Page 279 - Moving the Earth_ The Workbook of Excavation

PONDS AND EARTH DAMS

PONDS AND EARTH DAMS 6.15

the water will enter it. Chips of wood may be dropped at the upper end, and the time they take to
drift through checked with a stopwatch. Mud can be dropped into the water to find if the bottom
or sides have a perceptibly slower current than the top.
The flow in cubic feet per second may be found by multiplying the depth of the water in feet
or fractions of feet, by the inside width of the flume, and multiplying the product by the distance
the wood chip traveled in 1 second.
If the stream has a fairly regular channel, the cross-sectional area of the water in it may be cal-
culated, and the speed of flow measured in the same manner.
Most streams are subject to considerable and sudden changes in volume, and pumps used
should have extra capacity, unless it is possible to abandon the job during high water and return
to it when the flow is reduced to a volume that the pumps can handle. Diversion channels, pipes,
dikes, and dams should also be built to withstand high water.
Digging in Streams. If the stream cannot be diverted, the digging of each strip should start at
the upstream end and move downstream. The dirt loosened but not picked up by the bucket will
be washed downstream in considerable quantities which might entirely silt up any downstream
excavation.

Riparian Rights. Laws relative to stream use and pond construction vary in different states and
localities. Where riparian rights law holds, owners of land on a stream below the job must give
their permission before the stream can be diverted, even temporarily. They also can collect damages
if mud from the excavation work chokes the stream, or is washed onto their property. Excavation
permits are often required. It is good to have the law and the neighbors consulted before starting
any important pond project.
Permanent Stream Diversion. A pond usually is kept in the best condition and appearance if a
strong flow of water goes through it. However, if the pond is to be managed for the production of
fish, or if the stream is likely to fill the pond with silt, it may be advisable to make a channel for the
stream around the pond, keeping only a controlled flow from it into the pond through a pipe or ditch.
It is difficult to overestimate the power and destructiveness of even a small stream in flood,
and it is at flood time that the greatest damage can be done to a pond. It is therefore important to
take every precaution to prevent the stream from breaking out of its prepared channel.
The diversion should start, if possible, in a stream section headed in the right direction; and often
should be reinforced with heavy rocks or posts driven into the base of the bank on the outside of
the curve. If the turn must be in the artificial channel, it should be a gradual one, protected with
rocks, posts, or a well-anchored timber bulkhead. A high earth dike should be built between the
stream and the pond, planted with sod, bushes, or trees.
Figure 6.11 shows a safe arrangement. A low dam of concrete, masonry, or fitted rocks is
placed across the stream to raise its level a foot or so. A pipe leading to the pond is placed below
this water level, and a dike of earth or concrete placed over the pipe.
Water in excess of that which will pass through the pipe will flow over the dam into the channel.
The pipe may open into a ditch, or continue into the pond. Flow may be reduced by means of a
gate valve, or by partially obstructing it with a board, or by placing stones at its mouth.

SHORES

Spreading Piles. After a pond is dug, it is usually surrounded by spoil piles whose size and
arrangement depend on the reach of the machine, the digging plan, the shape of the pond, and
obstacles to digging or walking. These piles may be left to dry for ultimate sale or removal, but
more often are knocked down and graded into banks and slopes. This can be done immediately,
but if time is available and considerable yardage is involved, they may be left to dry and shrink.
Granular soils and some fine-grained ones should become firm enough that the shovel can work
without platforms, saving time and work. Peats and mucks are less likely to become firm, but lose
substantially in bulk and weight.