Completion of all system upgrades will take several years. However, improvements that result in the greatest benefit for neighbourhoods will be done first and as soon as funding is available. The following provides more background information on neighbourhood flood prevention options.
Dry ponds are manmade depressions developed in parkland or recreation areas to capture surface runoff. Water collects in a dry pond during a rainstorm and is held there until underground stormwater pipes have the capacity to drain it away. This usually takes less than 24 hours and is done via drains built into the sides or bottom of the pond.
Dry ponds are fully landscaped to blend into local surroundings. When dry, ponds are available for recreation or park use. The ponds are usually 1.5 to 3 metres in depth and can be any width or length.
To minimize the risk of accidents, dry ponds are gently sloped, kept relatively shallow and are well signed as to the potential water hazard.
System Capacity Standards
In Edmonton, the stormwater sewer pipe design standard is 1 in 5 years. This means the system can handle any typical rainstorm but could have its capacity exceeded once every five years. This is based on historical weather patterns. Since about 1980, stormwater lakes to service new neighbourhoods have been required in order to store water after rainstorms.
The sanitary sewer system design standard varies across the city. It is based on sewage flows, plus an allowance for water that gets in the system during wet weather. Since 1989, backflow valves in new homes have been required to protect against sewer backup.
The design standards were different when the 15 high-risk neighbourhoods were developed. In some communities, the drainage systems need to be upgraded to achieve today's service standards. In other cases, the systems are at current standard (other than a stormwater lake in every neighbourhood). Some homes have upgraded their drainage servicing with good lot grading and backflow valves but many have not.
Minimizing the flood risk means upgrading and trying to achieve today's standards whenever possible. Where this is not possible (for example, building a stormwater lake), options are to divert excess water away from homes and to places where it can do the least harm.
Drainage System Maintenance Schedule
There are about 58,000 catchbasins, 72,000 manholes and 5,700 km of sewer pipe in Edmonton. Scheduled maintenance of catchbasins, manholes and sewer pipes depends on the history of the neighbourhood or area. Neighbourhoods and areas with chronic drainage issues receive more maintenance attention than other neighbourhoods. In addition to a regular schedule, new problems identified during rainfalls are immediately investigated and appropriate action taken. Residents should call 311 to report a drainage problem.
City crews regularly inspect catchbasins and manholes to determine which ones require cleaning. Visual inspections of the system at manholes are done without special equipment. TV cameras are used to help define the condition of underground pipes.
Cleaning and Flushing
Once a problem is identified, it is investigated and, depending on the nature of the problem, sewer pipes are flushed and cleared and/or debris is removed from catch basins. One type of flushing is done by extending a hose from a fire hydrant into a pipe. The flow of the water loosens and sends debris down the system to pipes where sewer water is flowing continuously. These pipes carry the material to a wastewater treatment plant. A problem site might be visited once a year, with the cleaning operation taking two hours.
Catchbasins can get plugged quite often due to snow or ice cover, hail, leaves, or other debris. At the bottom of each catchbasin is a small reservoir or sump. City crews use "vacuum" trucks to remove collected materials from catchbasin sumps when they are full. Catchbasins along bus routes and major roads are cleaned once a year to remove debris and sand left from winter. Other catch basins are not cleaned unless a specific problem is noticed or reported.
Persistent problem areas may require re-lining or replacement of a sewer pipe. Similarly, manholes, catchbasins and outfalls that deteriorate or are damaged are repaired or replaced as part of Drainage Services' regular maintenance program.