Empire Communities (St. George) Ltd. Functional Servicing and … · 2017-10-27 · Empire Communities (St. George) Ltd. Functional Servicing and Stormwater Management Report August

Empire Communities (St. George) Ltd.

Functional Servicing and Stormwater Management

Report

August 2017

Submitted by:

SCS Consulting Group Ltd 30 Centurian Drive, Suite 100

Markham, ON, L3R 8B8 Phone 905 475 1900

Fax 905 475 8335

Project No. 1622

Functional Servicing and Stormwater Management Report Empire Communities (St. George) Ltd. – County of Brant August 2017

Project No. 1622 Page i

TABLE OF CONTENTS Page

1.0 INTRODUCTION .............................................................................................................. 1 1.1 Purpose of the Functional Servicing and Stormwater Report ......................................... 1 1.2 Study Area ....................................................................................................................... 1 1.3 Background Servicing Information ................................................................................. 2

2.0 STORMWATER MANAGEMENT .................................................................................. 4 2.1 Stormwater Runoff Control Criteria ............................................................................... 4 2.2 Existing Drainage ............................................................................................................ 4

2.2.1 Existing Site Characterization ............................................................................... 5 2.2.2 Existing Hydrologic Modelling ............................................................................. 5

2.3 Evaluation of SWM and Low Impact Development Practices ........................................ 6 2.3.1 Lot Level Controls................................................................................................. 6 2.3.2 Conveyance Controls ............................................................................................ 7 2.3.3 End-of-Pipe Controls ............................................................................................. 8 2.3.4 Selection of Low Impact Development Practices ................................................. 8

2.4 Proposed Storm Drainage ............................................................................................... 9 2.5 Stormwater Management Ponds.................................................................................... 10

2.5.1 Permanent Pool.................................................................................................... 10 2.5.2 Extended Detention ............................................................................................. 10 2.5.3 Quantity Control .................................................................................................. 11 2.5.4 General Pond Design Criteria .............................................................................. 12

2.6 Comparison of Existing Targets and Proposed Flows .................................................. 13 2.7 Storm Servicing ............................................................................................................. 14 2.8 Overland Flow Calculations .......................................................................................... 14 2.9 Water Budget ................................................................................................................ 15 2.10 Temperature Mitigation ................................................................................................ 15 2.11 Drainage Feature Realignment and Regional Flow Conveyance .................................. 15

3.0 SANITARY SERVICING ............................................................................................... 16 3.1 Existing Sanitary Sewer System ................................................................................... 16 3.2 Proposed Sanitary Sewer System .................................................................................. 16

4.0 WATER SUPPLY AND DISTRIBUTION ..................................................................... 18 4.1 Existing Water Distribution .......................................................................................... 18 4.2 Proposed Water System ................................................................................................ 18

5.0 SITE GRADING .............................................................................................................. 19 5.1 Existing Grading Conditions ......................................................................................... 19 5.2 Proposed Grading Concept ........................................................................................... 19

6.0 RIGHT-OF-WAYS AND SIDEWALKS ......................................................................... 20 7.0 EROSION AND SEDIMENT CONTROL DURING CONSTRUCTION ...................... 21 8.0 SUMMARY ..................................................................................................................... 22

Functional Servicing and Stormwater Management Report Empire Communities (St. George) Ltd. – County of Brant August 2017

Project No. 1622 Page ii

LIST OF TABLES

Table 2.1 Stormwater Runoff Control Criteria Table 2.2 Summary of Existing Flows Table 2.3 Recommended Stormwater LID Practices Table 2.4 Pond A Stage-Storage-Discharge Characteristics Table 2.5 Pond B Stage-Storage-Discharge Characteristics Table 2.6 Comparison of Existing Targets and Proposed Flows (SCS) Table 2.7 Comparison of Existing Targets and Proposed Flows (Chicago) Table 2.8 Rainfall Intensity Parameters

LIST OF FIGURES

Figure 1.1 Site Location Plan Figure 2.1 Existing Drainage Plan Figure 2.2 Proposed Drainage Plan Figure 2.3 Stormwater Management Pond A Figure 2.4 Stormwater Management Pond B Figure 2.5 Preliminary Storm Servicing Plan Figure 3.1 Preliminary Sanitary Servicing Plan Figure 4.1 Preliminary Watermain Distribution Plan Figure 5.1 Preliminary Site Grading Plan Figure 6.1 Preliminary Sidewalk Plan

LIST OF APPENDICES

Appendix A Draft Plan of Subdivision Appendix B St. George Area Study Background Servicing Drawings Appendix C Stormwater Management Calculations

C1 Existing Hydrology Modelling C2 Proposed Hydrology Modelling C3 Stormwater Management Pond Size Calculations C4 Erosion Threshold Analysis Modelling C5 Overland Flow Calculations C6 Realigned Drainage Feature & Andrew Street Extension Culvert Sizing

Appendix D Background SWM Report Excerpts Appendix E Geotechnical Investigation Excerpts Appendix F Sanitary Sewer Sizing Calculations

F1 SCS Consulting Group Ltd. Sanitary Sewer Sizing Calculations F2 Original Weslake Sanitary Sewer Sizing Calculations

SUBMISSION HISTORY

Submission Date In Support Of Distributed To 1st February 2008* Draft Plan Approval County of Brant2nd January, 2015 Draft Plan Approval County of Brant3rd August 2017 Draft Plan Approval County of Brant

*Note: Submission made by Weslake Inc.

Functional Servicing and Stormwater Report Empire Communities (St. George) Ltd., County of Brant August 2017

Project No. 1622 Page 1

1.0 INTRODUCTION

SCS Consulting Group Ltd. has been retained by Empire Communities (St. George) Ltd. (Empire) to prepare a Functional Servicing and Stormwater Report (FSSR) for the property located east of Scott Street and north of Highway 5, within the Community of St. George in the County of Brant.

