Moving the Metrics: Better Ways to Determine LID Effectiveness

Transcription

1 National LID Conference Philadelphia, PA 26Sep11 Moving the Metrics: Better Ways to Determine LID Effectiveness Bill Hunt Associate Professor & Extension Specialist North Carolina State University

2 About LID MARC Low Impact Development Mid Atlantic Research Consortium

3 About LID MARC Allen Davis University of Maryland Bill Hunt North Carolina State University Robert Traver Villanova University

4 About LID MARC Bridge between lab, field depth and field breadth research Bring information to practitioners and researchers Workshops Journal Publications

5 Moving Metrics: Outline Hydrologic Metrics Is all outflow equal? Streams are our friends! Water Quality Listen to Bugs It s all SCMs can do

6 Goals of Low Impact Development Reduce impervious surfaces Retain runoff on site Promoting infiltration and evapotranspiration Replicating pre development hydrologic conditions as closely as possible Davis, 2005

7 The Inspiration!

8 HYDROLOGIC CYCLE UNDER NATURAL CONDITIONS

9 Hursh and Brater, 1941

10 Bioretention is a key component of LID: it decreases peak flow rates and volumes, promotes infiltration and ET and improves water quality. Overflow Davis, 2008; Davis, 2005; Hunt et al., 2006; Li et al., 2009 Evapotranspiration Inflow Outflow Exfiltration

11 Bioretention Hydrology Inflow Outflow Discharge (L/s) (Hunt et al., 2008) Date/Time

12 ? =? BIORETENTION STREAMFLOW

13 Bioretention Study Sites

14 Median Flow Rates per Watershed HA DeBusk et al., JHE, March 2011

15 Confidence Intervals: Percent of Total Volume Passed DeBusk et al., JHE, March 2011

16 Current Evaluation BIORETENTION HYDROLOGY: Outflow (Drainage) Infiltration ET 50% 40% 10% COWEETA (PRE-DEV.) HYDROLOGY: Runoff 5% Evapotranspiration 50% Infiltration 45% Shallow Interflow 43% Deep Seepage 2%

17 Is the hydrologic benefit of bioretention being underestimated by current performance evaluations? Inflow Outflow Discharge (L/s) Shallow interflow equivalent? Date/Time

18 Metric Message Should we consider adding a 4 th Hydrologic Fate: Shallow Interflow (Equivalent) Discharge

19 Stormwater Control Measures Current SCM design standards: 1. Peak flow attenuation 2. Volume reduction 3. Enhancement of water quality Do NOT consider erosional processes of receiving streams

20 Impact of SCMs on Streams Less than 1 year Storm: 31 mm fell within 8 Hours Art Museum 36% impervious Art Museum in natural state Art Museum (5% impervious) with wet pond at outlet Critical Discharge Tillinghast et al. J.Hydrology. In Press

21 Procedure: Reference Streams Reference streams: Parts of a stream that have developed a stable dimension, pattern, and profile Used in stream restoration projects to restore disturbed streams to natural conditions and create state of dynamic equilibrium (Rosgen 1996)

22 Erosional Standards Annual Erosion Hours ~Annual Allowable Volume of Eroded Bedload

23 Long Term Analysis needs (PC)SWMM Used to model urbanized watersheds Spatially distributed model Model LID practices and wet ponds Long term continuous simulations Non linear reservoir routing

24 Procedure: Reference Streams

25 Erosional Standards for Piedmont NC Unit Critical Discharge Equation: Q c =0.0035(d 65 ) Annual Allowable Erosional Hours Standard: Log(AAEH)= 1.26Log(d 65 )+1.21 Annual Allowable Volume of Eroded Sediment: Log(AV)= 0.64(Q c ) 1.52 Tillinghast et al. J.Hydrology. In Press

26 House Creek: Art Museum

27 Methods: Calibrating Data

28 Results: Small Catchment Example: Art Museum w/ Wet Pond Modeled Erosional Hours (hrs/ha/yr) Empirical Allowable Erosional Hours (hrs/ha/yr) Modeled Volume Eroded Sediment (m 3 /m/ha/yr) Empirical Allowable Volume Eroded Sediment (m 3 /m/ha/yr) Location Institutional (Wet Pond) Institutional (No SCM) Institutional (Natural) Tillinghast et al. J.Hydrology. In Press

29 Metric Message We can and need to consider Stream Stability in LID (& SCM) design Stream/ SCM discharge standards will, though, be quite regionally specific

30 Other Hydrologic Metrics Calculate the Sponge Effect (Eric Strecker and Others) How much water does a target landscape hold until it begins to leak?

