Watershed Studies
Watershed studies provide an assessment of changes to surface runoff and groundwater infiltration due to urbanization or industrial projects. Potential impacts include flooding; erosion & sedimentation; degradation in base flows and/or water quality; and loss of wildlife or fisheries habitat. Comprehensive plans are used to address each of the above concerns.

Watershed studies are coordinated with parallel planning and environmental assessment pro-cesses. EHG staff use computer models such as OTTHYMO, OTTSWMM-EXTRAN, HEC-2 and Culvert Master™ as a first step to determine potential changes and to evaluate alternatives. Model results are complemented by additional analysis by experienced engineers and scientists who consider all relevant issues (see Table).

Storm Water Management (SWM)
SWM studies, though smaller in scale than watershed studies, are often as complex. Local solutions to environmental problems must be provided in the context of legal, regulatory and planning frameworks while achieving specific development objectives.

Due to their complexity, SWM studies are often undertaken in two phases:

• Draft Approval, in which a conceptual drainage plan is submitted to approving agencies for comments.
• Detailed Design, in which the detailed considerations and design challenges are resolved and documented.

EHG staff have completed over 100 SWM studies ranging from 1 to 100 ha in size - many with significant constraints due to drainage from nearby sites or hydraulic capacity concerns in sewers or bridges/culverts.

Site Drainage
In compliance with requirements set forth by watershed and SWM studies for the area, site drainage plans must provide:

• Economical outlets for the minor (sewer) and major (overland) drainage systems
• Adequate, safe parking lot or roof storage
• Sufficient water quality treatment or equivalent financial compensation

Completion within tight deadlines requires an experienced engineering team.

• Document and model pre-development (or existing or baseline) development conditions

• Respect local criteria for environmentally significant areas (ESA) and wetlands

• Consider nearby sites' (external areas) general plans, drainage and sewer systems, if any.
• Control water quantity using SWM ponds for flood control and to maintain base flows
• Address water quality issues and provide fisheries & terrestrial habitat compensation plans

• Provide erosion & sediment control and topsoil management plans during construction

• Post-construction inspections and monitoring for pond performance, downstream erosion...

• Investigations to determine causes of flooding, erosion or water quality problems