proposed moda development corporation …

PROPOSED

MODA DEVELOPMENT CORPORATION

DEVELOPMENT SITE

LOTS 55 AND 56

R-PLAN 89469

174 GLEBE AVENUE

CITY OF OTTAWA

STORM DRAINAGE REPORT

REPORT No. R-810-81 (REV. 1)

NOVEMBER 2011

T. L. MAK ENGINEERING CONSULTANTS LTD.

SEPTEMBER 2011

FILE REF. No. 810-81

INTRODUCTION The proposed Moda Development Corporation Glebe Avenue condominium site is located on the south side of Glebe Avenue and situated west of Lyon Street and east of Percy Street. Its legal property description is Lots 55 and 56 (R-Plan 89469). The property proposed for redevelopment is a compilation of two lots with municipal addresses consisting of 174 to 176 Glebe Avenue. A three-storey brick and stucco residential building presently occupies the site. A shared asphalt driveway located near the easterly limit of the property on 174 Glebe Avenue currently provides vehicular access to the rear of the lot for car parking. The developer is proposing to redevelop this ± 0.116 ha. property into a four-storey residential building site with an amenity area (Mechanical Room) above the fourth floor and a common joint use underground parking garage. Stormwater outlet for the said redevelopment property under consideration is a 525 mm diameter combined sewer along Glebe Avenue. According to the City of Ottawa Engineering Department, the allowable runoff into the 525 mm diameter combined sewer for this site shall be based on a pre-development C = 0.4, Tc = 10 minutes and a two year storm event. If the uncontrolled stormwater runoff exceeds the specified requirements, then on-site Stormwater Management (SWM) control measures are necessary. The post-development runoff coefficient for this site is estimated at C = 0.72 which exceeds the City’s criteria of C = 0.4. Stormwater runoff if uncontrolled will exceed the calculated pre-development flow based on a higher post-development “C” value, therefore, SWM measures are required for this redevelopment property. At this site, the maximum allowable rate of discharge established for review which was subsequently approved by the City of Ottawa and to be directed into the existing 525 mm diameter combined sewer is ± 15.0 L/s or equivalent to the flow of one (1) ICD plug with a 75 mm diameter orifice opening. This flow rate was established during a meeting with the City’s Mr. Josh White. The SWM calculations that follow will detail the extent of on-site SWM control to be implemented and the storage volume required on-site to attain the appropriate runoff release that will conform to the City’s established drainage criteria. SITE DATA 1.) Development Property Area

- Area characteristics of development lot

Roof Area = 786.0 m2

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Asphalt Area = 12.0 m2 Concrete/Paver Area = 67.70 m2

Grass Area = 292.24 m2

Total Area = 1,157.94 m2

C = (786.0 x 0.9) + (12.0 x 0.9) + (67.7 x 0.8) + (292.24 x 0.2) 1,157.94 = 830.81 1,157.94 = 0.717

Therefore average post-development “C” for the site = 0.72. - Tributary area consisting of approximately 625.24 m2 is directed off-site uncontrolled. The controlled site tributary area = 1,157.94 m2 – 625.24 m2 = 532.7 m2

2.) Controlled Area Data

Roof Surface Area = 532.7 m2

Total Stormwater Controlled Area = 532.7 m2

C = (532.7 x 0.9) 532.7 = 0.9

Therefore post-development “C” for the controlled stormwater drainage area is C = 0.9.

3.) Uncontrolled Area Data

Roof Area = 253.3 m2 Asphalt Area` = 12.0 m2

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Concrete/Paver Area = 67.7 m2 Grass Area = 292.24 m2

Total Stormwater Uncontrolled Area = 625.24 m2 C = (12.0 x 0.9) + (67.7 x 0.8) + (292.24 x 0.2) + (253.3 x 0.9) 625.24 = 351.38 625.24 = 0.562 C = 0.562

Therefore post-development “C” for the uncontrolled stormwater drainage area is C = 0.562.

