Subsidence and Regrading for Landscape Drainage | Chappaqua, NYMarch 21, 2019
Subsidence is a process by which the ground collapses. This often causes depressions or sink holes. It may be caused by decaying organic matter like tree stumps or ground water piping through the soil underground or creating voids below the surface of the ground. Not always easily identified or apparent. Probing may be necessary.
So what can you do about it?
First I recommend a little hand digging or excavating with a machine. It’s not unusual to find buried trash, construction debris, organic or inorganic material dumped underground, covered over and hidden.
Couple of examples:
1) While hand digging in backyard to install my small garden pond featuring a stream and waterfall, I discovered a truck-full of brick was buried during the construction of our home.
This was probably done by the builder to save cost of carting and dumping. This significantly added cost to the project.
2) During site development involving excavation to install/construct a gunite/in-ground swimming pool, we unearthed a significant amount of stumps buried in a pit and covered with fill. This poses a serious environmental problem as buried stumps and decaying organic matter which is covered by soil, not exposed to the air, contaminates the ground water by trapping gases. This is a federal violation of the Clean Water Act. In this case the original builder was notified of their responsibility to restore the site to pre-construction condition. The State DEC agency was notified. A mitigation plan was required before any work could resume.
Once the process of excavation had begun several automobiles and auto parts were discovered to be buried as well. Once everything was removed from the proposed site/location for the pool it was determined that a stream was buried/diverted in that spot. This involved alteration in design, required full grade beam engineering, (to lift the pool above ground water table), expanding new permit and board approval etc. This project involved a real team effort in communication and cooperation between contractors, licensed professional services, local and state agencies as well as the client and family.
These issues affect cost, environmental impact, and timeline for construction, to say nothing about the disruption to the client’s emotional state!
You can never be completely sure to anticipate every contingency but conducting test excavating or a perk test in lieu of expensive ground penetrating radar services can save much time, money, headaches and disruption in the project. Identifying flow paths, locating existing drainage features, wetlands, overall watershed profile, historical land use, adjacent property impacts, all can contribute useful information for design, planning, cost estimating, budgeting etc.
Solutions may involve design, engineering, bioengineering, grading, terraforming, land-contouring, soil amending, structural soil work, biological enhancements with compost or biostimulants, landscape planting, rain gardens etc.
The fabulously exciting part of ecological landscaping and ecological restoration is employing creativity and imagination to utilize natural resources (as well as financial) to invent beautiful, ecologically productive and efficient landscape system which provide an atmosphere and environment beneficial to our human health, happiness and well being.
Jay Archer, President