31 A Bridge Possibility: CN Davis et al., JHE, In Press

32 Ritter Field Stormwater Wetland Constructed 2007 Monitored June 2007 May 2008 Plant Establishment was slow (drought) Watershed Treated: 115 ac Wetland Size: 0.34 ac Watershed CN: 55 Lenhart and Hunt, 2011

33 From a Percent Removal Perspective TN TP TSS 51 % 0% 30% However, when comparing EFFLUENT concentrations from the wetland to those in the nearby Trent River Lenhart & Hunt. JEE. Feb 2011

34 Three Nearby Locations River Bend

35 Effluent Concentrations v. Ambient Water Quality (in mg/l) TN TP Ritter Field J J J Lenhart & Hunt. JEE. Feb 2011

36 The Concept Should BMP Performance be tied back to the (good) Health of Receiving Water Bodies? Dove Imaging

37 Rating Description of Benthos Sample Organisms by Scientific Name Excellent Very sensitive Ephemera Guttulata (mayfly), Litobrancha recurvata (mayfly) Good Sensitive Drunella allegheniensis (mayfly), Rhyacophila fuscula (caddisfly Good Fair Semi tolerant Amnicola (snail), Elliptio complanata (mussel) Fair Tolerant Cambarus (crayfish), Crangonyx (crustacean) Poor Very tolerant Enchytraeidae (worm), Limnodrilus cervix (worm) www2.mdbc.gov.au/.../invertebrates/mayfly.htm 5. jimswan.com/111/aquaticinsects.htm

38 Eco-regions

39 Piedmont McNett et al. JEE. May 2010

40 Metric Message Can we establish (as a starting point) naturebased effluent concentrations that seem reasonable for our LID practices to meet?

41 GrahamN GrahamS L1 CP SS HMBC RMgrass L2 Excellent TN Water Quality Standard Good TN Water Quality Standard Fair Good Effluent TN Concentration Probability Exceedance Plot TN Comparison plots for 8 different bioretention cells in Mid-Atlantic USA Effluent TN concentrations (mg/l) Exceedance Probability McNett et al. JEE. Sept

42 Effluent TP concentration Exceedance Probability Plot Graham N 1.4 Graham S L1 CP SS HMBC RMgrass L2 Excellent TP Water Quality Standard Good TP Water Quality Standard Fair TP Comparison plots for 8 different bioretention cells in Mid-Atlantic USA Effluent TP concentration, by site (mg/l) Exceedance Probability McNett et al. JEE. Sept 2011

43 Comparing SCM Effluent Concentrations to those of Reference Wetland Moore et al. (2011) UNCA DB BE EB CC CMS RB REF

44 Biological Systems Produce Healthy Concentrations of N Organic N Concentrations SWL + Reference Moore et al. Ecol.Eng. 2011

45 Metrics Message Practices (particularly those dominated by biological processes) may be bound to certain levels of efficiency Does not mean that concentrations can t be improved upon with human manipulation. Baseline effluent concentrations may be an (not the) appropriate measure

46 An Example of Linking Metrics Jordan Lake Watershed Central NC

47 BMP Efficiency Metric: Effluent Median Concentration Only applies to treated runoff Volume reduction varies by region Percent removal based on mass inflow concentration concentration determined by Simple Method OVERFLOW composite concentration INFLOW SCM OUTFLOW TREATED ET/EXFILTR. median effluent concentration

48 BMPs TN EMC TP EMC (mg/l) (mg/l) Bioretention Dry Detention Pond Grassed Swale Green Roof Level Spreader, Filter Strip Permeable Pavement Sand Filter Water Harvesting Wet Detention Pond Wetland

