Stormwater Management & Residential Flooding The Big Picture July 2007

Transcription

1 Appendix A White Paper Stormwater Management & Residential Flooding The Big Picture

2 Page 2 INTRODUCTION Recently, there have been a number of significant rainfall/runoff events that occurred on the following dates: July 28, 2006 December 2, 2006 March 26, 2007 Overall, the Region of Halton s sanitary sewer system and the City of Burlington s storm drainage system performed well in these extreme events. However, in the areas of the City that have developed since the adoption of higher and more comprehensive design standards including: how house foundation drain collection system are designed (1968); adoption of Storm Drainage Design Criteria manual (1977); and changes to flood standard in the City s urban creek system (1984), a number of residential properties in several older neighbourhoods in Burlington experienced flood damages or drainage problems from either sanitary sewer backup into the basement or stormwater runoff flooding, or a combination thereof. A common characteristic of these events is that they involved intense localized rainfall and/or pre-existing saturated ground conditions resulting in very high localized surface runoff and infiltration/inflow to the sewer systems. Sanitary Sewers: The responsibility for the sanitary sewer system vests with the Region of Halton, with funding for this service provided by the Region s sewer and water rates, approved annually by Regional Council. Storm Drainage: Stormwater management and storm drainage is a City responsibility, although Conservation Halton and other agencies have regulatory authority over watercourses, which form an integral part of the City s storm drainage system. Funding for the non-growth component of the City s storm drainage program is currently provided by through the municipal property tax levy. A contributing factor to the sanitary sewer back-up in houses built prior to approximately 1968 is likely flow contributions from foundation drain collection systems. Foundation drain collection systems are installed at the base of the basement wall around the exterior perimeter of homes (i.e. weeping tiles) to collect groundwater in the soil or surface water that has infiltrated down the basement wall. Until 1968, these drains were a permitted legal connection in Burlington, connecting to the sanitary sewer. The sanitary sewer design made allowance for a contribution from this flow source. However, persistently high ground water elevations and/or excessive infiltration/inflow can overload the capacity of the sanitary system. It is also possible that in some areas, roof leader drains or downspouts are also connected into the weeping tiles. This has

3 Page 3 never been an approved connection in Burlington. However, it is possible that either during the homes initial construction or at some subsequent point in time, these drains have been connected to the foundation drain and therefore contributing stormwater runoff into the sanitary sewer system. Less likely, but also possible, is the existence of other direct stormwater related connections to the sanitary sewer system from drains or catch basins. These connections were also never permitted. In May 2007, in response to 128 basement flooding incidents in Burlington since July 2006, the Region of Halton initiated a pilot program to address basement flooding related to sanitary sewer back-up through the basement floor drains. Details of this program are contained in regional report PPW85-07, which is attached to staff report Comser-09/07 as Appendix C. The purpose of this White Paper is to more specifically address the issues related to the City s storm drainage system. The White Paper will begin by providing an overview of the components of an urban drainage system, how they are related and how the design of the systems has evolved, particularly since the 1970 s. This information is intended to provide background and context to the more detailed discussion of specific storm drainage elements, design standards and programs currently in place, as well as recommended future strategies and actions. The flooding issues tied both to stormwater and sanitary are complex and interdependent and it is very important that these interdependencies, as well as the regulatory, legal and financial issues associated with them be understood in the formulation of any actions or programs aimed at improving the existing systems and the specific problems associated with basement and surface flooding. BACKGROUND OBJECTIVES OF URBAN DRAINAGE, THE BIG PICTURE Everything is connected to Everything Else Historically with urban development through the 1970 s, urban drainage design was premised on the philosophy of treating stormwater runoff as waste to be removed from the landscape and to be disposed of as quickly as possible through an ever increasing interconnected network of drains and sewers. A general philosophy of out of site, out of mind prevailed and little connection was made of the role of stormwater runoff in the urban ecosystem and the economic and practical realities of designing and building storm sewer systems for extreme rainfall and snowmelt events. The experience of Hurricane Hazel in 1954 and the mass destruction that ensued resulted in new policies being developed in Ontario to deal with flood plain management. With this event and the establishment of Conservation Authorities that were based on watershed areas, as opposed to political boundaries,

