Detailed Stormwater Management Report David Manchester Road

Transcription

1 Detailed Stormwater Management Report David Manchester Road Prepared for: Nortrax Canada Inc. 189 Cardevco Road Carp, Ontario K0A 1L0 Prepared by: McIntosh Perry Consulting Engineers Ltd. 115 Walgreen Road, RR3 Carp, ON K0A 1L0 January 2014 MPCE No.

2 Detailed Stormwater Management Report City of Ottawa David Manchester Road Table of Contents 1.0 PURPOSE SITE DESCRIPTION PROPOSED STORMWATER MANAGEMENT DESIGN CRITERIA AND METHODOLOGY RUNOFF CALCULATIONS PRE-DEVELOPMENT DRAINAGE DRAINAGE AREA A DRAINAGE AREA A POST-DEVELOPMENT DRAINAGE DRAINAGE AREA B DRAINAGE AREA B1A DRAINAGE AREA B FLOW RATE CITY OF OTTAWA, STRESS TEST BEST MANAGEMENT PRACTICES (BMPs) STORMWATER MANAGEMENT FACILITY (SWMF) STORMWATER MANAGEMENT FACILITY DESIGN STORMWATER MANAGEMENT FACILITY QUALITY CONTROL STORMWATER MANAGEMENT FACILITY QUANTITY CONTROL STORMWATER MANAGEMENT FACILITY MAINTENANCE PROVINCIAL POLICY STATEMENT, EROSION AND SEDIMENT CONTROL TEMPORARY MEASURES PERMANENT MEASURES EXTERNAL REFERENCES SUMMARY RECOMMENDATIONS...10 i

3 Detailed Stormwater Management Report City of Ottawa David Manchester Road LIST OF APPENDICES APPENDIX A: APPENDIX B: APPENDIX C: KEY PLAN PRE-DEVELOPMENT DRAINAGE PLAN & CALCULATIONS POST-DEVELOPMENT DRAINAGE PLAN & CALCULATIONS ii

4 Detailed Stormwater Management Report City of Ottawa David Manchester Road 1.0 PURPOSE This final stormwater management report will address the proposed stormwater management requirements for the road upgrade of David Manchester Road. Please refer to Appendix A: Location Plan for the site location. The proposed road upgrade will consist of a partial depth reconstruction. The proposed work will include widening and paving approximately 200m of the existing gravel driving surface as well as roadside ditches which will direct the runoff to existing roadside ditches. 2.0 SITE DESCRIPTION The proposed road upgrade on David Manchester Road is located between Hazeldean Road to the south-east and Richardson Side Road to the north-west. The site is an existing gravel road and is surrounded by wooded areas. The site topography ranges in elevation from 137.5m at the south-east corner to 134.5m at the north-west corner. 3.0 PROPOSED STORMWATER MANAGEMENT 3.1 DESIGN CRITERIA AND METHODOLOGY There is no subwatershed plan in the area, and as such the Ministry of Environment (MOE) Stormwater Management Planning & Design Manual March 2003 (hereby referred to as the MOE Design Manual) will be used as the primary design guideline in determining stormwater control for this development. Stormwater Best Management Practices (SWM BMP s) will be implemented at the Lot level and Conveyance.. These concepts will be explained further in Section 3.7. To summarize, water will sheet flow into proposed roadside ditches. The SWM facility will consist of roadside ditches treating quality with a normal level of quality control. The site matches post- to pre-development flow rates. 3.2 RUNOFF CALCULATIONS Runoff calculations presented in this report are derived using the Rational Method, given as: Q 2. 78CIA (L/s) Where C = Runoff coefficient I A = Rainfall intensity in mm/hr = Drainage area in hectares 1

