20110311 hbam spsc outfall channel presentation


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Anne Arundel County Presentation on SPSC Outfall Channels

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20110311 hbam spsc outfall channel presentation

  1. 1. Overview of Watershed Assessment and Modeling Data (A i WMT i f ti )(Accessing WMT information) Hala Flores PE Richard FisherHala Flores, P.E Richard Fisher Rapid Stream Assessment Protocolsp Janis Markusic Christopher Victoria Overview of SPSC Design Guidelines and Calculator Hala Flores, P.E HBAM Meetingeet g February 28th, 2011 Ron Bowen, P.E.
  2. 2. Anne Arundel County Stormwater Management Practices and Procedures Manual __________________________________________________ Chapter 11 Appendices 11.6 11 3 Li k t i d /i f ti 11 3 8 D t t f P bli W k t h d 11.3. Links to required resources/information 11.3.8. Department of Public Works watershed management tool htt // i ld t / /http://gis-world.aacounty.org/wers/
  3. 3. Anne Arundel County Watershed Management ToolWatershed Management Tool (WMT)(WMT) Stream AssessmentStream Assessment -- Physical HabitatPhysical Habitat -- Biological ConditionsBiological Conditions -- MorphologyMorphology -- Problem Area InventoryProblem Area Inventory Erosion,Erosion, HeadcutHeadcut, Dumpsites, Deficient, Dumpsites, Deficient Buffers, Infrastructure Impacts.Buffers, Infrastructure Impacts. -- Stream Crossings (H&H)Stream Crossings (H&H)Stream Crossings (H&H)Stream Crossings (H&H) -- Landscape (Imperviousness)Landscape (Imperviousness)
  4. 4. 2 000 estimated2 000 estimated milesmiles Anne Arundel County 2,000 estimated2,000 estimated milesmiles ofof nonnon--tidal waterwaystidal waterways P i l (S d W l d )Perennial (Streams and Wetlands) Ephemeral and Intermittent Pond/Lake/Floodway Other
  5. 5. BIOLOGICAL CONDITIONS B hi I d f Bi iBenthic Index for Biotic Integrity (BIBI) Score Number of Samples - 376p - 5% - 23%Fair Good 23% - 49% Fair Poor - 23%Very Poor
  6. 6. DEGRADED MORPHOLOGY Example of F and G channels – Highly Instablep g y Erosion  ‐‐ Patuxent River Watershed Headcut  ‐‐ South River Watershed
  7. 7. Stream Reach Priority  for Restoration Overall Rating Best Condition Worst Condition
  8. 8. Anne Arundel County Watershed Management Tool (WMT)Watershed Management Tool (WMT) Restoration Indicators Preservation Indicators Analysis and ModelingAnalysis and Modeling --HydrologyHydrology(Runoff and Discharge)(Runoff and Discharge) -- Pollutant Load AnalysisPollutant Load Analysis -- Landscape AnalysisLandscape Analysis
  9. 9. Subwatershed  Priority y for Restoration Overall Rating Best Condition Worst Condition
  10. 10. Subwatershed  Priority fory Preservation Lowest Priority for Preservation Highest Priority for Preservation
  11. 11. WERS Mapping Application Tour
  12. 12. Stream Assessment Protocol: an overviewoverview Anne Arundel County Department of Public WorksDepartment of Public Works Bureau of Engineering Watershed, Ecosystem, and Restoration Services Ecological Assessment ProgramEcological Assessment Program
  13. 13. Introduction • Regulatory Triggers G l W h d Ch i i• General Watershed Characterization – Land Use and Imperviousness – Drainage Area and Bankfull Indicator Determination G l St Ch t i ti• General Stream Characterization – Rosgen Level II Classification (pebble count, slope determination, valley type, etc.) • Lateral Stability DeterminationLateral Stability Determination – BEHI and NBS Evaluation – Bank armoring and localized versus widespread issues • Vertical Stability DeterminationVertical Stability Determination – Incision Ratio – Headcuts, control points, depositional features • Overall Reach Stability Determinationy – Includes a variety of trend and reach-level evaluations
  14. 14. Regulatory TriggersRegulatory Triggers • The use of the Stream Assessment Protocol is triggered by a finding of an “i d f ll” i h f d i i if O b k Fl d“inadequate outfall” in the context of determining if Overbank Flood Protection is required due to the impact of a given development site. • Once such an “inadequate outfall” finding is made, a downstream analysis iis necessary. • This method is applied only to a “…clearly defined open channel…” (Section 7.2.2.D.II; Chapter 7, p. 7.4) • The assessment reach comprises the channel from “…the outfall(s) from the site and progress[es] to the Point(s) of Investigation (POI).” (Section 7.2, Chapter 7, p. 7.2) • See the Procedures and Practices Manual for details on what constitutes an adequate or inadequate outfall and on how to establish the POI.
