Regulatory Floodplain Mapping Update for Lower Byersville Creek

The Otonabee Region Conservation Authority (ORCA) has undertaken a project to update the regulatory flood plain mapping for Lower Byersville Creek, located in the City of Peterborough. The reason for this update is to incorporate up to date hydrologic modeling into a new hydraulic model created using the latest topographic information. The results of this modeling have been used to generate new regulatory flood plain map sheets that will guide planning and regulation activities in the Lower Byersville Creek Study Area.

Details of the study are separated into four primary sections within this technical report.

1) The Hydrology section examines the modeling methods, setup and results of the study. Hydrologic modeling was primarily adopted from a series of studies completed by XCG Consulting between 2009 and 2013.

2) The Hydraulics section is a more in depth analysis of the methods and parameters used to create a new steady state hydraulic model, including an analysis of the results and   comparison to past studies.

3) A new digital elevation model (DEM) was created using topographic data obtained via Light Detection and Ranging (LIDAR) technology. The DEM is the primary source of elevation data used in creating new hydraulic cross sections and is the base layer for generating inundation mapping and ultimately regulatory flood lines.

4) Lastly, new regulatory flood plain mapping was produced with this study and is discussed in detail. The mapping has been reviewed with a focus on comparing flood lines to past studies and identifying properties that are at risk during a regulatory event.

The study has expanded on previous work completed by XCG in regards to a proposed flood reduction storage area and landform. The updated modeling further confirms the significant benefits of implementing a flood storage area and landform within the remnant wetland area south east of the Parkway and Lansdowne Street intersection. Preliminary results show these flood reduction measures will reduce spill flow to the Examiner Ditch system from 14.5m3/s to 3.7m3/s. A peak flow of 3.7m3/s within the Examiner Ditch system can be managed through the implementation of a spill policy. During detailed design, the available storage volume will be confirmed as well as the resulting peak flow to the Examiner Ditch. Should the resulting peak flow be appreciably higher due to less storage volume, the route of the spill should be reexamined, and may need to be mapped in accordance with regulatory flood plain mapping policies. Any changes to the LBC main stem peak flows will be minor, and revised mapping will not be required.

The results of the hydraulic analysis show a variance in water surface elevations (WSE) throughout the reach when compared to past studies. In some cases, primarily in the upper regions of Lower Byersville Creek, WSE’s in the current study have dropped, while in the lower regions they have increased. Specific reasoning for these changes is discussed in detail within the report. Two additional minor spills have been identified at the Parkway crossing west of the Costco development. In addition, the effect of sedimentation causes a significant blockage at the Parkway culverts; the reduced capacity increases the upstream WSE significantly. The City of Peterborough has agreed to clear and maintain the culverts, and therefore the regulatory flood plain mapping was produced assuming full capacity at this crossing.

The mapping that has been produced is of a high level of accuracy and detail and is recommended for implementation by ORCA. Prior to acceptance of the report and mapping by ORCA’s Board, the Authority will have presented the results to the City of Peterborough and affected stakeholders for discussion and comment.

A Public Information Session will be held on Tuesday, February 10, 2015 from 4:00 p.m. to 8:00 p.m. at St. Giles Church, 785 Park St. South, Peterborough, Ontario. For further information, please refer to this Public Notice of Information Session.

Review a copy of the Lower Byersville Creek Floodplain Mapping Update (Sept 2014 Final Draft)

View the Draft Flood Plain Maps: (click on the map to view a larger version)

Draft Floodplain Map 1       Draft Floodplain Map 2

Draft Floodplain Map 3       Draft Floodplain Map 4

View the Draft Flood Depth  Maps: (click on the map to view a larger version)

Draft Flood Depths Map 1         Draft Flood Depths Map 2

Draft Flood Depths Map 3         Draft Flood Depths Map 4

For additional information about this project, please contact:
Ian Boland, C.E.T., Engineering Technologist at 705-745-5791, ext. 231 or iboland@otonabee.com

Meredith Carter, Manager of environmental and Technical Services at 705-745-5791, ext. 223 or mcarter@otonabee.com