Alluvial Bar Morphology and Dynamics in the Middle Rio Grande: Application to Habitat Restoration for the Rio Grande Silvery Minnow

Transcription

1 Alluvial Bar Morphology and Dynamics in the Middle Rio Grande: Application to Habitat Restoration for the Rio Grande Silvery Minnow Mike Harvey Mussetter Engineering, Inc.

2 WORK CONDUCTED FOR: New Mexico Interstate Stream Commission Middle Rio Grande ESA Collaborative Program

3 WHAT IS A BAR?? Discrete alluvial feature formed by deposition and modified by erosion Can be mid-channel or bank-attached Can be subaerial or subaqueous Can be stationary or mobile Can be vegetated or unvegetated

4 PROJECT OBJECTIVES Evaluate bar changes over time in response to changes in flow, sediment supply and channel morphology Develop a bar classification Relate fluvial processes to bar types Apply results to river/habitat restoration

5 9 STUDY SITES MEI

6 MEI

7 Modified Braiding Index (Germanoski,, 1989) 2( L ) = BraidBar MBI + L Channel L n bars Channel

8 EXPECTED MBI RESPONSES (Germanoski and Schumm,, 1993; Germanoski and Harvey, 1993) If D 50 increases, and there is sediment supply: > MBI If D 50 increases, and there is no sediment supply: < MBI If the bed aggrades: > MBI If the bed degrades: < MBI

9 Pena Blanca Central Avenue Modified Braid Bar Index Modified Braid Bar Index Bar Index Alternate Bar Index Active Channel Width Average Channel Width (ft) Bar Index Alternate Bar Index Active Channel Width Average Channel Width (ft) Year Year Bernardo Bar Index Modified Braid Bar Index Alternate Bar Index Active Channel Width Average Channel Width (ft) Year 0

10 Escondida Modified Braid Bar Index Alternate Bar Index Active Channel Width Bar Index Average Channel Width (ft) Year 0 Bosque del Apache San Marcial Modified Braid Bar Index Alternate Bar Index Active Channel Width Modified Braid Bar Index Alternate Bar Index Active Channel Width 200 Bar Index Average Channel Width (ft) Bar Index Average Channel Width (ft) Year Year

11 Hierarchical Bar Classification for the Middle Rio Grande Bar Type Location Elevation Subaqueous or Subaerial Perennial Vegetation Linguoid Mid-channel Bed Subaqueous No Braid Mid-channel Level-1,2 Subaerial No Alternate Bank-attached Level-1 Subaerial No Mid-channel Mid-channel Level-1,2 Subaerial Yes Bank-attached Bank-attached Level-1,2 Subaerial Yes MEI

12 Linguoid bar

13 L-1 braid bars

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16 L-1 bank-attached bar L-2 braid bar mud drape L-1 braid bar

17 L-1 mid-channel bar L-2 braid bar L-1 braid bar Linguoid bar

18 L-2 mid-channel bar L-2 braid bar L-1 mid-channel bar

19 L-2 mid-channel bar

20 L-2 bank-attached bar L-1 bank-attached bar

21 HYDRAULIC ANALYSIS One-dimensional HEC-RAS models Fixed-bed analysis Calibrated to gauged flow at time of survey and 2005 peak flow (Tetra Tech. (2005)

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23 Central Site Bar Inundation Analysis % 5-yr Discharge (cfs) % 95% 98% Linguoid Bar Mean Inundation Discharge Minimum Inundation Discharge Maximum Inundation Discharge Mean Channel Capacity <1.01-yr 17% 47% 91% 1.05-yr Level-1 Braid Bar <1.01-yr <1.01-yr 16% 29% 51% Alternate Bar 1.1-yr <1.01-yr <1.01-yr 12% 7% 21% 1.4-yr 1.1-yr 1.03-yr Level-2 Braid Bar 5% 1% 8% Bar Feature 2.7-yr 1.6-yr 1.4-yr Level-1 Mid- Channel Bar 4% 1% 7% 2.7-yr 1.7-yr 1.4-yr Level-1 Bank- Attached Bar 1% 6% 2.9-yr 1.5-yr Level-2 Mid- Channel Bar 4% 1% 6% Mean-daily exceedance percent and peak flood return interval of inudation discharge show n next to plotted value. 2.9-yr 1.9-yr 1.5-yr Level-2 Bank- Attached Bar