- The SWM area to be controlled is 532.7 sq. m. Refer to the attached “Drainage Area Plan”

in Figure 1 for details. ALLOWABLE FLOW Maximum allowable off-site flow is the greater of either (i) or (ii) as shown below. (i) C = 0.4 Tc = 10 minutes I2 = 77.10 mm/hr (City of Ottawa, 2 year storm)

Using the Rational Method Q = 2.78 (0.4) (77.1) (0.116)

= 9.95 L/s OR

(ii) Equivalent flow of one (1) ICD plug with a 75 mm diameter orifice opening at rate of

15.0 L/s. Therefore the allowable flow off-site is (ii) which is 15.0 L/s allowable for this site.

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STORMWATER MANAGEMENT ANALYSIS The established flow rate of ± 15.0 L/s from this site is proposed to be directed into the existing 525 mm diameter combined sewer located on Glebe Avenue. Stormwater management attenuation for this site will incorporate flat rooftop storage only. It is proposed that the flat rooftop areas of the residential building Roof Area # 1, 2, 3, 4 and 5 will each incorporate a controlled roof drain to provide on-site stormwater detention. The flat rooftop for SWM detention of the building has a two tier level consisting of a main flat rooftop building level and a raised/elevated central rooftop (Mechanical Room) above the main rooftop. Both flat rooftop levels will be utilized for SWM purposes. For SWM attenuation purposes, each designated flat rooftop area will incorporate (1) controlled drain to control flow off-site. The smallest standard roof drain flow rate of 0.63 L/s (10 U.S. gal/min.) will be specified to release as low a flow as possible from the rooftops. Therefore from this building, (5) individual available flat roof areas each with a controlled drain is proposed and the minimum stormwater flow that can be controlled from the building and outletted off-site is 3.15 L/s. Roof Area # 1 = 167.0 m2 Roof Area # 2 = 136.4 m2

Roof Area # 3 = 39.0 m2

Roof Area # 4 = 104.2 m2 Roof Area # 5 = 86.1 m2 For the uncontrolled site area of 625.24 sq. m, the 100 year uncontrolled flow rate is estimated using the Rational Method. Q = 2.78 CIA C = 0.562

I = 120 mm/hr, Tc = 20 min. (City of Ottawa IDF data) A = 0.063 = 2.78 (0.562) (120) (0.063) = 11.81 L/s

Therefore the flow directly entering the 525 mm diameter combined sewer is the total of the controlled area from the rooftop drains and the flow from the uncontrolled drainage area

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(3.15 L/s + 11.81 L/s) which equals to 14.96 L/s. The total of the site controlled and uncontrolled area flow equals to 14.96 L/s which is less than the equivalent allowable flow of 15.0 L/s.

DESIGN DISCHARGE COMPUTATION The Rational Method was used to estimate peak flows. Q = 2.78 CIA To Calculate Roof Storage C = 0.9 will be used for sizing roof storage volume in this case. Inflow rate (QA) = 2.78 CIA where C = 0.9 A = Surface area of roof I = (mm/hr) The inflow rate or QACTUAL during the 100 year storm for each of the 5 sub-tributary/flat rooftop building areas of this site can be calculated as follows: For Tributary Area No. 1 (Roof Area # 1) QA1 = 2.78 CIA1 C = 0.90 A = 167.0 m2 I = (mm/hr) = 2.78 (0.9) (0.0167 ha.) I = 0.0418 I

For Tributary Area No. 2 (Roof Area # 2) QA2 = 2.78 CIA2 C = 0.90 A = 136.4 m2 I = (mm/hr) = 2.78 (0.9) (0.0136 ha.) I

= 0.0341 I

-5-


= 0.0098 I


= 0.026 I For Tributary Area No. 5 (Roof Area # 5) QA5 = 2.78 CIA5 C = 0.90 A = 86.1 m2 I = (mm/hr) = 2.78 (0.9) (0.00861 ha.) I = 0.0215 I The allowable discharge for Roof Area # 1 - 1 roof drain @ release rate of 10.0 U.S. gal/min. or 0.63 L/s. The allowable discharge for Roof Area # 2 - 1 roof drain @ release rate of 10.0 U.S. gal/min. or 0.63 L/s.

The allowable discharge for Roof Area # 3 - 1 roof drain @ release rate of 10.0 U.S. gal/min. or 0.63 L/s.

