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Alluvial Bar Morphology and Dynamics in the Middle Rio Grande

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Alluvial Bar Morphology and Dynamics in the Middle Rio Grande AlluvialAlluvialAlluvial BarBarBar MorphologyMorphologyMorphology andandand DynamicsDynamicsDynamics ininin thethethe MiddleMiddleMiddle RioRioRio Grande:Grande:Grande: ApplicationApplicationApplication tototo HabitatHabitatHabitat RestorationRestorationRestoration forforfor thethethe RioRioRio GrandeGrandeGrande SilverySilverySilvery MinnowMinnowMinnow Mike Harvey MMussetter EEngineering, IInc. WORKWORK CONDUCTEDCONDUCTED FOR:FOR: z New Mexico Interstate Stream Commission z Middle Rio Grande ESA Collaborative Program WHATWHAT ISIS AA BARBAR ?? “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 PROJECTPROJECT OBJECTIVESOBJECTIVES z Evaluate bar changes over time in response to changes in flow, sediment supply and channel morphology z Develop a bar classification z Relate fluvial processes to bar types z Apply results to river/habitat restoration 9 STUDY SITES MEI 1935 1955 1972 1992 1996 2001 MEI ModifiedModified BraidingBraiding IndexIndex ((GermanoskiGermanoski,, 1989)1989) 2( L ) n MBI = ∑ BraidBar + bars LChannel LChannel EXPECTEDEXPECTED MBIMBI RESPONSESRESPONSES ((GermanoskiGermanoski andand SchummSchumm,, 1993;1993; GermanoskiGermanoski andand Harvey,Harvey, 1993)1993) z If D50 increases, and there is sediment supply: > MBI z If D50 increases, and there is no sediment supply: < MBI z If the bed aggrades: > MBI z If the bed degrades: < MBI Pena Blanca Central Avenue 7.00 1600 3.00 1400 Modified Braid Bar Index Modified Braid Bar Index 6.00 1400 Alternate Bar Index 1200 Alternate Bar Index 2.50 Active Channel Width Active Channel Width 1200 5.00 1000 2.00 1000 4.00 800 800 1.50 3.00 600 Bar Index Bar Index 600 1.00 2.00 400 400 Average Channel Width (ft) Average Channel Width (ft) 0.50 1.00 200 200 0.00 0 0.00 0 1935 1945 1955 1965 1975 1985 1995 1935 1945 1955 1965 1975 1985 1995 Year Year Bernardo 4.00 1600 Modified Braid Bar Index 3.50 Alternate Bar Index 1400 Active Channel Width 3.00 1200 2.50 1000 2.00 800 Bar Index 1.50 600 1.00 400 Average Channel Width (ft) 0.50 200 0.00 0 1935 1945 1955 1965 1975 1985 1995 Year Escondida 2.50 1000 Modified Braid Bar Index 900 Alternate Bar Index 2.00 Active Channel Width 800 700 1.50 600 500 Bar Index 1.00 400 300 Average Channel Width (ft) 0.50 200 100 0.00 0 1947 1957 1967 1977 1987 1997 Year Bosque del Apache San Marcial 3.00 2000 1.20 250 Modified Braid Bar Index Modified Braid Bar Index 1800 Alternate Bar Index Alternate Bar Index 2.50 1.00 Active Channel Width 1600 Active Channel Width 200 1400 2.00 0.80 1200 150 1.50 1000 0.60 Bar Index 800 Bar Index 100 1.00 0.40 600 Average Channel Width (ft) Average Channel Width (ft) 400 50 0.50 0.20 200 0.00 0 0.00 0 1935 1945 1955 1965 1975 1985 1995 1972 1982 1992 2002 Year Year HierarchicalHierarchicalHierarchical BarBarBar ClassificationClassificationClassification forforfor thethethe MiddleMiddleMiddle RioRioRio GrandeGrandeGrande Subaqueous Perennial Bar Type Location Elevation or Subaerial 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 Linguoid bar L-1 braid bars L-1 bank-attached bar L-2 braid bar mud drape L-1 braid bar L-1 mid-channel bar L-2 braid bar L-1 braid bar Linguoid bar L-2 mid-channel bar L-2 braid bar L-1 mid-channel bar L-2 mid-channel bar L-2 bank-attached bar L-1 bank-attached bar HYDRAULICHYDRAULIC ANALYSISANALYSIS z One-dimensional HEC-RAS models – Fixed-bed analysis – Calibrated to gauged flow at time of survey and 2005 peak flow (Tetra Tech. (2005) CentralCentral SiteSite Bar Inundation Analysis 8000 0% 5-yr 7000 1% 2.9-yr 1% 2.9-yr 6000 Mean Inundation Discharge 1% 2.7-yr 1% 2.7-yr Minimum Inundation Discharge 5000 4% 1.9-yr Maximum Inundation Discharge 4% 1.7-yr Mean Channel Capacity 5% 1.6-yr 6% 1.5-yr 7% 1.4-yr 7% 1.4-yr 6% 1.5-yr 4000 8% 1.4-yr 3000 12% 1.1-yr Discharge (cfs) 17% 1.05-yr 16% 1.1-yr 2000 21% 1.03-yr 29% <1.01-yr 1000 47% <1.01-yr 51% <1.01-yr Mean-daily exceedance percent and peak flood return interval of inudation discharge show n next to plotted value. 