Deltalok USA makes soil-filled bags which can be stacked to create a sloping wall, on which vegetation can be established. Roots from plants then infiltrate the bags, holding them together and making the wall more or less permanent. The "lok" in the product's name refers to a spiked plate placed on top of each bag, intended to keep the bag above it from shifting.
Some of us would like to see Deltalok bags used for landscaping within the greenway, but Lisa Coleman is opposed to this, because she fears that if vegetation does not become established, then bank reinforcement could fail in a flood.
Of course, at the east end of the greenway and upstream from the present storm pipe, flooding would not be an issue. Deltalok could be used here to shore up the sides of two large rain gardens.
The issue is how to sculpt the valley with Deltalok bags, without placing them where floodwaters reach. Except at the east end, the valley is tight--without technical help, residents cannot determine whether this can be done.
Another issue is whether vegetation can be established on the bags. Shade will make it more difficult, although (unfortunately) there is going to be more sun after 65 trees are cut. I suspect that ferns can be established in the bags, if the right soil is used, and if they are watered during summer dry spells. Ferns would be beautiful and relatively tough.
For residents next to the greenway, Deltalok bags might be suitable for preventing erosion on their properties.
Deltalok can help save trees
The sides of the ravine are steep in places, and yet the channel has to be wide enough to accomodate floodwaters. If during construction, the channel is made wide, and if the sides do not slope much, then it follows that the higher slopes must be graded, and so more trees will be cut.
But if we can sculpt the ravine, leaving steeper slopes, then fewer trees need be cut. Likewise, if there's a magnificent tree close to the channel, it might be saved if the slope below it is shored up by Deltalok (or even stone, if in the area that floods).
So--if the ravine is graded with a shallow slope, with the channel relatively straight and uniform, more trees are cut. But if the ravine is sculpted, and varied as terrain and big trees require, then more trees are saved.
More ways to reinforce slopes, to sculpt the ravine
Here's a similar product--soil-filled rolls--sculpting a backyard on Falles Ct.
Along Starkweather Creek, layered stone slabs were used to reinforce the bank. With these, our channel could be made more narrow, to save trees, in a few places where necessary.
Photos of Deltalok projects near water.