Stormwater Management and Drainage

A complete system addresses runoff volume, peak flow, water quality, erosion, water balance, safe surface conveyance, and downstream capacity according to the approved design. Harrowgate builds the physical collection, storage, treatment, infiltration, control, and outlet components, then verifies the elevations and dimensions on which the hydraulic model depends.

Ontario's stormwater framework defines performance levels based on long-term suspended-solids removal and facility design. Current Ontario Regulation 137/25 requires at least enhanced protection for qualifying new works. The engineer identifies the approved treatment train and criteria; Harrowgate protects media, forebays, controls, and storage geometry needed to achieve that design.

Fine sediment from exposed earth can clog native soil, stone voids, geotextile, or engineered media before the facility begins operating. Harrowgate diverts dirty construction runoff, limits trafficking and compaction, keeps stone clean, and delays final connection until tributary surfaces are stabilized. Contaminated material is removed rather than hidden under a clean top layer.

Surveyed bottom, side slope, bench, berm, structure, and overflow elevations are compared with the approved stage-storage geometry. Harrowgate tracks fill and sediment so the constructed basin does not lose volume. Critical measurements occur before topsoil, liner protection, riprap, or water makes the earth surface difficult to inspect and correct.

High velocity, concentrated flow, poor alignment, undersized protection, missing filter, unstable receiving soil, or a tailwater condition different from design can mobilize the outlet. Harrowgate prepares the subgrade, installs specified geotextile, stone, apron, headwall, or energy dissipator, keys edges, and connects the discharge smoothly to the receiving channel.

The opening diameter, shape, invert, plate orientation, seal, fasteners, and upstream debris protection are physically measured against the detail. Harrowgate records the installed control before the chamber is closed. A small dimensional or elevation error can materially alter release rate and storage depth, so the supplier label alone is not accepted as verification.

Provide the approved stormwater report and model criteria, grading and sewer plans, structure details, Environmental Compliance Approval or registration conditions, erosion-control plan, geotechnical and hydrogeological data, liner and media specifications, outlet permits, planting requirements, survey criteria, commissioning tests, maintenance access, and phased temporary-drainage plan.