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

1. Po Delta and Venice Lagoon
Po Delta and Venice Lagoon
- a case study
Georg Umgiesser
ISMAR-CNR, Venice, Italy

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. Po Delta and Venice Lagoon

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. Po Delta and Venice Lagoon
Finite element grid
of the Adriatic Sea -
Venice Lagoon
High resolution area

20. Po Delta and Venice Lagoon
• No wind
• Scirocco
• Bora

21. Po Delta and Venice Lagoon
OUTFLOW INFLOW

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. 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. Po Delta and Venice Lagoon
Simulation of the 4 November 1966

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. Po Delta and Venice Lagoon
26
Thank you for your attention