INLAND WATER SURVEY 399 
14 ft: on the tail-water scale, but none of these represent the full ‘ natural ’ 
range between minimum and maximum flow, owing to the influence of the 
weir next down-stream, in artificially holding up the level in times of low flow. 
This feature renders a scale of flows for varying water levels very insensitive 
for low readings, but use is made of such station gauges for obtaining 
approximate estimates of flow when required. Water is ‘ drawn off’ or 
abstracted from the Thames: in very large quantities by the Metropolitan 
Water Board and other water companies. The quantities so abstracted 
are measured and calculated for each day and are added to the volume 
gauged at Teddington, the sum being then described as the ‘ natural flow ’ 
of the river. 
With such numerous and varied methods of abstraction as are employed 
it will be obvious that the measurements and calculations of the quantities 
are somewhat complicated, and they are made in very considerable detail 
to ensure accuracy. 
(3) Each lock (there are forty-six lock sites) is provided with a scale gauge 
at'the head- and tail-water sides, and ‘these are read and recorded at every 
gauge four times in the twenty-four hours. This is in addition to the 
automatic recorders at Teddington, and at certain other weirs. 
There are at present no station gauges or automatic recorders on any of 
the tributaries, but at certain critical times (periods of very low flow) 
gaugings have been made of the tributaries. 
(4) It may be mentioned that daily records of rainfall are taken at some 
seventeen stations distributed over the Thames Valley, and that daily 
rainfall averages, together with the records of, natural and gauged flow, are 
printed monthly, and are available to the public at a charge of 1s. per 
monthly sheet. 
Surveys of main tributary streams.are in progress, and information 
respecting the rainfall, maximum and minimum flows of these will be 
obtained in due course. 
It is in view for the future to establish a gauging station on each tributary 
from which daily estimates of the flow may be obtained, but for similar 
reasons to those mentioned in regard to the main river, there are features 
which render this a proceeding of considerable difficulty, and it is doubtful 
if the value of the results would at present justify the cost of obtaining them. 
APPENDIX D (2) (c). 
RIVER TRENT CATCHMENT BOARD. 
(REPLY TO QUESTIONNAIRE.) 
By W. H. Haltte. 
1. Methods of river gauging at principal site or sites—The weirs across 
the ‘ main river’ generally are of an antiquated character and are unreliable 
for computing river discharges. 
The more modern weirs are usually for the purpose of maintaining head- 
water for turbines. Part of the river flows over the weir, the remainder 
passing through the mill ; thus the weir discharge is not the correct river 
discharge. 
Up to date it has only been possible to take current meter observations 
for special Parliamentary litigation purposes. A start, however, has been 
made to take regular current meter readings in the river Trent, at all river 
levels, to obtain a rating curve of discharge. The site of the observations 
