices and facilities designed to drain surface water in a manner that will provide a more sustainable approach than what has been the conventional practice of routing run-off through a pipe to a watercourse. Street and public space design provides an opportunity to restore the environmental quality of our cities, making them better places to live. However, SUDS implementation has been often used with the single intention of mitigating the effects of ‘bad landscaping’ and there is a need to establish criteria that will improve the interaction between urban water cycles and city planning and landscaping, integrating SUDS in Urban Planning. This paper presents a set of principles that can help architects and town planners to develop a Water Sensitive Urban Design (WSUD) that will reduce environmental impacts generated by soil sealing in new and renewal landscaping. These criteria should be incorporated into planning regulations. Keywords: Urban Planning, criteria, Water Sensitive Urban Design, Sustainable Urban Drainage Systems, SUDS.

WIT Transactions on Ecology and The Environment, Vol 191, © 2014 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/SC141342

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1 Introduction Cities underwent enormous expansion during the twentieth century [1, 2]. In many cases this expansion was uncontrolled, in which the rate of change of land use from non-urban to urban areas was greater than the demographic change [3–5]. For example in Europe between 1980 and 200, the spread of built- up areas increased by 20%, while population density only rose by 10% [6]. This spread of built-up area has created progressive and unrelenting impermeability or soil sealing [7, 8], which is causing numerous environmental problems in our cities [9]. Such is the current importance of this phenomenon that the European Commission has created a Commission Staff to provide information on the magnitude of soil sealing in the European Union, its impacts and examples of best practice for its limitation, mitigation or compensation with a view to ensuring better land management. In 2012 this Commission created a working document on “Guidelines on best practice to limit, mitigate or compensate soil sealing” [10] which indicate the lines of action for policies, plans and programs in the different member states of the European Union related to soil. According to this report, Soil Sealing produces numerous environmental impacts on: Biodiversity: Loss of flora and fauna. Food security: In peri-urban areas it destroys special forms of agriculture. Social values and human well-being: Sealing and urban sprawl contribute to the loss and degradation of the landscape. Global climate: the removal of topsoil and subsoil during the process of sealing deprives us of their potential to serve as a natural fix for atmospheric carbon, thus influencing the carbon cycle and the climate. Urban climate: The complete or partial inhibition of the infiltration of rain water reduces the evapotranspiration and the storage of water in the subsoil, destroying natural refrigeration. Additionally, increased absorption of solar energy by rooftops and dark asphalt surfaces combined with the residual heat generated by cooling systems, along with industry and traffic, all contribute to heightening the temperature increase [11]. This effect, known as ‘Urban Heat Island’ [12, 13], is causing serious health problems (respiratory diseases [14]), air quality (accumulation of contaminants due to the lack of air renewal [15]), the economy (increase in energy demand [16]) and thermal comfort of cities (alterations in relative humidity and wind speed [17]). Some studies have shown how green zones considerably reduce these types of damage [18]. Filter capacity: Our activities lead to numerous pollutants (such as oil, sediments, fertilizers, pesticides, animal waste and litter) that can cause diffuse pollution and adversely affect the environment, which is not managed by traditional piped drainage. Pollutants or contaminants can be washed into sewers and eventually watercourses through surface water run-off making it difficult to comply with water quality legislation [19]. The organic matter and clay minerals in soil are able to filter particulate and to absorb many soluble pollutants (such as organic contaminants or heavy metals), reducing their migration into ground and surface waters. The purifying function of soil supports the provision of clean groundwater and reduces the need for technical cleaning of drinking water in

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waterworks. Especially healthy topsoil with its abundance of soil life is an effective filter for percolating water [20]. Water: The ability of a soil to store water depends on a range of factors including its texture, structure, depth and organic matter content. A cubic metre of a porous soil can hold between 100 and 300 litres of water [21]. Sealing reduces the amount of rainfall that can be absorbed by the soil, and the time it needs to reach rivers, increasing the amount of surface run-off and the peak flow, and therefore, the risk of flooding [22] (fig. 1). Built-up areas can be up to 4 times more impermeable than green zones or plots of land which have not been built on [23]. This means that the form of urbanization used directly conditions the quantity of infiltrated water. Some studies have compared the run-off produced by a single surface which is undeveloped and 100% impervious, and it has been suggested that to maintain satisfactory rates of surface infiltration, a minimum share of open space of as much as 50 % of the paved surface is required [24]. The continued impermeability of the basins has produced a rise in the number of flooding events and their seriousness with catastrophic consequences in Europe in recent years [25]. This situation is expected to worsen in coming years due to an increase in the intensity of rains predicted by scientists in different Climate Change Models (MikeSHE, MOUSE, etc.) [26]. Some studies predict that rains which will generate increases of between 20 and 40% in the volume of run-off water, according to the scenario which has been given [27]. This means that countries which currently have high average rainfall need to look for alternatives to manage rainwater. To solve this problem, progressive investment in the enlargement of sanitary networks has been necessary in order to be able to evacuate the ever increasing volume of run off originating from continued urbanization. Despite this, the collection system has always proved to be insufficient, generating a model of unsustainable management [26].

