SECTION X - STORM DRAINAGE SYSTEM 10.1 10.2 10.3 General Generally storm drainage shall be accommodated by a system of curb, gutter and storm sewers in all subdivisions except estate residential subdivisions for which open ditch drainage will be permitted if minimum design criteria can be realized. The storm drainage system is to be designed to limit flood damage and hazards under long term storm conditions, to provide a reasonable level of convenience and safety for pedestrian and traffic use by removal of lot and street surface runoff under short term storm conditions and to prevent the impairment of water quality and disturbance to natural streams. Service Area The system shall be designed to service all areas within the subdivision to their maximum future development in accordance with the Official Plan. Allowance shall be made for inflows from the appropriate adjacent storm, subdivisions or areas. Discharge of the system is to be to the appropriate adjacent sewer or watercourse. The exact location for connecting sewers or channels to adjacent sewers or areas shall be approved by the Township Engineer. Drainage and/or Storm water Management Report A Drainage and/or storm Water Management report setting out the existing and proposed drainage system shall be submitted for approval to the Township Engineer. The report may also have to be approved by the Ministries of the Environment and Natural Resources and the Nottawasaga Valley Conservation Authority. The report shall include a plan showing the major overland system design. When the Rational Method is used, the relevant figures are to be entered on storm Sewer Design Sheets. When computer modelling is used, the report shall indicate model parameters and assumptions used and to give outflow hydrographs and hydraulic grade line levels where applicable. November 25, 1989 23
Transcript
SECTION X - STORM DRAINAGE SYSTEM
10.1
10.2
10.3
General
Generally storm drainage shall be accommodated by a system of curb, gutter and storm sewers in all subdivisions except estate residential subdivisions for which open ditch drainage will be permitted if minimum design criteria can be realized. The storm drainage system is to be designed to limit flood damage and hazards under long term storm conditions, to provide a reasonable level of convenience and safety for pedestrian and traffic use by removal of lot and street surface runoff under short term storm conditions and to prevent the impairment of water quality and disturbance to natural streams.
Service Area
The system shall be designed to service all areas within the subdivision to their maximum future development in accordance with the Official Plan. Allowance shall be made for inflows from the appropriate adjacent storm, subdivisions or areas. Discharge of the system is to be to the appropriate adjacent sewer or watercourse. The exact location for connecting sewers or channels to adjacent sewers or areas shall be approved by the Township Engineer.
Drainage and/or Storm water Management Report
A Drainage and/or storm Water Management report setting out the existing and proposed drainage system shall be submitted for approval to the Township Engineer. The report may also have to be approved by the Ministries of the Environment and Natural Resources and the Nottawasaga Valley Conservation Authority.
The report shall include a plan showing the major overland system design. When the Rational Method is used, the relevant figures are to be entered on storm Sewer Design Sheets. When computer modelling is used, the report shall indicate model parameters and assumptions used and to give outflow hydrographs and hydraulic grade line levels where applicable.
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10.4
10.5
In cases where flows are diverted to adjacent . watersheds the drainage report shall show that the receiving system can accommodate the additional flows within the constraints applicable to the receiving system. The constraints include characteristics of the receiving watercourse both upstream and downstream of the diversion. The report shall also deal with the effects of the diversion on the original water course downstream of the diversion, including the need to satisfy the legal requirements of the riparian owners and the need if any to maintain base flow.
Design Flows
Potential increases in runoff rates resulting from new development shall be controlled as required by the Township . Where downstream constraints exist such as those established by the Township or the Conservation Authority, the drainage report shall demonstrate how run off rates will be controlled to satisfy those constraints. In the absence of such constraints the post-development flows from a 5-year return frequency storm generally shall not exceed the flows for pre-development conditions for the same storm at the outlet for the minor system unless it is demonstrated to the satisfaction of the Township Engineer that uncontrolled flows will have no adverse effects. Similarly for the major system post-development runoff from a 25-year return frequency storm generally shall not exceed the pre-development runoff for the same storm.
