Stormwater + Drainage

Objectives

  • Reduce the risks from surface ponding, flooding, and erosion to people and property in the P4G Region
  • Minimize the environmental impacts of stormwater quantity and quality on groundwater, surface water, wetlands, and habitat, and encourage the use of stormwater as a resource to improve environmental performance
  • Support municipalities in improving stormwater management to minimize local flooding issues and enhance system performance
  • Promote innovative solutions to stormwater management that integrate cost-effective natural and engineering solutions

 

Context

 

A summary map for the regional stormwater strategy is provided in Exhibit 3. Key elements of this map include the following:

  • Existing wetlands and surface water. Surface water features are provided on the overview map. A cursory assessment of wetland locations, based on visual identification from orthophotos and elevation data, is also included. Impacts to these features shall be considered in the planning and development of regional and local stormwater and drainage solutions.
  • Wetland DEM Ponding Model (WDPM) results. The map indicates ponding locations following a 200-mm precipitation event in the P4G Region, modeled using a Wetland DEM Ponding Model (WDPM) “fill-and-spill” model. This is provided for reference only, and details are provided in the supporting documentation for the Green Network Study Area.
  • Green Network Study Area. The Green Network Study Area is indicated as an important component of regional stormwater management, as it incorporates the conservation of swales, wetlands, drainage paths, and surface water to be used for regional storage and conveyance. These features should be maintained after the refinement of this area.
  • Proposed regional drainage improvements. The map includes the alignments for improvements proposed by the Opimihaw Creek Watershed Association (OCWA) to facilitate drainage in the Opimihaw Creek Watershed around Warman, Martensville and Osler within Corman Park.
  • Municipal drainage infrastructure. Available information on municipal stormwater drainage infrastructure is provided where relevant.

 

Drainage systems to manage stormwater are typically managed at the local level in the P4G Region. However, the municipalities of the P4G have been collaborating through the OCWA to manage significant drainage issues north of Saskatoon. The OCWA has developed plans that present an engineering solution to these drainage issues through three reports, with the first and second detailing the general design and cost for regional drainage, and the third providing more detailed engineering designs for the Osler drain.

OCWA Initiatives

As noted, the OCWA has conducted a series of studies to examine options for reducing flood damage in the northern area of the RM of Corman Park, the Cities of Martensville and Warman, and the Town of Osler, as well as the Town of Dalmeny outside of the P4G Region. Three main studies for flood control have been coordinated by the OCWA to date.

For the North Corman Park Flood Control Study Phase Two Report, which includes the most detailed studies done to date, elements and assumptions of note include the following:

  • Complete Information on culverts was not available for this study. Culverts not identified may have impacted the conclusions and recommendations of the analysis.
  • Peak design flows are based on snowmelt and rainfall estimated from 1:25 year events, allowing for temporary flooding of adjacent land.
  • Opportunities for wetland storage are not incorporated into the Phase Two Report design estimates.
  • An additional proposed drain (“Blumenheim Primary Drain”) is located outside of the P4G Region.

 

The summary map in Exhibit 3 indicates the drainage system alignments within the P4G Region detailed as Option 2 (the preferred option) in the Phase Two Report. This Option includes the following, with costs provided as of August 2013:

  • RR 3052 Primary Drain North. In the proposed system design, this drain provides the primary drainage for the areas between Warman and Martensville into Opimihaw Creek. This would require the construction of the Opimihaw Creek Primary Drain and Diversion to manage discharges into the Creek. (Estimated cost: $12.7 million)
  • Opimihaw Creek Primary Drain. The Opimihaw Creek Primary Drain would link the RR 3052 Primary Drain North with Opimihaw Creek to permit discharges of stormwater flow. (Estimated cost: $9.9 million)
  • Opimihaw Creek Diversion. This diversion mitigates increased stormwater flows into Opimihaw Creek to ensure that the volumes through Wanuskewin Heritage Park are no greater than current levels to prevent damage to the natural, cultural, and historic resources of the Park. (Estimated cost: $1.6 million)
  • RR 3052 Primary Drain South. This drain accommodates discharges from Martensville and the southern part of the basin, and links with Opimihaw Creek upstream from Wanuskewin Heritage Park. (Estimated cost: $7.5 million)
  • Osler Primary Drain. The Osler Primary Drain intercepts the southward flow of water from Buzz Slough located to the north and prevents this flow from impacting areas to the south. (Estimated cost: $13.9 million, revised to $15.3 million in Phase Three report)

 

Developing drainage infrastructure in the Opimihaw Creek watershed to date has been limited by the availability of funding for this work. Additional studies by OCWA are pending to review proposed drainage solutions and provide additional options, including the use of the Green Network Study Area to provide conveyance and storage.

Regional Actions

It is recommended that P4G pursue the following actions with respect to regional stormwater infrastructure:

  • Coordination with the OCWA. It is strongly recommended that ongoing efforts by P4G in regional stormwater infrastructure should be coordinated with the OCWA, given the efforts of this organization in managing drainage issues. Additional work may be coordinated between P4G and OCWA to ensure that sub-area and local stormwater infrastructure is developed to manage identified drainage issues and support identified development in the Regional Plan.
  • Inventory of stormwater drainage infrastructure. During the development of this Plan and the Regional Servicing Strategy, regional hydrological and flood modelling was limited by the lack of information on culverts and other drainage infrastructure that could impact stormwater flows and flooding. An inventory of these structures should be performed to support long-term efforts in stormwater infrastructure planning.
  • Coordination with First Nations. Ongoing efforts by P4G and municipalities in regional and local stormwater infrastructure should also be coordinated with First Nations. In several cases, requirements for drainage on treaty land entitlement holdings and reserves limit future development, and cooperation can help to reduce the planning, construction, and maintenance costs necessary to support productive uses in these areas.
  • Incorporation of natural infrastructure into detailed drainage design. P4G should coordinate with OCWA in developing more detailed engineering designs that incorporate wetlands and natural drainage features for detention and storage of stormwater in the north. The future refinement of the Green Network Study Area should be coordinated with these efforts to maintain and enhance drainage and conveyance, and reduce peak design flows.
  • Coordination with other regional infrastructure projects. Coordinating identified drainage projects with other regional infrastructure projects, especially transportation projects, can help to mitigate project costs. Planning for these projects by municipalities should be aligned with identified regional drainage infrastructure needs where possible.
  • Applications for supplementary funding from senior levels of government. Recognizing that the municipalities impacted by this drainage system may not be able to fully fund all improvements, P4G should coordinate with individual municipalities and the OCWA where applicable in presenting grant applications to senior levels of government. Funding applications will focus on the innovative aspects of these improvements, including the integration of green infrastructure into the design to reduce costs.
  • Support regional development levies, servicing agreement fees, and other cost-sharing for drainage improvements. New drainage infrastructure will allow areas prone to flooding to be used for more intensive development, and provide a significant benefit to impacted landowners. P4G should promote and assist in coordinating efforts between municipalities to collect development levies and servicing agreement fees to support regional drainage projects that impact multiple jurisdictions. These efforts may build a foundation for future cross-boundary efforts to manage fees and levies through regional cost-sharing mechanisms if P4G transitions to an Authority model.