384 REPORTS ON THE STATE OF SCIENCE, ETC. 
Water power undertakings, canals, electricity power stations, pumping 
stations, etc., practically measure only the water that they use, or may require 
to use. Even with river boards, the total flow of the river has not been 
dealt with seriously. At most ports and harbours will be found automatic 
tide gauges recording the rise and fall of the tide; but there are few of 
these to be found on any of our rivers, and generally a daily reading over 
a weir gives the estimate, by a laboratory formula, of the day’s flow. If a 
questionnaire went round to all water authorities and river boards, the 
answers would probably indicate a host of measurements and quite a 
number of records, dependent on some semi-appropriate formula. 
In these days, instruments and apparatus of considerable accuracy and 
efficiency exist for the measurement of river or stream flow. Measurements 
can be made in various ways, some of which, no doubt, require more 
experience for perfecting. The improved methods of measurement 
should be adopted, and with their adoption would come the keeping of 
continuous records of water level and flow at many important sites on our 
rivers ; and, in addition, records of rises and falls in lake levels, total flows 
from supply catchment areas, and water used daily in canals to cover 
evaporation, leakage and traffic. 
From the measurements and records the engineer would be assured of 
the correct values of available water on which to base his scheme and to 
design the works. 
Water authorities, corporations and individuals are in a position to keep 
the necessary records. Fishery boards, mill owners and water power 
companies, water supply authorities, canal and river authorities, boating 
associations, etc., have their data only in such a form as is sufficient for 
their own purposes. Every one of these individuals and authorities 
should be encouraged to see that, in the future, their measurements show 
not only what they themselves take but, when possible, how much they 
leave for others. 
In the closely-woven pattern of water utilisation in our crowded country, 
no single interest can take away, divert, pollute, hold up, or change the flow 
of our rivers without affecting the interests and rights of other users. This 
country has, therefore, reached that stage when a comprehensive system of 
records of total flow is required in order that the quantities available may 
be known. 
3. WaTER SURVEY IN RELATION TO LAND SURVEY. 
The catchment areas of streams and rivers, the areas and depths of 
lakes, reservoirs, canals, etc., the lengths and sections of rivers, the sites 
of springs and the capacity of flooded areas are all ordinary survey work, 
and can be recorded on the Ordnance sheets or on suitable plans and 
tables. They are the static measurements of surface water, and once 
done only require keeping up to date. 
All these measurements require accuracy, and if not actually made by 
our Ordnance Survey should at least be supervised by that authority. 
The Ordnance sheets to-day give the boundaries or river catchments, the 
sources of streams and rivers, and the sites of lakes, canals, etc., and some 
springs. On the Scottish maps the depths of all lakes are given, and of 
some of the English lakes the depths are known. Flooded areas are denoted 
to some extent on Ordnance sheets, and on main rivers the limit of tidal 
flow is shown. Subsidence areas require to be included where subject 
to flooding. The general slope of river beds requires some representation 
by longitudinal section, with the marking of critical points and the addition 
