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DSD-INT 2019 Po Delta and Venice Lagoon-Umgiesser

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Presentation by Georg Umgiesser (ISMAR, Italy), at the DANUBIUS Modelling Workshop, during Delft Software Days - Edition 2019. Friday, 8 November 2019, Delft.

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DSD-INT 2019 Po Delta and Venice Lagoon-Umgiesser

  1. 1. Po Delta and Venice Lagoon Po Delta and Venice Lagoon - a case study Georg Umgiesser ISMAR-CNR, Venice, Italy
  2. 2. Po Delta and Venice Lagoon • General overview of the principal characteristics of the system and the forcings • Description of the Po RDS model • Description of the dynamics of the Po delta • Analysis of the interaction between the water compartments
  3. 3. Po Delta and Venice Lagoon Present delta • AREA: 695 km2 • 7 Lagoons : 108 km2 • Fish farms : 65 km2 • 5 natural river branches and 1 waterway : 184 km • Agriculture • Aquaculture in closed fish farms • Clams farming in the lagoons • Fishery • Tourism Main activities Key problem • River flood protection • Subsidence • Salt water intrusion • Storm surges protection • Morphological stabilization • Lagoons flushing improvement
  4. 4. Po Delta and Venice Lagoon ➢ Highly interconnected with the 5 river branches and the sea ➢ The morphology of the connections is very dynamic • Small and very shallow • Poor morphological variability • Relevant freshwater input compared to their volumes Pump station [11] Gates [24] Connection [1] Connection river [18] Connection sea [20] Area [km2] marshes area % Vol. [Mil m3] avg. depth [m] Caleri 9.8 7.2% 13 1.4 Marinetta 11.1 5.4% 19 1.8 Barbamarco 6.8 5.9% 7 1.0 Basson 5.0 6.0% 3 0.6 Canarin 6.4 0% 6 0.9 Scardovari 28.1 1.4% 45 1.6 Goro 37.4 6.1% 48 1.4 PO DELTA 105 4.6% 141 1.3 VENICE 425 12% 700 1.9
  5. 5. Po Delta and Venice Lagoon The system is very complex and the different water bodies are connected with a large number of small channels that despite their tiny dimensions are very important because delivering freshwaters into the salty lagoons they are the main drivers of salinity and sediment distribution, and the responsible of baroclinic circulation. 3D baroclinic finite element model = SHYFEM • Complex geometry and bathymetry • Mixing of riverine and marine waters • Hydrodynamic driven by tide and density gradients • Necessity to represent coastal sea water circulation
  6. 6. Po Delta and Venice Lagoon ➢ Natural subsidence • Long term compaction of the deep soil (3000m) of the delta 1 mm/y • Long term soil compaction of the surficial soil (30-50 m) consisting of the recent alluvial deposition of the delta (latest 300 years) ➢ Anthropic subsidence • Recent compaction of the agricultural soil (peat oxidation) • Methane-rich water extraction
  7. 7. Po Delta and Venice Lagoon 20 April 2017 Discharge 870 mc/s Fresh water versus sea Saline water from sea 26 July 2017 Discharge 500 mc/s
  8. 8. Po Delta and Venice Lagoon River • Relevant intra-annual, seasonal and daily variability • 2 order of magnitude between min (156 m3/s) and max (10500 m3/s) Wind • Magnitude and direction are variable • N-E wind prevailing on the northern delta • S-E wind prevailing on the southern delta Tide • Max 1m tidal range • Relevant surges
  9. 9. Po Delta and Venice Lagoon 19 Nov 2014 - 8600 m3/s 2 Dec 2013 1530 m3/s - Bora 15 m/s 3 Apr 2015 1980 m3/s - Scirocco 8 m/s Image Landsat 8 resolution 30m – F. Braga, CNR ISMAR Venezia
  10. 10. Po Delta and Venice Lagoon • 3D baroclinic finite element • 1 grid with the 3 different water environments • The river is modeled 90 km upstream the mouth • spatial resolution from 5 to 2500 m • 1 model nesting on the sea boundary ADIGE river Po river total discharge Pontelagoscuro PO di LEVANTE {z;T;S;v} PORTO TOLLE PO di VOLANO Calibration (6 months, 2009) • Water level and fluxes in the lagoons and in the river Validation and analysis (2 years, 2010-2011) • Water level and fluxes in the lagoons and in the river • T/S in the lagoons and in the shelf {z;T;S;v} Marinetta Basson Canarin Scardovari sea Scardovari internal Offshore Buoy 6 m Salinity Bias -0.2 -5.7 -1.8 -0.6 0.8 -0.9 Salinity RMSE 4.5 7.5 4.6 4.5 2.9 3.4 Temp. Bias (oC) -0.9 -0.8 -0.8 -0.9 -0.6 -0.7 Temp. RMSE (oC) 2.0 1.2 1.5 1.5 1.4 1.9
