Problem

In the inlet library what is the 'design lengths' used for?

What do you enter in the 'design lengths' area if there is already a default grate length, default curb opening length, and structure length? 

Solution

The 'design lengths' are used with the constraint based design feature available with the GVF-Rational (StormCAD) solver. When the calculation options are set to Design and the inlet design constraints are set in the Design alternative, the program will select inlet sizes from the list in the Design tab, to attempt to meet your design constraints (depth and spread in sag, or efficiency on-grade).

These lengths are applied to the curb or grate length and you will see the respective field change in the catchbasin properties.

Combination Inlets

For a combination inlet, both the grate length and the curb opening length are adjusted together (the same value is selected). For example the design solver may select the 3.0 ft entry from the Design length list seen in the below screenshot (if that causes it to meet the design constraints), and you will see that both the "Grate length" and "Curb opening length" will be set to the same value of 3.0. If you have a combination inlet whose standard sizes have curb lengths that are different from its grate lengths, then you may need to manually design those inlets, or use the constraint based design results as a starting point and adjust manually from there. You can set "Design Inlet opening?" to false if you do not want the constraint based design to change a particular inlet's lengths.

See Also

Troubleshooting Constraint Based Design Result

What is the order of design priorities used in the StormCAD and SewerCAD?