24 BAR INUNDATION FREQUENCY & DURATION Table ES-1. Summary of frequency and duration of inundation of the classified bar types at sites without excessive aggradation or degradation.* Bar Type Inundation Recurrence Interval Days per Year of Inundation Percent of Year Inundated Level 1 braid bars < 1 year % Alternate bars < 1 year % Level 2 braid bars < 1 year 146 <40% Level 1 mid-channel bars 1.5 years 90 25% Level 1 bank-attached bars 1.5 years 90 25% Level 2 mid-channel bars 2 years 36 <10% Level 2 bank-attached bars 2 years 36 <10% *excluding the Pena Blanca, Bernalillo, Escondida and San Marcial sites.

25 BARS AND SHEAR STRESS Table ES-2: Comparison of maximum in-channel shear stresses to the prevalence of bars in the sand-bed sites. Maximum In- Site Names Channel Shear Stresses Prevalence of Active Bars (lb/ft 2 ) Central Avenue <0.1 moderate to high number of active bars Bosque del Apache, San Marcial 0.1 high number of active bars Bernardo, La Joya, Lemitar active bars are present Belen 0.2 moderate number of active bars Escondida 0.3 virtually no active bars

26 BARS AND VEGETATION Shear stress limit for vegetation establishment ~ < 1 psf Shear stress limit for vegetation removal ~ > 6 psf

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28 Central Site Cross Section 2 Ground Elevation Lingouid Bar L1 Braid Bar L2 Braid Bar L1 Mid-ch Bar Computed Water- Surface Elevation Peak Exceedance Percent yr 50-yr 25-yr 10-yr Mean-Daily Duration Peak Frequency Shear Stress 7,600 cfs 5-yr 4950 Elevation (ft) ,410 cfs 4,450 cfs 3,490 cfs 2-yr 1.5-yr ,110 cfs ,055 cfs 737 cfs 329 cfs Station (ft) Shear Stress (lb/ft2) Number of Days (Mean-Daily Duration)

29 BARS AND DEPOSITION Based on surveys of L1 and L2 bars in Albuquerque Reach, pre- and post high flows Comparison based on 0.5 ft contourinterval topographic mapping

30 POST-HIGH FLOW SEDIMENT DEPOSITION 2005 L1

31 L1 L2 L2 L1 Upstream Bar High Flow Downstream Bar High Flow L1 Upstream Bar Low Flow

32 BARS AND DEGRADATION Degradation causes hydrologic abandonment of bars If restoration is being considered is the bed currently stable? If degradation continues, restoration will be compromised

33 Abandoned L-2 mid-channel bar

34 Bernalillo Site Bar Inundation Analysis Mean Inundation Discharge Minimum Inundation Discharge Maximum Inundation Discharge Mean Channel Capacity 0% 100-yr Discharge (cfs) No Linguoid Bars Identified in Study Reach Linguoid Bar 32% 32% 33% Level-1 Braid Bar <1.01-yr 11% 0% 31% Alternate Bar 4.4-yr 1.2-yr <1.01-yr 6% 0% 20% 4.6-yr 1.6-yr 1.03-yr Level-2 Braid Bar 0% 0% 9% 8.6-yr 3.6-yr 1.2-yr Level-1 Mid- Channel Bar No Level-1 Bank-Attached Bars Identified in Study Reach Level-1 Bank- Attached Bar 0% 0% 8% 10.1-yr 4.2-yr 1.3-yr Level-2 Mid- Channel Bar 0% 4% Mean-daily exceedance percent and peak flood return interval of inudation discharge show n next to plotted value yr 1.8-yr Level-2 Bank- Attached Bar Bar Feature

