October 26th 2009

"The Dead River restoration"

     given by Professor Richard Hey of Birmingham University

After being introduced by the Steve Searle, this year's President, Professor Richard Hey started his talk by describing the catastrophic event that took place in May 2003 at the Silver Lake Dam on the Dead River in the state of Michigan in the USA.

The dam, a series of four built partly to control the flow of the Dead River in general and partly to provide a head for a hydroelectric power plant, was of an earthen construction. As is normal with this sort of dam it was provided with a layered clay 'fuse plug' which is normally removed in layers to control river flows in times when the dam is in serious danger of being topped.

Unfortunately for reasons that are not known the plug completely failed in a catastrophic manner allowing the Silver Lake to empty in a matter of hours!! The result was a raging torrent that was so fierce that much bank vegetation was ripped out, large masses of sediment taken downstream and in many places altering the course of the river from one side of a drainage basin to another. Richard desribed how the removal of the bank vegetation was a significant problem because there was no longer any natural blockage to movement of sediment to the lower reaches of the river. This was particularly important because it would mean that at the very least the lower dams would fill and no longer be capable of providing a significant head for the hydro-power plant there.

Clearly something had to be done and rapidly if the power plant was not to have to be shut down for very extensive periods of time. Richard briefly described the options which were either to try to completely restore the river to its original course, or to do nothing or to adopt an approach that attempted to stabilise the new flow pattern by creating a different natural functioning river given the morphology of the valley and the sedimentary materials.

The design team opted for the latter approach. He then discussed the various design procedures. He indicated that the best way in this case was to adopt an analogue approach where the Dead River was compared to other known river sections and then try to mimic them in the appropriate sections of the Dead River.

Richard then went through the details of this approach describing all the parameters that were needed to employ the analogue method.

He outlined the classification process whereby a stream type is identified for restoration design. Once the stream type had been identified appropriate bank and bed engineering was used to alter the river flow to a more desirable state. This is usually achieved by the use of vanes. Vanes are constructed from heavy rocks and boulders suffiently massive that they are not normally dislodged by the strongest flows experienced by a given river. The vane is usually a bar just below the normal surface angled to the river bank.

Vanes come in two basic varities: cross-vanes and J-Hooks. The former lie across the river and are usually in the form of a chevron with the apex downstream whereas the latter project out from the outer bank of a river bend.

These vanes are designed to create vortex flow directing it away from river banks or bridge structures. This reduces bank erosion thus enabling natural vegetation to return with the resulting root growth stabilising the river edges. He showed how this approach had been used successfully elsewhere e.g. Rio Blanco and the Blue River in Colorado.

Professor Hey concluded his 'tour de force' showing that in the case of the Dead River this approach had been very successful with a rapid return of vegetation and the consequential bank stabilisation. Richards talk was followed by quite a lengthy question and answer session. It was very clear from the resulting applause that was given after Professor Hey was thanked on behalf of the members by our Treasurer, Richard Aldridge, that his talk was much appreciated and enjoyed by members present.

Richard Aldridge    October 2009