§ 157.096  DRAINAGE.
   (A)   Purpose and intent. It is the purpose and intent of these regulations to ensure that developments shall be provided with such storm drains, culverts, drainageways, or other works as are necessary to collect and dispose of surface and stormwater originating on or flowing across the development, in order to prevent inundation and damage to streets, lots, and buildings, and to improve the water quality of the Chesapeake Bay and its tributaries.
   (B)   Plan of development submittal requirements.
      (1)   Compliance with requirements of this section. Plan of development proposals shall include the submission of sufficient evidence in the form of plans and attachments which establish that the plan complies with the requirements of this section.
      (2)   Stormwater management plan. The preliminary submission of a plan of development shall be accompanied by a stormwater management plan, if and as required by the Land Use Administrator, showing sufficient information to enable a determination to be made relative to the improvements necessary for controlling stormwater runoff, including drainage plans and flood control devices. This plan shall show natural drainage patterns and any proposal drainage improvements, including pipe sizes and types, stormwater detention and retention facilities, drainage easements and any other means for transporting drainage waters to a well-defined open stream. Areas subject to periodic flooding (100-year flood) shall be delineated on preliminary and final plans of development.
      (3)   Continuing management plan. A continuing management plan, including a property owners’ association or other appropriate maintenance entity as if necessary, shall be submitted for all elements of the drainage and flood control system which will not be the explicit maintenance responsibility of the county or the State Department of Transportation. The developer shall provide assurance that all facilities are in good repair and properly functioning when the development has been completed and prior to the responsibility for continuing maintenance and ownership of drainage systems being conveyed to the designated maintenance entity.
   (C)   General requirements.
      (1)   Provision of drainage and stormwater management facilities.
         (a)   Drainage and stormwater management facilities shall be provided, either on-site or off-site, to reduce drainage flows, pollutants, and sediment loading from the development to a level not exceeding the conditions prior to development, or to a lesser level, if deemed necessary to comply with the provisions governing pollutant and sediment discharges associated with § 157.047.
         (b)   The plan-approving authority shall approve, or approve with modifications, only those stormwater management facilities which comply with the intent of this chapter or with adopted overall drainage plans and policies, if any. In this regard, the plan-approving authority shall not generally approve, except as a temporary measure, on-site stormwater management facilities as an alternative to contributing to planned regional stormwater management systems, if and when such a management system is in effect.
         (c)   All management facilities shall be designed and constructed in accordance with § 157.097 as supplemented by the latest editions of the Virginia Erosion and Sediment Control Handbook and the Department of Transportation Drainage Manual as well as regulations, or policies adopted by the state or the county pursuant to § 157.047.
      (2)   Drainage easements. Where a development is traversed by a watercourse, drainageway, channel, or stream, there shall be provided a drainage easement of sufficient area and width to protect and preserve the aforementioned feature. Drainage easements shall be designed and drainage structures constructed in such a manner as to reduce the burden of maintenance, yet provide adequate access for necessary maintenance.
      (3)   Drainage of rights-of-way. All public rights-of-way shall be drained in accordance with the requirements of the State Department of Transportation.
      (4)   Appropriate grading considerations.
         (a)   No stormwater runoff or drainage water shall be so diverted as to overload existing drainage systems or create flooding or the need for additional drainage structures on other private properties or public lands without proper and approved provisions being made for taking care of these conditions.
         (b)   Lots shall be graded to secure proper drainage away from buildings and prevent the ponding of stormwater unless within an approved retention or detention basin and/or in a manner as intended by § 157.047.
         (c)   No grading shall occur within 100 feet of any perennial watercourse or wetland except as provided for specific waterfront erosion control, or water-dependent facilities or for necessary utilities and public street construction.
      (5)   Maintenance of existing drainage patterns. In general, the design of a development shall be such as to minimize grading and disturbance of natural vegetation. Natural contours and stormwater channels shall be respected and retained where possible.
      (6)   Minimize impervious surface areas.
         (a)   A stormwater management plan shall preserve natural drainageways and wetlands, maximize infiltration of stormwater and minimize off-site discharge of stormwater.
         (b)   In general, impervious surfaces near waterfronts and wetlands shall be avoided; grass swales shall be utilized and curb and gutter and paved ditches shall be avoided except where necessary to prevent erosion in accordance with the standards of the State Department of Transportation.
   (D)   Stormwater management area design considerations. Stormwater management areas include retention and detention basins, drainage ditches and swales, and wetlands areas. Sensitively designed basins and swales can benefit the health, safety, and welfare of county residents. The integration of these areas as desirable landscape features, naturalized wetland areas, or active and passive recreation areas, in addition to their stormwater management function is strongly encouraged whenever possible.
