For the first time, Bend has a clear picture of the problems throughout nearly all of its sewer system, and that could save taxpayers millions.
A new computer model of the system reveals serious problems in the sewers. But there are fewer than previously thought, and the city might have more time than it expected to fix some of them.
The information comes from a new hydraulic model that consultants recently completed, which covers 90 percent of the city system. It can identify current problems and predict issues that will arise.
“That actually produced some pretty good news,” said Tom Hickmann, Bend's engineering and infrastructure planning director. “While we certainly have problems, they weren't as extensive as we thought they may be. That was encouraging.”
A previous model covered only 30 percent of the sewer system. In some areas of the city, there are capacity shortages in the sewers that make it difficult for new businesses to open and for new development to occur. In particular, there are problems in southeast Bend, the central core of the city and the north end of the city around Cascade Village Shopping Center.
A 2007 city master plan would increase sewer capacity with new gravity trunk lines around the city, at an estimated cost of $170 million. This included a $61.6 million gravity line in southeast Bend, which the city already started to build. However, city officials put that plan on hold in May 2012 to develop the new hydraulic model and search for less costly solutions.
Hickmann said it's already clear the city will be able to defer or avoid tens of millions of dollars in sewer work.
“We will likely not be making the level of investment that we thought we were going to need prior,” Hickmann said.
It's too early to know exactly how much the city might save, Hickmann said.
The city created a citizen committee last year to evaluate the sewer problems and potential solutions. At a recent meeting of the group, Assistant City Manager Jon Skidmore said the results from the new computer model are worth the investment.
“This really to me proves the value of investing in collecting data,” Skidmore told the committee at a recent meeting. “By actually having 90 percent of our system modeled now, we just have a better understanding of what the constraints and challenges are.”
The city did make a significant investment in gathering data and creating the model. To ensure the computer model is accurate, the city did extensive monitoring of sewage flow throughout the city. Consultants used the data to calibrate the model. “By the time we are all done, including additional data gathering efforts, we will probably be in the neighborhood of about $3 million that we have spent between data collection efforts, the model and all associated analysis that goes with it,” Hickmann said.
One major decision officials will face is whether to pay for projects that would prepare the city for stormwater from unusually severe weather. They could also take the less costly route of preparing for runoff from typical Central Oregon storms.
“The big factor really comes down to storm events,” Hickmann said. “It's hard to collect sewer flow data that is timed with storm events. These flow monitors are very expensive to have out in the field and to maintain them.”
It costs roughly $150,000 for the city to rent and deploy 50 sewer flow monitors for two months, Hickmann said. City workers want to capture data during major storms, but that can be difficult. In recent years, the monitors recorded data from two storms: a typical Central Oregon event and a very high-intensity storm.
“When we modeled the system and how it responded to (the typical storm), it showed deficiencies on the 20-year horizon but was still relatively manageable at this point,” Hickmann said.
The city also collected data during a high-intensity storm in January 2011, and when workers fed that information into the computer model, it showed many more problem areas in 20 years.
The city needs more sewer data, and Hickmann said the citizen advisory committee might soon ask the City Council to approve more flow monitoring this fall and winter. The additional data could help officials decide whether it is necessary to spend more to prepare for severe storms.
The next step is for a consultant to use the model to develop projects that would fix the sewer problems. For example, this process might reveal that the city could save money through projects to reduce the amount of stormwater that flows into the sewer system. This could mean the city would purchase land and build catch basins, to collect stormwater in certain areas. Or it might make sense to fix problems in the sewers so they can handle all of the stormwater. Hickmann expects that a list of potential projects will be ready by late fall.
“The truth is, we may not produce significantly different results than prior studies,” Hickmann said. “But the idea is the results that we do get are based on better information that the council can buy in on, as well as the city.”
The plan is for the citizen committee to present a recommended plan of action to the City Council in fall 2014.