Oakville Harbours Sediment Management Strategy Study - culture... · Imran Khan, Service Group Manager – ... • Potential for high maintenance costs • Will still need to hire

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Open House #2Thursday, March 6, 2014

Oakville Harbours Sediment Management Strategy Study

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Study leads:

Dr. Jeff Doucette, Coastal and River Scientist, GHD

Imran Khan, Service Group Manager –Geomorphology, Canada, GHD

Presentation by:Dr. Jeff Doucette

Welcome

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We are here

Learn from Doing

Town of Oakville and stakeholders identify issues

Project awarded to GHD

Background review

Data collection and field observations

Public consultation #1Integration of stakeholder comments

Preliminary recommendations

Public consultation #2

Preparation of final report

Implementation of recommendations

Monitor and Adapt

Managing our harbours

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Tonight’s discussion

o Recapo Comments

from previous PICo Options considered

• Options in the watershed• Options in the harbours

o Evaluation of optionso Preliminary

recommendations

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How does sediment get into our harbours?

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How does sediment get into our harbours?

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Recap: What we did

Bronte Creek Watershed

Sixteen Mile Creek Watershed

Field Work: Total Suspended Solids (TSS)

Bronte Creek

Urban area 1,500 haAgricultural area 18,700 ha

Sixteen Mile Creek

Urban area 5,800 haAgricultural area 17,500 ha

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Comments from previous PIC Dot panels from previous PIC

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Watershed development and sediment load evolutionComments from previous PIC

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Lake level control and future lake levels

Comments from previous PIC

Time (yrs)

Wat

er D

epth

(m)

0 20 40 60 80 100

4ft

6ft

8ft

1.0

2.0

3.0

4.0

Natural Unregulated FlowNew Proposed PlanExisting Plan

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Comments from previous PIC W

ater

Lev

el (m

)

72.9

73.4

73.9

74.4

74.9

75.4

75.9

1918

1919

1921

1923

1925

1927

1929

1931

1933

1935

1937

1939

1941

1943

1945

1947

1949

1951

1953

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

2006

2008

2010

2012

Wat

er L

evel

(m)

Year

Historical Water Levels Lake Ontario 1918-201275.9

75.4

74.9

74.4

73.9

73.4

72.9

1918

1935

1959

1977

1998

2012

Year

Historical Water Levels of Lake Ontario

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Bronte Harbour

LegendDepth greater than 6 ft (1.8 m) below chart datum

Depth less than 6 ft (1.8 m) below chart datum

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Oakville Harbour

LegendDepth greater than 6 ft (1.8 m) below chart datum

Depth less than 6 ft (1.8 m) below chart datum

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o A study of 4 stormwater ponds by Town of Oakville found 60% efficiency in removal of TSS

o Urban soil loss rate: very low to low


Feature % Gravel % Sand % Silt % Clay

SWM Pond 3 15 65 17

Oakville Harbour 0.4 23 54 22

Bronte Harbour 0 31 53 16

Efficiency of Stormwater Ponds

Sediment Characteristics

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Comments from previous PIC Additional Documents Reviewed

Oakville Harbour: Halton’s Gateway to Lake OntarioAssociation of Oakville Harbours Stakeholders, July 2010

Sediment Management Study: Desired OutcomesAssociation of Oakville Harbours Stakeholders, January 2012

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Trends in erosion and sediment control

• Improvements in implementation of erosion and sediment control techniques

• Increase in monitoring requirements• Increase in compliance• Increase in training and awareness• Availability of standard guidelines

Recommendations from interviews and technical review

• Focus on compliance rather than new technologies or techniques

• Maintain or increase monitoring requirements • Improve implementation of existing technologies• Focus on erosion control in addition to sediment

control• Explore methods to reduce agricultural inputs

(e.g. vegetated buffers)

Options to consider in our watersheds

Managing Sediment Supply from the Watershed

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Hard Structures

Soft Structures

Sediment Traps

Operational Changes

Purchase of Suction Dredger

Maintenance Dredging

Relocation of Harbours

Offshore Disposal

Options to consider in our harbours

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Options to consider in our harboursHard StructuresConstruction of permanent docks and flow deflectors

Bronte Harbour Oakville Harbour

Proposed HardStructure

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Advantages• Encourage containment of high suspended

sediment concentrations within the main channel• Deflect and restrict flow to the main channel• Limit dispersion of suspended sediment to

quiescent areas• Effective year-round• Limited short-term maintenance requirements

Disadvantages• Lower flow velocities behind structures may

increase sedimentation• Will not eliminate the need for dredging • Relatively expensive compared to less-permanent

options• Likely difficult to obtain permits for construction• Potential water quality impacts• May cause deposition in other areas

Hard StructuresConstruction of permanent docks and flow deflectors

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Options to consider in our harboursSoft StructuresInstallation of baffles and turbidity curtains

