D. B. G R A Y E N G I N E E R I N G I N C.

Transcription

1 STORMWATER MANAGEMENT REPORT 22 Perkins Street Ottawa, Ontario Report No SWM February 6, 2015 D. B. G R A Y E N G I N E E R I N G I N. Stormwater Management - Grading & Drainage - Storm & Sanitary Sewers - Watermains 700 Long Point ircle Ottawa, Ontario K1T 4E9 dbgray@rogers.com 1

2 STORMWATER MANAGEMENT REPORT 22 Perkins Street Ottawa, Ontario This report addresses the stormwater management requirements of a proposed threestorey 17 unit apartment building development located on 510 sq.m. of land 22 Perkins Street in Ottawa. The site located at the foot of a rock cliff. This report forms part of the stormwater management design for the proposed development. Refer to drawings -1 to -4 prepared by D. B. Gray Engineering Inc. WATER QUALITY: omments and recommendations concerning the stormwater quality criteria for this site are required from the RVA to determine if permanent on-site quality control measures required. During construction, an erosion and sediment control plan has been developed (see notes 2.1 to 2.4 drawing -3). In summary: To filter out construction sediment: geotextile fabric will be placed between the grate and frame of all existing catch basins adjacent to the site and all new catch basins as they are installed. WATER QUANTITY: The stormwater management criteria for quantity control are to control the post development peak flows for the 5-year and 100-year storm events to peak flows during the 5-year storm event using a pre-development runoff coefficient or runoff coefficient of 0.5, whichever is less; and the calculated time of concentration, but not less than 10 minutes. It is calculated that the pre-development conditions reflect a 5-year runoff coefficient of Using the Airport Formula for sheet flow, it is calculated that the existing time of concentration is 5.7 minutes. Therefore based on runoff coefficient of 0.32 and a time of concentration of 10 minutes and using the Rational Method; the predevelopment (existing) peak flow is 3.51 l/s. The drainage area includes an adjacent off-site area between the property and the rock cliff that does not need to be controlled (Drainage Area I 22 sq.m.). Adding drainage from this area the Maximum Allowable Flowrate is 3.78 l/s for the 100-year event and 3.63 l/s for the 5-year event. alculations are based on the Rational Method. The runoff coefficients for the 100 year event were increased by 25% to maximum

3 Stormwater will be stored within the development on the roof of the proposed building and in a cistern located adjacent to the building. The runoff from the perimeter of the site primarily the front yard and between the proposed building and rock cliff (Drainage Area II 85 sq.m.) will be allowed to flow uncontrolled off the site. The flow from these areas is calculated at the five year event at 10 minutes concentration. The roof drain will be flow control type installed with a parabolic shaped slotted weir (1 slot per weir drain at l/s per mm per slot - 5 USgpm per inch per slot) causing the storm water to pond on the roof (Drainage Area III 330 sq.m.). The roof drain drains to the cistern so stormwater released from the roof drains to the cistern so is added to the stormwater runoff generated from (Drainage Area IV 117 sq.m.). An inlet control device (ID) located at the outlet pipe of the cistern will control the release of stormwater off the site. The ID will restrict the flow and cause the stormwater to back up into the upstream cistern. Stormwater released through the ID will be conveyed off the site via a 250mm storm sewer that will discharge onto the surface near the north-west corner of the property. The ID shall be a Hydrovex "VHV Vertical Vortex Flow Regulator" and shall be sized by the manufacturer for a discharge rate of 1.54 l/s at 0.92 m head. It is calculated that an orifice area of 1963 sq.mm. (50mm diameter) and a discharge coefficient of will restrict the outflow rate to 1.54 l/s at a head of 0.92 m. Based on this orifice the maximum outflow rate for the 1:5 year storm event is calculated to be 1.15 l/s at 0.51 m. Since the stormwater management facility discharges to a combined sewer it is expected that a Ministry of Environment Environmental ompliance Approval (EA) will be required. 3

4 ONLUSIONS: WATER QUALITY: omments and recommendations concerning the stormwater quality criteria for this site are required from the RVA to determine if permanent on-site quality control measures required. An erosion and sediment control plan as been developed to be implemented during construction WATER QUANTITY: One Hundred Year Storm Event: The maximum allowable release rate for the one hundred year storm event for the site is 3.78 l/s. The post-development release rate for the 100-year storm event is calculated to be 3.78 l/s. Therefore the maximum post development release rate for the 100-year storm event is equal to the maximum permitted release rate. A maximum stored volume of cu.m. is required to achieve the post development release rate. Five Year Storm Event: The maximum allowable release rate for the five year storm event for the site is 3.63 l/s. The post-development release rate for the 5-year storm event is calculated to be 2.29 l/s. Therefore the maximum post development release rate for the 5-year storm event is less than the maximum permitted release rate. A maximum stored volume of 9.28 cu.m. is required to achieve the post development release rate. 4

