Hello Shahid,

To expand a bit on what Craig has said above on getting your "ballpark estimate" and to give you some explicit guidance per your question please go here:

http://www.usace.army.mil/publications/eng-manuals/em1110-1-4008/toc.htm

Download Chapter 4 of this pdf file document and read page 4-15, et. al.

To find a trove of FREE manuals that you might find to be of some help in the future go here and look around:

http://www.usace.army.mil/publications/eng-manuals/em.htm

Regards, John.