8 1/2 Mile Relief Drain Drainage District Green

8 1/2 Mile Relief Drain Drainage District Green Infrastructure Analysis

Project No. 130620 March 24, 2017

REVIEW DRAFT

Fishbeck, Thompson, Carr & Huber, Inc. engineers | scientists | architects | constructors

8 1/2 Mile Relief Drain Drainage District Green Infrastructure Analysis

Prepared For: Office of Macomb County Public Works Commissioner

Clinton Township, Michigan

March 24, 2017 Project No. 130620

Review Draft

Table of Contents

1.0 EXECUTIVE SUMMARY ...................................................................................................................................1

2.0 INTRODUCTION .............................................................................................................................................1 2.1 8 1/2 MILE RELIEF DRAIN DRAINAGE DISTRICT ................................................................................2 2.2 CHAPATON RETENTION TREATMENT BASIN ....................................................................................4

3.0 DATA COLLECTION .........................................................................................................................................4 3.1 SOILS DATA .......................................................................................................................................4 3.2 SEMCOG LAND COVER ANALYSIS .....................................................................................................5

4.0 GREEN INFRASTRUCTURE OPPORTUNITIES...................................................................................................6 4.1 GREEN INFRASTRUCTURE OPTIONS .................................................................................................6

4.1.1 TREES ...................................................................................................................................6 4.1.2 BIO-RETENTION ...................................................................................................................7 4.1.3 UNDERGROUND DETENTION ..............................................................................................7 4.1.4 GREEN ROOFS ......................................................................................................................7

4.2 COMMUNITY INVOLVEMENT ...........................................................................................................7

5.0 8 1/2 MILE RELIEF DRAIN PERFORMANCE .....................................................................................................8 5.1 HYDRAULIC MODEL ANALYSIS ..........................................................................................................8 5.2 MODEL DEVELOPMENT OF BEST MANAGEMENT PRACTICES ..........................................................9

5.2.1 TREES ...................................................................................................................................9 5.2.2 BIO-RETENTION ...................................................................................................................9 5.2.3 UNDERGROUND DETENTION ..............................................................................................9 5.2.4 GREEN ROOF..................................................................................................................... 10

5.3 STORMWATER WATERSHED REDUCTION SCOPING TOOL ............................................................ 10 5.4 MODEL APPROACH AND RESULTS ................................................................................................. 11

6.0 RECOMMENDATIONS ................................................................................................................................. 12 List of Figures Figure 1 – 8 1/2 Mile Relief Drain Drainage District Map ...........................................................................................3 Figure 2 – Soil Hydrologic Group ................................................................................................................................5 Figure 3 – Screenshot of EPA SWMM LID Control Editor ...........................................................................................8 Figure 4 – Representative Hydrograph with and without Green Infrastructure..................................................... 12 List of Tables Table 1 – Hydraulic Model Results .............................................................................................................................4 Table 2 – Land Cover Summary ..................................................................................................................................5 Table 3 – Land Use Summary .....................................................................................................................................6 Table 4 – BMP Summary: 2-Year, 24-Hour Event .................................................................................................... 11 List of Appendices Appendix 1 SEMCOG Land Cover Analysis Appendix 2 Sub-Catchment BMP Summary Appendix 3 Stormwater Watershed Reduction Scoping Tool Z:\2013\130620\WORK\REPT\GI STUDY\GREEN INFRASTRUCTURE PHASE II REPORT\RPT_GI ANAYLSIS_2017_0324_DFT.DOCX i

Table of Contents

List of Abbreviations/Acronyms 8DR 8 1/2 Mile Relief Drain 9EB 9 Mile Emergency Bypass BMP best management practices cfs cubic feet per second CHA-PS Chapaton Pump Station CHA-RTB Chapaton Retention Treatment Basin Drainage District 8 1/2 Mile Relief Drain Drainage District FTCH Fishbeck, Thompson, Carr & Huber, Inc. GIS Geographic Information System GLWA Great Lakes Water Authority Gpm gallon(s) per minute LID Low Impact Development MG million gallon(s) MS4 Municipal Storm Sewer System NRCS Natural Resources Conservation Service OMCPWC Office of Macomb County Public Works Commissioner SAW Stormwater, Asset Management, and Wastewater SEMCOG Southeast Michigan Council of Governments SWMM Storm Water Management Model USEPA U.S. Environmental Protection Agency

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1.0 EXECUTIVE SUMMARY This green infrastructure analysis was completed as a component of the Office of Macomb County Public Works Commissioner (OMCPWC) Stormwater, Asset Management, and Wastewater (SAW) Program Grant, and focuses on assessing the benefits of installing green infrastructure in the 8 1/2 Mile Relief Drain Drainage District (Drainage District). This report evaluates the implementation of green infrastructure techniques within the Drainage District for the purpose of reducing the frequency and volume of treated discharges into Lake St. Clair from the Chapaton Retention Treatment Basin (CHA-RTB).

