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NOVATECH 2013 Integrated stormwater management as a long term strategy for preservation of building environment La gestion intégrée des eaux pluviales comme stratégie à long terme pour la préservation du patrimoine bâti L. Nie1, O. P. Skallebakke2, A. Campisano3 and J. Marsalek4 1 Department of SINTEF Building and Infrastructure, Forskningsveien 3B, 0314 Oslo, Norway. [email protected] 2 Unit for Technical Operation, Fredrikstad Municipality. Postboks 1405, 1602 Fredrikstad, Norway. [email protected] 3 Department of Civil and Environmental Engineering, University of Catania, Viale A. Doria 6, 95125 Catania, [email protected] 4 National Water Research Institute, Environment Canada. 867 Lakeshore road, Burlington, Canada. ON L7R 4A6. [email protected] RÉSUMÉ La gestion des eaux pluviales est un enjeu majeur, qui affecte tant la durabilité que la qualité des bâtiments. Les caractéristiques des eaux pluviales dépendent de plusieurs facteurs, notamment : le climat, la topographie, la densité des constructions, la population, les types d'occupation des sols, et le plan d'urbanisme municipal. La rapide urbanisation, parallèlement à des planifications inappropriées concernant l'utilisation des sols, ont mené aujourd'hui à des conséquences négatives telles qu'une augmentation du risque d’inondation (et des dommages associés), augmentation de la pollution et des émissions de gaz à effet de serre. L'observation de ces problèmes et des défis associés incitent à trouver de nouvelles solutions durables et intégrées. Le présent article, plutôt que de décrire dans le détail une méthodologie et ses résultats, présente un exemple d'une stratégie de gestion intégrée des eaux pluviales. L'expérience menée dans la ville de Fredrikstad en Norvège y est décrite pour montrer comment la gestion des eaux pluviales est prise en compte dans le développement urbain, depuis la simple unité de bâtiment, jusqu'à des échelles plus larges (locales et municipales). Le plan municipal de gestion des eaux pluviales, associé à la législation en vigueur, les instructions techniques, et l'expérience pratique, permet de formuler une base de recommandations pour la gestion intégrée des eaux pluviales comme stratégie à long terme en vue de la préservation du patrimoine bâti. ABSTRACT Stormwater management is a key factor that affects the sustainability and quality of life of the built environment; meanwhile the characteristics of stormwater is influenced and reshaped by the climate, topography, density of buildings, population, types of land use, and municipal planning. Due to rapid urbanization and inappropriate planning of land use development, the interactions between these different factors have resulted in negative consequences, such as increased risk of flooding and resulting damage, pollution, and Green House Gas (GHG) emissions. The observed problems and emerging challenges call for sustainable and integrated solutions. This paper rather than presenting deeply a research methodology and associating results, demonstrates an approach of integrate stormwater management strategy. It uses the experience in the city of Fredrikstad in Norway, illustrates how stormwater management is implemented during urban planning and building development process, from a single building unit to local and municipal scales. A municipal strategic stormwater management framework plan together with legal Acts and technical guidelines, and practical experience formulates a basis of recommendations for integrated stormwater management as a long term strategy for sustainable urban planning. KEYWORDS Climate, Ecosystem, Infrastructure, Stormwater management, Sustainability, Urban planning 1 A2 - STRATÉGIE D'AGGLO. / CITY SCALE STRATEGY 1 INTRODUCTION Stormwater in urban areas was traditionally managed by designed sewer systems for the prevention of the collection of excess water on urban surfaces and the reduction of risk to people, health, property, society and the natural and built environment. However, the existing sewer systems in European central cities were designed 50 – 100 years ago. They are aging and require rehabilitation or upsizing. As observed globally, climate change has caused more frequent extreme climate events, such as more intense precipitation period in one region or long drought period in another region, as well as extremes in temperature. Moreover, urbanization has caused more people are moving to urban areas that requires development of previously lightly or undeveloped land, replacing pervious with impervious surfaces. Consequently vegetation areas are thereby replaced by impervious building roofs, roads and parking places, resulting in increasing of urban runoff. This development also results in an urban island effect, with deterioration of the sustainable building environment due to large energy consumption, increased CO2 emission to the environment, and a decrease in biodiversity, and damage to ecosystems. Because of the challenges described above, stormwater management has evolved over time from a focus on water quantity or flood control, to water quality (pollution) control, and more recently to include recreation, aesthetic and water reuse aspects (Walesh, 