92% 95% <1.01-yr 91% <1.01-yr 0 98% Linguoid Bar Level-1 Alternate Level-2 Level-1 Mid- Level-1 Bank- Level-2 Mid- Level-2 Bank- Braid Bar Bar Braid Bar Channel Bar Attached Bar Channel Bar Attached Bar Bar Feature BARBAR INUNDATIONINUNDATION FREQUENCYFREQUENCY && DURATIONDURATION Table ES-1. Summary of frequency and duration of inundation of the classified bar types at sites without excessive aggradation or degradation.* Inundation Days per Percent of Bar Type Recurrence Year of Year Interval Inundation Inundated Level 1 braid bars < 1 year 290 80% Alternate bars < 1 year 290 80% 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. BARSBARS ANDAND SHEARSHEAR STRESSSTRESS Table ES-2: Comparison of maximum in-channel shear stresses to the prevalence of bars in the sand-bed sites. Maximum In- Channel Shear Site Names Prevalence of Active Bars Stresses (lb/ft2) 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 0.12 - 0.15 active bars are present Belen 0.2 moderate number of active bars Escondida 0.3 virtually no active bars BARSBARS ANDAND VEGETATIONVEGETATION z Shear stress limit for vegetation establishment ~ < 1 psf z Shear stress limit for vegetation removal ~ > 6 psf CentralCentral SiteSite –– CrossCross SectionSection 22 4953 Peak Exceedance Percent 1 2 5 10 203040506070 Ground Elevation Lingouid Bar Mean-Daily Duration L1 Braid Bar Peak Frequency 4952 L2 Braid Bar 100-yr Shear Stress L1 Mid-ch Bar 50-yr Computed Water- 25-yr 4951 Surface Elevation 10-yr 7,600 cfs 5-yr 4950 t) 5,410 cfs f 2-yr 4,450 cfs 1.5-yr 4949 3,490 cfs Elevation ( 4948 2,110 cfs 1,055 cfs 4947 737 cfs 329 cfs 4946 Shear Stress (lb/ft2) 0 0.1 0.2 0.3 4945 1000 1200 1400 1600 0 100 200 300 Station (ft) Number of Days (Mean-Daily Duration) BARSBARS ANDAND DEPOSITIONDEPOSITION z Based on surveys of L1 and L2 bars in Albuquerque Reach, pre- and post- 2005 high flows z Comparison based on 0.5 ft contour- interval topographic mapping POST-HIGH FLOW SEDIMENT DEPOSITION 2005 L1 L1 L2 L2 L1 Upstream Bar Downstream High Flow Bar High Flow L1 Upstream Bar Low Flow BARSBARS ANDAND DEGRADATIONDEGRADATION z Degradation causes hydrologic abandonment of bars z If restoration is being considered is the bed currently stable? z If degradation continues, restoration will be compromised Abandoned L-2 mid-channel bar BernalilloBernalillo SiteSite Bar Inundation Analysis 14000 Mean Inundation Discharge Minimum Inundation Discharge 0% 100-yr 12000 Maximum Inundation Discharge Mean Channel Capacity 10000 0% 13.5-yr 0% 10.1-yr 0% 8.6-yr 8000 0% 4.6-yr 0% 4.4-yr 0% 4.2-yr 0% 3.6-yr 6000 Discharge (cfs) 4% 1.8-yr 6% 1.6-yr 4000 9% 1.2-yr 8% 1.3-yr 11% 1.2-yr Identified in Study Reach No Level-1 Bank-Attached Bars 20% 1.03-yr 2000 32% 32% <1.01-yr 31% <1.01-yr Mean-daily exceedance percent and peak flood return 33% interval of inudation discharge show n next to plotted value. 0 No Linguoid Bars Identified in Study Reach Linguoid Bar Level-1 Alternate Level-2 Level-1 Mid- Level-1 Bank- Level-2 Mid- Level-2 Bank- Braid Bar Bar Braid Bar Channel Bar Attached Bar Channel Bar Attached Bar Bar Feature BernalilloBernalillo SiteSite –– CrossCross SectionSection 1010 5060 Peak Exceedance Percent 1 2 5 10 203040506070 Mean-Daily Duration Peak Frequency 5058 Shear Stress 100-yr 5056 50-yr 25-yr 8,940 cfs 10-yr 7,600 cfs 5-yr t) f 5054 5,410 cfs 2-yr 4,450 cfs 1.5-yr 3,490 cfs 5052 Elevation ( Elevation 2,110 cfs Ground Elevation L1 Braid Bar 5050 1,055 cfs Alternate Bar 882 cfs L2 Braid Bar 737 cfs L1 Bank-att Bar 5048 L2 Mid-ch Bar L2 Bank-att Bar Computed Water- Shear Stress (lb/ft2) Surface Elevation 0 0.1 0.2 0.3 5046 1000 1200 1400 1600 1800 2000 0 100 200 300 Station (ft) Number of Days (Mean-Daily Duration) BernalilloBernalillo SiteSite 2 Reach Averaged Hydraulics, D50=37 mm (WC4) XS8 Hydraulics, D50=37 mm (WC4) 1.5 1 Dimensionless Grain Shear 0.5 RI (years) 1.5 2 5 10 25 50 100 0 1000 3000 5000 7000 9000 11000 13000 Discharge (cfs) CONCLUSIONSCONCLUSIONS z Bar indices reflect changes in flow, sediment supply and channel morphology z Bar classification is a communication tool, and provides first-cut hydraulic assessments CONCLUSIONSCONCLUSIONS z Active braid bars require average shear stresses < 0.2 psf z Inundation of bars leads to vertical growth and reduced frequency and duration of inundation z Degradation will adversely affect restoration efforts, so vertical stability must be assessed APPLICATIONAPPLICATION TOTO RESTORATIONRESTORATION Bridge Blvd.
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