A dam must be built at the lower end of the bog, in such a manner
as seems necessary from the location and force of the water running
through the main ditch. If the main ditch is a brook which carries
a large amount of surplus water, the dam must be very strongly and
thoroughly built; but if, on the other hand, it is simply a ditch
filled by springs or small brooks found in the bog, a simple dam can
be thrown up at slight cost; although care must be taken to make
it strong enough, so that the high water in winter or spring will
not carry it away and leave the vines unprotected from the frost.
If the bog is of large size, and a large amount of water is needed,
of course a larger and more substantial dam must be built. The
accompanying illustration gives a section of a turf dam, preferably
about fifteen feet wide at the bottom by ten feet at the top,
constructed of turf, and sand or clay, in such a manner as to be
absolutely safe.
It will be seen that the walls slope from the foundation to the top,
and are composed outside of layers of turf, so laid one upon the
other that the joints are broken and a solid wall is made, between
which is filled in a mass of stone, clay, and sand, thoroughly tamped
down so as to make a firm structure in the centre of the dam. At the
end of the main ditch should be constructed a water-course or flume,
preferably of two-inch plank, with a waste-gate that can be raised or
lowered as the supply of water may be needed or allowed to run to
waste. This is simply made of plank, with an oak joist for a lever,
which, used as a pry, easily opens the gate.