Flood Plain Study
In May 2016, R.M. Administration recommended that Council undertake a two-dimensional (2D) hydraulic modelling and mapping study of the South Saskatchewan River flood plain to determine what areas of the flood plain are floodway (no or limited development allowed) and flood fringe (development may be allowed subject to conditions); a map of the study area can be found HERE. At the August 21, 2017 Council meeting a motion was passed that the R.M. will pay 100% of the costs of the study under the condition that 50% will be reimbursed through grant funds.
The R.M. has successfully applied for funding under the National Disaster Mitigation Program – Stream 2: Flood Mapping, administered by Public Safety Canada. The federal government will pay for 50% of the project costs and the R.M. will be responsible for the other 50%. In December 2018, the R.M. and provincial government through the Flood Damage Reduction Program entered into an agreement for the province to pay the R.M.'s other 50% of the project costs.
On April 16, 2018 Barr Engineering was selected by R.M. Council as the consultant for the study. The R.M. formed a Technical Committee comprising of R.M. Administration, Water Security Agency and Community Planning representatives to provide guidance to the consultant and review technical data and models during the study.
Phase 1: Data Confirmation & Field Survey (April – July 2018)
This phase included review of available background information including policy documents, data and related studies prior to development of the 2D model. Following a review of the data to identify any gaps, a field survey was completed to complete the data acquisition. This includes a hydrographic survey of the river as well as ground survey of culverts and other infrastructure.
Phase 2: Hydraulic Modelling & Assessment (July 2018 – January 2019)
During this phase of the project the terrain dataset was developed, the model parameters were defined, and model calibration, validation and sensitivity analysis occurred to ensure an accurate study which is crucial to ensuring a successful outcome. Following these steps the model was ran to stimulate the regulatory flood event (1:500) in addition to three smaller events (1:50, 1:100, and 1:200). The effect of full residential development (i.e. 5 per ¼) was also considered as part of a modelling exercise for the 1:500 to determine if increased densities would have an effect on the floodplain.
Phase 3: Mapping Support & Flood Mapping Report (October 2018 – February 2019)
These final phases of the study involve completing GIS maps illustrating the flood plain, floodway and flood fringe. A written report was also completed by the consultant to document data collection, the modelling assessment, flood mapping methodology and development of the flood plain maps.
A presentation by the consultants was made to R.M. Council on February 25, 2019. A copy of the final study can be found HERE. The modelling determined that some areas are considered flood fringe where development can occur subject to development conditions, however the majority of the floodplain has been identified as floodway where development cannot occur. Next steps include amending current R.M. policies to allow for development in flood fringe areas, public consultation with affected ratepayers and additional discussions with provincial agencies on emergency management and the implementation of provincial flood regulations.
For more information on the floodplain study please contact the R.M. project manager, Vicky Reaney at email@example.com or 306-975-1663.