§ 310-48. Storm drainage design criteria.

Storm drainage shall be provided and designed in accordance with the following standards:

A. 

Pipe. Sufficient pipe shall be installed within the subdivision to carry existing watercourses and to drain the proposed roads and/or easements which may reasonably be expected to be constructed at some future date on adjoining property which normally drains across the area of the proposed subdivision or which, in the opinion of the Town Engineer, would be the most practical course for such drainage. If in his judgment there will be no substantial danger from soil erosion or danger to the public health and safety, the Town Engineer may permit the discharge of rivers and large streams in their natural courses and may permit the discharge of stormwater and established watercourses in open ditches across proposed lots of one acre or larger. All pipe shall be of such diameter (not less than 15 inches) as will, in the judgment of the Town Engineer, be sufficient to properly carry stormwater expected to enter the pipe from the proposed subdivision and from other properties when developed which normally drain across the area of the proposed subdivision. The minimum slope for the fifteen-inch pipe shall be 0.75%. The intent of this subsection is that pipes shall be installed the full length in all proposed roads to permit the connection of house storm drains and cellar drains where required by ground conditions.

B. 

Manholes. Manholes shall be provided at each change in direction or grade of the pipe and shall not be spaced more than 400 feet apart. Manholes shall be constructed as shown on the standard detail. Only precast concrete units or solid concrete blocks shall be used.

C. 

Catch basins.

(1) 

Catch basins shall be provided in order that surface water will not travel without interception more than as shown in the following schedule of grades and distances:

	0.50% to 1%	250 feet
	1% to 2%	300 feet
	2% to 5%	350 feet
	5% to 8%	300 feet
	8% to 10%	250 feet

(2) 

Each catch basin shall be connected to a manhole or adjacent catch basin where no manhole exists. Construction shall conform to the standard detail. Only precast concrete units or solid concrete blocks shall be used.

D. 

Underdrains. In all roadway areas where a high water table is found to exist, either before commencing or during actual construction of the roadways, the developer shall be required to install underdrains as directed by the Town Engineer or his duly authorized agent to protect the stability of the roadway.

(1) 

If required, perforated concrete or metal pipe shall be used, backfilled with washed gravel or crushed rock of 1/2 inch nominal size to a depth of at least 12 inches over the top of the pipe. The remainder of the trench shall be backfilled with bank-run gravel as approved by the Engineer.

(2) 

Sufficient pitch shall be provided to allow this underground water to run freely to a point of discharge. The size and type of conduit shall be as directed by the Engineer.

E. 

Discharge. This discharge of all stormwater shall be into suitable drainage structures of watercourses. Where the discharge shall be onto private property within or adjoining the proposed subdivision, proper easements and discharge rights for the Town shall be secured by the applicant before approval of the final map and acceptance of the drainage plan by the Planning and Zoning Commission.