1 JRC – Ispra Numerical Hydrodynamics Study of Sacca di Goro Coastal Lagoon, Italian Northern...

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1 JRC – Ispra

Numerical Hydrodynamics Study of Sacca di Goro Coastal Lagoon, Italian Northern Adriatic Sea

D. Marinov¹, José-Manuel Zaldívar¹ and A. Norro²

¹ IES, Joint Research Centre, EC, Ispra (VA), Italy² MUMM, Inst. Natural Science, Brussels, Belgium

6- th ELOISE European Conference, Portoroz, 15-18 November 2004

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Contents:

1. Introduction2. COHERENS model3. Model results:

Flow patterns and Water surface elevationTravelling/Propagation timesParticle trajectories and Residence timesEffect of new open sea connection on temperature and

salinitySurface temperature and salinity in 1992 (movie)

4. Conclusions

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DITTY Project : Development of an Information Technology Tool for the Management of Southern European Lagoons

under the influence of river-basin runoffEVK3-CT-2002-00084

Te st site s

Da tac o m p ila tio n

Da ta b a seSyste m

G IS syste m

Ana lysisto o ls

M o d e llingto o ls

End -use rs

N a tura lsc ie ntists

Ec o no m ic a na lysis to o ls

Sc e na rioAna lysis

De c isio nsup p o rt syste m

So c io -Ec o no m icsc ie ntists

Be nc hm a rking

The objective of the project is to develop a scientific base and information technology tool for the sustained and rational utilization of the available resources in Southern European lagoons taking into account the impact of agriculture, urban and economic activities.

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Disruptions: macro algal blooms, anoxic crises, economic losses.

Sacca di Goro (Italy) Ulva proliferation

IntroductionLength ~ 11 km, Width ~ 5 km,

Area ~ 26 km², Mean depth ~ 1.5 m, Second big clams producer in Italy

8,000-15,000 tons/year

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W in d s tr e ss R iv e r in p u t H e a t f lu x e s

Te m p e r a tu r e

S o la r r a d ia tio n

C u r re n ts Tu r b u le n c e S a lin ityT id e s

A d v e c t io n -d if fu s io nm o d u le

O p tic a l m o d u le

B o tto m stre ssw a v e -c u r r e n tin te r a c t io n

S u r fa c e e le v a t io n

W a v e d a ta

COHERENS is complex 3-D hydrodynamic finite-difference model for coastal seas which is coupled with biological and contaminant models

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-0.5-0.4-0.3-0.2-0.10.00.10.20.30.40.50.60.70.8

0 4 8 12 16 20 24 28 32 36 40 44 48

Time [hours]

] Observations

Numerical results(a)

0 4 8 12 16 20 24 28 32 36 40 44 48

Time [hours]

Observations

Numerical results(b)

Model Verification 1

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4.97x 10

11 buoy

Bianco

Giralda

Po di Volano

Adriatic Sea

Bonello

Po di Goro

Meteo station

Ciavola, P., Gonella, M., Tessari, U. and Zamariolo, A., 2000. In: L. Terrazzi (Editor), Studi Costieri 2, Firenze, pp.153-173

Comparison of numerical results for the water surface elevation and current speed at the main lagoon-sea connection (point 7) with measurements of Ciavola et al. (2000) collected during an spring event of high tide with amplitude about 1m and NW wind of 4-6 m/s speed:

(a) water surface elevation; (b) current speed

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Model Verification 2

Time [hours]

] Observations

Numerical results

Time [hours]

Observations

Numerical results

2.302 2.304 2.306 2.308 2.31 2.312 2.314

4.97x 10

1.24.5

1.71.2

11 buoy

Bianco

Giralda

Po di Volano

Adriatic Sea

Bonello

Po di Goro

Meteo station

Comparison of numerical results for the surface temperature and salinity at the buoy station with hourly frequency observations (Bencivelli, private communication) collected during 1992 year:

(a) temperature; (b) salinity

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x 106 Elevation and currents for flood tide and SE wind

Model Results 1

Flow patterns and water surface elevationInvestigations of flow patterns and water surface elevation in Sacca di Goro coastal lagoon taking into account the effects of the new artificial connection with Adriatic Sea and considering different wind and tide forcing conditions.

