This is a simple, working example of system dynamics model which was used as a supporting material in my seminar in "What is System Dynamics?" on Feb 24th at Water Resources Research Institute, New Mexico State University.
This model replicates dynamics of crop selection in an agricultural system in which there are two groups of farmers: upstream and downstream. Upstream farmers have immediate access to surface water but downstream farmers can use surface water that is remaining after upstream use. Both groups of farmers grow two types of crops. Crop characteristics as well as other assumptions of the model could be changed by model users. Different scenarios for water availability are also available to the users.