Intense rain from several storm events over the last couple of years — the most recent of which passed through the Gorge just a few weeks ago — has challenged The City of The Dalles’ stormwater system past what it was designed to take; and while the city is working to improve its stormwater system, Public Works Director Dave Anderson expects that heavy rain events are only going to get more intense going forward.
“It just rained hard enough to really challenge some of our systems,” said Anderson in a report to The Dalles City Council on June 9. “…It rained harder than what our systems are designed to take.”
State regulations require a wastewater treatment plant to be capable of handling a 5-year storm event, or a storm that has roughly a 20 percent chance of happening any given year, based on the National Oceanic and Atmospheric Administration (NOAA)’s analysis of historical weather and rainfall patterns.
For The Dalles, said Anderson, that means the treatment plant has to be able to handle a flow just over 7-and-a-half million gallons per day. The major storm event that The Dalles saw a few weeks ago and the storm that blew through The Dalles last year each resulted in flows to the plant of about 14 million gallons per day.
The city’s stormwater collection systems are designed to be able to handle a larger, 25-year storm event, but these systems too are struggling with the intensity of these recent storms. “The intensity of these thunderstorms that we’re seeing more frequently now are more intense — it’s raining harder for shorter periods of time than is associated with these 25-year events,” said Anderson.
“One of the things that we do expect with climate change is an increase in severe weather intensity, that’s one of the ways I heard it described once was an increase in weather weirdness: Droughts may become drier, storm events may become stormier, rare rain events may happen more frequently, those types of things,” said Anderson, “And so … we’re trying to look ahead and at least pick the low hanging fruit to improve the function of our stormwater collection system to do a better job at handling these heavy thunderstorm and heavy rain events.”
Public works began installing a new stormwater sewer main on East 10th St. between Clark Street and J Street last week, with the intent of improving drainage of stormwater during rain events.
“We’re going to add some catch basins and try and do a better job of collecting the water before it builds up so much to the point that it’s running down driveways and into people’s basements,” said Anderson.
Public Works has also been working with the owner of a downtown building that experienced flooding in both this year’s and last year’s heavy storms due to issues with the building’s private piping system. No other improvements to the city’s system are planned for the immediate future, said Anderson, but further improvements will need to be made if these heavy rainstorms continue.
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