TAVISTOCK MASTER STORM SYSTEM DRAINAGE PLAN OUTLINE Introduction - - PowerPoint PPT Presentation

TAVISTOCK MASTER STORM SYSTEM DRAINAGE PLAN

OUTLINE

• Introduction
• Data Collection and Review
• Existing System Characteristics
• Alternative Improvement Measures
• Description of the Existing Environment
• Evaluation and Mitigation
• Preferred Alternative
• Recommendations and Implementation Strategy

INTRODUCTION

• Study Purpose
• Class EA Planning Process

– Municipal Class Environmental Assessment (EA) – Master Plan Process

• Public and Agency Consultation
• Notification
• Flood Prevention Working Group

Study Purpose

• Review existing storm sewer system
• Identify areas that are considered ‘high risk’ for flooding
• Review Township standards and comment/recommend any

necessary changes/strategies

• Review overland flow routes and identify areas of surface

restrictions and recommend improvements

• Develop alternative solutions to reduce current flooding
• Review the advantages of stormwater management

EXISTING SYSTEM CHARACTERISTSICS

• Current Design Criteria

– Private Drain Connections (PDCs)

• Minor System Performance – Existing Conditions

– Design Rainfall – Design Flow Rates – Runoff from External Areas – Minor System Capacity Analysis Results

• Major Overland Flow Rates

Current Design Criteria

• Review of current design standards - Township of East Zorra-

Tavistock Municipal Servicing Standards, Urban and Rural Developments

• Compare existing system to the current day design standards

Design Rainfall

• 1:5 year storm (current design standard for minor system)
• 1:10 year storm (current design standard for trunk storm sewers)

Minor System Performance – Existing Conditions

Design Flow Rates

• Determined using the Rational Method and current Township

Development Standards

• Additional allowance of 10% added to account for PDCs and

infiltration flows Runoff from External Areas

• Tavistock receives overland storm runoff from areas beyond the

village limits

Cont’d Minor System Performance – Existing Conditions

Minor System Capacity Analysis

• Each length of storm sewer pipe was considered in the analysis
• While parts of the existing system does not meet the current

day design standards, the system may have met or exceeded the design standards in place at the time of construction

Major Overland Flow Routes

• Major overland flow routes generally follow the path of

Municipal Drains that have been constructed

• Flow paths have been established along the road system of the

newer residential subdivisions

• Sections of the overland flow routes are unable to accommodate

the major design storm

ALTERNATIVE IMPROVEMENT MEASURES

• Alternative 1 – Do Nothing
• Alternative 2 – Storm Sewer Replacement
• Alternative 3 – Policy Review and Update
• Alternative 4 – Lot Level Controls
• Alternative 5 – Conveyance Improvement Measures
• Alternative 6 – Storage Facilities / Stormwater Management

Alternative 1 – Do Nothing

• Leave the existing storm system as is
• Does not meet the current study objective and flooding would

not be reduced within Tavistock

Alternative 2 – Storm Sewer Replacement

• Replacement of all local storm sewers unable to convey the

design storm

• Help alleviate some of the stresses on the storm sewer network
• The storm sewer replacement alternative would not eliminate

surface flooding and/or residential basement flooding

Alternative 3 – Policy Review and Update

• The Township’s Development Standards are on par with other

municipalities of the same size

• Minor changes to the development standards will aid in

reducing/preventing any flooding in future development areas

Alternative 4 – Lot Level Controls

Storage Controls

• Rear yard storage, Parking lot storage, Direct roof leaders to

rain barrels Infiltration Controls

• Direct roof leaders to rear yard ponding area or soakaway pits,

infiltration trenches, and vegetated buffers along flow paths PDC Disconnection

• Prevent gravity PDC, and require them to be constructed with

Township Development Standards

Alterative 5 – Conveyance Improvement Measures

Sewers

• Trunks sized to accommodate the 1:10 year storm
• Restrictor plates in catchbasins to control water entering storm

system Overland Flow

• More water may remain on the surface due to the restrictor

plates, therefore overland flow routes must allow continuous positive drainage away from buildings and to an acceptable

• utlet

Alternative 6 – Storage Facilities / Stormwater Management

• Effective option to help detain, store and control the outlet

flow of the stormwater

• Two detention facilities are anticipated to provide adequate

storage capacity for external drainage coming from the north and northwest of the village

Evaluation of Criteria

Socio-Economic/Cultural Environment

• Public acceptance
• Land Requirements
• Compatibility with Surrounding Land

Uses

• Heritage Resources
• Effects on safety
• Temporary Construction Impacts (Dust,

Noise, Vibration, detours, loss of business) Financial Factors

• Estimated Capital Costs
• Estimated Operation & Maintenance

Costs Natural Environment

• Designated Sites/Species
• Water Quality and Quantity
• Floodplain Lands
• Terrestrial Habitat
• Aquatic Habitat

Technical Factors

• Technical practicability
• Topographic considerations
• Reduction in flooding
• Effects on downstream users
• Effects on upstream developments
• Approvals/Permits

PREFERRED ALTERNATIVE

The preferred alterative is the combination of the following:

• Policy Changes – Alternative 3
• Lot Level Controls – Alternative 4
• Conveyance – Alternative 5
• Storage – Alternative 6