12.0 Storm Drainage System 1 Flashcards
1
Q
Stormwater System
A
- Not intended to include any sanitary wastewater (2 isolated systems)
- important component in the City’s strategic plan to mitigate the effects of climate change and include build infrastructure into the natural water cycle
- by gravity to a natural water resource
2
Q
Changes to the Natural Water Balance
A
- runoff volume increases in proportion to impervious area
- land uses with extensive roof and paving areas create more runoff than land uses with extensive areas of absorbent soils and forest cover
3
Q
Natural Ground Cover
A
- 40% evapotranspiration
- 10% runoff
- 25% Shallow Infiltration
- 25% Deep Infiltration
4
Q
10-20% Impervious surface
A
- 38% evapotranspiration
- 20% runoff
- 21% Shallow Infiltration
- 21% Deep Infiltration
5
Q
35-50% Impervious Surface
A
- 35% evapotranspiration
- 30% runoff
- 20% Shallow Infiltration
- 15% Deep Infiltration
6
Q
75-100% Impervious Surface
A
- 30% evapotranspiration
- 55% runoff
- 10% Shallow Infiltration
- 5% Deep Infiltration
7
Q
Changes to the Natural Water Balance
A
- Traditional ditch and pipe systems have been designed to remove runoff from impervious surfaces as quickly as possible and deliver it to receiving waters
- resulting stormwater arrives at the receiving waters much faster and in greater volume than under natural conditions
- Changes to impact
1. property
2. ecological
3. water quality
8
Q
Property Impacts
A
- multiple drainage culvert installations
- channel down-cutting (due to increased volume)
9
Q
Ecological Impacts
A
- urbanization
- water quality
- aquatic habitat
10
Q
Detention ponds
A
- accomodate existing and future upstream development
- weaken peak flows from storm water runoff
- lessen erosion downstream
11
Q
Integrated Stormwater Management Plan
Components
A
- Land development action plan
- habitat enhancement plan
- financial and implementation program
- flood risk mitigation plan
12
Q
Downsides of detention ponds
A
- provides a partial solution
- only treat consequences of increases impervious area (not the source)
- mitigates flooding but does not prevent the ongoing channel erosion that creates property and fisheries impacts
- do no support the sustained stream base flow (in dry months)
13
Q
Integrated Stormwater Management Plan
objectives
A
- drainage
- stream protection
- water quality
14
Q
Design storms consist the following:
A
- The minor system
- The major system
15
Q
The minor system
A
- consists of gutters, catchbasins, open channels, pipes, driveway culverts, watercourses, and stormwater management facilities designed to carry flows up to the 1:5-year return period storm under free flow conditions
- minimize inconvenenience of frequent surface runoff
16
Q
The major system
A
- consists of roadways, culverts, ditches, surface flood paths, watercourses, and stormwater management facilities designed to carry flows up to the 1:100-year return period storm
- provides safe conveyance of flows and to minimize damage to life and property
17
Q
2 methods to design the storm system
A
- the rational method (catchment area is less or equal than 20 ha)
- the hydrograph method
18
Q
Runoff coefficient
A
- (C) is based on ground slope, type if cover, type of ground surface, and development population density
- ranges from 0 (lots of infiltration) to 1 (heavily developed, all rainwater becomes runoff)
- must account for future development outlines in community plans and/or over a 100-year period
- generally preferable to develop a composite runoff based on the % of different types of surfaces in the drainage area
19
Q
Rainfall intensity
A
Calculated using Intensity Duration Frequency (IDF) curves or equation
20
Q
Tributary drainage area
A
- based on the applicable existing and proposed contours
- cumulative tributary drainage areas must be considered for catchments with multiple sub-catchments
- sub-catchment boundaries are determined by aggregating together sub-areas whose potential overland flow paths share a common direction and drain to the same collection channel
21
Q
Time of concentration
A
sum of the inlet time and travel time in the pipe or channel to the point of interest
22
Q
Manning’s Equation
A
Formula for open channel (unpressurized) flow
23
Q
Minimum size
A
- 200mm diameter (residential zones)
- 250mm diameter (all other zones)
24
Q
velocities and slope
A
- preffered min. = 0.76 m/s
- absolute min. = 0.61 m/s
- slope min. = 0.5%
- max. velocity = 4.6 m/s
- higher than 4.6 m/s, provisions shall be made for energy dissipation, erosion, and movement. Appropriate bank protection measures if discharging into open watercourses
25
Design of Storm Sewer Components
* size and material
* alignment
* depth
* velocities and slopes
* curvlinear sewers
* structural desgin
* maintenance holes
* catch basins
* culverts
* ditches
* service connections
* green infrastructure
26
Size of storm water pipes
* 200mm diameter (residential zones)
* 250mm diameter (for all other zones)
27
material
* PVC SDR35
* PVC C900 (low-cover)
* HDPE (trenchless)
* Vitrified Clay Extra Strength
* Non-Refinforced Concrete Cl.3
* Reinforced Concrete Cl. III, IV, and V
28
Downstream Pipe
* pipe size reduction only used in special circumstances
1. it has an increased slope to provide sufficient capacity
2. diameter >= 525mm
3. not redued by more than 2 pipe sizes
4. a detailed hydraulic analysis has been done
29
Alignment
* storm sewers shall be located on the high side of the street where only the high side is served by the lateral and on the low side of the street where both sides are served by the lateral
* where possible, the sewer shall be at a constant offset from the property line
* minimize crossing conflicts
* meet clearance and separation requirements
* minimize contruction, public, and traffic impacts
* minimize construction costs
* maximize maintenence access
* consider long term plans for separated and traditional sewer routing
* avoid trees and other surface features
30
Curvlinear Sewers
* horizontal and vertical curves will be permitted under special circumstances
* the rate of curvature must be uniform throughout the curve
