Haliburton Floodplain Mapping Project

Haliburton Floodplain Mapping Project

The main purpose of the Haliburton Flood Mapping Project is to prevent loss of lives, property and land caused by flooding. As noted in the Province’s Flooding Strategy (2020), flooding is considered the most significant natural hazard in Ontario in terms of death, damage and civil disruption and is the costliest type of natural disaster in Canada in terms of property damage. Priority #1 of the Province’s Strategy is ‘Understanding Flood Risks’ which is a vital first step to ensure Ontarians, including municipal and provincial agencies, are aware of their local flood risks, how these can be mitigated, and how risk management decisions are made.

https://www.ontario.ca/page/protecting-people-property-ontarios-flooding-strategy

The deliverables of this project include the preparation of flood hazard mapping for the County of Haliburton. This will involve the development of high-water level mapping for the reservoir lakes and creating new floodplain mapping for the connecting rivers that are frequently impacted by flooding. As a tool, accurate mapping ensures that applicable authorities are directing development away from areas that pose unacceptable risks to public safety and are regulating legacy development within the floodplain and flood fringe areas. Enhanced knowledge of the location of the flood susceptible areas will also allow the County and local municipalities to effectively manage flood susceptible assets and plan the most efficient emergency response efforts, reducing the impact of flooding on the population and making our communities more resilient.

The initial phase (Phase One) of the flood mapping project involved the collection of Light Detection and Ranging (LiDAR) data in 2019 for the project study area that focused on selected river and lake environs within the Gull and Burnt River systems. In 2021, Phase Two of the project commenced and involved the collection bathymetric (underwater) survey data for key portions of these two rivers to obtain channel elevations. These activities were supplemented by field survey efforts to document the various dams and numerous (100+) bridge and culvert structures within the study area.

How does LiDAR work?: https://www.youtube.com/watch?v=EYbhNSUnIdU

LiDAR point cloud data in Minden

What is Bathymetry?: https://www.youtube.com/watch?v=dTkJjTAbBOI

Rendering of Bathymetric Data collected in the Gull River

The LiDAR and Bathymetric data has been combined to create a digital elevation model (DEM) surface to be incorporated into the hydraulic models to support determination of the regulatory flood line and high lake levels for vulnerable portions of the two river systems.

Sample of LiDAR-based Digital Elevation Mode (DEM) in Minden

Sample of combined LiDAR and Bathymetry DEM with Test Floodplain from Hydraulic Model

For the final phases (Phases 3 and 4) of the project, Ganaraska Conservation and Kawartha Conservation have continued to act as the project's subcontractors on behalf of the County this year. They are principally responsible for creating the hydrology models (to estimate flood flows) and hydraulic models (flood elevations) which will form the basis of the flood hazard mapping for the Burnt and Gull Rivers. For 2023 and 2024, the project's deliverables include the following:

1. Completion of the remaining field survey work for the dam and culvert/bridge data for use in the models
2. Development of critical data products for use in hydrologic and hydraulic models and mapping i.e., land use layer, imperious surfaces layer, DEM surfaces that integrate LiDAR and bathymetry data, base map and orthophoto preparation for mapping etc.
3. Development and calibration of the hydrologic models to determine flood flows for both the Gull and Burnt Rivers for use in floodplain mapping
4. Development of the hydraulic models to provide flood elevations/flood lines used as basis for floodplain maps
5. Development of flood hazard line mapping for key lakes within the study area
6. Completion of floodplain maps
7. Public consultation for flood hazard mapping, including outreach to engage and educate the public on mapping products at the end of January 2024
8. Submission of the Flood Hazard Identification Mapping Project (FHIMP) deliverables to the Province at the beginning of March 2024

Ultimately when completed, the County's Floodplain Mapping Project will allow for the development of floodplain mapping for the river systems and high water level mapping for key reservoir lakes which can be included as schedules in the County and area municipal Official Plans and Zoning By-laws. Also, these flood hazard maps will provide landowners and residents with information on the potential for flooding, the extent of flooding, and will support their personal preparedness for flooding emergencies. The data and mapping, in coordination with public education, may divert potential property buyers and developers from the impacted areas, reducing potential property damages/losses and personal injuries/stress.

The development of digital floodplain models and mapping can provide the following benefits, among others:

• a reduction in effort, cost and time for development application review in flood-prone areas.
• a reduction in studies required by a proponent to undertake in advance of development.
• increased accuracy of flood hazard estimates.
• the production of floodlines for different flood events which can be used to identify flood-prone properties and municipal infrastructure, which will assist emergency services with notification, inspection and/or evacuation during a flood.
• models which can be used for other studies such as water management, climate change analyses, etc.
• data that can be used to support municipal road and sewer improvement projects, asset management planning, etc.

Information regarding the upcoming Public Information Centre (PIC) Presentation:

The Mapping Viewer can be found on the Project Page:

https://grca.on.ca/watershed-management/projects/haliburton-floodplain-mapping/