Above this level, channels become unstable and begin to erode, habitat quality becomes poor, and stream biodiversity drops. For streams in open, undeveloped watersheds where imperviousness is less than 15 percent, stricter controls on development and stronger efforts at stream protection could be required. Otherwise, the same level of stream restoration efforts and runoff controls are appropriate everywhere in a completely developed jurisdiction, and need not be focused on particular tributaries. A watershed approach to storm water planning means that a local government could write its ordinances to apply to only one part of its jurisdiction or apply its regulations differently in different areas. For new development, there is a long history of land use controls regulating activities in only part of a jurisdiction.
Some examples follow.
Zoning laws are one of the major limits on the activities of landowners, based simply on the location of the property. In Virginia, the Chesapeake Bay Preservation legislation governs what kinds of new development are permissible near tributaries to the Bay. The regulations also govern redevelopment, including improvements to single-family residences. The Four Mile Run 100-year detention requirement is an example of regulating development by watershed. Arlington's storm water ordinance applies more stringent standards to this watershed than to the remainder of the County.