49 Volume Reductions (Piedmont) Treated Outflow (dec) Overflow (dec) Total Volume Reduction Bioretention Dry Detention Pond Grassed Swale Green Roof Level Spreader, Filter Strip Permeable Pavement Sand Filter Wet Detention Pond Wetland

50 Developing a carbon footprint for SCMs Executive Order 13514: It is therefore the policy of the United States that Federal agencies shall increase energy efficiency; measure, report, and reduce their greenhouse gas emissions from direct and indirect activities; conserve and protect water resources through efficiency, reuse, and stormwater management

51 Carbon footprint of SCMs Conceptual model Raw material extraction Transportation to production facilities Transport of equipment and materials to site material manufacture Embodied carbon of construction materials + + Fuel use by equipment during construction Construction Carbon Footprint C Footprint = Embodied C + Construction of SCMs + (Maintenance Sequestration) xtime + Carbon sequestration by SCM vegetation Maintenance Fuel use by equipment during maintenance Embodied energy of maintenance materials Transport of equipment and materials to site

52 Results Embodied& Construction C Initial C footprint (kg C m 2 ) Construction Equipment Construction Transport Embodied C CSW WP LS VFS BRC PP GR RWH SF Moore & Hunt, ES&T, in prep

53 Results Maintenance & Sequestration SCM Type Maintenance emissions (g C m 2 yr 1 ) C sequestration (kg C m 2 yr 1 ) Net (kg C m 2 yr 1 ) Green roof a 0 Perm. Pavement Sand filter Bioretention cell b 0.06 b Rainwater harvesting Wetland Level spreader VFS Pond a green roof sequestration rate sustained 2 years (Getter & Rowe, 2009) b sequestration rate variable; 0.09 kg C m 2 yr 1 is average Moore & Hunt, ES&T, in prep

54 Results Net footprint with time Moore & Hunt, ES&T, in prep

55 Metrics Message To sell Green Infrastructure, we may appeal to dimensions beyond h2o. Ecosystem Services Vs.

56 Summary Evaluative Metrics are changing Near & Long Term Hydrology: How do we break down outflow rates & volumes? Water Quality: Should we set target effluent concentrations (in addition to loads)? Beyond Water? Implications for how we select and assess LID measures

57 Questions?

58 Procedure: Reference Streams

59 Unit Critical Discharges (L/s/hectare) y = x R² = 0.86 Unit Critical Discharge Qτ c = (1/n)A*R γ R c S 2/3 c S 1/ d 65 (mm)

60 Characterizing Stream Bed Sediment Bed Soil Particle Size

61 τ crit (kpa) Results: Unit Critical Discharge % of d 85 represented sub bankfull flows 1:1 Line % of of d d below 0.1 L/s/ha d50 d60 d65 d75 d τ bkf (kpa)

62 Unit Critical Discharge: For Model Unit Critical Discharges (L/s/hectare) y = x R² = d 65 (mm)

63 Erosional Standards Annual Erosion Hours ~Annual Allowable Volume of Eroded Bedload

64 Results: Annual Allowable Erosional Log(AAEH) Hours Log(AAEH) = 1.26Log(d 65 ) R 2 = Log(d 65 )

65 Results: Annual Allowable Volume of Eroded Bedload Log(AV) Log(AV) = 0.64 (Q c ) 1.52 R 2 = Unit Critical Discharge (L/s/ha)

66 Results: Erosional Standards Unit Critical Discharge Equation: Q c =0.0035(d 65 ) Annual Allowable Erosional Hours Standard: Log(AAEH)= 1.26Log(d 65 )+1.21 Annual Allowable Volume of Eroded Sediment: Log(AV)= 0.64(Q c ) 1.52

67 House Creek: Art Museum

68 Methods: Calibrating Data

69 Results: Small Catchment Example: Art Museum w/ Wet Pond Modeled Erosional Hours (hrs/ha/yr) Empirical Allowable Erosional Hours (hrs/ha/yr) Modeled Volume Eroded Sediment (m 3 /m/ha/yr) Empirical Allowable Volume Eroded Sediment (m 3 /m/ha/yr) Location Institutional (Wet Pond) Institutional (No SCM) Institutional (Natural)

