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HomeMy WebLinkAboutPDS-066-23Clarftwn Staff Report If this information is required in an alternate accessible format, please contact the Accessibility Coordinator at 905-623-3379 ext. 2131. Report To: Planning and Development Committee Date of Meeting: November 13, 2023 Report Number: PDS-066-23 Submitted By: Reviewed By: Carlos Salazar, Director of Planning and Infrastructure Services Mary -Anne Dempster, CAO By-law Number: File Number: P L N 17.3.4 Resolution#: PD-083-23 Report Subject: Graham and Wilmot Creek Floodplain Mapping Update Study Recommendation: 1. That Report PDS-066-23, and any related delegations or communication items, be received for information. Municipality of Clarington Report PDS-066-23 Report Overview Page 2 The purpose of this report is to inform Council of the completion of an update to the floodplain mapping for the Wilmot and Graham Creeks. Updating of the floodplain mapping was undertaken to reflect data improvements and technological advancements since the previous study was completed 46 years ago. It was completed in partnership with Ganaraska Region Conservation Authority and the Region of Durham, with funding support provided through the National Disaster Mitigation Program (NDMP). The updated floodplain mapping will inform municipal infrastructure planning, land use planning, and emergency preparedness planning. 1. Background 1.1 Floodplain mapping provides critical information to prevent and mitigate flooding. Floodplain mapping in Clarington is managed by the local conservation authorities. Mapping should be updated regularly to account for changes in land use, infrastructure, and improved mapping or modelling technology. 1.2 The previous floodplain mapping study for Graham and Wilmot Creek was completed in 1977 and is the oldest floodplain data set in Clarington. Since this date, there have been advancements in mapping methodologies and technology, data improvements, and urbanization within the watersheds. See Figure 1 for a map of the Wilmot Creek and Graham Creek watersheds and the existing (1977) floodplain mapping. 1.3 In 2021, the Municipality partnered with Ganaraska Region Conservation Authority (GRCA) and the Region of Durham to seek funding support through the National Disaster Mitigation Program (NDMP) for the Graham and Wilmot Creek Floodplain Mapping Update Study (Study). Report PDS-022-21, endorsed by Council (Resolution #PD-145-21) authorized a Municipal contribution towards proceeding with the Study. In June 2021, the Municipality was informed of its successful funding application, with the NDMP providing 50% of the funds required up to a maximum of $70,500. 2. Floodplain Mapping 2.1 Floodplain mapping studies use technical information to determine the extent of the floodplain or area of land adjacent to a watercourse that may be at risk of flooding during severe storms. This includes topographical information, field surveys, weather, and stream flow data. Detailed hydraulic and hydrologic models are then created that refine the limits of the floodplain and identify flood hazards. Municipality of Clarington Page 3 Report PDS-066-23 Figure 1: Wilmot Creek and Graham Creek Watersheds and Existing (1977) Floodplain Municipality of Clarington Report PDS-066-23 Page 4 2.2 Figure 2 identifies the floodplain data sets in Clarington, by year, prior to this most recent update. The Central Lake Ontario Conservation Authority (CLOCA) and GRCA have historically updated their data sets as funding and priority permitted. Updated floodplain mapping studies incorporate data improvements and technological advancements such as LIDAR, a remote sensing three-dimensional survey method, and changes in infrastructure, land use, population growth, and stream flows. 2.3 Knowing the extent of a floodplain is an important tool for land use planning, emergency management, and public safety. It informs the Official Plan, zoning by-laws, and the review of development applications, helping to direct future development outside of flood -prone areas, to avoid injury, loss of life and property damage. It is also used to identify where flooding may impact access to roads and emergency routes and can help property owners to understand their individual risk of flooding. In addition, floodplain mapping can be used to support assessments of the vulnerability of roads and culverts to riverine flooding across Clarington and the upgrading of appropriate infrastructure. Examples include locating trails away from flood prone areas and designing culverts and bridges that can handle peak flow rates. 3. Study Overview 3.1 The Study was initiated in spring 2022. The Study area included the Wilmot Creek and Graham Creek (Figure 1). While Foster Creek is a tributary of Wilmot Creek, it was not mapped as part of this project since the main branch was last updated in 2017 and the two tributaries were updated in 2019. The Study was carried out by the GRCA, with communications support and grant administration being provided by the Municipality. 3.2 The Study followed five phases including Background Data Review, Field Survey of Bridge and Culvert Structures (more than 400), GIS Data and Model Development, Report and Map Production, and Public Awareness and Education. 