Problem

When using StormCAD or the GVF Rational Solver, what do the calculation options "Neglect side flow?" and "Neglect Gutter Cross Slope for Side Flow?" mean?

Problem Number 31425

Solution

If you select True for "Neglect side flow?", only frontal views will be included in the inlet calculations. Frontal flow is the portion of flow that is in the gutter within the width of the grate. Side flow is the portion of flow on the pavement that is not within the width of the grate.

Select "False" for "Neglect Gutter Cross Slope for Side Flow?" if gutter cross slope is different from road cross slope and you would like it to be used in the calculation of the side flow factor when the grate width is less than the gutter width. Note that an abrupt and sometimes non-intuitive change in efficiency/captured flow can occur at the boundary between the grate width being less than or equal to the gutter width when this is set to "False". Setting it to "True" causes the road cross slope to always be used in the calculation of the side flow factor regardless of the grate width.

The purpose of these options is to provide results that are consistent with StormCAD version 5.6. Setting "neglect side flow?" to "true" should cause your results to match those of Version 5.6. Since version 5.6 (circa ~2005), improvements had been made to correctly account for side flow, which are enabled by choosing "false" for both.

See Also