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), Italy ² MUMM, Inst. Natural Science, Brussels, Belgium 6- th ELOISE European Conference, Portoroz, 15-18 November 2004 Numerical Hydrodynamics Study of Sacca di Goro Coastal Lagoon, Italian Northern Adriatic Sea JRC – Ispra

Contents: 1. Introduction 2. COHERENS model 3. Model results: Flow patterns and Water surface elevation Travelling/Propagation times Particle trajectories and Residence times Effect of new open sea connection on temperature and salinity Surface temperature and salinity in 1992 (movie) 4. Conclusions JRC – Ispra

DITTY Project : Development of an Information Technology Tool for the Management of Southern European Lagoons under the influence of river-basin runoff EVK3-CT-2002-00084 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. JRC – Ispra

Introduction Length ~ 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 Disruptions: • macro algal blooms, • anoxic crises, • economic losses. Sacca di Goro (Italy) Ulva proliferation JRC – Ispra

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

Model Verification 1 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 Ciavola, P., Gonella, M., Tessari, U. and Zamariolo, A., 2000. In: L. Terrazzi (Editor), Studi Costieri 2, Firenze, pp.153-173 JRC – Ispra

Model Verification 2 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 JRC – Ispra

Model Results 1 Flow patterns and water surface elevation Investigations 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. JRC – Ispra

Model Results 2 Travelling/Propagation times The 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. JRC – Ispra

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 JRC – Ispra

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. JRC – Ispra

Model Results 5 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. JRC – Ispra

Conclusions: • 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. • 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. Mar Menor (Spain) JRC – Ispra

Surface Temperatures in 1992 (monthly dynamics) for Sacca di Goro Coastal Lagoon JRC – Ispra

JRC – Ispra

Surface Salinity in 1992 (monthly dynamics) for Sacca di Goro Coastal Lagoon JRC – Ispra

JRC – Ispra

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