Win TR20 Project Formulation Hydrology Computer Program How

Win. TR-20 Project Formulation Hydrology Computer Program How does Win. TR-20 compute results ? Presented by: Win. TR-20 Development Team Win. TR-20 Computation Methods June 2015 1

Win. TR-20 Computation Differences l l l l 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 Win. TR-20 Computation Methods June 2015 2

Runoff Hydrographs l Win. TR-20 will compute runoff hydrographs according to NEH Part 630 Chapter 16 Hydrographs (2007). l The time increment used to develop the hydrograph is computed internally in Win. TR-20. l However, the user may set a time increment for output (interpolated values). Win. TR-20 Computation Methods June 2015 3

Runoff Hydrographs (cont) l To see the internal time increment in Win. TR-20, leave the Print Time Increment blank on the Global Output window. Win. TR-20 Computation Methods June 2015 4

Runoff Hydrographs(continued) The table above is the dimensionless unit hydrograph (DUH) with PRF 484. l The peak of the DUH is at point number 11. l Delta t = 0. 6 Tc / ((point number – 1) – 0. 5) l Delta t = 0. 063 Tc l Win. TR-20 Computation Methods June 2015 5

Runoff Hydrographs (cont) The table above the DUH for PRF 350. l The peak of the DUH is at point number 6. l Delta t = 0. 6 Tc / ((point number – 1) – 0. 5) l Delta t = 0. 133 Tc l Win. TR-20 Computation Methods June 2015 6

Calculating Time of Concentration (Tc) Besides direct entry of a Tc value, Win. TR-20 has two options for computing Tc. l Velocity Method for Tc from Win. TR-55 computer program. Uses sheet flow, shallow concentrated flow, and channel flow segments. l Lag Method for Tc calculation from EFH-2 computer program. Uses curve number, watershed length, and watershed slope. l Win. TR-20 Computation Methods June 2015 7

Velocity method for Tc Win. TR-20 Computation Methods June 2015 8

Calculating Sheet Flow Travel Time Win. TR-20 Computation Methods June 2015 9

Calculating Shallow Concentrated Flow Travel Time l Tt = Length (feet) / V (feet/sec) / 3600 (sec/hr) Win. TR-20 Computation Methods June 2015 10

Calculating Channel Flow Travel Time or Channel Velocity may be entered directly in data window. l Tt = Length (feet) / V (feet/sec) / 3600 (sec/hr) l Win. TR-20 Computation Methods June 2015 11

Lag Method for Tc Win. TR-20 Computation Methods June 2015 12

Lag Method for Tc Win. TR-20 Computation Methods June 2015 13

Viewing Tc calculations l Select Sub-Area Tc Computations. Tc calculations for each sub-area will be placed in the. dbg output file. Win. TR-20 Computation Methods June 2015 14

Viewing Tc calculations l From the View pull-down menu select Debug File. Win. TR-20 Computation Methods June 2015 15

Adjusting curve numbers Two methods have been added to Win. TR-20 to adjust the curve number of a sub-area. l One allows entry of an ARC value for a subarea (used in Texas and Kansas). l The second allows the user to reduce the curve number by a specific value for a subarea (used in Oklahoma). l These two methods are used to adjust curve number to calculate peak discharges for design of certain conservation practices. l Win. TR-20 Computation Methods June 2015 16

Adjust curve number by ARC may be any value from 1. 0 to 3. 0 l Original CN tables are based on ARC 2 l For example, adjust CN 80 from ARC 2 to ARC 1. 6 l If CN is 80 for ARC 2, then CN is 63 for ARC 1 l Use a linear interpolation to calculate CN 73. 2 for ARC 1. 6 l Win. TR-20 Computation Methods June 2015 17

Reduce curve number by specific value CN may be reduced by a number from 1 to 14. l For example, if the CN for ARC 2 is 78 and reduced by 8, Win. TR-20 will use a CN of 70 for this sub-area. l Win. TR-20 Computation Methods June 2015 18