1.1 Purpose of the Functional Servicing and Stormwater Report

The FSSR has been prepared in support of the application for Draft Plan approval of the above mentioned site. Per the County of Brant Official Plan, the site is currently designated for urban residential land use and natural heritage lands.

The Draft Plan includes single family homes, townhomes, open space, park area, mixed use residential and stormwater management areas as described in detail below (refer to Appendix A for the Draft Plan of Subdivision):

24.51 ha single family homes (Blocks 2-16, 18-37, 39-43, 46-60, 62-66, 68-71) located throughout the site;

2.42 ha townhomes development (Blocks 1, 17, 38, 44-45, 61, 67) located throughout the site; 3.60 ha of mixed use (Blocks 76-78 located at the south end of the site; 3.41 ha of stormwater management pond (Blocks 79, 80) located in the south and east portions of the site; 3.73 ha of park and parkette (Blocks 81-83) located throughout the site; 9.97 ha of open space (Blocks 84-91) located throughout the site; 2.12 ha of existing woodlot (Block 92) located in the northwest portion of the site; 17.07 ha of roads, road widenings (Block 93) and 0.30m reserves (Blocks 94-99) located throughout the site.

The development is proposed to be comprised of approximately of 1291 units (811 single family units, 120 townhouse units and 360 mixed use residential units).

The purpose of this report is to demonstrate that the development can be serviced in accordance with the County of Brant, Grand River Conservation Authority (GRCA) and the Ministry of the Environment and Climate Change (MOECC) design criteria.

1.2 Study Area

The study area is approximately 66.83 hectares in size and is bounded by Highway 5 to the south, Scott Street and Hampton Court to the east and existing agricultural lands to the west and north (see Figure 1.1).

The site in its current state is agricultural lands. Under existing conditions, Andrew Street terminates at Scott Street and the eastern site limits. Ultimately Andrew Street will be extended west to provide access to the site.



1.3 Background Servicing Information

The site servicing and stormwater management (SWM) strategy in this report are based on the following reports:

Stormwater Management Study – Westview Heights Subdivision, J.H. Cohoon Engineering Limited, dated March 1990;

Stormwater Management Study – Proposed Residential Subdivision – Northview Heights Subdivision (Phase 1), J.H. Cohoon Engineering Limited, dated April 1993;

Stormwater Management Study – Proposed Residential Subdivision – Northview Subdivision, J.H. Cohoon Engineering Limited, dated May 1995;

Hydrogeological Investigation, Norbert M. Woerns, dated January 14, 2008; Functional Servicing Report for St. George Property, Weslake Inc., dated

February 2008; Village of St. George Wastewater Conveyance Review, MTE, dated

September 2012; Preliminary Water Supply and Distribution Study – Report Addendum, MTE,

dated October 2, 2013; St. George Area Study - Final Drainage Overview, MTE, dated October 15,

2013; Preliminary Geotechnical Investigation, SPL Consultants Limited, dated

December 19. 2014; and Tributary of Fairchild Creek, St. George, Ontario – Erosion Threshold

Assessment, Geo Morphix, dated January 27, 2015 Based on these background reports and drawings, the following servicing approach and criteria have been established: Stormwater Management Based on the St. George Area Study – Final Drainage Overview prepared by MTE, typical stormwater management (SWM) objectives that serve to protect local water resources, which includes both surface water and groundwater, are:

Provide appropriate water quality control measures prior to discharge of stormwater to either surface water or groundwater systems, in order to protect the water quality and functions of these systems.

Control peak flow rates from the development lands into local creek systems to existing levels (or lower if required by existing downstream flow conveyance or flooding constraints), in order to minimize flooding threats as well as preserve natural creek and floodplain hydrologic functions.

Assess stream erosion conditions within the local creek systems and provide measures or controls that will maintain or improve upon the current natural rate of change within creeks.

Mitigate potential stream water temperature impacts where required in order to maintain the existing fisheries potential of local creek systems.



Maintain existing infiltration rates where required to sustain the function of either local environmental features or local sourcewater supply(s).

Maintain water balances for any dependant and significant environmental features such as wetlands.

Sanitary Servicing

Sanitary flow from the site will be directed south towards Highway 5 to the proposed sanitary sewers within the Losani Lands located on the south of Highway 5. The Losani Lands will be developing their lands within a similar time frame to Empire Communities. This will allow Empire’s sanitary flows to enter the Losani system to the south.

If the Losani Lands decide not to develop at the same time or prior to the Empire Communities lands then the sanitary flow from the site will be directed towards Highway 5 to the existing 200mm diameter sanitary sewer located on Highway 5, west of Scott Street. Sections of the existing sanitary sewer system between the site and the wastewater treatment plant (WWTP) may be replaced and upsized or twinned by the County in accordance with the St. George Area Plan studies.

Water Supply and Distribution

The subject lands will be serviced with a water distribution system by connecting to the existing watermain system located on Highway 5 and Andrew Street to provide continuous looping within the system.

The County is currently completing an Environmental Assessment to provide a new water source and distribution system to accommodate the proposed growth within the St. George Study area.

The Empire lands are able to proceed with their first phase without a new water supply. Staging of development is anticipated at 90 units per year based on proposed upgrades to the water and wastewater system.

Grading

The lands shall be graded to satisfy the County of Brant road grading criteria, provide continuous road grades for overland flow conveyance, minimize the need for retaining walls, minimize the volume of earth to be moved and minimize cut/fill differential and achieve the SWM objectives required for the site.



2.0 STORMWATER MANAGEMENT

2.1 Stormwater Runoff Control Criteria

The following stormwater runoff control criteria have been established based on the recommendations of the background reports listed in Section 1.3. The stormwater runoff criteria are summarized below in Table 2.1:

Table 2.1 – Stormwater Runoff Control Criteria

Criteria Control Measure

Quantity Control Control proposed to existing peak flows for the 2 through 100 year storm events.