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x 106 Elevation and currents for ebb tide and NE wind

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Wind directions and type of tides

Travelling Time [minutes]

Point 11 Point 3 Point 33 Point 8

SE wind, Ebb tide 60 65 70 85

SE wind, Flood tide 30 40 45 60

E wind, Ebb tide 60 65 70 85

E wind, Flood tide 40 40 45 60

NE wind, Ebb tide 65 70 70 85

NE wind, Flood tide 40 40 45 60

NW wind, Ebb tide 60 65 70 85

NW wind, Flood tide 45 45 50 65

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4.97x 10

11 buoy

Bianco

Giralda

Po di Volano

Adriatic Sea

Bonello

Po di Goro

Meteo station

Travelling/Propagation timesThe performed numerical tests evidence compatible results for both lagoon topologies.

Flood tides - the average travelling times is about 35 min for the central/western zone and ca. 45 min for the eastern zone.

Ebb tides - the travelling times for the different sections of Sacca di Goro are approximately doubled in comparison with those for the flooding cases.

Model Results 2

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4.97x 10

2.302 2.304 2.306 2.308 2.31 2.312 2.314

4.97x 10

Model Results 3

Water renewal and exchange

Investigations of particle trajectories in Sacca di Goro coastal lagoon taking into account the effects of the new artificial connection with Adriatic Sea

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Model Results 4

Residence times

The average residence times in 1992 for western part of Sacca di Goro lagoon are between 0.5-1 day. The observed for the same year minimal residence times in this part are in order of 6-7 hours while the maximal ones range to 2-4 days. The residence times for the western part of Sacca di Goro are less affected by the opening of the new connection with Adriatic sea.

The central zone of Sacca di Goro can be characterize in 1992 for non changed bathymetry with mean residence time values 3-6 days, minimal residence periods 12-13 hours and maximal residence intervals of order 10-24 days. In the case of the modified bathymetry the residence times for the southern central part are enlarged about 1.5-2 times.

In the eastern part of Sacca di Goro for non modified bathymetry during 1992 the average residence times reach values 7-18 days, the minimal residence intervals are 1-8 days but the maximal ones vary between 20-49 days. The launch of the new artificial connection reduces the residence time periods in the eastern part approximately 2 times.

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Effect of new connection on temperature and salinity fields

The extra mouth changes the temperature and salinity fields in the eastern and central parts of the lagoon because it improves the water exchange with the open sea. No serious influence on temperature and salinity in the western part of Sacca di Goro was found.

In general the new connection produces into the affected zones an increase of the temperature of the lagoon’s water during the winter and its reduction during the rest of the year. The water salinity shows higher values in the situation with the new channel.

It was found that the considered relatively small changes of the south-eastern border of the lagoon can lead to variations of range 10-20% for the temperature and salinity fields into Sacca di Goro.

Model Results 5

2.302 2.304 2.306 2.308 2.31 2.312 2.314

4.97x 10

11 buoy

Bianco

Giralda

Po di Volano

Adriatic Sea

Bonello

Po di Goro

Meteo station

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Mar Menor (Spain)

Conclusions:

1. The basic outcome of this part of DITTY project is that calibrated and verified 3-D hydrodynamic model for coastal lagoons has been work out.

2. The model was successfully applied for investigation an Italian Adriatic Sea coastal lagoon which is of special interest. The next step of our work will be coupling the hydrodynamic model with biological and contaminants fate models.

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Surface Temperatures in 1992 (monthly dynamics)

for Sacca di Goro Coastal Lagoon

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x 106 Surface temperature at 20/01/92 15:00

4.514.01

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271 m/s

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14 1 m/s

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12 1 m/s

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71 m/s

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Surface Salinity in 1992 (monthly dynamics)

for Sacca di Goro Coastal Lagoon

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x 106 Surface salinity at 20/01/92 15:00

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12 1 m/s

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342624

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1 JRC – Ispra Numerical Hydrodynamics Study of Sacca di Goro Coastal Lagoon, Italian Northern...

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