Page 277 - Moving the Earth_ The Workbook of Excavation

PONDS AND EARTH DAMS

PONDS AND EARTH DAMS 6.13

Removal of small or worthless trees near the pond, and of trees which would shade a beach or
float, is desirable from landscaping and recreational standpoints. A strip of grass on the pond edge
that can be trimmed will make it easier to keep the shoreline free of bushes and water weeds.
However, none of these factors justify an indiscriminate destruction of trees in the pond area.
A tree may be a landscape feature of as much value as the pond, and the cost of digging around
rather than through it may be only a small fraction of the entire cost of the project. Also, the cost
of cutting and removing a large tree and disposing of the stump may be greater than the cost of
operating the shovel for an extra day.
It is a good plan to consult a local tree expert, informing her or him of the scope of the exca-
vation, the changes in water level, and the height of any fill to be placed near the tree, to get an
expert opinion as to its chances of survival. This information may be given to the owner with an
estimate for the job both with and without removing the tree.

Rock. Ledge rock and boulders cause less difficulty as they interfere only with the digging, not
with the swinging. They may often be advantageously used for shoreline or islands, as a rock
slope is usually more attractive than a mud or grass bank.
Rock to be blasted must be cleaned off, and should be above water during the work if possible.
Standard blasting techniques are used. Refer to Chap. 9.

Bank Preservation. If the pond site includes a dry bank of suitable height, it may be advisable
to leave it as one edge of the pond, digging away from it as if it were the centerline in Fig. 6.1 for the
first cut, and disposing of all spoil on other edges. This technique can also be used to avoid tan-
gling with trees or landscaped areas. If the pond is wide and without truck access, saving the bank
may be too costly.

STREAM CONTROL

Digging Pattern. If a pond is to be excavated in the valley of a flowing stream, special precau-
tions should be taken.
The diagrams in Fig. 6.10 show procedures in excavating a pond similar to that in Figs. 6.1 and
6.2, except that a brook runs through the center of the swamp.
A diversion ditch deep and wide enough to contain the brook is dug, starting downstream at a
point lower than the proposed pond bottom, where it meets a ditch from a drainage hole, some-
what deeper than that described earlier. The diversion ditch is continued back to a meeting with
the brook on the upstream side of the job. Spoil is piled on the pond side of the ditch to form a
dike and to dam the original channel.
The dragline will have to walk across the brook. The banks may be dug away and platforms
laid on them or in the water, or the stream may be partly filled with saplings or long logs to permit
a crossing.
After diverting the water, one side of the pond is dug. A channel is cut below grade, midway
between the centerline and side lines. At the upper end, the shovel cuts a gradual ramp up from
the channel bottom, usually after crossing the dry streambed. This ramp should be covered with
a brush mat weighted with rocks, or logs or planks should be placed crosswise in the bottom to
avoid excessive erosion when the dike is cut and water permitted to flow down it. Sometimes a
hole is dug below grade at the foot of the incline to trap most of the dirt washed down, and the
protections are omitted. The water should now follow the channel in the pond bottom, and flow
over the sill into the drainage ditch, keeping away from the centerline where further digging is to
be done.
Another method is to straighten out the stream channel so that it lies on one side of the center-
line. The other side is dug and the pile extended well across the stream at the upper end, forcing
it to find its way behind the pile and back to the stream below the pond.

Temporary Stream Diversion. It is sometimes possible to put a temporary dam across the
stream well above the work area, and to divert it across a low ridge into another valley, or into a