WinTR-20 Project Formulation Hydrology Computer Program

1. WinTR-20Project Formulation HydrologyComputer Program Will TR-20 and WinTR-20 give the same results ?? Presented by: WinTR-20 Development Team WinTR-20 Computation Differences March 2009

2. WinTR-20 Computation Differences WinTR-20 Computation Differences March 2009

3. Runoff Hydrographs • With the same delta t, TR-20 and WinTR-20 will produce equal hydrographs. • However, the delta t is rarely the same. • Delta t is set by the user in TR-20. • Delta t is 6 % of the Tc in WinTR-20. WinTR-20 Computation Differences March 2009

4. Runoff Hydrographs(continued) • The minimum practical delta t in TR-20 is 0.1 hour. • There is no practical limit to delta t in WinTR-20 (delta t is set within WinTR-20). • For example, if Tc is 0.1 hour then delta t will be 0.006 hour. • This will cause peak discharges to be slightly higher (generally 5% or less) in WinTR-20 for small Tc’s. WinTR-20 Computation Differences March 2009

5. Runoff Hydrographs (cont) • The peak in TR-20 is determined based on a parabolic fit to the highest three consecutive hydrograph coordinates. • This is not a good mathematical approach. It is better to make the delta t smaller instead. • This may cause the TR-20 peak discharge to be significantly higher than the largest hydrograph coordinate for small Tc’s. WinTR-20 Computation Differences March 2009

6. Runoff Hydrographs (cont) • To see the internal delta t in WinTR-20, leave the Print Time Increment blank on the Global Output window. WinTR-20 Computation Differences March 2009

7. Adding Hydrographs • If two hydrographs with the same time interval are added, then TR-20 and WinTR-20 will produce equal hydrographs. • Again, the time intervals are rarely the same. • WinTR-20 will combine hydrographs with different delta t’s. WinTR-20 Computation Differences March 2009

8. 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. WinTR-20 Computation Differences March 2009

9. Adding Hydrographs(continued) • Whichever hydrograph has the higher peak is saved for further operations downstream. WinTR-20 Computation Differences March 2009

10. Diverting or dividing hydrographs • Given the same cross section elevation-discharge data and inflow hydrograph at the same delta t, the TR-20 and WinTR-20 will produce equal hydrographs. • Again, the time intervals are rarely the same. WinTR-20 Computation Differences March 2009

11. Structure Routing • For the same Structure elevation-discharge-storage data and inflow hydrograph, TR-20 and WinTR-20 will produce equal hydrographs. WinTR-20 Computation Differences March 2009

12. 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. WinTR-20 Computation Differences March 2009

13. Difference in Reach Routing • The Modified Att-Kin method in TR-20 was replaced with the Muskingum-Cunge method. • In general, the Muskingum-Cunge will give a higher peak discharge at the end of the reach when considering the same rating table, reach length, etc. WinTR-20 Computation Differences March 2009

14. The End WinTR-20 Computation Differences March 2009

15. WinTR-20 Computation Differences March 2009