Salt Dilution Method

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Salt Dilution Method

Salt dilution method is used in mountain rivers with rough cross section, big boulders and turbulent flow. An electrical conductivity (EC) meter was used for discharge measurement. Salt dilution method is particularly used for measurement of flow in mountainous stream and any other sites where high degree of turbulence exists to ensure complete mixing of injected solution in the pre-determined length of the channel. Under such condition of flow, the conventional approach to flow gauging such as current meter or calibrated structure are not feasible. NaCl was used for discharge measurement with the salt dilution methods. The amount of salt to be injected depends on flow estimation flow (generally 5 g/l). The salt was dissolved properly in a bucket. Then this solution was injected at once in the stream water almost 100 m from point of measurement. Base level conductivity of water was noted. As the salt reached to the place of measurement, the conductivity value started changing. The conductivity values were noted with 5 second interval. This was done until the measured value reached the base level conductivity again (Hofer, 1998). The rate of flow in channel (Q) can then be calculated by:

Q = qN

Where q = the rate of injection of solution and,

N = dilution ratio determined by direct measurement of concentration.

In Hilkot watershed discharge in l/s was calculated in MS Excel macros.

Volumetric Method

Volumetric method is simple way to measure discharge of water directly in the bucket, at known time. This method is applicable where discharge is very low.

Q=V_t/T

Where Q = discharge (l/s)

Vt = Total volume (liter)

T = Time (second)

Flood Hydrograph

A flood hydrograph shows how a s...

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...y for very short duration. The attempt has to be made to measure as many high flows as possible at all the hydro-stations.

Measured All measured values were plotted for stage –discharge relationship for all hydro stations. Regression analysis using Polynomial transform was used to develop relationships of discharge as function of a gauge. Rating curves for all the hydro stations were established and R2 values shows very strong correlation at all the hydro stations except hydro station No.5. CorelationCorrelation at hydro station No.5 was week is not very strong due to small limited number of observations, ,access to the area during high flood resulting . Low number of observation gives lless correlation value. The R2 values and regression equations established for different stations are shown in the table below. All five rating curves are shown in the Fig.3.

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