Page 291 - Moving the Earth_ The Workbook of Excavation

PONDS AND EARTH DAMS

PONDS AND EARTH DAMS 6.27

DRAINS

Gate Valve. When possible, means should be provided to drain a pond for repair, cleaning, and
other purposes. The best, but most expensive, means is to place a metal or concrete pipe under the
dam, connected with a gate valve, which may be located in the dam or at either end. Figure 6.17
shows an installation in which the valve is in the downstream face below frost line. To prevent bur-
ial and clogging, a vertical 8-inch pipe placed over the valve wheel extends to the surface, where
it is plugged or covered. The valve is opened or closed by removing this cover and turning the
valve wheel by means of a jaw on the bottom of a rod which can be turned from the top.
If the cover should be left off, and the vertical pipe filled with dirt and trash, it may be jetted
out by the use of an engine-driven water pump, delivering water at pressure through a small pipe
which is pushed down inside the casing, where it can break up and wash out the debris.
Elbow Drains. A much less expensive installation, which can be used in climates where freezing
is not expected, is shown in Fig. 6.18(A). A metal drainpipe under the dam is fitted with an elbow
on the downstream end into which a vertical pipe is threaded. Space is provided so that this pipe
can be turned into a horizontal position.
If the open end of the pipe is higher than the water in the pond, no water will move through it.
If it is lower, the water will flow through it until the pond level is lowered to the same elevation.
The pond level can therefore be adjusted to any height desired by turning the pipe up or down.
In cold climates, the exposed pipe would be subject to breakage because of water freezing in
it. This is not likely to occur if the movable pipe is placed in the pond as in (B), because of less
severe freezing and inward pressure of pond ice. However, the water makes the pipe difficult to

FIGURE 6.17 Drainpipe and gate valve.