National Weather Service changes flood warnings for Issaquah

September 24, 2011

By Warren Kagarise

NEW — 11 a.m. Sept. 24, 2011

Less than a year after conflicting flood information confused Issaquah residents during a December deluge, the National Weather Service plans to adjust flood warning levels for Issaquah Creek.

The agency plans to base flood warnings on the creek’s flow, rather than height. The agency plans to make the adjustments Oct. 1.

The switch is meant to avoid confusion between National Weather Service data and the city’s flood warning system.

The city bases warnings on real-time data from a gauge upstream from Issaquah in Hobart. The system can usually provide a few hours of lead time before flooding impacts Issaquah.

The data collected by the National Weather Service comes from a downstream gauge near the creek mouth in Lake Sammamish State Park.

Due to gradual changes in the steam bed — a result of years of flood-mitigation projects and other factors — means potential flooding impacts no longer pose as much of a risk.

Last December, Issaquah Creek data from the Hobart gauge indicated a rain-swollen creek, but not enough to cause more than localized flooding. Information from the downstream gauge and a notice from the National Weather Service, however, cautioned residents to prepare for widespread flooding in the city.

The flooding — the result of a Pineapple Express system barreling off the Pacific Ocean — flooded Issaquah streets and spawned mudslides.

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