35 Bernalillo Site Cross Section 10 Peak Exceedance Percent Mean-Daily Duration Peak Frequency Shear Stress ,940 cfs 7,600 cfs 100-yr 50-yr 25-yr 10-yr 5-yr Elevation (ft) ,410 cfs 4,450 cfs 3,490 cfs 2-yr 1.5-yr Ground Elevation L1 Braid Bar Alternate Bar L2 Braid Bar L1 Bank-att Bar L2 Mid-ch Bar L2 Bank-att Bar Computed Water- Surface Elevation 2,110 cfs 1,055 cfs 882 cfs 737 cfs Shear Stress (lb/ft2) Station (ft) Number of Days (Mean-Daily Duration)

36 2 Bernalillo Site Reach Averaged Hydraulics, D50=37 mm (WC4) XS8 Hydraulics, D50=37 mm (WC4) Dimensionless Grain Shear RI (years) Discharge (cfs)

37 CONCLUSIONS Bar indices reflect changes in flow, sediment supply and channel morphology Bar classification is a communication tool, and provides first-cut hydraulic assessments

38 CONCLUSIONS Active braid bars require average shear stresses < 0.2 psf Inundation of bars leads to vertical growth and reduced frequency and duration of inundation Degradation will adversely affect restoration efforts, so vertical stability must be assessed

39 APPLICATION TO RESTORATION

40 Bridge Blvd.

41 RIO GRANDE SILVERY MINNOW TARGETED LIFE STAGES: -EGGS - LARVAE - JUVENILES PHYSICAL NEEDS -LOW VELOCITY -SHALLOW DEPTH BIOLOGICAL TARGET 25 DAYS INUNDATION (~ 7 % EXCEEDENCE) POST-COCHITI ( ) Flow Duration Curve: ~ 4000 CFS

42 10,000 1,000 Rio Grande at Albuquerque, NM (Central Ave.) USGS Gage no Flow Duration Curves Dry Normal Wet Discharge (cfs) day Class Exceedance Discharge (cfs) Dry 1426 Normal 3493 Wet Day Exceedance Percent of Time Equaled or Exceeded

43 Central Avenue Site (Section 13) Discharge (cfs) Water-Surface Elevation (ft) 5600 cfs (Wet 25-day Exceedence) 1430 cfs (Dry 25-day Exceedence) 3500 cfs (Normal 25-day Exceedence)

44 Bridge Blvd.

45 Rio Grande Phase II SDC I-40 PDN NDC Note: Areas of inundation represent habitat increases at discharges greater than 1,000 cfs Area of Inundation (acres) cfs 3500 cfs 5600 cfs >6500 cfs Discharge (cfs)

46 Rio Grande Phase II SDC I-40 PDN NDC Note: Areas of inundation represent habitat increases at discharges greater than 1,000 cfs Area of Inundation (acres) / Channel Mile cfs 3500 cfs 5600 cfs >6500 cfs Discharge (cfs)

47 Potential Site Reject bb, ab L-I mcb, bab Bar Classification L-II mcb, bab SITE SELECTION SCREENING TOOL Reject Prior Use Private Property Infrastructure Impacts Site Availability & Constraints Available No Infrastructure Impacts Design Criteria -Egg Retention -Juvenile Habitat Hydrologic Analysis -25-day duration (6.8% Exceedence) Dry Design Wet 1,400 cfs Discharge 5,600 cfs Normal 3,500 cfs Hydraulics (HEC-RAS, FLO-2D) Water-Surface Elevation Design Elevation

48 cfs 5600 cfs 3500 cfs 2500 cfs 1400 cfs 300 cfs Phase II Features Channel Bed Elevation (ft) i 12i 11i 3b 10i 9i 7i South 8i 6i North 6i South 6i Chan 7i North Station (ft) 14i 3i 4i 1b South 2i Feature Areas (acres) PDN 13i PDN 12i PDN 11i PDN 3b PDN 10i PDN 9i PDN 8i PDN 7i PDN 6i PDN 14i PDN 1b PDN 4i PDN 3i PDN 2i

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53 TAKE HOME MESSAGES Restoration requires a clear understanding of river dynamics and biological objectives. Must be able to translate biological objectives into physical parameters to provide a basis of design. Bar classification provides a first-cut tool for relating fluvial process to habitat requirements and initial site selection.