There are studies applying satellite remote sensing for obtaining bathymetric data, e.g. this one:

http://www.sciencedirect.com/science/article/pii/S0169555X15301902#bb0205

But this depends of course on the scope of your work and the accuracy you need...

Hi Asid,

I am a transition environment geomorphologist, so I study rivers, lagoons and coastlands in Italy, Spain, Greece, California and since now India too.

I don't know if there are public agencies in your country which manage environmental issues. In Italy, as well as in EC and USA, there are several institutes and research center working on rivers: e.g,, the national, interregional and regional Basin Authorities of the main rivers, or Water Reclamation Consortia, many universities and research center (e.g., ENEA, CNR., etc.) which survey mainstem and tributaries as well as reservoirs through UAV, drones, ecographs, etc. If you are interested to EC rivers and tell me what, maybe I could address you sending some links or contacts.

Best wishes, Carlo

I think both widely accepted and used techniques have been mentioned in the question itself. I doubt whether there is any other technique available. Very intelligent question.

Dear Carlo

Thank you for extending your support. Actually I am thinking in context of Pakistan.

According to me, for solving exclusively regional problems, it is better to consult and discuss with the local experts. They will have extensive field experience and exhaustive knowledge of the region. Actually they are the champions as far as dealing with the local problems are concerned.