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The allowable discharge for Roof Area # 4 - 1 roof drain @ release rate of 10.0 U.S. gal/min. or 0.63 L/s. The allowable discharge for Roof Area # 5 - 1 roof drain @ release rate of 10.0 U.S. gal/min. or 0.63 L/s. Refer to Appendix B for typical standard roof drain details or equivalent to be used on this site. Please note the specified 10 U.S. gal/min. or 0.63 L/s roof drain for each of the (5) building roof areas will be custom made by the manufacturer to allow for a maximum release of 0.63 L/s under the specified head indicated in this report. This can now be used to determine the storage volume for the site using the Modified Rational Method. - Actual flow QACTUAL is calculated as:

QA(i) = 2.78 CIA(i) - QSTORED is calculated as:

QS(i) = QA(i) - QALLOW Summary results of the calculated inflow and the required storage volume of these (5) roof areas on this site to store the 100 year storm event are shown in Tables 1, 2, 3, 4 and 5. CONCLUSION The proposed Moda Development Corporation Glebe Avenue condominium site is comprised of a four-storey flat roof residential building complete with a common underground parking garage. The flat roof of the (4) storey building will be used for SWM detention. Above the central portion of the rooftop is a raised flat roof Mechanical Room (amenity area) which will be utilized for SWM storage also. Therefore the building consists of a raised central flat roof area and a main flat roof level. For stormwater management attenuation purposes, (1) controlled roof drain is proposed at the (5) available flat roof areas. Corresponding roof scuppers are proposed at the (2) flat roof levels per the architectural plan details. In order to control the 100 year event stormwater release rate off-site to an established allowable flow rate of 15.0 L/s, it is proposed that at each of the (5) flat roof areas a drain be installed and sized for a release rate of 0.63 L/s. Therefore, the controlled release rate off-site is 3.15 L/s from the building’s rooftops. Refer to the Proposed Servicing and Stormwater Management Plan Dwg. No. 810-81, S-1 for details. During the 100 year storm event for Roof Area # 1, the ponding depth on the flat roof area is estimated at 150 mm at the drain and 0 mm at the roof perimeter surface, assuming a 1% (typ.)

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TABLE 1

100 YEAR EVENT

REQUIRED STORAGE VOLUME AT ROOF AREA #1

tc

(min.)

I 100 YR. (mm/hr)

Q ACTUAL

(L/s)

Q ALLOW

(L/s)

Q STORED

(L/s)

VOLUME STORED

(m3) 5

10

15

20

25

30

40

50

60

70

80

242.7

178.6

142.9

120.0

103.8

91.9

75.1

63.9

55.9

49.8

45.0

10.15

7.47

5.97

5.02

4.34

3.84

3.14

2.67

2.34

2.08

1.88

0.63

0.63

0.63

0.63

0.63

0.63

0.63

0.63

0.63

0.63

0.63

9.52

6.84

5.34

4.39

3.71

3.21

2.51

2.04

1.71

1.45

1.25

2.86

4.10

4.81

5.27

5.57

5.78

6.02

6.12

6.16

6.09

6.00

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TABLE 2

100 YEAR EVENT

REQUIRED STORAGE VOLUME AT ROOF AREA # 2

tc

(min.)

I 100 YR. (mm/hr)

Q ACTUAL

(L/s)

Q ALLOW

(L/s)

Q STORED

(L/s)

VOLUME STORED

(m3) 5

10

15

20

25

30

35

40

50

60

70

242.7

178.6

142.9

120.0

103.8

91.9

82.6

75.1

63.9

55.9

49.8

8.28

6.10

4.88

4.10

3.54

3.14

2.82

2.56

2.18

1.91

1.70

0.63

0.63

0.63

0.63

0.63

0.63

0.63

0.63

0.63

0.63

0.63

7.65

5.47

4.25

3.47

2.91

2.51

2.19

1.93

1.55

1.28

1.07

2.30

3.28

3.83

4.16

4.37

4.52

4.60

4.63

4.65

4.61

4.49

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TABLE 3

100 YEAR EVENT


tc

(min.)

I 100 YR. (mm/hr)

Q ACTUAL

(L/s)

Q ALLOW

(L/s)

Q STORED

(L/s)

VOLUME STORED

(m3) 5

10

15

20

25

242.7

178.6

142.9

120.0

103.8

2.38

1.74

1.39

1.17

1.01

0.63

0.63

0.63

0.63

0.63

1.75

1.11

0.76

0.54

0.38

0.53

0.67

0.68

0.65

0.57

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TABLE 4

100 YEAR EVENT


tc

(min.)

