Irrigation works : $b the principles on which their design and working should be based, with special details relating to Indian canals and some proposed improvementsBellasis, E. S. (Edward Skelton)
Science
Irrigation works : $b the principles on which their design and working should be based, with special details relating to Indian canals and some proposed improvements
Bellasis, E. S. (Edward Skelton)
Canals; Irrigation
The roads in India are generally unfenced and the banks of canals close
to bridges, on both sides of the canal and both above and below the
bridge, are generally more or less worn down by cattle, which, when
being driven home in the evening and out to graze in the morning, go
down to the stream to drink. In order to prevent this damage the banks
are sometimes pitched, above the bridge as well as below it, but the
cattle generally make a fresh “ghát” further away. The best plan is to
allow a “ghát” on one bank either above or below the bridge and to
protect the other three places.
In the Punjab the widths of roadways between the kerbs and parapets of
bridges respectively have been fixed as follows:--
--------------+----------------+-------------------
KIND OF ROAD.| NEAR TOWNS.[20]|IN THE COUNTRY.[21]
--------------+------+---------+--------+----------
|Kerbs.|Parapets.| Kerbs. | Parapets.
--------------+------+---------+--------+----------
Provincial | 22 | 23·5 | 16 | 17·5
District | 18 | 19·5 | 14 | 15·5
Village | 14 | 15·5 | 8·5 | 10
--------------+------+---------+--------+----------
[20] The figures show the maximum. The general width should be the
same as for neighbouring bridges on the same road.
[21] The parapets should be whitewashed so as to be visible at night.
[Illustration: FIG. 15.]
Fig. 15 shows a head regulator for a distributary. The scale is 10 feet
to an inch. It has a double set of grooves for the insertion of the
planks with which the regulation is effected. Only one set of grooves is
ordinarily used, but when the distributary has to be closed for silt
clearance and all leakage stopped, both sets of grooves can be used and
earth rammed in between the two sets of planks. The floor is shown a
foot lower than the bed of the distributary. This reduces the action of
the water on the floor, and enables the bed of the distributary to be
lowered if ever the occasion for this should arise. This is a good
rule--in spite of the fact that in re-modellings the tendency is for the
beds to be raised--for all regulators or bridges, a raised sill being
added (in regulators) to reduce the length of the needles or the number
of the planks. Such sill should, where needles are to be used, be fairly
wide, especially if regulation is to be done while the masonry is
somewhat new. The distributary shown has a bed width of 10 ft. The span
of the two openings in the head might have been four feet each, but are
actually five feet, and this enables the distributary to be increased in
size at any time. The pitched portion of the channel tapers. Unless
needles are used, instead of horizontal planks, spans are not usually
greater than 5 or 6 feet. Longer spans would give rise to difficulties
in manipulating the planks. Sometimes distributary heads are built skew,
but there is seldom or never any good reason for this. A curve can
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