Paving Over a Stream to Stop Erosion?

Comments at Arlington County Board Meeting, March 23, 2021.

County Board is poised to approve a streambed restoration project to shore up Tributary B of Donaldson Run using a technique euphemistically referred to as Natural Channel Design. Infill dumped on the stream will destroy all aquatic life, and 83 trees will be removed to make way for the bulldozers. To a layman this sounds like swatting a fly with a sledge hammer. At least two experts agree.

Dr. John Field, a nationally recognized geomorphologist, and Rod Simmons, a respected Northern Virginia environmental consultant, have weighed in against the project. According to Field, natural channel design is premised on the existence of a natural floodplain into which flood waters can disperse, as well as alluvial soil into which meanders can be incised.

Neither of these conditions obtain in the upper reaches of Donaldson Run, where the surface soil is packed clay; the stream bed is bedrock; and no floodplain ever existed. According to Simmons, natural channel design is intended to restore the banks of low lying rivers, not upper head water streams like Donaldson Run.

Implementing this technique in the wrong setting will not only exacerbate erosion along Tributary B, it will also cause the stream to divert around the boulders placed on the stream bed to curtail its flow.

This, according to area residents, is precisely what happened to Tributary A, which was “redesigned” in 2006. While the County touts Tributary A as a natural channel design success story, a photo album produced by project opponents indicates that much of the work was washed out by a 2017 storm.

According to Field, Tributary B will likely go the same way:

“With the potential ramifications of increased sediment delivery downstream to [the] Chesapeake Bay and a return to eroding banks that threaten adjacent infrastructure, should nearly $2.5 million dollars be invested in a project with a better than even chance of beginning to unravel in the first 10 years? (p. 18).”

In a March 19, 2021 letter to County Board, Rod Simmons indicated that the weight of expert opinion has gravitated to Field. He reported that because natural channel design is not cost effective:

“Therefore, effective July 1, 2021, the stream construction industry will be regionally phasing out this outmoded approach in favor of alternative methods for reducing pollutants.”

Despite or perhaps because of this news, the County has doubled down on natural channel design for Tributary B, and I am confident that 1.8 million of your dollars will be squandered on it tonight.