The new Comprehensive Plan, Indianapolis Insight, is making use of a new secondary land use category called Environmentally Sensitive. This category designates areas where some characteristic of the site has a modifying effect on the primary land use, so that the two uses (both primary and secondary) should be considered together in making land use decisions for the site.

The Environmentally Sensitive land use category includes land possessing the following special environmental characteristics: steep slopes, high-quality woodlands, wetlands, wellfields, and floodplains. These characteristics require careful attention with regard to development proposals.

Marion County is relatively flat, but we do have some steep slopes that need careful consideration. For the purposes of the plan, slopes greater than 10% (10 feet of rise over 100 horizontal feet) have been classified in the plan as environmentally sensitive. Disturbance of steep slopes can easily lead to soil erosion, which is very harmful to stream water quality.

The plan designates as high quality woodland those areas that have been continually forested for more than fifty years. Indy Parks developed this information using current and historic aerial photographs followed up with site visits or windshield surveys. Woods of this age tend to have a greater range of tree, shrub and forb species and thus are more stable and contribute more opportunities for bird and animal habitat. The plan has also included many significant stands of trees that are less than fifty years old into the environmentally sensitive category for their aesthetic, recreational and environmental qualities.

The clean water benefits of wetlands have become widely known in the past 20 years. The plan designates wetlands from the National Wetlands Survey as environmentally sensitive to draw attention to these important natural features.

Approximately 25% of Marion County’s drinking water comes from wells. To protect the supply of drinking water wellfield protection areas have been designated by ordinance in terms of time of travel, the amount of time a drop of water (or a drop of a liquid contaminant) would take to travel from the soil surface to the well intake point. W1 wellfields take one year to travel to the well; W5 wellfields take five years. With proper containment and procedures most types of businesses and industries are legally allowed in the wellfields, however it is a standard of this plan to recommend land uses in wellfields that are less prone to accidental contamination of the groundwater. These uses include parks, offices and residential uses.

The plan shows floodplains as those areas where water would sit during a flood of a magnitude that it would be likely to happen once in one hundred years. (Floodways, where water flows during that same 100-year flood, are shown in their own category, handily titled Floodway. These areas are considered essentially unbuildable.) Under state law construction is permitted in the floodplain, but it must be built up at least 2 feet above the flood level. However extensive building in the floodplain can exacerbate upstream flooding and increase the amount of flooding damage. The plan seeks “to decrease the risk of flooding within each watershed and to minimize damages when flooding occurs.”