1989; Wang, 2012). Therefore Sustainable Urban Drainage Systems (also called Best Management Practice (BMPs) or Blue-Green (BG) solutions) have been accepted globally as measures to adapt to or counter changes in the climate and the effects of urbanization. They have been applied in many countries, e.g. EPA Stormwater water management program. One can find all types of information in a range of manuals of stormwater retrofit and BMP, regulations, guidelines and case studies, and municipal and industrial information. Literature shows the benefits of the adoption of various stormwater management approaches in Italy. Stormwater detention tanks with various design configurations (online and outline) and operating conditions have been integrated to the sewer system all along the peninsula which has demonstrated good performance with respect to environmental pollution (Todeschini et al., 2012). Also BMP techniques mainly based on the use of vegetated roofs on the top of public buildings in urban areas have been setup and tested in northern and central Italy showing to be able to mitigate storm water runoff generation in terms of runoff volume reduction, peak attenuation and increase of concentration time (Fioretti et al., 2010). Other emerging techniques based on the use of rainwater harvesting tanks have been recently tested by Campisano and Modica (2012), pointing out the possibility to use such techniques as tools to improve the sustainability of drainage systems by mitigating the generation of storm water runoff at the source and to limit the demand of potable water in houses. EU project prepared demonstrates the adaptation of SUDS in different countries and a case study of RWH in Turkey (Aldea et al., 2012) According to the feedbacks gathered from the participating cities being investigated in the project PREPARED, most of the cities have experienced problems related to aging such as sewer obstructions, cracks or collapse, and insufficient drainage capacity. SUDS have been applied extensively in the cities of Aahus of Denmark, Lyon of France and Barcelona of Spain (Aldea et al, 2012), but are not common in other other participating cities. In Norway some pilot projects applying stormwater management BG solutions have been performed in the newly developed areas (Lindheim, 2009; Tekna, 2012). A pilot research project testing infiltration basin in Sandli, Bergen has been reported by Thorolfsson et al. (1997) with some success. Some retention basins have been also established in the Oslo region in order to reduce the heavy metal pollution from main roads to the rivers (Åstebøl and Hvitved Jacobsen, 2006). However, practice is not common in existing building areas. Municipalities plan to disconnect surface stormwater inflow from private building areas to the public sewer systems (in fact some municipalities like Fredriksatd have already implemented it), which will require building owners to retain or infiltrate stormwater in private areas by grass land, rain garden or permeable or semi-permeable surface or private roads, or to construct infiltration trenches and basins, or use green roofs, etc. Although plenty of information and international experience is available for implementation of SUDS, it is unknown whether local areas have the potentials to accommodate the surface water by detention and infiltration measures. Solutions have to be found according to the local conditions. This paper presents an integrated approach that brings together legislation, municipal strategies for urban planning, technical guidelines for stormwater management from the scale of an individual building unit to the neighborhood, and from local areas (subcatchments or catchments) to the 2 NOVATECH 2013 municipal level, taking into account climate change and urbanization impacts on stormwater quantity and quality and ecological issues and the interdependency of critical infrastructure networks. The approach is demonstrated in a case study in Fredrikstad of Norway. 2 INTEGRATED STORMWATER MANAGEMENT APPROACH 2.1 Important issues to be considered 2.1.1 Stormwater runoff Stormwater is water generated from precipitation during rain and snowmelt events. Stormwater runoff is water flowing over land or impervious surfaces that does not percolate into the ground. As the runoff flows over the surfaces (such as paved streets, parking lots, and building rooftops) it also accumulates debris, chemical particles, sediment or other pollutants that could adversely affect water quality if the runoff is discharged without treatment. Inappropriate stormwater collection and disposal may cause urban flooding and pollution to the recipients and urban natural environment.The primary method to control possible negative consequences caused by stormwater is the use of Low Impact Development measures (LIDs, also called SUDSs or BMPs) during urban planning process.Stormwater management. 2.1.2 Objectives of urban stormwater management Primary objectives of urban stormwater are defined as follows: Protection of life and lessening the risk on public health and safety Reducing the risk of floods and monetary damage to private and public properties Minimizing the disruption on community affairs and indirect consequences Protecting the quality of surface and ground water resources Enhancing the quality of life in urban areas Managing the water in the contexts of physical, chemical, bio-ecological and sustainable perspectives. 