Page 303 - Moving the Earth_ The Workbook of Excavation

PONDS AND EARTH DAMS

PONDS AND EARTH DAMS 6.39

Two to three pounds to 1 million gallons of water, applied two or three times a year, should
keep a pond clean. If it is allowed to become heavily overgrown, applications of two to three times
that amount, at 2-week intervals, may be required.
Pond area may be roughly calculated from dimensions found by pacing, or by stadia as in Fig.
2.18. Soundings will indicate the depth. Area in square feet times average depth will give cubic
1
feet of water. One cubic foot equals 7 ⁄ 2 gallons.
Copper sulfate cuts down the food supply of fish by reducing the vegetable food that is the
basis of all animal life in the pond. Usually a balance can be preserved in which the plants are
reduced enough to be unobjectionable but sufficient food is left for a large number of fish.
In the proportions recommended, or even in much heavier doses, this chemical is harmless to
swimmers and to fish. However, the abrupt killing of very heavy plant growth may suffocate fish
by absorbing the water’s oxygen into decaying material.
This danger can be avoided by using light, repeated doses, or by treating only part of the pond
at a time.
There are a number of chemicals and compounds used to control algae in swimming pools,
which can also be effective in ponds. However, their price is usually higher, and application may
be more difficult without special equipment.
Many water weeds that resist copper sulfate may be killed by sodium arsenite. However, it has
been found that this very poisonous chemical tends to accumulate in mud bottoms. Its use is pro-
hibited in many areas, and even where permitted, it should be applied by an expert.
Pellets of clay containing 2,4-D or similar materials may be broadcast over the water surface.
The pellets break up and release the poison gradually at the plant roots.
Emergent weeds such as cattails and water lilies can be killed by a 1.0 percent spray solution
of 2,4-D, or kept from spreading by about one-tenth that strength.
Duckweed (lemna minor), a very simple plant consisting of small, flat, floating ovals with
roots dangling several inches below, is a problem in many shallow ponds. It often covers the sur-
face completely, giving the appearance of a pale green lawn.
Most of the growth can be killed by chemicals, including sprayed fuel oil spiked with 2,4-D,
but it may grow back almost immediately. It may be necessary to remove organic mud deposits
and deepen the pond.
State fish and game authorities can usually supply the names of contractors qualified to erad-
icate or control pond weeds. Permits may be required from state and/or local authorities for chem-
ical treatments.
In small areas the most effective way to get rid of pond weeds is to pull them out by hand and
with rakes, as often as they appear. This is a muddy job, but can be enjoyable as a group activity.

HYDRAULIC DREDGES

Hydraulic dredges are very efficient excavators in wetland. However, their use in digging small
ponds is limited by the expense of bringing them in and setting them up (see Fig. 6.27), interfer-
ence of brush and stumps with cutters and suction lines, lack of sufficient water, and problems in
spoil disposal.
Pond-cleaning work does not usually involve handling stumps and brush, and most water
weeds can be removed by hand or simple equipment. The pond provides some water. The com-
petitive position of the dredge is improved by the great difficulties that land machines have in
working pond bottoms too wide to reach from the shore.
This discussion will be limited to pond cleaning. However, the same problems arise in digging
a new pond where water is available and vegetation can be handled by other equipment. Dredge
construction, work characteristics, and operation are described in Chap. 14.
Water Supply. A 6-inch hydraulic dredge will pump water out of a pond at a rate between 800
and 1,200 gallons a minute, and will move 1,000 to 2,000 gallons for each yard of soil. An acre