HEC-ResSim is essential for modeling regulated flow time series and calculating reservoir holdouts in watersheds that contain multiple reservoirs. This is especially important when two or more reservoirs are located within the same watershed, or when upstream reservoirs influence the flow and benefits downstream. In such cases, creating a HEC-ResSim alternative is necessary to route holdouts accurately and fairly allocate the Average Flood Damage Reduction (AFDR) benefits among reservoirs.
There are two primary methods for distributing reduced flood damages among multiple reservoirs—whether they are arranged in tandem or in parallel:
- HEC-ResSim-Based Holdouts
- HEC-ResSim can generate a holdout time series at each computation point for each reservoir. This data represents the volume of water each reservoir "held out" or stored during a flood event. These holdout time series are then used in HEC-FIA to proportionally assign the total damages reduced to each contributing upstream reservoir.
- Fixed Percentage Allocation
- If known in advance, fixed percentage values can be assigned to each upstream reservoir to apportion damage reduction benefits directly, without relying on holdout calculations.
For guidance on implementing either method, refer to the HEC-FIA Model Setup documentation.
In watersheds with both reservoirs and levees, HEC-ResSim is used to compute regulated and unregulated flow scenarios. However, if you're analyzing a watershed with only levees and no reservoirs, HEC-ResSim is not required. In such cases, a no-levee scenario can be modeled by modifying the geometry in HEC-RAS.
New Program Order
If a new program order is created, a new Time-Series tab appears in the ResSim Alternative Editor. Verify the pathnames in this tab are correct before proceeding.
