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Are Detention Ponds Holding You Back? May 30 th, 2007 Brian Bates Don Alexander.

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Presentation on theme: "Are Detention Ponds Holding You Back? May 30 th, 2007 Brian Bates Don Alexander."— Presentation transcript:

1 Are Detention Ponds Holding You Back? May 30 th, 2007 Brian Bates Don Alexander

2 Stormwater Management in Greenville County May 30 th, 2007 Ground Rules True or False: “Detention ponds are a bad thing for water quality” FALSE

3 Stormwater Management in Greenville County May 30 th, 2007 Attributes of Detention  Peak discharge control  Volume control  Pollutant trapping −Sediment −Heavy metals −Floatables −Oil and grease −Nutrients −Bacteria …When Properly Designed, Constructed, and Maintained

4 Stormwater Management in Greenville County May 30 th, 2007 Ground Rules Continued  State Law – Regulation −Post development peak discharge not exceed predevelopment rates for 2 and 10-yr. Storm −Permanent quality ponds with a permanent pool must store and release the first half inch of runoff for 24-hrs. −Permanent quality ponds without a permanent pool must store and release the first inch of runoff for 24-hrs.  Greenville County is a delegated review authority under

5 Stormwater Management in Greenville County May 30 th, 2007 Quantity and Quality Standards  Good −Detention Peak flow comparison – 2, 10, 25, etc. −Water Quality 1-in. of runoff – dry detention ½-in. of runoff – wet detention

6 Stormwater Management in Greenville County May 30 th, 2007 Quantity and Quality Standards  Better −Detention Volume based comparison – 2, 10, 25, etc. −Water Quality Design storm runoff (e.g. 1-in. storm)

7 Stormwater Management in Greenville County May 30 th, 2007 Quantity and Quality Standards  Best −Detention Peak flow comparison and Volume based comparison −Water Quality Effluent standards

8 Stormwater Management in Greenville County May 30 th, 2007 Key Words  “Properly Designed, Constructed, and Maintained” −Historic Design Issues No small storm detention Short circuiting Pre-developed calculations (high CNs) Designed for built out conditions

9 Stormwater Management in Greenville County May 30 th, 2007 Pelzer Pond Example

10 Stormwater Management in Greenville County May 30 th, 2007 Key Words  “Properly Designed, Constructed, and Maintained” −Historic Construction Issues Sledge hammer orifice No riser Incorrect invert elevations 24 hour first flush drainage controls

11 Stormwater Management in Greenville County May 30 th, 2007 Pelzer Pond Example

12 Stormwater Management in Greenville County May 30 th, 2007 Key Words  “Properly Designed, Constructed, and Maintained” −Historic Maintenance Issues Sediment accumulation Vegetation Trash racks Damaged risers

13 Stormwater Management in Greenville County May 30 th, 2007 County’s approach  Review and inspect to assure compliance with current standards  Encourage water quality BMPs in conjunction with detention −Vegetated filter strips −Bioretention −Engineered devices −LID  Provide tools for design community −SUDS −IDEAL −Design manual  Explore ordinance revisions

14 BMP Retrofit Study

15 Stormwater Management in Greenville County May 30 th, 2007 Problem Statement What is the best way to meet water quality standards in developed areas? How many BMPs are needed? At what scale are BMP benefits insignificant? Where is the best place to locate? How do we measure improvement? We assume that standards/TMDLs cannot be met without retrofits to developed areas.

16 Stormwater Management in Greenville County May 30 th, 2007 Project Location  No construction  Basin size  Monitoring constraints

17 Stormwater Management in Greenville County May 30 th, 2007 Project Location

18 Stormwater Management in Greenville County May 30 th, 2007 Runoff Analysis  Three automatic samplers in parallel  Grab samples taken at each site for fecal coliform analysis  Sample analysis performed by Rogers & Calcott  To Date: −3 storms, samples taken and analyzed per storm for TSS, TN, TP −Fecal Coliforms samples per storm −H&H Model developed & trying to calibrate

19 Stormwater Management in Greenville County May 30 th, 2007 Study Update To Date 3 Storms, with samples taken and analyzed per storm Fecal Coliforms samples per storm H&H Model developed & trying to calibrate

20 Stormwater Management in Greenville County May 30 th, 2007 Bioretention  Retrofit at Our Lady of the Rosary Catholic Church has been successful  May be the best BMP for combining quantity and quality control  Can be modeled in IDEAL along with VFS, sand filters, ponds, and bioswales

21 Stormwater Management in Greenville County May 30 th, 2007 Greenville County

22 Stormwater Management in Greenville County May 30 th, 2007 Next Steps  Model BMP scenarios −Pond outlet structures −Conversion to another type of BMP −Engineered devices −Focused public ed.  Scenario selection based on B:C  Implement best scenario  Monitor post-retrofit runoff events and compare results

23 IDEAL Post-construction Water quality BMP Model

24 Stormwater Management in Greenville County May 30 th, 2007 IDEAL Integrated Design and Evaluation Assessment of Loadings Model

