New Development Standards for Detention:
Ponds shall be designed to reduce post-development peak flows to 30% below pristine conditions for the 25-year 6-hour storm and the 100-year 24-hour storm. The emergency spillway shall be designed to pass the 100-year 24-hour storm.
[Tech. Stormwater Standards 220.127.116.11]
Exemptions: [Tech. Stormwater Standards 1.4.1]
- Sites served by a regional detention system or master plan for which a fee-in-lieu has been established.
- Sites for which on-site detention would have insignificant effects on reducing downstream flood levels.
- Sites where detention is not needed to protect downstream property and the downstream drainage system has sufficient capacity to receive an increase in the 100-year storm.
- Constructing a detention basin would increase flood levels at some point downstream.
- Installing a detention system would not be in the best interest of the City or HWU.
Redevelopment Standards for Detention:
Detention shall be designed and constructed to reduce peak flows, after redevelopment, to 80% of the peak flows before redevelopment. Design storms are the same as for new development. [Tech. Stormwater Standards 1.7.3]
- Exempt if the imperviousness of the original site is reduced by at least 20%.
[Tech. Stormwater Standards 1.7.2]
New Development Standards for Treatment:
The Water Quality Volume (WQV – Volume of water to be treated for stormwater quality) is 0.60 inches times the entire impervious surface area proposed for a development project.
[City Code No. 23-27.3 (b)]
- Treat at least 50% of site with bioretention or infiltration unless approved by HWU, and
- Treat all rooftop and parking lot runoff with bioretention, infiltration, sand filter or manufactured device. [Tech. Stormwater Standards 1.5.2]
Redevelopment Standards for Treatment:
The WQV for redevelopment projects shall be 20% of the existing impervious area plus 100% of the new/proposed impervious area times 0.60 inches. [Tech. Stormwater Standards 1.7.4] A project that reduces the existing impervious area by at least 20% is not required to provide any other stormwater treatment (Existing impervious area is defined as any impervious surface area appearing on the Henderson City/County GIS orthophotography taken in 2003). [Tech. Stormwater Standards 1.7.2]
Maintenance of Private Stormwater Improvements
Property owner shall be responsible for maintenance. Perpetual maintenance shall be specified in a note on the face of the plat. If property is not platted, a land use restriction shall be recorded requiring perpetual maintenance of all stormwater structures or devices.
[City Code No. 23-27.5 (i)]
Erosion Control During Construction
Sites Disturbing More than 1 Acre:
For sites disturbing more than one acre, or for sites that are part of a common plan of development that is more than one acre total, the following items are required:
- An NOI (Notice of Intent) must be filed with the Kentucky Division of Water (KDOW), and
- An application must be made to HWU for coverage under their local general permit.
[City Code No. 7-202 (c)]
Links to the appropriate applications can be found at:
Sites Disturbing 1 Acre or Less of Soil:
For small construction sites of 1 acre or less, the following items are required.
[City Code No. 7-203 (h)]
- An approved construction entrance;
- Perimeter control, if there is potential for disturbed soil to be deposited onto or in streets, storm sewers, drainage channels or streams;
- Contained washout facility for concrete trucks;
- Trash control;
- Prompt cleanup of any sediment, mud, or other debris discharged to streets, gutters, storm sewers or streams.