Bronte Harbour Oakville Harbour

Proposed SoftStructure

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Advantages• Encourage containment of high suspended sediment

concentrations within the main channel• Deflect and restrict flow to the main channel• Limit dispersion of suspended sediment to quiescent

areas• Relatively inexpensive compared to more permanent

options• Adaptable to the results of effectiveness monitoring

Disadvantages• Lower flow velocities behind turbidity curtain may

increase sedimentation• Will not eliminate the need for dredging • Only deployed while docks are in place• May affect structural stability of docks due to force of

flow against the baffle• May cause deposition in other areas• Potential impact on water quality

Soft StructuresInstallation of baffles and turbidity curtains

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Options to consider in our harboursSediment TrapsInstallation of Sediment Traps Upstream of Harbours

Upstream of Bronte Harbour Upstream of Oakville Harbour

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Advantages

• None• Not likely to be more effective than existing

wetland vegetation

Disadvantages

• Ineffective at trapping fine sediments• Additional dredging will be required at the

sediment traps• Construction of the traps will destroy

existing wetland vegetation• Permits and approvals will be difficult to

obtain

Sediment TrapsInstallation of Sediment Traps Upstream of Harbours

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Options to consider in our harboursOperational ChangesReducing the operational depth of the harbours

4 ft (1.2 m) depth 8 ft (2.4 m) depth

Bronte Harbour

No dredgingrequired

Areas requiringdredging

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Options to consider in our harboursOperational ChangesReducing the operational depth of the harbours

4 ft (1.2 m) depth 8 ft (2.4 m) depth

Oakville Harbour

No dredgingrequired

Areas requiringdredging

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Advantages

• Significant dredging cost savings• Easy to implement from a technical

perspective

Disadvantages

• Will limit the use of the harbours by sail boats

• Significant loss of business and income for the Town

• Not likely to be acceptable to the boating community

Operational ChangesReducing the operational depth of the harbours

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Advantages

• Low mobilization costs• Potential for additional cost recovery• Moderate cost savings over contract dredging• Better control and monitoring of dredged areas• Greater flexibility in dredge timing and frequency

Disadvantages

• Need for trained staff to operate and maintain• High initial cost • Potential for high maintenance costs• Will still need to hire contractors to complete

chemical coagulation of material and the use of geotubes

Purchase of a Suction Dredger

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Options to consider in our harboursMaintenance Dredging

• More frequent dredging of problem areas will aid in maintaining functionality

• Dredging to occur every 2 years

• Suction dredge and geotubes to be used to minimize the release of suspended sediment

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Advantages

• Increased usability of rapidly infilling slips• Increased navigability and safety• Reduced environmental impact with the use of

suction dredging and geotubes• Reduced mobilization costs per operation given

the smaller size of equipment necessary

Disadvantages

• Additional cost associated with more frequent design and permitting requirements

• More frequent mobilization costs• More frequent sediment testing costs

Maintenance Dredging

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Advantages• Oakville shoreline has limited sand-sized sediment in the

nearshore that could accumulate in the entrance of a new harbour

• Dredging will likely not be necessary in new harbour• Aquatic habitat of existing harbours could be restored• Option is supported by Conservation Halton

Disadvantages• Large impacts due to modification of lake bed habitat• Localized impacts during construction• Potential water circulation and water quality effects• Very high planning, design, and construction costs• Challenges of finding a suitable location• Unknown local, social, and economic impacts

Relocation of HarboursRelocate docking capacity to new harbours located along the shore

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Advantages• Will not require geotubes, trucking, and disposal• Could be significant cost savings if an

inexpensive disposal site is no longer available• Dredge material could provide rooting substrate

for aquatic plants• Option is supported by Conservation Halton

Disadvantages• Not feasible at present given contamination levels• Complex approvals process including survey and

assessment of disposal site• If pumping material from a suction dredger,

booster pump may be required and could only be deployed in calm weather

Offshore DisposalDepositing accumulated sediment in deeper water

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Evaluation of options

Least Preferred

Option Effectiveness Environmental impacts

Adaptability Feasibility Cost Overall

SoftStructures

HardStructuresSediment

trapsOperational

changesMaintenance

dredgingPurchase of

a suction dredge

Relocation of Harbours

Offshore disposal

Current practice

Most Preferred

ModeratelyPreferred

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Preliminary recommendationsRecommended Sediment Management Strategy

Short Term:• Conduct large scheduled dredge at Bronte Harbour

in 2015, based on current practice

Long Term:• Conduct more frequent maintenance dredge

operations every second year at each harbour

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Preliminary recommendations

• Follow a maintenance dredging program with sediment removal in each harbour every second year

• Use bathymetric soundings to focus dredge operations and to better monitor rates of accumulation

• Conduct bathymetric soundings each spring to monitor accumulation of sediment

• Conduct pre- and post- dredge soundings• Use an adaptive management approach to determine volumes and

locations of removal each year• Conduct an ecological impact assessment to determine if dredging

could be conducted in November• Maintain detailed records of dredging operations including digital

data for all bathymetric soundings, volumes removed and costs• Use suction dredging techniques with geotube disposal to minimize

environmental impacts• Further investigate the offshore disposal option if sediment

contaminant levels decrease

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Thank you.Questions or comments?