STORM SEWERS - MUNICIPAL DRAINAGE
A storm sewer is a network of pipes that collect storm water runoff through a surface inlet and drain it to an appropriate outlet, such as
a river. Storm sewer systems can be small and simple, such as that used for a modest housing development, to complex systems used in metropolitan
areas serving a combination of residential, commercial, and industrial developments.
Storm water runoff is extremely important to the environment and is becoming highly regulated in terms of both its quality and quantity. In the
past storm water runoff was considered relatively â€˜clean and could be freely discharged into existing watercourses. It is now accepted that
runoff will contain components such as hydrocarbons and other chemicals, a wide range of solids as well as other debris that is picked up from
the ground surface during rainfall. Screening, filtration or hydrodynamic systems may frequently be used as part of a storm sewer system to
improve runoff quality. The quantity and the runoff rate is also very significant. Storm sewers are sized for specific runoff rates;
improperly sized systems may create a surcharged condition or upstream flooding. HDPE
corrugated pipe has the features necessary for well functioning storm sewer systems. Structural strength and good joint systems ensure proper
performance at all times.
Benefits of HDPE corrugated pipe in storm sewer applications.
- Suitable under traffic - Most storm sewers are installed under pavement and must withstand vehicular loads, often under just a minimum of cover. Properly installed HDPE corrugated pipe can withstand AASHTO HS-25 loads with a minimum 1 ft (0.3m) of cover for pipe 48-inch (1200 mm) and smaller, or 2 ft (0.6 m) of cover for larger pipe diameters.
- Withstands a range of covers - An individual system may have a wide range of cover requirements, especially when the ground is hilly or rolling. Flexible pipe, such as HDPE corrugated pipe, outperforms its rigid counterpart, reinforced concrete pipe, in deep burials due to the pipe's ability to interact effectively with the backfill. Properly backfilled, HDPE corrugated pipe can be buried at depths of 20 ft (6 m) or more.
- Efficient hydraulic properties - HDPE corrugated pipe with a smooth interior allows for efficient flow though the system. Often, smooth interior pipe can be reduced by at least one diameter from its corrugated interior counterpart. This allows for a narrower trench, reducing excavation and backfill requirements and helping to speed installation. The smooth interior also allows sediment to be flushed out of the system so that it maintains its capacity.
- Proven and accepted - HDPE corrugated pipe meets AASHTO M252 or M294, depending on the diameter. Both Type C, corrugated interior), and Type S, (smooth interior wall) are widely available. Pipe is available with a range of joint options , including watertight joints, which are most frequently specified for storm sewers. Most state Departments of transportation, regional agencies, and local municipalities have approved HDPE corrugated pipe for storm sewers and other applications.
- Cost-effective installations - Storm sewer applications demand high performance and minimized cost. HDPE corrugated pipe is priced competitively with other pipe alternatives. Installation costs of HDPE systems are frequently lower than other pipe materials, due to its light weight and joining systems. Fast installation minimizes traffic disruption and other nuisance factors associated with underground installations. Light product weigh means improved safety and reduced risk of injury during pipe handling..
resists chemicals and abrasives found in even the most aggressive environments. Many chemicals,
especially acids, can shorten a pipe's service life dramatically. HDPE
is often used to reline
or replace materials less resistant to their environment to ensure project service life requirements are met.
corrugated pipe with a smooth interior has a low Manning's 'n' factor and therefore
may permit a smaller diameter to be used. A smaller size means less excavation and reduced backfill; both of which help to increase installation rates and savings.
Corrugated HDPE - On The Job
The landfill for a southern California community was
performing its intended function well. But as a ponding basin for storm water runoff, not so much, to paraphrase the Environmental Protection
Agency (EPA). The landfill receives a fair amount of rain water runoff, and new EPA regulations now restrict overflow from collecting in
landfill basins. So engineers at the base needed an immediate solution.
Choosing corrugated high-density polyethylene (HDPE
) pipe provided the community with significant
savings over the $285 per foot (plus labor) that reinforced concrete pipe would have cost. That meant the project came in under the target cost.
Installation began in August 2003. The completion date was scheduled for early 2004.
The project called for the storm water to be diverted from the landfill to a creek via collection pipes that ranged from 24-inch to 48-inch diameters.
That water then would be funneled to 60-inch pipe before outletting into a rip rap filter that settles the sediment and some pollutants before
it reaches the stream.
"Quantity of storm water is no longer the only consideration for drainage projects," said Camille Rubeiz, director of engineering for the
Plastics Pipe Institute (PPI). "Managing the quality of the water is now a way of life for civil engineers and community leaders. Our manufacturing
members offer solutions to their challenges."