Gutter (Channel) and roadway hydraulics

Since DRAINS models catchment flows that flow in street gutters or channels and overflows that travel along streets, it has some facilities to deal with various gutter and roadway sections, as shown below:

Road cross-section characteristics can vary. In New South Wales, kerb heights of 120 to 150 mm and crossfall slopes of 3% are commonly used.

In the past the technical information set out below was used in DRAINS to determine flow times along street gutters or channels.

This feature has now been dropped from DRAINS, in favour of simpler constant-time estimates based on assumed velocities and gutter lengths. However, if this option was used in a DRAINS model created in the past (using the Comprehensive data option under the heading 'Use' in the Pit property sheet) then the models will still run. The information below is provided to explain the method.

Analysis Used in Horton (ILSAX)

The relationship for gutter flows given in Australian Rainfall and Runoff (1987) is derived from the U.S. Bureau of Public Roads (Searcy, 1969):

Australian Rainfall and Runoff (1987) gives values for F of about 0.9 for simple triangular channels and 0.8 for common gutter sections of the type shown above. Typical values of n are 0.012 for concrete, 0.014 for hotmix, 0.018 for flush seal and 0.025 for stone pitchers.

Although this is an awkward expression, it is constant for a specific gutter and roadway combination, provided that a typical depth can be set. This might be the depth corresponding to an allowable gutter flow width, usually the top of the kerb. This assumed value is included in the GUT factor.

Reference

Searcy, J.K. (1969) Drainage of Highway Pavements, U.S. Federal Highway Administration, Department of Transportation, Hydraulic Engineering Circular No. 12, Washington, D.C.