5 Summary Tables ONE HUNDRED YEAR EVENT Drainage Area AREA II (Uncontrolled flow off site) AREA III (Roof) Maximum Maximum Maximum Maximum Allowable Release Volume Volume Release Rate Required Stored Rate l/s l/s cu.m. cu.m AREA I & IV TOTAL FIVE YEAR EVENT Drainage Area AREA II (Uncontrolled flow off site) AREA III (Roof) Maximum Maximum Maximum Maximum Allowable Release Volume Volume Release Rate Required Stored Rate l/s l/s cu.m. cu.m AREA I & IV TOTAL

6 STORMWATER MANAGEMENT ALULATIONS The orifice calculations are based on the following formula: Q = d x A o 2gh x 1000 where: Q = flowrate in litres per second d = coefficient of discharge A o = orifice area in sq.m. g = 9.81 m/s2 h = head above orifice in meters Flow control roof drain calculations are based on the following formula: Q = N x S x d x F where: Q = flowrate in litres per second N = number of roof drains S = slots per weir d = pond depth at roof drain in mm F = flowrate through each slot litres per second per mm pond depth (5 USgpm per inch) Storage calculations on the roof are based on the following formula for volume of a cone: V = (A x d)/3 where: V = volume in cu.m. A = ponding area in sq.m. d = ponding depth in meters alculations for sub-surface storage (manholes and sewer pipes) are based on the following formula for volume of a cylinder: V = L x Pi x (d/2) 2 where: V = volume in cu.m. L = depth of water in manhole or length of pipe in meters d = diameter of manhole or pipe in meters 6

7 22 PERKINS STREET Ottawa, Ontario 05-Feb-15 STORM WATER MANAGEMENT ALULATIONS Rational Method ONE HUNDRED YEAR EVENT Maximum Allowable Release Rate Pre-development onditions Roof Area: 76 sq.m Asphalt/oncrete Area: 10 sq.m Gravel Area: 4 sq.m Landscaped Areas: 420 sq.m Total atchment Area 510 sq.m Area (A): 510 sq.m. Time of oncentration: 10.0 min. (see below - use not less than 10 min.) Rainfall Intensity (i): 77 mm/hr (2 year event) Runoff oeficient (): 0.32 Flow Rate (2.78Ai): 3.51 l/s Time of oncentration: Sheet Flow Airport Formula Tc = 3.26 (1.1 - ) (L) 1/2 Sw 0.33 min Runoff oefficient (): 0.32 see above Sheet Flow Distance (L): 31 m Slope of Land (Sw): 15 % Time of oncentration (Sheet Flow): 5.7 min DRAINAGE AREA I (Off Site Area Not Required to be ontrolled): Roof Area: 0 sq.m Asphalt/oncrete Area: 0 sq.m Landscaped Areas: 22 sq.m Total atchment Area 22 sq.m Area (A): 22 sq.m. Time of oncentration: 10 min. Rainfall Intensity (i): 179 mm/hr (100 year event) Runoff oeficient (): 0.25 Flow Rate (2.78Ai): 0.27 l/s Maximum Allowable Release Rate: l/s (including flow from off-site)

8 DRAINAGE AREA II (Uncontrolled Flow Off Site): (ONE HUNDRED YEAR EVENT) Roof Area: 0 sq.m Asphalt/oncrete Area: 32 sq.m Landscaped Areas: 53 sq.m Total atchment Area 85 sq.m Area (A): 85 sq.m. Time of oncentration: 10 min. Rainfall Intensity (i): 179 mm/hr (100 year event) Runoff oeficient (): 0.53 Flow Rate (2.78Ai): 2.25 l/s 8

9 DRAINAGE AREA III (Roof): (ONE HUNDRED YEAR EVENT) Roof Area: 330 sq.m Paved Area: 0 sq.m Landscaped Areas: 0 sq.m Total atchment Area 330 Ave No. of Roof Drains: 1 Slots per Wier: l/s/mm/slot (5 USgpm/in/slot) Depth at Roof Drain: 143 mm Maximum Release Rate 1.77 l/s Pond Area: 259 sq.m. Achieved Vol: cu.m. Max. Vol. Required: cu.m. Release Stored Stored Time i 2.78Ai Rate Rate Volume min. mm/hr l/s l/s l/s cu.m

