Hydro-geotechnical modelling of Como subsidence

XIII Convegno Nazionale GIT-SI 11-13 Giugno 2018 Fortezza Firmafede, Sarzana (Sp) Sessione tematica SI: "La gestione quantitativa delle risorse idriche sotterranee: effetti delle variazioni di utilizzo delle risorsa e delle variazioni climatiche". HYDRO-GEOTECHNICAL MODELLING OF COMO SUBSIDENCE Greta BAJNI1, Tiziana APUANI1, Giovanni Pietro BERETTA1 [email protected] (1) Dipartimento di Scienze della Terra “A. Desio” Università degli Studi di Milano DIPARTIMENTO DI SCIENZE DELLA TERRA COMO URBAN AREA Geological Framework Shoreline evolution Historical subsidence records Lake Flooding MESOZOIC UNITS • Gonfolite Lombarda Group • Moltrasio Limestone QUATERNARY DEPOSITS • Po Synthem • Cantù Synthem Mod. From Bini 1993 DIPARTIMENTO DI SCIENZE DELLA TERRA Hydro-geotechnical modelling of Como subsidence BAJNI et al. COMO URBAN AREA Geological Framework Shoreline evolution Historical subsidence records Lake Flooding SINCE ROMAN AGE:  Environmental remediation of marshy areas  Artificial deviation of fluvial streams (Valduce and Cosia)  Shoreline progradation and rettification by placing artificial reworked material  Ancient harbor conversion in the modern Cavour Square (1872) DIPARTIMENTO DI SCIENZE DELLA TERRA Mod. from Ferrario et al. 2015 Hydro-geotechnical modelling of Como subsidence BAJNI et al. COMO URBAN AREA Geological Framework Shoreline evolution Historical subsidence records Lake Flooding 70s-80s ANTHROPIC SUBSIDENCE 20 mm/year AQUIFER OVEREXPLOITATION 150-160 l/s Geometric levelling (1974 – 1984 – 1986 – 1996 - 1997 2004-2011-2014) PSInSAR Interferometry (1992 ÷ 2003, 2003 ÷ 2012) Natural trend: 2/3 mm/year DIPARTIMENTO DI SCIENZE DELLA TERRA Hydro-geotechnical modelling of Como subsidence BAJNI et al. COMO URBAN AREA Geological Framework Shoreline evolution Historical subsidence records Lake Flooding 2002 1976 1888 1901 DIPARTIMENTO DI SCIENZE DELLA TERRA Hydro-geotechnical modelling of Como subsidence BAJNI et al. WORKING FLOWCHART GIS environment visualization & processing DIPARTIMENTO DI SCIENZE DELLA TERRA High availability – but discontinuously distribuited in time – organized within a GIS platform • 5 geognostic survey • 116 boreholes • 32 piezometer • 35 geometric leveling points • 2500 Satellite PS Hydro-geotechnical modelling of Como subsidence BAJNI et al. DATABASE CREATION and INTERPRETATION Geotechnical data plotting PS SAR and geometric leveling data comparison Groundwater and lake mutual relationship analysis C1 B LAKE DIPARTIMENTO DI SCIENZE DELLA TERRA Hydro-geotechnical modelling of Como subsidence BAJNI et al. CONCEPTUAL MODEL REWORKED ANTHROPIC MATERIAL (R) 015 m. from g.l. UPPER SAND and GRAVEL (UGS) 3-25 m from g.l. ORGANIC PALUSTRINE SILTS (POS) 20-40 from g.l. SILTY INORGANIC GLACIOLACUSTRINE CLAYS (ICS) 25-70 m from g.l. LOWER SAND and GRAVEL (LSG) (60-170 m from g.l. Extreme R stratigraphical, spatial and geotechnical heterogeneity KRIGING GEOSTATISTICAL PROCEDURE DIPARTIMENTO DI SCIENZE DELLA TERRA Hydro-geotechnical modelling of Como subsidence BAJNI et al. CONCEPTUAL MODEL MAIN FEATURES Unconfined shallow aquifer R UGS POS ICS LGS  Unit R k heterogeneity 10-210-4 m/s  Variable Groundwater depth from 1.52 m along the shoreline to 1015 m at the SE end of the basin  Cosia and Valduce creek w/ cemented riverbed and rectified stream. Aquitard Confined deep aquifer DIPARTIMENTO DI SCIENZE DELLA TERRA RECHARGE  Mainly lateral supply from rocky reliefs  Local contribute from Respaù creek paleo-channel (SW) recharge anomaly  Localized karst phenomena Hydro-geotechnical modelling of Como subsidence BAJNI et al. NUMERICAL MODEL Background theory Numerical code Modflow 2000 Graphical interface Groundwater Vistas 6.0 SUB Package ℎ 𝑔 = 𝑝 Inelastic and elastic deformation