      (1)   Stormwater detention areas.
         (a)   One of the following landscape concepts for stormwater detention areas, or an alternative concept complying with the general statement set forth above, shall be used.
         (b)   Reforestation: this landscape treatment is most appropriate for detention basins and drainage areas that are adjacent to areas of mature woodlands or wetlands. It reverts the disturbed area to a revegetated, stable, low maintenance, natural landscape asset over time.
            1.   The area shall be graded to blend into the surrounding landscape and imitate a natural depression with an irregular edge. This shall include gentle berming. Linear, geometric basins are unacceptable.
            2.   The quantity of trees to be planted on the interior of the basins shall be equal to the number of trees that would be necessary to provide canopy cover of the entire area to the high water line or outflow elevation. Plantings shall not be located within 20 feet of low-flow channels to allow for channel maintenance. All woody and herbaceous plants shall be species indigenous to the area and/or tolerant to typical wet/dry floodplain conditions.
            3.   The perimeter area (slopes above the high water line) shall include shade trees, evergreen trees, ornamental trees, shrubs, and groundcover that results in screening that is as maintenance free as possible.
            4.   Provisions for emergency access as well as general maintenance of the basins shall be provided. Plantings shall be designed to disguise yet not hinder vehicular access.
            5.   Tree plantings are not permitted upon any dikes associated with a detention basin.
      (2)   Stormwater retention areas; open space/recreation features. This landscape treatment can take on a variety of landscape forms, from formal reflecting pools, fountain features to natural park-like lakes and ravines.
         (a)   Water fountains/features are encouraged in the design of developments.
         (b)   The waters edge shall be easily maintained and stable. Possible treatments might include riprap, stone walls, natural plantings, decking, and bulkheads.
         (c)   The planting of the perimeter of the feature shall integrate pedestrian paths, sitting areas, and other passive uses.
         (d)   Plants with pervasive root systems shall not be located where they may cause damage to drainage pipes or other underground utilities.
         (e)   All engineered basin structures shall be designed to blend into the landscape in terms of construction materials, color, grading, and planting.
   (E)   Stream and lake sampling.
      (1)   Predevelopment sampling.
         (a)   All major plans of development abutting lakes and streams shall submit, at the time application is made, water sample results with test and sample for:
            1.   Temperature;
            2.   Nitrogen, total kjeldahl;
            3.   Dissolved oxygen;
            4.   Chloride;
            5.   pH;
            6.   Phosphorous;
            7.   Alkalinity; and
            8.   Fecal coliform.
         (b)   These tests shall undertaken at the time of major preliminary plan of development submission and the date of the test shall be so noted.
         (c)   Samples shall be taken and tested in accordance with generally accepted procedures by or under the jurisdiction of a qualified testing laboratory.
         (d)   Tests shall be taken at the intersection of any tract boundary and the inflowing streams, and at the outfall points where the watercourse leaves the tract.
      (2)   Post-development sampling. If the major plan of development is approved and constructed, a second set of tests shall be taken by the developer at the discretion of and at a time decided by the Land Use Administrator, but not after performance and maintenance guarantees have been released. All results and comparisons shall be given to the Land Use Administrator for review and analysis. Performance and maintenance guarantees may be applied to correct any degraded water-quality conditions, which in the opinion of the Land Use Administrator, are as a result of the implementation and construction of the plan of development.
   (F)   Off-site drainage costs.
      (1)   Applicability. The developer shall be required to pay a pro rata share of the cost of providing reasonable and necessary drainage improvements located outside of the property limits of land owned or controlled by him or her whenever all of the following conditions exist:
         (a)   The plan-approving authority determines that such off-site improvements are necessitated at least in part by the construction or improvement of the development;
         (b)   The county has established a general drainage improvement program for an area having related and common drainage conditions. The developer’s property is located within the designated area covered by this program;
         (c)   The estimated cost of the total drainage improvement program has been determined; and
         (d)   The estimated stormwater runoff has been established for the designated area served by such program.
      (2)   Cost determination. The developer’s share of the estimated cost of improvements shall be limited to the proportion of such estimated cost which the volume and velocity of stormwater runoff to be caused by his or her development bears to the total estimated volume and velocity of runoff from such area in its fully developed state.
      (3)   Payment provisions. Any cash payment received by the county shall be expended only for construction of those facilities identified in the established drainage facilities improvement program and until so expended, shall be held in a separate account for the individual improvement program.
(Ord. passed 11-9-1995)  Penalty, see § 157.999