Specific Standards and Best Practices:
Urban Stormwater Management

Table of Contents

Background

Urban and rural stormwater management refers to activities involving the connection of urban and rural drainage systems to streams. Streams are critical components of all municipal, urban and rural stormwater systems. As stormwater outfalls are the direct links between upland land-uses and streams, they can have significant impacts to aquatic species and habitats by altering the storm flow volume and timing within watercourses, blowing out pool and riffle habitats, scouring out spawning gravels or covering them with sediment, and reducing critically low flows or base flows in streams. Stormwater systems also impact a stream’s water quality by introducing pollutants through spills and non-point source pollution.

Stormwater is typically managed only for flood control. However, recent studies, including a study conducted by the GVRD, have clearly shown that urbanization has had significant impacts on stream health and productivity in the absence of stormwater management systems that would protect fish and wildlife species and their habitats. This GVRD report can be found at the following website:

http://www.gvrd.bc.ca/services/sewers/
drain/Reports/stormwater_rpts_1997-2002/
rpts.htm#impactsml

Discharges from new multi-lot residential subdivisions, multi-family residential developments, as well as commercial, institutional or industrial sites are considered stormwater system connections and require a Notification. Perimeter drain discharges include proposed new discharges from independent single lot single-family residential properties only, and do not require a Notification.

Objectives

To prevent harmful impacts to water quality, riparian and aquatic habitats and fish and wildlife species through activities related to the connection of stormwater management systems to local streams, the following approach is provided:

Objective: Putting Water Back into the Ground - Volume Reduction

To reduce and mitigate the total runoff volume caused by increased urban development and subsequent increasing impervious areas, as well as to maximize the amount of runoff returned to shallow groundwater via recharge.

Objective: Preserving or Improving the Water - Water Quality

To mitigate water quality impacts to fish habitat by collecting and treating “first flush” events of smaller storms, more frequent runoff events from impervious areas.

Objective: Holding Back the Water – Rate Control/Detention

To restrict the post-development peak runoff flow rate to that of the pre-development peak runoff flow rate for selected design return periods.

The provincial document, “Stormwater Planning: A Guidebook for British Columbia” helps to introduce and orient local governments towards addressing stormwater management in urban and rural developments. The document is available at the following website:

http://www.env.gov.bc.ca/epd/epdpa
/mpp/stormwater/stormwater.html

In the highly urbanized and fast developing GVRD, much work has been conducted on stormwater management through the Liquid Waste Management Planning process. See the following websites for additional information, as well as reports and publications:

http://www.gvrd.bc.ca/services/
sewers/drain/Reports%20and%20
Publications.html#Stormwater%20sub

http://www.gvrd.bc.ca/services/
sewers/drain/Reports/
stormwater_rpts_1997-2002/rpts.htm

Standards for Stormwater Management

All proposals for the connection of a new stormwater system to a stream, or the connection of a new system to an existing stormwater system that is connected to a stream must address the protection of riparian and aquatic habitats and their supported fish and wildlife species through the design and implementation of a stormwater management system that will mitigate to the greatest extent the harmful impacts of stormwater to water quality, and aquatic and riparian habitats.

All stormwater management system designs and outfall constructions for which you are submitting instream works notifications or approvals must be compliant with the General Standards as listed in the Standards and Best Practices section of this document for:

• Compliance with Other Legislation;
• Land Ownership;
• Public safety;
• Completion of work;
• Protection of water quality;
• Protection of Species and Habitat; and
• Protection of other water users.

Specific Standards associated with this type of work (Water Act Regulation Section 44(1)) authorize works completed as the following work types and under the following conditions

Construction or maintenance of storm sewer outfalls (Subsection 44(1)(l)), provided that the storm sewer outfall is designed by a professional engineer, and constructed, maintained and used so as not to obstruct the flow of water in the stream or to cause erosion or scour in the stream.

Note:

Temporary diversion construction around or through a work site (Subsection 44(1)(x)) is permitted for works providing that the worksite is no larger than the minimum area required, and

1. if pumps, pipes or conduits are used to divert water around or through the worksite,
    
   1. the pumps, pipes or conduits are sized to divert the 1 in 10 year maximum daily flow for the period of construction, and
       
   2. any pump or intake withdrawing water from fish bearing waters is screened in accordance with the Fish Screening Directive of the Department of Fisheries and Oceans (Canada),
       
2. if cofferdams are used to isolate successive parts of the construction at the worksite,
    
   1. the cofferdams are designed by a professional engineer and constructed in accordance with that design, and
       
   2. the natural channel remaining outside of the cofferdams is adequate to pass the 1 in 10 year maximum daily flow during the period of construction, or
       
3. if ditches are used to divert flow around the worksite,
    
   1. the flow of water diverted remains within the stream channel,
       
   2. the ditches are designed and constructed to divert the 1 in 10 year maximum daily flow around or through the worksite and are protected from any anticipated erosion during the period of construction and use of the ditch, and
       
   3. the ditches are completely backfilled and the area returned as closely as possible to the natural state on completion of the works.

