Comments at Arlington County Board Meeting on January 23, 2021.
I am disturbed that the County has not only declined to consider alternatives to clearcutting and streambed leveling to address erosion along Donaldson Run Tributary B, it has ignored an alternatives analysis for Tributary B prepared by Dr. John Fields, one of the nation’s foremost fluvial geomorphologists.
Here are excerpts from his concluding remarks.
“Natural Channel Design is an appealing approach to stream restoration as it promises to put an end to bank erosion, poor water quality, and degraded habitat by simply creating a channel that mimics the size and pattern of a channel expected to form in an unaltered watershed. Unfortunately, . . .
The proposed design channel for Donaldson Run Tributary B will more efficiently transport sediment downstream towards Chesapeake Bay counter to the project’s intent.
“Increasing the slope and narrowing the width of the channel will make it unstable. Over time likely within the first 10 years of construction, the design channel will begin to unravel during a large flood or unexpected event that clogs the channel. Once the armor layer of rock and boulders in the design channel is weakened, outflanked, or bypassed entirely, the channel will adjust relatively rapidly to reestablish itself. Consequently, any short-term improvements in bank stability, water quality, and aquatic habitat will prove unsustainable.
“A process-based restoration approach using wood can avoid many of the pitfalls of the traditional Natural Channel Design approach. By adding wood rather than completely realigning the channel, the project can achieve its goals with less of a short-term and long-term impact and at a greatly reduced cost.