Nays3Dv is 3Dimensional model developed for calculation of vertical and horizontal movement of fluid with density currents.
The Nays3Dv solver is developed by Professor Yasuyuki Shimizu from Hokkaido University.
Density currents occured due to density differences, arise from temperature variations, suspended solids or dissolved materials. Therefore, formation and evolution of density currents are induced by natural conditions such as saline intrusions, oil spills etc. Density flow is important for problems in lakes, reservoirs and estuaries.

online manual is here
for iRIC v4
for iRIC v3

The source code is published here.
https://github.com/iRICsolvers/v4_nays3dv