Quality Control MOECC Enhanced Level Protection (80% TSS Removal).

Erosion Control Provide measures or controls that will maintain or improve upon the current natural rate of change within creeks.

Water Budget Maintain existing infiltration rates where required to sustain the function of either local environmental features or local sourcewater supply(s).

2.2 Existing Drainage

The subject lands are located within the Fairchild Creek Watershed. As illustrated by Figure 2.1, the subject lands generally drain in a southeast direction, exiting the southern limit of the site at three (3) locations, Nodes A, B, and C. The majority of the subject lands (Catchment 101 - 20.23 ha and Catchment 102 - 34.28 ha) drain via sheet flow towards Node A, collecting in an existing drainage feature running south along the eastern boundary of the site. A total of 278.65 ha of external lands also drain towards Node A. Runoff from Catchment 201 (163.06 ha) drains via sheet flow in a southeast direction, collecting in the drainage feature prior to entering the subject lands. Catchment 202 (17.55 ha) and Catchment 203 (53.18 ha) drain via sheet flow into Catchments 101 and 102 respectively before collecting in the drainage feature. The storm drainage from the two (2) existing subdivisions (Catchment 205 and Catchment 206), located to the east of the subject lands, drains to Node A via the existing drainage feature running south along the eastern boundary of the subject lands. Stormwater management reports and drawings prepared for the SWM design of the existing subdivisions were obtained from the County of Brant. This information was used to establish drainage boundaries, modelling parameters, etc., as outlined below, and is provided in Appendix D. Catchment 207 (0.28 ha) drains via sheet flow to Node A. In total, 333.16 ha of land drain to Node A via the drainage feature located on the eastern boundary of the subject lands. The drainage feature continues south, flowing underneath Highway 5 through an existing culvert. Catchment 103 (11.37 ha) drains via sheet flow to Node B, and conveys an additional 10.61 ha of external lands (Catchment 204). Runoff from Catchment 103 and 204 collects at a low



point at the south boundary of the subject lands and continues to flow south within an existing drainage feature, flowing underneath Highway 5 through an existing culvert. Catchment 104 (0.89 ha) drains via sheet flow to Node C. Runoff from Catchment 104 drains south to the existing Highway 5 ditch which continues west along Highway 5 towards an existing culvert under the highway approximately 145 meters west of Industrial Boulevard. 2.2.1 Existing Site Characterization

The soil classifications were identified using the Ontario Soil Survey Report No. 55 and land uses visible in recent aerial photography. The report identifies that the soils within the study limits are predominantly sandy loam and sandy silt. Refer to Appendix C1 & C2 for the Soil Conservation Service Curve Number (CN) and runoff coefficient used for both of these Hydrologic Soil Groups. 2.2.2 Existing Hydrologic Modelling

An existing drainage plan was prepared for the subject lands (Figure 2.1). The drainage boundaries were determined using a combination of the Ontario Base Mapping (OBM) and the information provided by the field survey data completed for the site. Hydrologic modelling was undertaken using the Visual Otthymo Version 2.0 software (VO2) based on the 3-hour Chicago and 24-hour SCS Type II Distribution storms. The subject lands are located within the County of Brant, therefore, the Intensity Duration Frequency (IDF) rainfall information was obtained from the County of Brant design standards to determine the existing peak flows to the various outlet locations. Table 2.2 provides a summary of existing flows at the outlet locations (Nodes A, B and C), as well as at two locations downstream of the site (Nodes D and E).

Table 2.2: Summary of Existing Flows

Return Period Storm

Node A Node B Node C Node D Node E 24-

Hour SCS

3-Hour Chicago

24-Hour SCS

3-Hour Chicago

24-Hour SCS

3-Hour Chicago

24-Hour SCS

3-Hour Chicago

24-Hour SCS

3-Hour Chicago

2 Year 0.728 1.327 0.159 0.229 0.010 0.012 0.841 1.493 3.590 5.678 5 Year 1.689 2.678 0.343 0.510 0.020 0.028 1.938 3.086 5.664 9.011 10 Year 2.467 3.668 0.495 0.756 0.029 0.042 2.844 4.249 7.448 11.900 25 Year 3.480 5.100 0.721 1.102 0.042 0.060 4.035 5.939 9.842 14.995 50 Year 4.324 6.319 0.914 1.405 0.054 0.077 5.029 7.380 12.214 18.027

100 Year

5.216 7.606 1.121 1.729 0.066 0.096 6.082 8.905 14.246 21.673

A summary of modelling parameters and an existing VO2 schematic are provided in Appendix C1. A CD containing the VO2 hydrology model and output is provided in Appendix C2.



2.3 Evaluation of SWM and Low Impact Development Practices

In accordance with the Ministry of Environment Stormwater Management Planning and Design Manual (2003), a review of stormwater management best practices was completed using a treatment train approach, which evaluated lot level, conveyance system and end-of-pipe alternatives. The following site characteristics were taken into consideration:

The topography ranges from elevations of 274.0 m to 248.0 m; Based on the Geotechnical investigation, site soils consisted of clayey silt and

gravelly sand soils; The hydraulic conductivity of the soils ranges from 2.5 x 10-5 cm/s to 2.1 x

10-2 cm/s; Within the installed site wells, groundwater was observed at a maximum

depth of 7.4 m below existing grade; The residential portion of the proposed development is approximately 66.83

ha and consists of a low and medium density housing; and The site generally drains southeast toward Highway 5.

