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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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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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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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 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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