Watershed Review Board Cases (Includes all Agenda Notes), click here
Planning Board Notes (10/4/05) Related to 10/70
Revised Ordinance: Attachment 1
Planning Board Notes (9/6/05) Related to 10/70
Attachment 1 - List of ordinances in other counties
MS Word Version with active links
How the 10/70 rule would apply to the WS-IV Protected Area in Chatham County
- 10/70 Development Option of the Watershed Protection Program (Vol. 6, No. 1)
- Limiting Impervious Surfaces Protects Water Quality (Vol. 1, No. 5)
- Impervious Implications (Vo. 6, No. 3)
- Selected Major Topics
- Back Issues
Stormwater Fact Sheet:
Stormwater Problems & Impacts: Why All The Fuss? (Fact Sheet No. 1)
- Impervious Surfaces and Water Quality: A Review of Current Literature and Its Implications for Water Planning (Journal of Planning Literature)
- Water Supply Watershed Protection Program under the NC Division of Water Quality (NCDWQ)
- Watershed Classification Table (Note: This table is the minimum established by NCDWQ; Chatham County has additional watershed classifications above this minimum standard)
- Watershed Academy Web (US Environmental Protection Agency)
Ordinances & Maps:How the 10/70 Rules Works
Under the current Watershed Protection Ordinance standards the amount of impervious surface allowed in the WS-IV Protected Area (WS-IV PA) for non-residential projects is 36% (24% if curb and gutter is used). A total of 134,380 acres of land within the County's jurisdiction is designated as WS-IV PA.
The total amount of impervious area currently allowed in the WS-IV PA = 36% x 134,380 or 48,376 acres @ 36%.
Using a 5/70 rule, 95% of the total acreage could be 36% impervious, or 95% x 134,380 x 36% = 45,958 acres @ 36%
5% of the total acreage could be 70% impervious, or 5% x 134,380 x 70% = 4,703 acres @ 70%
Total impervious acreage = 50,661 acres using a 5/70 rule.
Using the 10/70 rule, 90% of the total acreage could be 36% impervious, or 90% x 134,380 x 36% = 43,539acres @ 36%
10% of the total acreage could be 70% impervious, or 10% x 134,380 x 70% = 9,407 acres @ 70%
Total impervious acreage = 52,946 using a 10/70 rule.
So, the 5/70 rule would allow an additional 2,285 impervious and the 10/70 rule would allow an additional 4,570 impervious acres above the current 36% standard. This assumes full development of all eligible acreage.