User:Jcreer/TR-55 Parameters

See TR-55 Edit Parameters.

The TR-55 parameters dialog is accessed by right-clicking on a basin or outlet then selecting the Edit Paremeters command. The dialog allows setting model parameters for either "Basins" or "Outlets" depending which option is selected at the top of the dialog. Parameters can be set for the "Selected" basin or outlet, or for "All" basins or outlets based on the selected option at the top of the dialog.

Options available include:

Basins

See TR-55 Basin Data.

TR-55 dialog

• Basin Name – Enter the desired name for the basin. The basin name is used to identify individual basins within a larger watershed. As with all basins created automatically in WMS, the name is defaulted to “ID”B where ID is an internal identification number and B stands for basin. The name can be changed to something more identifiable at any time. While TR-55 does not require that basin names are unique, other models supported by WMS do.
• Time of Concentration (TC)(hr) – Displays the current time of concentration value which can be manually edited.
• Compute Tc – Basin Data – Opens the Basin Time Computation dialog.
• Compute Tc – Map Data – Opens the Travel Time Computation dialog.
• Drainage Area (Am)(mi^2) – Indicates the size of the sub-area drainage area. Enter the area of the basin in this edit field. If having delineated a watershed from feature objects, a DEM, or a TIN, the drainage area can be computed and will automatically be updated in this field.
• Rainfall (P)(in) – Estimated 24-hour rainfall value.
• Runoff Curve Number (CN) – Value used to predict direct runoff or infiltration from rainfall excess.
• Pond and Swamp Area (%) – Percentage of watershed area covered by pond or swamp area that has not been included in the time of concentration computation.
• Rainfall Distribution – Select one of four rainfall distribution methods for the United States:

• "Type I" – Represent the Pacific maritime climate with wet winters and dry summers.
• "Type IA" – Represent the Pacific maritime climate with wet winters and dry summers.
• "Type II" – Represents the rest of the country.
• "Type III" – Represents Gulf of Mexico and Atlantic coastal areas where tropical storms bring large 24-hour rainfall amounts.

• Unit Peak Discharge Computation Method – Option can be for "Normal" method or "New Mexico" method.
• Potential Maximum Retention (S)(in)
• Runoff (Q)(in)
• Initial Abstraction (Ia)(in)
• Initial Abstraction / Rainfall (Ia/P)
• Unit Peak Discharge (Qu)(cfs/mi^2/in)
• Pond and Swamp Factor (Fp) – Adjustment for swamp and pond areas.
• Peak Discharge (Qp=Qu*Am*Q*Fp)(csf)
• Compute Hydrograph – Selecting the Compute button will generate a hydrograph for the selected basin. The hydrograph can be viewed using the Select Hydrograph tool after exiting the dialog.

Time of Concentration

Three different options exist for determining the basin time of concentration (tc).

1. The time of concentration can be computed outside of WMS and entered into the appropriate edit field.
2. The Compute Tc – Basin Data button can be chosen and one of the time of concentration (or lag time) equations specified (this option is only available when having computed basin data from either a TIN or a DEM).
3. Finally, a series of time computation arcs may be used to define overland, sheet, and channel flow with in a basin and then travel times for each arc are summed to compute the total travel time or time of concentration for the basin. The Compute Tc – Map Data button accesses the dialog which allows combining arcs within the currently selected basin to compute a time of concentration. A description of the time computation coverage can help in understanding how to do this. See the Overview of Map Data Equations help page for a detailed description of the TR-55 travel time equations that can be assigned to arcs in a time computation coverage.

Outlets

WMS allows defining the watershed as a single basin or subdivide the watershed into multiple sub-basins. Besides computing peak flows using the standard TR-55 equations, storm hydrographs may also be computed for each basin and then combined/lagged to downstream outlets (junctions) using the TR-55 tabular hydrograph method.

When creating a watershed with multiple sub-basins, define the time of travel from one outlet (junction) to the next. The travel time for an outlet is defined by selecting the outlet and then entering the appropriate travel time. If desired, use a time computation arc to compute the travel time.

See TR-55 Outlet Data.

Outlet parameters available are:

• Outlet Name – Enter the desired name for the outlet.
• Travel Time (hr)
• Compute Travel Time – Opens the Travel Time Computation dialog.
• Compute Hydrograph – Selecting the Compute button will generate a hydrograph for the selected basin. The hydrograph can be viewed using the Select Hydrograph tool after exiting the dialog.