School of Civil and Environmental Engineering Water Balance
School of Civil and Environmental Engineering Water Balance and the Influence of Soil Structural Changes on Final Covers for Landfill Closure Melissa Salt, University of Adelaide Mark Jaksa, University of Adelaide Jim Cox, CSIRO Paul Lightbody, Tonkin Consulting Life Impact The University of Adelaide
School of Civil and Environmental Engineering Research Objectives • Measure and compare the drainage to determine if phytocovers reduce drainage to the same extent as conventional covers • Correlate changes in drainage patterns over time from the phytocover and conventional cover changes with changes in bulk density, soil water characteristic curve and permeability • Assess the tendency for anthropomorphic soil to tend towards the natural profile of the borrow source or toward a new stable profile • Determine the effect of changes in bulk density, soil water retention curve and permeability on the predictability of the water balance as estimated from pre-construction laboratory testing Life Impact The University of Adelaide 1
School of Civil and Environmental Engineering Water Balance • P = ET + R + L + D + ΔS Precipitation (P) Evapotranspiration (ET) Runoff (R) COVER Soil moisture storage (S) Lateral flow (L) Drainage (D) WASTE Leachate Life Impact The University of Adelaide 2
School of Civil and Environmental Engineering Methodology – Field Scale Earthen berms Runoff collection Soil cover layer Root barrier Drainage layer 1. 5 mm LLDPE geomembrane Monitoring nest Interim cover Drainage collection not to scale • Precipitation - Weather station • Runoff - Flow meters • Drainage and lateral flow - Tipping bucket rain gauges • Soil moisture content – MP 406 • Soil suction – CS 229 Life Impact The University of Adelaide 3
School of Civil and Environmental Engineering Life Impact The University of Adelaide 4
School of Civil and Environmental Engineering Life Impact The University of Adelaide 5
School of Civil and Environmental Engineering Life Impact The University of Adelaide 6
School of Civil and Environmental Engineering Life Impact The University of Adelaide 7
School of Civil and Environmental Engineering Life Impact The University of Adelaide 8
School of Civil and Environmental Engineering Methodology – Small Scale • 1 m x 1. 5 m deep • Replicate conventional and phytocover from Adelaide, including plants • Irrigation and measure drainage • Destructively sample 1 box of each cover type every 6 months • Analyse samples for bulk density, soil water characteristic curve and permeability Life Impact The University of Adelaide 9
School of Civil and Environmental Engineering Methodology – Core samples • To measure any change in permeability or bulk density as a result of alternate saturation and then drying the soil layers proposed to use in the Adelaide A-ACAP trial. • Prepared core samples at known bulk density of phytocover soil and clay barrier • Wet using falling head permeability apparatus until saturated and hydraulic conductivity measured • Dry in oven at 30 o. C until equilibrated and observe shrinkage and cracking • Repeat process Life Impact The University of Adelaide 10
School of Civil and Environmental Engineering Water Balance Modelling Moisture content at depth through conventional profile over first 3 years modelled Life Impact The University of Adelaide 11
School of Civil and Environmental Engineering Water Balance – Adelaide Site Water balance Phytocover (mm/yr & %) Conventional (mm/yr & %) 1 m 1. 5 m 2 m As placed Dried P 515 515 515 I 117 (23) 123 (24) 103 (20) 125 (24) ET 349 (68) 357 (69) 364 (71) 412 (80) 369 (72) R 0. 7 (0. 1) 0. 8 (0. 1) L 0 0. 5 0 D 48 (9) 34 (7) 28 (5) 0. 2 (0) 23 (4) Life Impact The University of Adelaide 12
School of Civil and Environmental Engineering Water Balance Predictions Predicted annual runoff volumes when surface soil permeability is reduced by one order of magnitude Life Impact The University of Adelaide 13
School of Civil and Environmental Engineering Results – Adelaide Soil Moisture Life Impact The University of Adelaide 14
School of Civil and Environmental Engineering Results – Adelaide Topsoil Moisture Content Life Impact The University of Adelaide 15
School of Civil and Environmental Engineering Results – Melbourne Soil Moisture Life Impact The University of Adelaide 16
School of Civil and Environmental Engineering Outcomes • Water balance comparison of phytocaps for Australian environment • Variability of water balance predictions from selected models • Quantification of soil structural changes in the short to medium term • Impact of soil structural changes on sustainability of the phytocaps • Determination of best soil input parameters for pre -construction modelling Life Impact The University of Adelaide 17
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