Categories of Land Within the Critical Area
Intensely Developed Areas (IDAs)
Intensely Developed Areas (IDAs) are defined as areas of twenty of more adjacent acres where residential, commercial, institutional or industrial land uses predominate. IDAs are areas of concentrated development where little natural habitat occurs. In IDAs, the Law requires that new development and redevelopment be accompanied by techniques to reduce water quality impacts associated with stormwater runoff. These techniques are often referred to as best management practices (BMPs). The Criteria specify that these techniques be capable of reducing pollutant loads generated from a developed site to a level at least 10% below the load generated at the same site prior to development. This requirement is commonly referred to as the "10% Rule". BMPs for meeting the 10% rule include filter and infiltration systems along with stormwater wetland and pond systems. In some cases IDA on-site compliance with the 10% rule proves impossible. In those cases, local jurisdictions may provide an offset program by which equivalent water quality benefits are achieved off-site but within the same watershed. In addition, the clustering of development reduces the amount of impervious surfaces and increases the area of natural vegetation thereby lessening adverse impacts to water quality and habitat areas. The Criteria also specify that development activities minimize destruction of forest and woodland vegetation and secure Habitat Protection Areas. Urban forestry programs benefit water quality by controlling sediment, by reducing runoff and by removing nutrients and other potential pollutants. They also furnish direct habitat value by providing sources of food and areas of temporary shelter for some wildlife species.
Limited Development Areas (LDAs)
Limited Development Areas (LDAs) are areas in which development is of a low or moderate intensity. LDAs contain areas of natural plant and animal habitats but are not dominated by agriculture, wetland, forest, barren land, surface water or open space. The quality of runoff from these areas has not been substantially altered or impaired. Housing densities in LDAs are between one dwelling unit per five acres and four dwelling units per acre. Areas with IDA characteristics but with fewer than 20 acres are classified LDA. Development or redevelopment of LDAs must not change the prevailing character of land use and must improve water quality. It must also conserve existing areas of natural habitat and incorporate wildlife corridors that ensure continuity of wildlife and plant habitat. The retention and increase of forested areas is of paramount concern to the health of the Chesapeake and its tributaries. Forest cover affords the Bay a host of benefits including habitat and water temperature mediation. Forest cover also reduces and filters runoff. The Criteria stipulate that developers replace cleared forest cover in ratios ranging from 1:1 to 3:1. When it is impossible to replace forest cover at these prescribed rates, local jurisdictions collect fees-in-lieu that are used to reforest other areas in the Critical Area or other locations beneficial to the Critical Area. In areas of new development or redevelopment, where no forest coverage existed previously, 15% of the area must be planted with trees. The Criteria allow development in areas where slopes rise 15% or more above grade only if such development can be shown to control soil erosion and runoff. Impervious surfaces (those through which water will not run) contribute to runoff and so threaten the quality of the Bay's waters. Such coverage in LDA development or redevelopment is limited to between 15% and 25% according to the nature and history of the site. Developers are strongly encouraged to use permeable surfaces.
Resource Conservation Areas (RCAs)
RCAs are characterized by natural environments or by resource-utilization activities. Resource-utilization refers to such activities as agriculture, aquaculture, commercial forestry and fisheries activities which the Criteria consider protected land uses. The Criteria limit new development in RCAs to one dwelling unit per 20 acres because studies indicated that when large amounts of resource-utilization land have been converted to residential development, it is usually in parcels of 2-, 5- and 10-acre lots. The "1-in-20" criterion is intended to ensure that RCAs maintain a natural character, preserving favored land uses while avoiding fragmentation of areas adequate to robust wildlife and plant habitat. New commercial and industrial facilities are not allowed in RCAs and that development which is allowed in the RCAs must conform to the standards set for LDAs. The Criteria require that farmers develop plans that promote the use of BMPs to prevent the runoff of soil, nutrients and other materials that degrade water quality. The feeding and watering of livestock must be kept well away from tidal waters although low-impact grazing is permitted. Timber harvests conducted in the Critical Area must be done pursuant to a Timber Harvest Plan approved by the Maryland Department of Natural Resources. Such plans, prepared by professional foresters, provide for the protection of water quality, continuity of habitat and the reforestation of timbered areas.
CRITICAL PRIMER