Methods of computation
Pre-development peak flows shall be computed by the Rational Method or by an approved hydrograph . Watershed definition and pre-development flows must be approved by the Township Engineer.
Preliminary estimates of post-development flow rates may be computed using the Rational Method.
For all systems and for the design of surcharged sewers and detention facilities, the latest version of the computer model OTTHYMO is recommended. other hydrograph methods may be considered if it is demonstrated that the results are comparable to those from OTTHYMO.
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Post-development design flows may be determined using the Rational Method only where the design area is less than 40 hectares and runoff control facilities are not considered.
Rainfall intensity-duration frequency equations or their curves and design storm hydrographs must be approved by the Township Engineer.
Where the first leg of a residential storm sewer system is sized using the Rational Method, the initial inlet time shall be 15 minutes for the 5-year storm and 5 minutes for the 2-year storm.
This shall apply where the upstream drainage area does not include large open space areas. Where peak flows from external areas enter a subdivision sewer system, the more critical case based on either the time of concentration including the external area or the time of concentration excluding the external area shall be used. Actual velocities of computed peak flows shall be used to estimate time of concentration.
A design evaluation of inlet times must be submitted to justify inlet times different from those specified above, especially in the cases where the sewer is designed for certain surcharge levels for larger storms and where the sizing is optimized for both situations. Such an elevation should be approved by the Township Engineer prior to submission of design drawings.
Where the Rational Method is used, the parameters are defined as follows:
where:
Note:
Q = Q = R = A = I =
N =
R*A*I*N flow in litres per second runoff coefficient, dimensionless area in hectares or square metres average intensity in millimetres per hour or millimetres per second conversion factor as determined by A and I units:
where A is in hectares and I is = 2.778 or where A is in sq.m. mm/s.; N = 1.0 and Q = A*I*R.
in mm/hr.; N and I is in
Runoff coefficients are given by component of surface treatment and by Land Use. The Land Use values are intended as a guide only. The designer is encouraged to develop an appropriate coefficient using a composition calculation.
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Composition Calculations
Sodded area under 7% slope
Sodded area over 7% slope
Paved area with storm sewer
Paved area with sodded swales -
dependent on relative area of swale to paved area and on type of swale.
Roof area to storm sewer
Roof area to paved area with storm sewer
Roof area to sodded area or paved area with sodded swales
Flat roof area with detention hoppers
Foundation connection
Residential Lots
Description B
Single Family, Semi Detached Duplex, Triplex Quad. 0.40 - 0.55
Small Lot Single (9m), Small Lot Semi (7.5m), Street Townhousing (6, 7 . 5m) 0.40 - 0 . 55
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0.25
0.30
0.90
(0.30- 0 . 85)
0.90
0.70
RN (Rx2. 778)
0.69
0.83
2.50
(0.83-2.36)
2.50
1. 94
(0.30-0.55) (0.83-1.53)
0.10 0.28
0.075 L/s/unit
RN (Rx2.778)
1.11 - 1.53
Foundation Connection
0.075 L/s/ unit
1.11 - 1.53 0 . 075 L/ s / unit
Block Development
Description R
Block Townhousing 0.55 to Stack Townhousing 0.65 Apartments
Neighbourhood Commercial 0.70
Commercial Centre 0.75
Industrial 0.75
Institutional 0.70
Open Areas
Description
Park , Recreation Centre Cemetary with any roof leaders or pavement to sodded areas
Unimproved Open Space Under 7% slope
Unimproved Open Space Over 7% slope
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RN (Rx2. 778)
1. 53 to 1. 81
1. 94
2.08
2.08
1. 94
R
0.25
0.25
0.30
Roof Hoppers (flat roof
0.40
0.45
0.55
0.45
0.55
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Swale RN storage
(Rx2.778) (designed)
1.11
1. 25
1. 53
1.25
1. 53
0.30
0.30
0.30
0.30
0.30
RN (Rx2.778)
0.69
0.69
0.83
RN (Rx2.778)
0.83
0.83
0.83
0.83
0.83
10.6
10.6.1
For estimating flows from storms larger than the 5-year return storm the runoff coefficients should be increased to account for the increase in runoff due to saturation of the soil, . with the estimate becoming less accurate for larger storms. Coefficients for the larger storms can be derived as follows : .