  11. 11. Po Delta and Venice Lagoon 84% 16% 17% 5% 48% 14% 13% 28% 7% ➢ <20% flows in the northern coast of the delta and an amount is southward deviated by the coastal current ➢ ≈ 30% flows from the Pila mouth ➢ 50% flows in the southern coast of the delta → 80% of riverine freshwater is driven to southern delta • The main branch (Po di Pila) is prevailing on the lateral branches for high discharges • In the 3 mouths of the Po di Pila the Busa Dritta mouth prevails for low discharges and Busa di Scirocco capacity is reduced almost to zero. 100%
  12. 12. Po Delta and Venice Lagoon Average surface circulation Typical Surface circulation during a flood • The footprint of Po river outflow on the shelf is clearly visible both in the average circulation than during the floods . • PO river outflow is the main (not the only) driver of the coastal hydrodynamics. Coastal mixing in multiple river-mouth deltas: a case study in the Po Delta, Italy Poster A.336
  13. 13. Po Delta and Venice Lagoon Tidal range • Damping along coast due to tidal propagation in the Northern Adriatic sea • Almost similar between sea and lagoons The water flushing time is in the order of few days and correlated with tidal range Tidal prims • In the order of the lagoon volumes • Lagoons are hydrodynamically active
  14. 14. Po Delta and Venice Lagoon • Po river 7700 m3/s flood , 12 days long • 2 billion m3, twice the water volume exchanged between the sea and the lagoons in the same period • Relevant speed at the river mouths (up to 0.8 m/s) • Freshwater plume ➢ The riverine plume is partially wind driven ➢ Plumes extension in modulated by the tidal action ➢ River plume is buoyant in the first 2 meters up to 20 km
  15. 15. Po Delta and Venice Lagoon • The 34 psu isohaline (sea water average salinity measured in 2010-2011 at PTF) has the same distance from the coastline of the 2 psu isoline of salinity variability. • The Po ROFI is a 14-15 km wide area 34 psu 34 psu 2 psu 2 psu • Coexistence of both marine than riverine environments • Low salinity due to the freshwater confinement, multiple connection with the river or limited hydrodynamics
  16. 16. Po Delta and Venice Lagoon • The tidal forcing influences more the WRTs of the smaller lagoons • The wind is not influencing the WRTs because of their limited area • The high percentage of WRTs variance unexplained is due to the non-linear characteristics of the PO RDS system and interaction between the forcings The WRT is the time needed to lower the concentration of a passive tracer from 1 to 0.33 (Takeoka, 1984), is a general descriptor of the lagoons dynamics. WRTs were calculated in the analysis simulation every 30.5 days (24 maps) • WRTs are generally low (5 days avg.) • WRTs locally are lowered by freshwater inputs • Marked season variability (twice values in summer) • Limited spatial variability (except Scardovari Lagoon)
  17. 17. Po Delta and Venice Lagoon
  18. 18. Po Delta and Venice Lagoon WFT = 𝑑𝑎𝑖𝑙𝑦 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑙𝑎𝑔𝑜𝑜𝑛 𝑑𝑎𝑖𝑙𝑦 𝑣𝑜𝑙𝑢𝑚𝑒 𝑒𝑥𝑖𝑡𝑖𝑛𝑔 𝑡ℎ𝑒 𝑙𝑎𝑔𝑜𝑜𝑛 (Umgiesser et al., 2014) Mixing Efficiency = 𝑊𝐹𝑇 𝑊𝑅𝑇 0 < ME <1
  19. 19. Po Delta and Venice Lagoon Finite element grid of the Adriatic Sea - Venice Lagoon High resolution area
  20. 20. Po Delta and Venice Lagoon • No wind • Scirocco • Bora
  21. 21. Po Delta and Venice Lagoon OUTFLOW INFLOW
  22. 22. Po Delta and Venice Lagoon (http://gisportal.insula.it) the city of Venice The pavement level in the city is low with respect to the sea level even moderate surge can produce flooding in the city i.e. ‘high water’ events pavement lower than 90 cm sea level flooded surface of the city 190 cm 100% 140 cm 90% 130 cm 69% 120 cm 35% 110 cm 12% 100 cm 4% (sea and pavement levels are referred to the conventional datum of Punta Salute 1897)
  23. 23. Po Delta and Venice Lagoon Finite element grid of the Mediterranean Sea. Forcing: ECMWF pressure and wind fields. Operational at CPSM from November 2002. Operational at APAT/ISPRA from 2001 ISMAR-CNR Venice
  24. 24. Po Delta and Venice Lagoon Simulation of the 4 November 1966
  25. 25. Po Delta and Venice Lagoon Astronomical tide, surge and total sea level at the oceanographic tower. Time (hours) goes from 00 UTC of 29 till 12 UTC of 30 October 2018. The blue line shows the model surge.
  26. 26. Po Delta and Venice Lagoon 26 Thank you for your attention

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