Land use, land owner, and soils data were collected to evaluate the most viable green infrastructure techniques that may be utilized within the Drainage District. The Drainage District is primarily single-family residential with soils that have low infiltration rates. Trees, bio-retention, underground detention, and green roof best management practices (BMPs) were chosen to be evaluated in this study for their ability to be retrofitted within the existing developments and transportation corridors within the Drainage District.

An existing calibrated hydraulic model of the Southeastern Macomb County Collection System was obtained and utilized to evaluate the impacts of implementing green infrastructure BMPs within the Drainage District with the goal of reducing stormwater runoff volume and delaying peak discharge into the 8 1/2 Mile Relief Drain (8DR).

Underground detention has been identified as the most effective BMP at lowering the peak discharge from the CHA-RTB due to the high impervious area treated to BMP size ratio. However, site locations for underground retention are limited to large commercial, industrial, and public properties, which are less prevalent within the Drainage District. Tree planting, however, could be completed more extensively throughout the Drainage District within private properties and transportation corridors. Implementing green infrastructure should be considered as funding sources, including grants, become available. The stormwater reduction spreadsheet scoping tool that has been developed as part of this study should be utilized in future planning efforts to assist with identifying the potential benefits of implementing green infrastructure within the Drainage District.

2.0 INTRODUCTION The Drainage District serves the City of Eastpointe and the southern portion of the City of St. Clair Shores. The Drainage District consists of the following six facilities:

1. 8 1/2 Mile Relief Drain 2. 9 Mile Emergency Bypass (9EB) 3. Chapaton Pump Station (CHA-PS) 4. Chapaton Retention Treatment Basin 5. Chapaton East 6. Chapaton Canal Control Structure

The 8DR is considered a combined sewer. The sewer system upstream of the 8DR is mostly separated; however, both storm and sanitary sewers connect to the 8DR. There is currently no other outlet for the storm flows in this area.

The 8DR is lower than the Jefferson Interceptor; therefore, during dry weather flow, the CHA-PS is used to pump the flows from the 8DR into the Jefferson Interceptor which ultimately makes its way to the Great Lakes Water Authority (GLWA) Wastewater Treatment Plant. During wet weather events, the flows from the 8DR are pumped by the CHA-PS into the CHA-RTB for temporary storage and return to the Jefferson Interceptor, or for discharge into Lake St. Clair after receiving primary treatment.

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The CHA-RTB has capacity to store wet weather flow up to a 1-year, 1-hour design storm. Larger events result in treated discharges to Lake St. Clair.

This study has been prepared as a component of the OMCPWC SAW Program Grant and focuses on assessing the benefits of installing green infrastructure in the Drainage District. Green infrastructure techniques can be an effective way of reducing stormwater runoff into storm sewer and combined sewer systems. This report evaluates the implementation of green infrastructure techniques within the Drainage District for the purpose of reducing the frequency and volume of treated discharges into Lake St. Clair.

2.1 8 1/2 MILE RELIEF DRAIN DRAINAGE DISTRICT The Drainage District is roughly bounded by 9 Mile Road to the north, Lake St. Clair to the east, 8 Mile Road to the south, and Gratiot Avenue to the west, as depicted in Figure 1.

The Drainage District is a highly developed urban area that includes the cities of Eastpointe and St. Clair Shores, and includes approximately 2,300 acres (3.6 square miles). The Drainage District is predominantly residential, consisting of mostly single-family homes with an average lot size of 0.2 acres. Existing non-residential properties are generally occupied by churches, schools, parks, and commercial developments along the major roadways of Gratiot Avenue and Harper Avenue.

The Drainage District was previously modeled by others and has been broken down into 33 sub-catchments which represent smaller drainage areas with individual outlet points along the 8DR. Sub-catchments were delineated in this report from the inlet nodes in the hydraulic model and as-built drawings of the 8DR and georeferenced in the Geographic Information System (GIS). The 8DR and sub-catchment boundaries are illustrated in Figure 1. Sub-catchments were given a numerical ID between 1 and 33.