I 100 YR. (mm/hr)

Q ACTUAL

(L/s)

Q ALLOW

(L/s)

Q STORED

(L/s)

VOLUME STORED

(m3) 5

10

15

20

25

30

35

40

50

242.7

178.6

142.9

120.0

103.8

91.9

82.6

75.1

63.9

6.31

4.64

3.72

3.12

2.70

2.39

2.15

1.95

1.66

0.63

0.63

0.63

0.63

0.63

0.63

0.63

0.63

0.63

5.68

4.01

3.09

2.49

2.07

1.76

1.52

1.32

1.03

1.70

2.41

2.78

2.99

3.11

3.17

3.19

3.17

3.09

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TABLE 5

100 YEAR EVENT

REQUIRED STORAGE VOLUME AT ROOF AREA #5

tc

(min.)

I 100 YR. (mm/hr)

Q ACTUAL

(L/s)

Q ALLOW

(L/s)

Q STORED

(L/s)

VOLUME STORED

(m3) 5

10

15

20

25

30

35

40

242.7

178.6

142.9

120.0

103.8

91.9

82.6

75.1

5.22

3.84

3.07

2.58

2.23

1.98

1.78

1.62

0.63

0.63

0.63

0.63

0.63

0.63

0.63

0.63

4.59

3.21

2.44

1.95

1.60

1.35

1.15

0.99

1.38

1.93

2.20

2.34

2.40

2.43

2.42

2.38

PROPOSED


DEVELOPMENT SITE

174 GLEBE AVENUE

CITY OF OTTAWA

APPENDIX A

STORM DRAINAGE AREA PLAN

FIGURE 1

PROPOSED


DEVELOPMENT SITE

174 GLEBE AVENUE

CITY OF OTTAWA

APPENDIX B

TYPICAL STANDARD

ROOF DRAIN DETAILS

PROPOSED


DEVELOPMENT SITE

174 GLEBE AVENUE

CITY OF OTTAWA

APPENDIX C

DETAILED CALCULATIONS FOR

100 YEAR

AVAILABLE STORAGE VOLUME

ROOFTOP STORAGE Roof area # 1 to 5 inclusive will be used for stormwater detention. Each area will be drained by a controlled drain designed for a release rate of 10.0 U.S. gal/min. 0.63 L/s. The building flat roof area is comprised of two different levels, a raised flat roof area of the amenity area above the fourth floor (Mechanical Room) and a main flat roof area of the fourth floor. Both levels of the building flat roof will be utilized for stormwater management attenuation. 100 Year Event 1.) Roof Storage Area # 1

- Available flat roof area for storage = 142.0 m2 @ roof slope of 1% (typ.) therefore the available roof area will store a volume as shown below using the reservoir equation. = (0.15 m) (142.0 + 4 (36.21) + 0) = (0.15) (286.84) 6 6 = 7.17 m3

The available storage volume of Roof Area # 1 is 7.17 m3 > required 100 year storage volume of 6.16 m3 from Table 1. The ponding depth at the proposed Roof Drain # 1 location is approximately 0.15 m or (150 mm) and 0 mm depth at the perimeter of this roof area. Therefore, it is recommended that roof scuppers be installed at 25 mm or 1 inch above the perimeter height of the rooftop for emergency overflow purposes in case of blockage from debris build up at the roof drain.

2.) Roof Storage Area # 2

- Available flat roof area for storage = 103.66 m2 @ roof slope of 1% (typ.) therefore the available roof area will store a volume as shown below using the reservoir volume equation. = (0.15 m) (103.66 + 4 (24.14) + 0) = (0.15) (200.22) 6 6 = 5.01 m3

(i)







The available storage volume of Roof Area # 4 is 3.61 m3 > required 100 year storage volume of 3.19 m3 from Table 4.

(ii)

(iii)

The ponding depth at the proposed Roof Drain # 4 location is approximately 0.15 m or (150 mm) and 0 mm depth at the perimeter of this roof area. Therefore, it is recommended that roof scuppers be installed at 25 mm or 1 inch above the perimeter height of the rooftop for emergency overflow purposes in case of blockage from debris build up at the roof drain.

5.) Roof Storage Area # 5 - Available flat roof area for storage = 82.36 m2 @ roof slope of 1% (typ.) therefore the available roof area will store a volume as shown below using the reservoir volume equation. = (0.1 m) (82.36 + 4 (20.73) + 0) = (0.1) (165.28) 6 6 = 2.76 m3


During the 100 year event, the required rooftop storage volume is 17.11 m3 and the available storage volume is 19.71 m3 at a ponding depth of 0.15 m at Roof Drain # 1, 2 and 4 and 0.1 m ponding depth at Roof Drain # 3 and 5. At the perimeter of the (5) different roof areas the ponding depth is 0 mm.

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