Minimizing the transport of excavated sand lowers construction costs.
Tidmarsh, February 2016: the earthen berm in which these concrete spillways were embedded had to be dug out and hauled away before the concrete could be demolished. The sand from the berm was used to fill a portion of the old stream channel in an adjacent bog cell to the north.
Comments
Microtopography creates pit and mounds across the growing surface; this results in variable soil moisture. In contrast, restoration projects are increasingly scraping sand from more areas to to insure the growing surface is sufficiently wet to encourage the development of wetland plant communities across large areas. In order to do this, these projects sets "depositional areas", areas where additional sand can be added. Windswept on Nantucket provides a great example of this.
Kelly Omand recently presented at the sandplain grasslands network. According to NCFs initial monitoring at windswept placing raw cranberry material on uplands did xeric conditions they were targeting to establish sandplain grassland vegetation. An additional layer of sand is needed on top of the deposited bog sand, so that the area is sufficiently dry and nutrient poor.
This discovery was because the Windswept project was done in two phases. During phase one they created an island out of scraped cranberry mat any sand cap. The mixed peat from old cranberry mat provided additional water retention and nutrients that favored faster growing plants with higher nutrient and water requirements. In phase two the depositional mounds were capped with ~1 foot of sand (my recollection from accounts of Fuss & O'Neill), and under these conditions, so far, NCF monitoring indicates that species present on the phase 2 mounds resemble sandplain grasslands.
Insight about phased work and adaptive management during construction: https://projects.livingobservatory.org/insights/23
At the Mattapoisett Bogs restoration project, all sand that was removed from the bog surfaces and from removal of dikes was re-used onsite.
Moving sand is expensive, but scraping the surface of the bog cells here was necessary to provide flood storage capacity because of the elevation of the bogs in relation to the immediately adjacent and low-lying public road. At other sites, microtopography to mix up the sand layer and distribute organic material is a less expensive option.
Bog sand was scraped from the surface of the bog cells to a depth of 1 to 2 feet and the resultant material deposited in adjacent upland areas, or used to fill bog cells that were originally upland. Material was used to fill all ditches and to create subtle 1:10 side slopes to serve as gradual transition areas between the upland and restored wetland. Bog surfaces were not seeded. Transitional side slopes were seeded for quicker vegetation establishment.
Sandplain grassland habitat was restored in the upland sand placement areas. I developed two custom seed mixes for the grassland areas - 1) a modified warm-season grassland seed mix from NEWP (which favored Little Bluestem as the dominant grass), and 2) a warm-season grass/forb mix to add wildflower diversity to the site. The lower cost modified grass only mix was used throughout most of the site. The grass/forb mix was used in two smaller areas as nursery areas from which those forb species could expand out over time.
Bog sand placed on the upland surface in some areas was not seeded (for turtle nesting habitat). Despite not being seeded, they revegetated well with grassland species on their own due to the seeds that were in the deposited sandy soil. There was no visual difference between unseeded and seeded upland deposition areas. For turtle nesting mounds, we did place a cap of clean sand (from the site) on the deposition area to keep it more nutrient poor and discourage vegetation.
In addition to re-using sand near where it is excavated, projects should incorporate locations for sand islands on project areas that have higher elevations, allowing more sand to be removed from the lowland areas.