APPENDIX I

SEDIMENT CONTROLS

During the construction of the individual subdivision the Subwatersheds, an important aspect of development will be the control of erosion and sediment production. Construction activities such as clearing, stripping and shaping of land for development purposes exposes disturbed soil to precipitation and to surface water runoff. If uncontrolled, these activities could create major increases in the sediment loadings to the ravines and tributaries draining the Subwatersheds. This, in turn, could contribute to the impairment of water quality and environmental degradation.

It is imperative that the provisions for erosion and sediment control measures be identified and incorporated into site plans so that they are implemented first in the site development process prior to initiating construction. Once implemented, sediment control measures must be cleaned, checked and maintained in place, for all phases of the construction. The overall objectives of the control measures are to prevent erosion or retain virtually all sediment on-site.

Erosion and sediment controls which should be considered for implementation into individual site plans include:

1.	site management practices;

2.	construction scheduling;

3.	temporary sediment traps;

4.	temporary sediment basins;

5.	seeding and mulching;

6.	silt fences;

7.	brush barriers;

8.	check dams;

9.	drainage diversions;

10.	conveyance channels;

11.	storm drain inlet protection; and

12.	vibration pads.

Where possible, the principles governing the design of erosion and sediment control measures should follow Provincial guidelines outlined in the following documents:

13.	Guidelines on Erosion and Sediment Control for Urban Construction Sites (MNR, et al., 1987b).

14.	Technical Guidelines, Erosion and Sediment Control (MNR, 1989).

15.	Erosion and Sediment Control. M.T.C. Drainage Manual, Volume 2, Chapter F (MTO, 1985).

Site Management Practices

These practices involve the careful management of site activities such as:

16.	locating stockpiles away from the watercourses and stabilizing them against erosion;

17.	constructing and stabilizing site drainage features before initiating major construction works;

18.	phasing of construction and confining work areas with perimeter fencing;

19.	restricting site access to designated entrance/exit points; and,

20.	washing of construction vehicle tires to remove mud and prevent sediment from being carried off-site.

Construction Scheduling

Proper construction scheduling will help ensure planned and orderly development of the site while minimizing and restricting the potential for erosion and sedimentation. Scheduling for the phased development of the site will minimize the duration of exposed areas and limit wind blown dust during summer months. All temporary and permanent control facilities should be constructed prior to the installation of any services on the site or the commencement of earth moving (or filling) operations. This would include the construction of the storm water management facilities (e.g. artificial wetlands, wet ponds, etc.), which should be scheduled before other works, so that they can be used as sediment control facilities.

Temporary Sediment Basins

Sediment basins are large temporary basins that utilize a controlled storm water release structure to achieve greater efficiencies in trapping sediment. Sediment basins offer the greatest potential for the treatment of storm water during construction within the Subwatershed. Strategic placement of the basin, in conjunction with improvements to the natural drainage system (ie. ditches, diversion dykes, etc.), will allow for the interception of the largest possible amount of runoff from the disturbed areas. In addition, sediment basins offer the advantage of being adaptable as permanent water quality ponds when the site is developed. Sediment basins should be sized based on a storage volume of 125 m3 per hectare of drainage area.

Temporary Sediment Traps

Sediment, or silt traps create small temporary ponding areas to treat sediment-laden storm water. Sediment traps would be used in development site areas not serviced by the larger sediment basins. Silt traps are generally applied for areas <2 ha and are formed by constructing an earthen embankment with a gravel outlet across a drainage swale.

Sediment traps are temporary measures and focus on removing only the coarse soil particles. The sediment traps should be sized with an initial storage volume of 125 m3 per hectare of drainage area.

Seeding and Mulching

A standard technique for reducing the erosion of soils during the construction period is to seed or place a mulch which promotes vegetative growth. These measures are utilized in areas where construction has been completed, either finally or for a prolonged period. The use of seeding and/or mulches is only effective during the growing season. Therefore, an important aspect of erosion control is scheduling of work so that exposed areas can be seeded and are not left exposed during the winter and spring periods.

Seeding is most appropriate for flat areas and, as such, should be considered fully for development areas within the Subwatershed where gentle to moderately undulating overland slopes prevail.

Silt Fences

A silt fence is a temporary sediment barrier consisting of a filter-fabric stretched across a wire fence and staked into the ground for support. Depending upon fabric type, silt fences can have very high filtering efficiencies for sediments. Silt fences would be used below disturbed areas where erosion would occur in the form of sheet and rill erosion. Consequently, silt fences would be best suited for application in the large, flat tablelands currently used for agricultural practices.

Brush Barriers

Brush barriers are constructed of residual woody material (tree limbs, roots) and minor amounts of soil and rock generated from site clearing and grubbing operations. The material is pushed or dumped into windrows along the toe of the slope to intercept and retain sediment from disturbed areas. Once constructed, brush barriers need to be inspected and repaired after each rainfall. Accumulated sediment should be removed when it reaches one-half the height of the barrier.

Check Dams

Check dams are small temporary dams constructed of stone or rock, wood and/or logs, or metal. Check dams are used to reduce the velocity of concentrated storm water flows and accordingly, are placed in surface drainage routes and ditches. Check dams are used to control erosion. Although some trapping of sediments is possible, they are not recommended to be used as such.

Since the majority of the developable area within the Subwatershed is agricultural tableland, surface runoff tends to occur as broad, overland sheet flow. Therefore the use of check dams would be limited in application. Silt fences would be more beneficial; however, check dams could be utilized in ditches constructed to create an artificial drainage system for the conveyance of storm water to other sediment facilities such as sediment traps and basins.

Drainage Diversions

Drainage diversions are small dikes or earth cuts designed to divert site drainage away from exposed areas or to direct runoff to a sediment trap or pond. These types of diversions are very temporary measures, in place for only a few days, and should be applied to areas less than 2 ha.

Conveyance Channels

Conveyance channels lined with grass, stone or rip rap are used to safely convey excess runoff away from site areas. They are usually temporary measures, but could be permanent if constructed as part of the storm water drainage system (e.g. roadside ditch). Conveyance channels can be v-shaped ditches lined with grassed for small volumes of water with low velocities, or parabolic or trapezoidal shaped to convey moderate to large volumes of water, in which case the channel should be lined with rip-rap or stone to prevent scouring and erosion. Grass-lined channels require re-seeding/sodding if scoured. Rip-rap or stoned-lined channels require periodic maintenance to check for scour and to replace any dislodged stones.

Storm Drain Inlet Protection

Storm drain inlet protection, also referred to as catchbasin controls, consist of an excavated ponding area or sediment filter around the storm sewer inlets. The purpose is to filter out sediment from the storm water prior to its discharge to the storm sewer. Numerous different configurations of inlet protection are possible. The most common generally consist of filter cloth and rip rap (or crush stone) placed around or on top of the catchbasin inlet.

Proper scheduling of inlet protection construction is essential, both during the progression of storm sewer installation and disturbance to the site area. Inlet protection requires routine inspection, repair and clean out after each rainfall event.

Vibration Pads

Vibration pads are temporary devices constructed of reinforced concrete, coarse stone or rip rap. The pads are a minimum of 150 mm thick and 15 m in length. The pads promote the removal of mud from construction vehicle tires and trap the sediment preventing it from being transported off site. Vibration pads should be constructed at each access point (entrance/exit) to the development sites.