Updates on condition of Newport’s two drinking water reservoirs – neither dam would probably survive a major earthquake
Newport City Councilors got another update on efforts to figure out what to do with the city’s two drinking water reservoirs on Big Creek. A state dam safety inspector told the councilors that both dams were built with softer materials which would not fare well in a major earthquake – in fact both would likely fail causing a huge flood downstream and inundate many houses at the west end of the lower reservoirs.
It’s widely agreed that of the two reservoirs, the upper one is far more valuable. The lower one stores less water due mainly to the fact that over the decades the lower lake has filled up with sand and silt making for a wide but very shallow lake. He said the upper reservoir, which is much newer, holds the most water by far but was built with weaker soils than would be approved of today. The inspector said the upper reservoir could be a good candidate for being strengthened in that bedrock is well within reach under the dam.
Public Works Director Tim Gross said he is in negotiations with a contractor that will perform more detailed analysis of the upper dam and develop estimates for strengthening it or even rebuilding it. He said it’ll take at least a couple more years of study and financial evaluation to come up with a credible way forward on the project. If the upper dam is strengthened or rebuilt, the city’s water treatment intake system would have to be extended up to it – a good half-mile. Over the past couple of years there’s been talk of simply draining the lower reservoir rather than leaving a lot water behind the dam that would certainly be unleashed during a severe earthquake. Draining the lower reservoir might also create additional outdoor recreation opportunities.