Appendix K. Stormwater Management Plan

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1 Regional Municipality of Halton - Steeles Avenue (Regional Road 8) Class EA - Industrial Drive to Regional Road 25/Martin Street Appendix K Stormwater Management Plan PR Rev. 2 PR.DOT, 00/01

2 MEMO To Mark Armstrong From Matt Knowles Date October 7, 2010 Project # Reference Stormwater Management Plan Page 1 of 4 CC Thom Budd The Halton Transportation Master Plan (2004) has identified the need to widen Steeles Avenue from two to four lanes within the study limits between Industrial Drive and Regional Road 25/Martin Street. The preferred alternative is to widen symmetrically about existing Steeles Avenue right-of-way. Roadway improvements are required to meet the needs of Halton Region to the year A hydrologic/hydraulic analysis of the Steeles Avenue corridor is required in order to establish the preliminary design criteria for stormwater management under the proposed roadway improvements. This memorandum summarizes the preliminary design for stormwater management to date. Current Conditions The study area is situated within the Sixteen Mile Creek watershed in Subwatershed #2 (PPEL, 1999). The Sixteen Mile Creek flows in a southeasterly direction crossing under Steeles Avenue via a single span concrete bridge to the west of the Study Area. From the bridge, the Sixteen Mile Creek meanders approximately 420 m before flowing through the CNR embankment via twin steel culverts. Downstream of the CNR, the Creek continues in a southeasterly direction passing under Bronte Street via a single span concrete bridge. Conservation Halton has prepared flood line mapping along Sixteen Mile Creek to identify potential hazards related to flooding. Review of the flood line maps (and computer model) indicates that the twin culverts under the CNR have insufficient capacity to convey the Regional (Hurricane Hazel) Storm flow under full flow conditions, resulting in a significant backwater that extends upstream of the CNR to Steeles Avenue. Storm water runoff from Steeles Avenue and the lot frontages along Steeles Avenue is collected and conveyed westward towards Sixteen Mile Creek by a drainage system consisting of overland flow, open ditches, driveway culverts and storm sewers. For the most part, the drainage system of ditches and driveway culverts is well defined east of the CNR, on the north side of Steeles Avenue. However, sediment build-up in the ditches, blocked and collapsed culverts were observed during a field reconnaissance conducted in March On the south side of Steeles Avenue, east of the CNR, the ditches and driveway culverts are present in the vicinity of Bronte Street, but are less well-defined closer to Regional Road 25/Martin Street. Existing developed areas along Industrial Drive, north of Steeles Avenue and west of the CNR 2800 Speakman Drive Mississauga, Ontario L5K 2R7 T F P:\HALTON\226401\DOCS\PR\ESR\FINAL ESR\APPENDICES\Appendix K - Stormwater Management Plan - Ready\Documents\1-SWM Memo.doc

3 MEMO To Mark Armstrong Date October 7, 2010 Page 2 of 4 are collected by a storm sewer system that discharges into an existing stormwater management facility that is located at the northwest corner of Industrial Drive and Steeles Avenue, which services the properties along Industrial Drive. At this location, a gabion basket outlet structure is present, which allows for ponding of storm water within a vegetated area prior to its conveyance southward under Steeles Avenue via culverts which discharge into Sixteen Mile Creek. The facility uses an existing outlet culvert approximately at Chainage to discharge to Sixteen Mile Creek. The existing culvert consists of two corrugated steel pipes. Proposed Design The proposed stormwater drainage system would have storm water from Steeles Avenue collected by curb side catch basins spaced 90 metres apart along the north and south side of the proposed alignment and directed towards 16 Mile Creek south of Industrial Drive. A dual Stormceptor (Model STC14000) would be located prior to the outlet structure to Sixteen Mile Creek which would intercept sediment and petroleum hydrocarbons from the runoff prior to discharge to the watercourse. The outlet structure to Sixteen Mile Creek will be located approximately at Chainage and will require construction of a new outlet swale to the creek. Some modification may be required to the existing stormwater management facility located at the northwest corner of Industrial Drive and Steeles Avenue due to the additional property required for the widening of Steeles Avenue. Retaining walls are proposed to minimize the affect of the loss of area for the stormwater management facility. During discussions with Conservation Halton it was ascertained that no design information regarding the existing stormwater management facility was available. An assessment of the effect to existing stormwater management and design of modifications is to be completed at detailed design in consultation with Conservation Halton. The existing outlet culvert should also be inspected during detailed design and replaced as part of the culvert extension to accommodate the widened road profile. In discussion with Conservation Halton, at detailed design of the outlet structures for both the new Stormceptor system and the existing Industrial Drive facilities will be designed using bioengineering principles to incorporated vegetated erosion and scour protection as well as riparian cover to mitigate thermal effects from stormwater discharge to Sixteen Mile Creek. The design of the required stormwater management facilities will be undertaken in consultation with Conservation Halton during detailed design. Hydrologic Analysis The hydrologic analysis of the proposed Steeles Avenue Study Area was completed using the Rational Method, which is widely used across the Province of Ontario and provides sufficient accuracy for preliminary analysis Speakman Drive Mississauga, Ontario L5K 2R7 T F

