Planning Considerations for Stormwater Management in Alberta R. D. (Rick) Carnduff, M. Eng., P. Eng. February 20, 2013 Photo Optional
Purpose The purpose of urban stormwater management is to provide solutions for handling drainage in such a manner that it provides protection against flood and erosion damages within the community and the natural environment.
Stages of Stormwater Management Watershed Drainage Plan Regional Drainage Plan Master Drainage Plan Staged Master Drainage Plan Subdivision Design Retrofits Improvements into Existing Communities
Watershed Drainage Plan Eg. Nose Creek, Pine Creek, Fish Creek Typically the highest-level Emphasis on discharge targets (rate and volume) Land use planning not a factor Limited environmental considerations Pine Creek Basin
Regional Drainage Plan Eg. Shepard Corridor, North Regional Usually a special high-level study area Topography and drainage characteristics General servicing considerations Conveyance alignments and outfalls Detention storage locations Pre-development runoff targets Key environmental areas identified Wetlands Natural drainage courses Financial requirements for municipally funded infrastructure Limited land use considerations
Master Drainage Plan In support of an Area Structure Plan Eg. West Macleod, NE Residential, Keystone, etc. Servicing concepts and discharge targets usually established previously
Master Drainage Plan Guided by land use and environmental planning
Master Drainage Plan Attempts to incorporate environmental areas (wetlands, natural drainage courses)
Master Drainage Plan Preliminary alignments of conveyances and outfalls Detention storage requirements LID Requirements Computer model analysis and water balance calculations Municipally funded infrastructure
Staged Master Drainage Plan Detailed storm servicing in support of a land use re-designation application Close interaction with land use planning regarding storm ponds, LID measures, stormwater reuse, wetlands and natural drainage courses
Staged Master Drainage Plan Discharge targets typically established previously Finalized locations and sizing of storage facilities Hydrologic computer modelling with water balance calculations Finalized alignments of conveyances and outfall
Staged Master Drainage Plan Addresses environmentally significant areas Wetlands Natural drainage courses Escarpment slopes Compensation, preservation or incorporation into the SWM plan Prepared in conjunction with the BIA
Staged Master Drainage Plan LID concepts and details of stormwater reuse Geotechnical and hydro-geological considerations to support LID
Staged Master Drainage Plan Detailed layout and grading of detention storage facilities
Urban Drainage System Major-Minor systems Minor or storm sewer system - 5 year design storm - 70 115 L/s/ha - 45 L/s/ha with LID - No surcharging - ICDs used in CBs
Normal Sewer Flow
Surcharge Sewer Flow
Major System Major or overland system - 100 year design storm - No flooding of buildings - Trap low storage used to control flow depths and velocities - Maximum 0.5 m ponding - Emergency spill route for > Q 100 - Adequate pathways to ponds, downstream infrastructure or natural drainage courses
Elements of Stormwater Analysis Computer model Rainfall Snow Snowmelt Infiltration Catchment area Surface roughness Groundwater recharge Groundwater discharge Soil characteristics Ground cover Imperviousness Catchment slope Catchment width Depression storage Pond storage LID measures Evaporation Temperature Wind Time step Routing method Discharge rating Outfalls Junctions Manholes Catch basins Weirs Orifices Pumps Pollutant Loading Pollutant washoff Conveyance geometry Conveyance length Conveyance slope Conveyance roughness Natural storage Treatment Dividers Rating curves Aquifers Stormwater reuse etc..