Figure 1:

Influence of land cover on the hydrological cycle [10].

SUDS have gained popularity in recent years as a way of solving the environmental problems associated with Soil Sealing, especially those related to the water cycle. These systems, also known as BMP (Best Management Practices) or LID (Low Impact Development) are a sequence of water management practices WIT Transactions on Ecology and The Environment, Vol 191, © 2014 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

1582 The Sustainable City IX, Vol. 2 and facilities designed to drain surface water in a manner that will provide a more sustainable approach than what has been the conventional practice of routing run-off through a pipe to a watercourse [8]. Streets and public space design provides an opportunity to restore the environmental quality of our cities, making them better places to live. However, SUDS implementation has been often used with the single intention of mitigating the effects of ‘bad landscaping’ and there is a need to establish criteria that will improve the interaction between urban water cycles and city planning and landscaping, integrating SUDS in Urban Planning. This paper presents a set of principles that can help architects and town planners to develop a Water Sensitive Urban Design (WSUD) that will reduce environmental impacts generated by soil sealing in new and renewal landscaping.

2 Sustainable Urban Drainage Systems (SUDS) and Water Sensitive Urban Design (WSUD) As previously stated, the Sustainable Urban Drainage Systems (SUDS) have been shown as a solution to Soil Sealing and as a more sustainable alternative to the management of run-off, trying to restore the natural hydrological cycle which has been altered by the continued impermeability of cities. These systems fundamentally consist of harvesting rainwater (by filtration through permeable materials and or pipes, channel it and store it for the maximum amount of time possible, retaining the run-off for later use or simply to let it filter in subsoil and replenish the aquifers [28]. Countries like The United States, The United Kingdom, France or Australia have been using these systems for more than a decade, thus improving the environmental quality of their cities [29]. The implementation of these systems has numerous benefits that are summarized in [30]: Flood risk management: SUDS schemes can be designed to slow water down (attenuate) before it enters the watercourse, provide areas for water storage in natural contours, and SUDS can be used to allow water to soak (infiltrate) into the ground or evaporate from surface water and transpire from vegetation (known as evapotranspiration). Water quality management: Some SUDS components provide water quality improvements by reducing sediment and contaminants from run-off either through settlement or biological breakdown of pollutants. Amenity and biodiversity: SUDS can improve a development by creating habitats that encourage biodiversity and simultaneously provide open spaces and opportunities to create visually attractive green (vegetated and landscape) and blue (water) corridors in developments connecting people to water. Furthermore, the permeability of surfaces helps to reduce the Heat Island Effect. Water resources: Some SUDS components that soak water into the ground can replenish underground aquifers (where there is no risk of polluting the aquifer) and capture, or harvest rainwater that can be used for functions that do not require treated water from the mains (flushing toilets, irrigation, etc.). Community benefits: Well-designed SUDS can incorporate attractive public open spaces that create better places to live, work and play. WIT Transactions on Ecology and The Environment, Vol 191, © 2014 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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Recreational benefits: SUDS can deliver recreational benefits through the dual use of components and facilities such as using attenuation and storage areas and overland conveyance routes for play and/or sports areas. Also, multifunctional use of SUDS components can have other benefits such as the incorporation of recreational open spaces into a development that otherwise may be deemed impractical by a developer. Educational benefits: In addition to improvements to the visual appearance of a development, many SUDS components have been used for recreational and educational purposes with schemes located in school grounds with very favorable results. Benefits for developers: SUDS can provide savings on the overall construction and maintenance of drainage schemes, and can be integrated into strategies for public open space and green infrastructure within developments, linking urban areas through the development of blue/green corridors. For the implementation of SUDS to produce these benefits, their integration into Urban Planning is necessary, and should not be applied as a measure to solve an existing environmental problem (flood risk, water quality, etc.). Technical manuals currently exist which help us to design and implement these systems [10, 28, 31]; however, these can sometimes be complicated to apply because of their technical workload. Because of this, the development of other types of guides aimed at town planners and landscape architects are needed, that place greater emphasis on the design of the solutions and their integration in Urban Planning and Landscape. Some recent references have started to work on this idea [30], to generate planning criteria which helps designers to develop a new way of designing urban space. This philosophy can be summarized in the phrase ‘Water Sensitive Urban Design’ (WSUD), and goes a step further than SUDS, not only integrating these systems in cities, but also incorporating a series of general criteria that help to plan a model of more sustainable land occupation in accordance with hydrological processes.

