INLAND WATER SURVEY 387 
the river—sundry minor losses will vary according to the duration of the 
floods and the extent of flooding. ‘Thus the aggregate flow of flood periods 
is a definite figure which may be compared with the rainfall; it is inde- 
pendent of the temporary effect of storage areas and of critical blocking 
points ; it is a figure alike of natural and of controlled flow, to be amended 
only by definite figures of impounded storage and by figures of remaining 
or residual off-flow down to some standard low-water level. 
The peak flows and their times at various points are due to configuration, 
natural or artificial, and their investigation gives the information required 
for river improvement or any required modification of storage and intensity 
of flow. 
The characteristics of the river reaches which determine the selection 
of the actual flow gauging site are better left to the Memorandum on River 
Gauging; it is the characteristics of the whole river basin which indicate 
the general position at which flow measurements are required. It may 
be that artificial works will create a site for flow measurements. ‘The values 
of flow ‘at well-chosen sites will be the best basis for estimates of flow at 
intermediate points. 
The selection of these sites and the continuous records of water levels 
should clearly come under the Catchment Boards; the actual measure- 
ments of flow at principal points should be carried out by trained men 
with the very best apparatus that can be devised. 
A river basin may be subdivided in a general way as follows :— 
(a) The uplands, mountain streams, tarns and springs and artificial 
reservoirs. 
(6) Main tributaries and main rivers in narrow valleys with, generally, 
a considerable water slope and no extensive flooded areas. 
(c) The same, passing through wide valleys with winding courses and 
sometimes lakes, and often with other considerable feeding streams. 
(d) Lowland plains at the junction of tributaries or in the final estuary 
of the main river. 
(a) Streams and springs are measured generally by weirs, preferably at 
the outlet of pools. 
These measurements are made at present only in connection with water 
supply and water power schemes, and the records are often discontinued 
after the completion of the works. With regard to other springs and 
streams it is unlikely that much will be done at this stage, and knowledge 
of rainfall and of measured streams will suffice. 
In any organisation of water measurements and records it is clear that 
water supply and water power authorities should instal apparatus for 
providing complete records of total run-off from their catchment areas. 
Undoubtedly these water supply and water power areas afford an 
excellent theatre for complete water measurement. A great number of 
rain gauges may be installed with daily readings and possibly others of a 
recording type. 
With suitable apparatus for the recording of water levels and flow, not 
only may the total flow be ascertained for any short or long period of time, 
but, in addition, accurate values of flow over different weir crests may be 
ascertained. Also, valuable data will be obtained, on the reservoirs, of 
the period of concentration of floods on upland areas. 
* All this data has already been called for by the Floods Committee of the 
Institution of Civil Engineers in order that a knowledge of flood flows may 
allow of correct design of reservoir spillways. Such data will eventually 