Manning's Formulae shall be used to determine the capacity of the sewers . For concrete sewers a roughness coefficient of 0.013 shall be used . For corrugated pipe used as culverts, not storm sewers, an appropriate roughness coefficient shall be used.
In general the sewer system shall be designed to convey not less than the 5-year return frequency storm without surcharge. Surcharged design may be considered for higher design levels where suitable methods are used, or where foundation drains are not connected to the storm sewer, subject to the approval of the Township Engineer.
Design Levels
The system is to be designed to provide drainage for frequent storms (minor system) protection from rare events (major system) .
Minor system
convenience and flood
storm sewers are to be designed for at least a 5- year return frequency storm without surcharge where adequate overland drainage capacity exists to satisfy the major system requirements.
Exceptions to this may be considered under the following circumstances and subj ect to approval by the Township Engineer:
When the major system is inadequate either because there is no outlet for overland flows or there is insufficient surface detention potential, the sewer system shall be designed to carry as much flow as necessary to achieve the minimum 25-year level of protection for the major system as specified in section 10 . 6.2.
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10.6.2
Location
Walkways,
When the major system has a high capacity due to steep slopes or proximity to outlets, and where foundation drains are protected from flooding as specified in 10 . 7.2, the sewer system may be designed for a 2-year return frequency storm.
Maior system
Runoff rates in excess of the design capacity of the minor system shall be conveyed via streets and swales to a safe outlet. The combination of overland flow system and minor system shall be designed for a minimum 25-year return frequency storm, to prevent flooding of private property with maximum level of road flooding and surface detention as defined below.
It shall also be demonstrated that overland flow conditions resulting from the lOa-year return frequency storm will not cause unacceptable flooding damage to private property with a maximum level of road flooding and surface detention as outlined below.
storm Return Frequency (Years)
5 25 100
minor surface as required as required
open Spaces flow up to 25mm deep on walks
for overland flow outlets
for overland flow outlets
Collector and Industrial Roads
Arterial Roads
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1.0m wide in gutter or 0.10m deep at low point catch basins
1. am wide in gutter or 0.10m deep at low point catch basins
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up to crown
1 lane clear
0.10m above crown
up to crown
Private Property minor ponding in swales
no structural damage, ponding in yard areas below building openings-no basement flooding
no structural damage from overland flow, basements may flood via doors or windows
Public Property minor ponding in swales or ditches
no structural no structurdamage, pond- al damage, ing flat areas, ponding in no erosion flat areas,
10.6.3
some erosion
street grading must provide a continuous gradient to direct street flows to a safe outlet at low points. outlets can be walkways or open sections of roadways leading to parks, open spaces or river valleys.
open Ditches
In estate residential subdivisions open ditches may be permitted by the Township. Ditches shall be constructed below the subgrade of the roadway a maximum of 0.5 m and a minimum of 0.15 m.
The minimum ditch grade shall be 0.5% and the maximum 6%. In exceptional cases and where ditches are on easements off the Road Allowance, ditches with grades greater than 6 percent may be allowed by the Township Engineer but these shall be suitably protected against erosion to the satisfaction of the Township Engineer.
The minimum ditch protection on all ditches shall be 75 rom of topsoil and staked sod on the side slopes and bottom of the ditch regardless of the ditch gradient.
Normal ditch to ditch road culverts shall be installed where required as follows:
Minimum length; as required from centre of ditch to centre of ditch;
Minimum size; 500 mm diameter for road crossing, 400 mm driveway. Material; standard galvanized corrugated pipe; spira lly corrugated pipe will not be permitted;
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10.6.4
Gauge; as recommended by manufacturer for H20 Highway loading, minimum 2.0mm thickness;
Cover; 300 mm minimum for road crossings;
Bedding; culverts shall be bedded and backfilled with granular material in accordance with OPSS.