5 Detailed Stormwater Management Report City of Ottawa David Manchester Road It is recognized that the rational method tends to overestimate runoff rates. As a by-product of using extremely conservative prediction method, any facilities that are sized using these results are expected to function as intended in real world conditions. The overland travel time of concentration for each of the drainage areas was derived using the Airport Formula: (1.1 c) L L d 60 Tc, (min) 0.33 S V w Where: C= Balanced Runoff Coefficient L= Length of Overland Sheet Flow (m) S w = Average Slope of Watershed (%) L d = Length of Ditch (m) V = Velocity of Water (m/s) The following coefficients were used to develop an average C for each area: Buildings / Asphalt 0.90 Gravel Roads 0.70 Grass 0.30 Rainfall intensities are derived from the Intensity-Duration-Frequency curves for the City of Ottawa. As per the City of Ottawa Sewer Design Guideline, the balanced C value must increase by 25% when going from a 5- year storm to a 100-year storm event to a maximum value of 1.0. Stormwater sewers/culverts are designed and checked based on Manning s Equation, which is V= 1/n x R 2/3 x S 1/2 Where, V = velocity (m/s) n = roughness coefficient (0.010 for PVC and CP) R = hydraulic radius (area/wetted perimeter) S = slope of pipe Using the continuity principal: Q= V x A Where, Q = flow (L/s) A = cross-sectional area (m 2 ) V = Velocity (m/s) 2

6 Detailed Stormwater Management Report City of Ottawa David Manchester Road 3.3 PRE-DEVELOPMENT DRAINAGE A Pre-Development Drainage Area Plan, provided in Appendix B, details the limits to the drainage areas in the vicinity of the subject lands. The drainage schemes have been detailed further below: DRAINAGE AREA A1 Pre-development drainage area A1 represents the area north east of David Manchester Road. This drainage area has an existing road side ditch along the paved portion of David Manchester Road. The south-eastern portion of this drainage area drains to the south east into the existing road side ditch that flows to the west. From the limit of the existing ditch the drainage continues to sheet flow to the north-west. This drainage area is flat with only a small variance in topography from 137 m at the eastern limits to 134.5m at the western limits. This area covers approximately 0.75 hectares, and generates estimated peak runoff rates of 67 L/s and 143 L/s for the 5- and 100-year storms, based on runoff coefficients of 0.40 and 0.50 respectively DRAINAGE AREA A2 Pre-development drainage area A2 encompasses the area south-west of David Manchester Road. Drainage from this area sheet flows towards the northwest where it will enter into an existing roadside ditch. The topography from this area varies from 138m at the east boundary to 134.5m. This area is comprised of vacant treed sections with an existing section of gravel road. This area covers approximately 3.19 hectares, and generates estimated peak runoff rates of 105 L/s and 223 L/s for the 5- and 100-year storms, based on runoff coefficients of 0.32 and 0.40 respectively. Refer to Appendix B for the Pre-Development Drainage Plan and associated calculations. Table 1: Pre-Development Runoff Summary Area ID Drainage Area (ha) Runoff Coefficient T c (min) Peak Flow (L/s) 5-year 100-year - 5-year 100-year A A Total David Manchester Road - Pre-Development Drainage Area Results sheet located in Appendix B 3.4 POST-DEVELOPMENT DRAINAGE The Post-Development Drainage Area Plan is provided in Appendix C. The left roadside ditch will be extended to an existing easement from there the drainage will sheet flow to the North West. To adhere to the City of Ottawa requirements, the balanced runoff coefficients for the 100-year event were increased by 25%. In addition, the City has released a Technical Bulletin ( ) which notes that the system must be tested for an increase of 20% of the total intensity rates based on the City s IDF curve. To ensure the worst case scenario, only the post-development intensities were increased. The roadside ditches have been designed to accommodate the major storm events. The post-development drainage areas are detailed below: 3

