Overflow route data base property sheet
This sheet allows you to set up cross-sections of overflow routes, for which DRAINS calculates flow characteristics (depths, widths, velocities and depth-velocity products). These can be displayed after a run, and are used in the DRAINS design method to define pit inlet types and pipe sizes and invert levels.
Each section is identified by a title that will appear in a drop down menu in the Overflow Route property sheet.
The section is defined by pairs of X-Y coordinates, with the X origin set to the left of the cross-section, looking downstream. The Y coordinates can be to any datum. The graphical cross-section will also be displayed. As each X-Y pair is added in to the table on the top left, the picture of the section is drawn progressively.
DRAINS allows for division of the section into three parts, with different Manning’s roughness values. This can be used to define footpaths, gutters and roadway surfaces with different roughnesses. The dividing line between the sections with different roughnesses can be set by the X value inserted in the box labelled X coordinate of LOB / Main dividing line and/or X coordinate of Main / ROB dividing line.
Above this, there is provision for a Flow Correction Factor, which is an adjustment to the Manning’s Equation used for calculations to allow for particular cross-sections. This is covered in Technical Note 4 in Australian Rainfall and Runoff, 1987 Chapter 14 and in the notes on gutter and roadway hydraulics.
The three lowest boxes are used to set allowances for the DRAINS design method. The program aims to produce minor and major storm overflows that meet these requirements for safe depths (or widths, if required) and for a safe depth x velocity product. The latter applies to both minor and major storms, with the latter being the critical case.
Overflow route cross-sections can be removed, provided that they are not being used by any routes in the drainage system.