INLAND WATER SURVEY 409 
SuB-MEmMorANDUM D (s). 
CANALS. 
By T. SHrRLEY HAWKINS. 
1. Inconsidering what water measurements it may be desirable to take in 
the case of canal authorities it would first be as well to set out what different 
forms the canals may take, i.e. 
(i) The artificially cut canal ; 
(ii) the combination of artificially cut canal and the canalised river ; 
(iii) the canalised river ; 
and with these large differences in type it will be seen that the number 
and character of the measurements required would vary for each of the 
three types. 
2. There are, however, four common purposes for which all three types 
of canals require a supply of water, viz. to replace losses caused by :— 
(a) Traffic requirements. 
(6) Evaporation from the water surface. 
(c) Percolation and absorption through the earth banks and waste due 
to leakage. 
(d) Leakage at the lock gates and sluices and under and around the 
locks themselves. 
The measurements, so far as (b), (c) and (d) are concerned, have not to 
my knowledge ever been accurately measured or gauged. The amount 
required for (a) is easily calculated, and the only quantitative knowledge 
we have so far as regards (5), (c), and (d) is the amount of feed water that 
has to be let down to keep the several reaches filled and to meet the traffic 
requirements, so by deducting the known requirements from the total 
we can find the necessary amount of water that is required for (0), (c) and 
(d), but I know of no means of separating these three into distinct units. 
The leakage coming under (d) is often considerable and can be traced 
to faulty construction, the state of repair and maintenance, the careless 
closing of the gates, and to obstructions that get across the bearings of 
the stops, mitres and meeting faces. 
3. I next come to the question of supply of water to meet these several 
requirements and they differ in all the three cases. Generally, supplies 
may be obtained from any of the following sources : 
(i) By the rainfall over a catchment area which can be collected and 
stored in artificially made reservoirs. 
(ii) By the flow directly.into the canal of rivers, streams, etc. 
(iii) The storage water obtained under (i) being taken to the canal either 
by gravitation or pumping, according to the level of the supply 
water in its relation to the canal water level. 
(iv) By pumping water from rivers near by the canal, but which are at 
a lower level than the canal. 
(v) By returning the water ‘ used up’ by traffic to the higher reaches 
by means of pumps erected on the lower reach. 
4. So far as the ‘ artificially cut canal’ is concerned, its supply may be 
derived from all the before-mentioned sources, and a lot of very useful 
nN could be obtained by arranging for systematic measurements being 
en :— 
At the reservoirs to ascertain the rate of fall in the level of the water in 
the reservoir due to the feed water supply that is kept on, and also 
