Last May, NMT volunteers participated in a riparian restoration workshop conducted by Bill Zeedyk on private land along the Rio Cebolla about two miles downstream from Fenton Lake. Bill is famous for his Induced Meandering technique that has been successfully applied on many stream restoration projects.
Bill identified two degraded sections along the stream that were candidates for demonstrating several of his restoration techniques. One spot was a meander that had a high bank being eroded into the stream, accompanied by the deposit of a large amount of sediment. Bill and the team installed a Post Vane, namely a series of 25 four-inch posts pounded into the stream bottom in a particular pattern along the eroding bank that will slow the water flow enough to deposit sediment and reverse the erosion.
The second spot was a deep gulley that Bill selected to demonstrate two techniques for slowing runoff and reducing sediment transport into the stream. The first structure volunteers built was a One Rock Dam, a series of five or more parallel rows of rocks one layer thick, perpendicular to the gulley direction. Over time, silt deposits in the rock interstices and native seeds sprout and the whole structure knits together to stabilize and raise the level of the gulley. Bill also demonstrated a Log Mat, the placement of partly trimmed tree trunks in the gulley with the tips pointing downhill. Over time the structure fills with sediment, and that part of the gulley fills in and the gulley slope is reduced, which slows water velocity.
Visits to this site last October and November showed that the Post Vane structure built by NMT volunteers has started to produce the expected beneficial effects on the stream. The accompanying photograph shows the back eddy caused by the Post Vanes and the deposit of sediment between them and the original bank edge. Over time more sediment will be trapped behind the Vanes, vegetation will take root, and a new, more stable bank will be created.
The one rock dam structures function only when runoff is coming down the gulley. There had not been enough rain between construction and the time of our last visit for the one rock dams to show any effect, so they are there waiting for when they are needed. FR 376 in now closed to vehicles and is not scheduled to be opened until mid-April. The snowfall over the past several months may increase Spring runoff, so I’ll be interested to see how our structures fared once FR 376 is reopened to the public.