  15. 15. This is a field-based assessment! You must leave the office to apply it correctly!
  16. 16. Watershed Characterization Standard Header Items •Watershed Date DrainageWatershed, Date, Drainage Area, etc. Watershed Characterization •Should be mostly an office exercise •Land use and land cover are the primary items to determine, both in the basin, and adjacent to the reach of interest •DA calculation needed for bankfull determinationbankfull determination •Significant land uses that may impact stream stability conditions
  17. 17. Stream Characterization and Classification •Rosgen Level II Classification is basicClassification is basic characterization •Not discussed in detail here •All standard work, all found in Rosgen (1996): Width, depth, slope, D50, sinuosity, W/D ratio, entrenchment, etc. •Bankfull channel dimensions using known regional relationships developed by others are necessary forothers are necessary for Rosgen classification
  18. 18. You can find these relationships within thewithin the document or in other references…
  19. 19. …and they are easily used in a spreadsheet to h h l h i icompute these channel characteristics.
  20. 20. Lateral Stability DeterminationDetermination •Lateral stability. What is it? Side to side movement of stream channel which is a function ofchannel, which is a function of two major influences: •A streambank’s characteristics that make it resistant to erosion •The work done on the bank of interest related to the hydraulic characteristics of the overall channel (Near Bank Stress) Done on dominant bank( ) •How are these two opposing forces evaluated? Using Rosgen’s BEHI and NBS ratings Done on dominant bank within the assessment reach. If two bank types are t d ll threpresented equally, the higher BEHI and/or NBS rating (i.e.—more unstable) is used.)
  21. 21. BEHI Forms Near Bank Stress Field Key
  22. 22. Vertical Stabilityy Determination •Primary determination using the Incision Ratiothe Incision Ratio •Also used presence of the following: •Head Cuts •Depositional Features •Bed Control •Taken together, these features i i i h i i lgive insight into vertical stability
  23. 23. Depositional Features Head CutsHead Cuts Grade Control
  24. 24. Overall Reach Stabilityy Determination •Stream Sensitivity, Sediment Supply, and Recovery Potentialy •From Rosgen (1996) •Evolution Stability Sequence •Evolution Stability Trend •Overall Reach StabilityOverall Reach Stability
  25. 25. Stream Evolution Scenarios (2 of 9 in SAP manual)
  26. 26. Final Steps • Using weight of evidence, a finding of either 1) localized or widespread i bili 2) bl di i iinstability or 2) stable conditions is made for the assessment reach • Report is produced for the assessment h h d ib h bilireach that describes the stability conditions observed • Photodocumentation is a required f hiaspect of this report
  27. 27. Links Guidance Documents: • Stream Assessment Protocols: http://www aacounty org/DPW/Watershed/DownstreamAdequacyProtocols cfmhttp://www.aacounty.org/DPW/Watershed/DownstreamAdequacyProtocols.cfm • Stormwater Practices and Procedures Manual: http://www.aacounty.org/PlanZone/Resources/Practices_Procedures_Manual.pdf GIS/M i Li kGIS/Mapping Links: • AA County Watershed Mapping Application: http://gis-world.aacounty.org/wers/ • GIS Hydro: http://www.gishydro.umd.edu/ Information Links • US Fish and Wildlife CBFO:US Fish and Wildlife CBFO: http://www.fws.gov/chesapeakebay/stream.html • DNR Rosgen Spreadsheets: http://www.dnr.state.oh.us/soilandwater/water/streammorphology/default/tabid/9188/Defaulhttp://www.dnr.state.oh.us/soilandwater/water/streammorphology/default/tabid/9188/Defaul t.aspx