2.3.1 Lot Level Controls

Lot-level controls are at-source measures that reduce runoff prior to stormwater entering the conveyance system. These controls are typically proposed on private properties. Incorporating controls that do not require maintenance can be an effective method in the treatment train approach to SWM; however, enforcement of controls that require ongoing maintenance can be more challenging for the municipality. The following lot level controls have been considered: Increased Topsoil Depth – An increase in the restored topsoil depth on lots can be used to promote lot level infiltration and evapotranspiration. This practice would work well in conjunction with reduced lot grading. Similar to reduced lot grading, increased topsoil depth will contribute to lot level quality and water balance control. A minimum depth of 0.3 m is recommended in all landscaped areas. Through discussions with the Municipality at detailed design, topsoil depths will be maximized in the SWM pond and park blocks. Passive Landscaping/Bio-Retention – Planting of gardens and other vegetation designed to minimize local runoff or use rainwater as a watering source can be used to reduce rainwater runoff by increasing evaporation, transpiration, and infiltration. By promoting infiltration through passive landscaping, water quality and quantity control is provided for the volume of water retained. Passive landscaping can provide significant SWM benefits as part of an overall treatment train approach. Roof Runoff to Soak-away Pits – Directing roof runoff to subsurface soak-away pits can be used to promote infiltration. By promoting infiltration water quality and quantity control is provided for the volume of water retained. Infiltration of roof runoff can provide a significant SWM benefit as part of an overall treatment train approach.



Roof Runoff to Retention Cisterns – Directing roof runoff to rainwater retention cisterns (i.e. rain barrels or greywater re-use) will contribute to water quality and water balance control. The retained rainwater can be harvested for re-use such as irrigation and/or greywater use. A typical rain barrel ranges in size from 190 to 400 liters. Green Roofs – Best suited for flat roofs, green roofs provide rainwater retention in the growing medium where it is evaporated, evapo-transpirated, or slowly drains away after the rainfall event. Rooftop and/or Parking Lot Detention Storage – Often employed with large rooftop or parking lot footprints, flow attenuation for quantity or extended detention control can be provided via a flow restriction with stormwater storage provided via ponding either on rooftops or parking lots. Roof Leaders to Grassed Areas – Directing roof leaders to grassed areas will contribute to water quality and water balance control by encouraging stormwater retention. Pervious Pavement – By encouraging infiltration and filtration, pervious pavement can contribute to water quality, balance and erosion control. Vegetated Filter Strip – At source filtration and infiltration may be encouraged through the use of vegetated filter strips by directing sheet flow from impermeable areas to the strip prior to being collected via the storm system. Vegetated filter strips are best suited to parking lot areas with landscaped borders or islands. A summary of the suitability of potential lot level controls for the subject lands is provided in Table 2.3. 2.3.2 Conveyance Controls

Conveyance controls provide treatment of stormwater during the transport of runoff from individual lots to the receiving watercourse or end-of-pipe facility and present opportunities to distribute stormwater management techniques throughout a development. The following conveyance controls have been considered: Grassed Swales – A grassed swale will promote infiltration, filtration, and evapotranspiration, contributing to water quality and quantity control. Grassed swales need an unimpeded and relatively wide stretch of landscaped area, such as within a wide boulevard with no driveways, to function properly. There are no areas on the subject lands for conveyance level grassed swales but it is noted that smaller grassed swales will be utilized at the individual lot grading level. A summary of the suitability of potential conveyance controls for the subject lands is provided in Table 2.3.



2.3.3 End-of-Pipe Controls

Stormwater management facilities at the end of pipe receive stormwater flows from a conveyance system and provide treatment of stormwater prior to discharging flows to the receiving watercourse. While lot level and conveyance system controls are valuable components of the overall SWM plan, on their own they are not sufficient to meet the quantity and quality control objectives for the subject lands. The following end of pipe controls have been considered: Underground Stormwater Detention Facility – To meet quantity erosion control targets, flow restrictors can be used to control stormwater release rates. To accommodate the reduced release rate, stormwater detention facilities are required to store stormwater runoff. In certain cases, stormwater storage can be provided by oversized storm sewers and controlled with flow restrictors prior to discharging to the receiving infrastructure. Wet Ponds, Wetlands, Dry Ponds – Sized in accordance with the MOECC criteria, these end of pipe facilities can provide water quality, quantity, and erosion control treatment. 2.3.4 Selection of Low Impact Development Practices

Table 2.3 summarizes the suitability of the various stormwater management controls identified for the subject lands.



Table 2.3 - Recommended Stormwater LID Practices

STORMWATER MANAGEMENT PRACTICE

FEASIBLE TO IMPLEMENT

(Yes/No)*

RECOMMENDED (Yes/No)*

Increased Topsoil Depth Yes Yes

Passive Landscaping/Bio-Retention Yes Yes

Roof Leader to Soak-away Pits Yes No

Roof Runoff to Retention Cisterns Yes No

Green Roofs No No

Rooftop and/or Parking Lot Detention Storage

No No

Roof Leaders to Grassed Areas Yes Yes

Pervious Pavement Yes No

Vegetated Filter Strips No No

Grassed Swales Yes Yes

Stormwater Detention Facility No No

Wet Ponds, Wetlands, Dry Ponds Yes Yes

*Note: Where LID’s are feasible but not recommended, they are not required to achieve water budget targets or less desirable to be within public ownership.