Figure 1 – 8 1/2 Mile Relief Drain Drainage District Map


2.2 CHAPATON RETENTION TREATMENT BASIN In dry weather, flow from the 8DR is pumped into the Jefferson Interceptor via the CHA-PS. The 9EB (part of the Southeast Macomb Sanitary District) discharges directly into the Jefferson Interceptor by gravity. During large wet weather events, flows from the 8DR are pumped into the CHA-RTB. Depending on the size of the rain event, flows from the 9EB are either sent directly to the Jefferson Interceptor, diverted by gravity to the CHA-RTB, or pumped into the CHA-RTB with flows from the 8DR. The 8DR is interconnected with the 9EB and provides relief to the 9EB under significant wet weather conditions.

A calibrated XP Storm Water Management Model (SWMM) hydraulic model of the Southeastern Macomb County Collection System was obtained from the OMCPWC. The model was used for this analysis with the understanding that it is a calibrated network and accurately depicts the performance of the Southeast Macomb Sewer System. No updates or calibrations to the model were performed as part of this study. The model includes the 8DR and 9EB, as well as tributary drainage areas from the north.

The 2-year, 24-hour event was used to quantify wet weather flow contributions to the CHA-RTB for this evaluation. This event was selected because it is generally the maximum design storm that green infrastructure techniques are most effective at mitigating. The calibrated hydraulic model utilizes the Natural Resources Conservation Service (NRCS) Type II rainfall distribution and Bulletin 71, Rainfall Atlas of the Midwest rainfall data equating to 2.26 inches of rainfall.

Table 1 summarizes total modeled volume and peak flows generated by the 8DR for the evaluated rainfall event. The total volume is nearly 2 times higher, and the peak discharge is 250 cubic feet per second (cfs) higher, for the 2-year, 24-hour storm compared to the 1-year, 1-hour storm. The green infrastructure projects proposed in this report will focus on storage and retention of stormwater runoff to mitigate the volume and peak discharges generated up to the 2-year, 24-hour event.

Table 1 – Hydraulic Model Results

1-Year, 1-Hour Rainfall (1.03-inch)

2-Year, 24-Hour Rainfall (2.26-inch)

8DR Peak Discharge (cfs) 1,016 1,266

8DR Total Volume (MG) 41 85

The following sections address the feasibility of BMPs in the Drainage District based on land use and soils data as well as the performance of selected green infrastructure techniques from a hydraulic model analysis.

3.0 DATA COLLECTION There are several factors that should be considered when incorporating green infrastructure into a drainage district. Land use, land owner information, and soils data were analyzed to determine which types of green infrastructure are feasible for the Drainage District as a whole, and to identify land use/land cover types at the sub-catchment level that are suitable for each BMP.

3.1 SOILS DATA Soils data for the Drainage District was downloaded from the NRCS soil survey. Figure 2 indicates each soil type within the Drainage District and the corresponding soil hydrologic group.


Figure 2 – Soil Hydrologic Group

Soil hydrologic groups are broken into Types A, B, C, and D based on runoff potential of the soil. Type A soils are typically sandy or gravely soils with high infiltration rates. Type D soils, on the opposite end of the range, typically consist of clayey soils with very slow infiltration rates. Types B and C soils, in the middle of the range, exhibit moderate and slow infiltration rates, respectively.

According to Figure 2, the Drainage District is composed of Type A/D, C/D, and D soils. Soil types with dual classes such as C/D represent the hydrologic soil group of the second letter, unless they are artificially drained through a tile drainage system. Tile drainage is common in agricultural areas which are not present in the Drainage District. Therefore, the entire Drainage District is best characterized as having a Type D soil which exhibits slow infiltration rates and high runoff potential. This indicates that underdrains would be appropriate for many green infrastructure techniques that incorporate infiltration measures to maintain the system’s performance.

3.2 SEMCOG LAND COVER ANALYSIS The Southeast Michigan Council of Governments (SEMCOG) provided an analysis of land cover for the Drainage District based on their inventory of geospatial data. Their analysis includes land use, land cover, right-of-way, and public and private properties for the entire Drainage District as shown in Appendix 1. Summary tables for land use and land cover are provided in Tables 2 and 3, respectively.

According to Table 2, approximately 50% of the total land cover is impervious surface from building structures or pavement.

Table 2 – Land Cover Summary Land Cover Area (Acres) Impervious Surfaces: Paved: Drain to Sewer 767 Open Space – Grass/Scattered Trees: Grass cover > 75% 637 Impervious Surfaces: Buildings/Structures 405 Trees: Grass/turf understory: Ground cover 50% - 75% 375 Trees: Impervious Understory 52 Trees: Grass/turf understory: Ground cover > 75% 25

Table 3 summarizes the land use types within the Drainage District. Land use in the Drainage District is primarily single-family residential, representing approximately 60% of the total land use area, and a large portion of the Drainage District is also taken up by transportation, communications, and utility corridors.


