Municipal Class Environmental Assessment for Pottersburg Creek Slope Stability Study South of Hamilton Road, Schedule B February 13, 2013
Municipal Class EA Process We are here
Purpose and Objective of Study Purpose: Develop bank stabilization options To protect properties and servicing infrastructure To protect, maintain and enhance ecological processes, stream function and natural features of the area Objective To develop and evaluate viable options (review agency and public input) Recommend an alternative
Study Limits 80 m of channel downstream of Hamilton Road
Problem and Opportunity Problem: East bank slope is unstable, and requires remedial action Residences and servicing infrastructure in critical condition Opportunity: Develop remediation options that ensures public safety Protect key services Protect environmental and ecological conditions of Pottersburg Creek
Background Natural slope was modified by engineering works in 1989 Portions of slope built steeper than original recommended Residential units and servicing infrastructure located within hazardous slope stability area Focus of this study is on remediation works
Environmental Assessment Study The following investigations completed : Geotechnical Soil Chemistry Hydrology and Hydraulics Fluvial Geomorphology Terrestrial Ecology Fisheries Habitat
Geotechnical Engineering Inventory of of existing soil conditions (soil and slope stability) Undertaken detailed geotechnical analysis Establish stable top of slope MNR Understanding Natural Hazards
Soil Chemistry Elevated levels of PCB s identified in two samples No PCB waste Removal of contaminated material from subject site City of London Ayerswood MCC229
Fluvial Geomorphology Evaluated existing fluvial channel behaviour Downstream of Hamilton Road is a natural meander bent (bend in the river) Erosion rate high at the bend Natural channel will erode bank and Natural channel will erode bank and migrate inland
Hydrology and Hydraulics Hydrology (watershed flows) Establish watershed runoff by applying a water resources model Range of inputs used according to engineering standards Hydraulics (velocities & depths of flow) Topographic survey completed from Gore Road to Thames River Numerical model to establish water levels under various conditions Used for impact assessment
Terrestrial Habitat Seven vegetation communities of low land forests identified Two types of deciduous swamps Plants and wildlife corridor within the river corridor catalogued No species at risk found (confirmed No species at risk found (confirmed with MNR)
Fisheries Habitat Aquatic habitat evaluated This reach of creek rated between good and fair Creek is spawning ground for fish Number of species found No species at risk identified Small mouth bass Creek chub
Option 1: Do Nothing Slope is unstable and unsafe Residential units located on top of unstable slope (public risk) Key servicing infrastructure at risk (water and sewer) Environmental impacts of potential malfunction or breaks in services Not a viable option
Option 2: Buyout of residences Acquire and demolish five residential units Relocate services Remove rock from slope Allow river to erode Creek could freely move and adjust with time No adverse disruption to vegetation and wildlife (no improvement either) Loss of fish habitat with ongoing erosion Cost: High
Option 3: New retaining wall 60 m of vertical wall New wall to be owned by individual property p owners Heavy insurance requirements Long term maintenance required Residences and servicing infrastructure to remain Rock berm in front of wall required Elimination of fish spawning grounds Cost: Very High
Option 4: Channel Re alignment Residences and services remain To facilitate shift, need new retaining walls near bridge Reshape bank, line with rock Remove contaminated PCB from west bank Design in stream fish habitat improvements Native vegetation planting above rock Minor maintenance required Cost: Moderate
Ranking of Options Option 1 Option 2 Option 3 Option 4 Criteria/Option Do Nothing Buyout New Wall Re-alignment Land acquisition Erosion Flooding Stream morphology Aquatic habitat Terrestrial habitat Technical complexity Social Implications Costs Level of Preference c c Low (worst) Medium High (best)
Draft Preferred Option Option 4: Channel Re alignment ranked highest Demolition of private property not required No adverse impact of flooding/erosion from re aligned channel Some environmental disruption during construction Fish habitat improvements Loss of riparian vegetation along banks Long term stream health could be improved (new features in channel) Technically feasible Lowest costs
Next Steps Public input (this meeting) Review agency comments Finalize the report City council 30 day public review period
Public Input Handwritten comments Email Phone Fax Mail Comments due by: Fb Feb 27, 2013 (two weeks) k) Pat Prodanovic, Ph.D., P.Eng. Water Resources and Marine Engineer Riggs Engineering Ltd. 1240 Commissioner s Road West Suite 205 London, Ontario N6K 1C7 Phone: 519 647 1040 Fax: 519 657 8631 E mail: pprodanovic@riggsengineering.com Billy Haklander, P. Eng. Environmental Services Engineer Stormwater Management Unit Environmental and Engineering Services Department 300 Dufferin St., 9th Floor London, Ontario N6A 4L9 Phone: 519 661 2500, ext. 5862 Fax: 519 661 2355 E mail: bhakland@london.ca
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