Drains or inlets appearing in ditches and medians are usually grate inlets and are also termed “drop inlets.” The operation of the inlet is enhanced by a concrete riprap collar that forms a type of bowl around the inlet.

Often, such an inlet is in a sag (sump) configuration created by a ditch block. Department research ( ) indicates that a six inch ditch block may not be adequate to ensure complete capture of flow; a taller ditch block may be necessary. However, the designer must either determine the required depth for complete capture, or account for flow over the ditch block to the next inlet. Care must be taken to ensure that the ditch block slopes meet clear zone standards.