Protect Natural Drainage Paths and Drainage Areas
P4Protect Natural Drainage Paths and Drainage Areas
This credit is required.
Why this matters to the lake?
Natural topography is uneven, forcing stormwater runoff to follow a meandering path with many small depressions that capture water and prevent concentrated erosive flows. Human-made changes in topography can adversely affect water quality by concentrating flow paths, causing erosion and carrying sediments and pollutants directly to the lake. Conversely, diverting existing flow paths away from wetlands and streams can adversely alter wetlands and streams by removing important sources of water. Increasing or decreasing drainage areas can increase or decrease water flows, adversely impacting natural systems. Altering channel materials, such as adding hardscape or concrete to a channel, can reduce infiltration capability and increase runoff. Maintaining existing drainage paths supports the hydrologic balance and sustains ecosystem services by reducing the amount of runoff and pollutants entering the lake.
- Maintain drainage areas and sub-drainage areas to existing flow paths before and after development. Do not increase or decrease drainage areas
- Protect the natural hydrology that minimizes erosion and streambed scouring by diverting additional flow
- Protect existing channels or flow paths that maintain water velocity through the site
- Reduce runoff by maintaining or increasing the velocity of flows and increasing the length of flow path. Maintain or increase the time of concentration (Tc)
Design site layouts and grading to maintain natural topography and water flow patterns, and protect existing natural drainage features such as closed depressed areas, springs, swales, intermittent streams, and wetlands. Avoid grading that changes natural drainage patterns and decreases the time of concentration. Implement practices such as vegetated swales and disconnection of impervious areas. Install protective fencing or compost socks to protect critical environmental areas and sensitive sites.
For all site situations that involve grading and earth disturbance, show on the Proposed Site Plan existing site contours and proposed grading demonstrating that natural drainage patterns are being maintained. Provide sub-drainage area maps before and after development, including pre- and post-development flow paths as well as the time of concentrations (Tc).
Include the following information with application:
✓ As a part of the Proposed Site Plan, the applicant must show original and final grading and drainage areas on the site, pre- and post-development flow paths and time of concentration values.
✓ In a narrative , describe practices that maintain existing flow paths and avoid increasing the flow rate across the site.
✓ Engineering calculations and/or narrative to demonstrate that the overall time of concentration has not been reduced (e.g. leaving the site from stormwater practices).
- "Better Site Design." New York State Department of Environmental Conservation, Division of Water.
Existing Regulatory Guidance/Requirements
Lake George Park Commission, Part 646-4 – Stormwater Management
Town of Queensbury Town Code Chapter 147 - Stormwater Management.
Lake George Town Ordinance, Chapter 175-21- Erosion, sedimentation and stormwater runoff control
Lake George Village Ordinance, Chapter 220 - Article IX - Stormwater Management Regulations
Bolton Town Ordinance, Chapter 125 – Stormwater and Erosion Control
Lake George Park Commission, Permit Forms. http://www.lgpc.state.ny.us/permits/permitsstormwater.html