A. 
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.
B. 
Details for all proposed drainage structures and structure and pipe schedules shall be provided on the road plans.
C. 
Pipe profiles are required for all storm drain systems, including public and private roads, commercial sites, and residential lots.
A. 
Inlets shall be spaced to collect runoff from the ten-year storm and the twenty-five-year storm at sump areas. The allowable spread of water in a curb or curb and gutter section shall be eight feet on residential/local roads, and eight feet on collector roadways. Inlets shall be located on the upgrade side of all public road intersections, at median breaks, and in superelevation transitions approximately 50 feet ahead of the section where the cross slope is level. Inlets shall be spaced to intercept at least 85% of the total gutter flow where practicable. Bypass flow shall be included in the total gutter flow contributing to the next inlet downstream, unless it is otherwise intercepted.
B. 
Maximum allowable flow through an intersection with concrete curb and gutter shall be three cubic feet per second or four cubic feet per second for an extreme uphill intersection. Maximum depth of inlets shall not exceed 12 feet unless otherwise approved by the Director.
C. 
Structures proposed in the County road pavement area shall not be permitted unless prior approval is granted by the Director.
D. 
All grated inlets within County rights-of-way shall have traffic-bearing, bicycle-proof grates.
E. 
Where curbs are used, runoff from cut slopes and areas off the right-of-way shall be intercepted by ditches in order to prevent mud and debris from being carried onto the pavement, particularly on the high side of superelevated highways.
A. 
Bend structures shall be provided on all storm drains, when deflection requirements exceed manufactured recommendations. Bend structures shall include pipe bends and elbows, manholes, inlets, horizontal pipe curves, or special design structures. The minimum center-line radius of the flow line within the bend structure shall be two times the diameter of the pipe. If the length of the curve shall not fit within a standard structure, a special structure shall be designed.
B. 
Manholes shall be provided when the length of pipe exceeds 300 feet and at all junctions and bend structures for access.
C. 
The maximum depth of all storm drain structures shall not exceed 15 feet unless approved by the Director.