2.4 Proposed Storm Drainage

In accordance with the “Final Drainage Overview” prepared by MTE (October 2013), two wet SWM ponds (namely Ponds A and B) are proposed to service the subject lands. As illustrated on Figure 2.2, Pond A is located on the south side of the extension of Andrew Street, east of Street B in the easterly portion of the site and Pond B is located immediately north of the proposed mixed-use Block 77, north of Highway 5 in the south portion of the site. Both ponds will outlet to the existing drainage feature along the southeastern portion of the site. As illustrated on Figure 2.2, approximately 42.32 ha will drain to Pond A (external Catchment 202, 17.55 ha, Catchment 301 – 23.47 ha, and Catchment 303 – 1.30 ha). Approximately 96.00 ha will drain to Pond B (external Catchment 203 – 53.18 ha, external Catchment 204 – 10.61 ha, Catchment 304 – 30.25 ha, and Catchment 305 – 1.96 ha). Drainage from Catchment 302 (approximately 3.73 ha of rear yards and open space) and Catchment 307 (approximately 5.83 ha of open space) will drain uncontrolled to the existing



drainage feature along the east portion of the site. Drainage from Catchment 306 (approximately 0.02 ha of road right-of-way adjacent to Highway 5) will drain uncontrolled to the existing Highway 5 ditch (Node C), and continue west along Highway 5 to an existing drainage feature. Drainage from Catchment 308 (approximately 0.22 ha of sloping adjacent Highway 5) will drain uncontrolled to the existing Highway 5 ditch toward an existing culvert flowing underneath Highway 5 (Node B), and continue south within an existing drainage feature. Percent Impervious values assigned to Catchments 301 – 308 were calculated based on proposed land uses and typical house siting’s provided by Empire Communities. Existing drainage (up to the 100 year storm) from the external Catchment 202 to the north (approximately 17.55 ha) will be captured and piped to Pond A. Existing drainage (up to the 100 year storm) from the external Catchments 203 and 204 to the west (approximately 53.18 ha and 10.61 ha respectively) will be captured and piped to Pond B. Adjacent to the property boundary on the south ends of Street A, Street D and Street C, 100 year capture locations are proposed to capture runoff from Catchment 304 up to the 100 year storm event prior to draining to Highway 5 and pipe flows to Pond B. 2.5 Stormwater Management Ponds

Preliminary grading for the Ponds A and B is illustrated on Figures 2.3 and 2.4, respectively. 2.5.1 Permanent Pool

The function of the permanent pool is to provide sediment removal from the storm runoff conveyed to the pond. Pond A will be designed to provide permanent pool storage of 76 m3/ha based on MOECC’s Enhanced Level Protection for a wet pond having a 29% impervious drainage area (see Table 3.2, 2003 MOE Guidelines). The required permanent pool volume is 3,497 m3 based on a total developed area draining to the pond of 42.32 ha (see calculations in Appendix C3). The available permanent pool storage is 4,312 m3 (see Figure 2.3 and calculations in Appendix C3). Pond B will be designed to provide permanent pool storage of 51 m3/ha based on MOECC’s Enhanced Level Protection for a wet pond having a 21% impervious drainage area (see Table 3.2, 2003 MOE Guidelines). The required permanent pool volume is 5,544 m3 based on a total developed area draining to the pond of 96.00 ha (see calculations in Appendix C3). The available permanent pool storage is 8,314 m3 (see Figure 2.3 and calculations in Appendix C3). 2.5.2 Extended Detention

An erosion threshold assessment was completed by Geo Morphix Ltd. (January 2015). Flow targets were developed to assure rates of erosion were not exacerbated beyond existing natural conditions. A detailed geomorphological assessment was completed on the most sensitive reach downstream of each proposed ponds and the subject development. An



erosion threshold was quantified based on the bed and bank materials, and local channel geometry, which was converted to a discharge. Theoretically, above this discharge, entrainment and transport of sediment may occur. Two targets were selected based on 25 mm, 2-year and 5-year synthetic storm events:

1) Time of exceedance of the erosion threshold, which is the period in which sediment can be transported during an event; and more importantly,

2) Cumulative effective discharge, which is the total discharge through an event where the erosion threshold is exceeded and sediment can be theoretically entrained and transported.

Given concerns with erosion, Geo Morphix recommended that cumulative effective discharge be equal or lower than existing in the proposed condition. Based on the proposed attenuation of runoff and controls in the two SWM ponds that is required to have proposed peak flows not exceed existing rates downstream of the site, over-control of the cumulative effective discharge resulted. This over-control will result in a reduction of the erosion potential, helping to address downstream concerns. Based on the proposed outlet design for Pond A, the maximum storage required during a 25 mm rainfall event is 3,216 m3 (see Appendix C3). This volume will be released over a 51.9 hour period. This volume is greater than the 2003 MOECC guidelines minimum extended detention volume of 40 m3/ha or 1,693 m3 based on the 42.32 ha drainage area. Based on the proposed outlet design for Pond B, the maximum storage required during a 25 mm rainfall event is 6,077 m3 (see Appendix C3). This volume will be released over a 58.6 hour period. This volume is greater than the 2003 MOECC guidelines minimum extended detention volume of 40 m3/ha or 3,840 m3 based on the 96.00 ha drainage area. 2.5.3 Quantity Control

The proposed ponds will control proposed flows from the site to existing flow rates for the 2 to 100 year storm events. Proposed hydrology modelling was completed using the VO2 model to determine the required pond volumes. Refer to CD containing VO2 hydrology model provided in Appendix C2. The 3-hour Chicago and the 24-hour SCS Type II design storms, with County of Brant IDF data, were used to model the proposed conditions. The stage-storage-discharge characteristics of Ponds A and B are provided below in Tables 2.4 and 2.5.



Table 2.4: Pond A Stage-Storage-Discharge Characteristics

Return Period Storm

Stage (m) Storage

(m3) Discharge

(m3/s)

2 Year 252.83 4803 0.050 5 Year 253.16 7107 0.230

10 Year 253.36 8586 0.390 25 Year 253.61 10553 0.630 50 Year 253.80 12102 0.830

100 Year 253.99 13698 1.050 Note: The 3-hour Chicago design storm resulted in the largest storage volume requirements in the stormwater management pond.

