The two softwares are used sometimes in seiries being the first a 1D river hydraulic simulation tool providing the water surface elevations in your area for an assigned flood event and the second an information system software helping the in the representation and in the delineation of the flooded area. If you have a DEM or a TIN of your area you can manage the mapping procedure by HEC-GEO RAS, an arc gis tool very useful both for processing and creating your mapping procedure http://www.hec.usace.army.mil/software/hec-georas/

I think its better use a vector format GIS, like ARC GIS

Arc GIS

What about using Quantum Gis (Qgis)? It's a very good Gis software and it's for free!

I'd like to make a case for SAGA GIS - it's also free, and open source. It contains a lot of module libraries, probably the most comprehensive collection of GIS-/DEM-related geomorphological methods. As you asked for HEC RAS, you're probably interested in hydrological and/or hydraulic modelling. In version 2.1. of SAGA, the hydrological models TOPMODEL and IHACRES are implemented (as module libraries). Take a look at http://www.saga-gis.org/en/index.html

Thanks all of you for the comments, just a bit of concern from my side, does using a freeware hinder chances of a research paper being selected or rejected.

Not at all. I guess that many of the reviewers work (also) with that kind of software. The reason why I use SAGA is its enormous versatility in my field of study compared to expensive software like ArcGIS, not specifically the fact that it's free.

Yes, I can only underline what Richard wrote !

I have DEM of the area generated already

I am going for Flood Maps

Amol, I am sure you have got comprehensive suggestions from Tobias and Richards, I would like to add that there are much versatility in these open sources software and there is no effect on the research publications. The publications are more dependent on quality of work. I therefore will go for favoring the suggestions from Richard.

ARCMAP is a good software but very expensive. We choose in France to work more and more with Qgis ans other GIS software like GRASS. After, we can develop or use some tools for flood mapping, automatic 1D modelling...

We give some french information on http://wikhydro.developpement-durable.gouv.fr/index.php/CARTINO_PC or http://wikhydro.developpement-durable.gouv.fr/index.php/Notice_de_DICARTO

The two software packages that you mention do entirely different things. In order to do floodplain mapping you will need both HEC-RAS and a Geographic Information System. There are several good ones, as is mentioned above.

thank you all'

@ Amol D Pawar. Sure it's ArcGIS because there is an extension in ArcGIS called HEC-GeoRAS.

i think GIS is better one.

Just a note of caution that all software can plot the flood lines when the topo and hydraulics are simple. However all of them seem to break down in complex situations, e.g., a high degree of meandering, rapid change in water level or energy grade, wide floodplains, etc. etc. So, engineering judgement, checking and rechecking, and manual intervention by the engineer are required.

GIS is one of the best