WMS:MODRAT Conveyance Type

Each reach in an MODRAT model must be assigned to be one seven conveyance types. Certain parameters must also be defined to describe the geometry of the conveyance. Boxes in which to enter these parameters will appear when a conveyance type is selected. The conveyance types are:

• Variable – if this type is selected, MODRAT will begin flood routing in a street section, change from street to pipe when the flow depth reaches the curb height, from pipe to rectangular channel when a pipe diameter of 8 feet is exceeded. Routing will continue in the rectangular channel until a maximum depth of 13 feet is reached.
• Mountain channel – no additional parameters need to be defined for this conveyance type.
• Natural valley channel – no additional parameters need to be defined for this conveyance type.
• Street channel – the street width (feet) and the curb height (inches) must be selected when using this option.
• Circular pipe – the diameter of the pipe (feet) of proposed or existing drains may be entered; otherwise, leave this at zero and MODRAT will compute the needed diameter of this conveyance type.
• Rectangular channel – the roughness of the channel sidewalls and either the base width (feet) –OR– the depth of the channel (feet) are needed for this conveyance type.
• Trapezoidal channel – channel side slope, maximum peak velocity (ft/s), side wall roughness, and either the base width –OR– depth of the channel are needed for MODRAT routing computations.

Related Topics

• Editing MODRAT Parameters
• Length
• Slope
• Manning's N
• Relief Drains
• Reservoirs