Only 52 acres within the Drainage District are publically owned by the City of Eastpointe, City of St. Clair Shores, Macomb County, or the State or Michigan. There are four public schools within the Drainage District which cover 19 of the 52 acres. There are often good opportunities to implement green infrastructure on publicly owned properties.

Table 3 – Land Use Summary Land Use Area (Acres) Single-Family Residential 1,370 Transportation/Communications/Utilities 596 Commercial 156 Governmental/Institutional 66 Multiple-Family Residential 51 Parks, Recreation, and Open Space 21 Industrial 5

4.0 GREEN INFRASTRUCTURE OPPORTUNITIES 4.1 GREEN INFRASTRUCTURE OPTIONS The Drainage District is almost entirely developed with the majority being single-family residential developments. Therefore, green infrastructure opportunities are primarily going to be retrofitted into the existing developments and within transportation corridors, or installed as part of redevelopment projects. Although many green infrastructure techniques are available, four BMPs were selected for evaluation. These four best represent the measures most likely to be implemented within the Drainage District; they include:

• Trees. • Bio-Retention. • Underground Detention. • Green Roofs.

For a comprehensive list of available green infrastructure techniques please reference SEMCOG’s Low Impact Development Manual for Michigan.

4.1.1 TREES Planting trees is an easy way to intercept rainfall from entering the drainage system. Tree planting for storm water runoff reduction is an option currently being implemented by other community organizations, such as the Greening of Detroit. Macomb County has actively been pursuing grants for tree planting and has established a program that aids residents with the purchase of trees to plant both within the right-of-way and on private properties. The existing tree cover is less than 20% of the total Drainage District area and significant opportunities exist for planting of additional trees.


According to the U.S. Department of Agriculture Center for Watershed Protection, an increase of tree canopy cover by 10% could result in a 2% to 5% reduction in stormwater runoff for rainfall events that are 2-year, 24-hours, or less.

Trees provide several other services in addition to stormwater management. In terms of air quality, trees adsorb odors and pollutant gases and provide oxygen. Similarly, trees mitigate climate change impacts by removing and storing excess carbon dioxide. According to TreePeople.org, neighborhoods with tree lined streets and properties are aesthetically more appealing which drives up property values and increases business traffic.

4.1.2 BIO-RETENTION Bio-retention covers engineered vegetated infiltration systems for commercial site development, rain gardens, and bio-swales. Opportunities exist for construction of these measures both on a small scale for a residential lot, but also on a larger scale for parks, churches, schools, and transportation corridors. Although these measures are somewhat limited in their ability to infiltrate within the Drainage District due to the clayey soils, they are further aided by plant uptake of water resulting in a moderate amount of volume reduction. For the purposes of this study, it is assumed engineered bio-retention systems would incorporate an underdrain for proper function due to the underlying soil conditions.

4.1.3 UNDERGROUND DETENTION Underground detention systems evaluated as part of this study may include pervious pavement systems, underground storage chambers, and stone infiltration systems. Often, these systems incorporate infiltration into the underlying soil, but due to the limited infiltration capacity of the soil in the area, any design of underground detention should include an underdrain for proper function. Underground detention is suitable for larger properties that contribute runoff from parking lots and rooftops, such as commercial developments, schools, parks, institutional, or government owned parcels. Commercial and industrial sites with expansive parking lot areas are also considered candidate sites for underground detention.

4.1.4 GREEN ROOFS Green roofs involve the placement of a vegetated roof, typically sedum, on a building. These systems rely on plant uptake for volume storage and reduction. There are several large building complexes within the Drainage District with potential space to accommodate a green roof. Therefore, this BMP could be considered to capture rainfall from larger buildings such as schools, churches, libraries, government centers, and commercial/industrial complexes.

4.2 COMMUNITY INVOLVEMENT As part of this study, a team consisting of representatives from OMCPWC, Macomb County Planning and Economic Development, and Fishbeck, Thompson, Carr & Huber, Inc. (FTCH) met with the Cities of St. Clair Shores and Eastpointe to discuss the potential implementation of green infrastructure within their communities. Each community expressed an openness to implementing various measures when they believe it is economically feasible and reduces the impact of stormwater. The implementation of these measures can be supported by available and future grant programs. In addition, redevelopment projects will need to meet the stormwater requirements set forth in the communities and/or OMCPWC stormwater standards. These standards include the


channel protection requirement, which requires that any increase in discharge volume and rate must be mitigated when a site of one acre or greater is developed or redeveloped, up to a 2-year, 24-hour storm event. These standards are most commonly met through the use of green infrastructure techniques and also conform to the Municipal Storm Sewer System (MS4) permit requirements.

