Well seems you want us to write a book :) I think first understand the terrain characteristics, stream net, watershed coverage, meteorological/climatological conditions and the past flood events. would you like to share what kind of evaluation you want? related to flood/discharge or something else?
Shahzad Sultan.............Actually i have to evaluate the hydrological characteristics of a small area and it covers the mines, residential areas, part of river. So from where i have to start ?
The small area you have talked about should be contained within the same river drainage basin. Collect historical climate data (rainfall, Evaporation), discharge data, and catchment characteristics (topography (use digital elevation model), vegetation cover, and other land use activities