Wednesday, July 23, 2008

Erosion Control Update 3

Site A embankment in good shape

I visited the Erosion Control Site on July 7. It is now into July and no further work has been done. Admittedly, July is usually a period where there is less rain and this July is on track to become one of the wettest on record. Unless August starts being a lot drier it may be September or October before the work gets done on Site B. The main problem is access to the downstream site requires a temporary river crossing to be constructed. This can't happen if the river is flooding once per week.

As to the completed work I noted a few observations. The dogwood and willow twigs that were placed in the Site A embankment have actually sprouted leaves. At least one of them has produced flowers. The bank itself has held up well even after some moderately heavy rainfalls. Debris in places shows that water levels have come about halfway up the bank.

Dogwood cuttings (Cornus spp.) are sprouting vigorously

Debris litters the embankment which indicates that recent storm events have pushed water levels halfway to top of bank.

At the downstream end the river is doing something interesting. Adjacent to the rock lined area is a clay embankment. The river has started to scour this heavily, eroding it faster than just further downstream. Water may be speeding up as it passes over the rock creating an eddy as it leaves the rocks and hits the natural surface. This may require some additional bank tinkering to reduce this effect.

Clay embankment shows additional scouring at downstream end of Site A

Some plantings have been done at the top of bank. The plants are looking a little forlorn since any mulch has washed away. Some additional maintenance may be required although they have certainly been getting enough water. The adjacent railway embankment is a total loss in that it is completely covered with Dog-strangling Vine (Cynanchum rossicum). Some serious treatment regime is needed here or the restoration will be overwhelmed by DSV in a few years.

Some plantings have been done as part of the restoration plan.

Dog-strangling Vine accounts for about 95% of the ground cover on the railway embankment.

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