Evaluating Release Rates for Specific
Watersheds in Cook County
ASFPM
May 4, 2017
MWRD (District) Overview
2
MWRD (District) Overview
3
• 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
4
Reversal of the Chicago River
5
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)
6
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
Reservoir
ConstructionMainstream
Pump Station
Summary of MWRD Facilities
7
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
McCook Reservoir Phase I - 3.5 BG Online in 2017Phase 2 - 6.5 BG Online in 2029
Watershed Management Ordinance
8
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
9
How much Stormwater Detention?
A matter of perspective…
Floodplain regulator
Private Land Developer
Watershed Specific Release Rate Study
10
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
Watershed Specific Release Rate Study
12
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
Watershed Specific Release Rate Study
13
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”
Watershed Specific Release Rate Study
14
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
15
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
17
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
19
Future Condition:
Increased Development
WMO Requirement
Base Condition:
DWP H&H
with some updates
Future Development Scenario
22
Based on best available data• Historical Land Use Change
• GoTo2040 Population Projections, CMAP
Sensitivity analysis
23
Model versions completed to evaluate the method as a release rate planning tool:
Development impact on hydrology
24
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
25
Future scenario with 0.3cfs/ac
Upper Salt Creek Results
26
Future scenario with 0.15cfs/ac compared to the base conditions
Upper Salt Creek Results
27
Future scenario with 0.20cfs/ac compared to the base conditions
Upper Salt Creek Results
28
Future scenario with 0.25cfs/ac compared to the base conditions
Upper Salt Creek Results
29
Future scenario with 0.30cfs/ac compared to the base conditions
Upper Salt Creek Results
30
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?
31
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
Amanda Flegel, P.E., CFM
Illinois State Water Survey
2204 Griffith Dr, Champaign, IL 61820
(217) 300-3468