EGU 2012 LEVEE VEGETATION RESEARCH SYMPOSIUM 2012 Sacramento, California, August 28 30, 2012 The Impact of Woody Vegetation on Levees Research Experiences from Austria Walter LAMMERANNER Institute of Soil Bioengineering and Landscape Construction University of Natural Resources and Life Sciences, Vienna, Austria
Institute of Soil Bioengineering and Landscape Construction Department for Civil Engineering and Natural Hazards University of Natural Resources and Life Sciences (BOKU) Vienna, Austria Head: Prof. Dr. Florin Florineth
2006 floods in Austria
March River VIENNA Lower Austria border river to Slovakia ~ 50 km from Vienna
Levee failures Poor condition of levees (construction 1882-1905) Overtopping of levees
Levee failures But also only poor reinforcement and protection through grass-vegetation
Soil bioengineering techniques using woody plants These techniques have a long history within riverbank stabilization and restoration works Why do not use them on levees as well? Source: Florineth, 2004 Source: Florineth, 2004
Decision to test willow-brush-mattresses on levees What impacts do these vegetation structures have on levees?
Potential negative impacts of woody vegetation Facilitated water movement along root penetration paths Decaying roots lead to voids, threaten structural integrity and facilitate percolation Additional load through trees which transfer forces (wind, water, snow) into the levee Windthrow of trees can lead to damage or even collapse of the levee
Potential negative impacts of woody vegetation Surface erosion along stems through water turbulences Attractive habitat for burrowing animals Hindering effective levee inspections and defense operations
Vegetation grown from brush-mattresses potentially can: Protect the surface trough dense and flexible stems Reinforce the upper soil layer and protect the surface from erosion by a dense rooting system Transpire moist from the soil which aids to soil stability (even below the rooting zone) Reduce the flow velocity near the levee surface
And potentially do not: Led to additional load (which is minimized) Endanger the levee through windthrow plants stay shrubby and if getting too large they can be cut to the ground and grow again afterwards
And potentially do not: Led to decaying roots Vegetation is kept vital through repetitive cutting to the ground
And potentially do not: Led to surface erosion along stems Dense stand of flexible and thin stems
And what about:? Attracting burrowing animals Are burrowing animals attracted by woody plants? And if not which species? Especially if the vegetation is very dense?
And what about:? Hindering levee inspection and defense Woody vegetation has to be limited to particular areas of the levee
Objectives Test willow-brush-mattresses on levees compacted to modern standards Investigations regarding to: Plant performance and development (above- and below ground) Impact on seepage and soil water balance Impact on the structural performance of the levee
Site layout
Cross section and measurement devices
Grain size distribution silt-sand-gravel composite
Compaction Proctor density
Compaction tests Dynamic plate load tests Sampling rings Isotope probe
Willow-brush-mattresses Using Purple-Willow (Salix purpurea) a shrubby willow with a large ecological amplitude and very good propagation properties
Plant performance 4 th growing season After implementation
Plant performance above-ground diameter and length
Seepage tests
Seepage tests
Seepage line water-side slope face 160,0 160,0 159,5 159,5 159,0 159,0 158,5 158,5 158,0 158,0 157,5 157,5 1 23 4 56 7 89 10 11 12 13 14 15 16 17 18 1 23 4 56 7 89 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 water level bassin willows grass-herb-vegetation water level bassin willows grass-herb-vegetation Test 1 Test 2 (two weeks later)
Seepage line middle of the crest 160,0 160,0 159,5 159,5 159,0 159,0 158,5 158,5 158,0 158,0 157,5 157,5 1 23 4 56 7 89 10 11 12 13 14 15 16 17 18 1 23 4 56 7 89 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 water level bassin willows grass-herb-vegetation water level bassin willows grass-herb-vegetation Test 1 Test 2 (two weeks later)
Root investigations 1 1 1 2 2 2 3 3 3 4 4 4
Root investigations Measurable maximum rooting depth ~ 80 cm in the 3 rd growing season Concentration of roots in the upper 30 cm
Root investigations Fleece-like dense network of fine roots
root mass 1. vegetation period above-ground biomass 1. vegetation period 600 600 500 500 biomass per m² [g] 400 300 200 191,9 194,0 biomass per m² [g] 400 300 200 149,2 211,2 100 100 62,0 0 2,1 0 roots <2 mm roots 2-5 mm total roots branches leaves total biomass
Root-shoot ratio: 0,9 root mass 1. vegetation period above-ground biomass 1. vegetation period 600 600 500 500 biomass per m² [g] 400 300 200 191,9 194,0 biomass per m² [g] 400 300 200 149,2 211,2 100 100 62,0 0 2,1 0 roots <2 mm roots 2-5 mm total roots branches leaves total biomass