5.0 8 1/2 MILE RELIEF DRAIN PERFORMANCE 5.1 HYDRAULIC MODEL ANALYSIS The green infrastructure model analysis was completed using the calibrated XP SWMM and U.S. Environmental Protection Agency (USEPA) SWMM. The XP SWMM was provided to FTCH by OMCPWC, and was utilized with the assumption that it accurately depicts the performance of the Southeast Macomb Sewer System, which in part includes the Drainage District and CHA-RTB. The XP SWMM model was converted to EPA SWMM to take advantage of that program’s Low Impact Development (LID) tool. This tool allows the modeler to describe a green infrastructure control through a series of vertical layers describing the surface, soil, storage, and underdrain characteristics, as represented in Figure 3.

Figure 3 – Screenshot of EPA SWMM LID Control Editor


5.2 MODEL DEVELOPMENT OF BEST MANAGEMENT PRACTICES

The SEMCOG land cover analysis was utilized to evaluate the potential available area in each sub-catchment that could be reserved for each BMP type. A summary table of the unit size and treated impervious area for each BMP type by sub-catchment area is provided in Appendix 2. These values vary for each sub-catchment based on the land cover/use and impervious area. These values were input into the model for the model runs simulating green infrastructure. A description regarding how the BMP size and model parameters were developed for each BMP is described below.

5.2.1 TREES For simplification, tree planting was limited to residential parcels. It was assumed that 75% of the residential properties in the Drainage District could accommodate a minimum of one additional tree. The EPA SWMM LID controls do not offer a tree BMP type. The storage volume capture performance from a tree was evaluated as a rain barrel BMP with the equivalent tree performance in the model. A medium sized tree has a tree canopy of approximately 100 square feet and a rainfall storage capacity of 9 cubic feet, according to the Western Michigan Environment Action Council Rainwater Rewards tool. Therefore, each modeled rain barrel represents a single tree capable of treating 100 square feet of impervious area with a total storage capacity of 9 cubic feet of rainwater.

5.2.2 BIO-RETENTION Potential land area suitable for bio-retention was evaluated for larger sites including schools, public institutions, and parks. According to the Low Impact Development Manual for Michigan, impervious area to BMP size should not exceed a 5:1 ratio. The maximum BMP size for each sub-catchment was calculated by dividing the total impervious area from schools, public institutions, and parks by 5. For each sub-catchment, the bio-retention BMP was modeled as a single BMP with a larger footprint, rather than several individual units.

Bio-Retention cells were set up as an LID control with a 1-foot berm height, followed by 3 feet of top soil, and 9 inches of gravel storage layer at the bottom. The ratio of void space to solid space was set to 0.47 for the soils layer and 0.67 for the gravel layer. An underdrain was set at the bottom of the BMP with zero offset to promote slow drainage back into the collection system as the unit fills.

5.2.3 UNDERGROUND DETENTION Potential land area suitable for underground detention was evaluated for larger sites with high amounts of impervious area including schools, public institutions, and commercial/industrial sites. According to the Low Impact Development Manual for Michigan, impervious area to BMP size should not exceed a 10:1 ratio. The maximum BMP size for each sub-catchment was calculated by dividing the total impervious area from schools, public institutions, and commercial/industrial sites by 10. For each sub-catchment, the underground retention BMP was modeled as a single BMP with a larger footprint, rather than several individual BMPs.

Underground detention cells were set up as an LID control with 24 inches of storage depth and an underdrain. The ratio of void space to solid space was set to 0.67 for the gravel layer. The underground detention cell does not have a permeable bottom; therefore, the underdrain invert elevation was set at the bottom of the BMP with zero offset to promote slow drainage back into the collection system as the unit fills. 3/24/2017 DRAFT 9 Z:\2013\130620\WORK\REPT\GI STUDY\GREEN INFRASTRUCTURE PHASE II REPORT\RPT_GI ANAYLSIS_2017_0324_DFT.DOCX

5.2.4 GREEN ROOF Green roofs are a green infrastructure BMP suitable for large, flat roof surfaces typically found on large commercial, industrial, and school buildings. It was assumed that 25% of the roof area for schools could be utilized for this BMP. It is unlikely that many commercial and industrial sites would be receptive to a green roof on their building due to the cost of retrofitting. Therefore, a modest 1% of the total roof area from all commercial and industrial sites was designated as potential green roof area.

The LID control for a green roof is broken into three components including a 1-inch surface layer, 6 inches of soil depth, and a 2-inch granular storage layer. The ratio of void space to solid space was set to 0.64 for the soils layer and 0.67 for the gravel layer. The green roof bottom is impermeable so an underdrain was set at the bottom of the BMP with zero offset to send flow away from the green roof as it begins to fill.