  28. 28. SPSC – What are they? SPSC are open-channel conveyance structures that convert, through attenuation pools and a sand seepage filter s rface storm flo to shalloseepage filter, surface storm flow to shallow groundwater flow. Wetland Seepage System Perennial Application Step Pool Storm Conveyance Ephemeral Application
  29. 29. Types of BMPs Pipe Conveyance i i Receiving Stream Micro Practice (Off-line) Pipe Conveyance Receiving Stream Macro Practice (On-line) A shift in Paradigm Receiving SPSC Conveyance SPSC Integrated System Receiving Stream
  30. 30. A, ?? STEP POOL STORM CONVEYANCE FOR EPHEMERAL OUTFALLS B, 32% The physical characteristics of the SPSC channel are best characterized by the Rosgen A or B stream classification types, where “bedform occurs as a step/pool, cascading channel which often stores large amounts of sediment in the pools associated with debris dams” (Rosgen, 1996).
  32. 32. SPSC – Can be designed to provide: - Safe 100-year Conveyance - Attenuation - Energy DissipationEnergy Dissipation - Water Quality Treatment
  33. 33. Hard Engineering Solutions for conveyance Not so hard!Not so hard!
  34. 34. Expensive restorations that don’t work and don’t provide water quality benefits
  35. 35. Harvesting the taming powers of the floodplain Before Restoration – Rosgen G Channel Any size floodplain bench is better than a hardened wall After Restoration – Rosgen B Channel The larger and more accessible theThe larger and more accessible the floodplain is, the more sustainable the restoration
  36. 36. Hard Engineering Solutions for conveyance Not so hard!
  37. 37. Conventional upland BMPs do not necessarily  correlate with a stable downstream! Stormwater detention ponds are wet structures that are often used to capture and detain stormwater runoff from residential and Erosion and Headcut  Inventory o es de t a a d commercial areas. Impervious Area Draining to BMP Less than 20% 20%< and >50% More than 75% 50%< and >75%
  38. 38. Undesired Consequences of Peak Detention Potential Effect of Cumulative Detention Basins on Downstream Conditions • Longer duration of higher flows • Cumulative effect will increase peak discharge downstream g g
  39. 39. Stormwater Management Best Management Practices (BMPs)( ) SPSC Infiltration Conditional on underlying soil conditionsInfiltration Conditional on underlying soil conditions Filtration Sized for 100% CreditS ed o 00% C ed t Wetland Creation Seepage berm designWetland Creation Seepage berm design Wet Ponds Function of Seepage berm design Extended Detention Outflow is discharged as shallow groundwater seeps
  40. 40. Implementation of SPSC Systems 1- As an outfall or stream retrofit techniqueq 2- As mitigation for development2 As mitigation for development Structural BMP Or P t f th ESD T iPart of the ESD Train
  41. 41. Functional Components of Step Pool Storm Conveyance (SPSC) Functional Components of Step Pool Storm Conveyance (SPSC) Design Water Surface Riffle Boulder Pools Riffle Cobble Sand/Wood Chip Footer Boulders Pools = 0% Slope Geotextile
  42. 42. Other Geometric Configurations (Wetland Seepage)Other Geometric Configurations (Wetland Seepage)
  43. 43. Other Geometric Configurations (Wetland Seepage)Other Geometric Configurations (Wetland Seepage)
  44. 44. Mapping the SPSC Horizontal Alignment Difference in Elevation = 40 ft Straight Length = 100 ft           Slope = 40% Difference in Elevation = 40 ft, Cascade Heights = 25 ft Meandering Length = 220 ft           Overall Slope = 18% Length at 5% slope = 100‐150 ft