3.3 To update the mapping, GRCA used the province's 2016 LIDAR data, topographic maps, new ground surveys, updated land use conditions, and the latest provincial and federal floodplain mapping guidelines. To accurately identify the flood hazard, ground- truthing was carried out where access to private property was granted. This information was incorporated into new hydrologic and hydraulic models that ultimately yielded the updated floodplain mapping. Municipality of Clarington Page 5 Report PDS-066-23 Figure 2: Floodplain Mapping in Clarington by Year Municipality of Clarington Page 6 Report PDS-066-23 3.4 Notice of the study was sent to landowners within 100 metres of the 1977 floodplain limits, both at Study commencement and prior to a Public Information Centre (PIC) that took place on March 20, 2023. A webpage hosted by GRCA was also set up that explained the purpose and approach for updating the floodplain mapping and answered some frequently asked questions. Articles noting the study commencement ran in the Orono Times and in Durham Radio News. 3.5 The PIC was held to share the preliminary updated floodplain mapping and receive comments from the public. It involved a presentation, poster boards, and an interactive map that attendees could use to explore the changes to the floodplain. Staff members from the Municipality and GRCA were available to answer any questions. There were approximately 40 attendees. Figure 3: Photo from Public Information Centre held March 20, 2023 3.6 The study yielded updated mapping that refines the limits of the floodplain for land use planning purposes. Overall, the resulting mapping was similar to the 1977 model, but with some refinements. This included some land being removed and some being added into the floodplain. As stated in the Wilmot & Graham Creek Floodplain Update Study (GRCA, March 2023), "the increases are attributable to increased watershed area due to more precise watershed delineation based on LiDAR, increased development in the watershed, altered peak flow timings of the tributaries, and adherence to modern floodplain mapping guidelines." 3.7 On October 19, 2023, the Study and updated floodplain mapping was presented to and endorsed by the GRCA Board. The final Study report and updated mapping will be available to the public on GRCA's website (Graham and Wilmot Creek Updated Floodplain Mapping). The final Study report and mapping will subsequently be submitted to the NDMP, marking project completion. Municipality of Clarington Report PDS-066-23 Next Steps Page 7 3.8 The final updated mapping will be used by several Municipal departments for purposes including the following: • The review and assessment of development inquiries and applications; • Future updates to Municipal Zoning By-laws and the Clarington Official Plan; • Infrastructure planning and design; • Asset management planning; • Emergency management planning; and • Climate change risk assessment and mitigation planning. 3.9 GRCA is working to update the remaining floodplain datasets in its regulated area of Clarington. Recently, the Region of Durham and GRCA successfully applied for funding from the federal Flood Hazard Identification and Mapping Program (FHIMP) to update floodplain mapping for Lovekin, Bouchette Point, and Port Granby Creeks as well as the northwest portion of the Ganaraska River watershed. Work was initiated in April 2023 and is planned to conclude in March 2024. The Municipality's involvement in these additional updates is limited to in kind support, such as providing GIS information. 4. Financial Considerations 4.1 The total actual costs to undertake the Study was $151,950, an increase of $10,950 from the original project estimate. Additional costs were incurred as a result of additional time needed to complete the field work due to property access approval delays and wireless connectivity issues in more remote areas of the watersheds which impacted the function of surveying equipment. The additional costs were incorporated into the Planning & Infrastructure Services Department's 2023 budget. The Study is eligible for 50% funding up to $70,500 through the NDMP. NDMP's review of project costs for reimbursement is on -going. 5. Concurrence 5.1 This report has been reviewed by the Deputy CAO/Treasurer who concurs with the information. Municipality of Clarington Report PDS-066-23 6. Conclusion Page 8 6.1 The updated floodplain mapping for Graham and Wilmot Creeks provides the latest data to assist with land use and emergency preparedness planning, including flood prevention and mitigation. Updating the floodplain mapping enables residents, businesses, and farm operations to better understand their flood risk and to prepare for a flood event. The Study represents a successful collaboration between the Municipality, GRCA, the Region of Durham, and a federal grant funding opportunity. Staff Contact: Amy Burke, Project Manager, Corporate Performance, 905-623-3379 ext. 2423 or aburke(a_clarington.net. or Lisa Backus, Manager of Community Planning, 905-623-3379 ext. 2413 or Ibackus(aclarington.net Interested Parties: List of Interested Parties available from Department.