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Humber Creek Erosion Control Class Environmental Assessment
Humber Creek Erosion Control Class Environmental Assessment
CULTURAL AND NATURAL HERITAGE Humber Creek Erosion Control Class - - PowerPoint PPT Presentation
CULTURAL AND NATURAL HERITAGE Humber Creek Erosion Control Class - - PowerPoint PPT Presentation
CULTURAL AND NATURAL HERITAGE Humber Creek Erosion Control Class Environmental Assessment 1 SLOPE STABILITY AND EROSION RISK ASSESSMENT Humber Creek Erosion Control Class Environmental Assessment 2 EVALUATION APPROACH AND PROPOSED CRITERIA
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Humber Creek Erosion Control Class Environmental Assessment
EVALUATION CRITERIA Score Explanation Score Explanation Score Explanation Physical and Natural Criteria 0.0 1.4 1.4 Erosion Rate of erosion, slope failures, and loss of table / parklands Continued erosion, slope failsures and loss
- f table / parklands
3 Engineered riffle replacing the failed gabion structure would provide effetive erosion control 4 Minimized rate of erosion and loss of table / parklands, provided stable slopes
Water Quality Impact on water quality Backwatered area remains and lack of tree canopy keeps water warmer. No improvement to water quality.
1
Improving the backwatered area will improve water quality by lowering the amount of stagnant water, improving water quality downstream.
1
Improved backwater area will provide improved water quality. Restoration plantings would slow runoff from yards.
Aquatic Habitat Impact on contributing aquatic habitat No improvement to habitat. Possibility the habitat will degrade as channel continues to become incised.
1
The possible water quality improvements would make this reach suitable for different types of forage for fish.
2
The constraints of the narrow corridor mean introducing a meandering pattern will not have as a great an impact as elsewhere, but would still allow better form. Substrate other than cobble could be added to the reach.
Terrestrial Habitat Impact on connectivity, diversity and quantity/quality of habitat Habitat stays in current condition; Habitat quality potentially degrades over time as exotic and invasive species outcompete native species.
3
Localized loss of vegetation due to construction will be mitigated by planting native species; Removal of invasive shrubs along access routes; Likely removal of candidate bat maternity roosting sites.
2
Likely removal of candidate bat maternity roosting sites; Removal of invasive species throughout the reach; Enhance reach-scale biodiversity through native species planting.
Terrestrial Vegetation Impact on existing riparian vegetation, inlcuding mature trees Vegetation composition remains the same with exotic species dominating; Continued loss of herbaceous, shrubs, and some trees from erosion.
3
Potential removal of dead ash trees and invasive shrubs along access routes.
2
Vegetation loss due to construction will be mitigated through native species plantings throughout the reach; Removal of dead ash trees and invasive shrubs; Potential transplant of locally rare species required.
Social and Cultural Criteria 0.6 1.9 2.0 Public Safety Impact on public safety 1 Continued erosion and unstable slopes would create risks to public safety
3 Improved public safety by reducing erosions and stablizing slopes 3 Stable slope and removal of deteriorated infrastructure, flooding risks minimized
Landowner Impacts Impact on adjacent private properties and City of Mississauga Woodington Green Park 1 Continued erosion and unstable slopes would potentially lead to loss of table / parklands
3 Localized restoration and minimized negative impacts to adjacent lands during construction while reduce risks of property loss 2 Minimized risks of property loss and increased value of the park
Benefit to Community Access to trails, enjoyment of surrounding lands 1 Access to trails, enjoyment of surrounding lands
4 Access to trails, enjoyment of surrounding lands 4 Access to trails, enjoyment of surrounding lands
Aesthetic Value Impact on existing and proposed aesthetic value 1 Low aestheric value due to structure failures within the channel
2 Improving aesthetic value by repairing failed infrastructure within the corridor 4 Comprehensive reach restoration, replacement of failed channel works and vegetation restoration
Technical and Engineer Criteria 0.6 1.9 2.5 Impact on Existing Infrastructure Protection or potential exposure of infrastructure (storm sewer, road / bridge network) 1 Continued degradation of storm outfalls and risks to sanitary sewers & MHs
3 Repair of degraded storm outfalls and reduce risks to sanitary sewers & MHs 4 Deteriorated existing infrastructure will be repaired
Lifespan of Works Expected lifespan / years of works before intervention needs to be repeated 1 Structures approaching end of lifespan
3 Moderate lifespan 4 Lifespan of works is estimated to be > 50 years
Economic Criteria 1.3 1.9 0.9 Capital Costs One time cost to City 4 No capital cost to City
3 Moderate costs associated with local restorations Highest costs associated with reach work
Operations & Maintenance Costs Requirement for regular, irregular or no maintenance activities and ensure effectiveness of implemented measures Regular monitoring and maintenance to mitigate the deterioration of the channel and storm sewer outfalls. Works would
- ccur under emergency basis.