3 Objectives The main objective of this paper is to establish planning criteria for WSUD, aimed at landscape architects and town planners, who decide whether a working methodology can be incorporated into city planning and landscaping. From this main objective the following secondary aims can be derived: To minimize the environmental impacts generated by Soil Sealing. To ensure the efficiency and safety of urban water systems. To introduce water to the urban environment the planning process and to provide the opportunity to bring WSUD into the public arena, addressing the aspirations of the public for a better, cleaner and greener urban environment. Pass the basic concepts of WSUD to landscape architects and town planners, so that water can be incorporated as another factor in Urban and Landscape Planning. Act as a base for the incorporation of these criteria into planning regulations. WIT Transactions on Ecology and The Environment, Vol 191, © 2014 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

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4 Planning criteria for Water Sensitive Urban Design The inclusion of WSUD in the planning stage has a significant effect on the viability and cost-effectiveness of SUDS integration and on the benefits produced. Setting the design criteria at the start of the project ensures that the drainage components area is considered in the requirements for the site. To ensure this inclusion, planning criteria needs to be developed that provides a strategic approach to consider the requirements for a development. An inclusive urban design approach to regenerate or develop areas creates better places to live, work and play. Planning criteria sets out the relationship between SUDS and Urban Design and promote the integration of cities with the natural environment and the management of flood risk, water quality and the provision of biodiversity and amenity. Planning criteria will be integrated in the distinct phases of the planning process, to help town planners incorporate water in Urban Design. An explanation of what form this implementation will take follows. Step 1. Pre-planning Planning policy: Town planners should meet with the authorities to agree on WSUD and developments and to confirm potential restrictions. Involve stakeholders in planning: Communities have a vital role in the success of WSUD, so consultation and discussion is vital in every stage of Planning. Multidisciplinary nature: WSUD should be addressed by a multidisciplinary team in which town planners, urban designers, landscape architects, and highway and hydraulic engineers should be present, to ensure benefits and respond to the complexity of the urban problem. Step 2. Early planning Analyze site (fig. 2, part a):  Analyze physical system; topography, geology, etc.  Run-off Model. Identify flow paths and local flood risk.  Identify green infrastructure and multifunctional spaces to be used as potential infiltration areas. Link blue/green corridors (fig. 2, part b):  Create blue corridors. Identify new flow paths, infiltration areas and new local flood risk (New Run-off Model). Modify the gradients of streets and crossings by using elements that intercept the overland flow (fig. 3) so that the flow paths are as long as possible, therefore increasing retention.  Link blue/green corridors in infiltration areas. In this manner, a large part of the run-off produced is reduced.



Figure 2:

Figure 3:

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Early planning in Water Sensitive Urban Design.

Element to intercept overland flow and divert it to the infiltration areas.

Step 3. Develop planning Reduce impermeable surface. Minimize run-off by rationalizing paved areas and maximizing permeable surfaces. Integrate developments with SUDS. Before designing cities (streets, open spaces, etc.) town planners should know which elements ought to be incorporated into the Urban Design in order to meet the WSUD aims. To achieve this, the Table 1 shows the most appropriate SUDS to be integrated in each type of WIT Transactions on Ecology and The Environment, Vol 191, © 2014 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

1586 The Sustainable City IX, Vol. 2 Table 1: Integrating SUDS into developments. Type of development

Design element

Description and objectives

Green roof

Roof with plants to retain and treat rainwater, and promote evapotranspiration

Rainwater harvesting

Element to collect rainwater from roofs and use for non-potable water uses

Permeable pavement

Permeable surface that drains through voids between solid parts of the pavement to infiltrate rainwater from pavements residential areas

Rain garden

Element vegetated to infiltrate rainwater from roofs

Infiltration trench

Stone-filled trench to infiltrate rainwater from roofs and pavements residential areas

Soakaway

Sub-surface structure to infiltrate rainwater from roofs

Residential

Rain garden

Rill

Element vegetated to infiltrate rainwater from sidewalk areas

Open vegetated channel to transport rainwater to infiltration areas

Sidewalk Channel

Channel to transport rainwater to infiltration areas

Street Permeable pavement

Permeable surface that drains through voids between solid parts of the pavement to infiltrate rainwater from sidewalk areas

Infiltration trench

Stone-filled trench to infiltrate and store rainwater from roads

Pervious pavement

Pervious surface that drains through voids between solid parts of the pavement to infiltrate rainwater