  45. 45. Mapping the SPSC Vertical Alignment In the event that the proposed SPSC connects to an incised downstream channel, the elevation of the floodplain p p , p terrace shall be used as the downstream elevation.  An in‐stream weir design with a top of weir elevation set at the  floodplain terrace is required at the tie‐in location. Notes and Preliminary Assumptions: Maximum slope = 5% Minimum length of pool = 12 ft Maximum length of riffle = 10 ft Depth of filter media is minimum 18 inches below the lowest structure L pool L Riffle Depth of pool is minimum 18 inches Un‐armored Pool side slopes shall be laid back at 3H:1V  Special attention to paid at the inflow and outflow tie in locations Silica Cobbles 1 ft (typ.) (12 ft min.)(10 ft max.) Boulders hf Typical (18 in. min.) In‐stream  Boulders In‐stream 100 – Year floodplain may  inundate last SPSC structure Sand/Wood Chip Mix d ( ffl )d ( l) df (riffle) Existing Ground Filter Fabric df (pool) min 18 inches Sand Mix “Sandbags from E&S  phase maybe left in place”
  46. 46. Mapping the SPSC Vertical Alignment ‐ Cascade and Weir boulders maybe placed at a maximum (1V:1H) slope ‐ Cascades shall not be more than 5 ft in height at any single location ‐ Cascades shall be followed by three consecutive pools Boulders Cascade  Max 10ft @ 50% Slope Pool #1 Pool #2 Pool #3 Silica Cobbles Boulders hf cascade (per design) hf (Typical) hf (Typical) Existing Ground Filter Fabric Sand/Wood Chip  Cascade Profile – Three Pools following Cascade Mix g
  47. 47. Design the typical cross‐section for the riffle/cascade Design Criteria:Design Criteria: ‐ Conveyance shall be designed to address the 100‐year Peak Discharge 1959, 2 3 2 22 2 Chow DW RadiusHydraulic SolutionalMathematic WD Area = = , 83 22 DW y + Q =        (1.49/n) (A) (Rh)2/3 (S)1/2 Must be > or =  Q 100 W (8 ft min.) D Where: Q        = 100 year ultimate flow (cfs) 1.49 = conversion factor n = Manning’s n, determined by USDA, 2006 equation A = cross‐section area of a riffle channel, which for a parabola = 2/3(W)(D), Riffle Section through Boulder 2 x d50 n = D1/6/ (21.6 log (D/d50)+14),  (USDA, 2006). A cross section area of a riffle channel, which for a parabola   2/3(W)(D),  where W is top constructed width (ft) and D is the constructed depth (ft) Rh = hydraulic radius (ft), calculated using Chow 1959 relationship for parabolas S = average slope over entire length of project (ft/ft) V =  velocity in the riffle channel (ft/sec), V = Q/A Riffle Section through Cobble ( g ( ) ) ( ) Where: n = Manning’s n, use 0.05 for cascades. D = depth of water in the riffle channel associated with unmanaged  100‐year Q design, ft.,  d50 = cobble size, ft 
  48. 48. Design the typical cross‐section for the riffle/cascade Checking for Super Critical Flow:g p gD V Fr =‐ Froude Number exceeding 1 indicates the flow is supercritical ‐ Froude Number = 1 indicates that the flow is critical ‐ Froude Number less than 1 indicates the flow is subcritical To reduce the Froude number 1‐ Widen channel 2‐ Decrease Slope
  49. 49. Checking/Sizing the Riffle Cobbles Use a trial D0 = 6 inches Actual Velocity  Must be < Maximum Allowable Velocity ( ) FormulaIsbashDgCVelocityAllowableMaximum w ws 5.0 0 5.0 2 ×⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − ×××= γ γγ 0 y y Where: C            = 0.86 for prevailing supercritical flow  1.2 for prevailing subcritical flow g             = 32.2 ft/sec2 γ stone density (lb/ft3)γs                  = stone density (lb/ft3) Γw               = water density (lb/ft3) D50             = cobble stone diameter (ft) NRCS 2007
  50. 50. Designing the Rock Weir and pool ‐The Rock Weir shall be placed in a curvilinear manner to deflect the flow to the center of the pool A A’ Ineffective Flow  Areas Flow B B’ Flow
