Introduction

The intent of this section is to share information on how a forecast can be setup in the CAVI to compute flood damages reduced. It is assumed that an HEC-FIA alternative has been configured and imported into the CAVI. This section demonstrates how to contain all the pieces required to compute flood damages reduced for an event in a single CAVI forecast – note this not the only avenue to compute flood damages reduced leveraging your CWMS models. 

HEC-ResSim Alternative

In the HEC-FIA Holdouts compute, HEC-ResSim flow holdouts results can be used to apportion damages to reservoirs throughout the system. The option to compute Holdouts flows in the can be selected in the HEC-ResSim alternative editor as shown below. When the option is selected and the model is computed DSS records be written to the forecast.dss with the format:

To provide input for the HEC-RAS unregulated plan, check the option to compute unregulated flows as well. 

HEC-RAS Alternative

A new HEC-RAS alternative should be created to simulate the unregulated event. The quickest way to achieve this is to perform a Save As on the existing plan and give the new plan a name specifying it is unregulated. 

The boundary conditions for the unregulated HEC-RAS model will be the mostly the same, other than at the reservoirs. At the reservoirs, change the flow boundary conditions to use the unregulated outflow from the reservoir element in the HEC-ResSim model. Another option is to use the inflow to reservoir element from the HEC-HMS model.

Program Order and Forecast Run

In order to include the regulated and unregulated HEC-RAS alternatives in a forecast, a new Program Order can be added to the watershed. Ensure that the Advantaged Options are checked in the CAVI Options menu allowing multiple Program Orders. Next, from the Models menu open the Program Order Editor and create a new program order. This program order will be similar to the default, but will include an additional HEC-RAS alternative.

 Create a new Forecast Run and select the appropriate model alternatives for each program order item. Recall one of the HEC-RAS alternatives should be regulated and the other should be unregulated. 

Verify that the model linking for the new Forecast Run is appropriate, particularly for the HEC-RAS and HEC-FIA alternatives.

Forecast Events

As compared to a typical reservoir operations forecast, the main difference for a flood damages reduced forecast is the simulation time window. Computing flood damages reduced in a CAVI forecast is completed after a flood event has occurred. This allows the hydrologic and hydraulic models to be calibrated to observed data, and allows for observed reservoir operations to be used instead of relying on a rule set. That said, the time window of a forecast used to compute flood damages should be almost entirely in the lookback period, and the models in the forecast should be calibrated to observed data wherever available. In any year, you may have multiple events that are appropriate for computing flood damages reduced. In that case, you may create forecasts and compute flood damages reduced for each of them.