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How to Have a Cost-Effective and Minimal Impact Drainage Model by Sophie J. Parker

By CSI HQ posted 06-25-2020 04:51 PM


How to Have a Cost-Effective and Minimal Impact Drainage Model

By Sophie J. Parker

Editor's Note: CSI is pleased to publish this blog from Sophie J. Parker, Editor in Chief at Surehand Inc. If you have an idea or opinion you would like to share with your colleagues in the construction industry, please contact CSI Content Strategist Peter Kray at He would love to help publish your thoughts.

Leaks can be problematic in drainage runs on any building and may lead to a myriad of issues if undetected and unresolved. Unfortunately, leaks in these systems are often harder to identify than in clean water supply pipes, as they are empty at least some of the time, and often have very little head (i.e., difference in depth).

Ensuring drains and pipes are watertight is essential in reducing a building’s financial costs, structural integrity and the burden that it places on the environment. The question is not if design and planning should be executed in a way that minimizes leaks; it’s how. Careful thought and considered decisions are the answer.

Choose the Right Pipes and Runs

When designing a drainage or sewage system, opt for straight pipe runs with as few connections as possible, and with adequate downfall. Sharp bends generally lead to blockages and should be avoided, and the fewer connections you use, the fewer leakage risks there are.

Where connections and bends must be used, aim to position them for easy installation and subsequent maintenance. If the installer is working mostly by touch, it’s very difficult to guarantee a watertight finish.

You should also incorporate the required junctions for any future connections that might be needed from the first construction and make sure sewer gases are properly ventilated. If not, these gases can corrode almost any pipe material over time.

While on the subject of material, plastic should be used wherever possible, for several reasons. First, the pipes tend to be longer than their rigid counterparts. Plastic is also more forgiving and flexible, so it’s able to accommodate and absorb minor deflections on the overall system.

Consider Tree Locations

Tree locations, both presently existing and planned for the future, should be factored into any drainage design.

Roots seek out the greatest accumulation of water in close proximity to wherever they are – which can translate into their penetration into pipes.

To avoid this situation and its subsequent leaks, planners often use Rootboxes, which are installed near trees and create a water tank that the roots can access. The rainwater is led to the Rootbox via a perforated pipe, and once the box is full, excess fluid passes out to the conventional rainwater drainage.

Perform Rigorous Leak Tests

Leak tests are defined as nondestructive quality control assessments of manufactured parts and completed systems to ensure fluids can’t leak out or into them.

The tests must be conducted exhaustively, checking performance under high and low temperatures, pressure and impact. There are several local and international standards that apply to leak testing, including the European Standards EN1610, Construction and Testing of Drains and Sewers, for systems that will operate under pressure and/or be buried, and EN 752-5, that covers rehabilitated sewers.

The EN 1610 tests to a standard watertight pressure of max 0.5 bar, or a 5-meter water column, as well as 0.3 bar, or a 3-meter water column under laboratory conditions only. The former recreates the outward pressure of a pipe that is full of water, and the latter does the same for inward pressure that comes from permanent groundwater.

The finished system must also be tested, using smoke and pneumatic and/or hydraulic testers. The smoke test identifies any misconnection, while the pneumatic and hydraulic testers check that the system is watertight with no leaks.

The assessments of the drainage structures are done once the trench has been backfilled fully, first by flushing the systems with high-pressure water and then by performing out-of-round or deflection tests on any plastic pipes.

Thereafter, all openings are closed off and the pipe is filled with a slow stream of water (from its lowest point, so air can’t escape) to confirm that there are no leaks.

Manholes, which are so important to effective drainage mechanisms, have their own test requirements as set out in EN 13598-2. They must hold their shape under load at high and low ground temperatures for at least 50 years, remain leak-tight no matter how the pipes feeding into them move, and withstand continuous traffic loads.

Follow-Up Inspection and Maintenance

Once a system has been successfully installed it should be regularly inspected by an industry professional and maintained to ensure it remains leak-free.

Ground can settle following the completion of development and extreme weather events or natural underground watercourse changes can also have an effect. In addition, chemical attack, corrosion, and high pressure or blockages due to tree roots are also risk factors that can wreak havoc on a drainage system if undetected.

By designing drainage systems to allow for checks and maintenance, leaks can be largely avoided. Additionally, by including measures in your plans to deal with any small problems, you can stop serious issues in their tracks.

These design elements go a long way to ensuring you have a low cost, minimal impact model that provides effective and leak-free drainage.

1 comment



Good blog post and thanks for posting it.  Many of the principles of designing drainage piping for a building are similar to those used by civil engineers for storm sewers and process-mechanical engineers in designing industrial and treatment system piping.  In designing drainage piping, flowing either partly-full via gravity or under low pressure (often, gravity-induced) for water and wastewater treatment facilities, I've often designed cleanouts or other access points at appropriate locations in the piping system (such as 90-degree changes in direction) to facilitate future cleaning, when needed.  For a building, such cleanout locations should, optimally, be reasonably easily accessible for bulding O&M personnel.

It is important to avoid high points in piping and, when a high point is necessary in piping htat will flow full, it is important to include a means to release air from the high point, or else the pipe's capacity may be reduced by "permanent" air pockets at high points.  Air/vacuum valves are available to exhaust air when the pipe is filled and admit air when the pipe is emptied.  Air release valves can exaust small amoutns of entrained air that accumulate during operation.  Combination air valves incorporate the features of both air/vacuumm valves and air release valves.  Special types of valves are avialable fo these three types for liquids that contain solids, such as sewage.

For storm water drainage piping to operate optimally, screens or other means to restrict solids, such as leaves and other matter, from entering the drainage piping are necessary.  The entry points should be regularly checked and such foreign matter removed, to ensure proper operation of the building's drainage system.

Adequate ventilation of systems intended to operate partly-full or under low-pressure (full, but flowing by gravity) is always important for proper operation.