Implications of Diverting Inflows to Mono Lake


This simulation model allows you to explore the implications of diverting inflows to Mono Lake. It is a simple water balance model, based on an example described in Andrew Ford's book "Modeling the Environment". You can click on the "Reference" button to view the book's website. This particular model modifies the example presented by Ford by simulating the precipitation stochastically, and assuming all inflows are perfectly correlated to the precipitation.

This model also provides examples of a negative feedback loop and of the use of scenarios with a dashboard. The model demonstrates a negative feedback loop in which evaporation reduces the water level in the lake, which in turn reduces the surface area (an hence the evaporation rate). Additionally, the model highlights some of intricacies of using scenarios along with dashboards as well as the differences between the function of scenarios and dashboards between GoldSim and GoldSim Player. The primary difference between the function of the two software options is that the GoldSim Player user never sees the "Live Model". A companion player file version of this model has been developed to illustrate the difference in options available to the GoldSim user and GoldSim Player user.

The key decision variable in this model is the amount of water diverted from Mono Lake. The amount of water diverted is modified by changing the "Export Rate" in the dashboard. You can select the value of the export rate (from between 0 KAF/yr to 100 KAF/yr where KAF is a thousand acre-feet). Note that the selected "Export Rate" value will be saved to whichever scenario is selected in "Scenario Controller" in the dashboard.

The Scenario Controller provides access to the Scenarios capability in GoldSim. A scenario is a model with a specific set of input parameters which in this case is a specific "Export Rate". An advantage of using scenarios is that the model can be run for each scenario and then the results for the scenarios can be compared to each other (via the "Mean Water level" statistic and the plots available from the dashboard). The model stores the inputs and the results for each scenario when in Scenario Mode.

The "Scenario Controller" on the dashboard allows the GoldSim user the evaluation of four preset "Export Rates" or scenarios (Live Model, Scenario 1, Scenario 2, and Scenario 3) as well as the addition or deletion of scenarios (each with a specified "Export Rate"). The GoldSim Player user only has access to the Scenario 1, Scenario 2, and Scenario 3 options and not to the Live Model option. The GoldSim Player user, however, can still add and delete scenarios using the "Scenario Controller".

After one or more scenarios are run, the model is generally in "Scenario Mode". This is the only option available to the GoldSim Player user. However when "Live Model" is selected by the GoldSim user and run, the model is in "Results Mode" and only stores the "Export Rate" and the results for that one simulation. The "Live Model" option is not available to the GoldSim Player user and the GoldSim Player user does not have access to "Results Mode" when using a player model that employs scenarios.


Making Better Decisions In An Uncertain World