Sep 14, 2012

Ottawa Tackles System Overflow, Flooding With Inlet Control

Over the past few decades, rain events throughout North America have become more frequent and substantial. More rain combined with outdated infrastructure means that many municipality storm sewers and drainage systems are forced to exceed capacity, resulting in flooding and additional expenses.
As a result, municipalities are turning to inlet control devices (ICDs) to manage the amount of storm water runoff that can enter a system during a storm event. ICDs control water flow at the sewer inlet, allowing excess water surge to remain in catch basins or temporarily above ground until the storm subsides, thus preventing sewer system backups and overflows.  

In the mid-1980s, the city of Ottawa introduced the concept of a dual drainage system. This features a minor underground system designed to handle typical rainstorm activity and a major system that involves the grading of roads and water retention facilities to handle significantly larger and less frequent storms. Unfortunately, several communities that were built prior to the 1980s did not have the level of protection provided by the balanced dual drainage system found in newer communities.

In the summer of 2009, the city of Ottawa experienced a significant rainstorm that generated more than 100 mm of rain in a 24-hr period. In the west end of the city, 1,500 basements were flooded when surface drainage entered the storm sewer without flow restriction. As storm water entered basements through window wells, foundations, and improperly sealed backwater valves and cleanouts, it began to drain into the sanitary sewer system.

After the flooding, an investigation was initiated to pinpoint the problem and determine a flood control solution to prevent future flooding in high-risk areas. A combination of municipal and public input, field assessments, topographical surveys, and sewer system testing and inspection demonstrated the need to limit the amount of storm water entering the storm sewer system to prevent exceeding capacity.

To limit the amount of water that can enter the storm sewer, the city of Ottawa decided to install ICDs in catch basins, seal maintenance hole covers and ensure proper storm water storage through the strategic use of berms, regrading and open space. The city determined that ICDs were the most cost-effective solution with minimal disruption to the existing community. The Tempest ICD system from IPEX was selected to provide the required flow control in several catch basins throughout the city.

Available in flow rates from 32 to 270 gpm, Tempest units are mounted over existing sewer inlets to restrict flow to a more narrow range. A quick release mechanism on the unit can be accessed with a reach bar to lift out the unit for easy maintenance. In addition to controlling flow, the systems help alleviate odor emissions and prevent floating debris from entering the sewer system.

“Our only other solution was to excavate and replace the pipes with larger pipes,” said Graeme Stewart, senior standards engineer for the city of Ottawa. “While ICDs were not a new idea, we wanted something that we could easily remove, inspect and maintain without having to go into the catch basin. We also wanted to control odor and prevent floatables from entering the sewer. The Tempest met our criteria, and IPEX was proactive in addressing our concerns and further developing the solution to meet our needs.”

Now during significant rainfall events, the city of Ottawa can rest easy. “We are confident that the ICDs and the additional measures we’ve taken will ultimately help us minimize the impact of storm water where we had problems before,” Stewart said. “It’s all part of an integrated system, and certainly the ICDs play their part.”

Ultimately, the solution was much less expensive, less disruptive and less time-consuming than traditional approaches that often require full catch basin and pipe replacement—saving the city of Ottawa significant cost, hassles and future risk.

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