WMS:TR-55 Hydrographs: Difference between revisions
No edit summary |
|||
| Line 7: | Line 7: | ||
== Information about discrepancies between the TR-55 Hydrograph peak flow values and the Unit Peak Discharge method peak flow values == | == Information about discrepancies between the TR-55 Hydrograph peak flow values and the Unit Peak Discharge method peak flow values == | ||
One question that is frequently asked about TR-55 hydrographs is why the peak flow computed from the TR-55 unit peak discharge method is different from the peak flow on the TR-55 computed hydrograph. Though the TR-55 tabular hydrograph method, which is used to compute TR-55 hydrographs, may give similar results to the TR-55 unit peak discharge method, which is used to compute a peak flow, the peak flows from these two different methods will usually be different. WMS uses the method described in Exhibit 5 in the TR-55 manual to compute a hydrograph using the tabular hydrograph method. Hydrograph ordinates used in the the TR-55 tabular hydrograph method were originally obtained from a series of TR-20 runs with different times of concentration and other values, as described in the TR-55 manual. See the [ | One question that is frequently asked about TR-55 hydrographs is why the peak flow computed from the TR-55 unit peak discharge method is different from the peak flow on the TR-55 computed hydrograph. Though the TR-55 tabular hydrograph method, which is used to compute TR-55 hydrographs, may give similar results to the TR-55 unit peak discharge method, which is used to compute a peak flow, the peak flows from these two different methods will usually be different. WMS uses the method described in Exhibit 5 in the TR-55 manual to compute a hydrograph using the tabular hydrograph method. Hydrograph ordinates used in the the TR-55 tabular hydrograph method were originally obtained from a series of TR-20 runs with different times of concentration and other values, as described in the TR-55 manual. See the [ftp://ftp.wcc.nrcs.usda.gov/wntsc/H&H/other/TR55documentation.pdf TR-55 manual] for more information. | ||
=== Additional Information === | === Additional Information === | ||
| Line 14: | Line 14: | ||
Values for the Tc, Tt, Ia/P, and Am*Q are used as input values for this table, and all hydrograph values are linearly interpolated or extrapolated from the values for Tc, Tt, and Ia/P. The difference between the WMS method and the method described in the manual is the WMS hydrograph is linearly interpolated. The method described in the manual just rounds the values for Tc, Tt, and Ia/P. So you should basically get the same results, but the WMS results will be more accurate and can go beyond the minimum and maximum values for Tc, Tt, and Ia/P (this is not recommended). | Values for the Tc, Tt, Ia/P, and Am*Q are used as input values for this table, and all hydrograph values are linearly interpolated or extrapolated from the values for Tc, Tt, and Ia/P. The difference between the WMS method and the method described in the manual is the WMS hydrograph is linearly interpolated. The method described in the manual just rounds the values for Tc, Tt, and Ia/P. So you should basically get the same results, but the WMS results will be more accurate and can go beyond the minimum and maximum values for Tc, Tt, and Ia/P (this is not recommended). | ||
==Related Topics== | ==Related Topics== | ||
Revision as of 19:09, 22 February 2013
Using the TR-55 tabular hydrograph method (see TR-55 reference manual for details), hydrographs for a selected basin or outlet may be computed. The Compute Hydrograph(s) button is chosen once all of the necessary input for basins and outlets have been entered and a new set of hydrographs will be computed.
If you have a basin selected when you compute hydrographs, then a hydrograph for only the selected basin will be computed. However, if you have an outlet selected when you compute hydrographs, then a new hydrograph for each upstream basin will be computed along with the routed hydrographs at outlet points.
You may notice a slight difference between hydrographs computed by WMS-TR-55 implementation and those in the TR-55 reference manual. This difference occurs because the Ia/P value is rounded to the nearest hydrograph value for the standard version of TR-55. In WMS hydrographs are determined by linear interpolation between two hydrographs using the actual Ia/P value.
Information about discrepancies between the TR-55 Hydrograph peak flow values and the Unit Peak Discharge method peak flow values
One question that is frequently asked about TR-55 hydrographs is why the peak flow computed from the TR-55 unit peak discharge method is different from the peak flow on the TR-55 computed hydrograph. Though the TR-55 tabular hydrograph method, which is used to compute TR-55 hydrographs, may give similar results to the TR-55 unit peak discharge method, which is used to compute a peak flow, the peak flows from these two different methods will usually be different. WMS uses the method described in Exhibit 5 in the TR-55 manual to compute a hydrograph using the tabular hydrograph method. Hydrograph ordinates used in the the TR-55 tabular hydrograph method were originally obtained from a series of TR-20 runs with different times of concentration and other values, as described in the TR-55 manual. See the TR-55 manual for more information.
Additional Information
WMS uses exhibit 5 in the TR-55 manual for the tabular hydrograph method.
Values for the Tc, Tt, Ia/P, and Am*Q are used as input values for this table, and all hydrograph values are linearly interpolated or extrapolated from the values for Tc, Tt, and Ia/P. The difference between the WMS method and the method described in the manual is the WMS hydrograph is linearly interpolated. The method described in the manual just rounds the values for Tc, Tt, and Ia/P. So you should basically get the same results, but the WMS results will be more accurate and can go beyond the minimum and maximum values for Tc, Tt, and Ia/P (this is not recommended).
Related Topics
WMS – Watershed Modeling System | ||
|---|---|---|
| Modules: | Terrain Data • Drainage • Map • Hydrologic Modeling • River • GIS • 2D Grid • 2D Scatter |  |
| Models: | CE-QUAL-W2 • GSSHA • HEC-1 • HEC-HMS • HEC-RAS • HSPF • MODRAT • NSS • OC Hydrograph • OC Rational • Rational • River Tools • Storm Drain • SMPDBK • SWMM • TR-20 • TR-55 | |
| Toolbars: | Modules • Macros • Units • Digitize • Static Tools • Dynamic Tools • Drawing • Get Data Tools | |
| Aquaveo | ||
