Erica Sachs, US EPA Region 1, presented on vernal pool mitigation at the 4/7/10 Vulnerable Wetlands Forum hosted by NEIWPCC. I do not recall that her angle focused on substrate/liner issues, but she might be a resource worth checking in with anyway.
Way down here in NJ, where I shy away from having to get involved with mitigation whenever possible, one needs to either intercept seasonal high groundwater, as is possible in the coastal plain, or to perch a surface water source. To achieve the latter, most proposals I come across propose a synthetic liner. Not aware of any detriment they might cause to the environment, as I believe they are relatively inert. Would be interested in any actual concerns which might have been brought to your attention. It is certainly "un-natural" and may simply be a turn off for that reason. (You may be able to address that issue straight up w/ the public and educate them about liners and wether or not there are issues there at all). Clay lenses have also been discussed, but I cannot share any first hand experience regarding costs or effectiveness. Properly installed, I suspect they are equally effective, though Biebighauser cautioned extensively about the calamitous effects which certain species of crayfish can have on clay liners, due to their burrowing behavior. Not sure that is an issue in our parts, or with your (presumed) small pool. Liners too are not fail safe, may degrade, and can be inadvertently punctured during subsequent plantings/maintenance, etc.
In my humble opinion, the water budget is the biggest issue. Put down any liner and your asking for a pond, not something ephemeral. "Normal" pool losses do typically include slow recharge into the ground as well as extensive vegetative uptake by plant roots, which are usually also above the barrier and have direct access to the perched water source. These losses will be greatly lessened if not completely eliminated with a small pool constructed over a liner. Accordingly, you may want to design some "control" over your hydrologic inputs (whatever they might be). This is also "artificial" and may turn off the public, but might allow you to "turn off" the hydrology at some point to allow the pool to dessicate via straight evaporation or transpiration of what little plant materials you might be able to design into the footprint of the pool. Could be as simple as having a swale divert surface water to the pool when needed, but having a way to divert the flows when not wanted any more. Devil's in the details of where you construct, how large a pool, etc. Maybe you get lucky and it runs fine on precipitation alone!
An interesting venture ... Best of luck!
John Heilferty
>>> djcowell@usfca.edu 10/26/2010 3:02 PM >>>
I am an ecologist with a consulting company which has been tasked with creating a vernal pool for a local municipality, not as a regulatory mitigation requirement, but as a general habitat improvement and educational opportunity. The design we specified has a "fish grade" plastic liner sandwiched between fabric padding, however this was met with some public out cry that the liner is unnatural and will cause some detriment to the environment. From what I've read, the alternative of capping the pool with compacted clay is labor intensive, expensive, and not as durable, as the clay may crack following repeated wet/dry and frost/thaw cycles. Does anyone in this forum have any experience with created vernal pools using alternative methods to either clay or plastic liners? Are there any good success stories, ideally in the New England Region, where either clay or plastic liners have worked? Any information is greatly appreciated. Thank you.
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.