7 Detailed Stormwater Management Report City of Ottawa David Manchester Road DRAINAGE AREA B1 Post-development drainage area B1 represents the area north-east of David Manchester Road. This area will sheet flow to the south west before entering the roadside ditch. The proposed north-east roadside ditch will accommodate the flows from drainage area B1 and B1A and will flow towards the north-west until it ties into an existing easement. From this point the flow will continue to sheet flow as per the pre-development conditions. This area is 0.75 hectares and has runoff coefficients of 0.48 and 0.57, resulting in estimated peak flow rates for the 5-,100- and 100-year (stress test) events of 88 L/s, 185 L/s and 222 L/s respectively DRAINAGE AREA B1A Post-development drainage area B1A represents the area south-east of David Manchester Road. This area will sheet flow towards the north-west prior to entering the south-west roadside ditch. The flow in this section of the roadside ditch will enter into a road crossing culvert that will outlet into the north-east road side ditch in drainage area B1. This area is 1.22 hectares and has runoff coefficients of 0.34 and 0.42, resulting in estimated peak flow rates for the 5-,100- and 100-year (stress test) events of 56 L/s, 118 L/s and 141L/s respectively DRAINAGE AREA B2 Post-development drainage area B2 represents the area south-west of David Manchester Road. Similar to the pre-development flow this area will sheet flow towards the north-west prior to entering the south West roadside ditch. The flow in this section of the roadside ditch will pass through a driveway culvert ultimately tying into the existing roadside ditch. The 1.97 hectare drainage area with runoff coefficients of 0.32 and 0.40 will produce estimated peak flows for the 5-,100- and 100-year (stress test) events of 72 L/s, 154 L/s and 185L/s respectively. Refer to Appendix B for the Pre-Development Drainage Plan and associated calculations. Table 2: Post-Development Runoff Summary Area ID Drainage Runoff Coefficient T c (min) Peak Flow (L/s) Stress Test Area (ha) 5-year 100-year Peak - Flow 5-year 100-year 100-year B1+B1A B Total David Manchester Road - Post-Development Drainage Area Results sheet located in Appendix C 3.5 FLOW RATE The stormwater management approach is a post-development design which does not exceed the peak predevelopment flow rate during the 100-year post-development. The overall post-development flow rate for the 100-year storm event matches the pre-development flow rate however the north-east ditch will 4

8 Detailed Stormwater Management Report City of Ottawa David Manchester Road experience an increase of 42L/s. This increase is due to the flow from drainage area B1A being directed into the north-east ditch through a road crossing culvert. In the pre-development conditions this flow was directed into the south-west ditch. Based on the overall pre and post-development drainage pattern the flow in the south-west ditch will travel in a northerly direction and will eventually cross David Manchester Road. The increase in the north-east ditch will not have an impact on the downstream infrastructure as the flow from the south-west ditch eventually merges with the flow from the north-east ditch. 3.6 CITY OF OTTAWA, STRESS TEST The City of Ottawa has implemented a new requirement for developments in its area to account for the future anticipated climate change. The stress test recommended by the City of Ottawa Technical Bulletin section 4 describes that the drainage system must be tested at an increase of 20% of the City s IDF curve rainfall values. It also notes that further modification to the drainage system will be required should severe flooding to properties be identified. All roadside ditches have been reviewed for the calculated stress tested peak runoff rates and have the capacity to accommodate the 100-year storm stress tested event. 3.7 BEST MANAGEMENT PRACTICES (BMPs) The entire site will employ Best Management Practices (BMP s) wherever possible. The intent of implementing stormwater BMP s throughout the site is to ensure that water quality and quantity concerns are addressed at all stages of construction. BMP s will be implemented at the conveyance and end of pipe levels. The conveyance system to be used in the site is overland flow. All ditches will be constructed at minimal gradient where possible, thus promoting absorption and infiltration, as well as providing opportunity for particle filtration. All disturbed areas shall be re-vegetated as soon as possible. The roadside ditches will implement end-of-pipe BMP s by providing a total suspended solids removal rate of 70% and matching the post-development flows to pre-development runoff rates STORMWATER MANAGEMENT FACILITY (SWMF) The Mississippi Valley Conservation Authority relies on the MOE Design Manual as the current guideline applicable to the stormwater component of this project. The ultimate goal of the stormwater management facility is to manage both quantity and quality of runoff released to the roadside ditch. Our past experience with similar projects has given us a good frame of reference in selecting appropriate quality control requirements. The roadside ditches will allow for both large particle settlement and ground water recharge. The proposed roadside ditches will be constructed as flat bottom ditches with grassed lined side slopes. To ensure the volume requirements are met for the roadside ditches, the flat bottom sections will be 0.75m wide. During the 5- and 100-year storm events, the roadside ditch has the storage required to meet post- 5