Table 2.5: Pond B Stage-Storage-Discharge Characteristics

Return Period

Storm Stage (m)

Storage (m3)

Discharge (m3/s)

2 Year 250.47 9226 0.060 5 Year 250.73 12145 0.560

10 Year 250.85 13594 1.000 25 Year 251.00 15364 1.600 50 Year 251.11 16798 2.120

100 Year 251.23 18244 2.680 Note: The 3-hour Chicago design storm resulted in the largest storage volume requirements in the stormwater management pond.

2.5.4 General Pond Design Criteria

Preliminary pond grading is provided on Figures 2.3 and 2.4. The pond block sizes were established based on the following general criteria:

A 4 m wide maintenance access road will be provided from a proposed municipal road with a maximum longitudinal slope of 10% and a crossfall of 2% (max). It will be used to facilitate machinery to access the forebay during scheduled maintenance as well as to access the outlet structure for maintenance purposes;

A maximum slope of 5:1 from the pond bottom to 0.5 m below the normal water level will be provided;

A maximum slope of 6:1 from 0.5 m below and above the normal water level will be provided; and

A maximum slope of 3:1 will be provided from 0.5 m above the normal water level to the pond grading limits.

As outlined in the Preliminary Geotechnical Investigation, prepared by SPL Consultants Ltd., soils found within the pond blocks are permeable and an impermeable liner is required for both ponds. The liner is to be 600 mm thick of clayey silt or silty clay material, and is to be



covered with a minimum of 300 mm of sand and gravel or other suitable material. Excerpts from the preliminary geotechnical report prepared by SPL are provided in Appendix E. 2.6 Comparison of Existing Targets and Proposed Flows

To the extent possible, the site was designed to control proposed runoff to the existing levels. Tables 2.6 and 2.7 provide a comparison of existing and proposed flows at the various outlet locations (Nodes A, B and C), as well as at two locations downstream of the site (Nodes D and E), for the 24-hour SCS and the 3-hour Chicago design storms, respectively.

Table 2.6: Comparison of Existing Targets and Proposed Flows (SCS)

Return Period Storm

Node A Node B Node C Node D Node E

Pre Post

Pre Post

Pre Post

Pre Post

Pre Post 2 Year 0.728 0.727 0.159 0.015 0.010 0.000 0.841 0.762 3.590 3.620 5 Year 1.689 1.099 0.343 0.023 0.020 0.000 1.938 1.389 5.664 5.625 10 Year 2.467 2.049 0.495 0.029 0.029 0.000 2.844 2.445 7.448 7.422 25 Year 3.480 3.241 0.721 0.037 0.042 0.000 4.035 3.790 9.842 9.842 50 Year 4.324 4.129 0.914 0.044 0.054 0.000 5.029 4.868 12.214 12.215

100 Year 5.216 5.059 1.121 0.050 0.066 0.001 6.082 5.961 14.246 14.288

Table 2.7: Comparison of Existing Targets and Proposed Flows (Chicago)

Return Period Storm

Node A Node B Node C Node D Node E

Pre Post

Pre Post

Pre Post

Pre Post

Pre Post 2 Year 1.327 0.969 0.229 0.026 0.012 0.000 1.493 1.130 5.678 5.734 5 Year 2.678 2.379 0.510 0.040 0.028 0.000 3.086 2.832 9.011 9.062 10 Year 3.668 3.478 0.756 0.051 0.042 0.000 4.249 4.124 11.900 11.968 25 Year 5.100 4.977 1.102 0.063 0.060 0.001 5.939 5.885 14.995 15.154 50 Year 6.319 6.211 1.405 0.073 0.077 0.001 7.380 7.309 18.027 18.271

100 Year 7.606 7.497 1.729 0.084 0.096 0.001 8.905 8.818 21.673 22.013 As shown in Table 2.7, the proposed flows are less than or equal to the existing flows for the 2 through 100 year storm events at all target locations, with the exception of flows at Node E. The proposed flows at Node E slightly exceed the existing flows by a maximum of 2% which is considered negligible.



2.7 Storm Servicing

The storm sewer system (minor system) will be designed for the 5 year return storm as per the County of Brant standards. The major system flow drainage (up to the 100 year storm event) will generally be conveyed overland along the road right-of-ways. The storm sewer system will typically be designed with grades between 0.5% and 2%. Throughout the site, the storm sewer will be constructed at a minimum depth of 1.2 m to provide frost protection. The preliminary layout for the proposed trunk storm sewers within the subject lands is provided on Figure 2.5. As shown on Figure 2.2, three (3) 100 year capture points are located along the north and west boundary of the subject lands. These 100 year capture points will capture flows from external Catchments 202, 203, and 204, and direct the flows into the proposed storm sewers. Flows will be conveyed to ponds A & B. The storm sewer system has been sized to accommodate the 100 year flows from these external catchments. The storm drainage system will be designed in accordance with the County of Brant and MOECC guidelines, including the following:

Pipes to be sized to accommodate runoff from a 5 year storm event, Minimum Pipe Size: 300 mm diameter, Maximum Flow Velocity: 6.00 m/s, Minimum Flow Velocity: 0.8 m/s, and Minimum Pipe Depth 1.2 m to obvert for frost protection (otherwise

insulated).

The following rainfall intensity will be calculated as follows, where ‘i’ is the rainfall intensity (mm/hour) and A, B, and C are as per Table 2.8:

Table 2.8: Rainfall Intensity Parameters

Return Period Storm

A B C

2 Year 743 6.0 0.79895 Year 1593 11.0 0.8789

10 Year 221 12.0 0.908025 Year 3158 15.0 0.935550 Year 3886 16.0 0.9495100 Year 4688 17.0 0.9624

2.8 Overland Flow Calculations

Major system flows (greater than the 5 year up to the 100 year storm event) will be conveyed within the road right-of-ways to the ponds. Right-of-way capacity calculations are provided in Appendix C5 and show that the major system flows can be safely conveyed within the proposed road right-of-ways.



