Flow Segments Vista

Use the Flow Path Vista to edit flow segment data and to add flow segments of the type required for the catchment area.

Create Flow Segments

Starts the Create Flow Segments command at the command line and adds a new segment to the Flow Segments Vista.

Note: The Create Flow Segments and Delete Flow Segments buttons are not enabled if the flow path Time of Concentration Calculation Method is set to User‐Defined. User-defined flow paths cannot have multiple segments. Multiple segments can be used to represent varying terrain for use in the TR-55 Time of Concentration equation. If you are specifying a User-Defined Time of Concentration, multiple segments are not required.

Delete Flow Segments

Deletes the selected flow path segment. Deleting a flow segment will merge the lengths of the flow segments; slopes will be reread from the surface (if applicable) or recalculated. Velocity and time of travel will be recalculated as well. After clicking , you are prompted to select the start point of the flow segment you want to delete.

Note: You can also right-click a flow segment in the vista and click Delete.

Select Reference Surface

Specifies the reference surface on which to base the flow path slopes. Slopes for all segments are based on a single surface. When you change the reference surface to another surface, the slope fields are updated. If you change the reference surface from an existing surface to <none>, the slope fields become active so you can edit the slopes, but the existing values in those fields remain unchanged.

Note: Flow path segment slopes can reference a surface even if the catchment and flow path were created from polylines.

Segment

Displays the flow segment number. Selecting a row in the Flow Path vista highlights its corresponding flow segment in the drawing.

Tip: You can right-click a flow segment in the vista and click Zoom To or Pan To to move to the flow segment in the drawing.

Flow Type

Specifies the flow segment type. The SCS flow types are available if the Time of Concentration method for the flow path is set to TR-55.

• SCS 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.

• SCS Shallow 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 drainage channel material (paved or unpaved). Typical areas where shallow flow occurs are in swales between houses and the channel section of a carriageway.

• SCS Drainage Channel Flow:

  Drainage channel flow type begins where surveyed drainage channel cross section information has been obtained, where drainage channels are visible on aerial photographs, or where streams are indicated on OS (Ordnance Survey) quadrangle sheets.

• User-Defined: Available if the Time of Concentration method for the flow path is set to User-Defined.

Length

Displays the flow segment length.

Gradient

Specifies the flow segment slope. If a surface is specified for the flow path, the slope field displays the surface slope. When no surface is selected, you can enter a slope value.

2-yr 24-hr Rainfall

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.

Surface Type

Specifies the surface type over which the shallow concentrated flow travels.

Manning's Roughness

Specifies the default Manning's roughness coefficient to apply to sheet flow or drainage channel flow segments.

Cross-sectional Area

Specifies the cross-sectional area for the open drainage channel. This is the drainage channel cross sectional area for bank-full conditions (when the drainage channel is filled to the bank). This value is used as input in the TR-55 Time of Concentration equation to calculate the drainage channel flow travel time.

Wetted Perimeter

Specifies the wetted perimeter for the open drainage channel. In cross section view, a drainage 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 drainage channel flow travel time.

Velocity

Displays the calculated velocity for shallow concentrated flow and drainage channel flow segments.

Time

Displays the calculated travel time for the flow segments.