depending on the preconsolidation stress – effective stress mutual relationship Preconsolidation stress = Soil maximum effective stress = Piezometric minima (or p minima) of the simulation DIPARTIMENTO DI SCIENZE DELLA TERRA 𝑤 ’ = − 𝑔ℎ 𝑤 COUPLED HYDROGEOTECHNICAL MODEL Hydro-geotechnical modelling of Como subsidence BAJNI et al. NUMERICAL MODEL Setting and parameterization 1. TEMPORAL and SPATIAL DISCRETIZATION  561 R X 524 C Parameter R  GRID 5x5m  k4(m/s) layer 5,3x10-4  9 Stress Periods: 1 SS e 8 TR Sy ofrom Ss (-) 2004 to 2011 0.3 Sske(1/m) 6x10-6 2. BOUNDARY CONDITIONS UNIT SOURCE  NO-FLOWLA – Rocky reliefs UGS POS 2.6x10-3 0.2 3x10-6  CHD –Medium annualpumping lake level , oedometric,  -6Pumping Wells – 25 l/s -9 borehole permeability tests 7x10 4.73x10  Lateral recharge–injection wells 450 l/s (THORNT-WAITE model +CN procedure) Pumping tests, empirical 0.01 0.006 equations, previous studies 6x10-6 6x10-6 3. MODEL PARAMETERS Calibration process of the parameters, varying the values within the observed real data ranges, until obtaining an acceptable RMS (<10%) Geotechnical literature -2 1.3x10 shoreline Sski (1/m) 1.76x10-2 Cavour 3x10-6 Hi s tori ca l 3x10-6 4.2x10-3 3.77x10-3 Oedometric tests and empirical equations town Modeled urban area Modeled lake area DIPARTIMENTO DI SCIENZE DELLA TERRA Hydro-geotechnical modelling of Como subsidence BAJNI et al. NUMERICAL MODEL Calibration Root Mean Square error (RMS) Anderson & Woessner (1992) Piezometric calibration Subsidence calibration RMS 6.93% RMS 8.35% DIPARTIMENTO DI SCIENZE DELLA TERRA Hydro-geotechnical modelling of Como subsidence BAJNI et al. NUMERICAL MODEL Results PIEZOMETRIC MINIMA 2004-2005 INELASTIC and ELASTIC SUB CYCLES smax =0.93cm smax =1.44cm smax = 1 cm smax =2.7 cm smax =0.85cm DIPARTIMENTO DI SCIENZE DELLA TERRA Hydro-geotechnical modelling of Como subsidence BAJNI et al. Annual groundwater level variation m m Annual subsidence variation DIPARTIMENTO DI SCIENZE DELLA TERRA NUMERICAL MODEL Results Deformation per layer Elastic recovery linked to the coarser unit Unit R and POS contribute to almost the whole deformation ICS contribuite negligibly to the phenomenon due to its depth and low k DIPARTIMENTO DI SCIENZE DELLA TERRA Hydro-geotechnical modelling of Como subsidence BAJNI et al. NUMERICAL MODEL Verification ANTHROPIC PERTURBATION 100 l/s PZ1 PS213 LOCALIZED DEFORMATION INCREMENT UP TO A MAXIMUM OF 6-7 cm DIPARTIMENTO DI SCIENZE DELLA TERRA PZ2 PS259 Hydro-geotechnical modelling of Como subsidence BAJNI et al. DIPARTIMENTO DI SCIENZE DELLA TERRA Urban management -Pool A induced subsidence evaluation (R 12 m) -Groundwater response assesment linked to anthropic or natural perturbations. -Constant recharge (annual model) - Most recent and complete available data 2004-2011 -No-delay beds =instantaneous deformation UNIT Sskv (m-1) R LIMITATIONS anthropogenic perturbation of the acquifer system could induce a deformation of the relative solid skeleton of soils. -Development of an effective procedural scheme to analyze and forecast subsident critical zone: it cannot prescind from the hydrogeotechnical comprehension of the subsoil APPLICATIONS -Natural or CONCLUSIONS CONCLUSIONS – APPLICATIONS - LIMITATIONS  Kv (m/s) 1.3x10-2 bav (m) 8 POS 4.2x10-3 30 7x10-7 Instantaneous (<1day) 15÷30 days ICS 3.77x10-3 40 4.73x10-9 10 years Hydro-geotechnical modelling of Como subsidence BAJNI et al. TIME DELAY ESTIMATION – Riley equation 5.3x10-5 Thanks for your attention! Dott.ssa Greta BAJNI ([email protected]) Prof.ssa Tiziana APUANI Prof. Giovanni Pietro BERETTA ACKNOWLEDGMENTS We would like to acknowledge Dr. Jacopo Terrenghi for the precious help in approaching the numerical model. Additional thanks go to Local Authorities and Municipality of Como for the data made available.