2.9 Water Budget

Where feasible, measures to minimize impacts on the water budget will be incorporated into the development design. As noted in the Hydrogeological Investigation prepared by Norbert Woerns, infiltration losses resulting from the development of the subject lands can be mitigated by directing all roof runoff to pervious areas. Therefore, all roof leaders are proposed to be directed to pervious areas. In addition to directing roof leaders to pervious areas, sump pumps are to be discharged to rear yard pervious areas to further enhance the proposed water balance mitigation measures. Additional BMPs as outlined in Table 2.3 will be explored at detailed design. 2.10 Temperature Mitigation

The St. George Area Study - Final Drainage Overview, prepared by MTE, indicates that the existing drainage feature located along the east boundary of the subject lands is considered a coldwater watercourse. In order to mitigate potential stream water temperature impacts by discharging to the existing drainage feature, Ponds A and B are proposed to have bottom draw outlets, drawing from a point in the pond where cool water is located. In addition, cooling trenches will be incorporated to the SWM pond outlets at the detailed design stage. 2.11 Drainage Feature Realignment and Regional Flow Conveyance

The existing drainage feature along the eastern portion of the site is proposed to be realigned north of the Andrew Street extension within the proposed open space block (Block 77). The realigned drainage feature will have a 7.5 m wide bottom with 3:1 side slopes. The realigned drainage feature has been sized to convey flows from a Regional Storm (Hurricane Hazel) event that result in the existing condition (approximately 13.1 m3/s). This is considered to be the most conservative design approach, as this is the condition where the most flows are directed to the location of the proposed culvert. In the proposed condition, the drainage area directed to the proposed culvert will be less than the existing condition (approximately 85% of the existing area), and flows will therefore be less. A 6.0 m x 1.8 m concrete box culvert is proposed to convey flows under the Andrew Street extension. The culvert has been sized to convey the flows from a Regional Storm (Hurricane Hazel) event that result in the existing condition (approximately 13.1 m3/s). Supporting calculations for the proposed realigned drainage feature configuration and the proposed culvert are provided in Appendix C6.



3.0 SANITARY SERVICING

3.1 Existing Sanitary Sewer System

The community of St. George has an existing sanitary sewer collection system, draining by gravity in a generally south-east direction to a wastewater treatment plant (WWTP) located in the south-east corner of the community. The existing sewer system was not specifically designed to accommodate flows from the subject lands. A 200 mm diameter sanitary sewer is located on Hwy 5, approximately 60 m west of Scott Street, adjacent to the Empire Communities site. The existing sanitary system drains east along Highway 5 and Beverly Street to High Street, then south on West Street, Hawk Street and Main Street South, ultimately draining east along Victor Boulevard to the existing wastewater treatment plant (see Figure 4.0 in Appendix B for overall existing sanitary system drainage). The existing system has limited residual capacity for additional growth as noted in the Wastewater Conveyance Review prepared by MTE (see Appendix B – Figure 5.0) and included within the approved St. George Area Study. SCS Consulting Group Ltd. has completed a sanitary sewer analysis of the existing sanitary system (see Appendix F1). The analysis utilized the St. George – Sanitary Sewer Capacity – Existing Conditions design sheets completed by Weslake Inc. in February 2008 (see Appendix F2) as well as the recommendations within the Wastewater Conveyance Review completed by MTE in September 2012. Using the current County of Brant standards (May 2014), the existing sanitary design sheets were updated to use the County’s current design flow criteria as well as using equivalent population densities of 38ppha for residential flows, 62.2 ppha for commercial and institutional flows, and 100 ppha for industrial flows. As shown within Appendix F2, a section of the existing sewer on High Street, Hawk Street and Victor Boulevard are currently close to full flow capacity and one section of existing sewer on West Street is slightly over full flow capacity. As per the Class Environmental Assessment the existing wastewater treatment plant (WWTP) has a rated capacity of 1300 m3/d with an actual plant processing capacity of 1000 m3/d. The current average daily plant influent flow (2012) is 656 m3/d with a maximum daily flow (2012) of 977 m3/d. The County of Brant is completing a Class Environmental Assessment to accommodate additional growth, which will assess options to upgrade the capacity of the existing WWTP to accommodate additional growth. The Class Environmental Assessment is scheduled to be completed mid to late 2017. 3.2 Proposed Sanitary Sewer System

The preliminary layout for the proposed sanitary sewer within the subject lands is provided on Figure 3.1. As shown, the subject lands (approximately 66.83 ha) will ultimately drain into a proposed sanitary sewer within the proposed Losani lands located on the south side of Highway 5. The Losani lands will be developing within a similar time frame to Empire Communities. This will allow Empire’s sanitary flows to enter the Losani system to the south, and ultimately be conveyed to the up-graded existing WWTP.



If the Losani Lands decide not to develop at the same time or prior to the Empire Communities lands the alternative is to direct the sanitary flow from the site towards Highway 5 to the existing 200mm diameter sanitary sewer located on Highway 5, west of Scott Street.

An analysis of the existing system was completed to include the Empire lands and Future External lands to identify where upgrades are required (see Appendix F1). As shown, the existing sanitary sewer system upstream of the existing WWTP has insufficient residual capacity based on theoretical design criteria flows to accommodate the full build-out of the subject lands and the potential future external lands. The existing sewer system will be upgraded by the County in accordance with the St. George Area Study recommendations. An analysis of potential required changes to the existing sanitary system to accommodate the Empire lands and future external lands has been included within Appendix F1. The sanitary sewers within the site will have slopes ranging between 0.5% and 2% (typically) and will be provided at generally 3 m to 5 m deep. A number of locations have been identified on Figure 3.1 where deeper sewers are required (eg. 6 m). Two sanitary sewer options have been provided for the sanitary sewer within Street ‘A’ on the west side of the site. Option one is to construct the sanitary sewer east from Street ‘A’ within an easement between Blocks 7/8 and Block 79, which is the stormwater management block, ultimately connecting the flows to the proposed sanitary sewer within Street ‘G’. Option two is to continue the sanitary sewer south within Street ‘A’ and complete construction within the proposed mixed use Block 77, ultimately connecting to the proposed sanitary sewer within Street ‘G’. The downstream sanitary sewer capacity analysis completed for the Area Study assumed a tributary area of 49.8 ha for the subject lands, with 891 units and a population of 2495. The proposed maximum density on the site includes 1291 units (811 singles, 120 TH and 360 Mixed Use) with a total population of 3155 using the County’s population density for low, medium and high density residential (see below). The sanitary sewer system will be designed in accordance with the County of Brant and MOECC criteria, including but not limited to:

