Q. What do you mean by Dilution method?

Dilution methods are more suited especially in hilly streams and torrents where current meter measurements are not feasible on account of excessive velocity and turbulence, small depth of flow, moving gravel and coarse materiel etc. In chemical dilution method, the chemical may be injected suddenly only once or it may be injected continuously. The former is called sudden injection method and the latter constant injection method. The apparatus and chemical to be used, specifications of techniques of injection, sampling and also the methods of analysis.

Radio tracer technique is similar to chemical dilution methods. A known quantity of suitable radio tracer is dumped and after it is thoroughly mixed some distance, downstream, the number of click caused by the tracer in its passage are monitored on the Geiger counter at the downstream station on the river bank. If the total number of counts is N, it varies inversely as the rate of flow Q since flow with lower velocity will allow more time for counts to accumulate on the register. On the other hand N varies directly as A, the quantity of radio tracer. Thus N = AF/Q or Q = AF/N.  In this expression F is the proportionality factor which is the characteristic of the isotope, the counter and the geometric relationship of the stream.