Most likely Excel is part of your Windows installation, so everybody should have the software.
Bill Werrick has put together this MOCK model to show what can be done using Excel. Below are some snapshots from his model pages.
The entry page of the program that gives the main controls and choices
Summary of demands, levels, flood reduction and irrigation potential
The actual simulation page, where most of the formulas are programmed
Demands and instream flow requirements
Flood rules
Calcualtions of benefits from flood protection and irrigation
Calculation of costs
Gage data
Click Here to download the whole Excel model (10Mgb).