4 Page 4 significant advancements were made in undertaking remedial works throughout the province to address areas vulnerable to surface flooding from rivers and creeks. Perhaps more importantly, standardized provincial regulations were put in place regulating any new development in areas susceptible to flooding from the Regional Storm (defined as the greater of a 1:100 year event or Hurricane Hazel) along major creeks and rivers. These regulations however were generally put in place in larger creek and river systems only. In Burlington this includes the Grindstone and Bronte Creeks. Development around smaller creeks like Roseland, Tuck, Shoreacres and Sheldon were typically regulated or designed to a 1:50 year standard flood standard. Although regulation of development in major floodplains was a significant step forward, it did not deal directly with the issues of urban storm drainage system designs (major and minor) and related impacts. Across Ontario, local storm drainage design continued to rely on enclosures and piped systems with little regard to where the water would go if the capacity of the pipes were exceeded or water was unable to enter because of blocked or inadequate inlets. However, in the period through the 1970 s to the late 1980 s, it became increasingly apparent that piping stormwater was effective for dealing with common rainfall and snow melt events only. These piped or minor systems were limited in their capacity as it was inevitable that conditions would exist that they could not be accommodated and that the design and construction of a parallel major system comprised of overland flow routes was required. It is important to note that this major system always exists it is the route water will follow if it is unable to be accommodated by the minor system due to either capacity constraints or inlet blockages. If the major system is properly designed, it will avoid flooding homes or causing excessive or unsafe water levels on roads, etc. If the major system is not properly designed, excessive ponding in roadways or worse, runoff may be directed overland towards buildings resulting in flooding of these areas. The City formally adopted a major/minor storm drainage system design in 1977 with the adoption of a new storm drainage criteria manual. By the mid-1980 s this same design approach was generally used across Ontario. As cities across Ontario expanded it became apparent that issues of increased localized flooding, poor water quality and closed beaches in our lakes, declining fisheries and erosion in creeks and rivers were all related. In the late 1980 s when the Crombie Royal Commission began to study the problems associated with the Lake Ontario waterfront in the Greater Toronto Area, they quickly realized that the degraded state of the waterfront was really a culmination of the activities on the landscape draining to the lake. The problem was not so much a waterfront problem but rather a watershed problem, leading to a fundamental conclusion; that if we are to address the conditions that society find to be unacceptable on the waterfront then we really need to address how we manage water on the land. What happens on an individual lot or subdivision level, with respect to how drainage is handled, is important for managing not only water quality but also the greater urban ecosystem.

5 Page 5 URBAN STORMWATER MANAGEMENT WHAT IS IT TRYING TO ACHIEVE Nature meant for most of the rainfall to soak back into the earth, present practices often prevent it Urbanization results in changes to the natural runoff characteristics of a watershed. As outlined below, there are three main impacts which modern stormwater management is intended to address. The challenge is to address these impacts while at the same time providing an acceptable level of service for stormwater drainage from individual properties, roads etc., since solving one problem may often create another much larger problem. For example, improving local drainage in a neighbourhood or residential area that is serviced by poorly defined swales and ditches with a new storm sewer system may improve the drainage in this local area. However, if the storm sewer outlets to a watercourse, increased flooding, erosion and water quality impairment may result in that watercourse. These factors all need to be carefully considered in any new design and ultimately any impacts need to be balanced against the benefits of any new system. 1. Increase Peak Flow Rates Increasing impermeable surface through the construction of paved surfaces, roofs, patios etc. and increasingly efficient drainage system through the construction of swales, gutters storm sewers etc. all have the effect of directing more water in a shorter time period to receiving water courses, resulting in higher and more frequent peak flows. The first objective of urban stormwater management is to manage these changes to the flow by either slowing the runoff down at source (lot level), increasing the capacity of conveyance elements such as sewers and channels, building storage facilities to temporarily store water and discharge it at a controlled rate to the receiving system (detention ponds) or a combination of the above methods. 2. Increase in Stream Erosion Rates Urbanization, as discussed, above results in less water infiltrating the ground and the resulting surface runoff flowing faster or more efficiently into receiving watercourses. Urbanization therefore results in higher peak flow rates and a higher percentage of the total rainfall being conveyed to the watercourse via surface runoff. On an annual basis this higher volume of runoff can be quite significant. For example, a natural forested landscape will result in approximately 15% of precipitation being discharged to creeks as runoff, whereas in a typical urban area approximately 60% of the precipitation will be discharged to creeks as runoff. The result of the increased peak flow and volume of runoff dramatically increases erosion rates in the receiving stream as the stream tries to adjust to the changing flow regime. To manage this impact, measures are taken to enhance infiltration or slow down runoff on a lot level, or over control flows in stormwater ponds prior to discharge to receiving watercourses.