* only 1 curve (v:h) is allowed between consecutive maintenance holes
* curves must be formed through join deflection or bends and not by bending of the pipe
* the join deflection must not be greater than 50% of the recommended max. by the pipe manufacturer
* the radius must also meet min. requirements
31
Curvliniear sewers type
1. Vitrified Clay
2. Concrete pipe
3. PVC
32
Maintenance Holes
Must be placed at the following locations:
* at terminal ends
* at all grade changes
* at all size changes
* at all alignment changes (except curved sewers)
* At all sewer intersections
* Max. Spacing 180m pipe length
* At the downstream end of a curved sewer
1. the min. size of standard maintenance hole is based on the largest pipe diameter entering the maintenance hole
2. the angles, elevation and the number of incoming pipes must also be considered to ensure safe entry and structural integrity of the maintenance hole
* The Drop from the inlet invert elevation to the outlet invert elevation in the maintenance hole must meet the City's requirements
* The crown of the inlet pipe is to be the same elevation or higher than the crown of the outlet pipe
* Drop structures should be avoided by adjusting the grade of the sewer
* where drop structure cannot be avoided, the MH structure type depends on the difference in invert
33
Maintencance Hole covers
* for safety reasons, all maintenance hole covers in playgrounds, schoolyards, and other areas that pose a safety hazard shall be buried 150mm below grade and secured (bolt-down cover and frame)
34
Catch Basins
| review catchment areas on the lecture slides
* Placed to collect the full minor flows as well as the major system flows if the major system is designed to be conveyed in the minor system piping
* located to meet the catchment areas and spacing requirements
* not located within painted crosswalks or curb ramps
* located at the begining of the curb return or higher side of crosswalk
* prevent overflows to driveways, bicycle lanes, privated properties, boulevards, and sidewalks
* catch basins located at low points may provide a double catch basin with leaf catcher (side inlet) if adjacent to treed boulevard
35
Lawn Basins
* used to collect water in fields, swales, yards and lots and direct the flow of water to the storm sewer system
* not recommended for paved areas, they work well when placed in landscaped areas, gravel parking lots and fields with turf surrounding them
36
Grates
All catch basin grates shall be designed to accomodate loading from all design vehicles
37
Culverts
* Typically designed to accomodate the minor flow
* erosion proection measures
* min. culvert diameter is
1. 300mm for driveway crossings
2. 600mm for roadway crossings
38
Ditches
* Designed to convey minor system flows
* typically trapezoidal in shape having max. side slopes of 1.5H:1V and a min. bottom width of 0.5m (depends on soil)
* min. ditch profile is 0.5%
* max. velocity in an unlined ditch is 1.0 m/s
* Higher velocities may be permitted where soil conditions are suitable or where erosion protection has been provided
39
Service Connections
| min horizontal dist, diameter, velocity, cover, slope
* Service connections shall not exceed 30m in length as measured horizontally between the lateral sewer and the property line
* if the service must be longer than 30m, a maintenance hole must be placed such that the longest section of service does not exceed 30m
* min. size is 150mm
* storm services typically are sized based on a 10-year design storm with a 50min inlet time and a runoff coefficient of 1.0 for the site area
* The preffered connection depth to invert at the property line shall be 1.5m below the centreline of the street or lane. (1m cover may be accepted as an exception)
* in no case shall the connection have less than 1.0m cover or greater than 2.4m depth at the property line
* service connections shall be designed with a slope (min. 2%)
* preferred min. velocity is 0.92 m/s
* absolute min. velocity is 0.76 m/s
40
MBE
* the onsite connection elevations must meet the building code requirements
* The MBE is to be 0.6m plus the higher of
1. the 100-year design storm hydraulic grade line of the main at the connection (to avoid flooding onto the building)
2. the invert of the service connection at the building location
41
Green Infrastructure
* infiltration, evapotranspiration, and reuse of rainwater to the greatest extent practicable
* encompasses various designs that mimic natural processes to manage stormwater and mitigate urban heat
* these elements are integral to suitable urban planning, providing crucial ecological and environmental benefits
42
Clearance and Separation requirements
* minimum 3m horizontal separation (pipe center to center)
*minimum 1.5m horizontal separation to large structures (outside of the utility to the outside of the structure
1m minimum horizontal utility separation between watermains, sanitarym and storm sewers to a property line (outside of the utility to property line)
* Where a water main crosses a sanitary sewer or storm sewer:
1. Install the water main above the sewer with a minimum clearance of 0.5m
2. wrap the joints of the water main over a length extending 3m either side of the sewer crossing
43
Depth
| + tench depth
* minimum depth cover is 1m
* generally the max. depth of trench depth is 6m. greater than 6m or poor soil conditions require desin by a professional engineer
* The storm sewer must also be sufficiently deep to
1. service basements by gravity
2. allow for tie-ins of other mains and services
3. structurally withdstand surface loading
4. avoid conflicts with other utilities
5. prevent freezing
6. accomodate future sewer separations and consider long term plans for separated sewer routing
44
Structural Design
* ensure that the pipe is sufficiently designed to withstand loading that will be applied to it without deflection or damage as per manufacture specifications
45
Green Infrasturcture examples
1. Absorbent landscapes
2. infiltration swale systems
3. infiltration rain gardens
4. pervious paving
5. green roofs
6. infiltration trench and soakaway manholes