3 Regular monitoring and maintenance 3 Minimal maintenance required.
TOTAL SCORE 2.5 7.0 6.8 Reach 1 Alternative 1 - Do Nothing Alternative 2 - Local Restorartion Alternative 3 - Reach Based Restoration
EVALUATION APPROACH AND PROPOSED CRITERIA
Each reach (#1-3) will be specifically evaluated to determine the preferred method for restoration. The evaluation uses a ranking scheme which accounts for Physical and Natural Environment, Social and Cultural Conditions, Economics, and Technical Considerations. A preliminary ranking has been applied to each alternative for each reach. The alternative with the highest score will define which method of restoration is preferred for each reach. The ranking score has been normalized to provide equal weighting for each category
- f
evaluation criteria. Comment Sheets are provided to gain public input on the preliminary ranking. The ranking will be finalized
- nce public input has been incorporated.
An Example is illustrated in the adjacent table:
Highest Score = Preferred Alternative 3
No / Negative Impact 1 2 3 4 Ideal / Most Positive Impact Ranking Scale
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Humber Creek Erosion Control Class Environmental Assessment
Potential Alternative #1 – Do Nothing
Alternative # 1 – Do Nothing Definition: No restoration measures taken, except on emergency basis. Description: This alternative would involve leaving the existing channel as is. Existing problems associated with eroding of streambanks, failure of gabion grade control, risks to infrastructure and barriers to fish would
- continue. Habitat conditions would continue to degrade due to erosion.
Although no capital costs have been assigned to this alternative, ongoing operation and maintenance activities would continue. Under emergency conditions (ie. failure) would works occur. Monitoring would be necessary. Preliminary ranking of the Do Nothing Alternative is provided in the adjacent table. Public input will be incorporated into the ranking to identify the preferred solution. The ranking scale is shown in the table below.
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Existing / Do Nothing Conditions
No / Negative Impact 1 2 3 4 Ideal / Most Positive Impact Ranking Scale
Score Score Score Score 0.0 0.0 0.0 0.3 Erosion Rate of erosion, slope failures, and loss of table / parklands 1 Water Quality Impact on water quality Aquatic Habitat Impact on contributing aquatic habitat Terrestrial Habitat Impact on connectivity, diversity and quantity/quality of habitat Terrestrial Vegetation Impact on existing riparian vegetation, inlcuding mature trees 1 0.6 0.6 0.6 1.4 Public Safety Impact on public safety 1 1 1 2 Landowner Impacts Impact on adjacent private properties and City of Mississauga Woodington Green Park 1 1 1 1 Benefit to Community Access to trails, enjoyment of surrounding lands 1 1 1 4 Aesthetic Value Impact on existing and proposed aesthetic value 1 1 1 2 0.0 0.3 0.0 0.6 Impact on Existing Infrastructure Protection or potential exposure of infrastructure (storm sewer, road / bridge network) 1 1 Lifespan of Works Expected lifespan / years of works before intervention needs to be repeated 1 1.3 1.3 1.3 1.3 Capital Costs One time cost to City 4 4 4 4 Operations & Maintenance Costs Requirement for regular, irregular
- r no maintenance activities and
ensure effectiveness of implemented measures TOTAL SCORE 1.9 2.2 1.9 3.5 Alternative 1 - Do Nothing REACH 1 REACH 2 REACH 3 REACH 4 EVALUATION CRITERIA Physical and Natural Criteria Social and Cultural Criteria Technical and Engineer Criteria Economic Criteria
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Humber Creek Erosion Control Class Environmental Assessment
Potential Alternative #2 – Local Restoration
Alternative # 2 – Local Restoration Definition: Stream restoration works at strategic locations in order to limit the impact of existing erosion problems . Description: This Alternative would involve undertaking stream restoration works at priority problem locations. The proposed works would prevent local erosion of the channel by stabilization of the bed, banks and
- slopes. Where erosion is creating risks to infrastructure, local bank or slope stabilization treatments / channel realignment would be placed, using either hardened (engineered) type treatments, or more natural
(vegetation & biotechnical engineered) type treatments. Benefits of local works include minimal disruption to the local natural environment, quick implementation to minimize short term risk. The lifespan of these works are generally defined as moderate. Intermediate and long term fluvial processes often / eventually undermine works, or similar issues are transcribed downstream.