9 Detailed Stormwater Management Report City of Ottawa David Manchester Road development flow rates. The depth of storage required in the 5-year event within the North East roadside ditch is approximately 0.24m and 0.14m for the south-west roadside ditch. The depth of storage required in the 100-year event within the north-east roadside ditch is approximately 0.35m and 0.21m for the southwest roadside ditch. It should be noted that all the ditches will be constructed with rip rap on the bottom. The ditches will be constructed with a minimum 0.3 m rock shatter in areas where rock is present. This will allow additional storage, while also providing improved quality as it facilitates infiltration and large particle settlement. Furthermore, 200 mm of sandy import material overtop of 300 mm of clear stone wrapped in geotextile will be placed below the ditch invert where the ditch slopes exceed 0.5%. This will provide additional quality measures as well as supplementary storage. It should be noted that this available storage has not been accounted for in the calculations, resulting in a conservative design. Maintenance on the roadside ditch can be facilitated from the roadway therefore a maintenance easement on the opposite side of the roadside ditch will not be required. 3.8 STORMWATER MANAGEMENT FACILITY DESIGN STORMWATER MANAGEMENT FACILITY QUALITY CONTROL Stormwater management quality control will be provided within the roadside ditch. The target TSS removal rate for a ditch providing a normal level of protection is 70%. All the ditches will be constructed with rip rap on the bottom. In the areas where the ditch slope exceeds 0.5%, the ditches will be lined with 200mm of sandy material and 300mm of clear stone below the ditch invert, as well as 300mm of rock shatter when ditches are in rock. In order to illustrate the sediment loading for the proposed road upgrade, the sediment loading spread sheet typically used for stormwater management ponds is altered to represent a ditch. The proposed enhanced roadside ditches will see a relatively wide flat bottom in addition to minimal slopes wherever possible. The proposed roadside ditch will see a 70% removal based on its physical characteristics. The following outlines the comparison between the MOE standards and our design, for which the proposed design meets or exceeds almost all aspects of the design. Table 3: MOE Design Guidelines vs. MPCE Design MOE Design Guidelines MPCE Design Drainage Area <5 hectares <5 hectares Side Slopes >2.5 : 1 2 : 1 Depth Shallow / minimized m Bottom Width >0.75m 0.75m Roadside Ditch Velocity <0.5m/s m/s Grade <1% 0.5% -2.3% *Values in Table 3 based on 5 year storm event. 6

10 Detailed Stormwater Management Report City of Ottawa David Manchester Road From the results provided in Table 3 our design exceeds the side slopes and the grades recommended. The grade on the north-east ditch meets the required 0.5% however the south-west ditch varies from 0.5% to 2.3%. Measures will be taken to increase the permeability of the ditches in areas where the grade exceeds 0.5%. To further increase the permeability, the ditches will be lined with 200mm of sandy material and 300mm of clear stone below the ditch invert, as well as 300mm of rock shatter when ditches are in rock. All of the ditches have side slopes of 2:1 however the flow depth is minimal. During a 5-year storm event the depths vary from 0.14m to 0.24m. Based on the minimum flow depth the proposed quality control measures are adequate to remove the required TSS STORMWATER MANAGEMENT FACILITY QUANTITY CONTROL As there is no increase in runoff from the site during the 5-year storm event and 100-year storm event, the capacity of the culverts downstream will not be compromised. As such detailed calculations to ensure that an increase would be able to pass through the culverts will not be required STORMWATER MANAGEMENT FACILITY MAINTENANCE The proposed infiltration ditches will provide the benefits of increased overall quality and quantity management however the ditches will also require maintenance. Maintenance of stormwater measures is a standard requirement. The benefits generated from the ditches greatly outweigh the minor maintenance required when spread across its operating life cycle. The ditches will be accessible to perform any necessary cleanout, vegetation removal or debris removal. In order to provide the Best Management Practices, it will be necessary for routine maintenance checks which will aid in the long-term performance of the stormwater management facilities. Recommended maintenance for a typical infiltration ditches, as per Table 6.1 of the MOE Stormwater Management Planning & Design Manual, includes routine inspection, grass cutting as required, removal of accumulated sediment, and trash removal. The level of oversight and general maintenance required would be considered low. It is recommended that during the first two years of operation, inspections should be made after every significant storm event (approximately four inspections per year). After the first two years, only annual inspections may be required. The MOE also suggests stormwater measures are to be maintained once a 5% reduction is volume is observed. Again, based on the limited sediment loading this requirement is not believed to be of great concern however, it should be reviewed annually during the inspections. 3.9 PROVINCIAL POLICY STATEMENT, 2005 The Provincial Policy Statement, which came into effect on March 1, 2005, and was issued under Section 3 of the Planning Act, notes that Planning authorities shall protect, improve or restore the quality and quantity of water by: 7