5.3 STORMWATER WATERSHED REDUCTION SCOPING TOOL A stormwater watershed reduction scoping tool was developed in Excel® using output from hydraulic model simulations. The intent of this tool is to provide a means to evaluate the potential benefits of implementing green infrastructure within the Drainage District, and the impact on volume and peak flow reductions from the 8DR and reductions in discharge volume to Lake St. Clair from the CHA-RTB. Although this tool was developed based on the calibrated hydraulic model made available for this study, individual BMP performance may vary as it is implemented due to variations in design. Consequently, the scoping tool is best used as a planning and tracking tool.

The scoping tool was developed by running model simulations with underground detention, bio-retention, trees, and green roof BMPs at each sub-catchment individually. A linear relationship was developed from each model run based on the flow volume and peak flow reduction to the 8DR in the post-BMP model simulation compared to the pre-BMP model simulation (existing conditions).

All model simulations were based on the 2-year, 24-hour event. This storm event was selected because it represents the greatest potential rain event that green infrastructure techniques are capable of mitigating. The impervious area treated and BMP unit size follow the table in Appendix 2; however, these values are fairly conservative and it is likely that BMPs could be constructed at a larger footprint than identified in the land use analysis.

The stormwater watershed reduction scoping tool is provided in Appendix 3. The scoping tool is equipped with a BMP inventory page where the user can enter the sub-catchment number and the number or size of the BMP where it will be implemented. The sub-catchment numbering is consistent with Figure 1 and is included in the Appendix 3 for reference. The results tab of the scoping tool provides a summary of the runoff and flow volume reduction for each BMP by sub-catchment and the total improvement for the Drainage District.


5.4 MODEL APPROACH AND RESULTS Model simulations were completed to determine the effectiveness of each BMP type under the 2-year, 24-hour design storm. Existing conditions model simulations were run to establish baseline conditions for the 8DR and CHA-RTB.

An independent model run was completed for each BMP and for each sub-catchment to develop performance estimates for the scoping tool. For the purposes of summarizing potential benefits, a separate model run was completed for each BMP assuming it was applied throughout the Drainage District.

Model results comparing the pre-BMP and green infrastructure model simulations are provided in Table 4. The peak discharge and total discharge are measured from the CHA-RTB into Lake St. Clair. Peak discharge and total volume from the CHA-RTB, based on the unit area of BMP in the sub-catchment, has also been provided. For example, Table 4 indicates there is a 96 gallon discharge reduction from the CHA-RTB into Lake St. Clair for each square foot of bio-retention constructed within the Drainage District. These numbers are based on square footage of green infrastructure in the Drainage District as a whole and could vary by sub-catchment.

Table 4 – BMP Summary: 2-Year, 24-Hour Event

Model Condition

Chapaton RTB

Total BMP Area (square feet)

Peak Discharge Reduction from RTB per square

foot BMP (gpm/sq ft)

Discharge Volume

Reduction from RTB per square

foot BMP (gallons/sq ft)

Peak Discharge

(gpm)

Total Discharge

(MG)

Pre-BMP 559,063 104.2 n/a n/a n/a Bio-Retention 545,001 98.4 60,883 0.23 96 Underground Detention 517,300 101.8 146,108 0.29 16 Green Roof 555,894 97.6 30,245 0.10 217 Trees 502,897 102.6 389100 0.14 4

The primary goal of stormwater volume reduction into the 8DR as a result of implementing green infrastructure measures, is to provide a reduction of discharge of treated overflow from the CHA-RTB. A secondary goal evaluated with the implementation of green infrastructure measures is to reduce and delay the peak discharge into the CHA-RTB, allowing the CHA-RTB’s capacity to recover to accommodate the delayed inflow into the basin. Although the peak flow into the CHA-RTB is delayed with green infrastructure measures, it was observed in the calibrated model that peak flow contributions into the CHA-RTB from the Jefferson Interceptor occur approximately 6 hours after the peak discharge from the 8DR and 9EB into the CHA-RTB. As a result, the delayed inflow from the 8DR (with green infrastructure implementation) occurs during peak flow contributions from the Jefferson Interceptor, and the overall benefit to the CHA-RTB capacity due to delaying the inflow from the 8DR is not as significant.