6 Page 6 3. Increased Pollution Loadings To Receiving Watercourses and Lakes - Stormwater runoff washes pollution from roads, driveways parking lots, lawns, etc. into the receiving watercourses and lakes. Controlling this pollution involves an integrated strategy consisting of: minimizing the accumulation of pollutants on the ground through best practices such as limited fertilizer application, washing cars at commercial establishments, street sweeping etc. encouraging infiltration off patios, driveways, roof leaders, etc., to vegetated areas where the water is naturally filtered and allowed to infiltrate into the ground end of pipe treatment in the form of stormwater retention ponds designed to allow particulate mater to settle out of suspension prior to the water discharging to receiving watercourse. The practice of stormwater management and urban drainage has evolved significantly since the 1980 s. Prior to this time, efforts were primarily directed at conveying flow from lots and roads as efficiently as possible. Since the 1980 s, stormwater management practices have been employed in the development of new communities in Burlington. Initially these were limited to quantity or peak flow control, but more recently with the development of communities such as the Uptown, Orchard and Alton Communities and planning for the North Aldershot lands, comprehensive plans have been developed and implemented to address all three impacts. URBAN DRAINAGE SYSTEM COMPONENTS: MINOR & MAJOR SYSTEMS Urban Drainage Systems are comprised of many components all of which need to be designed and maintained carefully and systematically to provide satisfactory drainage and protection from flooding. Generally speaking, urban drainage design is categorized into two parts: Minor System and Major System. Minor System: The Minor storm drainage system is made of a collection of gutters, inlets, pipes etc. The purpose of this system is to provide for the convenient disposal of storm runoff from streets, walkways, yards etc. It is typically designed to handle runoff from more frequent events, like small storms or rainfall that would normally occur on average once every 2 to 5 years. Given that this system is comprised of gutters, pipes, inlets etc., it is not economically feasible or practical to size these systems for more extreme storm events. These systems rely on a series of stormwater inlets to capture the flow into the pipes. By design, stormwater inlets have limited capacity to collect flow, especially from short very intense storm events. Inlets are also susceptible to blockage from leaves, debris, snow, hail etc. Good design can mitigate these factors to an extent but it cannot eliminate

7 Page 7 them. This is an important limitation to understand when assessing flooding events and protection measures. Unlike many other infrastructure elements, such as sanitary sewers, water mains, bridges, dams, etc. that are designed for extreme events, storm sewer systems are not. Their design capacity is limited to more frequent events only. Major System: The Major storm drainage system is best described as the overland flow route water will follow once the minor system is at capacity or if runoff cannot get into the pipes. The system is comprised of lot grading, overland flow routes along swales, walkways, roadways and ultimately open watercourse such as creeks and rivers. Properly designed and maintained this system will convey flows from extreme runoff events without damaging buildings and maintaining passage of roadways for emergency vehicles etc. When not properly designed or maintained, these overland flow routes may result in water being directed to buildings or collecting at unacceptable depths in low spots along roads etc. Prior to 1980, common practice in Ontario did not provide for a proper continuous major flow system along streets. The standard practice today in new subdivisions requires considerable design effort and cost to grade building lots and provide for continuous overland flow routes along swales, paths and roads to direct runoff to receiving ponds or creeks. The City of Burlington adopted a major/minor drainage system design approach in conjunction with the adoption of the storm Drainage Criteria Manual in Historically, early urban drainage systems relied too much on the minor drainage system. Major drainage systems were often compromised by constructing creek enclosures, not requiring continuous overland flow routes to be designed and constructed to properly accommodate flows should the minor system be at capacity or flow entry into be blocked. Over the past 15 years, failure of the minor system in areas without an adequate major system has been a significant factor in storm water flooding events effecting properties in the City. Examples of this include flooding in the Leighland Community in 1992, flooding of commercial lands adjacent to the Roseland Creek enclosure south of the QEW and flooding of homes in Tyandaga and Kirkburn areas in the May 2000 storms. As a result of these and other situations, the City has undertaken extensive capital works involving the construction of drainage diversions, flood control ponds and inlet improvements. DESIGN STORMS AND CLIMATE CHANGE Storm drainage design, including flood protection, is often expressed as being of a certain design frequency. For example, a storm sewer system may be designed for a 1:5 year storm, where as a bridge opening may be sized for the 1:100 year event. Typically the design process would involve looking at the historical rainfall records for a period of years from a recognized rain gauge station. In Burlington, the Atmospheric and Environment Services (AES) gauge

8 Page 8 located at the RBG has been utilized since This gauge has a continuous record extending back to Other AES gauges are located at Hamilton Airport, Guelph Arboretum and Pearson Airport. The City also has it s own gauge located on the roof of Mainway Arena which has been operational since the late 1990 s. Once a rainfall record is identified, analysis is undertaken to identify statistics on the rainfall to determine rainfall amounts that correspond to a certain frequency. This is then used in the design calculations. Conceptually a specific rainfall event that produced a constant amount of rainfall over an entire watershed would be identified as the design event. Although this is generally a satisfactory approach, it somewhat over simplifies how actual storms impact on specific areas, as has been the case recently for all 3 events since July This approach also assumes that the historical precipitation pattern will be representative of current and future precipitation conditions. In reality, storms are dynamic. They can be very localized and have varying intensities and different durations. The actual amount of runoff that any given storm produces is also dependent on the existing moisture content in the soil from prior storms or spring snow melt. This is particularly relevant for drainage areas that are undeveloped or have a high percentage of permeable surface area, as is the case for the headwaters for all the City s creeks, which are located north of the urban boundary along the Niagara Escarpment. This means that quoting the return period of any given storm is very difficult and does not necessarily equate to the return period of the runoff. Short, intense, localized storms like we experienced over the last year can cause severe, isolated flow conditions in the local drainage system but are relatively less significant in larger systems, like creeks near their outlets to the lake. Looking to the future current research and data on climate change suggests that storm patterns are changing and that short, intense and flashy storms are replacing the long drawn-out rainfall events of the past. (David Philips Environment Canada, Toronto Star July 20, 2007.) Research to date, indicates a trend toward heavier rain events and more frequent intense events in Southern Ontario (Planning For Extremes, Adapting To Impacts On Soil and Water from Higher Intensity Rains with Climate Change in the Great Lake Basin, April 2006, Soil & Water Conservation Society). Other research has projected that rain and snow events could be more intense, and occur in more extreme events. In Canada by 2050, a 24 hour storm event, which now has a return frequency of about 40 years, is projected to occur once every 20 years (Weather and Climate in Southern Ontario, M. Sanders, University of Waterloo, 2004.) These factors have several implications to the design of drainage systems. The implications of this to the City include: Relying on statistics of past rainfall events may no longer be appropriate for predicting design conditions;