2.1.3 Integration of stormwater management with other types of urban infrastructure Important urban infrastructure usually includes the utility systems that supply public services, such as electricity, water supply and drainage systems, heating and gas supply systems, transportation, telecommunication; and the systems that provide for welfare and social and economic service such as hospitals, financial centres, as well as systems for safety and emergency services such as fire stations, police stations, flood warning and forecasting systems and associating buildings (Gordon and Dion, 2008; Lhomme et al., 2012). In the contexts of stormwater management in the built environment, the urban sewer system (also called minor system) and the road system (also called major system) and electric power system are the most relevant. A failure in one system (or its components) may cause a chain of failures in other systems, e.g. the electric power distribution system may be cut during flooding or storm surge because of strong wind and heavy precipitation, which may cause failure to operate the pumping stations of the drainage system or failure to lift the gates of the spillways. Similarly inundation of the pumping station may cut off the electric supply systems, causing further flooding and related consequences. In order to make the city more resilient in the face of various natural disasters or system failures the linkages between different infrastructure network systems should be considered during city planning. 2.2 Integrated stormwater management approach Given the above-mentioned considerations, a comprehensive stormwater management and their interaction with buildings, important infrastructures and other influence factors are illustrated in Figure 1. In order to ensure appropriate implementation of the framework at difference levels and scales during the urban development process, a holistic approach is introduced in Figure 2. This paper uses the city of Fredrikstad as an example, illustrates how the stormwater is handled in the 3 A2 - STRATÉGIE D'AGGLO. / CITY SCALE STRATEGY municipality from strategy to urban planning and how various measures are implemented in practice. Roads Buildings Urban drainage systems Integrated stormwater management Climate Social economy Lakes, rivers and streams Open surface Figure 1. Integration of stormwater management with important infrastructure and other important factors Water course Act Legislation at national level Pollution control Act Integrated stormwater management Planning and Building Act Water resources and land use planning Regulation and planning at municipal level level Regulation on flood and pollution control Harmony of building development and landscape Non‐structural measures Dams and flood ways ( e.g. rivers or streams) Rehabilitation of minor and major drainage systems SUDS measures at municipal, local and individual levels Implementation of Blue‐green solutions Control of stormwater runoff quality and CSOs Restoration of urban bio‐ecological systems Figure 2. A holistic approach for integrated stormwater management in different levels in Norway 4 NOVATECH 2013 3 3.1 CASE STUDY Fredrikstad Fredrikstad is situated in the South of Norway. It has population of over 75 000 and total area of 289 km2. The largest river in Norway – Glomma passes by the city before its tributary merges to the sea while the main branch goes to the Øster River. Thus, the city has contact with sea and in the right side of river Glomma. The soil is dominated by bedrock and clay in the city areas. The groundwater level is very shallow, which can be 1-2 m below the surface. The potential for infiltration of stormwater is low in the city area. The mean monthly temperature varies from -3.1 oC in January to 16.7 oC in July. Total annual precipitation is 825 mm in average. Intense precipitation in very short time periods (10-15 min) have been observed in recent years (Skallebakke, 2011) and projections of the future climate scenarios indicate that the city will be exposed to more frequent heavy rain events and sea level rise and storm surges (Hanssen-Bauer, et al., 2009). Before 1978 there was no technical guideline for sewer design in Norway. The stormwater drainage system in the urban areas has been developed based on a principle that leads the stormwater as quickly as possible to the underground sewer systems and discharges it to the nearest receiving waters. From 1978 to 1998 the sewers were designed based on a guideline mandated by the National Pollution Control Authority (SFT, 1978), according to design rains with return periods of 1 in 10 to 15 years. Since 1998, the design standard of EN 754 was adopted as a national standard for design outdoor urban drainage systems in Norway (NS-EN 752, 1998). About 20% of water and wastewater (including stormwater) systems (WWS) in Fredrikstad was developed before 1940, for which no written information is available. According to the statistics of the municipality (FM, 2010), from 1940 to 1979 the WWS was developed steadily with an increase of less than 10% in each decade. The development of the water and wastewater infrastructure after 1980 increased at double the rate of previous decades. About 40% of sewers carry combined flow. Climate change and recent quick urbanization have caused significant increase of surface stormwater, subsequently more inflow was discharged to the sewer system than it was designed to be, which have caused waterlogging in local areas, basement flooding and pollution in the recipients. These challenges call for sustainable stormwater management both in the existing and new developing areas, taking into account of the water quantity, quality and ecological and environmental aspects. 