Oshawa Creek Municipal Natural Assets Initiative

MNAI’s natural asset methodology follows the standard asset management process of assess, plan, and implement steps, highlighting novel considerations required for local natural assets and associated services. MNAI’s process begins with an initial engagement session with local government representatives including Parks, Public Works, Geographic Information Systems, Engineering, Planning, Water and Wastewater, and Finance. During the initial engagement session, plans and priorities of the community are discussed and key natural assets within the jurisdictional boundaries of the community are identified along with the important services those assets provide. The objectives of this initial engagement session are to identify:

• Natural asset(s) that will be the focus of the natural asset assessment
• Geographic boundary/ies of the focus assets
• Skill sets and expertise of relevance to the natural asset assessment
• Local government personnel that will engage in the assessment process
• Data needs of the assessment and the sources for the relevant data

Following the initial community engagement session, the MNAI team works with local government partners to complete a natural asset assessment. This involves:

1. Defining the scope of natural assets to be considered
2. Inventorying and conducting a condition assessment of the assets
3. Quantifying existing service levels from the assets, as well as co-benefits
4. Quantifying the financial value of the natural assets if the services they provide had to be delivered by an engineered alternative
5. Developing scenarios to explore alternative management plans and future implications for existing service levels
6. Quantifying services levels under alternative scenarios
7. Developing operation and management (O&M) plans based on existing conditions, risks, and desired service level trajectories

The assessment of natural asset conveyance services examines the stormwater management functions that are provided by the creek and its surrounding floodplain systems including conveyance capacity, flood mitigation to surrounding properties, peak flow attenuation, and water quality treatment. The regulatory event is determined to be the greater of the 100-year design storm or the “regional storm”, which is understood to mean a major event, specifically the 1954 Hurricane Hazel.

Determining the value of services provided by natural assets in the Oshawa Creek corridor requires consideration of both the value of Oshawa Creek and the floodplain surrounding it. Totalling these values provides a service value estimate for the project area. Importantly, this estimated value only accounts for the potential construction cost of engineered assets. It does not account for the value of features such as access to green and recreational space for residents, hydraulic detention, and water quality functions, consideration of which would increase the recorded value.

The steps for understanding the services provided by Oshawa Creek and their value include:

1. Determine the stormwater management functions that are provided by the creek and its surrounding floodplain system. These functions can include conveyance capacity, flood mitigation to surrounding properties, peak flow attenuation, and water quality treatment. The basis for this includes:
   1. Oshawa Creek Watershed Plan
   2. Oshawa Creek Hydrological and Hydraulic Modelling brief; and,
   3. Existing hydraulic models
2. Model land-use and climate change scenarios that increase stressors to the system. This establishes the extent to which the creek system can adapt to changing conditions without compromising its health and integrity. The scenarios considered were:
   1. Scenario 1: Existing land use conditions under current climatic conditions
   2. Scenario 2: Future land use conditions under current climatic conditions
   3. Scenario 3: Future land use conditions under future climatic condition
3. Determine value of creek’s functions. This is achieved by determining the cost and scale of engineered assets required to provide comparable service to the natural assets; and by considering any limits to how much the natural assets can adapt, as identified in Step 2, above. Functions that cannot be replaced by engineered infrastructure are also identified

A survey of other creek rehabilitation and restoration projects was conducted to gather data on the cost of constructing open channels, ensuring that the creek had a comparable flow rate to Oshawa Creek. Many projects initially identified as possible references were discounted as their flow rates were too small to provide a comparison for Oshawa Creek. As a guideline, projects included in the data collection met the following criteria:

• Documentation on the project’s description, flow rates, width of channel, and length of construction were publicly available;
• Flow rates were generally within one-third to one-half of Oshawa Creek’s 2-year and regional storm flows; and
• Proposed works included channel realignment works.

The findings from the above considerations were then compared to the Vaughan Metropolitan Centre Black Creek Renewal Case to provide an estimated value of Oshawa Creek assuming green field conditions that consider:

• Land Value
• Cost of Greenfield Channel Works
• Cost of Naturalized and Urban Buffers
• Contingency

A detailed breakdown of the asset valuation can be found in the case study linked in the Resources section.

Inventory, assessments and modelling activities indicate that the 7 km project area in the Oshawa Creek, excluding the floodplain, has a current value of $18.9 million in terms of current stormwater conveyance services. Operations and maintenance data was not available and therefore lifecycle costs comparisons were not possible. The total value of Oshawa Creek watershed including both the creek and surrounding floodplain, ranges between $392 million and $414 million.

This value relates only to stormwater management and does not include many co-benefits provided by the natural assets in the corridor including reduced flood risk, habitat for aquatic and terrestrial organisms, improved aesthetics of creek corridors, improved human health and well-being, air quality/cooling/shade, and connecting priority neighbourhoods.

Importantly, some of the co-benefits can create particular value for areas identified as Priority Health Neighbourhoods. Under the current watershed management program, the City of Oshawa provides funding to restore erosion sites along the creek, but work is largely remedial and reactive. Therefore, through this project, additional preventative measures to protect against erosion have been identified and modelled in City-owned riparian lands to improve the function of natural assets. These included the development of infiltration trenches, although the analysis suggests that these would need to be developed upstream of the project area for maximum effectiveness.

The MNAI project team has identified and modelled additional ways the City of Oshawa can improve the function of natural assets to further protect against and prevent erosion in City-owned riparian lands, mitigate the negative impacts of urbanization, and avoid having to build additional engineered assets. Recommendations include:

• Use the Oshawa Creek analysis and its quantifiable data as the first major step in a holistic asset management approach
• Develop a natural asset policy
• Develop a natural asset management roadmap
• Enhance co-benefits
• Implement additional preventative measures

Oshawa Creek targets in the CLOCA watershed plan are, based on recommendations from Environment and Climate Change Canada include:

• Target for 30% natural cover
• Target for 10% wetland cover
• Target for less than 10% imperviousness on ORM or Greenbelt
• Target for 75% riparian cover
• Stormwater management targets

CLOCA and the City of Oshawa are working to achieve these objectives.

Link to Full Case Study

Additional Resources:

• Project Summary
• Municipal Natural Assets Initiative Cohort 2 Communities
• CLOCA Watershed Plan (Draft)
• City of Oshawa Strategic Plan
• Durham Community Climate Adaptation Plan