10 DRAINAGE AREA IV (ONE HUNDRED YEAR EVENT) Roof Area: 0 sq.m Asphalt/oncrete Area: 32 sq.m Landscaped Areas: 85 sq.m Total atchment Area 117 sq.m Water Elevation: m ID Invert: m (Outlet Pipe of istern): istern Head: 0.92 m Area Depth sq.m. m Orifice Diameter 50 mm cu.m. Orifice Area: 1963 sq.mm. oefficient of Discharge: Achieved Vol: 7.00 cu.m. Maximum Release Rate: 1.54 l/s Max. Vol. Required: 7.00 cu.m. Flow From Total Release Stored Stored Time i 2.78Ai Roof Inflow Rate Rate Volume min. mm/hr l/s l/s l/s l/s l/s cu.m

11 FIVE YEAR EVENT Maximum Allowable Release Rate Pre-development onditions Roof Area: 76 sq.m Asphalt/oncrete Area: 10 sq.m Gravel Area: 4 sq.m Landscaped Areas: 420 sq.m Total atchment Area 510 sq.m Area (A): 510 sq.m. Time of oncentration: 10.0 min. (see below - use not less than 10 min.) Rainfall Intensity (i): 77 mm/hr (2 year event) Runoff oeficient (): 0.32 Flow Rate (2.78Ai): 3.51 l/s Time of oncentration: Sheet Flow Airport Formula Tc = 3.26 (1.1 - ) (L) 1/2 Sw 0.33 min Runoff oefficient (): 0.32 see above Sheet Flow Distance (L): 31 m Slope of Land (Sw): 15 % Time of oncentration (Sheet Flow): 5.7 min DRAINAGE AREA I (Off Site Area Not Required to be ontrolled): Roof Area: 0 sq.m Asphalt/oncrete Area: 0 sq.m Landscaped Areas: 22 sq.m Total atchment Area 22 sq.m Area (A): 22 sq.m. Time of oncentration: 10 min. Rainfall Intensity (i): 104 mm/hr (5 year event) Runoff oeficient (): 0.20 Flow Rate (2.78Ai): 0.13 l/s Maximum Allowable Release Rate: 3.63 l/s (including flow from off-site) 11

12 DRAINAGE AREA II (Uncontrolled Flow Off Site): (FIVE YEAR EVENT) Roof Area: 0 sq.m Asphalt/oncrete Area: 32 sq.m Landscaped Areas: 53 sq.m Total atchment Area 85 sq.m Area (A): 85 sq.m. Time of oncentration: 10 min. Rainfall Intensity (i): 104 mm/hr (5 year event) Runoff oeficient (): 0.46 Flow Rate (2.78Ai): 1.14 l/s 12

13 DRAINAGE AREA III (Roof): (FIVE YEAR EVENT) Roof Area: 330 sq.m Paved Area: 0 sq.m Landscaped Areas: 0 sq.m Total atchment Area 330 Ave No. of Roof Drains: 1 Slots per Wier: l/s/mm/slot (5 USgpm/in/slot) Depth at Roof Drain: 109 mm Maximum Release Rate 1.36 l/s Pond Area: 153 sq.m. Achieved Vol: 5.57 cu.m. Max. Vol. Required: 5.57 cu.m. Release Stored Stored Time i 2.78Ai Rate Rate Volume min. mm/hr l/s l/s l/s cu.m

14 DRAINAGE AREA IV (FIVE YEAR EVENT) Roof Area: 0 sq.m Asphalt/oncrete Area: 32 sq.m Landscaped Areas: 85 sq.m Total atchment Area 117 sq.m Water Elevation: m ID Invert: m (Outlet Pipe of istern): istern Head: 0.51 m Area Depth sq.m. m Orifice Diameter 50 mm cu.m. Orifice Area: 1963 sq.mm. oefficient of Discharge: Achieved Vol: 3.71 cu.m. Maximum Release Rate: 1.15 l/s Max. Vol. Required: 3.71 cu.m. Flow From Total Release Stored Stored Time i 2.78Ai Roof Inflow Rate Rate Volume min. mm/hr l/s l/s l/s l/s l/s cu.m