Best Practices

Integrated stormwater management planning at a watershed level, as committed to by the GVRD, should be conducted wherever possible and practical. Such plans should address fish and wildlife habitat and species protection as watersheds change from activities associated with urban and rural development. Stormwater management systems designed for urban rural developments should be consistent with these municipal plans where they exist. See the following website for the GVRD’s stormwater planning template:

http://www.gvrd.bc.ca/services/
sewers/drain/Reports%20and%20
Publications.html#Stormwater%20sub

The following section outlines recommended best practices to support the standards, which should be addressed in urban stormwater management systems and connection design and construction where an integrated stormwater management plan has not been completed:

Stormwater Management Systems:

The design of a stormwater system and its connections will determine the extent to which impacts to fish and wildlife habitats and populations may be avoided or mitigated. When proposing a new stormwater outfall, you should have confirmation through a technical rationale that the outfall is necessary, and that alternatives such as draining the site to the ground or draining the site to a constructed drainage facility like a rock pit or drainage trench are not appropriate. The connection should be designed by an appropriately qualified professional(s), and constructed in accordance with that design.

To ensure impacts to fish and wildlife habitats and populations are minimized, stormwater systems should use the following design recommendations which have been adapted from the “Urban Stormwater Guidelines and Best Management Practices for Protection of Fish and Fish Habitat” 2001 DFO draft discussion paper:

Putting Water Back Into the Ground –
Volume Reduction (VR)

Design Best Practices:
Volumes from smaller rain events from impervious areas should not be discharged. They should be infiltrated to ground

Structural Best Management Practices:
Ground infiltration systems, biofiltration swales or burrows, or long-term storage in constructed wetlands or ponds.

Preserving or Improving the Water –
Water Quality (WQ)

Design Best Practices:
The volume of the 24-hour event equaling the majority of the total rainfall from impervious areas should be collected and treated with suitable BMPs.

Structural Best Management Practices:
Biofiltration swales or burrows, constructed wetlands, or exfiltrating dry detention pond systems.

Holding Back the Water –
Rate Control/Detention (RC)

Design Best Practices:
The post-development flows should match the volume, shape and peak instantaneous rates of pre-development flows for larger flood events using appropriate BMPs.

Structural Best Management Practices:
Suitable BMPs include dry detention ponds, constructed wetlands, wet detention ponds, or storage swales.

Hydrological Design:

In order to accurately determine rates of runoff for stormwater management systems, sites should be monitored and flows modelled using analysis programs with continuous simulation. Site hydrological data should be collected for a minimum of 12 months unless there is acceptable regional data.

Storm Sewer Outfall Design:

In addition to these best practices, the design for your stormwater outfall connection should also:

• be located where it will minimize impacts to the existing riparian vegetation and/or alterations to the channel and active floodplain and associated fish and wildlife habitats;
• be located to mimic natural site drainage patterns and not alter existing watershed boundaries;
• provide appropriate water energy dissipation;
• minimize erosion and discharge flow impacts to the channel by directing the discharge to a maximum 45 degree angle to downstream flow;
• minimize impacts to the riparian corridor continuity by having a minimal footprint;
• minimize direct and Indirect impacts to onsite and adjacent fish and wildlife individuals, populations and species; and
• minimize direct and indirect impacts to other properties or services.

For further information on the design of stormwater connections and perimeter drains, please consult:

• Greater Vancouver Sewage and Drainage District Best Management Practices Guide for Stormwater, Oct. 1999. http://www.gvrd.bc.ca/services/
  sewers/drain/BestMgmtGuide.html

Operational Best Practices:

All individuals carrying out instream works should be made aware of and trained in the listed best practices. To comply with the Water Act Regulation’s Protection of Habitat (Section 42(1)) and Protection of Water Quality (Section 41) standards, you should follow these best practices:

Monitoring

• Construction activities should be monitored full-time during start-up and any instream works or sensitive activity, otherwise on a daily basis to the completion of the project. The environmental monitor(s) must be an appropriately qualified professional(s) and will be provided with written authority to modify and/or halt any construction activity if deemed necessary for the protection of fish and wildlife populations or their habitats. A sign should be posted listing the monitor’s company name and phone number at the entrance to or immediate vicinity of the job site.
• Forward a copy of this document listing standards and best practices for your works, and all appropriate plans, drawings and documents to the contractor/crew supervisor and keep it readily available at all times at the site while the work is proceeding.
• Hold a pre-construction meeting between the environmental monitor and the contractor undertaking the work on the site to ensure an understanding of the mitigative best practices for the project.
• Within 60 days of completion of this project the environmental monitor will complete and submit a minimum of one (1) copy of a monitoring report consistent with the recommended standard format to his/her client;

For more information see Appendix I: Monitoring.

