(B) General design requirements.
(1) Required right-of-way:
(a) The minimum right-of-way width is 50'; however
(b) The road right-of-way must be of sufficient width to provide for the following:
1. Drainage;
2. Pavement or rock travel way;
3. Shoulders;
4. Signage;
5. Trees; and
6. Utilities such as street lights and overhead/underground utility lines (electric, telephone, cable TV, gas, water, and sewer).
(2) Required minimum street section: Streets shall have a minimum travel way width of 22'. The travel surface shall be at least equal to the type of surface with which it is being connected (pavement or rock). If development characteristics warrant, the Public Works Director can approve a reduction in the surface type. Written requests for a reduction in surface type shall be directed to the Public Works Director with an accompanying justification statement.
(3) Required minimum street elevations: The minimum street centerline elevation at finish grade shall be 6.5' above mean sea level.
(4) Required minimum profile gradient: The minimum street profile centerline gradient shall be 0.4% except for causeways where land areas adjacent to the road embankment are jurisdictional wetlands or critical areas.
(5) Street centerline minimum curve radius criteria: Street centerline curve radii shall meet AASHTO guidelines for the design speed limit.
(6) Where streets are designed for less than a 30 mph speed limit, the design professional shall provide supporting design data, including traffic control signage.
(7) All roads shall be designed with a minimum road centerline radius of 125'. Horizontal sight distances shall be considered in the design process. Vertical curves shall have a minimum length of 100'.
(B) General requirements for design of drainage systems. The design of drainage facilities for a development must be done with consideration being given to the entire drainage basin. Provisions must be made to receive and manage runoff from upstream areas and to ensure that downstream areas are not adversely impacted by discharges or runoff. The current zoning of upstream properties and associated runoff factors representing that land use, assumed to be fully developed, shall be used in determining design runoff rates and quantities. It is not to be assumed that existing developed properties without stormwater detention systems will have them in the future.
(C) Roadway drainage design.
(1) For roadways with open roadside swale ditches; the swale ditches shall be graded as shown on details in Article A.6. The drainage plan shall show the drainage basin areas contributing stormwater runoff to the roadside ditches. Roadside swale drainage ditches and driveway pipes shall be designed for a five (5) year average return frequency storm (minimum driveway pipe size shall be 15" in diameter). Cross drains, outfall ditches and piped systems shall be designed for a 10 year average return frequency storm. Average return frequencies are defined in § A.4.2(D). The invert elevation of the roadside swale ditch shall be no less than 18" and no greater than 24" inches below the corresponding centerline street finish grade elevation and longitudinal grades shall be no less than 0.4% nominal grade, unless otherwise approved by the Public Works Director. Roadside ditch inverts shall parallel the finish road longitudinal gradient except as approved by the Public Works Director. Drainage shall not be carried in roadside ditches for a distance exceeding 700' (accumulated distance) except as approved by the Public Works Director.
(2) Outfall ditches to wetland areas shall be piped for a minimum length of 20' at their outfall ends; or an alternative means of defining wetlands' limits for maintenance identification purposes shall be submitted for consideration.
(D) Maintenance plan.
(1) When detention or retention facilities are required by local or state agencies or proposed by the design professional, a comprehensive stormwater management system maintenance plan must be submitted for approval by the Public Works Director. The maintenance plan shall address: frequency of maintenance, disposal of material, access to the facility, and other site specific data. The responsible entity shall acknowledge in writing their maintenance obligation and their assent to the maintenance plan. All stormwater runoff and maintenance requirements described herein shall be applicable.
(2) The Town of James Island will maintain public detention facilities to ensure that public drainage systems function as designed (stage-storage capacity of the ponds remain adequate). Any facility not maintained by the Town of James Island shall be maintained by another responsible entity. Acceptable arrangements for proper and perpetual maintenance shall be presented to the Town of James Island at the time of the project's final construction inspection. Detention ponds, lakes, or impoundments which function as a conveyance of stormwater downstream of the proposed development require dedicated drainage easements and maintenance shelves constructed along those systems in accordance with these regulations, unless otherwise approved by the Public Works Director.
(E) Construction plans and specifications.
(1) The construction plans shall clearly show all work to be performed in plan view, profile, cross section, details, and specifications. Specifications providing written descriptions of the work, workmanship, appearance, materials, etc., and/or special provisions may either be shown on the drawings or presented in booklet form separate from the drawings. Specifications shall comply with the CTC (SS) or the SCDOT (SS), unless otherwise directed by the Public Works Director.
