Innovation-March_April 2013

Mythical Impediments

Design Solutions for Rainwater Management on Single Family Lots

Well-draining amended soil mixes with 50%-70% sands, <30% silts and clays, and 8%-15% organics won’t feel “soggy.” Include lawn basins with gravel bedding and overflow to building sump/municipal drainage system. Use a maximum impervious/pervious ratio of 2:1 (impervious area to grass area). Underground facilities can be constructed under lawns, driveways or patios. Orifice outlets in underground trench/reservoir can be used in poor-draining soils to discharge water slowly at baseflow rates. Most municipalities are encouraging rainwater management measures and are willing to work with applications, but interdepartmental education and bylaw changes are needed. Design and construct facilities to meet the Code’s intention of keeping water away from building foundations. Soakaway facilities must be at least 1 to 2 m from foundations and a low permeability barrier constructed between foundations/footing drains and the rock trenches/soakaway pits. Use splash pads to carry runoff at least 1 m away from building foundation and grade ground away from house (always good drainage practice). Use a sump between roof leaders and soakaway pits to settle out sediments. Discharge pavement runoff to grassed area wherever possible to filter runoff and minimize clogging.

Too much rain; disconnected roof leaders mean soggy lawns

Not enough space on lot

Municipalities don’t allow non- traditional storm servicing

Contravenes Building Code for 5 m foundation setbacks Disconnected roof leaders just drain roof runoff to perimeter drains

Soakaway pits clog up

most single family lots with simple measures. If their use becomes more widespread, the cumulative benefits of their use will become apparent in slowing the process of degradation in BC’s streams and creeks. v Water Resources Engineer Laurel Morgan, P.Eng., PE., M.Sc. and Stormwater Sector Leader Crystal Campbell, P.Eng., are with Kerr Wood Leidal Associates.

The Future of Single Family Development Includes On-Site Rainwater Management Measures Performance monitoring has shown that simple measures such as 300 mm of absorbent soil layers and underground soakaway pits can capture and infiltrate significant amounts of rainwater. Pilot projects are encouraged to demonstrate effectiveness and further debunk myths. Rainwater management targets can be met on

BCIT engineers.

BCIT graduates award-winning engineering students to our high standards in: > Electrical engineering > Mechanical engineering > Civil engineering > Graduate program in Building Science. Our engineering students recently earned top honours at the Canadian Engineering Competition. Learn more: bcit.ca/engineering

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1 Ad Name: Engineering campaign 2 Media: Innovation (APEGBC) 3 PO#: A2012-0384A

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