Stormwater Regulations & Considerations Morse Study Area. Pam Fortun, P.E. CFM Senior Stormwater Treatment Engineer Engineering Services Division

Size: px

Start display at page:

Download "Stormwater Regulations & Considerations Morse Study Area. Pam Fortun, P.E. CFM Senior Stormwater Treatment Engineer Engineering Services Division"

Nathan Jackson
5 years ago
Views:

1 Stormwater Regulations & Considerations Morse Study Area Pam Fortun, P.E. CFM Senior Stormwater Treatment Engineer Engineering Services Division

2 Stormwater Regulations Development Considerations Floodplain Issues Stream Corridors

3 Floodplain Issues

4 What is a Floodplain? Area expected to be under water in the 100-year storm FEMA has mapped floodplains for larger creeks and rivers Smaller creeks also have floodplains but not all are mapped

5 What exactly is a 100-year storm? Storm that has a 1% probability of happening in any given year at a specific location 100-year storm can happen multiple times in a year or not for 200 years Not all 100-year storms are the same Can vary greatly in a short distance

6 Flood Risk Statistics There is a 5% chance that a house will catch fire during the life of a 30-year mortgage For a house located within the floodplain, there is a 26% chance that it will be flooded during the life of a 30-year mortgage That probability increases to 39% over a 50 year period For more information about flood risks, go to floodsmart.gov

8 Mapped Floodplains in Morse Study Area

9 Why Regulate the Floodplain? Reduces future flood risks Allows residents to purchase flood insurance through National Flood Insurance Program (NFIP) Limits need for expensive flood control projects Minimizes loss of life and property from flooding

10 Regulated Activities in the Floodplain Construction of new structures or buildings Additions to existing buildings Substantially improving existing buildings Parking or storing recreational vehicles Subdividing land Placing mobile homes Temporary buildings Accessory structures Agricultural buildings

11 Regulated Activities in the Floodplain (Continued) Temporary or permanent materials storage including gas/liquid tanks and sand/gravel Roads, bridges, and culverts Paving Filling, grading, excavating, mining, and dredging Pile driving Altering stream channels Land clearing Activities by other government agencies

12 Development in or near the Floodplain Residential: No platting of new residential lots in the floodplain Elevation requirements for new buildings on existing lots Non-Residential: Buildings must be elevated or floodproofed Parking areas located so that vehicles won t flood No storage of hazardous materials Existing Buildings in the Floodplain: Substantial improvements trigger floodplain compliance requirements

14 Stormwater Regulations Development Considerations Floodplain Issues Stream Corridors

15 Stream Corridors Stream Corridor Ordinance adopted in developments have preserved stream corridors Almost 11 miles of streams preserved Over 200 acres of green space preserved

16 Stream Corridors Key Points Protected corridors must be left in natural state Limited grading, limited utility encroachment, limited road crossings Usually in a dedicated tract maintained by Homeowners Association Can be incorporated into greenway linkage trail systems Lakes allowed in stream corridors

17 Stream Corridors Benefits Keeps buildings out of flood areas

18 Stream Corridors Benefits Protects buildings and property by keeping them away from eroding streams

19 Stream Corridors Benefits Provides green space for residents and critical habitat for wildlife

20 Stream Corridors Width Drainage Area Setback (both sides) <25 acres * 15 feet acres * 30 feet acres 60 feet 160-5,000 acres 100 feet 5,000+ acres 120 feet * Stream corridor can be replaced by underground pipe system

21 Stream Corridors PROPOSED STREAM CORRIDOR SYSTEM (Less Than 40 Ac.)

22 Stream Corridors PROPOSED STREAM CORRIDOR SYSTEM (Greater Than 40 Ac.)

23 Drainage Area = 37 acres Setback Required 30 feet (each side)

24 Drainage Area = 100 acres Setback Required 60 feet (each side)

25 Drainage Area = 240 acres Setback Required 100 feet (each side)

26 Drainage Area = 16,000 acres Setback Required 120 feet (each side)

27 Stream Corridors in Morse Study Area

28 Stream Corridors & Floodplain Morse Study Area

29 Stormwater Regulations Other Considerations Stormwater Detention Stormwater Quality

30 Stormwater Detention What is it? A basin or pond that reduces the peak storm runoff rate from a development site Designed to not increase the peak runoff rate for the 100-year and lesser storms Can be a dry basin or a wet pond Approximately 10% of site

31 INSERT EXAMPLE PICTURES DRY BOTTOM BASIN Typical dry bottom basin

32 Typical wet bottom basins

33 When is Stormwater Detention required? Detention required ONLY when downstream flooding is identified or will be a problem after development occurs Flooding of habitable buildings or excessive road flooding on improved roads Yard flooding that doesn t flood a habitable building doesn t trigger detention

34 These flooding problems may warrant upstream detention

35 This type of flooding typically would not warrant upstream detention

36 Stormwater Regulations Other Considerations Stormwater Detention Stormwater Quality

37 Stormwater Quality Stormwater Treatment Ordinance adopted in 2008 Compliance requirements under federal EPA Clean Water Act regulations New approach to stormwater must address quantity and quality of runoff Approximately 6%-10% of site

38 Stormwater Treatment Facilities Wetlands

39 Stormwater Treatment Facilities Rain Gardens

40 Stormwater Treatment Facilities Permeable Pavement

41 Stormwater Treatment Facilities Bioretention cells

42 Stormwater Treatment Facilities Impacts on New Development Typical Development Without Stormwater Treatment

43 Stormwater Treatment Facilities Impacts on New Development Same Development with Stormwater Treatment More common open space Slightly smaller lots Less underground storm sewer pipe

44 Questions?

NAI Principles In Gwinnett County

NAI Principles In Gwinnett County By Cornelius Ani, LSIT, CFM Contributors: Adena Fullard, P.E., CPSWQ Rudresh Bihalli, P.E., CFM Ken Kagy, P.E., CPESC, CPSWQ Ligia Negru, M. Sc., CFM Maja Radovic, CPESC,