Timing of Works (Subsection 42(1)(a))

• If works are scheduled for fish-bearing streams or if fish presence in the watercourse in not known, complete in-channel or bank work during the instream reduced risk work window approved for your region. To find out what the timing window requirements are for your area, contact your regional MOE office.
• Be advised that for certain fish and amphibian species at risk, there may be no window of least risk. Please contact your local WLAP office for more information.
• Only clear vegetation for worksite access and stream crossing right-of-way within the vegetation clearing timing window.
• Only undertake works during favourable weather and low water conditions.
• Complete the works as quickly as possible once started

For more information see Appendix II: Timing of Works.

Deleterious Substance Control/Spill Management (Subsections 41(a)(b) & 42(1)(d))

• Prevent the release of silt, sediment or sediment-laden water, raw concrete or concrete leachate, or any other deleterious substances into any ditch, watercourse, ravine or storm sewer system. The recommendations for sediment and erosion control outlined in the Land Development Guidelines for the Protection of Aquatic Habitat (Chilibeck et al, 1992) can also be used for reference.
• Ensure equipment and machinery is in good operating condition (power washed), free of leaks or excess oil and grease. No equipment refueling or servicing should be undertaken within thirty (30.0) metres of any watercourse or surface water drainage
• Ensure all hydraulic machinery to be used instream uses environmentally sensitive hydraulic fluids which are non-toxic to aquatic life, and which are readily or inherently bio-degradable
• Keep a spill containment kit readily accessible on-site in the event of a release of a deleterious substance to the environment. Train on-site staff in its use. Immediately report any spill of a substance toxic to aquatic life of reportable quantities to the Provincial Emergency Program 24 hour phone line at 1-800-663-3456
• Do not use treated wood products in any construction below the high water mark of the stream channel to prevent the release of preservatives toxic to fish.

For more information see Appendix III: Deleterious Substance Control/Spill Management.

Concrete Works (Subsections 41(e) & 42(d))

• As concrete leachate is alkaline and highly toxic to fish and other aquatic life, ensure that all works involving the use of concrete, cement, mortars, and other Portland cement or lime-containing construction materials (concrete) will not deposit, directly or indirectly, sediments, debris, concrete, concrete fines, wash or contact water into or about any watercourse. Concrete materials cast in place must remain inside formed structures.
• A CO₂ tank with regulator, hose and gas diffuser must be readily available during concrete work to neutralize pH levels should a spill occur. Train staff in its use.
• Provide containment facilities for the wash-down water from concrete delivery trucks, concrete pumping equipment, and other tools and equipment.
• Report immediately any spills of sediments, debris, concrete fines, wash or contact water to 1-800-663-3456. Implement emergency mitigation and clean-up measures, like use of CO₂ and removal of the material immediately.
• Completely isolate all concrete work from any water within or entering into any watercourse or stormwater system.
• Monitor the pH frequently in the watercourse immediately downstream of the isolated worksite until completion of the works. Emergency measures will be implemented if downstream pH has changed more than 1.0 pH unit, measured to an accuracy of +/- 0.2 pH units from the background level, or is recorded to be below 6.0 or above 9.0 pH units.
• Prevent any water that contacts uncured or partly cured concrete during activities like exposed aggregate wash-off, wet curing, or equipment washing from directly or indirectly entering any watercourse or stormwater system.
• Isolate and hold any water that contacts uncured or partly cured concrete until the pH is between 6.5 and 8.0 pH units, and the turbidity is less than 25 nephelometric turbidity units (NTU), measured to an accuracy of +/- 2 NTU;

For more information see Appendix IV: Concrete Works.

Isolation of the Work Area (Subsections 42(b) & 44(x))

• Isolate your work area from all flowing water, but do not cut off flow to downstream portions of the stream at any time during construction.
• Temporarily divert, enclose or pump the water around the work site. Ensure the point of discharge to the creek is located immediately downstream of the work site to minimize disturbance to downstream populations and habitats;

For more information see Appendix V: Isolation of the Work Area.

