SCENARIOS

1. SCENARIOS Tests of model robustness, usefulness

2. Discussion points • December tests of changed recharge showed no problems • Recent questions about model response to drying of river raise issues that should be resolved • The fact that we can force the model to dry up may suggest a path forward • Need to replicate prior tracking and accounting scenario to verify problems fixed

3. Scenario: Effect of environmental release In a year when river is dry, if Lake McConaughy outflows are increased by X cfs for instream flows, what is the increase in river flow at various locations in the central Platte (i.e. Overton, Grand Island, and Duncan)? • Operational question, outside scope • Phase 3 issue, requires SW rules change to bypass environmental flows • Prolonged drying not encountered in most of 1985-2005 calibration period • Current model does not simulate the drying and loss that does occur • The model can be forced to “go dry” but it would take considerable effort to know if the results are reasonable

4. Scenario: Pumping curtailment to maintain river flow If under a baseline set of conditions with wells pumping, the central Platte River were to go dry in the summer for one month or more, what reduction in pumping, if any, might instead result in the river not going dry? • This is a “change” which should be capable of being simulated • December scenarios showed river drying from low recharge (high pumping); so this can be done in reverse • Need closer look at model behavior to be sure the change from wet to dry, or dry to wet is hydrologically correct

5. Model can be forced to dry up river

6. Scenario: Tracking and Accountingconfirm prior issues solved