Page 305 - Moving the Earth_ The Workbook of Excavation

PONDS AND EARTH DAMS

PONDS AND EARTH DAMS 6.41

Reusing dredge water has the important advantage of reducing or eliminating the problem of
fouling streams or other property below the fill with muddy water.
Any natural flow into a pond reduces the water problem. A pond with no inflow in the summer
or dry season may have an ample supply pouring into it in the wet season. If the dredge is operated
on a single shift, it could operate on a steady inflow of one-half or one-third of its output.

Disposal Area. Desirable features for a fill disposal area include location close to the pond,
drainage back to the pond, good conditions for separation of soil and water, need for fill, and
absence of trees and brush.
A 6-inch dredge may be expected to pump spoil from 800 to 1,500 feet, depending on its
coarseness and weight, the percentage carried in the water, and the alignment and gradient of the
pipe. Maximum distance is obtained with light load, straight pipe, and low lift. A downhill line
could be much longer.
Production is reduced by long lines and uphill flow, as these conditions reduce both the volume
of liquid and the percentage of solids that can be carried. For maximum output the spoil should
be discharged close to the dredge, or downhill from it.
If it is necessary to reuse the water, and two or more dump areas are available, the loss of pro-
duction from uphill pumping to get gravity flow back to the pond must be balanced against the
expense of a return pump at the same or a lower level.
A close location reduces the cost of providing and handling pipe.
Soil settles out most rapidly and completely when water is still. A discharge or settlement pond
is usually kept more or less agitated by flow from the pipe. Increasing its area and depth reduces
rate of water movement and allows more particles to settle out. The overflow or the sump for
pumping should be as far from the flowing water as possible. The size and depth of the pond
diminish as it fills during work.
The cost of pond cleaning may be best justified when good use can be made of the material
removed. The value of swampland may be greatly increased by building it up to a higher level.
Rocky or stumpy fields may be filled over to smooth surfaces.
Fill obtained from cleaning a pond should include both a layer of the original bottom forma-
tion and rich black mud built up by the pond water. It is usually of rich fill or topsoil quality, and
may be salable after drying.
Mud is held in the area to be filled by putting a dike around it. This may be built by a dozer on
firm ground or a dragline where it is soft. A wood dam with movable boards, as in Fig. 6.16, will
provide for overflow and height regulation.
Both the owner and the contractor may be liable for any damages caused on neighboring prop-
erty or downstream by mud or too much water.
However, dredged material has been successfully used throughout the United States for the
development of wetlands and aquaculture. It has been used for beach nourishment, shoreline stabi-
lization, and erosion control projects. Also, its use has made for betterment of agriculture, forest,
and horticulture. And the U.S. Army Corps of Engineers lists the use of dredged material for
open-cast-mine reclamation, solid waste management, construction and industrial projects, and
material transfer for fills.
Filling around Trees. Many swampy areas that should be filled are covered with vegetation ranging
from brush to big trees. Undesirable brush usually survives partial burial, but trees are very likely to
die. The biggest and most valuable specimens have a smaller chance of survival than younger ones.
Trees that will die anyhow should be cut before the fill is brought in. This will allow burial of
stumps and unwanted logs. Such logs should be cut in short pieces to avoid later interference with
trenching or basement digging.
If a tree is cut after ground is filled, there will be an unsightly stump. This will be extremely
difficult to remove because of the depth of the roots under the new surface.
Brush should be cut and burned, or at least knocked down flat, before filling. Afterward it will
be difficult to take out and will make grading very difficult.
Wood may decay very slowly under a hydraulic fill.