Salvage of Fish and/or Wildilfe (Subsection 42(1)(e)

• Complete a fish and amphibian salvage for works prior to the start of works if any portion of the wetted channel will be isolated and/or dewatered. An appropriately qualified professional(s) must complete the salvage. It is the responsibility of the salvage crew to obtain the necessary permits required by the British Columbia Fisheries Regulations or Canada Fisheries Act prior to conducting the salvage activities;

For more information see Appendix VI: Salvage of Fish and/or Wildlife.

Sediment Control (Subsections 41(a)(b)(c) & 42 (1)(c)(d)(f))

• Ensure material, such as rock, riprap, or other materials placed on the banks or within the active channel or floodplain of the watercourse, is inert and free of silt, overburden, debris or other substances deleterious to aquatic life.
• Ensure machinery works from the bank of the stream and not in the stream channel to minimize impacts and to better enable mitigation of sedimentation.
• Minimize the disturbance to existing vegetation on and adjacent to the stream banks.
• Place sediment control measures before starting any works that may result in sediment mobilization.
• Construct any ditches, water bars or water diversions within the work area so they do not directly discharge sediment-laden surface flows to the stream. Divert such flows to a vegetated area where flows can slowly infiltrate.
• Remove excavated material and debris from the site or place it in a stable area above the high water mark or active floodplain of the stream, as far as possible from the channel.
• Protect this material from erosion and reintroduction to the watercourse by using mitigating measures including, but not limited to covering the material with erosion blankets or seeding/planting with native vegetation.
• When material is moved off-site, dispose of it in such a manner as to prevent its entry into any watercourse, floodplain, ravine, or storm sewer system;

For more information see Appendix VII: Sediment Control.

Vegetation Management (Subsections 41(c) & 42 (f)(g))

• Limit vegetation clearing for access and at your work area.
• Consider other options when contemplating the need to remove vegetation. It is very often not the best choice for fish and wildlife habitat and species.
• Wildlife trees are important for many wildlife, bird, and amphibian species. You should avoid vegetation activities that will impact trees used for nesting or roosting. Section 34(b) of the Wildlife Act prohibits the your interference with bird nests, young, or eggs. This means that a wildlife tree containing an active nest, or a nest of species listed under the Act (i.e., raptors or species at risk), even outside of the breeding season, may not be felled.
• If you are proposing to top or remove trees, have the trees within the riparian area assessed by an appropriately qualified profession who is also a Wildlife Danger Tree Assessor to determine the presence and nature of the hazard.
• Where the danger can be removed by topping or removal of the dead limb this should be undertaken in preference to removal of the entire tree.
• Where the entire tree must be removed then the tree replacement criteria should be applied.
• Also in consideration of the importance of large woody debris to the stream/fish habitat and the importance of large diameter trees to wildlife populations, the stub of the trees should be retained where it is deemed safe to do so.
• Fall or top all trees so that the branches do not enter the stream channel. If any branches do inadvertently end up in the channel they should be removed offsite to where they will not enter the channel during high flows. Removal of limbs from the channel must be completed in a manner that will not disturb aquatic organisms.
• Fall the tree across the stream when falling across the stream cannot be avoided because of safety reasons (faller safety, buildings etc) and all methods of tree removal have been considered but cannot be safely employed. Removal of the felled tree must be completed in a manner that does not damage the banks and the bed of the stream. If possible, leave and anchor the trunk as large woody debris to be left within the riparian zone.
• Fall the tree away from the channel unless there is an immediate threat to life and limb and remove the material within the instream work window.
• Equipment used for vegetation removal should comply with this document’s listed best practices for deleterious substance control.
• Danger trees/limbs prior to the instream window to allow works to be scheduled within the timing window.

For more information see Appendix III: Vegetation Management.

Restoration of the Site (Subsections 41(a)(c) & 42(1)(c)(f)(g))

• Grade disturbed areas to a stable angle of repose upon completion of the work. These areas should also be revegetated to prevent surface erosion and subsequent siltation of the watercourse.
• Protect disturbed soil areas on the banks and areas adjacent to the stream from surface erosion by hydroseeding with a heavy mulch, tackifier, seed mix; by installing erosion blankets; and/or by heavily revegetating;
• Plant native trees, shrubs, and herbaceous plants that are appropriate to the site conditions to revegetate and replace impacted riparian vegetation.
• Restore all in-channel or active floodplain habitats that have been disturbed during the completion of works to a condition that is enhanced from their original state. The restoration will be consistent with a no-net-loss of fish and wildlife habitat
• Remove any remaining sediment and erosion control measures (i.e., silt fence). Ensure all equipment, supplies, and non-biodegradable materials have been removed from the site.
• Complete post-construction multiyear monitoring to ensure your revegetation meets full survival.

For more information see Appendix IX: Restoration of the Site.

Stream Bank and Lakeshore Stabilization | Habitat Enahncement and Restoration

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