25 Stormwater Management in Greenville County May 30 th, 2007 An OCRM Dilemma  Compliance with Antidegradation & TMDLs  Needed an explicit BMP model −Model Hydrology & Hydrualics and pollutant yield from urban areas. −Estimate BMP performance. −Base predictions on accepted predictive procedures

26 Stormwater Management in Greenville County May 30 th, 2007 IDEAL Initiated  Woolpert hired by OCRM  Scope of Model  Literature review  Watershed Framework  Post Construction BMP Design Aid Manual and IDEAL Spreadsheet

27 Stormwater Management in Greenville County May 30 th, 2007 IDEAL Development  Primary Researchers Dr Bill Barfield – Oklahoma State University Dr. John Hayes – Clemson University

28 Stormwater Management in Greenville County May 30 th, 2007 IDEAL OCRM version  BMP Trapping Sedimentology and soil isotherms  Hydrology Single storm and Total annual runoff  4 pollutants  3 BMPs  Pond routing  Single watershed  Post-construction

29 Stormwater Management in Greenville County May 30 th, 2007 Pervious Imp Pervious and Unconnected Impervious Impervious Directly Connected Impervious BMP Dry/Wet Detention Basin Outflow From Watershed Watershed Modeling Framework

30 Stormwater Management in Greenville County May 30 th, 2007 Rainfall Statistics Growing Season P=0.664 AMC 1 P=0.797 AMC 2 P=0.104 AMC 3 P=0.100 Dormant Season P=0.336 AMC 1 P=0.543 AMC 2 P=0.231 AMC 3 P= Storms 0.25’’ to 10.5’’ Values for Greenville, SC Precip Amount Prob P

31 Stormwater Management in Greenville County May 30 th, 2007 Loading  Sediment −Pervious Areas - MUSLE − Impervious Areas - EMC Approach  Nutrients and Bacteria - EMCs

32 Stormwater Management in Greenville County May 30 th, 2007 BMP Trapping  Predicts trapping of sediments in ponds through overflow rate calculations for 5 particle classes.  Predicts nutrient trapping by settling of particulate matter and sorbed portion on trapped active clay content of the sediment by isotherms.  Predicts bacteria trapping using isotherms and mortality

33 Stormwater Management in Greenville County May 30 th, 2007 IDEAL OCRM Model Limitations  Only for use on the SC coast  Limited outlet configurations  Numerous spreadsheet constraints  Untested BMP algorithms  No resuspension, denitrification, direct loading on BMP, or bacteria growth.

34 Stormwater Management in Greenville County May 30 th, 2007  Woolpert hired by County  Isotherms and Rainfall Analysis  Continue to use spreadsheet Greenville County

35 Stormwater Management in Greenville County May 30 th, 2007 Greenville County  Dry pond verification study

36 Stormwater Management in Greenville County May 30 th, 2007 Greenville County  VB GUI developed  Bioretention cell research begun  Multiple watersheds  Literature review −Swales & Engr. Devices

37 Stormwater Management in Greenville County May 30 th, 2007 Greenville County Sept  EPA BMP Design Manual EPA/600/R-04/

38 Stormwater Management in Greenville County May 30 th, 2007 Greenville County  Bioretention cell added and revised −Greenhouse study −Greenville Co. study  FC loading function

39 Stormwater Management in Greenville County May 30 th, 2007 Greenville County  Bioretention cell added and revised −Greenhouse study −Greenville Co. study  FC loading function

40 Stormwater Management in Greenville County May 30 th, 2007 Greenville County

41 Stormwater Management in Greenville County May 30 th, 2007 Greenville County  Sand filter and bioswale added  Conceptual algorithms developed for engr. devices  Conveyance routing algorithms −Pipe, Channel, Simple translation  Model presented to EPA Region 4  VB GUI revised to current layout −Distributed Jan 2007 to GC engineers

42 Stormwater Management in Greenville County May 30 th, 2007 Greenville County  Object oriented VB.net “Drag n Drop” version

43 Stormwater Management in Greenville County May 30 th, 2007 Ongoing Improvements  Technical Advisory Group −Barfield and Hayes −Dr. John Sansalone -Fla −Dr. Bob Pitt –Ala −Mike Borst – EPA-ORD −Mark Schlautman – Clemson −Khaled Gasem – Okla State  Enhanced Bioswale research with EPA-ORD, Edison, NJ  User’s Manual

44 Stormwater Management in Greenville County May 30 th, 2007 Summary of versions OCRM Spreadsheet VB.Net PollutantsSediments, Nutrients, Bacteria Watersheds1200+ BMPsWet/Dry Ponds, VFS Wet/Dry Ponds, VFS, Bioretention cells, Sand filter ConveyancesNone Pipes, channels, and translation only Isotherms & Rainfall Analysis SC CoastGreenville Co.

45 Stormwater Management in Greenville County May 30 th, 2007 Uses  BMP design for small to large developments projects  TMDL compliance  Antidegradation restrictions  Watershed master planning  LID design

46 Stormwater Management in Greenville County May 30 th, 2007 Future Steps  Bacteria growth function  Engineered device algorithms development  Bioswale algorithm revision  Conveyance design functionality  GIS/CAD interface  Optimization  Large scale watershed considerations  Performance enhancement and user support  Continue to use best science available

47 Questions?


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