Use this dialog box to view and change catchment-related settings
This topic documents settings in all catchment-related Edit Settings dialog boxes (drawing-level, feature-level, and command-level).
Exclusionary catchments exclude any other catchments whether the other catchments are exclusionary or not. If a catchment is exclusionary, its boundary (and flow path) can be modified either by existing catchments as it is being created or by new catchments as they are being created.
As a catchment is created, it will check all other catchments for two situations:
Specifies the runoff coefficient for the catchment. Acceptable values are between 0.01 and 1.00. A runoff coefficient is used when calculating runoff with the Rational methods. This value is not used ; however, it is exported as part of catchment data so it can be used in Storm and Sanitary Analysis.
The Sheet Flow, Shallow Concentrated Flow, and Channel Flow settings are all used when TR-55 is used as the Time Of Concentration (Tc) calculation method. If you specify a user-defined Time Of Concentration, these flow values are not used. These settings can be modified in the Catchment Properties.
Sheet flow is a very shallow flow over plane surfaces. It is the first component of Tc and starts at the hydraulically most distant watershed point. Sheet flow normally occurs at a depth of 0.1 ft. or less, and the length of sheet flow rarely exceeds a few hundred feet. The maximum length of sheet flow is 300 ft. Data used to compute the sheet flow are the length of flow, the slope, the 2-year 24-hour rainfall amount, and the ground roughness as measured by Manning's n.
Specifies the default number of sheet flow segments to create for each flow path.
Specifies the default Manning's roughness coefficient to apply to sheet flow segments.
Specifies the 2 year, 24-hour rainfall intensity value for the catchment area. This value is used in the TR-55 Time of Concentration equation to calculate the sheet flow travel time.
Shallow concentrated flow type normally occurs after a maximum of 300 feet of sheet flow. The average velocity of shallow concentrated flow is determined by watershed slope and channel material (paved or unpaved). Typical areas where shallow flow occurs are in swales between houses and the gutter section of a roadway.
Specifies the surface type over which the shallow concentrated flow travels.
Channel flow type begins where surveyed channel cross section information has been obtained, where channels are visible on aerial photographs, or where streams are indicated on USGS quadrangle sheets.
Specifies the default Manning's roughness coefficient to apply to channel flow segments.
Specifies the cross-sectional area for the open channel. This is the channel cross sectional area for bank-full conditions (when the channel is filled to the bank). This value is used as input in the TR-55 Time of Concentration equation to calculate the channel flow travel time.
Specifies the wetted perimeter for the open channel. In cross section view, a channel has an approximate U-shape. The wetted perimeter is the length of this "U." This value is used as input in the TR-55 Time of Concentration equation to calculate the channel flow travel time.
Specifies which method to use for calculating the Time Of Concentration, TR-55 or User-Defined.