  51. 51. Additional Stability Features at the Transition from Riffle Section  to Pool Section Additional Stability Features at the Transition from Riffle Section  to Pool Sectionto Pool Sectionto Pool Section
  52. 52. The pretreatment, recharge, and water quality sizing criteria presented in the Anne Arundel C SPSC id li f ll l l h S f M l d’ i i f i l Designing the water quality sand filter system County SPSC guidelines follow closely the State of Maryland’s criteria for a typical stormwater filtering device. 2000, MDECriteriaSizingFiltering dxWQ A fv f = 2000, )( MDECriteriaSizingFiltering tdhK A fff f + 2 x d W (8 ft min.) D hf (18 inch min.) df (riffle) Sand/Woodchip Mix 2 x d50 Df  (18 in min.) Wsand (2 ft min.) Sand/Woodchip Mix Pool Cross Section df (pool) 18 inches min. Riffle Weir Cross Section through Cobble sand ( ) Silica Cobbles L pool (10 ft min.)(10 ft max.) Boulders hf Typical L Riffle In‐stream Boulders Sand/Wood Chip Mix 1 ft (typ.) hf Typical (18 in. min.) In‐stream 100 – Year floodplain may  inundate last SPSC structure Typical Profile – Alternating Pools and Riffles df (riffle) Existing Ground Filter Fabric df (pool) min 18 inches Sand Mix “Sandbags from E&S  phase maybe left in place” Footer boulder shall extend 6 inches below the lowest  point in the excavated pool
  53. 53. Checking Storage/Quantity Management Th d SPSC ill ti f k t flThe proposed SPSC will satisfy peak management flow  requirements if two conditions are met: a‐ First, adequate storage volume within the pools  and sand/woodchip voids shall be provided to meet  the required storage volume/quantity managementthe required storage volume/quantity management  for the project  b Second it must be demonstrated that the designb‐ Second, it must be demonstrated that the design  renders the hydraulic power equivalent to the  predevelopment/desired hydraulic power through  the proposed energy dissipation pools.
  54. 54. Checking Storage/Quantity Management a‐ First, adequate storage volume within the pools and , q g p sand/woodchip voids shall be provided to meet the required  storage volume/quantity management for the project  Vin = Qpost /Ain Storage Volume in Pools Design Water Surface Elevation Din Dout2 Dout3 Dout1 Driffle L out3 Df Storage Volume in Voids Df x L x Wsand x Porosity Sand/Woodchip mix Porosity = 30% Df (Average filter bed area= (Driifle +Dpool)/2
  55. 55. Checking Storage/Quantity Management b‐ Second, it must be demonstrated that the design renders the , g hydraulic power equivalent to the predevelopment/desired  hydraulic power through the proposed energy dissipation pools. E Di i i (Potential + Kinetic + Static) Energies SPSC entrance =  (Potential + Kinetic + Static) Energies SPSC outlet + Head loss within SPSCsystem ‐ Energy Dissipation = Post  Development  Pre Development  Energy p Energy
  56. 56. SPSC Design Guidelines i h kliDesign Checklist Inspection Checklist
  57. 57. SPSC – FAQ Can SPSC systems be used to provide water quality credit? SPSC systems can be designed as micro or macro systems.  When designed as macro  systems, they are treated as structural practices and can provide water quality via  filtration above the ESD to the MEP criteria When designed as a micro system theyfiltration above the ESD to the MEP criteria.  When designed as a micro system, they  behave as an ESD filtering device. Can SPSC systems be used to provide quantity management?Can SPSC systems be used to provide quantity management? SPSC systems will provide runoff attenuation via storage within the pools and voids  within the substrate.   HOWEVER……..
