Stream Restoration Workshop Part 1

I attended a workshop titled "Erosion Control and Arroyo Restoration" taught by Bill Zeedyk. It was held at Empire Ranch in the Cienega Creek Watershed. It was a two day workshop and we started out the morning with power point lecture by Bill as he discussed the basic concepts behind his theory of "Induced Meandering."

Induced meandering is one method of restoring streams that uses structures to direct the water to reshape the channel and restore the natural sinuosity. By putting structures into a straightened channel, the water is forced to slow down and meander around structures. Bill Zeedyk's motto is to "let the water do the work." He places structures along a stream, but ultimately it is the stream that carves out its new meandering pattern. This process can take many years, depending on weather conditions and stream flows. Bill explained that the natural tendancy of streams is to take on a meandering pattern, and he is simply speeding up the process.
Slowing down the water causes sediment to accumulate on point bars and helps to sort sediment by size class.
When streams are loose the sinuoisty and increase their velocity, sediment particles are more easily transported by the flow. This deprives upstream areas of fine sediment. By slowing down the flow and establishing flood plains, streams will drop the larger cobbles first along the stream, then finer sediments will accumulate on floodplains as the velocity slows down. It is important for streams to have the layers of sediment that range from larger cobbles at the bottom to finer grains near the surface and on the floodplains. Finer sediments are more conducive for growing vegetation, while the large grains allow for infiltration and retain water.  A slower moving stream allows for the stratification of sediment. Bill emphasized the importance of stratified sediment for healthy vegetation.

Bill finished up his power point by introducing us to the various structures that he uses. Baffles are structures that are shaped like a right triangle, with the hypotenuse of the triangle along the bank, and the the 90 degree angle pointing out into the stream. This structure forces the water to meander around it, slowing down the water and creating a more sinous channel. The baffle itself should emulate the natural slope of a point bar and allow for the deposition of sediment, so that the strucutre can eventually become part of the stream.

One layer rock dams are used to create artificials ripples in the stream. They are usually 1/3 the height of the bankflow and located halfway down the meander. During low flow, sediment is able to accumulate between rocks to solidify the structure.

Zuni bowls are used to slow down water and reverse the downcutting of a channel. They are constructed out of rocks and shaped like small pools. When there is are headcuts in a stream, placing a series of Zuni bowls will slow down the flow and reduce the erosion.

What I liked about Bill's method was that the stuctures he builds are made from natural materials found around the site. They structures then become part of the stream as sediment builds up around them and eventually you would not know they were ever there. I also liked his idea of letting the stream do the work. Rather than redesigning the entire channel, he places structures in key places and allows the stream to redefine its channel.