Mud Creek Cumulative Impact Assessment

Class Environmental Assessment On-line Open House

November 1 – December 2, 2019

Mud Cumulative Impact Assessment

Class Environmental AssessmentOn-line Open House

November 1 – December 2, 2019

Creek

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Welcome

The City of Ottawa is undertaking a Municipal Class Environmental Assessment (Class EA) study to determine the preferred measures to restore and maintain the three kilometre reach of Mud Creek between Pagé Road and Renaud Road.

This on-line Open House reviews: • Study background and project need; • Purpose of the Class EA process; • Existing environmental conditions; • Project alternatives and preferred solution; • Opportunities for public input; and • Next steps and project schedule.

Photo of Mud Creek adjacent to Renaud Road

Photo of Mud Creek at near eastern Renaud Road crossing

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Background

The City of Ottawa is undertaking a Municipal Class Environmental Assessment (Class EA) that is studying the cumulative impact of existing and planned development on changes that could be experienced in the flow regime of Mud Creek, downstream from the East Urban Community Mixed Use Centre.

This study is required to develop, evaluate, and recommend an optimal combination of at-source stormwater management controls, conventional end-of-pipe controls, and the scope of in-stream works required to improve existing erosion sites, and to establish a stable creek corridor as urbanization of the Mud Creek watershed continues over the next 10-20 years.

Mud Creek Subwatershed (~1,750 ha)

Area Diverted to Mud Creek From McKinnon’s Creek (~100 ha)

Mud Creek Study Area

The study is following Schedule B of the Municipal Class Environmental Assessment which will identify preferred alternatives and a conceptual design of the recommended in-stream improvements.

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Mud Creek existing conditions & future land use – East Urban Community Mixed Use Centre

For information on existing conditions of Mud Creek, please see the City Stream Watch -Mud Creek 2018 Catchment Report - Rideau Valley Conservation Authority available at the following webpage:

https://www.rvca.ca/media/k2/attachments/CSW2018_MUD.pdf

For information related to the East Urban Community Mixed Use Centre – Community Design Plan, please refer to the following webpage that includes consultation related to future development, environmental planning and proposed servicing in the upper Mud Creek watershed:

https://ottawa.ca/en/city-hall/public-engagement/projects/east-urban-community-mixed-use-centre-community-design-plan

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Cumulative Impact Assessment of existing and planned development on Mud Creek channel erosion: Erosion Threshold Analysis

• A detailed investigation of erosion conditions at 9 sites in the Mud Creek watershed was completed in 2013, including four sites in the Cumulative Impact Study area.

• The Cumulative Impact Study assessed how future urban runoff could affect erosion conditions at Sites 6-9.

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2 7

4 5

8 9

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CIS study area

This figure shows the nine erosion locations investigated along Mud Creek in “Establishing Static and Unit Thresholds for Erosion, Mud and McEwan Creeks” for the National Capital Commission, by JTB Environmental Systems, 2013. Findings at sites 6-9 informed decision making in this study.

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Erosion Threshold Analysis Approach

Computer models were created to represent runoff rates and conditions from the existing land use and road network, and for future build-out of the Mud Creek watershed (routed through East Urban Community stormwater management Ponds 1, 2, and 3) including planned road projects.

Hourly flow rates were computed for existing and future development conditions using a 25-year record of observed rainfall conditions (1975-2000). The resulting 25-year computed existing and future flow rates were compared against critical flow rates required to cause erosion of small, medium and large sized particles in Mud Creek identified in the 2013 erosion study at Sites 6-9.

The total number of hours where computed flows exceeded the critical flow rates over the 25-year period based on the existing and future development conditions were tallied to gauge the potential increased risk of channel erosion due to future urbanization.

Erosion Threshold Analysis

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Findings

• Under existing conditions, smaller soil particles throughout the study area are already highly susceptible to mobilization, and conditions will worsen in the future if corrective measures are not taken.

• Under existing conditions, the lower reach of the study area (downstream of Site 6) is susceptible to mobilization of particles of all sizes (this is related to historical development with minimal stormwater management controls, and detrimental agricultural land use practices).

• Urbanization of the upper watershed will add to existing instabilities in the lower reach, but the greatest impact of future development on the flow regime will be experienced in the reaches upstream of Site 6, where a sharp increase in the frequency that medium size particles will be mobilized will be experienced, if corrective measures are not taken.

The change in land use from rural / agricultural to urban in the upper watershed (and the sediment control provided in East Urban Community stormwater management Pond 1) will result in a reduction in the current sediment supply to Mud Creek.

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Assessment of Alternative Erosion Control Measures

Alternatives Evaluated:

1. Increase the level of stormwater control provided in the East Urban Community Stormwater Management ponds;

2. Implement Low Impact Development mitigation measures to reduce the post-development runoff volume generated in the East Urban Community Mixed Use Centre (Runoff Volume Controls (RVCs) of 5mm & 10mm were assessed);

3. Implement alternative in-stream protection measures (Channel reinforcement, Natural Channel Design, or a combination thereof).

Assessment of Alternative Erosion Control Measures

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Findings

Alternative 1 - Increase controls in East Urban Community Stormwater Management Ponds

• Limited space is available to expand stormwater management ponds.

• The coincident timing of the increased period of extended detention discharges from enlarging the East Urban Community stormwater management ponds results in increased flow rates in the Study Area and durations that exceed the erosion threshold rates.