9 Page 9 The relatively sparse network of rain gauges may no longer be adequate in identifying design events More intense events early in the year when the ground is saturated could result in more severe runoff events than the rainfall event alone would indicate under normal summer ground moisture conditions. Usable and liveable areas in areas susceptible to flooding may need to be re-evaluated Resourcing for other storm related activities such as winter control activities and storm damage to trees may need to be re-evaluated. In light of these potential implications it is recommended that staff actively participate in studies looking at these issues, including a financial contribution to a proposed study by Environment Canada and that staff implement at least two additional rain gauge locations within the City to provide better data for both the regions sanitary sewer basement back up pilot program and in assessing the operation and appropriate design criteria for the City s storm drainage design. DRAINAGE ISSUES FACING THE CITY The previous sections have attempted to provide a context for how storm drainage design has evolved and the often-conflicting objectives that present-day stormwater management strives to achieve. The following section will deal more specifically with the stormwater issues facing the City and its residents. As previously introduced, basement flooding via backup through the basement floor drain has been a major flooding factor effecting at least 128 homes, following the three recent major storm events. As a recent research study by Canada Mortgage and Housing Corporation (CMHC Research Report Practical Measures for the Prevention of Basement Flooding Due to Municipal Sewer Surcharge, October 2003) concludes basement flooding cannot be addressed in isolation because it often represents one symptom among many that stem from municipal drainage systems. Preventing basement flooding involves a deeper understanding of ecosystems, watersheds, municipal infrastructure systems and the diversity of building connection types to these systems. In short basement flooding is a complex issue with many contributing factors that need to be considered involving both the sanitary sewer systems and storm drainage. Over the course of the development of the City the function and expectation for the use of basements has evolved from being a foundation for the house superstructure to include first usable and more recently liveable space. Unlike many parts of the U.S. and other warmer climate countries where the basement is considered to be outside the building envelope, in Canada the basement is

10 Page 10 presumed to be inside the envelope. (CMHC, Performance Guidelines for Basement Systems and Materials) Another observation is that in addition to having warmer climates these areas also have very different precipitation patterns, in that intense down pours are more common. As indicated previously, one of the effects of climate change in Southern Ontario is that our precipitation patterns are predicted to change to be more like those of southern warmer climates. The increased expectation of homeowners to have greater use of their basements has resulted in many design improvements to basement design over the years. However, the challenge is how to meet this expectation in older homes whose basements were not designed and built with the intent that they would provide liveable space. This is a major issue for municipalities across Canada. It is estimated that across Canada wide there are on average 30,000 to 40,000 incidents of basement flooding per year (CMHC, 2003). One of the areas in which basement design has evolved significantly over the last 50 years is how basement walls and foundations are constructed and drained. Prior to 1968, foundation drains were allowed to be connected to the sanitary sewer in Burlington. Appendix B to report Comserv illustrates the residential subdivision registration pre and post 1968, providing an approximate indication of the areas where foundation drains are connected to the sanitary sewer verse those that are connected to the storm sewer or drain via sump pumps. Almost all the reported basement flooding incidents in Burlington over the past year are located in areas developed prior to As indicated, post 1968 foundation drains were not permitted to discharge to the sanitary sewer and are required to outlet to either the storm sewer system or are drained via sump pumps. Earlier systems discharging to the storm sewer system have the potential to surcharge due to back up through the storm sewer system from adjacent creeks. Higher design standards and analytical methods were employed from the mid 1980 s reducing this risk. Sump pump drainage systems require maintenance and are the responsibility of the homeowner. Sump pumps generally do not have back-up power systems and are therefore prone to failure during power outages, which often occurs during storm events. Additional issues associated with sump pump systems include nuisance complaints from occupants and neighbours for systems that operate frequently in areas with high ground water levels and/or inappropriate location for sump discharge. Basic strategies to address basement flooding include: Modifications to the sewer lateral servicing the house through installation of backflow valves Modifications to foundation drain collection systems including installation of sump pumps Strategies to minimize water flow to foundation drains through lot grading and eavestrough/downspout disconnection