70 Larger Catchment: Tanyard Branch

71 White = Residential Black = Downtown Blue = UNC Campus

72 Results: Erosional Standards Log(AAEH) Log(AV) Qd c 65 = (mm) (d = 0.64(Q = (d 65 ) mm c ) ) +1.21

73 Conclusions Current SCM design standards fall short of protecting stream geomorphic stability That is, they do not account for stream stability! LID/WSUD practices with a wet pond maximized storage and infiltration within watershed Wet ponds alone extended erosional hours but decreased volume of eroded bedload BUT Highly impervious watershed was incapable of meeting strict stream erosion metrics

74 Future Work Incipient motion analysis with urban reference streams Apply unit critical discharge model, erosional standards, and alternative outlet structure to multiple, diverse watersheds Analyze impact of time

75 Questions?

76 Outline Background and Research Objective SCM Design Standards to Limit Stream Erosion for Piedmont North Carolina Increasing Stream Geomorphic Stability Using LID Practices and/or Wet Ponds in Chapel Hill Cost Benefit Analysis Summary and Final Recommendations

77 Methods: Gathering Data

78 Pond (full or under sized)

79 Residential Practices

80 Campus + Downtown

81

82 Results: Alternative Outlet Overflow Weir Structure Overflow Weir 0.48 m 1.52 m m 0.31 m 1.52 m Modeled erosional hours from 19.6 to 15.4 hrs/ha/yr 1.52 m cm Orifice 1.22 m 25.4 cm Orifice cm Orifice Modeled volume of eroded sediment from 0.06 to 0.07 m 3 /m/ha/yr Current Design Alternate Design

83 Outline Background and Research Objective SCM Design Standards to Limit Stream Erosion for Piedmont North Carolina Increasing Stream Geomorphic Stability Using LID Practices and/or Wet Ponds in Chapel Hill Cost Benefit Analysis Summary and Final Recommendations

84 Cost: Cost Benefit Analysis Capital cost (materials, construction, removal sewer/water lines, acquiring necessary residential land, etc.) Yearly maintenance Stream restoration Stream compensatory mitigation Benefits: Nutrient reduction Flooding Ecosystem services

85 Results: Cost Inflation rate: 2.46% Life Span: 30 years

86 Under Sized Wet Pond Land area = 0.3 ha Sewer Lines

87 Full Sized Wet Pond Necessary Land area = 0.7 ha

88 Results: Nutrient Reduction Reduction in annual nitrogen and phosphorous loads from constructing LID practices and/or wet ponds (potential cost paid by Town of Chapel Hill due to nitrogen and phosphorous exceedences in ()

89 Results: Ecological Benefits

90 Results: Flooding Storm Event As-Is Restored Channel Under-Sized Wet Pond Required Sized Wet Pond 100-year, 24-hour Yes Yes Yes 50-year, 24-hour Yes Yes Yes 25-year, 24-hour Yes Yes No 10-year, 24-hour Yes Yes No 5-year, 24-hour Yes No No 2-year, 24-hour Yes No No 1-year, 24-hour No No No

91 Conclusion Higher geomorphic stability in stream, the higher cost of project Under sized wet pond provided minimal mitigation in terms of eroded sediment and nitrogen and phosphorous reduction Unless full sized wet pond chosen, need additional nitrogen removal

92 Outline Background and Research Objective SCM Design Standards to Limit Stream Erosion for Piedmont North Carolina Increasing Stream Geomorphic Stability Using LID Practices and/or Wet Ponds in Chapel Hill Cost Benefit Analysis Summary and Final Recommendations

93 Conclusions SCM design standards need to consider stream erosional processes Developed Q c, AAEH, and AV standards can be used in urbanized watersheds LID practices with wet ponds and alternate outlet structure increased stream stability Increased geomorphic stability of streams = higher cost of projects

94 Acknowledgements Dr. William Hunt (Chair) Dr. Gregory Jennings (Co Chair) Dr. Sankar Arumugam (Committee) NCDENR Patricia D Arconte (Town of Chapel Hill) Jon Hathaway Aaron Poresky (Geosyntec) Shawn Kennedy Kathy DeBusk Ryan Winston Michael Schaffer Mathew Webb Stacy Luell

95 Questions?

96 Under Sized Wet Pond

97 Full Sized Wet Pond