root mass 2. vegetation period above-ground biomass 2. vegetation period 600 600 500 500 biomass per m² [g] 400 300 200 263,4 294,9 biomass per m² [g] 400 300 200 253,4 313,4 100 31,5 100 60,0 0 0 roots <2 mm roots 2-5 mm total roots branches leaves total biomass
Root-shoot ratio: 0,9 root mass 2. vegetation period above-ground biomass 2. vegetation period 600 600 500 500 biomass per m² [g] 400 300 200 263,4 294,9 biomass per m² [g] 400 300 200 253,4 313,4 100 31,5 100 60,0 0 0 roots <2 mm roots 2-5 mm total roots branches leaves total biomass
root mass 3. vegetation period above-ground biomass 3. vegetation period 600 500 523,2 601,9 600 500 517,8 557,3 biomass per m² [g] 400 300 200 biomass per m² [g] 400 300 200 100 0 60,8 17,9 roots <2 mm roots 2-5 mm roots 5-10 mm total roots 100 0 39,5 branches leaves total biomass
Root-shoot ratio: 1,1 root mass 3. vegetation period above-ground biomass 3. vegetation period 600 500 523,2 601,9 600 500 517,8 557,3 biomass per m² [g] 400 300 200 biomass per m² [g] 400 300 200 100 0 60,8 17,9 roots <2 mm roots 2-5 mm roots 5-10 mm total roots 100 0 39,5 branches leaves total biomass
Research on soil water balance Lysimeter like design Impact of vegetation on soil water balance Comparison of rooting systems between willows and grass-herb vegetation
Research on soil water balance Lysimeter like design soil moisture probes tensiometers soil material drain weighing device
Research on soil water balance Lysimeter like design
Soil water moisture 30 cm depth 1 st vegetation period without vegetation grass-herb-vegetation willows 0,25 0,20 0,15 0,10 0,05 0,00 01.01.2009 15.01.2009 29.01.2009 12.02.2009 26.02.2009 12.03.2009 26.03.2009 09.04.2009 23.04.2009 07.05.2009 21.05.2009 04.06.2009 18.06.2009 02.07.2009 16.07.2009 30.07.2009 13.08.2009 27.08.2009 10.09.2009 24.09.2009 08.10.2009 22.10.2009 05.11.2009 19.11.2009 03.12.2009 17.12.2009 31.12.2009 volumetric water content [Vw/Vt] time Axis
Pore water pressure 30 cm depth 1 st vegetation period 1000 without vegetation grass-herb-vegetation willows pore water presure [hpa] 800 600 400 200 0 01.01.2009 15.01.2009 29.01.2009 12.02.2009 26.02.2009 12.03.2009 26.03.2009 09.04.2009 23.04.2009 07.05.2009 21.05.2009 04.06.2009 18.06.2009 02.07.2009 16.07.2009 30.07.2009 13.08.2009 27.08.2009 10.09.2009 24.09.2009 08.10.2009 22.10.2009 05.11.2009 19.11.2009 03.12.2009 17.12.2009 31.12.2009 time axis
Soil water moisture 30 cm depth 2 nd vegetation period without vegetation grass-herb-vegetation willows 0,25 0,20 0,15 0,10 0,05 0,00 01.01.2010 15.01.2010 29.01.2010 12.02.2010 26.02.2010 12.03.2010 26.03.2010 09.04.2010 23.04.2010 07.05.2010 21.05.2010 04.06.2010 18.06.2010 02.07.2010 16.07.2010 30.07.2010 13.08.2010 27.08.2010 10.09.2010 24.09.2010 08.10.2010 22.10.2010 05.11.2010 19.11.2010 03.12.2010 17.12.2010 31.12.2010 Volumetric water content [Vw/Vt] Times axis
Pore water pressure 30 cm depth 2 nd vegetation period 1000 without vegetation grass-herb-vegetation willows 800 600 400 200 0 01.01.2010 15.01.2010 29.01.2010 12.02.2010 26.02.2010 12.03.2010 26.03.2010 09.04.2010 23.04.2010 07.05.2010 21.05.2010 04.06.2010 18.06.2010 02.07.2010 16.07.2010 30.07.2010 13.08.2010 27.08.2010 10.09.2010 24.09.2010 08.10.2010 22.10.2010 05.11.2010 19.11.2010 03.12.2010 17.12.2010 31.12.2010 pore water presure [hpa] Time axis
Root investigations
Root mass comparison root mass per soil volume 2. vegetation period root mass/soil volume [mg/cm³] 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 root mass per soil volume 2. vegetation period root mass/soil volume [mg/cm³] 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 depth [cm] 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70 70-75 75-80 Drain Willow vegetation depth [cm] 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70 70-75 75-80 Drain Grass-herb vegetation
Root length comparison willow vegetation root length per soil volume 1. vegetation period root length/soil volume [cm/cm³] 0 2 4 6 8 root length per soil volume 2. vegetation period root length per soil volume [cm/cm³] 0 2 4 6 8 depth [cm] 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70 70-75 depüth [cm] 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70 70-75 75-80 Drain 0<.L.<=0.25 0.25<.L.<=0.5 0.5<.L.<=1 1<.L.<=2 2<.L.<=5 5<.L.<=10 0<.L.<=0.25 0.25<.L.<=0.5 0.5<.L.<=1 1<.L.<=2 2<.L.<=5 5<.L.<=10 1 st vegetation period 2 nd vegetation period
Overall Preliminary conclusions Shrubby willows grown from brush-mattresses seem to be an appropriate vegetation form for well compacted levees They develop a dense and near surface root system They form a dense stand of thin and flexible stems Up to now they don t have a significant impact on seepage They have a significant positive impact on soil water balance But: Research work has to be continued on the long term run
Many thanks to all staff members and students who have been involved in the project!
Thanks for your attention!