Floods washing away Sandy Cove Park in Snoqualmie
February 27, 2009
By Michael Rowe
Mother nature has taken her toll on Sandy Cove Park, next to the Snoqualmie River. The January floods have caused significant erosion along the riverbanks.
Snoqualmie’s GIS coordinator Mel Soares has put together some information the city can use as a reference to tell just how much stream bank was lost due to flooding during the last decade. GIS stands for Geographic Information System. GIS integrates information from global positioning systems with aerial and other maps to gain information on an area’s geographic features.
Soares took a GPS unit to Sandy Cove in December 2008 after the November floods, and he went back to the park after the January 2009 floods. His GPS unit is not capable of producing survey grade readings, but it can determine a position within an accuracy of plus or minus one foot.
The banks of Sandy Cove Park have lost as much as 17 feet of ground.
He took the information he got from the GPS readings and plotted it on an aerial map of Snoqualmie made in 2000. His findings showed that there has been significant erosion to the riverbank in several areas of the park.
One area showed a loss of 17 feet from where the shore is now compared to where it was in 2000. Another area showed a loss of about 14 feet, Soares said.
A variety of factors lead to different patterns of erosion along the riverbank, Soares said. In some areas, riverbank erosion is greater because there is not as much vegetation anchoring the bank in place. In other areas, differences in soils can cause erosion to happen quicker and more dramatically.
The information on the loss of shoreline cannot be used for engineering purposes, but it provides a handy reference for what is going on at the park and along the riverbank, Soares said.
Sandy Cove Park is a nice place to have a picnic along the banks of the Snoqualmie River, Parks Director Al Frank said. In addition to picnic tables, the park features horseshoe pits. The picnic tables are stored during the winter months to avoid being swept away in a flood, which as it turns out, is a pretty good idea. The tables will be set back up in April.
Frank said that he has noticed that, every time the river floods, more of the riverbank disappears.
The January flood event caused the loss of a live cottonwood tree on the banks of the river. The root ball of the cottonwood tree was uprooted by the floodwaters, Frank said. The uprooted tree was roughly 50 feet tall and at least 6 feet broad. It still lies in the river, along with other trees from the flood.
It takes hundreds or even thousands of years to make a sandbar like the one at Sandy Cove Park, Interim Public Works Director Alan Lobdell said. The city has considered stream bank stabilization to limit damage caused by future flood events, but this is probably too costly. Fixing the stream banks to limit erosion would cost in the millions, Lobdell said.
“There is not a whole lot we can do,” Frank said.
The parks department is considering signage to warn the public about the dangers of walking on the riverbank. The erosion caused by the flood could cause the bank to give way under the feet of someone walking along the shore, and the drop from the shore to the water is 8-10 feet in the park.
The flood damaged other city parks too, and Snoqualmie’s parks department is still cleaning up after the historic flood. Frank said that his department was busy trying to get fields ready for Little League.
Reach reporter Michael Bayless Rowe at mrowe@snovalleystar.com or 392-6434.
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