What is a Regulated-Unregulated Flow Function?

The relationship defines the flow transformation between unregulated flows into regulated flows. An example is an inflow-outflow function. An inflow-outflow function defines the outflow (flow) rate from a reservoir for a given inflow into the reservoir.

What is the Purpose of a Regulated-Unregulated Flow Function?

A regulated-unregulated flow function is used to model the way that a structure such as a dam reduces the flow rate, and represents a part of the hazard piece of the risk equation. When dams are used to reduce peak flow rates, lower flows mean lower stages and therefore lower damages.

Where Do I Get a Regulated-Unregulated Flow Function?

Engineers develop this relationship using hydrologic software, including but not limited to, HEC-ResSim and HEC-HMS.

Working with Regulated-Unregulated Flows in HEC-FDA

The regulated-unregulated flow function should be provided as paired data with uncertainty: a column of inflows and columns defining the outflow distributions. 

Differences Between HEC-FDA Versions 1 and 2

Regulated-unregulated flow functions are entered as unique objects. That is, regulated-unregulated flow functions are no longer entered through the frequency function dialogue. 

Steps to Define a Regulated-Unregulated Flow Function

To create a regulated-unregulated transform relationship:

  1. From the Study Tree right-click on Regulated-Unregulated Transform Functions and select the create new option.
    Regulated-Unregulated transform functions shortcut command options for creating or importing relationships.
  2. Enter the name for the function and a description (optional, but recommended). 
  3. Select the Distribution Type from the options: 
    • Deterministic
    • Uniform
    • Normal
    • Triangular (default selection)
    • LogNormal
  4. Enter the inflows and specify the distribution of outflows.
    Regulated-Unregulated Transform Flow Function
  5. Click Save and Close to create the new relationship.