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Unit Hydrographs - II (Synthesis)

Synthesis does not use rainfall-runoff data.

• Uses measurements on the watershed to postulate parameters of a parametric unit hydrograph.

Parametric Unit Hydrographs (in HEC-HMS)

HEC-HMS has several different UH models available (eg. NRCS DUH, Clark, etc.). These models are described by “parameters”

• NRCS (Tp or Tc)

• Clark (Tc, R) Selection of the parameters selects the shape of the UH and the time base (or time to peak). The analyst can also enter an empirical (user specified) unit hydrograph.

Useful parametric models along with their parameters include:

• NRCS DUH : Tlag (Timing only)

• Clark : Tc, and R (Timing and a storage-delay)

• Snyder : Tlag, Cp (Timing and a peak rate factor)

• Gamma : (User-Specified) Tc, K (Timing and a shape factor)

Note

Aalysis uses data (rainfall and runoff observations) to develop unit hydrograph models. Choices include:

Follow FHWA methods

• Essentially back-substitution or OLS

Use HEC-HMS and parametric UH, adjust values of parameters to fit observed runoff

• Less tedious than back-substitution or OLS

Use HEC-HMS and a user supplied UH, adjust values of UH ordinates (and re-scale to maintain a unit response) to fit observed runoff

• Less tedious than back-substitution or OLS

Example

Work the example(s) below:

Cleveland, T. G. (2017) Surface Water Hydrology Notes (Unit-Hydrographs in HEC-HMS) to accompany CE-3354, Department of Civil, Environmental, and Construction Engineering, Whitacre College of Engineering. Go to Slide 32

A fully provisioned Windows Implementation of HEC-HMS is located at:

• server_name: kittyinthewindow.ddns.net

• user_name: texas-skew

• passwd: peakfq73$hare

Users must access using Remote Desktop Protocol (Built into Windows, Apple Store has a free Mac application).

Example powerpoint DES-606-EX6

Data Files for Examples:

1. Example7.xls (Same as in Notes Above)

2. Precipitation data for Ash Creek 1972 5 October Storm (Elapsed time)

3. Runoff data for Ash Creek 1972 5 October Storm (Elapsed time)

4. Initial Abstraction - Constant Loss Worksheets

5. Ash Creek 1978 21 May Storm

References

1. Gupta pp 343-372

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Unit Hydrographs - I (Analysis)

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Hydrograph Routing - I