Modelling a fractured aquifer: what can be learned by the Mulino delle Vene springs (northern Apennines)? F. Petronici 1, L. Borgatti 1, D. Errigo 2, F. Cervi 1. 1 DICAM - Dipartimento di Ingegneria Civile, Chimica, Ambientale e dei Materiali - Università di Bologna 2 ARPA Emilia-Romagna
Introduction Numerical model Steady state simulation Calibration Transient simulation Validation
WHERE: Mulino delle Vene springs, Carpineti, Reggio Emilia Province, northern Apennines. ACTIVITY: Hydrogeological modelling of a non-porous aquifer. GOALS: Water resources analysis. First results of the numerical modelling and advancements in the understanding of fractured aquifers. Tresinaro River, Mulino delle Vene (Carpineti, RE). Croveglia s pool (Carpineti,RE).
Why Mulino delle Vene? Despite the wide outcropping of rocky aquifers in the mountainous sectors of Italy, mathematical approaches for simulating their hydrological behavior have not been exploited extensively to date. This is mainly due to: 1. Heterogeneity of the hydrogeological properties characterizing the fractured aquifers; 2. Scarcity of continuous monitoring data. Continuous monitoring of discharge Mulino delle Vene Geological data Pumping tests Groundwater level monitoring PECULIAR CASE STUDY
Geological data The springs originate at the bottom of a 50 m long slope. This slope is the southern termination of a continuous and poorly-deformed arenite slab (PAT4) that overlay almost impermeable marls (CTG). The bedding of the slab is gently dipping towards the southeast (where the springs are located). A Geological map and cross-section AA, Carpineti, Reggio Emilia Province. A A A 1:40000 LEGEND: PAT4 Santa Maria Formation, arenitic units. PAT Pantano Formation, arenitic units. CTG Contignaco Formation, marly units. CIG Cigarello Formation, arenitic units. Cross-section. Mulino delle Vene springs, 420 m a.s.l.
Recharge area Hydrogeological analysis (pumping tests and estimation of permeability from geomechanical surveys) allowed to define the recharge area of Mulino delle Vene springs. Extension of 5,5 km 2. Average elevation of 580 m a.s.l. All the water coming from the springs then flows into the Tresinaro River, few meter downslope. Wells RMR Study area, Carpineti, Reggio Emilia Province.
Hydrological and discharge data 1) Effective daily rainfall (R) (corrected with Penman-Monteith formula and Corine Land Cover data) from 15 th March 2013 to 31 st October 2013; 2) Continuous discharge (Q) from Mulino delle Vene springs (15 th March 2013 to 31 st October 2013), linked to the discharge from the weir equipped with an electric-transducer (acquisition time set at 1 hour) with a curvilinear regression. 45000 30 Q (m 3 d -1 ) 40000 35000 30000 25000 20000 15000 25 20 15 10 R (mmd -1 ) Weir and electric transducer, Mulino delle Vene, 430 m a.s.l. 10000 5000 5 0 Mar-13 May-13 Jul-13 Aug-13 Oct-13 time 0 Effective rainfall Discharge
Numerical model Geometry: Top slice: Digital Elevation Model; Bottom slice: 8 geological sections; Boundary of the recharge area defined by a geomorphological and hydrogeological analysis. Elevation (m a.s.l.) Equivalent Porous Medium (EPM) approach MESH PROPERTY: 7395 nodes; 9442 triangle elements; dimension of 30 50 m. Mulino delle Vene springs Seepage face condition
Steady state simulation Goals: Hydrogeological balance (P=Q); One layer model Dynamic storage ~ 1,6 Mm 3 ; Fitting groundwater level in wells. ok Two layers model Parameters k (ms -1 ) s Layer 1 6x10-5 0,01 Layer 2 1x10-7 0,001 k: permeabilty; s: storativity. Elevation (m a.s.l.) Hydraulic head (m a.s.l.) Q Water surface.
Calibration - Transient simulation Calibration period: from June to August 2013, without rainfall recharge. Calibration parameters: permeability (k) and storativity (s) of the first layer. Layer k (ms -1 ) s 1?? 2 10-7 10-6 Observed Mulino delle Vene springs discharge (01/06/2013 29/08/2013) Two steps approach: 1. Steady state simulation 2. Transient simulation k s day
Test 1 k = 10-4 ms -1 Δh = 357 m 1. Steady state simulation P = Q (1 st June 2013) Hydrogeological analysis k mean = 4,05x10-5 ms -1 Test 2 k = 5x10-5 ms -1 Δh = 603 m Test 3 k = 10-5 ms -1 Δh = 2962 m (Δh: difference between hydraulic head in the farthest point from the springs and the springs themselves) Water surface, Test 1. Elevation of the topographic surface. Hydraulic head Prova 1 (m a.s.l.) Elevation (m a.s.l.)
Simulated discharge (m 3 d -1 ) GIT Geology and Information Technology 2. Transient simulation Initial hydraulic head is set as the one obtained in the steady state simulation, then the run is started for the calibration period (from June to August) estimating the storativity that allowed the best simulation of the depletion curve to be obtained. Test 1 k = 10-4 ms -1 Δh = 357 m s = 1x10-3 R 2 = 0,9822 14000 13000 Test 2 k = 5x10-5 ms -1 Δh = 603 m s = 3x10-4 R 2 = 0,9828 Test 3 k = 10-5 ms -1 Δh = 2962 m s = 1x10-6 R 2 = 0,9846 12000 11000 10000 9000 8000 7000 6000 5000 Test 1 Test 2 Test 3 Real discharge 4000 4000 6000 8000 10000 12000 14000 Discharge (m 3 d -1 )
Validation Rainfall and snowmelt have been applied and then simulated discharge values were compared to the daily springs outflow for the whole monitoring period. R 2 01/04/2013 31/05/2013 30/08/2013 31/10/2013 Test 1 0,7811 0,2474 Test 2 0,7498 0,2685 Test 3 0,7876 0,2177 Q (m 3 d -1 ) 45000 40000 35000 April-May Calibration Sept.-Oct. 30 25 R (mmd -1 ) 30000 20 25000 20000 15 15000 10000 5000 10 5 R Real discharge Test 1 Test 2 0 time 0 Test 3
Conclusions: 1. Hydrogeological model of the fractured aquifer was successfully implemented. 2. The large amount of available data allow analysis aimed at water resources management. 3. The results have highlighted the general capability of the EPM approach for simulating springs discharging from fractured aquifers in the depletion period, however, the approach is not an efficient way to simulate discharge in the whole hydrogeological year. Outlook: Since a calibrated model can support water resources management, further efforts will be spent to take into account the different hydrogeological characteristics of the aquifer which feed Mulino delle Vene springs, particularly of the upper part which is crossed by the moreopened and less-spaced fractures, even considering more sophisticated approaches such as Multi-Domain EPM, Discrete Fracture Network (DFN) and Hybrid (EPM for matrix and DFN for fractures). Hydrogeology Springs discharge Hydrology Calibrated model
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