Page 282 - Moving the Earth_ The Workbook of Excavation

PONDS AND EARTH DAMS

6.18 THE WORK

A difficult drainage and landscaping problem is presented by a swamp sloping gently up away
from the center, changing gradually from wet swamp to dry meadow. Even when tapered to a thin
edge, the fill is liable to create a wet spot where it meets the meadow, either because a dike is
formed holding surface water on the lowest part of the meadow, or because the whole fill is rela-
tively impervious to water, stopping underground seepage and causing it to overflow at the top
edge of the fill.
If possible, the excavation should yield a sufficient volume of spoil to carry it far enough into
the meadow to be well above pond level. When sufficiently dried, the lower part of the meadow
and the upper part of the fill should be deeply plowed and disked, then blended together with a
bulldozer or grader.
If wet spots still appear, they can usually be relieved by mole drainage starting at the pond
shore. If this is ineffective, tile or rubble drains may be required.
Shore Erosion. Freshly built banks will wash and gully badly in heavy rains unless protected.
Drainage coming from undisturbed slopes across the fill is particularly destructive. This can often
be diverted by shallow ditches made with a plow or by hand. These may be leveled after the banks
are anchored by a firm sod.
Disking hay or straw into the surface of the ground increases its resistance to erosion and may
supply ample grass and weed seeds. Unless applied with a nitrogen fertilizer, it may delay the growth
of vegetation by temporarily absorbing this element from the soil. Such mixing in or scattering
hay on the surface is helpful in holding soil that has been graded too late in the year for planting.
Beaches. If a pond is to be used for swimming, a beach is very desirable. It may also be of use
for wading, picnicking, and getting small boats in and out of the water.
A maximum exposure to sunlight is desirable for at least part of a beach. This is best obtained
by locating it on the north or east bank, so that midday or afternoon sun, or both, comes over the
water. Reflection intensifies its heat, and the slope of the beach is favorable to its reception. In
most localities, more swimming is done in the afternoon than in the morning.
If the beach must be located so that its sunlight comes over the land, it may be necessary to cut
a number of trees to obtain exposure. If the beach is large, enough trees should be spared to give
shade over some part of it, or over a lawn area adjoining it. Sometimes a tall tree that is removed
may be profitably replaced with one or more smaller ones to shade a smaller area.
If the pond is being dug, or can be emptied, the beach site can be graded. A gradual underwater
slope is desirable for small children and nonswimming adults. Vigorous swimmers are likely to
prefer a steep underwater slope, particularly if the water is usually cold. The dry section is usually
gently sloped or flat.
A beach must be protected against runoff of water from surrounding land, as this will wash away
the sand, spread dirt on it, or do both. A grass-covered ridge immediately behind the sanded area
will serve to divert water, and may also function as a very welcome windbreak and heat conserver.
It is desirable for the beach subgrade to be a cut rather than a fill, and be of firm material. If
this is the case, 3 inches of sand might suffice for a cover for swimming purposes, but not for
building of sand castles. Six inches to a foot is a safer but more expensive depth.
If part of the pond bottom is sand or fine gravel, some of it may be pushed or carried to the
proper location during the excavation work.
If the subgrade is soft mud, an attempt may be made to stabilize it with clean bank gravel, pea
gravel, or fine crushed rock. A layer of lawn clippings or hay, placed immediately before the sand,
may prevent mixing with the mud. This, of course, is not practical underwater.
An attempt should be made to extend the sand blanket to a depth of 4 or more feet below pond
level, so that swimmers who are sensitive about walking on mud will be able to take off before
they reach it.
Any clean sand that is suitable for concrete or plaster can be used for beach sand. Coarse
grades are more attractive than fine, and light colors are better than dark. Where obtainable, white
sand from ocean beaches or bars is most satisfactory, but it is apt to be much more expensive than
pit or mason’s grades. Sometimes the bulk of the beach is made with sand of a cheap quality, and
the surface dressed up periodically with a better grade.