WinTR-20 Computation Methods June 2015 1

WinTR-20 Project Formulation Hydrology

Computer Program

How does WinTR-20 compute results ?

Presented by: WinTR-20 Development Team

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WinTR-20 Computation Differences

Runoff hydrographs Time of Concentration Adjusting curve numbers Adding hydrographs Diverting or dividing hydrographs Structure Routing Reach Routing Smoothing NOAA Atlas 14 and NRCC data

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Runoff Hydrographs

WinTR-20 will compute runoff hydrographs according to NEH Part 630 Chapter 16 Hydrographs (2007).

The time increment used to develop the hydrograph is computed internally in WinTR-20.

However, the user may set a time increment for output (interpolated values).

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Runoff Hydrographs (cont)To see the internal time increment in WinTR-20,

leave the Print Time Increment blank on the Global Output window.

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Runoff Hydrographs(continued)

The table above is the dimensionless unit hydrograph (DUH) with PRF 484.

The peak of the DUH is at point number 11.Delta t = 0.6 Tc / ((point number – 1) – 0.5)Delta t = 0.063 Tc

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Runoff Hydrographs (cont)

The table above the DUH for PRF 350.The peak of the DUH is at point number 6.Delta t = 0.6 Tc / ((point number – 1) – 0.5)Delta t = 0.133 Tc

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Calculating Time of Concentration (Tc)

Besides direct entry of a Tc value, WinTR-20 has two options for computing Tc.

Velocity Method for Tc from WinTR-55 computer program. Uses sheet flow, shallow concentrated flow, and channel flow segments.

Lag Method for Tc calculation from EFH-2 computer program. Uses curve number, watershed length, and watershed slope.

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Velocity method for Tc

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Calculating Sheet Flow Travel Time

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Calculating Shallow Con-centrated Flow Travel Time

Tt = Length (feet) / V (feet/sec) / 3600 (sec/hr)

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Calculating Channel Flow Travel Time

or Channel Velocity may be entered directly in data window.

Tt = Length (feet) / V (feet/sec) / 3600 (sec/hr)

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Lag Method for Tc

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Lag Method for Tc

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Viewing Tc calculations

Select Sub-Area Tc Computations. Tc calculations for each sub-area will be placed in the .dbg output file.

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Viewing Tc calculations

From the View pull-down menu select Debug File.

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Adjusting curve numbersTwo methods have been added to WinTR-20

to adjust the curve number of a sub-area.One allows entry of an ARC value for a sub-

area (used in Texas and Kansas).The second allows the user to reduce the

curve number by a specific value for a sub-area (used in Oklahoma).

These two methods are used to adjust curve number to calculate peak discharges for design of certain conservation practices.

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Adjust curve number by ARC

ARC may be any value from 1.0 to 3.0Original CN tables are based on ARC 2For example, adjust CN 80 from ARC 2 to

ARC 1.6If CN is 80 for ARC 2, then CN is 63 for

ARC 1Use a linear interpolation to calculate CN

73.2 for ARC 1.6

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Reduce curve number by specific value

CN may be reduced by a number from 1 to 14.

For example, if the CN for ARC 2 is 78 and reduced by 8, WinTR-20 will use a CN of 70 for this sub-area.

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Adding Hydrographs

Two hydrographs may be combined or added such as where two streams join at a junction.

If the time intervals are the same, the discharges are added directly.

If time intervals are different (as they generally are) WinTR-20 will combine hydrographs using the following method.

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Adding Hydrographs (cont)

For example, let us add hydrographs A and B.Hydrograph A has a time interval of 0.1 hour

and Hydrograph B has an interval of 0.33 hour.Hydrograph A is interpolated to a time interval

of 0.33 hour and added to Hydrograph B.Hydrograph B is interpolated to an interval of

0.1 hour and added to Hydrograph A.

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Adding Hydrographs (continued)

Whichever hydrograph has the higher peak is saved for further operations downstream.

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Diverting or dividing hydrographs

There are two methods of splitting a hydrograph in WinTR-20.

Split based on two cross section rating curves.

Divert an inflow hydrograph above a specific discharge.

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Divide based on two rating curves

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Divert above a specific discharge

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Structure Routing

The storage indication method (described in NEH Part 630 Hydrology Chapter 17) is used to route the inflow hydrograph through the structure.

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Maximum number of Hydrograph Points

The maximum number is 100,000.This allows WinTR-20 to save hydrographs at

extremely short time intervals.Sometimes with structure routings with very

low release rates, this 100,000 point limit can be exceeded.

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Channel Reach Routing

The Muskingum-Cunge method is described in NEH Part 630 Chapter 17. Examples are provided.

WinTR-20 training module 8 presents the Muskingum-Cunge method of routing.

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Smoothing NOAA 14 and NRCC Data

When importing NOAA 14 or NRCC rainfall data there is an option to smooth the data.

The 60-minute and 24-hour precipitation values are not changed. Precipitation for other durations may be adjusted.

Smoothing the data provides for a smooth rainfall distribution and relatively smooth runoff hydrograph.

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Smoothing NOAA 14 and NRCC Data

Import and select Smooth option. From the View pull-down menu select Smoothed NOAA/NRCC File.

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Smoothing NOAA 14 and NRCC Data

This example is for the 25-year return period NOAA 14 data at College Park, MD.

“Precip” is the original NOAA 14 data.“Inc_Int” is the incremental intensity for the

original NOAA 14 data.The “Sm” refers to smoothed data.

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Smoothing NOAA 14 and NRCC Data

Incremental Intensity is the difference in precipitation divided by the difference in duration converted to inches / hour.

At 5-minute duration,

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Smoothing NOAA 14 and NRCC Data

At 30 minute duration,

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Smoothing NOAA 14 and NRCC DataIncremental Intensity is the difference in

precipitation divided by the difference in duration converted to inches / hour.

At 5-minute duration,

At 30 minute duration,

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Smoothing NOAA 14 and NRCC Data

Smoothed Incremental Intensity.

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Smoothing NOAA 14 and NRCC Data

Smoothed precipitation values.

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The End

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