4 MEMO To Mark Armstrong Date October 7, 2010 Page 3 of 4 Catchment boundaries were delineated based on 5m contours provided by the Region of Halton as per attached Storm Drainage Plan sketch. The Rational Method is based on the following formula for runoff flow: Q CiA Where Q is the flow in cubic meters per second (m 3 /s); C is the runoff coefficient; i is the rainfall intensity in millimeters per hour (mm/hr) based on the Intensity-Duration-Frequency (IDF) values for a 1 in 5 year return period storm; and A is the area in hectares (ha). A runoff coefficient of 0.80 was used for preliminary analysis which is representative of industrial, residential, and commercial land uses. The intensity of rainfall (i) is based on Town of Halton Hills (1988) IDF Parameters for a 1 in 5 year return period storm event, provided in the following equation: i ( t 7.0) Where i is the rainfall intensity in millimeters per hour (mm/hr) and t is time in minutes. Detailed hydrologic calculations are provided as an attachment. Hydraulic Analysis The Town of Milton Engineering and Parks Development Standards (2004) require that the minor on convenience system, comprising street gutters, catchbasins and storm sewers, shall be designed to a minimum 1 in 5 year unsurcharged standard. In higher value commercial areas this may be increased to 1 in 10 year. For the purposes of this EA preliminary design a return period of 1 in 5 years was used. For the proposed design manholes were assumed to be spaced at 90m intervals connected by circular concrete pipe. Typical slopes for the sewer pipe would be 0.5%, with the exception of the section between MH7 and MH8 which would be 2.88%. Velocity and flow capacity for the storm sewers was determined using Manning s equation as follows: R V 2 3 S n Speakman Drive Mississauga, Ontario L5K 2R7 T F

5 MEMO To Mark Armstrong Date October 7, 2010 Page 4 of 4 Q V A Where R is the hydraulic radius of the pipe, S is the slope (m/m), and n is Manning s roughness coefficient. A roughness coefficient of was used for all pipes, which is consistent typical values for concrete pipe. Based on the hydraulic analysis the required nominal pipe sizes ranged from 375mm to 900mm nominal sizes of circular concrete pipe. Nine manholes were required to provide one manhole per 90m. Conclusions Based on the preceding analysis the proposed stormwater management system consists of approximately 555 meters of concrete pipe ranging in size from 375mm to 900mm, 16 single catchbasins, eight manholes, and a double Stormceptor (Model STC14000) to provide a 1 in 5 year design return period for the proposed modifications to Steeles Avenue. The dual Stormceptor would be located prior to the outlet structure to Sixteen Mile Creek, intercepting sediment and petroleum hydrocarbons from the runoff prior to discharge to the watercourse. References Phillips Planning and Engineering Limited (1999). Sixteen Mile Creek Subwatershed Study Areas 2 & 7, Subwatershed Management Strategies - Interim Working Paper #1. Town of Milton (2004). The Town of Milton Engineering and Parks Development Standards. Region of Halton (2004). Transportation Master Plan. Retrieved May 20, 2009 from Town of Halton Hills (1988). Intensity Duration Frequency Chicago Rainfall Distribution. 1 page received by fax. The Town of Milton (2004). Engineering and Parks Development Standards Speakman Drive Mississauga, Ontario L5K 2R7 T F

6 TABLE K.1 RATIONAL METHOD STORM SEWER DESIGN CALCULATIONS DRAINAGE AREA INFORMATION TIME OF CONCENTRATION STORM SEWER PIPE INFORMATION STREET FROM TO AREA DRAINAGE RUNOFF Area x C CUMML CUMML INLET FLOW TOTAL RAINFALL TOTAL FULL FLOW UPSTM DNSTM UPSTM DNSTM FLOW FLOW/PIPE UPSTM DNSTM ID AREA COEFF AREA AxC TIME TIME TIME INTENSITY RUNOFF MATERIAL MANNING SLOPE DIAMETER LENGTH VELOCITY CAPACITY OBVERT OBVERT INVERT INVERT TIME CAPACITY MH MH Aa Ca AaxCa At AtxCt Tci TCf TCt I Qr n So D L Vf Qf TCf (Qr/Qf) (ha) (ha) (min) (min) (min) (mm/hr) (m3/s) (m/m) (mm) (m) (m/s) (m3/s) (m) (m) (m) (m) (min) Steeles Ave concrete Steeles Ave concrete Steeles Ave concrete Steeles Ave concrete Steeles Ave concrete Steeles Ave concrete Steeles Ave concrete Steeles Ave concrete Steeles Ave concrete Steeles Ave concrete Steeles Ave 11 outfall concrete Town of Milton IDF Parameters derived from Pearson AES year I = / (TCt )^ year I = / (TCt )^ year I = / (TCt )^ year I = / (TCt )^ year I = / (TCt )^ year I = / (TCt )^0.776

CHECKLIST FOR PHASE II DRAINAGE REPORT

I. COVER SHEET CHECKLIST FOR PHASE II DRAINAGE REPORT A. Name of Project B. Address C. Owner D. Developer E. Engineer F. Submittal date and revision dates as applicable II. GENERAL LOCATION AND DESCRIPTION