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 Humber Creek Erosion Control Class Environmental Assessment Each reach (#1-3) will be specifically evaluated to Reach 1 determine the preferred method for restoration. EVALUATION Alternative 1 - Do Nothing Alternative 2 - Local Restorartion Alternative 3 - Reach Based Restoration CRITERIA Score Explanation Score Explanation Score Explanation The evaluation uses a ranking scheme which Physical and 0.0 1.4 1.4 Natural Criteria accounts for Physical and Natural Environment, Social Engineered riffle replacing the failed gabion Rate of erosion, slope failures, and Continued erosion, slope failsures and loss Minimized rate of erosion and loss of table / parklands, Erosion 0 structure would provide effetive erosion 3 4 provided stable slopes loss of table / parklands of table / parklands and Cultural Conditions, Economics, and Technical control Backwatered area remains and lack of tree Improving the backwatered area will improve water Improved backwater area will provide improved water quality. Considerations. Water Quality Impact on water quality 0 canopy keeps water warmer. No 1 1 quality by lowering the amount of stagnant water, Restoration plantings would slow runoff from yards. improving water quality downstream. improvement to water quality. No improvement to habitat. Possibility the The constraints of the narrow corridor mean introducing a meandering Impact on contributing aquatic The possible water quality improvements would make pattern will not have as a great an impact as elsewhere, but would still Aquatic Habitat 0 habitat will degrade as channel continues to 1 2 this reach suitable for different types of forage for fish. allow better form. Substrate other than cobble could be added to the habitat become incised. reach. A preliminary ranking has been applied to each Habitat stays in current condition; Habitat Likely removal of candidate bat maternity roosting sites; Removal of Impact on connectivity, diversity quality potentially degrades over time as Localized loss of vegetation due to construction will be Terrestrial Habitat 0 3 2 invasive species throughout the reach; Enhance reach-scale mitigated by planting native species; Removal of and quantity/quality of habitat exotic and invasive species outcompete biodiversity through native species planting. invasive shrubs along access routes; Likely removal of native species. alternative for each reach. The alternative with the candidate bat maternity roosting sites. Vegetation composition remains the same Vegetation loss due to construction will be mitigated through native Terrestrial Impact on existing riparian with exotic species dominating; Continued Potential removal of dead ash trees and invasive species plantings throughout the reach; Removal of dead ash trees 0 3 2 shrubs along access routes. and invasive shrubs; Potential transplant of locally rare species Vegetation vegetation, inlcuding mature trees loss of herbaceous, shrubs, and some trees highest score will define which method of restoration required. from erosion. Social and is preferred for each reach. 0.6 1.9 2.0 Cultural Criteria Continued erosion and unstable slopes Improved public safety by reducing erosions Stable slope and removal of deteriorated infrastructure, Public Safety Impact on public safety 1 3 3 and stablizing slopes flooding risks minimized would create risks to public safety The ranking score has been normalized to provide Localized restoration and minimized Impact on adjacent private Continued erosion and unstable slopes negative impacts to adjacent lands during Minimized risks of property loss and increased value of Landowner Impacts properties and City of Mississauga 1 would potentially lead to loss of table / 3 2 construction while reduce risks of property the park Woodington Green Park parklands loss equal weighting for each category of evaluation Benefit to Access to trails, enjoyment of Access to trails, enjoyment of surrounding Access to trails, enjoyment of surrounding 1 Access to trails, enjoyment of surrounding lands 4 4 lands Community surrounding lands lands criteria. Impact on existing and proposed Low aestheric value due to structure failures Improving aesthetic value by repairing failed Comprehensive reach restoration, replacement of failed Aesthetic Value 1 2 4 infrastructure within the corridor channel works and vegetation restoration aesthetic value within the channel Comment Sheets are provided to gain public input on Technical and 0.6 1.9 2.5 Engineer Criteria the preliminary ranking. The ranking will be finalized Protection or potential exposure of Impact on Existing Continued degradation of storm outfalls Repair of degraded storm outfalls and infrastructure (storm sewer, road / 1 Deteriorated existing infrastructure will be repaired 3 4 reduce risks to sanitary sewers & MHs Infrastructure and risks to sanitary sewers & MHs bridge network) once public input has been incorporated. Expected lifespan / years of works Lifespan of Works before intervention needs to be 1 Structures approaching end of lifespan Moderate lifespan Lifespan of works is estimated to be > 50 years 3 4 repeated Economic Criteria 1.3 1.9 0.9 An Example is illustrated in the adjacent table: Moderate costs associated with local Capital Costs One time cost to City 4 No capital cost to City Highest costs associated with reach work 3 0 restorations Ranking Scale Requirement for regular, irregular or Regular monitoring and maintenance to Operations & no maintenance activities and mitigate the deterioration of the channel 0 Regular monitoring and maintenance Minimal maintenance required. 3 3 Maintenance Costs ensure effectiveness of and storm sewer outfalls. Works would implemented measures occur under emergency basis. No / Negative Ideal / Most Positive 0 1 2 3 4 TOTAL SCORE 2.5 7.0 6.8 Impact Impact Highest Score = 3 Preferred Alternative
Potential Alternative #1 – Do Nothing Humber Creek Erosion Control Class Environmental Assessment Alternative 1 - Do Nothing REACH 1 REACH 2 REACH 3 REACH 4 EVALUATION CRITERIA Score Score Score Score Physical and Natural Criteria 0.0 0.0 0.0 0.3 Rate of erosion, slope failures, and Erosion 0 0 0 1 loss of table / parklands Water Quality Impact on water quality 0 0 0 0 Impact on contributing aquatic Aquatic Habitat 0 0 0 0 habitat Impact on connectivity, diversity Terrestrial Habitat 0 0 0 0 and quantity/quality of habitat Terrestrial Impact on existing riparian 0 0 0 1 Vegetation vegetation, inlcuding mature trees Social and Cultural Criteria 0.6 0.6 0.6 1.4 Public Safety Impact on public safety 1 1 1 2 Impact on adjacent private Landowner Impacts properties and City of Mississauga 1 1 1 1 Woodington Green Park Benefit to Access to trails, enjoyment of 1 1 1 4 Community surrounding lands Impact on existing and proposed Aesthetic Value 1 1 1 2 aesthetic value Technical and Engineer Criteria 0.0 0.3 0.0 0.6 Protection or potential exposure of Impact on Existing infrastructure (storm sewer, road / 0 1 0 1 Infrastructure bridge network) Expected lifespan / years of works Lifespan of Works before intervention needs to be 0 0 0 1 repeated Economic Criteria 1.3 1.3 1.3 1.3 Capital Costs One time cost to City 4 4 4 4 Existing / Requirement for regular, irregular Operations & or no maintenance activities and Do Nothing Conditions 0 0 0 0 Maintenance Costs ensure effectiveness of implemented measures TOTAL SCORE 1.9 2.2 1.9 3.5 Ranking Scale No / Negative Ideal / Most Positive 0 1 2 3 4 Impact Impact 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 4 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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