A model alternative is a single configuration with a specific set of input and parameters. A second model alternative would be defined by a different configuration or different input or parameters. Since model alternatives do not include time-specific data, you can use a model alternative with any time window.
Initially, you develop alternatives using the software of the native model (e.g., HEC-HMS, HEC-ResSim, HEC-RAS, and HEC-FIA). Then, you import these alternatives into CWMS. Once they have been imported, you use the Setup module to configure and edit specific model alternatives for CWMS.
For example, since MFP deals with future precipitation, you can configure model alternatives to use in conjunction with HEC-HMS to compute a variety of future precipitation scenarios. Since HEC-HMS simulates watershed response to precipitation, then you can use HEC-HMS alternatives to forecast future flows.
These future flows can be used with the reservoir application HEC-ResSim to compute reservoir releases. Regulated flows and stages can be input to HEC-RAS and HEC-FIA. Basically, all of the individual model alternatives created in the native programs are available to CWMS.
In the Setup module, you will create model alternative keys that will be used in creating a forecast run. Each key is a single alpha-numeric identifier that represents a model alternative. For example, the Key N might represent normal conditions, the Key W might represent wet conditions, and the Key D might represent dry conditions. Refer to Chapter 19 for additional information on model alternatives.