  58. 58. SPSC – FAQ What type of maintenance access is required for SPSC  systems? The intend behind the vehicular access requirement is to allow the County access toThe intend behind the vehicular access requirement is to allow the County access to  public structures for routine maintenance and in the event of structural failure to  perform necessary fixes.    • Probability of future utilization of access road‐ Delicate balance • Considering relaxing current policy of requiring vehicular access to all weirs to  requiring access to the any point throughout SPSC and existence of sufficient public  easement around the system to allow the County future access if needed.
  59. 59. SPSC Design Calculator
  60. 60. Innovative Outfall &Innovative Outfall & Stream RestorationStream Restoration Riva 400Riva 400 -- Constructed in Dec 2009Constructed in Dec 2009 Techniques:Techniques: Step Pool StormStep Pool Stormpp Conveyance (SPSC)Conveyance (SPSC) Riva 400 Before Restoration (2004)Riva 400 Before Restoration (2004) ConveyanceConveyance StabilityStability HabitatHabitatHabitatHabitat Water QualityWater Quality 61
  61. 61. Central Sanitation FacilityCentral Sanitation Facility S h G l R iS h G l R i Before RestorationBefore Restoration Stretch Goal RequirementsStretch Goal Requirements Public ProjectPublic Project Drainage Area = 94 AcresDrainage Area = 94 Acres Impervious Treated = 23 AcresImpervious Treated = 23 AcresImpervious Treated 23 AcresImpervious Treated 23 Acres Total Project cost = $700,000Total Project cost = $700,000 After RestorationAfter Restoration Length of Stream Restored = 0.5 milesLength of Stream Restored = 0.5 miles Acres of Wetlands created =Acres of Wetlands created = Project equivalent to 13,650 rainProject equivalent to 13,650 rainj q ,j q , barrels at $1,365,000barrels at $1,365,000 or 190 bioretention facilities, at theor 190 bioretention facilities, at the cost of $20 000/each or $3 800 000cost of $20 000/each or $3 800 000 62 cost of $20,000/each or $3,800,000cost of $20,000/each or $3,800,000
  62. 62. Before RestorationBefore Restoration Saefern Outfall RestorationSaefern Outfall Restoration Steep Slope ApplicationSteep Slope Applicationp p ppp p pp Community ProjectCommunity Project After RestorationAfter Restoration After RestorationAfter RestorationAfter RestorationAfter Restoration 63
  63. 63. Construction Access = Substrate Filter Fill
  64. 64. SeepageSeepage BermsBermsConstruction of the substrate filter fill (Sand compost mix)
  65. 65. Immediately after construction
  66. 66. One year after construction
  67. 67. Six Year Evolution to Forest Ecosystem
  68. 68. Contact Information Janis Markusic Christopher Victoria Program Manager Environmental Scientist pwmark02@aacounty.org pwvict16@aacounty.org Anne Arundel County Department of Public Works Watershed, Ecosystem, and Restoration Services Ecological Assessment ProgramEcological Assessment Program 2662 Riva Road Annapolis, Maryland 21401 410.222.4240410.222.4240
  69. 69. Contact Information Hala Flores, P.E. Richard Fisher Program Manager Environmental Scientist Hala.flores@aacounty.org rfisher@aacounty.org Anne Arundel County Department of Public Works Watershed, Ecosystem, and Restoration Services Ecological Assessment ProgramEcological Assessment Program 2662 Riva Road Annapolis, Maryland 21401 410.222.4240410.222.4240