3.2 Assessment of climate change impacts on urban drainage systems After the severe flood event in 2002 (65 mm rain in six hours, the return period of the event is estimated more than 100 years) caused more than 250 house basements flooded and total economic damage of about 17 million Norwegian crowns (equivalent to 2.1 million EURO (Lindholm et al, 2006), several other flooding events occurred in in 2006, 2007, 2008 and 2009 in the city. The IntensityDuration-Frequency (IDF) has been an important factor indicating the change of climate. Figure 4 presented the changes of IDF curve calculated according to the historical events (control period) and according to the projected scenarios (2071-2100) (Nilsen, 2013). A stantistics showing that the intense storm event in 2008 has a higher intensity than the values for 100 years' flooding (Skallebakke, 2012). Climate change impacts on the sewer system in Veumdalen catchment of Fredrikstad have been continually studied since 2002 (e.g. Røysted and Lindholm, 2006; Tøndel, 2007; Nie et al., 2009; Myking, 2012). These studies provided some assessment results of the potential consequences with regard to the given climate scenarios, mainly increase of precipitation intensities and change of air temperature. The main consequences are waterlogging in local areas and flooding of house basements and resulting erosion and contamination problems. 3.3 Integrating stormwater development process management in the municipal building Since large economic damages have been caused in buildings and private properties in the building basements, as well as the project scenarios of climate change, stormwater management has been an 5 A2 - STRATÉGIE D'AGGLO. / CITY SCALE STRATEGY important issues in the overall municipal urban development planning. In 2007 Fredrikstad municipality worked out a comprehensive stormwater management plan as a municipal strategy. Operation Implementation of measures Final plan Obligated announcement and evaluation Preliminary plan Land use classification Municipality Plan According to the national Planning and Building Act (DM, 2008), the municipality introduces standard process to control and supervise building development process from planning to implementation (or construction) and operation stage (Fig.3). This ensures the efficient implementation of the legislation and municipal strategies regarding land use, stormwater management, flood and pollution control. Advices, approval and control from technical units Figure 3. Progress plan for building application and implementation 3.4 Stormwater management and sustainable solutions In order to support municipalities and building owners to handle stormwater safely and sustainably, technical guidelines of stormwater management have been made in water, building and transportation sectors (Lindholm et al., 2008; Statens Vegvesen, 2011; Hafskjold,L.S. 2012). Based on the legal Acts and the sectoral guideline for stormwater management, large municipalities have made their own regulation plan and technical guideline and norms for stormwater management and promotion of various SUDS solutions (Oslo VAV, 2011). These guidelines recommend municipalities to take into account stormwater management in municipality’s plan for development, such as (1) the municipality should plan for storm runoff that cannot be drained by the underground sewers, to be handled on surface; (2) applying sustainable urban drainage solutions (SUDS) such as infiltration, retention and detention solutions and green infrastructure. The SUDS should be incorporated into all levels at the municipalities’ area planning; (3) the stormwater cannot be handled by stormwater measures will be conveyed in open floodways (major drainage systems) without causing significant damages. The return period of design rains for the analysis of safe open flood ways should be 100 years; (4) polluted storm runoff should be treated before to be discharged to receiving water bodies. In combination the technical guidelines with the practical situations in Fredrikstad, several stormwater control measures have been implemented in the municipality. 3.4.1 Disconnection of roof stormwater In order to diminish the risk of basement flooding and overflow from public sewers, stormwater from 3000 building roofs have been disconnected from public sewers. For single house with garden, they lead the roof water to the garden for infiltration (although it can be difficult in wet seasons, and low infiltration potential because of the hard bedrock and clay, and high ground water levels). Each building owner has received subsidy from the municipality about 400-500 NOK for the implementation of a single measure (Figure). 