| Rain Harvesting by Rock
Catchment
Solid rock, better if unfractured, offers good
opportunities to construct rock catchments.
Run-off water can be captured by constructing vertical
walls around the outer edge of a
depression or hollow in a rocky surface. Masonry walls
can be built in all length and size
depending from a number of factors such as the size of
the reservoir, the shape of the site
where the masonry wall is being constructed. In effect,
there is no standard design for the
wall itself. The size of the reservoir is ultimately
determined by the size of the catchment,
the water requirement, the rainfall regime, the number of
users and by other local factors.
Gutters can be useful to enlarge the catchment area and
to convey the run-off water into
the reservoir. This is seen in the photo below.
As the rock surface dips come in a variety of slopes and
sizes, the shape of the dam wall
varies too. For instance, for a V shaped small valley in
the rock surface, a single wall dam
will be appropriate. For a funnel shaped depression, a
more adequate wall dam will have a
V shape. Finally, for a continuous slope where the dip is
down slope, a U shaped wall dam
is required.
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