11 Page 11 Programs to reduce other infiltration/inflow source to sanitary sewer systems and or the provision of additional planned storage in the sewer system In addition to basement flooding, the potential for surface flooding, water course erosion and water quality impacts are all factors that require maintenance and capital improvements with associated financing needs in the coming years. These issues will be explored in more detail in the following sections of the white paper. This discussion will be broken down into the following key issues: a) Building Connections and Foundation Drains b) Lot Grading Including Eavestroughs/Downspouts c) Local Surface Water Flooding Lack of adequate drainage outlet d) Inlets & Enclosures e) Watercourse Flooding f) Watercourse Erosion g) Storm Water Management Facilities Some fundamental policy issues are common to most of these issues. They include: 1. Evolving Design Standards Design standards relating to surface and subsurface flood protection for properties has increased significantly over the past 50 years, as is the case with many areas in new residential and commercial/industrial construction, (i.e. electrical systems, insulation, structural, etc.) are all built to a higher standards today than in established older areas of the City. At issue is what is the local government s responsibility to up-grade the storm drainage system to current standards if the current performance does not meet today s standards, recognizing that in new construction, the purchaser pays for the high standard in the purchase price of their homes. The second required question, is it even practical or feasible to upgrade the design standard? 2. Property Ownership - Effective storm drainage and flood protection is comprised of a number of elements some of which some are located entirely on public lands (street storm sewers) and responsibility for the design, construction and ongoing maintenance rests with the City. Other elements such as lot grading and foundation drains are located on private property. The City may have had a role in approving or inspecting the original subdivision design to the standards of the day, (which encompasses individual lot grading) but over time, site alterations may have taken place without city approval or knowledge. Additionally, some elements of the system, like the City s creeks are located both on private and public lands. In some cases the City has easement rights where the creek is on private

12 Page 12 property. These different property ownership situations present fundamental and complex legal/ liability issues that need to be considered in any proposed policies or programs. A) BUILDING CONNECTIONS AND FOUNDATION DRAINS Overall, this section deals in large part with the interconnection issues between the sanitary and storm drainage at the individual property level, which is also dealt with extensively in the Region of Haltom Report PPW-85-07, attached as Appendix C to report Comserv As illustrated in Figure 1, foundation drains or weeping tiles are a drainage collection system located around the perimeter of a building at the bottom of the foundation wall. This drainage is located just below the elevation of the basement and therefore requires an outlet that is either below the basement floor elevation or the drainage collected by this system needs to be directed to a sump pit and pumped to the surface. Up to 1968, City policy permitted the connection of these foundation drains to the sanitary sewer pipe (referred to as lateral ), servicing the house. This was viewed as an effective outlet due to its depth and the fact that under normal conditions, foundation drains were anticipated to contribute relatively modest flows to the sanitary sewer system. However, in some cases, foundation walls may extend into areas with a high water table, poor grading practices around the perimeter of the house and non-compliant connections such as roof leaders discharging below grade into the foundation drain could result in dramatic increases of ground water and storm drainage flows to the sanitary laterals and downstream sanitary sewer system, including pumping stations and treatment plants.

13 Page 13 Since 1968 the City has not permitted the connection of foundation drains into the sanitary sewer laterals, as this drainage is to be directed into either the storm sewer lateral or sump pump system. While this approach was effective in limiting flows to the sanitary sewer system, it did create other design and operational issues. In order to function properly the foundation drains need an outlet that is below the foundation of the house. Up to 1968, storm sewer systems may have been constructed at much higher elevations, typically four to six feet below the road grade in order to provide for adequate frost cover and clearance from other utilities. It was generally not required to extend storm sewers across all residential lot frontages since these were only picking up road catch basins. While now having to construct more and deeper storm sewers added to the cost of servicing subdivisions, the real concern became getting a suitable outlet for the storm sewers themselves. Storm sewers typically outlet into the City s creeks at road crossings. During low flow conditions, the water level in creeks is generally low and providing a sewer outlet close to the creek bed works quite well. During high stage flood events however, the creek water level can be several metres higher and may result in water actually flowing backward through these pipes into the foundation drains. Although properly constructed basement