Figure 4 – Representative Hydrograph with and without Green Infrastructure

The 9EB Drainage District has very similar land cover and land use characteristics as the 8 1/2 Mile Relief Drain District. The total modeled existing flow contributions for the 2-year, 24-hour event from both the 8DR and 9EB are 82 and 85 MG, respectively. Although the evaluation of the 9EB Drainage District is outside the scope of this study, it is reasonable to assume that implementing the same green infrastructure measures within the 9EB Drainage District would yield similar results to those modeled in the 8 1/2 Mile Relief Drain Drainage District.

The results in Table 4 indicate underground detention is the most effective method for lowering the peak discharge from the CHA-RTB per square foot of BMP. This is likely due to the higher impervious area treated to BMP size ratio. The availability for installation of underground detention systems is somewhat limited compared to planting trees, which can be installed on a much more widespread basis within the Drainage District and is currently supported by existing Macomb County programs.

6.0 RECOMMENDATIONS Green infrastructure techniques are a viable option for reducing treated overflows from the CHA-RTB though their overall effectiveness is partially limited by low permeable soils within the Drainage District and timing of peak flows in the Southeast Macomb Sewer System. Opportunities for implementing green infrastructure within existing developments such as schools, churches, parks, and transportation corridors should be considered as grant opportunities and community stormwater funds are available. As commercial properties are redeveloped, green infrastructure techniques should be considered as part of the site’s overall stormwater management plan which will assist with meeting the OMCPWC and community stormwater standards. Existing tree planting programs should continue to be promoted by Macomb County and individual communities for stormwater benefits. Trees will also improve air quality and help reduce the urban heat island effect.

As green infrastructure opportunities are identified, the potential benefit of these measures should be evaluated with the scoping tool to identify potential overall benefit, and to assist with determining where the measures would be most effectively implemented. The scoping tool serves as a planning and tracking tool and as a resource to support grant applications.

Hydrograph without Green Infrastructure

Hydrograph with Green

Infrastructure


Appendix 1

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EastpointeSt. Clair Shores

Detroit Harper WoodsGrosse Pointe Woods

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8 1/2 Mile Project BoundaryMacomb County

Southeast Michigan Council of Governments1001 Woodward Avenue, Suite 1400, Detroit, Michigan 48226-1904Phone (313) 961-4266, Fax (313) 961-4869www.semcog.org Copyright: SEMCOG, 2016 November 2016

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8

33

10

2 209

29

2612

25

24

3011

161521 28

27

4

32

17

187

6

13

31

23

22193


Warren

Land Use8 1/2 Mile Project Area



0 500 1,000Meters

0 1,000 2,000Feet

1:29,442


¯

Land UseSingle-family residentialMultiple-family residentialCommercialIndustrialGovernmental / institutionalPark, recreation, and open spaceTransportation, communication, utilities

15

14

8

33

10

2 209

29

2612

25

24

3011

161521 28

27

4

32

17

187

6

13

31

23

22193


Warren

Public Property8 1/2 Mile Project Area



0 500 1,000Meters

0 1,000 2,000Feet

1:29,442


¯Public Property

CITY OF EASTPOINTECITY OF ST CLAIR SHORESCOUNTY OF MACOMBSTATE OF MICHIGANSCHOOL PROPERTY

15

14

8

33

10

2 209

29

2612

25

24

3011

161521 28

27

4

32

17

187

6

13

31

23

22193


Warren

Right-of-Way Ownership8 1/2 Mile Project Area



0 500 1,000Meters

0 1,000 2,000Feet

1:29,442


¯ROW Owner

CityMacomb CountyState of Michigan

Appendix 2

BMP Summary

Sub Number Area (Acres)BMP Area (sq

ft)Surface Width

Treated

Impervious

Area (acres)

Percent of

Impervious

Area Treated

BMP Area (sq

ft)Surface Width

Treated

Impervious

Area (acres)

Percent of

Impervious

Area Treated

BMP Area (sq

ft)Surface Width

Treated

Impervious

Area (acres)

Percent of

Impervious

Area Treated

Number of

Parcels

Number of

Lots Suitable

for Trees

Total BMP

Area (sq ft)

Number of

Trees

Treated

Impervious

Area (acres)

Percent

Impervious

Area Treated

1 105.9 3,619 60 0.37 0.35% 1,911 44 0.04 0.04% 26,090 162 5.99 5.66% 482 362 36,150 362 0.83 0.78%

2 70.4 4,946 70 0.51 0.73% 1,164 34 0.03 0.04% 13,481 116 3.09 4.40% 303 227 22,725 227 0.52 0.74%

3 26.0 819 29 0.02 0.07% 5,044 71 1.16 4.45% 9 7 675 7 0.02 0.06%

4 34.5 11,892 109 1.23 3.56% 14,088 119 3.23 9.38% 74 56 5,550 56 0.13 0.37%

5 97.0 553 24 0.06 0.06% 1,833 43 0.04 0.04% 21,250 146 4.88 5.03% 419 314 31,425 314 0.72 0.74%