(2) The following standards shall be observed and the information listed below shall be provided in the design and preparation of plans, profiles, details, drainage plans, and written specifications for construction:
(a) Include a copy of the approved preliminary plat.
(b) Plans and profiles shall be prepared on 24" x 36" or 22" x 34" sheets, having a profile at the bottom and a plan view at the top, with both the plan and profile stationing oriented in the same direction.
(c) All elevations shall be referenced to the mean sea level datum for NGVD 29.
(d) Scales shall be: vertical 1" = 2' and horizontal 1" = 50' or larger.
(3) The following shall be shown in the plan view:
(a) Stations along the centerline of the proposed road with appropriate ties at intersecting streets.
(b) The width of the right-of-way and names of the proposed roads and existing roads.
(c) Alignment information, including curve data with P.C., P.T., and P.I. angle points, as well as angles at intersections.
(d) Arrows indicating the direction of drainage flow within the right-of-way, along drainage ways, through lots, and at intersections.
(e) Existing and proposed utility lines and utility easements.
(f) Size, type, and location of trees proposed to remain within a road right-of-way or drainage easement.
(g) Road cross sections with sidewalks (when required).
(h) Existing and proposed drainage structures and drainage easements along with rights-of-way and drainage way cross sections.
(i) DHEC/OCRM Critical Line and USACOE jurisdictional wetlands.
(j) Details shall show pond outfall structures, sight distances, traffic control devices, design speeds for roads, and other related information.
(k) Benchmarks with locations, descriptions, coordinates, and datum, etc. Other general construction details required to define the scope of work.
(4) Profiles shall show:
(a) Existing street centerline elevations showing all breaks in grade, but in no case more than 100' apart. Profiles shall include existing streets to which ties are being made with elevations extending approximately 200' from intersections.
(b) Proposed street centerline profile with centerline elevations every 50' on vertical curves and at every 100' along tangents and at intersections.
(c) Vertical curve data.
(d) Proposed and existing storm drains, sanitary sewers, water mains, pipe under drains, and cross line pipes.
(e) Proposed grades of all ditches and swales on or off site. Show existing grades of incoming and outfall drainage ways for 200' upstream/downstream if no grade changes are proposed.
(f) An overall drainage plan shall be submitted along with the plans and profiles and detail sheets.
1. The drainage plan sheet shall show the street layout and the entire drainage system to be constructed or improved along with the sizes and invert elevations of drainage pipes, the widths of proposed and existing drainage easements, the direction of drainage flow (using arrows), detention ponds, outfall structures, lot drainage, and existing canals, tidal streams, etc.
2. The drainage plan shall include pertinent drainage data such as drainage areas, runoff coefficients, times of concentration (with computations), runoff volumes, soils data, detention pond routing, pond crest elevations, and other related information.
(5) Statement to be placed by design professionals on road and drainage plans: "ALL MATERIALS AND WORKMANSHIP SHALL BE IN ACCORDANCE WITH REQUIREMENTS OF THE TOWN OF JAMES ISLAND ZONING AND LAND DEVELOPMENT REGULATIONS."
(6) Statement to be signed by the owner or the authorized agent of the owner: "I certify as an agent for or as a record owner, lessee, or record easement holder, I have, or will have prior to undertaking the work the necessary approval or permission from all other persons with a legal interest in said property to conduct the work proposed in the approved subdivision construction plans."
(F) Clearing and grubbing. Except as otherwise stated herein, all secondary town road rights-of-way shall be cleared and grubbed for the full width of the right-of-way. Any/all tree canopies shall be pruned to a minimum height of 15'. This work shall include the removal and disposal of all trees, stumps, brush, rubbish, roots, and other objectionable materials.
(G) Clearing of drainage easements. The full width of all drainage easements shall be cleared of all trees, buildings, fences, stumps, brush, logs, rubbish, roots, overhanging tree limbs, overhanging utility wires or cables, or any other item that may, in the judgment of the Public Works Director, interfere with the drainage facility or the maintenance of the facility. Existing obstacles may be left in place upon approval of the Public Works Director provided that all of the following criteria are met: a) the drainage system or the obstacle cannot be easily relocated; b) adequate and safe operational easement space for maintenance by mechanized equipment is provided; c) the drainage way is not obstructed; and d) the drainage easement width is increased to accommodate the obstructions.