Adding Hydrographs Two hydrographs may be combined or added such as where two streams join at a junction. l If the time intervals are the same, the discharges are added directly. l If time intervals are different (as they generally are) Win. TR-20 will combine hydrographs using the following method. l Win. TR-20 Computation Methods June 2015 19

Adding Hydrographs (cont) For example, let us add hydrographs A and B. l Hydrograph A has a time interval of 0. 1 hour and Hydrograph B has an interval of 0. 33 hour. l Hydrograph A is interpolated to a time interval of 0. 33 hour and added to Hydrograph B. l Hydrograph B is interpolated to an interval of 0. 1 hour and added to Hydrograph A. l Win. TR-20 Computation Methods June 2015 20

Adding Hydrographs (continued) l Whichever hydrograph has the higher peak is saved for further operations downstream. Win. TR-20 Computation Methods June 2015 21

Diverting or dividing hydrographs There are two methods of splitting a hydrograph in Win. TR-20. l Split based on two cross section rating curves. l Divert an inflow hydrograph above a specific discharge. l Win. TR-20 Computation Methods June 2015 22

Divide based on two rating curves Win. TR-20 Computation Methods June 2015 23

Divert above a specific discharge Win. TR-20 Computation Methods June 2015 24

Structure Routing l The storage indication method (described in NEH Part 630 Hydrology Chapter 17) is used to route the inflow hydrograph through the structure. Win. TR-20 Computation Methods June 2015 25

Maximum number of Hydrograph Points The maximum number is 100, 000. l This allows Win. TR-20 to save hydrographs at extremely short time intervals. l Sometimes with structure routings with very low release rates, this 100, 000 point limit can be exceeded. l Win. TR-20 Computation Methods June 2015 26

Channel Reach Routing The Muskingum-Cunge method is described in NEH Part 630 Chapter 17. Examples are provided. l Win. TR-20 training module 8 presents the Muskingum-Cunge method of routing. l Win. TR-20 Computation Methods June 2015 27

Smoothing NOAA 14 and NRCC Data When importing NOAA 14 or NRCC rainfall data there is an option to smooth the data. l The 60 -minute and 24 -hour precipitation values are not changed. Precipitation for other durations may be adjusted. l Smoothing the data provides for a smooth rainfall distribution and relatively smooth runoff hydrograph. l Win. TR-20 Computation Methods June 2015 28

Smoothing NOAA 14 and NRCC Data l Import and select Smooth option. From the View pull-down menu select Smoothed NOAA/NRCC File. Win. TR-20 Computation Methods June 2015 29

Smoothing NOAA 14 and NRCC Data This example is for the 25 -year return period NOAA 14 data at College Park, MD. l “Precip” is the original NOAA 14 data. l “Inc_Int” is the incremental intensity for the original NOAA 14 data. l The “Sm” refers to smoothed data. l Win. TR-20 Computation Methods June 2015 30

Smoothing NOAA 14 and NRCC Data Incremental Intensity is the difference in precipitation divided by the difference in duration converted to inches / hour. l At 5 -minute duration, l Win. TR-20 Computation Methods June 2015 31

Smoothing NOAA 14 and NRCC Data l At 30 minute duration, Win. TR-20 Computation Methods June 2015 32

Smoothing NOAA 14 and NRCC Data Incremental Intensity is the difference in precipitation divided by the difference in duration converted to inches / hour. l At 5 -minute duration, l l At 30 minute duration, Win. TR-20 Computation Methods June 2015 33

Smoothing NOAA 14 and NRCC Data l Smoothed Incremental Intensity. Win. TR-20 Computation Methods June 2015 34

Smoothing NOAA 14 and NRCC Data l Smoothed precipitation values. Win. TR-20 Computation Methods June 2015 35

The End Win. TR-20 Computation Methods June 2015 36

Win. TR-20 Computation Methods June 2015 37