6 21.4 414 20 0.10 0.44% 98 74 7,350 74 0.17 0.79%

7 23.0 974 31 0.10 0.44% 1,513 39 0.35 1.51% 98 74 7,350 74 0.17 0.73%

8 76.4 3,227 57 0.33 0.44% 266 16 0.01 0.01% 4,675 68 1.07 1.40% 330 248 24,750 248 0.57 0.74%

9 69.6 14,308 120 1.48 2.12% 11,344 107 0.26 0.37% 8,678 93 1.99 2.86% 330 248 24,750 248 0.57 0.82%

10 115.6 553 415 41,475 415 0.95 0.82%

11 77.2 1,060 33 0.11 0.14% 389 20 0.01 0.01% 4,462 67 1.02 1.33% 391 293 29,325 293 0.67 0.87%

12 100.8 1,424 38 0.15 0.15% 1,419 38 0.03 0.03% 7,844 89 1.80 1.79% 495 371 37,125 371 0.85 0.85%

13 33.2 1,163 34 0.27 0.81% 131 98 9,825 98 0.23 0.68%

14 133.2 5,320 73 0.55 0.41% 538 23 0.01 0.01% 7,239 85 1.66 1.25% 776 582 58,200 582 1.34 1.00%

15 76.5 3,296 57 0.34 0.44% 828 29 0.02 0.02% 10,592 103 2.43 3.18% 138 104 10,350 104 0.24 0.31%

16 78.9 10,265 101 1.06 1.34% 7,759 88 0.18 0.23% 7,733 88 1.78 2.25% 164 123 12,300 123 0.28 0.36%

17 41.0 1,121 33 0.03 0.06% 8,955 95 2.06 5.01% 188 141 14,100 141 0.32 0.79%

18 40.5 852 29 0.02 0.05% 2,887 54 0.66 1.64% 209 157 15,675 157 0.36 0.89%

19 15.4 1,304 36 0.13 0.88% 983 31 0.23 1.47% 39 29 2,925 29 0.07 0.44%

20 113.3 509 23 0.05 0.05% 394 20 0.01 0.01% 5,181 72 1.19 1.05% 432 324 32,400 324 0.74 0.66%

21 74.4 346 19 0.01 0.01% 4,321 66 0.99 1.33% 429 322 32,175 322 0.74 0.99%

22 15.9 0 52 39 3,900 39 0.09 0.56%

23 29.0 0 2,000 20 0.05 0.16%

24 91.5 13,438 116 1.39 1.52% 11,541 107 0.26 0.29% 7,123 84 1.64 1.79% 423 317 31,725 317 0.73 0.80%

25 94.8 0 398 299 29,850 299 0.69 0.72%

26 102.6 4,639 68 0.48 0.47% 2,437 49 0.06 0.05% 28,922 170 6.64 6.47% 261 196 19,575 196 0.45 0.44%

27 56.2 6,859 83 0.71 1.26% 6,205 79 0.14 0.25% 11,587 108 2.66 4.73% 168 126 12,600 126 0.29 0.51%

28 74.1 0 322 242 24,150 242 0.55 0.75%

29 111.7 8,750 94 0.90 0.81% 9,400 97 0.22 0.19% 11,631 108 2.67 2.39% 476 357 35,700 357 0.82 0.73%

30 89.6 3,914 63 0.40 0.45% 1,687 41 0.04 0.04% 16,508 128 3.79 4.23% 254 191 19,050 191 0.44 0.49%

31 28.2 6,685 82 0.69 2.45% 1,279 36 0.03 0.10% 16,885 130 3.88 13.75% 43 32 3,225 32 0.07 0.26%

32 49.3 148 12 0.02 0.03% 512 23 0.01 0.02% 5,058 71 1.16 2.35% 178 134 13,350 134 0.31 0.62%

33 120.0 2,142 46 0.22 0.18% 1,217 35 0.03 0.02% 13,964 118 3.21 2.67% 455 341 34,125 341 0.78 0.65%

*Greyed Out Cells Indicate the BMP Control is not suitable for the Subcatchment

Trees (Modeled as Rain Barrels)Subcatchment

Number/AcreageGreen Roof Underground Detention (Modeled as Pervious Pavement)Bio-Retention

Appendix 3 The Stormwater Watershed Reduction Scoping Tool (Excel

document) is available in the "Attachments" (paperclip) panel on the left.

Documents

8 1/2 Mile Relief Drain Drainage District Green