ABSTRACT
The dilution m e t h o d is general ly used for purposes of calibration or for spot gaugings mainly because of the costs of performing a gauging and a chemical analysis of the tracer samples . Never the less the me thod can often provide very accurate results given a suitable reach of river. T h e outs tanding advantage of the dilution technique is that it is an absolute m e t h o d because discharge is computed from volume and t ime only. Tracer concent ra t ions need be de te rmined only in d imens ionless relative readings . In rock-s t rewn shal low s t reams, the dilution me thod m a y provide the only effective m e a n s of es t imat ing flow. T h e main disadvantages of the m e t h o d are the difficulties in obtaining comple te mixing of the tracer wi thout loss of tracer and the problem of obtaining permiss ion in s o m e countr ies to inject tracers into rivers. There are two basic injection techniques , several sampl ing techniques and a large number of possible tracers of three main types - chemical , f luorescent and radioactive. T h e technique is normal ly carried out by specially trained personne l and a l though the m e t h o d is most ly used for smaller rivers, d ischarges o f up to 2 0 0 0 m 3 s - 1 have been measured with conf idence.
