[PPT] - Stormwater Master Plan Presentation to South Gateway Neighborhood PowerPoint Presentation

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Updating Salem’s

Stormwater Master Plan

Presentation to South Gateway Neighborhood Association

October 10, 2019

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Introductions

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Robert Chandler, PhD, PE Assistant Public Works Director Glenn Davis, PE, CFM Chief Development Engineer Hans Hadley, PE, CFM WEST Consultants, Inc. Robin Dalke, CFM Floodplain Program Manager

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“The Walhamette River from a Mountain” by Paul Kane, 1847 (Royal Ontario Museum, Toronto)

One cannot start with a river valley…

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Google earth (Imagery Date 12/13/2015)

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replace it with a major metropolitan area…

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December 1964 (Photo Credit: Statesman Journal)

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…and not irrevocably alter how the landscape responds to rainfall.

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Happening….

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Flooding => Historic/Future New development => Continuous Creeks & habitat impacts => Historic/Future Stormwater Master Plan => 2020 Battle Creek Park Master Plan => 2020 Plans, policies, procedures => Ongoing

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Agenda

How is the City involved in this basin?

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➢ What we’re doing now – Examples

⚫ Community Rating System (CRS) ⚫ Floodplain Management ⚫ Stormwater Programs

➢ Battle Creek Basin Plan

⚫ Data & modeling methodology and results ⚫ Detention & other measures to reduce flood risks

➢ Questions/Discussion ➢ Next Steps

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Floodplain/Stormwater

➢ Community Rating System (CRS)

⚫ 2008 – Class 8 (10% reduction) ⚫ 2009 – Class 7 (15%) ⚫ 2012 – Class 6 (20%) ⚫ 2016 – Class 5 (25%) – 1 of 3 Best in Oregon ⚫ 2020-21 – Class 3 Goal (35%) – Top 10 Nationwide

➢ Floodplain Stormwater

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Floodplain/Stormwater

Key Elements:

➢ Floodplain management plan

⚫

41 Action Items in 2018 Plan

Preventive Activities (12)
Property Protection (5)
Natural Resource Protection (7)
Emergency Services Measures (8)
Structural Projects (3)
Public Information (6)

⚫

1st Year Annual Review

23 items complete or on-going
18 items remaining

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Floodplain/Stormwater

Stormwater Program

➢ Stormwater Management Plan

⚫ 66 Best Management Practices

➢ Operations and Maintenance ➢ Flood Warning System ➢ Development Codes/Standards ➢ Stormwater Master Plan

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Stormwater Master Plan

Assumptions/ Policies Flood Simulations Improvement Plans Financial Strategies

Stormwater Master Plan

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Assumptions/Policies

➢ Based on Existing Land Use Laws

⚫ Development rights within UGB ⚫ Plan does not establish new regulations

➢ Maximize Cost Effectiveness

⚫ Establishes total costs needed ⚫ Does not generate new revenue

➢ Minimize Flood Damage

⚫ Project prioritization

➢ Downstream Effects

⚫ Does not merely move problems downstream

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Hydrologic Model

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Model Calibration/Verification

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January 2012 Storm Calibration (~100-yr 48-hr / ~50-yr 72-hr)

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January 2012 Storm Calibration (~100-yr 48-hr / ~50-yr 72-hr)

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Design Storm Development

(Normalized to 1-inch depth)

SCS Type 1A (24-hr) January 2012 (72-hr) November 1996 (48-hr) February 1996 (72-hr)

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Storm Duration & Distribution Selection

24-hr = 5.1 inches 48-hr = 7.2 inches 72-hr = 8.6 inches

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Existing Development Conditions

100-yr (48-hr) Storm

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Existing Development Conditions

100-yr (48-hr) Storm

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Existing Development Conditions

100-yr (48-hr) Storm

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Full Build-out Assumptions

Primary Subbasin Name Existing % Impervious Full Build-Out % Impervious Battle Creek (Upstream of I-5) 12 21 Jory Creek 5 14 Powell Creek 7 25 Scotch Creek 11 17 Waln Creek 31 42

Based on land use classification in July 2015 Salem Area Comprehensive Plan
City’s green infrastructure requirements not considered (worst-case)
Existing impervious surface = 12%, Full build-out impervious surface = 21%
Between 14% and 19% increase in peak basin discharges

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Full Build-out Conditions

100-yr (48-hr) Storm

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Full Build-out Conditions

100-yr (48-hr) Storm

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Full Build-out Conditions

100-yr (48-hr) Storm

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Project No. BA-BC2

Description: Project creates two large storage areas downstream of the Waln Creek-Battle Creek confluence and installs two floodgates to retain water before reentering Battle Creek. A combined 19.5 acres of floodplain grading is split into a 12 acre parcel north of Battle Creek and a 7.5 acre parcel south of Battle Creek.

Cost Estimate = $3,140,000 Annual Maintenance = $15,900

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Project No. BA-BC3

Description: The project includes approximately 1,000 linear feet of Battle Creek channel grading to increase the channel size and create overflow benches similar to Waln Creek just upstream of the Battle Creek confluence.

Cost Estimate = $330,000 Annual Maintenance = $2,200

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Project No. BA-BC4

Description: The project includes approximately 1,800 linear feet of Battle Creek channel grading to increase the channel size and create

verflow benches similar to Waln Creek. Properties and easements will

need to be acquired by the City to provide room for channel grading. Cost Estimate = $1,000,000 + Real Estate Costs Annual Maintenance = $2,900

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Project No. BA-BC5

Description: The project includes approximately 1,300 linear feet of Battle Creek channel grading to increase the channel size and creates

verflow benches similar to Waln Creek. Easements will need to be

acquired by the City to provide room for channel grading. Cost Estimate = $290,000 + Real Estate Costs Annual Maintenance = $1,600

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