Module 8: Engineering Considerations Flashcards
List and describe the five services required for a subdivision proposal
Road
Type of road?
Driveway access?
Effect of topography and climate?
Sanitation sewers
Not always required in rural settings
Need sewage collection system AND treatment plant
Max service with lowest cost
Much less volume than storm
No creeks or watercourses!
Impacts of new subdivisions? How to manage?
Water access
2 uses: firefighting and domestic consumption
Must utilize local source AND distribution system
Objectives???
Homeowners
Min supply at reasonable pressure
Firefighters
Huge supply at min operating pressure
Engineer
Adequate demand at required operating pressures, meet current and future needs
Storm sewers
Based on gravity flow
Not always required in rural settings
Peak runoff? Timing?
Nature of surface (impervious, vegetation)
Catch basins, sewers; ditches? Local creek or water course? adequate??
Connections to houses
Upgrades needed?
Management plan? Where does it go?
Electricity
BC Hydro supplies it
2 systems
Overhead
underground
Recognize and explain the relationship between topography, road alignment and lot access requirements
Topography
limits road placement due to slope steepness
Too steep and snowfall means too dangerous; restricts slope limits (18% is upper limit I think)
Vertical curvature at intersections? Different for local vs collector
Restricts line of sight
Cross slope at intersections
Cul de sacs?
Very limited by slope
Vehicles must be able to exit easily, especially emergency vehicles and larger commercial vehicles
Must look at the contours; aerial photos or topographic surveys
Road alignment
Its how to avoid max road grades
Must make roads parallel to contours (lots on one side above and below)
Cut and fill? Just cut?
May make road less parallel to contours; makes it more steep, but less access and servicing problems
Lot access requirements
If roads are parallel to contours, driveway grades may be too steep for access
Especially cut policies
Also affects sewer services and lot drainage
Adequate turnaround movement?
Identify and explain the design criteria standards for road proposals based on topographic mapping
Roadway Design Criteria based on topographic mapping
Grade
Cul de sacs not over 8%
Max grade only used due to topographic constraints
You can increase slope of minor street to avoid increasing slope/compromising design of major street
Vertical curvature
Transition between two sloped roadways; want to negotiate the elevation rate at a gradual rate rather than sharp cut
Cross slope
Slope of footpath at right angles to the direction of travel
Helps with drainage
Maybe less dependent on topography
Sidewalks
Grade and cross slope; have topographical restraints
Driveways
Driveway profile; max grade and vertical curvature (<20%)
Recognize and explain the relationship between topography, lot layout proposals and gravity servicing corridors and the related design criteria
Topography
Again, slope and grade affect gravity system services
Lot layout proposals
Lots should drain to municipal drainage system independently of adjacent lots
Lots lower than adjacent roadways should be avoided where possible,
Buildings should be above the Major System hydraulic grade
Layouts proposed to counter problems with steep topography may interfere with surface drainage flows
May need retaining walls
More subdivisions may overload storm sewers; need upgrades?
Soil permeability
- Gravity servicing corridors
Least cost system is a shallow system with gravity connections to house on both sides of street
Gravity sewers need to be quite deep to provide good connections to low side lot
May need parallel sewers in rear yard, or rear yard use may be restricted due to steep grade
This requires additional RoWs
Storm sewers: May cause excessive water pressure around foundations and seep through basement walls
Service connections need to be at property lines
There is also the relationship between velocity and grade
Steeper grades are desirable
Also affects placement of manholes
Crown of downstream pipe shall not be higher than upstream pipe crown
Location of catch basin and catch basin spacing
Sanitation sewers
Also gravity systems; velocity, grades (steeper is better)
Location
Service connection should be 4m from low side of lot boundary if slope makes centre location impractical
Two additional but not critical services
Gas
Communications
Two basic categories of road design. Restrictions on street design? Why are TAC standards not always used?
Primary reference and guide is Geometric Design Standards by Transportation Association of Canada. Referred to for design of roads
categories:
Horizontal alignment
Vertical alignment
Restrictions
Local topography
Climate
Political or community decision
TAC
Topography creates situations where maximum road grades are unacceptable
Excessive construction costs
Just not practical
What do road design criteria relate (as in deal with)?
Relate
Speed, visual distance with the type of vehicle using the road
Different design considerations for significantly larger volumes of trucks, buses and larger vehicles are expected
One aspect common to all types of traffic?
Common aspect
Climate
Snow removal is a strong consideration
Serious implications on final road design wirth respect to grades
Storm sewers. Impact of urban development? How to control? Primary concern? How to manage. What are the principles of storm sewer design based on?
Impact
Increase in peak runoff and timing of peak flows from surface of the land for any local storm condition
Its the impervious nature of constructing roads, buildings and the removal of natural vegetation
Higher instantaneous runoff volumes
Control
Install catch basins and sewers
Houses have storm sewer connection for draining the foundation tile of house
Runoff goes through storm sewers and ditches until it discharges into a local creek or watercourse
Concern
Are sewers and ditches adequate to convey anticipated flows; today and in the future
Should sewers be upgraded or made larger?
Manage concern by
City should establish an overall stormwater management plan
Detail what water flows into its jurisdiction and where it goes
Enact policies to restrict amount of water discharged into creeks
Provide retention/detention ponds where specific depressed areas are allowed to fill with storm drainage water and stored temporarily and drain more slowly
Based on
Gravity flow
System should operat under gravity and not require pumping
Pumping is only last resort (facilities are very expensive)
Provision of flood protection by local approving authority ideas?
Identify floodplains (Restrict development there?)
Identify inadequate draining systems
Restrict basement homes where they might be subjected to flooding
Remember: after a new subdivision is completed, local government becomes responsible for the operation and maintenance of storm water system after a brief maintenance period
Storm Drainage Design methods and components
Design methods
Conventional Method
Storm Water Management Method of design
(Can save costs, but takes alot of engineering design work for each proposal and an overall watershed design criteria by municipality)
Drainage systems components
Minor system
Major system
Foundation and roof drains
Most areas its mandatory that they are connected to storm sewer
Water distribution
Separate water mains and service connections from sewers
Hydrants
80% made by vancouver manufacturer
They should be standardized
Sanitary sewer
Minimum pipe grades and distance between manholes (Ministry of Environment
Flatter sewer grades mean increased maintenance costs but reduced capital costs
Utilities
Location of utilities is set out in a general manner showing corridor areas rather than specific dimensions. Location determined by local conditions
Local conditions
Rock (means all utilities must be moved to one side of RoW)
Existing mains or trunks located in RoW prior to development taking place
Two additional but not critical services
Gas
Communications
Two basic categories of road design
Horizontal alignment
Vertical alignment
Restrictions on street design?
Local topography
Climate
Political or community decision
Why are TAC standards not always used?`
Topography creates situations where maximum road grades are unacceptable
Excessive construction costs
Just not practical
