Water and Soil - Project Planning and Management for Ecological Restoration - page 108

Soil depth and texture can vary widely over relatively short distances. For example, alluvial
deposits on floodplains and benches adjacent to streams are typically composed of a mosaic of
gravel, sand, silt, and clay. Restrictive layers—for example, lenses of clay—can prevent or retard
root penetration. Restrictive layers can be a detriment if you are trying to get plant roots to grow to
the depth of permanent groundwater, or they can be an asset if you are trying to restore a vernal
pool or pothole where the intent is to hold seasonally ponded water. Additionally, lenses of sand
or gravel beneath irrigated plants can intercept and conduct water away laterally, preventing roots
from growing downward to the water table.
Some restorationists always dig several backhoe trenches on their project site to inspect for
variations in the soil profile. (Note: If you dig a trench, be sure to follow Occupational Safety
and Health Administration standards for shoring up the sides of the trench to prevent collapse on
observers.) If the site was formerly planted with an agricultural crop, it may be possible to identify
areas of problem soils by analyzing historic aerial photographs and looking for differences in plant
growth (e.g., the health of orchard trees). This type of information can also be obtained by talking
with farmers who formerly worked the land.
Soil Preparation and Handling
Earthwork can be very time-consuming and expensive in terms of labor and equipment costs, es-
pecially if soil must be hauled and dumped off-site. One of the highest component costs in most
wetland restoration projects is earthwork. In most cases, earthwork activities involve mechanized
equipment and skilled operators to achieve safe, efficient, and desired results. Earthwork activities
for restoration projects vary, from scraping off a thin layer of earth, to removing an undesirable seed
bank, lowering the finished grade by a yard or more to establish a soil surface that is much closer to
the known water table level, or performing cleanup activities from erosion or sedimentation prob-
lems on your site. We encourage you to seek the services of knowledgeable professionals to help
you develop an earthwork or grading plan. This will ensure that you maximize the opportunities to
balance your earthwork activities to minimize the need for importing or exporting any earth ma-
terial from your site. The following factors should be considered as you plan earthwork activities:
• Earth moving should be planned to be accomplished in a single operation during optimal
weather conditions. Grading during the winter months exposes the soil to rainfall and the
high potential for surface erosion and stormwater pollution. Know how long it will take to
conduct the grading and the specific measures you will use to prevent excessive erosion.
Will the area being graded have suitable topsoil or duff that can be used on other parts of
the project or applied to the newly graded surface? If so, then you may need to stockpile
the soil until you are ready to apply it to the final contours. When stockpiling the soil,
make sure to separate the topsoil from the subsoil (see the discussion on maintaining soil
stockpiles at the end of this section).
• Excavated material needs to have a place to be relocated, preferably permanently. The
specific location of the receiving site from the source site will affect the cost and time of
the operation. In some instances, it may be possible to sell the material and have the buyer