This article was published on: 05/24/19 12:00 AM
In his May 2 guest column “We need to remove the silt from Mirror Pond,” Ned Dempsey blames stormwater outfalls from the city of Bend as the source for the sediment load in Mirror Pond.
His point of view is not widely held. “Sediment from the upper portions of the subbasin is carried into Mirror Pond by flows in the Deschutes River.” (Upper Deschutes Subbasin Assessment, page 176, available online.)
The Department of Environmental Quality has listed the Deschutes River between Bend and the Wickiup Reservoir as a 303 (d) impaired stream due to excessive turbidity and sediment load. The source? Streambank erosion.
Mr. Dempsey asserts, “Actual silt samples taken from the pond do not support this concept.” Yet, the 2016 Apex sediment study commissioned by the Bend parks district shows no significant variation in particle-size distribution in sediment samples taken throughout the pond, even in samples adjacent to stormwater outfalls.
Such a uniform outcome in analytical results suggests a common source for the bulk of the sediment, namely upstream erosion, not, as Mr. Dempsey claims, the widely varying material found in urban runoff.
The Bend City Council should not be shamed into spending precious public funds for a nonurgent and unnecessary dredging operation. Any “blame” for the Mirror Pond sedimentation must go to mismanagement of the river and the presence of the Pacific Power dam.
Finally, if the Deschutes River carries only buoyant material that never settles out, then how, Mr. Dempsey, do you explain the recent formation of the Colorado Street dam wetland?
Foster Fell