Residential Sanitary Generation Rate: 350 l/c/d; Light Commercial Area Sanitary Generation Rate: 40.5 m3/ha/day; School Sanitary Generation Rate: 12.1 m3/ha/day; Population Density (Low Density): 2.89 people/unit; Population Density (Medium Density): 1.94 people/unit; Population Density (High Density): 1.29 people/unit; Peaking Factor: Harmon (Maximum 5.0); Infiltration Rate: 0.23 L/s/ha; Minimum Pipe Size: 200 mm diameter; Minimum Pipe Depth: 2.40 m; Minimum Actual Velocity: 0.60 m/s; and Maximum Velocity: 3.0 m/s.



4.0 WATER SUPPLY AND DISTRIBUTION

4.1 Existing Water Distribution

The existing watermain system adjacent to the subject lands is shown in Appendix B - Figure A1. As shown, the system includes:

200 mm, 250 mm and 300 mm diameter watermains on Highway 5; and 200 mm diameter watermain on Andrew Street and Scott Avenue.

4.2 Proposed Water System

The preliminary layout for the proposed watermain system is provided on Figure 4.1 and is based on the Preliminary Water Supply and Distribution Study – Report Addendum prepared by MTE (see Appendix B – Figure A3) and included within the approved St. George Area Study. As shown, the ultimate system includes 300 mm diameter watermains on Street ‘A’, Street ‘B’, Street ‘C’, Street ‘O’, Street ‘J’ and Street ‘M’ as well as 150 mm and 200 mm diameter watermains within the remainder of the site to provide a looped water supply. There are two, 300 mm watermain connections proposed on Street ‘A’ and Street ‘B’ which will connect into the existing watermain located on Highway 5. A 200 mm watermain is proposed to connect to the existing 200 mm watermain on Andrew Street. A detailed water model analysis of the proposed watermain system for the Empire lands will be completed by the County of Brant’s engineer at the detailed design stage. The MTE report also details the anticipated staging of the Landowner Group’s developments over the next 10 years taking into consideration the required upgrades to the existing water supply and distribution system for which the County of Brant is currently completing a Class Environmental Assessment to accommodate the proposed additional growth within the St. George Area. As per the MTE report the Empire lands can proceed without a new water supply well and can proceed with a first phase of approximately 90 units per year. The existing watermain system will be upgraded by the County in accordance with the St. George Area Study recommendations. The watermain system will designed in accordance with the County of Brant, and MOECC criteria including:

Water Demand Rate: 350 L/c/d; Population Density (Low Density): 2.89 people/unit; Population Density (Medium Density): 1.94 people/unit; Population Density (High Density): 1.29 people/unit; Schools: 12.1 m3/ha/d Light Commercial Water Usage Rate: 40.5 m3/ha/d Community Services: 18 m3/ha/d Light Industrial: 45 m3/ha/d Minimum Pipe Size: 150 mm dia.; Minimum Pipe Depth: 1.8 m; and Maximum Hydrant Spacing: Townhouses: 150 m.



5.0 SITE GRADING

5.1 Existing Grading Conditions

Under existing conditions, the site generally slopes to the south toward Highway 5. The ground surface elevations through the study area range from approximately 279 m along the north western boundary to approximately 249.50 m along the south eastern boundary. 5.2 Proposed Grading Concept

In general, the site will be graded in a manner which will satisfy the following goals:

Satisfy the County of Brant road grading criteria which includes following the latest version of the Transportation Association of Canada’s (TAC) Geometric Design Guide for Canadian Roads Part 1 and 2;

Provide continuous road grades for overland flow conveyance; Minimize the need for retaining walls; Minimize the volume of earth to be moved and minimize cut/fill differential;

and Achieve the SWM objectives required for the site.

A preliminary grading plan is provided on Figure 5.1. The site will be graded to match the existing grades along all boundaries.



6.0 RIGHT-OF-WAYS AND SIDEWALKS

Streets A and B will utilize a County of Brant standard 26.0 m ROW with 9.14 m of pavement width. All other roads will utilize the County of Brant standard 20.0m ROW with 9.14 m of pavement width. As per the County of Brant design standards a sidewalk will be provided on one side for an urban local residential road and on each side for an urban collector residential road. The preliminary sidewalk plan is shown on Figure 6.1.



7.0 EROSION AND SEDIMENT CONTROL DURING CONSTRUCTION

During the detailed design stage, standard temporary erosion and sediment control measures will be designed, including sediment control fencing, construction entrances and temporary sediment control facilities. These measures will be designed and constructed as per the “Erosion and Sediment Control Guideline for Urban Construction” document (December 2006). A detailed erosion and sediment control plan will be prepared for review and approval by the Municipality and Conservation Authority prior to any site grading being undertaken. This plan will address phasing, inspection and monitoring aspects of erosion and sediment control. All reasonable measures will be taken to ensure sediment loading to the adjacent watercourses is minimized both during and following construction.

Empire Communities (St. George) Ltd. Functional Servicing and … · 2017-10-27 · Empire Communities (St. George) Ltd. Functional Servicing and Stormwater Management Report August

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