11 Detailed Stormwater Management Report City of Ottawa David Manchester Road (a) using the watershed as the ecologically meaningful scale for planning; (b) minimizing potential negative impacts, including cross-jurisdictional and cross-watershed impacts; (c) identifying surface water features, ground water features, hydrologic functions and natural heritage features and areas which are necessary for the ecological and hydrological integrity of the watershed; (d) implementing necessary restrictions on development and site alteration to: 1. protect all municipal drinking water supplies and designated vulnerable areas; and 2. protect, improve or restore vulnerable surface and ground water, sensitive surface water features and sensitive ground water features, and their hydrologic functions; (e) maintaining linkages and related functions among surface water features, ground water features, hydrologic functions and natural heritage features and areas; (f) promoting efficient and sustainable use of water resources, including practices for water conservation and sustaining water quality; and (g) ensuring stormwater management practices minimize stormwater volumes and contaminant loads, and maintain or increase the extent of vegetative and pervious surfaces. In regards to the stormwater management plan for the proposed site, subsections (e), (f) and (g) of the above directly apply. With respect to subsection (e), the stormwater management plan provides that postdevelopment drainage patterns will be consistent with pre-development patterns such that natural features existing within the site are not negatively impacted by altered drainage flows. Currently this site sheet flows into existing roadside ditches along David Manchester Road that flow in a north-westerly direction. Drainage from the reconstructed roadway will be directed to these locations. With respect to subsections (f) and (g), it is expected that the stormwater will be treated to a normal level. This will be achieved through the use of best management practices. 4.0 EROSION AND SEDIMENT CONTROL 4.1 TEMPORARY MEASURES Before construction begins, temporary silt fence and rock flow check dams will be installed at all natural runoff outlets from the property. Silt fences will be installed where shown on the final engineering plans, specifically along the existing ditches. The Contractor, at their discretion or at the instruction of City of Ottawa, Mississippi Valley Conservation Authority or the Contract Administrator shall increase the quantity of sediment and erosion controls on-site 8

