Download this App HEC-RAS

HEC-RAS (Hydrologic Engineering Centers River Analysis System) is a computer program that models the hydraulics of water flow through natural rivers and other channels. The program is one-dimensional, meaning that there is no direct modeling of the hydraulic effect of cross section shape changes, bends, and other two- and three-dimensional aspects of flow. The program was developed by the US Department of Defense, Army Corps of Engineers in order to manage the rivers, harbors, and other public works under their jurisdiction; it has found wide acceptance by many others since its public release in 1995.
3D view

The Hydrologic Engineering Center (HEC) in Davis, California developed the River Analysis System (RAS) to aid hydraulic engineers in channel flow analysis and floodplain determination. It includes numerous data entry capabilities, hydraulic analysis components, data storage and management capabilities, and graphing and reporting capabilities.

(Info from: Wikipedia)

Notes:

Tested on Mac OS X 10.7.1, and it should work on any 10.6.x and 10.7.x, it won't on earlier versions due to OS incompatibilities with the used engine.. It works on 10.5.x as well; thanks for checking, waves.
Wine AppDB rating: SILVER.
The application is freeware, see below for the official site link.
Posted in answer to viewtopic.php?f=36&t=8947

Links:
Official site: http://www.hec.usace...s-download.html
AppDB: http://appdb.winehq....TestingId=56776