Preliminary Considerations for Nearshore Preliminary Considerations for Nearshore Placement of Mixed Dredged Sediments on Placement of Mixed Dredged Sediments on a North Adriatic shoreline (Italy) a North Adriatic shoreline (Italy) Contact: ROBERTA GUERRA University of Bologna Centro Interdipartimentale di Ricerca per le Scienze Ambientali (C.I.R.S.A.), 163, Via S.Alberto, 48100 Ravenna, Italy Phone: +39 0544 937305 Fax: +39 0544 937303 e-mail: roberta.guerra@unibo.it
Index Index I I - - Background Background � Area description � Area description � � Relevant physical Relevant physical process process � Water Quality Quality � Water II – – Problem Problem description description II � Coastal erosion erosion: : causes causes & & effects effects � Coastal � Natural forces forces � Natural � � Land subsidence Land subsidence III – III – Solutions Solutions/ /Measures Measures � Coastal defence defence: hard & soft : hard & soft measures measures � Coastal � � Beach Beach nourishiment nourishiment � Nearshore placement placement of of mixed mixed dredged dredged material material � Nearshore � � Sediment sampling sampling Sediment � Pre- -nourishment nourishment conditions conditions � Pre III- - Effects Effects and and lessons lessons learnt learnt III � � Placement Placement site site factors factors � Planning and designing designing � Planning and � Conclusions � Conclusions 2 2
I - - Background Background I
Area Description Area Description � Lido di Dante is a seaside resort located 7 km from Ravenna tow Lido di Dante is a seaside resort located 7 km from Ravenna town, in n, in � Emilia- Emilia -Romagna region (Italy) Romagna region (Italy) � The area is on The area is on the West side of the North Adriatic Sea, and is bordered by the West side of the North Adriatic Sea, and is bordered by � the mouths of the rivers Fiumi Fiumi Uniti Uniti and and Bevano Bevano. . the mouths of the rivers 4 4 Figure 1. Location map of Lido di Dante.
Morphology of the coast Morphology of the coast � Lido di Dante is characterised Lido di Dante is characterised by a beach stretching 3 km from the by a beach stretching 3 km from the � edge of coastal protection structures to the Bevano Bevano river mouth; river mouth; edge of coastal protection structures to the � In the area outside the tourist facilities it is still possible In the area outside the tourist facilities it is still possible to find to find � natural dunes in the back of the beach. Nowadays this system is natural dunes in the back of the beach. Nowadays this system is pretty narrow due to the development of tourist facilities and erosion rosion pretty narrow due to the development of tourist facilities and e problems; problems; � Since the submerged breakwater has been built, the North part of Since the submerged breakwater has been built, the North part of the the � littoral has remained stable whereas the South part has undergone e littoral has remained stable whereas the South part has undergon increasing erosion, particularly during winter storms. increasing erosion, particularly during winter storms. Northern beach Southern beach Beach dune Submerged breakwaters Figure 2. Hard defence structures and natural dune in Lido di Dante . Figure 2. 5 5
Landscape features features Landscape � The site includes the mouths of the rivers The site includes the mouths of the rivers � Bevano and and Ghiaia Ghiaia, the related coastal , the related coastal Bevano area, the natural dune system, small area, the natural dune system, small brackish wetlands, a pinewood Pinus brackish wetlands, a pinewood Pinus , and cultivated land. pinea , and cultivated land. pinea � Natural Park of the Po River Natural Park of the Po River � � National Nature Reserves National Nature Reserves � � Wetlands of international importance Wetlands of international importance � (Ramsar Ramsar Convention) Convention) ( � Special Protection Area (SPA) & Site Special Protection Area (SPA) & Site � of Community Importance (SCI) of Community Importance (SCI) Aerial view of the Bevano Bevano River River Figure 3. Aerial view of the mouth & protected wetlands. mouth & protected wetlands. 6 6
Relevant physical processes Relevant physical processes � Winds & Waves Winds & Waves � � Lido di Dante is exposed to winds coming from Lido di Dante is exposed to winds coming from � NE (Bora), ESE and SSE (Scirocco Scirocco) and NW ) and NW NE (Bora), ESE and SSE ( (Maestrale Maestrale). ). ( � The strongest winds occur during winter from The strongest winds occur during winter from � NW- -N N- -NE. NE. NW � Summer is characterized by high frequency of Summer is characterized by high frequency of � southern winds. The different distribution and southern winds. The different distribution and intensity of the winds are due to the different intensity of the winds are due to the different dimensions of the fetch area characterising the dimensions of the fetch area characterising the two main wind directions. two main wind directions. � Wind directions and wave time series analysis Wind directions and wave time series analysis � showed that the most frequent storms come showed that the most frequent storms come from Scirocco Scirocco, but the strongest ones from , but the strongest ones from Bora Bora from (Ciavola Ciavola et al., 2007). et al., 2007). ( Figure 4. Wind rose offshore and wave climate offshore, Figure 4. 2002-2004 (data from www.idromare.com/index.php). 7 7
Water quality Water quality Figure 5. Water monitoring data, 2002-2004. Figure 5. � Water monitoring for bathing in the area of study, as well as in Water monitoring for bathing in the area of study, as well as in 92 92 � sampling points of the regional shoreline, is carried out by the sampling points of the regional shoreline, is carried out by the Environmental Protection Agency of Emilia- -Romagna Region (ARPA) Romagna Region (ARPA) Environmental Protection Agency of Emilia from April to September on a year basis. from April to September on a year basis. � Monitoring parameters are pH, dissolved oxygen (O Monitoring parameters are pH, dissolved oxygen (O 2 ), transparency, 2 ), transparency, � coliforms, etc. (data from coliforms , etc. (data from www.arpa.emr.it/balneazione www.arpa.emr.it/balneazione). ). 8 8
II – – Problem Problem description description II
Coastal Erosion: causes and effects Coastal Erosion: causes and effects Coastal erosion results from a combination of various factors factors , both natural natural Coastal erosion induced , which has different time and space patterns and have and human- -induced and human different nature (continuous or incidental, reversible or non-reversible). In addition, uncertainties still remain about the interactions of the forcing agents, as well as on the significance of non-local causes of erosion (EUROSION, 2004). Coastal erosion at regional & local level Coastal erosion at regional & local level Beach erosion affects over 40 km of coastline in Emilia-Romagna resulting in shorelines retreating. The main causes are (Regione Emilia-Romagna, 2006): � Significant decrease of sediment supply due to the dredging of gravel and sand from river beds, and the trapping of sediment in embankments and dams; � Presence of coastal structures (breakwaters, groins, etc.) has changed the longshore current flows, interrupting the sand distribution along the coast; � Intensive agriculture and urban development very close to the beach, led to the disappearance of the coastal dunes systems; � Subsidence rate has greatly increased as a result of water and natural gas extraction from coastal and marine areas ( ARPA Emilia-Romagna, 2004 ). 10 10
Natural forces Natural forces level rise , which is a long-term factor, taking place very slowly over � Sea Sea- -level rise � decades causes shorelines to retreat inland. Storms combined with high tides cause beaches an dunes to retreat of � Storms combined with high tides � tenths of meters in a few hours resulting in dramatic beach changes, loss of beach equilibrium, massive damages to coastal infrastructures, and serious beach erosion (Ciavola et al., 2007). Figure 7. Dune profile in Lido di Dante surveyed after a major storm on 24-26 Figure 7. September 2004 (Perini et al., http://www.regione.emilia-romagna.it/wcm/geologia/canali/ costa/progetti/02_analisi_pericolosita.htm ). 11 11
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