There are plenty of methodologies. I guess spectral and textural characterization of soil classes is quite straight forward and then you can integrate it with a digital elevation model, which can be built at no cost using SRTM data at 3 arc second which is free. If you want a better accuracy of DEM, it can be generated using ASTER data (band 3 3N and 3B) will give a stereoscopic vision. The water shed demarcation will also be easy with DEM integrated vector data. Probably you are going to use ArcGIS or some other software.

If you need any specific information I would love to be of help.

@Saif,

Please suggest some papers on texural spectral characterisation of soil classes.

Well said Saif Uddin

Geoinfomatics is interesting topic. 

Here is an article that describes an approach in mapping hydrologic soil groups:

S.Y. Hong et al., Development of soil information system and its application in Korea, 2011:

http://fftc.imita.org/htmlarea_file/library/20110808160738/eb612.pdf

See page 10 for details.

Thank you James. Your input is really helpful than other suggestions.

Mr. James,

Please I could not get access to the link that you have attached to Mohammad