Analysis Approaches 1. Single storm event Actual or design rainfall event Hydraulic analysis of sewers & overland flow Sizing of storm ponds 2. Continuous simulation Historic rainfall and snowfall Runoff volume analysis Long term system performance Storm pond sizing Treatment (Eg. sediment removal)
The Analysis Tool Computer Modelling
Precipitation Data Environment Canada Rainfall Snowfall Temperature Wind City of Calgary Rainfall monitoring stations
Example Storms - Cedarbrae Station July 20, 2010 45.2 mm 115 minutes Peak intensity = 127.2 mm/hr June 17-18, 2005 107.6 mm 30 hours Peak intensity = 31.2 mm/hr
100 Year Design Storm (Calgary) Chicago distribution 24-Hours Duration 89.7 mm Peak intensity = 168.1 mm/hr 1-Hour Duration 35.2 mm Peak intensity = 168.1 mm/hr
Pre-Development Runoff, 79 ha Parcel
Post Development Runoff, 79 ha Residential Development
Rate Control Guidelines Critical factor for pond sizing 1:100 discharge at pre-development levels - Eg. Nose Creek q 100 = 1.257 L/s/ha; Pine Creek q 100 = 1.0 L/s/ha - Ponds sized for 100 year volume with emergency overflow Matching of frequencies - Eg. Fish Creek Return Period (Years) q (L/s/ha) 2 0.14 5 0.35 10 0.58 20 0.93 25 1.06 50 1.63 100 2.42
Pre-Development vs Post-Development Discharges, 79 ha Parcel Catchment Runoff Discharges to Drainage Course
Volume Control Average annual runoff volumes at predevelopment levels - Eg. Nose Creek (2013) = 16 mm - Pine Creek = 17 mm - Source control required to retain excess runoff Typical annual runoff - Average precipitation = 409 mm - Low density residential 107 mm - High density residential 133 mm - Commercial/industrial 207 mm
Precipitation 1960 to 2009 (Calgary)
Controlled Post-Development Discharges to Drainage Course, 79 ha
Comparison of Flow Durations
Storm Ponds Dry ponds Wet ponds Constructed Wetlands
Dry Ponds Maximum allowable depth of 1.5 m for 100 year event 5H:1V Side Slope Multi-use MR credit Low flows bypass under pond bottom Not suitable for treatment Typically 7% of development required for pond site
Dry Ponds
Wet Ponds Maximum allowable depth of 2.0 m above NWL for 100 year event 5H:1V Side Slope Typically 4.5% of development required for pond site Primarily for sediment removal and stormwater reuse Upper Normal Water Level (UNWL) is the level controlled by the outlet Lower Normal Water Level (LNWL) is the lowest level allowed for reuse
Wet Ponds
Constructed Wetlands Maximum allowable depth of 1.0 m above NWL is recommended Objective to avoid impact of prolonged water level fluctuations Enhance pollutant removal and amenity value Typically 4.5% 7.0% of development required for wetland site Requires pre-treatment for sediment removal Not suitable for stormwater reuse
Constructed Wetlands
Slope Constraints
Incorporating Wetlands for Storage Integrating preserved wetlands as part of the stormwater facility
Environmental Considerations Hydrologic impacts on natural wetlands Water loss or excess In collaboration with the BIA
Environmental Considerations Integration of natural ravines Need to meet pre-development runoff rates and volumes
Emerging Issue Preservation of natural drainage courses with setbacks (Keystone Hills)
Source Control and LID Measures Directing roof drainage onto pervious areas
Source Control and LID Measures Directing parking lot drainage onto pervious areas
Source Control and LID Measures Soft streetscapes
Source Control and LID Measures Road ditches rather than curb-gutter in industrial areas
Source Control and LID Measures Absorbent landscaping
Source Control and LID Measures Vegetated swales
Source Control and LID Measures Bio-retention basin
Source Control and LID Measures Bio-retention Basin
Source Control and LID Measures Bio-retention basin in freeway interchange
Source Control and LID Measures Porous pavements
Source Control and LID Measures Green roofs
Source Control and LID Measures Silva cells
Stormwater Reuse Irrigation of park & open space areas
Stormwater Reuse Replenishment of preserved wetlands
Lost Opportunities Bio-retention within Park-n-Ride site
Lost Opportunities Boulevard bio-retention within light industrial areas
Lost Opportunities Bio-retention areas within mid-block MR sites
Lost Opportunities Bio-retention areas and vegetated swales within neighbourhood parks
Lost Opportunities Bio-retention within round-a-bouts
Planning Considerations That Affect Stormwater Runoff 1. Higher densities translates to more runoff and less opportunity for LID 50 x 150 lot 45% impervious 30 x 118 lot 60% impervious Multi-family 65% to 85% impervious 2. Re-development of older sites with increased impervious coverage 3. Lanes increase runoff 4. Strategically locating open spaces and school sites for irrigation reuse 5. Efficient use of MR dedication to provide large enough park areas for irrigation reuse 6. Softer streetscapes that reduce pavement width and incorporate LID features 7. Road ditches rather than curb-gutter for industrial areas 8. Irrigation of private sites or adding dedicated pubic spaces in industrial/commercial developments 9. Water supply for retained wetlands on site in lieu of irrigation reuse 1 ha wetland with E T 1.25 ha park irrigation @ 600 mm/yr 10. Ability to incorporate multi-use facilities (dry ponds/mr; wetlands/er)