What's the Issue?
Many of GPSD's largest sewers follow along or within stream and creek basins to allow for gravity flow. This approach, while being very economical, has a drawback. Stream and creek beds and banks are prone to erosion. This erosion can lead to catastrophic failure of adjacent sewers due to washouts, debris impact, and undermining of the surrounding structural soils. If this potential damage is not recognized and repaired, the sewers will eventually fail and result in ecological impairment of the receiving stream due to wastewater pollution.
Due to this concern, GPSD regularly inspects and monitors sewers near streams and creeks. As a result of this routine inspection and monitoring, GPSD Engineers identified an area where failure of a large diameter sewer could occur if work is not performed to stabilize the erosion. This location is within Dry Run Creek – East Branch within Laura Bradley Park adjacent to Parkside Drive.
What's the Solution?
GPSD has worked local Engineers, Contractors, the Illinois Department of Natural Resources, the US Army Corps of Engineers and the City of Peoria to develop and permit an ecologically responsible approach to repair the creek and stabilize the sewer.
GPSD has a comprehensive solution to repair the creek and stabilize the sewer by using two approaches: hydraulic countermeasures and hard armoring. Hydraulic countermeasures are localized improvements to a stream or creek basin where the geometry is modified to change the amount of energy stored in the flowing water. Similar to how a speed bump works on a road.
Prior to the installation of a speed bump cars can travel fast down a stretch of road since they don’t have to slow down or stop. When a speed bump is installed on a road a car must slow or stop for the speed bump. If the car does not slow down or stop, the impact from hitting the speed bump changes the car’s energy from moving forward to moving upward, which will result in a loss of forward velocity. Water works in much the same way. If we install a speed bump (often called a weir or grade control structure) then under low flow the water must slow down to go over the speed bump. Under high flow the water can pass over the speed bump, but the direction of the water’s momentum changes and reduces the water’s available energy to cause erosion.
Hard armoring is exactly like it sounds and entails evaluating areas of a stream or creek basin with extremely high velocities (e.g., 12 feet per second or greater) and replacing the existing bed and banks (which are subject to erosion) with an erosion resistant material such as large boulders or concrete mats.
What's the Timeline & Route?
GPSD is proposing to complete this work within the 2021 calendar year. The actual work will likely take between three and four months, but due to material availability constraints, COVID-19 working protocols, and potentially unpredictable weather conditions, the actual timeline is subject to change.
The route GPSD and its contractors will utilize to access the creek is not determined at this time.
What's the Cost?
GPSD estimates this Project will cost between $1.3 and $1.6 million; however, until final bids are received these are just estimates. To ensure GPSD receives the best possible pricing, this Project will be publicly bid and will be awarded to the lowest bidder that meets all required bid conditions in accordance with GPSD policies and State Statutes.
Greater Peoria Sanitary District was recently discussed in the American Society of Civil Engineers' Source magazine for its upcoming work in the City of Peoria's combined sewer system. Click here to view the article.
The American Society of Civil Engineers (ASCE) represents more than 150,000 members of the civil engineering profession in 177 countries. Founded in 1852, ASCE is the nation’s oldest engineering society.
ASCE stands at the forefront of a profession that plans, designs, constructs, and operates society’s economic and social engine – the built environment – while protecting and restoring the natural environment.
For more information about ASCE, click here.
For more information on GPSD's work in the combined sewer system, click here.
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