From the little information you have given guess can start by reading materials from the links below. They are more related to SWAT: Again how large is your large? Where is your study area? Do you already have an idea of the remotely sensed data you intend to use?...

Please if you make these and other things clear then I may be able to suggest a few things that will be more helpful. But in the mean time check the links below to see if they will be useful especially the last one (3).

1. http://adsabs.harvard.edu/abs/2008AGUSM.H43B..07T

2. http://onlinelibrary.wiley.com/doi/10.1111/j.1752-1688.2008.00276.x/abstract;jsessionid=ABFD67113C647F5BA47A38A7384703B3.d03t04

3. http://nil-pipraen.blogspot.com/2012/04/hydrological-modeling.html

the River basin is Brhamaputra, drainage area 580 000 sq km. I will use RADAR SAR data. Data collected

LANDSAT TM 30 31 Jan. 1996 Dry

RADARSAT ScanSAR Narrow 2 Beam 50 3 Sep. & 12 Sep. 1996 Monsoon

LANDSAT TM 30 18 February 1997 Dry

RADARSAT ScanSAR Narrow 50 29 Jul., 22 Aug., 7 Sep., 1997 Monsoon

LANDSAT TM 30 5 February 1998 Dry

RADARSAT ScanSAR Wide 50 26 Aug., 17 Sep. 1998 Monsoon

RADARSAT ScanSAR Narrow 2 Beam 25 10 Sep. 1998 Monsoon

LANDSAT TM 30 23 January 1999 Dry

LANDSAT 30 19 February 2000 Dry

RADARSAT ScanSAR Wide 50 20 Jul., 13 Aug., 6 Sep., 30 Sep., 25 Oct. 2000 Monsoon

LANDSAT TM 30 28 January 2001 Dry

RADARSAT ScanSAR Wide 50 21 Jun., 15 Jul., 8 Aug., 2001 Monsoon

RADARSAT ScanSAR WideB 50 1 Sep., 25 Sep. 2001 Monsoon

RADARSAT ScanSAR WideB 50 6 Dec. 2001 Dry

LANDSAT TM 30 24 February 2002 Dry

RADARSAT ScanSAR WideB 50 23 May 2002 Pre Monsoon

RADARSAT ScanSAR WideB 50 16 Jun., 10 Jul., 27 Jul., 28 Jul., 3 Aug., 27 Aug., 20 Sep., 14 Oct., 2002 Monsoon

RADARSAT ScanSAR WideB 50 7 Nov. 2002 Post Monsoon

Fakhruddin what you can do to make the discussion a bit easier is, for each data collected(LANDSAT, RADARSAT...) tell me what you intend to extract from it then I can take it from there. Also be clear what you intend to do with the output? or you just what to develop a methodology for generating discharge using remotely sensed data?

Satellite soil moisture data can be very useful for improving discharge prediction. For very large river basins, I strongly believe that soil moisture can provide a significant added-value. On this topic, you can look at the following papers: Brocca et al., 2010 ( http://dx.doi.org/10.5194/hess-14-1881-2010 ), Meier et al., 2011 ( http://dx.doi.org/10.5194/hess-15-999-2011 ) and Tramblay et al., 2012 ( http://dx.doi.org/10.5194/hessd-9-9361-2012 ). All these papers are open access. Moreover, ASCAT and AMSR-E satellite soil moisture data are freely available, just search at data providers (e.g. TuWien for ASCAT: http://www.ipf.tuwien.ac.at/ ).

On the other hand, SAR data can be useful for delineating flooded areas and, hence, to calibrate hydraulic modelling (e.g., http://dx.doi.org/10.5194/hess-14-1773-2010 ).

No literature reference but you might want to have a look at the work that Robert Brakenridge and I are currently doing, running the Dartmouth Flood Observatory by applying only remote sensing techniques (http://floodobservatory.colorado.edu/).

Apart from floods we are also monitoring river discharge (see links on the lower part of the frontpage).

Hope that helps.

For large rivers it could be an option to look at radar altimetry, e.g. This paper which is open access.

River monitoring from satellite radar altimetry in the Zambezi River basin. / Michailovsky, Claire Irene B. ; McEnnis, S. ; Berry, P. A. M. ; Smith, R. ; Bauer-Gottwein, Peter.

In: Hydrology and Earth System Sciences, Vol. 16, No. 7, 2012, p. 2181-2192.