Buffers provide a transition from development to water bodies and adjacent environmentally sensitive areas within both the Neuse and Cape Fear Watersheds. Some activities and uses are restricted in these areas, depending on the location, type of stream, type of development and type of vegetation. Buffers are generally required to stay vegetated to allow some of the velocity of stormwater runoff and any pollutants to settle out before reaching streams. In addition to the buffers established by the Jordan Lake Rules and the Neuse Rules, Cary’s LDO also establishes a Zone 3 Urban Transition Buffer, an additional 50’ buffer that applies in some cases. See our Stream Buffer page for more information. LDO Section 14.6

Development that increases Built Upon Area (BUA) is required to take measures to limit the amount of pollutants, including nitrogen, phosphorus and suspended solids, in stormwater runoff. Reduction options may include a combination of Stormwater Control Measures (SCMs), nutrient offset payments, impervious surface limitations, and open space conservation by designating areas as permanently-protected forest. LDO Section 7.3.2

Development located outside of a Water Supply Watershed Protection Overlay is required to control peak runoff and reduce Total Suspended Solids (TSS) based on density and the amount of impervious surface proposed. This is typically accomplished through the use of SCMs. LDO Section 7.3.3 

In order to minimize damage to streams caused by storm flows, new development projects (both in and outside of a Water Supply Watershed Protection Overlay) are required to achieve no net increase in peak stormwater runoff leaving a development for the 1-year design storm, compared to pre-development. LDO Section 7.3.4

In addition, a Downstream Impact Analysis is also required with development plan submission, to calculate the post-development peak runoff discharges for the 2, 5, 10 and 100-year storms. The development is required to provide detention to mitigate each storm event to the calculated pre-development rate. LDO Section 14.7.9

Inlet structures and catch basins, as well as pipe networks, are reviewed with development plans to ensure they are sized appropriately and have the capacity to convey stormwater runoff from the new development. All storm drainage infrastructure must conform to Cary's Standard Specifications and Details.

Any project that disturbs soil must provide erosion control measures to prevent sediment from leaving the site during construction in accordance with Cary’s sediment and erosion control requirements. If the area of disturbance exceeds 12,000 sq ft, or one acre for a single-family residential lot, a land disturbance/grading permit is required. Proposed developments must include erosion control plans as part of their development plan submittal. Design specifications and construction standards for erosion control measures are found in Cary’s Standard Specifications & Details Section 4000. There are also specific requirements for smaller Projects on Residential Lots – see below.

Cary has established design specifications and construction standards for infrastructure installed to support new development and redevelopment projects. Cary’s Standard Specifications & Details Section 8000 provides the design and installation criteria for new stormwater pipe networks, including materials, sizing, and construction methods.