12 Detailed Stormwater Management Report City of Ottawa David Manchester Road to ensure that the site is operating as intended and no additional sediment finds its way into the ditches on site. The rock flows, straw bales and silt fences shall be inspected weekly and after rainfall events. Care shall be taken to properly remove sediment from the fences and check dams as required. Work through winter months will be closely monitored for erosion along sloped areas. Should erosion be noted, the Contractor shall be alerted and will take all necessary steps to rectify the situation. Should the Contractor s efforts fail at remediating the eroded areas, the Contractor shall contact the Mississippi Valley Conservation Authority to review the site conditions and determine the appropriate course of action. As the ground begins to thaw, the Contractor shall place silt fencing at all required locations as soon as ground conditions both warrant and permit. 4.2 PERMANENT MEASURES Rip rap will be placed all along the bottom of the proposed left and right ditch. Where the ditch slopes exceed 0.5%, the roadside ditches will have 200mm of sandy material and 300mm of clear stone placed below the ditch invert. This will provide an additional opportunity for particle settlement and filtration. When in rock, the ditch will have a 300mm rock shatter bottom, thereby providing additional sediment control measures. It is expected that the Contractor will promptly ensure that all disturbed area receive topsoil and seed and that grass be established as soon as possible. Any areas of excess fill shall be removed or levelled as soon as possible and must be located a sufficient distance from any watercourse to ensure that no sediment is washed out into the watercourse. As the vegetation growth along the proposed roadside and stormwater ditches provides a key component to the control of sediment for the site, it must be properly maintained once established. 5.0 EXTERNAL REFERENCES In regards to the sequence of the implementation of the site stormwater management, the Contractor will be required to place all temporary sediment and erosion controls throughout the site prior to commencement of work. The Ministry of the Environment ECA will be required prior to any ditch construction on site and any concentrated flow leaving the site towards the outlets described in the report. Once the ECA has been approved and received, the Contractor will be permitted to commence ditch construction and place permanent sediment erosion controls where required. The Contractor will also be required to topsoil and seed all areas that have been disturbed as soon as possible to limit the potential suspended solids should a large rain event occur. 9

13 Detailed Stormwater Management Report City of Ottawa David Manchester Road 6.0 SUMMARY Drainage will be directed into the roadside ditch where post-development peak flow-rates will not exceed pre-development levels for either the 5- or 100-year storm events. Best Management Practices will be implemented to provide adequate quality control. Matching post- to pre-development flow rates will ensure that no downstream infrastructure will be negatively affected by the proposed road upgrade. 7.0 RECOMMENDATIONS Based on the information presented in this report, we recommend that the City of Ottawa and the Mississippi Valley Conservation Authority approve this revised Final Stormwater Report in support of David Manchester Road Reconstruction. Regards, Karen Forbes, C.Tech McIntosh Perry Consulting Engineers T: (2214) E: Phil Whelan, P.Eng. McIntosh Perry Consulting Engineers T: (2215) E: 10

14 APPENDIX A KEY PLAN

15

16 APPENDIX B PRE-DEVELOPMENT DRAINAGE PLAN & CALCULATIONS

17 1 ISSUED FOR REVIEW JAN 23, 2014 No. Revision/Issue Date Check and verify all dimensions before proceeding with the work Do not scale drawings Stamp: Client: Nortrax Canada Inc. 189 Cardevco Road Carp, Ontario Project: 190 David Manchester Road DAVID MANCHESTER ROAD UPGRADE Ottawa ON Drawing Title: PRE-DEVELOPMENT DRAINAGE AREAS Scale: Drawn by: Checked By: Designed By: Date: NOT TO SCALE KF PW CDM JAN 23, 2014 Project Number: Drawing Number: SHEET 1 of 2

18 PRE-DEVELOPMENT RUNOFF COEFFICIENT CALCULATIONS Area A1 Type C (5-yr) C (100-yr) Area (m²) Product (5-yr) Product (100-yr) Hard Surface Granular Surface Grass Avg C Area A2 Type C (5-yr) C (100-yr) Area (m²) Product (5-yr) Product (100-yr) Hard Surface Granular Surface Grass Avg C

19 PRE-DEVELOPMENT RUNOFF CALCULATIONS Location Area (ha) Run-off Coeficient (5yr) Run-off Coeficient (100yr) A A Total Time of Concentration Location Length (m) Velocity (m/s) Run-off Coeficient Slope (%) Airport Formula Tc Channel Flow Tc Total Tc Ditch A Overland A Overland A Rainfall Intensity Area Tc(min) 5-Year (mm/hr) 100-Year (mm/hr) A A Year Storm Event Flow Rate Area Run-off Coeficient (5yr) Rainfall Intensity Area (ha) Flow (L/s) A A Year Storm Event Flow Rate Area Run-off Coeficient (5yr) Rainfall Intensity Area (ha) Flow (L/s) A A