14 Page 14 floor and wall system are waterproof, and there are no direct openings or connections inside the house, a typical basement floor cannot withstand hydrostatic pressure created by more than six to twelve inches of water. What this means is that if the water level (hydraulic grade line) at the storm sewer outlet is higher than this, the floor or foundation wall can crack and water can seep in. This was identified as a potential issue for homes in the Longmoor Drive area adjacent to Shoreacres Creek as part of the Tuck Shoreacres Creek Appleby Creek in the 1990 s in conjunction with infill development along Fairview Street. This was one of the first residential areas to develop after the policy change in 1968 prohibiting foundation drains from being connected to the sanitary sewer. A subsequent more detailed study was undertaken in the early 1990 s, The Longmoor Drive/Shoreacres Creek Flood Damage Reduction Study, and a number of possible remedial works were identified, and a number have already been implemented. Another alternative for dealing with foundation drainage is to discharge the foundation drain into a sump pit in the basement and pump this water to the surface. The advantage of this system is that it eliminates any connection or possibility of backup from the storm sewer system and eliminates the foundation flows from the sanitary sewer system. However the system is dependent on the proper maintenance and functioning of the sump pump and the system will not work during a power failure. This approach is common practise in many areas, however it is generally not the preferred approach in areas where the foundation may extend into or below the water table. In this case the pump would be running almost continuously and therefore more likely to fail. Add to this the associated nuisance problems if the pump discharge is to the surface around the house. Proposed Strategies and Actions: City staff continue to work closely with the Region in their pilot foundation drain disconnection program and report back to Council on moving forward as a partner following completion of the pilot project; City Council wave any City building or other permit fess associated with the pilot project City staff to provide direct and timely customer service, including technical assistance to residents, as required in any retrofits associated with accommodating sump pump discharges, roof leader disconnection and lot grading improvements; City staff, in conjunction with the Region, investigate and monitor groundwater elevations in the areas of the pilot program; and,

15 Page 15 City to undertake and/or fund, any assessments of the storm drainage system in the pilot project area including video assessments, topographic surveys and roof leader/catchbasin testing. B) ISSUE 2 LOT GRADING Overall residential lot grading is established at the subdivision design stage although many older areas of the City would have development without any formal subdivision grading plans. Typically lot grading is either one-way, meaning the entire lot is sloped to the front street line or two-way (split) drainage, meaning that the front half is directed to the street and the rear half to the rear property line where it is typically collected in a rear yard swale and storm drainage catchbasin system. A single catchbasin would typically service several lots connected by a rear yard swale. Figure 2 illustrates these typical lot grading designs. Figure 2:

16 Page 16 From a drainage stand point, it is fundamentally important that residential lots be graded such that they slope away from the house in order to protect against surface water entering the house via window wells, patio doors etc., and also that drainage into the foundation system be minimized. This includes ensuring roof leaders from eavestroughs either have appropriate extension pipes or discharge to splash pads directed away from the house. Existing Process/Programs Lot grading is established and approved by the City during the subdivision design and building construction stages and is inspected prior to the subdivision being assumed by the City. Over time, activities on the property, including construction of patios, pools, gardens, trees etc., can impact drainage and the intended function of the lot grading if not properly designed and constructed. Annually, the Engineering Department staff typically receive over 500 enquiries per year regarding lot drainage issues. Many of these can be dealt with over the phone by providing general guidance and information to residents. However approximately 50% of these calls involve site visits and or a review of the original grading plans for the property. The City adopted a site alteration permit process in 2003, requiring a property owner to obtain a permit when undertaking works which may impact lot grading and drainage of adjacent properties. However, the majority of these works are

17 Page 17 relatively minor and undertaken by homeowners without notification and approvals from the City Proposed Strategies and Actions: City staff prepare a public education program for homeowners informing them of the importance of maintaining proper lot grading and the benefits of eavestrough/downspout disconnection City staff develop design guidelines and How to Manual, instructing homeowners how to implement proper grading improvements and eavestrough /downspout disconnections, including possible partnerships with local home improvement suppliers City staff review and report back to Committee on the appropriate level of City involvement on assessing and advising homeowners on grading improvements on private property including possible modifications to the existing site alteration permit requirements C) LOCAL SURFACE WATER FLOODING LACK OF ADEQUATE DRAINAGE OUTLET As indicated earlier, residential flooding may be very local or isolated. For example, one or more properties in an area may experience ponding as a result of stormwater not being able to flow off the property to the City s stormwater drainage system. For small rainfall events the ponded surface water typically infiltrates into the ground or evaporates over a range of a few hours (more typical in areas with sandy soils) to several hours or weeks (more typical in areas with clay soils). For large and intense stormwater runoff events, the ponded water often has the potential to accumulate to a depth whereby an adjacent structure, such as a home, may be flooded. Local flooding may occur in areas with or without an adequate storm drainage outlet. Local flooding may occur in areas where an adequate storm drainage system exists, but as a result of one or more private property obstructions placed within the drainage route of the stormwater, stormwater is trapped on the property. On residential properties with one-way drainage, stormwater can be trapped in the back yard because of the addition of gardens, sheds, pools, trees, landscaped structures, etc. Depending on the location and grading of the privately constructed works, the real, unintended possibility exists for residents to flood themselves during significant rainfall events. In these cases, the City has provided information on how the drainage system was intended to function, and how the resident could potentially improve the drainage. However, it is considered the responsibility of the resident(s) to address the situation on their property(ies).