Road


Example


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Table 1: Continued. Type of development

Parking

Design element Modular pavement

Modular surface to infiltrate rainwater from the parking surface

Infiltration trench

Stone-filled trench to infiltrate rainwater from parking surface

Bioretention

Depression backfilled with a soil mixture with vegetation to improve water quality from the parking surface

Modular pavement

Modular surface to infiltrate rainwater

Natural pavement

Natural surface to infiltrate rainwater

Swale

Open space, flood plain, green infrastructure and infiltration area


Vegetated area to transport and infiltrate rainwater

Filter drain

Gravel trench to drain rainwater

Infiltration basin

Depression with vegetation area to infiltrate rainwater

Wetland

Retention pond with aquatic vegetation to treat rainwater

Retention pond

Artificial pond to store water and release it slowly

Bioretention

Depression backfilled with a soil mixture with vegetation to retain rainwater


Example

1588 The Sustainable City IX, Vol. 2 Table 1: Continued. Type of development

Other spaces

Design element


Spaces between infrastructures

Infiltration basin

Depression with vegetation to infiltrate rainwater

Slope areas

Natural retention

Slope area with vegetation to infiltrate rainwater

Example

Design elements and its description have been adapted from [28, 30]. All photographs are be extracted from [32, 33].

development and its main aim regarding the problem that it is trying to prevent (infiltration and retention in flood areas, filtration in polluted zones, etc.). More details on the characteristics of these systems, their building process and maintenance can be consulted in [28]. Following these recommendations, City Planning will not produce the problems caused by Soil Sealing. Retrofit urban areas. It is important to repave built-up areas to compensate for the impermeability caused by new developments. Manage land uses to reduce pollution and integrate specific SUDS to provide water treatment (SUDS for filtration), in those places where it is necessary. Indicate the amount of surface water run-off from the impermeable areas and the effect of the proposed WSUD on the volume and pollution. The authorities could consider creating taxes regarding the quantity and quality of run-off which has not been managed using WSUD as a mechanism to promote it. Discussion with property owners and managers and feedback on the solutions proposed. Designers develop a maintenance plan. Step 4. Post-planning Involve Stakeholders in maintenance. Information on how WSUD work and must be maintained should be provided to communities for ensuring efficient operation and preventing failure. Evaluate designs to ensure that they are delivering what was expected. Redesign, maintain and renovate systems which are in in need.



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5 Conclusions City growth in the last century has not taken water cycle into consideration which has caused very serious environmental impacts. This has created the need to carry out WSUD to restore the natural water flow, reevaluating urban surroundings and improving the quality of the landscape and environment of cities. Because of this the application of SUD’s has gained popularity in recent years, but in many cases only as palliative measures that solve already existing problems. Therefore, Urban Planning should be a framework of reference in which these systems should be integrated, not as something isolated, but as part of a planning process based on the application of planning criteria for WSUD. This paper shows a proposal of criteria that could be incorporated in policy and regulatory drivers and that could help town planners and landscape architects to design more sustainable cities that are more pleasant to live in.

Acknowledgements The authors would like to thank the FEDER of European Union for financial support via project “Gestión Sostenible de Aguas Pluviales en Zonas Urbanas” of the “Programa Operativo FEDER de Andalucía 2007–2013”. We also thank all Agency of Public Works and the Ministry of Furtherance and Housing of Andalusia Regional Government staff and researchers for their dedication and professionalism.

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[24] Technische commissie bodem, Advisory report on general conditions for soil sealing in urban areas. TCB A063, The Hague and references therein, 2010. [25] EEA, The European environment – State and Outlook 2010: land use. European Environment Agency, Copenhagen, 2010. [26] Olsson, J., Berggren, K., Olofsson, M. & Viklander, M., Applying climate model precipitation scenarios for urban hydrological assessment: A case study in Kalmar City, Sweden. Atmospheric Research, 92(3), pp. 364-375, 2009. [27] Semadeni-Daviesa A., Hernebringb C., Svenssonb G. & Gustafssonc L., The anthropogenic sealing of soils in urban areas. Landscape and Urban Planning, 90(1-2), pp. 1-10, 2009. [28] CIRIA C697, The SUDS Manual. CIRIA, London, 2007. [29] CIRIA C521, Sustainable urban drainage systems, design manual for Scotland and Northern Ireland. CIRIA, London, 2000. [30] CIRIA C687, Planning for SUDS-making it happen. CIRIA, London, 2010. [31] MWB Melbourne Water Corporation, Water Sensitive Urban Design, Melbourne, 2013. [32] SUSDRAIN, www.susdrain.org [33] WSUD, www.wsud.org
