As a proposal may be one of the most suitable method is to use the conductivity of the water where the salty water has much higher conductivity than the fresh water. One needs only to make an array of metallic needle like probes and measures the spreading resistance of each probe. The spreading resistance of every probe can be calibrated in water resistivity. In this way one can easily measure the boundary between the salty and fresh water.

Best wishes

Some types of radars, especially the "surface wave radars" and some other types can be used to map the surface for salinity. E.g.

Measuring sea surface salinity from an airborne SAR in the Gironde region, France

• November 2002
• DOI:
• 10.1109/OCEANS.2002.1191933

https://ntrs.nasa.gov/search.jsp?R=20150005800

Dear Murugesan Balamurugan

As from Mr.Abdelhalim Zekry 's answer we can get the conductivity of the water. It doesn't need too much programing skill as mentioned in the question. You can use simple Arduino for this kind use. Put to metallic plate in fixed distance. And measure the conductivity of the water with the Analogue pin and test it with different saline and pure water and make a table for the same.!!

Thanks everyone, for your comments. I read more after seeing your comments and key words. however, i summarize with the following options and merit - demerits.

1. Field EC from (more practical way - also this is the only way for cross validation of any other method),

2. Surface wave radars (more accurate with respect to time but high cost).

3. Concept of two metallic plate and conductivity (no idea or proof of concept- so do not want to take risk without a solid reference). may be an interesting stuff to do a bit of research.

Finally, decided to go with GPR test. It seems very promising for shallow depth and quick processing - easily one can compare the interpretations with EC as validation content.