18 Page 18 On residential properties with split or two-way drainage, local flooding may occur as a result of two reasons, as outlined below: The City s stormwater catchbasin and/or storm drainage lead from a rear yard to the City s stormwater system may cease to function. In this case the City is responsible for repairing the system. Local flooding may occur as a result of one or more obstructions (i.e. gardens, sheds, pools, landscaping, etc.) placed within the rear yard swales that direct stormwater to the City s rear yard catchbasin. Historically, this has been treated as civil a matter between property owners, though the City provides advice and direction on how the system was designed to operate. Recently, with By-law (Site Alteration), the City has a mechanism to provide assistance to property owners who are negatively impacted by other property owners. Situations of localized surface flooding without adequate outlets exist in numerous areas in Aldershot and rural Burlington. The 2007 Capital Budget provides for a drainage study in the Greenwood Drive, Sunset Road and Cedar Avenue area where overland drainage is being impeded and local flooding is reoccurring. The 2007 Capital Budget also provides for a drainage assessment on Spring Gardens Road West of Botanical Drive where roadside flooding has been prevalent. No funds have been provided in the Capital Forecast to implement works should the study results warrant action. The funding requirements could approach in excess of $1.0 million in order to address these problems due to the lack of an adequate drainage outlet. There are also other areas in rural Burlington where lack of adequate outlets, due to flat grades, past development in flood plains and environmental constraints associated with many of the small tributaries to Bronte Creek make seemingly straightforward drainage issues very difficult to resolve. Infill development also faces challenges, as infill development is often proposed in older areas that lack an adequate drainage outlet. In these situations the City works closely with the proponent to find a workable drainage solution. Proposed Strategies and Actions: Staff investigate and report back in fall 2007, on possible mechanisms for providing additional assistance (i.e. direct programs, customer service practices, etc.) to individual property owners or neighbourhoods on drainage issues.

19 Page 19 Engineering and Roads & Parks Maintenance staff continue to give priority and respond to residential drainage enquiries as per current standards and practices. D) SURFACE FLOODING DUE TO BACK-UP FROM INLETS/ENCLOSURES Evolving design standards and the approach to storm drainage has been discussed in previous sections. This issue is again very important in understanding the capacity and function of the City s stormwater related structures and watercourses. In the early 1960 s, planning by both then the Town of Burlington and the Halton Region Conservation Authority (now Conservation Halton) to accommodate anticipated future community growth through 1980 was premised on designing flood protection in open water courses to a flood frequency that would occur on average once every 50 years (1:50), and that all watercourses north of the CN Oakville Subdivision located north of Fairview Street be enclosed in storm sewers. (Ref July 1964 report on Flood Control Works in the Town of Burlington for the Halton Region Conservation Authority). The current standard is to maintain watercourses in a natural condition and ensure no development within the greater of the 1:100 year or the Hurricane Hazel Design Storm equivalent. Fortunately, the full enclosure of these watercourses, as proposed in the 1960 s did not occur, however a legacy or partial enclosures does exist on Falcon Creek, Indian Creek, Roseland Creek and remnant sections of Hager and Rambo Creek through the downtown core. In addition, there are numerous enclosures of more minor tributaries throughout the City, many of which have been problematic for flooding, like the enclosures in the Kirkburn, Forestvale, Mountainside and Tyandaga areas. Watercourse enclosures cause several major problems, some more obvious than others: Enclosures are under-designed relative to today s standards in terms of flow conveyance. Enclosures rely on inlets and invariably require safety grates at the inlets to prevent entry into the systems. These inlets are prone to blockage and represent a major on-going maintenance problem during storm events. Enclosures are a major contributor to downstream erosion problems Enclosures result in a major destruction of the aquatic ecosystem both in the creeks and the lake by eliminating critical habitat required for fish spawning and food sources for other aquatic organisms. In most cases there is no provision for a planned major or overland flow route should the enclosure inlets be blocked or the capacity of the enclosure exceeded.

20 Page 20 Some alternatives are available to the enclosures and include upgrading the design of existing inlets or revert existing enclosed systems back to open water courses. Associated with the storms in May 2000, inlet capacity limitation and blockage was identified as a major contributing factor to flooding. Since then an active program of re-designing the inlets to enclosures has been implemented by the City with 10 inlets upgraded to date or scheduled to be upgraded. Proposed Strategies and Actions: Continue program of upgrading and enhancing the design of existing inlets Increase capital funding for storm conveyance and inlet works to accelerate this program E) WATERCOURSES The majority of storm sewers within Burlington discharge to the numerous creeks within the urban area of the City, with the balance of the storm sewers discharging directly to either Lake Ontario or Burlington Bay. Accordingly, the creeks are part of the stormwater conveyance system within the City, although not all creeks are located on City property. As discussed under watercourse enclosures, design standards for the City s watercourses have evolved from no formal standards for the old Hager and Rambo Creeks in the downtown to a 50 year design standard through the 1960 s and 1970 s, to the greater of 1:100 year Hurricane Hazel flood incidence by the late 1980 s. In general, each creek includes a low flow channel, a bank full channel and a floodplain. The low flow channel carries a base flows, or in plain language, the flow one sees during periods of dry weather. The bank full channel typically has the capacity to convey the 2-5 year storm event, similar to storm sewer systems throughout the City of Burlington. When flows exceed the capacity of the creek banks, over bank flows occur in the floodplain. It is important to realize that creeks overflow their banks regularly and that flow within the floodplain can therefore be anticipated to be a regular occurrence. In addition, flows can be directed to the floodplain as a result of flows exceeding the capacity of culverts under roadways and driveways, and/or due to the blockage of culverts with debris. Floodplains provide an important natural flood control function. In addition to providing additional flood conveyance capacity they provide storage of flood waters and slow flow velocities which, in turn, reduces the flood impact on downstream reaches.

