Output: Flow-Related Increase Above Baseline

This calculation is accomplished by the output of the flow-duration curves showing the increase in magnitude and duration of flow. The post-treatment flows are routed through the same calculation as in Step 16, but with different flows. The excess water calculation output from the snowmelt model from WRENSS (USEPA, 1980) or similar model integrates the flow into flow-duration changes. Dimensionless flow-duration curves are also converted to dimensioned values by multiplication of the bankfull discharge value. Reference conditions for watersheds in relative hydrologic recovery are compared to watersheds where streamflow has been increased or decreased by either change in vegetation or by reservoirs and/or diversion.

Stormflow models such as TR-55   need to compute new bankfull values, converting dimensionless values to new dimensioned flow-duration. It is important in these models to calibrate the bankfull discharge. In other words, the precipitation probability for a given antecedent moisture content and runoff curve number which generates the bankfull discharge needs to be determined. Any greater flow will be distributed on floodplains or a flood-prone area, if the stream is not entrenched. Thus, flow-related sediment changes are determined by the use of dimensionless sediment rating curves and dimensionless flow-duration curves.

Programmed versions of FLOWSED and TR-55 are available in RIVERMorph.  Other appropriate models can also be used at this step based on the user's familiarity with the models. The data and calculations for FLOWSED are summarized in Worksheet 24 and Table 19.

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