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).
- Drawing-level ambient settings are identified by the
drawing icon. - Catchment feature settings are listed near the top of this dialog box, after the General property group, and are identified by the
catchment icon. - Catchment command settings are identified by the
command icon.
Default Styles
- Catchment Style
- Specifies the default style to apply to new catchments.
- Catchment Label Style
- Specifies the label style for the catchment area.
- Flow Segment Label Style
- Specifies the label style for flow segments.
Catchment
- Catchment Group Name Template
- Specifies the default name format for new catchment groups.
- Catchment Name Template
- Specifies the default name format for new catchments.
- Exclusionary
- Specifies whether a catchment will exclude other catchments.
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:
- If another catchment is exclusionary, and if the new catchment has some (or all) of its boundary within it, the other exclusionary catchment will exclude the new catchment from itself.
- If the new catchment is exclusionary, and if the other catchment has some (or all) of its boundary within it, the new catchment will exclude the other catchment from itself.
Hydrological Properties
- Runoff Coefficient
-
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, when you use the Edit in Storm and Sanitary Analysis command, it is exported as part of the catchment data so it can be used in Storm and Sanitary Analysis.
TR-55 Sheet Flow, Shallow Concentrated Flow, and Channel Flow Settings
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
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.
- Sheet Flow Segments
-
Specifies the default number of sheet flow segments to create for each flow path.
- Sheet Flow Length
- Specifies the default length of sheet flow segments. Note: All specified sheet flow segments are created first, then shallow concentrated flow segments, then channel flow segments. If one Sheet Flow Segment is specified and one Shallow Concentrated Flow Segment is specified, and the flow path is longer than the specified Sheet Flow Segment length, then the remainder of the flow path is created as Shallow Concentrated Flow.
- Sheet Flow Manning's Coefficient
-
Specifies the default Manning's roughness coefficient to apply to sheet flow segments.
- Sheet Flow Rain Intensity
-
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
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.
- Shallow Concentrated Flow Segments
- Specifies the default number of shallow concentrated flow segments to create for each flow path.
- Shallow Concentrated Flow Length
- Specifies the default length of shallow concentrated flow segments.
- Shallow Concentrated Flow Surface Type
-
Specifies the surface type over which the shallow concentrated flow travels.
Channel Flow
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.
- Channel Flow Segments
- Specifies the default number of channel flow segments to create for each flow path.
- Channel Flow Length
- Specifies the default length of channel flow segments.
- Channel Flow Manning's Coefficient
-
Specifies the default Manning's roughness coefficient to apply to channel flow segments.
- Channel Flow Cross-sectional Area
-
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.
- Channel Flow Wet Perimeter
-
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.
Time Of Concentration
- Time Of Concentration Method
-
Specifies which method to use for calculating the Time Of Concentration, TR-55 or User-Defined.