The Storm Water Quality Benefits of Flood Buyouts. City of Birmingham Edwin Revell, CFM March 10, 2011 ASCE Alabama Section Winter Meeting

Transcription

1 The Storm Water Quality Benefits of Flood Buyouts City of Birmingham Edwin Revell, CFM March 10, 2011 ASCE Alabama Section Winter Meeting

2 Outline Floodplain Mgmt & Storm Water Mgmt MS4 NPDES Permit Requirements Addressed Non-Traditional BMP Water Quality/Quantity Benefits Case Study Example Summary Conclusions

3 Floodplain Management Mgmt of Natural Resource DHS/FEMA NFIA/NFIP Floodplain Ordinance Flood Hazard Mitigation Quantity Control to Reduce Flood Losses Resource, Property and Life Protection Improve Quality of Life and Place Storm Water Management Mgmt of Natural Resource EPA CWA/NPDES NPDES MS4 Permit BMP Controls Quality Control via Quantity Control to reduce Pollutant Loads Resource, Property and Health Protection Improve Quality of Life and Place Flood Buyouts

4 NPDES MS4 Permit Requirements Addressed Areas of New Development/Significant Redevelopment PHF Management and Public Education Requirements TMDL Implementation Flood Control Project Requirements

5 New Development and Significant Redevelopment Objective: Minimize or Decrease pollutant loadings from newly re/developed sites. Before Buyouts After Buyouts Creates Permanent Open Space Permanent Impervious Cover Removal Eliminates direct connections Reduces Runoff Volume Reduces Pollutant Loading Flood Buyouts

6 PHF Requirements Objective: Reduce discharge of pollutants related to storage and application of PHFs and through public education. Flood buyouts: Converts residential properties to permanent natural open space Converts occupied land to unoccupied land Reduces use of PHF

7 TMDL Implementation Requirements Flood Buyouts: Provide stream buffer areas to help reduce erosion and sedimentation Reduce in nutrient loadings from residential properties Provide additional protection for impaired streams

8 TMDL and Buyouts

9 Flood Control Project Requirements Objectives: Floodplain Management Projects assessed for water quality impacts; existing flood control structures evaluated for additional pollutant removal benefits from retrofits Flood buyouts: Flood mitigation project that provides water quality benefits by reducing runoff volume and pollutant loading

10 Non-Traditional BMP (Storm Water Retrofits) Flood Buyouts Park Space Creation Remediated Brownfield Sites

11 Water Quality/Quantity Benefits In general: (Storm Water Retrofits) Reduced contaminant sources Reduced contaminant load from reduced runoff Trap and remove contaminants

12 Water Quality/Quantity Benefits (Flood Buyouts) Homes are Demolished Less anthropogenic activity Reduced sources of contaminants Site is Revegetated and Left as Green Space Reduced impervious area Increased water infiltration opportunity Reduced contaminant load from reduced runoff Act as Grass Buffer Treat runoff from up-gradient areas

13 Method Case Study Example (Flood Buyouts) 334 Acres flood buyout areas (aggregate) 2-yr rainfall period and SCS Runoff Method (med res & open space) Pollutant Event Mean Concentration (Literature) Calculated pollutant loading (Simple Method)

14 Average Annual Runoff Reduction Estimates Pre-buyout: 490 ac-ft; inches Post-buyout: 16 ac-ft; 0.57 inches No runoff for events up to about 3 in In over two Permit years of analysis, there were only six events with > 3 in rainfall depth

15 lbs lbs lbs Counts lbs lbs Pre Vs Post Buyout Contaminant Loads from Buyout Areas 1.E+05 1.E+05 8.E ,790 TSS 3.E+03 3.E+03 2.E+03 2,395 TN 6.E+04 4.E+04 2.E+03 1.E+03 Load Reductions 2.E+04 0.E+00 Pre-Acquisition 1,220 Post-Acquisition 5.E+02 0.E+00 Pre-Acquisition 48 Post-Acquisition Contaminant % Reduction 3.E+02 3.E+02 2.E+02 2.E+02 1.E+02 5.E+01 0.E+00 8.E Pre-Acquisition 73,196 TP 9 Post-Acquisition 4.E+13 3.E+13 3.E+13 2.E+13 2.E+13 1.E+13 5.E+12 0.E+00 1.E E+13 Pre-Acquisition 13,308 Fecal Coliform E+11 Post-Acquisition Fecal Coliform (Counts) 98 BOD (lb) 98 COD (lb) 98 TSS (lb) 99 TN (lb) 98 TP (lb) 97 6.E+04 COD 1.E+04 1.E+04 BOD 4.E+04 8.E+03 6.E+03 2.E+04 0.E+00 Pre-Acquisition 1,351 Post-Acquisition 4.E+03 2.E+03 0.E+00 Pre-Acquisition 218 Post-Acquisition

16 Average Annual Up-Gradient Runoff Treatment (Flood Buyouts as a Vegetative Filter Strip) Pollutant Percent Removal* Total suspended solids 84 Nitrate+nitrite 20 Total phosphorus 40 Area treated: 15 acres Length of filter strip: 300 feet Width of filter strip: 2300 feet ( ft) *Literature published removal efficiencies for a typical grass filter, 150 ft in length (Source: EPA Fact Sheet)

17 Estimated Pollutant Treatment Levels of Buyout Areas Contaminant Up-Gradient Load to Grass Buffer (lb) Load Leaving Grass Buffer(lb) Load Reduced (lb) TSS TN TP

18 Summary: Benefits of Buyouts Flood Plain Management Reduce Flood Loss Creation of Permanent Open Space Restoration of Natural Function Removal of Obstructions Storm Water Management Permanent Removal of Impervious Surfaces Reduction of Runoff Volume Reduction of Pollutant Loading

19 Conclusions Flood buyouts address floodplain management and storm water management requirements Flood buyouts are regional storm water BMPs Flood buyouts are low maintenance permanent storm water BMPs Flood buyouts can be used to meet TMDL implementation requirements Flood buyouts could provide pollutant loading credit or trading opportunities