21 Page 21 Current land use planning policies are designed to ensure that no new building structures are constructed within floodplains. In Burlington, Conservation Halton (CH) currently regulates floodplains and other hazard lands under Ontario Regulation 162/06. Prior to May 2006, CH regulated floodplains under Ontario Regulation 150/90. For both of these regulations, the extent of the floodplain on a creek system is taken as the floodplain as determined by either the 100-year event or Hurricane Hazel, whichever is greater. Before approximately 1984, the flood plain was generally measured as a 50-year event and was used to define development limits within Burlington. In older areas of Burlington, structures may currently be located in areas that are subject to flooding more frequent than the 50-year event. This occurrence is common throughout Southern Ontario, with origins dating back to the original settlers, who located close to watercourses for historical reasons, such as travel and close proximity to water availability. As a result of Hurricane Hazel in1954, which caused widespread devastating flooding throughout Southern Ontario, land use planning practices started to regulate development farther from creek systems and their floodplains. As a result of historic settlement patterns in the downtown along the Rambo and Hager Creeks, the City has through the 1980 s and 1990 undertaken extensive capital works to reduce the flood risk to the downtown area. The construction of the Rambo Hager Diversion Channel and subsequent diversion and flood control ponds constructed in conjunction with Highway 407 (formerly 403) have resulted in approximately 80% of the flow in these creeks being diverted into Hamilton Harbour. Floodplain limits along the creek systems within Burlington are currently determined by CH and the City, with CH having responsibility for the larger creek systems (Grindstone Creek and Bronte Creek) and the City having responsibility for the smaller creek systems (Indian, Falcon, Hagar, Rambo, Roseland, Tuck, Shoreacres, and Sheldon). Conservation Halton regulations are applicable on all the creeks. Floodplain limits are currently identified in Appendix H in the City s Official Plan. In response to often asked questions, it should be noted that new development in Burlington does not increase watercourse flooding in older, established areas, since stormwater management facilities have been incorporated into new developments since the 1980 s. The stormwater management facilities receive stormwater from a developments storm sewer system and release the stormwater flows at a rate so as not to increase peak flows downstream. The stormwater management asset category of the City s capital budget includes specific projects to reduce flood risk. Recently constructed works include; Area 8 Flow Diversion implemented in conjunction with the Ministry of Transportation's Guelph Line interchange project to reduce flooding along Roseland Creek:

22 Page 22 Sheldon Creek Culvert upgrade implemented in conjunction with the newly constructed Appleby CNR underpass north of Upper Middle Road to reduce flooding along Sheldon Creek and into the newly constructed railway underpass on Appleby Line north of Upper Middle Road; Oversizing of the Alton community s W1/W2 stormwater management pond to reduce flood risk on Sheldon Creek. Future planned projects include: Oversizing of the Leon s stormwater management pond (Roseland Creek); Falcon Creek stormwater management Tuck Creek culvert improvements at New Street. Historically, stormwater management capital works have been funded from the general tax base and by development charges, where appropriate. Currently, municipalities in Canada and the United States are seriously investigating or implementing a new stormwater user rate approach to fund erosion control and other stormwater management capital works. A stormwater user rate is generally seen as the most appropriate means to fund stormwater capital works through a dedicated rate-based levy and is usually based on site area and/or impervious area rather than assessed value. Using site area and/or impervious area is appropriate given that the larger the site and the more impervious the site, the greater the volume of stormwater from a site. Proposed Strategies and Actions: Continue with capital works program to reduce flood risk and increase non-growth funding to accelerate program Develop a long term capital rehabilitation and renewal program for the structural components (including; storm sewers, creek enclosures, Rambo/Hager Diversion Channel and engineered creek channels) of city s storm drainage conveyance system Investigate opportunities for a stormwater rate for long term funding of flood control works. F) WATERCOURSE EROSION Watercourse erosion is a natural process whereby the creek banks are eroded by on-going stream flows. Historically, watercourse erosion has been accelerated by urban development since drainage practices up to approximately 1980, discharged stormwater as fast as possible to creek systems. Further, stormwater management practices from approximately 1980 to 1993 were primarily focussed on flood control only. Accelerated creek erosion, as a result