EA204 Environmental EA204 Environmental TechnologyTechnology

Pavement DrainagePavement Drainage

Stormwater Sewer DesignStormwater Sewer Design

Objectives of Pavement DrainageObjectives of Pavement Drainage

to collect stormwater on the surface to collect stormwater on the surface and move it into the minor system and move it into the minor system (i.e. gutters, catchbasins, ditches)(i.e. gutters, catchbasins, ditches)

to maintain a safe driving surface for to maintain a safe driving surface for the movement of trafficthe movement of traffic

Road Cross-Section: RURALRoad Cross-Section: RURAL

rural cross-sections have ditchesrural cross-sections have ditches normal crossfall is 2%normal crossfall is 2%

2.0%2.0%2.0%2.0%

Centre line (crown)Centre line (crown)

ShoulderShoulder

DitchDitch

Side SlopeSide Slope

Back SlopeBack Slope

LaneLane

Road Cross-Section: URBANRoad Cross-Section: URBAN

urban sections have curb, gutter, urban sections have curb, gutter, catchbasins, and storm sewerscatchbasins, and storm sewers

2.0%2.0%2.0%2.0%

Centre lineCentre line

Curb &Curb &GutterGutter

BoulevardBoulevard

LaneLaneSidewalkSidewalk

PropertyPropertyLineLine

Storm SewerStorm Sewer

PropertyPropertyLineLine

Minimum Pipe SizesMinimum Pipe Sizes

min diameter for storm sewers -min diameter for storm sewers -

250 mm250 mm min diameter for service leads -min diameter for service leads -

200 mm200 mm reduces chance of objects getting reduces chance of objects getting

stuckstuck enables maintenance & cleaningenables maintenance & cleaning

Minimum Cover DepthMinimum Cover Depth

below depth of frost below depth of frost penetrationpenetration

below 1.2 m to avoid below 1.2 m to avoid crushing from large crushing from large truckstrucks

below water supplybelow water supply above sanitary above sanitary

sewer systemsewer system

Flow VelocitiesFlow Velocities

Velocity in pipes is controlled by many Velocity in pipes is controlled by many elements:elements:

slopeslope

hydraulic radiushydraulic radius

roughness of pipe’s inside surfaceroughness of pipe’s inside surface

Min & Max?Min & Max?

MinimumMinimum velocities are set to prevent velocities are set to prevent sedimentation in pipessedimentation in pipes

(this would reduce pipe cross-section and (this would reduce pipe cross-section and capacity)capacity)

MaximumMaximum velocities are set to prevent velocities are set to prevent scouring and premature wear in pipesscouring and premature wear in pipes

(large objects will not be carried through (large objects will not be carried through pipes and damage them)pipes and damage them)

Manhole SpacingManhole Spacing

Stormwater sewers run in straight lines on Stormwater sewers run in straight lines on a constant slope from one manhole to a constant slope from one manhole to the next:the next:

alignment (bearing)alignment (bearing) slope (%)slope (%)

pipe size (diameter in mm)pipe size (diameter in mm) maintenance limitationsmaintenance limitations

Manhole SpacingManhole Spacing

whenever a sewer whenever a sewer changes direction changes direction (bearing) we need a (bearing) we need a manholemanhole

when the slope of a when the slope of a sewer changes we sewer changes we need a manholeneed a manhole

alignment (plan)alignment (plan)

slope (profile)slope (profile)

Manhole SpacingManhole Spacing

a manhole is a manhole is needed when we needed when we change the size of change the size of sewersewer

manholes are manholes are needed so we can needed so we can get in and clean and get in and clean and repair sewersrepair sewers

diameter (mm)diameter (mm)

maintenancemaintenance

Catchbasin & Inlet SpacingCatchbasin & Inlet Spacing

Water must be “caught” before it becomes a Water must be “caught” before it becomes a hazard:hazard:

road grade and low points (sags)road grade and low points (sags) crossfall and roadwidthcrossfall and roadwidth

design stormdesign storm pedestrian crosswalkspedestrian crosswalks

intersectionsintersections public and private drivewayspublic and private driveways

Catchbasin & Inlet SpacingCatchbasin & Inlet Spacing

steeper grades steeper grades require closer require closer spacing to keep spacing to keep velocity in gutter lowvelocity in gutter low

double inlets are double inlets are needed to handle needed to handle water from both water from both sides of sagsides of sag

road graderoad grade

low points (sags)low points (sags)

Catchbasin & Inlet SpacingCatchbasin & Inlet Spacing

inlets needed where inlets needed where water moves from water moves from crown to curb & crown to curb & guttergutter

wider roads mean wider roads mean more water and more water and closer spacingcloser spacing

crossfallcrossfall

road widthroad width

Catchbasin & Inlet SpacingCatchbasin & Inlet Spacing

higher return times higher return times mean more water mean more water and closer spacing and closer spacing to intercept waterto intercept water

inlets must be inlets must be located immediately located immediately upstream of ped upstream of ped crosswalkscrosswalks

design stormdesign storm

pedestrian pedestrian crosswalkscrosswalks

Catchbasin & Inlet SpacingCatchbasin & Inlet Spacing

inlets must be inlets must be located upstream of located upstream of intersection to intersection to prevent “rivers” prevent “rivers” flowing through flowing through intersectionintersection

inlets must be inlets must be located at least 1.5m located at least 1.5m away from drivewaysaway from driveways

intersectionsintersections

private & public private & public drivewaysdriveways

Catchbasin & Inlet Catchbasin & Inlet SpacingSpacingCross Cross

SectionSectioncc

Plan ViewPlan View

LL

CrestCrest

Min. Drive Min. Drive WidthWidth