End protection shall be provided on all road culverts and driveway culverts with either concrete headwalls, wolmanized timer or interlocking precast sections of approved design as approved or directed by the Township Engineer.
Where it is necessary to construct culverts under roadways or driveways larger than the minimum size the cross-sectional end area shall be calculated by the rational design method as noted previously. The culverts shall be of reinforced concrete or corrugated metal and detail drawings and calculations shall be submitted for the approval of the Township Engineer.
Driveway entrance culverts for each lot shall be installed by the Developer and shall be a minimum size of 400 mm diameter, a minimum of 1 . 6 mm thickness and a minimum length of 7.0 m with end protection as previously noted.
open Channels
Open channels are to be designed as follows:
For the Regional storm where the upstream watershed area exceeds 1 square kilometre;
For a minimum 25 year return frequency storm with protection from erosion damage for larger storms if required by the Township Engineer;
To maintain the natural storage characteristics of the watercourse;
To maintain a natural appearance as far as possible;
To meet specific requirements of the Conserv ation Authority in each case.
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10.6.5
10.6.6
outfalls
outfall structures to existing channels or watercourses shall be designed to minimize potential erosion or damage in the vicinity of the outfall from maximum design flows .
Detention Facilities
Detention facilities shall be provided for both the major and minor systems as required to reduce runoff increases and to meet downstream flow constraints. Both wet and dry detention facilities may be considered. A wet facility is a permanent pond which provides storage in a freeboard allowance while a dry facility is a temporary storage site that may be used for other purposes during dry weather.
Minor System Detention - Where storage is required to reduce post-development 5-year return frequency storm pipe flows to pre-development storm runoff rates or to meet downstream flow constraints, land area set aside expressly for this storage where it is not part of a privately owned facility (i.e. roof top storage or otherwise incorporated into industrial/commercial lands) shall be designated as a "stormwater detention site" and dedicated by the Developer to the Township. It shall not be considered as part of the park system.
Maior System Detention - Where detention facilities are designed to control runoff increases in the major system, storage may be considered in designated park areas. The area required, the duration and frequency of use of the site for storage of runoff shall be specified when multiple use of the site is considered (i.e. park and storm runoff detention). In all cases, the detention of runoff in multiple use facilities shall not occur more frequently than once in five years.
Dual System Detention - If the facility is used to control major and minor system runoff increases, the land area required to store the 5-year return frequency storm runoff increase shall be designated as part of the drainage system, while storage in excess of this may be obtained from adjacent designated park lands as an overflow or freeboard allowance.
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10.7.0
10.7.1
10.7.2
10.7.3
10.7.4
outlet Design All detention facilities s hall be provided with an outlet (overflow spillway) designed to accommodate a loa-year return frequency storm flow without failure. suitable erosion protection shall be provided downstream of the outlet for a ll flow conditions. operation during spring snow melt or freezing conditions shall be investiga ted and any required changes will be incorporated.
Water Quality - The potential use of detention facilities for water quality control shall be investigated only as directed by the Township Engineer .
General Design criteria for piping
Minimum Size
Concrete or PVC pipe sewers shall be a minimum of 250 millimetres in diameter.
Minimum Velocity
The minimum velocity shall be obtained by selecting a slope to ensure that cleansing velocities occur once in t wo years on the average. Generally 0.75 metres per second for the 5-year return storm design flows may be used.
Minimum Grade
The minimum grade for pipes shall be the grade needed to meet the minimum velocity requirement.
Maximum Velocity
The norma l maximum velocity shall be 5. 00 metres per second at full flow for sewers and 1. 50 metres per second for channels. Energy dissipators at outlets will be designed to reduce velocities to 1.00 metre per second or less.