20 APPENDIX C POST-DEVELOPMENT DRAINAGE PLAN & CALCULATIONS

21 1 ISSUED FOR REVIEW JAN 23, 2014 No. Revision/Issue Date Check and verify all dimensions before proceeding with the work Do not scale drawings Stamp: Client: Nortrax Canada Inc. 189 Cardevco Road Carp, Ontario Project: 190 David Manchester Road DAVID MANCHESTER ROAD UPGRADE Ottawa ON Drawing Title: POST-DEVELOPMENT DRAINAGE AREAS Scale: Drawn by: Checked By: Designed By: Date: NOT TO SCALE KF PW CDM JAN 23, 2014 Project Number: Drawing Number: SHEET 2 of 2

22 POST-DEVELOPMENT RUNOFF COEFFICIENT CALCULATIONS Area B1 Type C (5-yr) C (100-yr) Area (m²) Product (5-yr) Product (100-yr) Hard Surface Granular Shoulder Grass Avg C Area B1-A Type C (5-yr) C (100-yr) Area (m²) Product (5-yr) Product (100-yr) Hard Surface Granular Shoulder Grass Avg C Area B2 Type C (5-yr) C (100-yr) Area (m²) Product (5-yr) Product (100-yr) Hard Surface Granular Shoulder Grass Avg C Area B1 + B1-A Balanced C Type C (5-yr) C (100-yr) Area (m²) Product (5-yr) Product (100-yr) Hard Surface Granular Shoulder Grass Avg C

23 POST-DEVELOPMENT RUNOFF CALCULATIONS Location Area (ha) Run-off Coeficient (5yr) Run-off Coeficient (100yr) B B1-A B B1+B1-A Balanced Total B1-A Time of Concentration Location Length (m) Velocity (m/s) Run-off Coeficient Slope (%) Airport Formula Tc Channel Flow Tc Total Tc Overland B1-A Ditch B1-A Total 35 Rainfall Intensity Tc B1+B1A Time of Concentration Location Length (m) 5-Year (mm/hr) 100-Year (mm/hr) Velocity (m/s) Run-off Coeficient Slope (%) Airport Formula Tc Channel Flow Tc Total Tc Overland B1A Ditch B1+B1A Total 44 Rainfall Intensity Tc Year (mm/hr) 100-Year (mm/hr)

24 POST-DEVELOPMENT RUNOFF CALCULATIONS B2 Time of Concentration Location Length (m) Velocity (m/s) Run-off Coeficient Slope (%) Airport Formula Tc Channel Flow Tc Total Tc Overland B Ditch B Total 44 Rainfall Intensity Tc Year (mm/hr) 100-Year (mm/hr) Year Storm Event Flow Rate Area Run-off Coeficient (5yr) Rainfall Intensity Area (ha) Flow (L/s) B1A B1+B1A B Year Storm Event Flow Rate Area Run-off Coeficient (100yr) Rainfall Intensity Area (ha) Flow (L/s) B1A B1+B1A B

25 POST-DEVELOPMENT STRESS TEST CALCULATIONS B1-A Time of Concentration Location Length (m) Velocity (m/s) Run-off Coeficient Slope (%) Airport Formula Tc Channel Flow Tc Total Tc Overland B1-A Ditch B1-A Total 35 Rainfall Intensity Tc B1+B1A Time of Concentration Location Length (m) 5-Year (mm/hr) 100-Year (mm/hr) Velocity (m/s) Run-off Coeficient Slope (%) Airport Formula Tc Channel Flow Tc Total Tc Overland B1A Ditch B1+B1A Total 44 Rainfall Intensity Tc B2 Time of Concentration Location Length (m) 5-Year (mm/hr) 100-Year (mm/hr) Velocity (m/s) Run-off Coeficient Slope (%) Airport Formula Tc Channel Flow Tc Total Tc Overland B Ditch B Total 44 Rainfall Intensity Tc Year (mm/hr) 100-Year (mm/hr)

26 POST-DEVELOPMENT STRESS TEST CALCULATIONS Year Storm Event Stress Flow Rate Area Run-off Coeficient (100yr) Rainfall Intensity Area (ha) Flow (L/s) B1A B1+B1A B