evaluating release rates for specific watersheds in …...development impact on hydrology 24 three...

Evaluating Release Rates for Specific

Watersheds in Cook County

ASFPM

May 4, 2017

MWRD (District) Overview

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MWRD (District) Overview

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• Independent Unit of Gov.– Established in 1889

– Special-purpose district

– Taxing body

– Not part of City of Chicago

• Statutory Responsibilities– Wastewater Reclamation

– Stormwater Management

• Demographics– 91% of Cook County

– 883 square miles

– 126 municipalities

– 5.25 million people

Reversal of the Chicago River

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Reversal of the Chicago River

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7 Water Reclamation Plants(including one of the worlds largest)

~ 554 Miles of Interceptors~ 109 Miles of Deep Tunnels~ 10.6 Billion Gallons of CSO Storage

Includes Thornton Reservoir online in 2015

Tunnel and Reservoir Plan (TARP)

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Reservoir

ConstructionMainstream

Pump Station

Summary of MWRD Facilities

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McCook Reservoir Phase I - 3.5 BG Online in 2017Phase 2 - 6.5 BG Online in 2029

Watershed Management Ordinance

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Watershed Management Ordinance (WMO) became effective May 1, 2014

• Applies to all development within the boundaries of Cook County, Illinois, and qualified sewer construction within the District’s corporate boundaries or service agreement areas

• Components which are regulated under the WMO include:

• Qualified Sewer Construction

• Drainage and Detention

• Volume Control

• Floodplain Management

• Isolated Wetland Protection

• Riparian Environment Protection

• Soil Erosion and Sediment Control

• Provides uniform stormwater management regulations to prevent future commercial, municipal, and residential development and redevelopment projects from exacerbating flooding and protects environmentally sensitive areas

Watershed Specific Release Rate Study

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How much Stormwater Detention?

A matter of perspective…

Floodplain regulator

Private Land Developer


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The NIPC Study

• Recommendations• Stormwater detention volume should be computed

using a hydrograph method• The modified rational method should not be used

for stormwater detention design• Bulletin-70 rainfall data should be used• Release rates should limit stormwater discharges:

• 2-year release rate of 0.04 cfs/acre• 100-year release rate of 0.15 cfs/acre

• A larger watershed should be studied

Upper Salt Creek Watershed


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Collar County Release Rates(100-Year Detention Requirements)

CountyRelease Rate

(cfs/acre)Methodology

Original Adoption Date

Lake 0.15 Hydrograph 10/18/1992

McHenry 0.15 Hydrograph 1/20/2004

Will 0.15Hydrograph &

Modified Rational Method

1/1/2004

DuPage 0.10 Hydrograph 9/24/1991


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Public Comment Release Rate ConcernsInitial WMO Ordinance Draft Prior to 2014

• Initially: 0.30 cfs/ac, decreasing to 0.15cfs/ac after 5-years

• Provides transition period to 0.15 cfs/acre

Comments:• “Serious concerns over the potential negative impacts to development and

redevelopment due to increased cost”

• “Reasonable compromise”

• “This will put Cook County at a competitive disadvantage”

• “Make no further compromises on release rates”

• “Water quality and erosion control must improve, proper release rates based on science are a critical part of the WMO”


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Final WMO Release Rate Decisions WMO Development 2014

Staff Recommendation:

During First Five Years of Implementation:• SPO Average Historical Release Rate at 0.30 cfs/ac• Investigate Watershed Specific Release Rates• Implement offsite detention “trading”• Learn from experience with permit issuance and variance requests

After Five Years of WMO implementation:• Watershed Specific Release Rates if possible to determine and greater

than 0.15 cfs/acreor

• 0.15 cfs/ac default release rate

Overview of ISWS

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Illinois State Water Survey

Coordinated Hazard Assessment and Mapping

Program

• State Research Agency• 1895- started as part of the Chemistry

Department at University of Illinois• 1917- State Department Registration

and Education• Late 1970s- Illinois Department of

Natural Resources• 2008- Prairie Research Institute,

University of Illinois

• Research topics• Atmosphere • Climate Change/Modeling • Weather Impacts• Groundwater• Surface Water• Water quality• Water supply planning• Floodplains/ Coordinated Hazards

Assessment and Mapping program (CTP with FEMA)

Two Phases

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Phase I • Evaluate two pilot study areas

• Develop streamlined methodology and set of assumptions

• Evaluate release rates for pilot study areas

Phase II

• Use same methodology as Phase I

• Determine release rates for watersheds under WMO regulation

Upper Salt Creek

Stony Creek

Two Study Areas

Basis of Methodology

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Future Condition:

Increased Development

WMO Requirement

Base Condition:

DWP H&H

with some updates

Future Development Scenario

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Based on best available data• Historical Land Use Change

• GoTo2040 Population Projections, CMAP

Sensitivity analysis

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Model versions completed to evaluate the method as a release rate planning tool:

Development impact on hydrology

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Three ways future development impacts hydrology:

1. Release rate compared to existing runoff rate

2. Watershed timing

3. Increased runoff volume / restrictive structures

Pre-Development

Runoff

Urbanized Runoff

Detention Outlet Flow

Stony Creek Results

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Future scenario with 0.3cfs/ac

Upper Salt Creek Results

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Future scenario with 0.15cfs/ac compared to the base conditions


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Impact/Selection Criteria 0.15 cfs/ac

0.20 cfs/ac

0.25 cfs/ac

0.30 cfs/ac

Percentage of stream length with increase in peak WSEL>0.1’

0.7% 0.8% 1.9% 28.5%

Maximum reservoir WSEl change (ft)

1.25 1.25 1.26 1.31

Increase in reservoir maximum XS from 0.15 cfs/ac release rate(ft)

-- 0.18 0.87 1.31

Maximum XS WSEl change (ft) 0.72 0.72 0.87 1.31

Increase in reservoir maximum XS from 0.15 cfs/ac release rate (ft)

-- 0.19 0.87 1.31

What does this all mean?

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Cook County Release Rate Assessment lessons learned:

1. There is benefit to variation of release rate requirement across watersheds.

2. We don’t need to model every last acre.

3. Further modeling is required to determine release rates for the entire county and will be completed in Phase II.

Contact Information

Daniel Feltes, P.E.

Principal Civil Engineer

Local Sewer Systems Section

MWRDGC

111 E. Erie St., Chicago, IL 60611

(312) 751-3247

[email protected]

Amanda Flegel, P.E., CFM

Illinois State Water Survey

2204 Griffith Dr, Champaign, IL 61820

(217) 300-3468

[email protected]

evaluating release rates for specific watersheds in …...development impact on hydrology 24 three...

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