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Example of Local Restoration
Score Score Score Score 1.5 0.9 1.0 1.8 Erosion Rate of erosion, slope failures, and loss of table / parklands 3 3 3 4 Water Quality Impact on water quality 1 1 2 2 Aquatic Habitat Impact on contributing aquatic habitat 2 1 1 2 Terrestrial Habitat Impact on connectivity, diversity and quantity/quality of habitat 3 1 1 3 Terrestrial Vegetation Impact on existing riparian vegetation, inlcuding mature trees 3 1 1 3 2.0 1.3 1.4 2.3 Public Safety Impact on public safety 3 2 3 4 Landowner Impacts Impact on adjacent private properties and City of Mississauga Woodington Green Park 3 3 3 4 Benefit to Community Access to trails, enjoyment of surrounding lands 4 1 1 4 Aesthetic Value Impact on existing and proposed aesthetic value 3 2 2 3 1.9 1.9 1.9 2.2 Impact on Existing Infrastructure Protection or potential exposure of infrastructure (storm sewer, road / bridge network) 3 3 3 4 Lifespan of Works Expected lifespan / years of works before intervention needs to be repeated 3 3 3 3 1.9 1.6 1.6 1.9 Capital Costs One time cost to City 3 3 3 3 Operations & Maintenance Costs Requirement for regular, irregular
- r no maintenance activities and
ensure effectiveness of implemented measures 3 2 2 3 TOTAL SCORE 7.3 5.6 5.8 8.2 REACH 3 REACH 4 REACH 1 REACH 2 Alternative 2 - Local Restorartion EVALUATION CRITERIA Physical and Natural Criteria Social and Cultural Criteria Technical and Engineer Criteria Economic Criteria
No / Negative Impact 1 2 3 4 Ideal / Most Positive Impact Ranking Scale
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Humber Creek Erosion Control Class Environmental Assessment
Potential Alternative #3 – Reach Scale Restoration
Alternative # 3 – Reach Scale Restoration Definition: Restoration of the stream to a more naturalized form, maintaining a fixed (existing ) alignment where property constraints dictate. Description: This Alternative would involve complete restoration throughout the length of the study area, recreating the channel bed and banks using a combination of natural channel design techniques as well as engineered methods. During construction, this option will involve the highest level of disruption to landowners, local residents, and habitat (including existing vegetation). Once completed however, it will provide improved conditions in terms of the natural function and processes of the watercourse. All disrupted areas will be restored with native plantings and seed mixes designed to provide stability and sustainability.
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Example of Reach Based Restoration
Score Score Score Score 1.8 1.8 1.8 1.8 Erosion Rate of erosion, slope failures, and loss of table / parklands 4 4 4 4 Water Quality Impact on water quality 3 3 3 3 Aquatic Habitat Impact on contributing aquatic habitat 3 3 3 3 Terrestrial Habitat Impact on connectivity, diversity and quantity/quality of habitat 2 2 2 2 Terrestrial Vegetation Impact on existing riparian vegetation, inlcuding mature trees 2 2 2 2 1.9 2.3 2.3 2.3 Public Safety Impact on public safety 4 4 4 4 Landowner Impacts Impact on adjacent private properties and City of Mississauga Woodington Green Park 3 3 3 3 Benefit to Community Access to trails, enjoyment of surrounding lands 1 4 4 4 Aesthetic Value Impact on existing and proposed aesthetic value 4 4 4 4 2.5 2.5 2.5 2.5 Impact on Existing Infrastructure Protection or potential exposure of infrastructure (storm sewer, road / bridge network) 4 4 4 4 Lifespan of Works Expected lifespan / years of works before intervention needs to be repeated 4 4 4 4 0.9 0.9 0.9 0.9 Capital Costs One time cost to City Operations & Maintenance Costs Requirement for regular, irregular
- r no maintenance activities and
ensure effectiveness of implemented measures 3 3 3 3 TOTAL SCORE 7.1 7.5 7.5 7.5 REACH 1 REACH 2 REACH 3 REACH 4 Alternative 3 - Reach Based Restoration EVALUATION CRITERIA Physical and Natural Criteria Social and Cultural Criteria Technical and Engineer Criteria Economic Criteria
No / Negative Impact 1 2 3 4 Ideal / Most Positive Impact Ranking Scale
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Humber Creek Erosion Control Class Environmental Assessment
PRELIMINARY PREFERRED ALTERNATIVES
Reach 1 – Local Works Stream restoration works at strategic / priority locations in order to limit the impact of existing erosion problems. Reach 2 – Reach Scale Works Continuous Restoration of Entire Reach to a More Natural Form, and enhance terrestrial ecology. Reach 4 – Local Works Stream restoration works at strategic / priority locations, staying within City easement. The preliminary preferred alternatives for restoration are summarized below. Your comments on the ranking and preferred method of restoration are encouraged and appreciated. The study team will compile and review all feedback, and then finalize the preferred alternatives for each reach. 7 Reach 3 – Reach Scale Works Continuous Restoration of Entire Reach to a More Natural Form, and enhance terrestrial ecology.
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NEXT STEPS
- Comment forms available for input.
- Compile and review feedback. Confirm or adapt preliminary preferred alternatives.
PUBLIC CONSULTATION – July 2018
- EA Project file posted for 30 day review period.
SUBMIT EA PROJECT FILE AND OBTAIN AGENCY APPROVALS – September 2018
- Detailed design and permitting completed as per City Planning and Budgeting
- Construction scheduled for 2019 / 2020.