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10.7.5
10.7.6
10 . 7 . 7
10.7.8
10.7.9
10.7.10
Hydraulic Losses
A sufficient drop shall be provided across each manhole to offset any hydraulic losses, the obverts of inlet pipes shall not be lower than obverts of outlet pipes, and drop structures shall be used only when drops of more than 0.9 metres are necessary. Calculations for hydraulic losses shall be included with storm design information.
Downstream Size
Except for special cases, the downstream pipe diameter shall always be greater than or equal to the upstream pipe diameter.
Roof Leaders
Leaders are to be discharged to the ground surface to splash blocks and flows to be directed away from the building in such a way as to prevent ponding or seepage into weeping tile. Where flat roofs are used, as in commercial or industrial sites, detention roof hoppers requiring smaller or fewer roof leaders may be used as part of the storm water management design. No connections are to be installed directly to storm sewers.
Foundation Drainage
Foundation drains shall be connected to the storm sewer system only when it can be demonstrated to the Township Engineer that an acceptable level of protection against basement damage will be provided under major storm conditions.
other Connection
All other connections to the storm sewers shall be made as approved by the Township Engineer.
Materials
All materials shall be supplied in accordance with these specifications and the Township requirements .
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10.8.0
10.8.1
10.8 . 2
Layout Details
Trunk and Local Sewers
storm sewers shall generally be located in accordance with the Township standard.
When storm sewers or open drainage channels are located on easements the easement width shall be 6.0 m minimum.
A minimum depth of 1.5 metres to the spring line from the finished road or ground surface elevation, or a sufficient depth for any foundation drains or other connections shall be provided.
Minimum clearances between services shall be provided in accordance with MOE guidelines.
Manholes
Manholes shall be placed at the end of each sewer, at changes in size and material and at abrupt changes in grade and alignment . Curved or properly deflected sewer lines are allowed with the approval of the Township Engineer.
Manhole types and sizes shall be in accordance with M. O. E. guidelines. All manholes are to be benched to the satisfaction of the Township Engineer and frost straps are to be provided between the upper through to the base manhole section.
The maximum spacing between manholes shall generally be according to the following:
metres
- 200 to 900 millimetres dia. 110
- 975 millimetres dia. and greater 180
Drop manholes shall be provided for all sewer junctions having an elevation difference in excess of 0 . 9 metres that cannot be eliminated by changing sewer grades.
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10.8.3
Where manholes are located in areas to be flooded by the major storm design and surcharged sewer design is not used, manhole covers shall be of the sealed variety. Where manholes are located where the surcharged sewer design hydraulic grade line is higher than the rim elevation, manhole covers shall be of the bolted variety. In all other areas standard manhole covers shall be used.
catchbasins
catchbasins are to be located at all low points, (doubles) upstream of pedestrian crossings and not within 1.0 m of curb depressions. Preferably catchbasins where required will be adjacent to lot lines.
The maximum allowable spacing shall be 90 m where catchbasins are not used as inlet controls. Where catchbasins are designed for inlet controls, spacing shall be determined by design.
For catchbasin depths in excess of 2 metres, 1.2 m by 1.2 m catchbasin manholes shall be used conforming to O.P.S.D.
Catchbasin capacities shall be determined in conjunction with the overall storm water management system. On roadways, catchbasins shall have a minimum capacity to pass the runoff from the 5-year return frequency storm. Where the pipe system is required to convey flows in excess of the 5-year return frequency storm, sufficient catchbasin capacity shall be provided to permit the design flows to enter the sewer system. Inlet control devices may be used where the hydraulic grade line needs to be strictly controlled i.e. - to prevent surcharging of the sewer line and to allow storm sewer house connections.
Catchbasin leads shall be minimum 250 rom at 0.7% grade for single catchbasins and 300 rom at 0.7% grade for double catchbasins. Leads shall connect to manholes where possible. Where catchbasins are designed for inlet controls, lead sizes down to 150 rom for singles or doubles can be used where such sizes will limit flows to the gravity capacity of the sewer system.
No catchbasin shall discharge directly into another catchbasin.
