Storm drains and all closed systems passing longitudinally or transversely
to the roadway shall be designed so that the hydraulic gradient for
the ten-year storm shall be 1.0 foot below the bottom of the manhole
covers and inlet grates. In determining the hydraulic gradient, Manning's
Formula, or charts derived from Manning's Formula, with proper
"n" value as selected from Manning's Formula - Value of "n,"
as found on Plate SD-6 of the Calvert County Construction Standards
for Roads, Streets, and Incidental Structures shall be used. The hydraulic
gradient shall be determined in total length. Inlets may be spaced
to pick up only a portion of the gutter flow for the ten-year storm,
but storm drains shall be designed for the total flow from the design
storm at any location.