3.4.2 Pipe detention In the existing building areas without gardens, the owners are recommended to use large pipe (D=12m) as a detention but with small outlet in order to control the discharge to the trunk sewers. 6 NOVATECH 2013 3.4.3 Domestic rainwater harvesting Because of the geological and soil condition, as well as high groundwater level in Fredrikstad, the potential for infiltration of stormwater is low, especially in wet seasons. In order to control the stormwater discharge to the terrain from building roofs and other impervious surface, the authors examined the potential benefits of applying domestic rain water harvesting (DRWH) techniques based on the retention and reuse of the collected rain water from the rooftop. Preliminary simulations for the present climate condition during control period (1961-1990) and scenario periods (scenario IS92A for period 2013-2042; scenario A2 for period 2071-2100) have been specifically run. For scenario A2, the simulation results indicate that for given stormwater reuse demand in the house (d=0.2, 0.5, 1.0 and 2.0), the overflow discharge to urban surface can be reduced up to 25%, 55%, 90% and 100% depending on the DRWH system hydraulic characteristics and size (for frequency level fi =0.75). The methodology for the analysis of the benefits of the DRWH systems is introduced by Campisano and Modica (2012). The DRWH model and a testing case carried out in Oslo, Norway were presented in another paper (Campisano, et al, 2013). Simulation results based on a similar approach obtained in Fredrikstad are presented in Figure 4. Based on the simulation results, the authors suggest the municipality investigate potential to use Domestic Rain Water Harvesting (DRWH) tanks or ponds as a retention option to reduce the surface runoff and discharges to the sewer systems. Figure 4. Overflow discharge (Ov) values as function of reuse factor (d) and retention factor (Sm) (where f is the exceedance frequency) for scenario A2 (2071-2100) 3.4.4 Re-open the closed rivers During 50-60 years, some rivers are closed and replaced by culverts or underground tunnels. Because of the effects of climate change and urbanization, the importance of having free water surface in the urban neighbourhood and restoration of natural floodways have been realized in more recent years. It is vital for restoration of the natural biological and ecological environment and consideration of aesthetic and recreative use of urban landscape, and also for flood control. Green, nourishment aquatic vegetation and infiltration areas will be important for the purification of polluted storm water and reduce surface runoff. In the future, the municipality will give priority to the following principles for stormwater management: 7 A2 - STRATÉGIE D'AGGLO. / CITY SCALE STRATEGY Stormwater systems should preferably be open rather than closed systems. Where appropriate, consideration will be given to open existing stream that was closed some decades ago. Reopening Veum stream is such an on-going project. In built-up areas, storm water to the greatest extent should be possibly dealt with at the source through retention and infiltration, e.g. green roof, rain beds or rain gardens. Upon renewal of surface water systems and existing infrastructures, solutions that make the water visible and establish free surface water self-treatment basins or tanks (from urban areas and main roads, etc.) and measures that replace impervious road shoulders by permeable materials should be given priority. 4 DISCUSSIONS AND RECOMMENDATIONS Integrated stormwater management has proven vital to the restoration of sustainable urban landscapes and preservation of a sustainable built environment, in particular to adapt to the impacts of urbanization and climate change. This paper also indicates that it is important to take into account the interaction of stormwater management with buildings and the other urban infrastructure networks like electricity, roads and buildings. Several adaptive SUDS measures applied in practice in Fredrikstad are introduced in this paper. Reopening of the closed river and stream sections, disconnecting roof water and using large pipes as an option for detention are popular measures in Fredrikstad and other municipalities in Norway. Because of sufficient fresh water resources, reuse of stormwater and DRWH are not common practice in Norway. However concerning on the potentials for stormwater detention in building areas, and reduction of inflow to public sewer systems, the use of Rain Water Harvesting (DRWH) tanks or ponds as a retention option should be further investigated, e.g. use DRWH in combination with rain beds and rain garden are recommended to be investigated in the near future. Norway is a country situated the most north in the world. It has both continental and maritime climate, i.e. heavy rain in very short time in summer or autumn, sometimes in winter, long rain period in autumn, rain and snowmelt in early or late spring, which complicates the application of SUDS solutions. 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