Alternative 2 - Use of Low Impact Development measures for runoff volume control

Opportunity to implement Low Impact Development measures to reduce runoff volume in the East Urban Community Mixed Use Centre is challenging due to:

• high groundwater levels (with shallow perched water table) restricting the effectiveness of Low Impact Development measure (less than 1 m clearance from seasonal high-water table)

• low permeability glaciomarine clay/silt soils limit infiltration potential

• Industrial Areas – deemed “Higher risk activities” where use of LIDs should be avoided

Computer modelling of runoff volume controls showed little benefit would be realized by implementing Low Impact Development measures to reduce the duration of flow rates exceeding erosion thresholds in the Study Area.

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In-stream Protection Alternatives

Approach 1 - Channel Reconfiguration

Reach 1 Reach 2

Reach 3

Reach 4

Reach 1 – Regrade slopes; increase floodplain width; create 10m buffer

Reach 2 – Move Mud Creek away from Renaud Road embankment and establish in new 30m corridor

Reach 3 – Regrade channel slopes; stabilize slopes with plantings; increase floodplain width in areas; add 10m buffer

Reach 4 – Regrade slopes; increase floodplain width; create 10m buffer

Approach 1 included reconfiguration measures in locations with the greatest existing erosion problems in the study area, but excluded improvements downstream of Reach 1 and upstream of Reach 4

In-stream Protection Alternatives

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Approach 2 – Reinforce Existing Channel

Approach 2 would involve the placement of rock on the channel bed and banks of Mud Creek throughout the study area, such as illustrated in the photo above.

In-stream Protection Alternatives

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Approach 3 - Hybrid (Select channel reconfiguration and channel reinforcement)

Reach 1 Reach 2

Reinforce existing channel

Reach 1 – Regrade slopes; increase floodplain width; create 10m buffer

Reach 2 – Move Mud Creek away from Renaud Road embankment and establish in new 30m corridor

Channel bed and banks downstream of Reach 1 and upstream of Reach 2 reinforced per Approach 2

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Evaluation - Instream Work Alternatives Approach Advantages Disadvantages Cost

($Million) Rank 1) Channel

Reconfiguration • Natural solution

which meets Greens Creek Watershed Goals and Objectives

• Provides resilience and storage which helps downstream

• Requires land • Some creek sections

untreated and vulnerable

• Highest cost

$5.7 3

2) Channel Reinforcement

• Requires little if any additional land

• Entire creek section of interest treated

• Least costly approach

• Hardening solution • Transfers problems

downstream to less protected areas

$3.4 2

3) Hybrid • Entire creek section of interest treated

• More cost effective than channel reconfiguration alone

• Targeted approach • Can be done in

stages

• Requires sensitive design

• Requires land

$6.1 1

==>

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Mud Creek Cumulative Impact Study Recommended erosion control approach

1. Implement hybrid in-stream protection works- Combination of channel reinforcement and targeted channel reconfiguration to be implemented

as development of East Urban Community Mixed Use Centre proceeds- Mud Creek in-stream protection works project to be added to Area-specific stormwater

management development charge bylaw- Proposed share of costs of in-stream works between City (40%) and East Urban Community

Developers (60%) to be based on proportion of existing vs. ultimate % watershed impervious lands.

2. Implement Runoff Volume Control measures in East Urban Community where feasible:- Innes Park Woods to be protected (including buffer): area accounts for about one-half of

predevelopment infiltration volume in East Urban Community Mixed Use Centre- tree planting program to be employed in parks- infiltration trenches to be installed in backyards- additional wider Rights of Way (~10%) to be included in Draft Plans for healthy street trees

Community Design Plan / Master Servicing Study will identify these requirements and be included as conditions of development in future Planning Act approvals. Planning of in-stream protection works downstream of Cumulative Impact Study area to proceed in near future.

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Questionnaire Questions and comments on the Cumulative Impact Study findings & recommendations are welcome. Prior to recommending proposed actions to Council for implementation, we would appreciate receiving your feedback on the Study’s findings and recommendations, including:

1. Do you agree with the recommendation to use reduce the scope of application of Low Impact Development measures due to limited in-stream benefit, shallow groundwater conditions and tight soils? Yes / No; comments.

2. Do you agree with the recommended scope of in-stream works? Yes / No; comments.

3. Do you agree with the proposed cost-sharing of the in-stream works (43% City and 57% future development / development charges)? Yes / No; comments.

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Opportunities for Public Input

▪ On-line Open House (November 1 to December 2, 2019);

▪ East Urban Community Mixed Use Centre Community Design Plan report to Planning Committee (early 2020)

▪ Notice of completion (early 2020)

Next Steps

▪ Confirm or revise preferred solution based on public input and agency comments;

▪ Cumulative Impact Study approval by Council as supporting document for the East Urban Community Mixed Use Centre Community Design Plan early 2020;

▪ Post Notice of Completion for 30 day public review period (early 2020);

▪ Detailed design/approvals (2021-2022);

▪ Staged Construction of Project (>2023);

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Thank you

▪ Please provide your comments by mail/fax/email to the contact below on or before December 2, 2019

Ted Cooper, M.A.Sc., P. Eng.

Project Manager

Asset Management

City of Ottawa

110 Laurier Avenue West, 3rd Floor

Ottawa, ON K1P 1J1

Phone: 613-580-2424 ext. 13116

E-mail: ted.cooper@Ottawa.ca

Fax: 613-580-2578