Preliminary Considerations for Nearshore Preliminary Considerations - - PowerPoint PPT Presentation
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:
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
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I I -
Background
Area description
Relevant physical process process
Water Quality Quality II II – – Problem Problem description description
Coastal erosion erosion: : causes causes & & effects effects
Natural forces forces
Land subsidence subsidence III III – – Solutions Solutions/ /Measures Measures
Coastal defence defence: hard & soft : hard & soft measures measures
Beach nourishiment nourishiment
Nearshore placement placement of
mixed dredged dredged material material
Sediment sampling sampling
Pre-
nourishment conditions conditions III III-
Effects and and lessons lessons learnt learnt
Placement site site factors factors
Planning and designing designing
Conclusions
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Lido di Dante is a seaside resort located 7 km from Ravenna town, in n, in Emilia Emilia-
Romagna region (Italy)
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 the mouths of the rivers Fiumi Fiumi Uniti Uniti and and Bevano Bevano. . Figure 1. Location map of Lido di Dante.
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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 edge of coastal protection structures to the Bevano Bevano river mouth; river mouth;
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 e pretty narrow due to the development of tourist facilities and erosion rosion problems; problems;
Since the submerged breakwater has been built, the North part of the the littoral has remained stable whereas the South part has undergon littoral has remained stable whereas the South part has undergone e increasing erosion, particularly during winter storms. increasing erosion, particularly during winter storms.
Northern beach Southern beach
Submerged breakwaters Beach dune
Figure 2. Figure 2. Hard defence structures and natural dune in Lido di Dante .
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The site includes the mouths of the rivers Bevano Bevano and and Ghiaia Ghiaia, the related coastal , the related coastal area, the natural dune system, small area, the natural dune system, small brackish wetlands, a pinewood brackish wetlands, a pinewood Pinus Pinus pinea pinea, and cultivated land. , and cultivated land.
Natural Park of the Po River
National Nature Reserves
Wetlands of international importance ( (Ramsar Ramsar Convention) Convention)
Special Protection Area (SPA) & Site
Figure 3. Aerial view of the Aerial view of the Bevano Bevano River River mouth & protected wetlands. mouth & protected wetlands.
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Lido di Dante is exposed to winds coming from NE (Bora), ESE and SSE ( NE (Bora), ESE and SSE (Scirocco Scirocco) and NW ) and NW ( (Maestrale Maestrale). ).
The strongest winds occur during winter from NW NW-
N-
NE.
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 showed that the most frequent storms come showed that the most frequent storms come from from Scirocco Scirocco, but the strongest ones from , but the strongest ones from Bora Bora ( (Ciavola Ciavola et al., 2007). et al., 2007).
Figure 4. Figure 4. Wind rose offshore and wave climate offshore, 2002-2004 (data from www.idromare.com/index.php).
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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 Environmental Protection Agency of Emilia-
Romagna Region (ARPA) from April to September on a year basis. from April to September on a year basis.
Monitoring parameters are pH, dissolved oxygen (O2
2), transparency,
), transparency, coliforms coliforms, etc. (data from , etc. (data from www.arpa.emr.it/balneazione www.arpa.emr.it/balneazione). ). Figure 5. Figure 5. Water monitoring data, 2002-2004.
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Coastal erosion Coastal erosion results from a combination of various factors factors, both natural natural and human and human-
induced, which has different time and space patterns and have 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).
Beach erosion affects over 40 km of coastline in Emilia-Romagna resulting in shorelines
from river beds, and the trapping of sediment in embankments and dams;
longshore current flows, interrupting the sand distribution along the coast;
disappearance of the coastal dunes systems;
extraction from coastal and marine areas (ARPA Emilia-Romagna, 2004).
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Sea-
level rise, which is a long-term factor, taking place very slowly over decades causes shorelines to retreat inland.
Storms combined with high tides cause beaches an dunes to retreat of 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. Figure 7. Dune profile in Lido di Dante surveyed after a major storm on 24-26
September 2004 (Perini et al., http://www.regione.emilia-romagna.it/wcm/geologia/canali/ costa/progetti/02_analisi_pericolosita.htm).
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Coastal
areas have experienced an increasing trends in subsidence over the years with a reduction around the 1980s due to regulations
groundwater extraction (Figure 8). Recent data indicate an average subsiding rate of about 1 cm/yr along the regional coastal areas in period 2002-2006 (Bonsignore, 2007).
In the last decades, along Lido di Dante
coastal area, the subsiding rates ranged between 0.42 and 0.66 cm/yr (ARPA Emilia-Romagna, 2004).
The northern littoral towards the Fiumi
Uniti River shows an increase in land subsidence (Figure 8).
In contrast, the southern littoral displays a
decreasing trend over time (Figure 8).
Figure 8. Figure 8. Subsidence trends in Marina di Ravenna (up), and subsidence rates in coastal areas near Lido di Dante (bottom) (ARPA Emilia-Romagna, 2004).
0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999
Elevation (m) 0.35 0.30 0.61 0.42 0.43 0.45 0.45 0.5 1 1.5 2
Ravenna P.ta Marina Fiumi Uniti Lido di Dante Lido di Classe Lido di Savio Milano Marittima
subsidence (cm/year)
1984-1993 1993-1999 Northward Sourthward
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Submerged breakwater (shore parallel)
Structures that effectively reduce the amount of wave energy reaching the protected stretch of shoreline; designed to prevent the erosion of an existing beach or a beach fill, or to enhance natural sediment accumulation to form a new beach.
Groins (shore perpendicular)
Narrow structures that are used to: (i) build or widen a beach by trapping longshore drift (ii) to stabilize a beach that is subject to severe storms or to excessive seasonal shoreline recession (iii) to reduce the rate of longshore transport out of an area (iv) to reduce longshore losses of sand from an area by compartmenting the beach, and (v) to prevent sedimentation or accretion in a downstream area by acting as a barrier to longshore transport.
Beach and dune nourishment
Beach or dune nourishment are quasi-natural methods to increase sand volumes in the foreshore via the supply of suitable material. Replenishment of sand eroded from the beach does not solve an
Emilia-Romagna coast (northern Adriatic Sea) come from: (i) mainly
formed during the last Adriatic post-glacial transgression (Preti, 2006); and (ii) dredged materials dredged materials from ports (Peretti, 2006).
Groyne 1978 Groins 1983 Semi-submerged breakwater 1995
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Sand deposits: 30-
50 km offshore; water depth 35-
42 m
Sand volume: 800,000 m3
Project costs: 13.5 M€
Duration: 146 days, 2007
Renourished shores: 9 km; shores: 9 km;
Average beach accretion: 40 m.
Location Nourishment activities [days] Shore lenght [m] Beach accretion [m]
RICCIONE SUD 9 1,100 40 BELLARIA – IGEA MARINA 8 1,600 30 MISANO ADRIATICO 10 1,500 40 MILANO MARITTIMA 8 1,000 50 CESENATICO 7 700 50 LIDO DI DANTE 5 1,000 40 PUNTA MARINA 9 2,000 40
Totals 56 8,900
Table 1. Beach nourishment data ( Table 1. Beach nourishment data (Regione Regione Emila Emila-
Romagna, 2007) , 2007) Figure 9. Map of Emilia-Romagna costal area (ARPA, 2002).
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Nearshore placement of uncontaminated sand/silt mixtures placement of uncontaminated sand/silt mixtures has applications as a beneficial use approach (US Army, has applications as a beneficial use approach (US Army, 1998): 1998):
Supplements beach profile by adding material to the
littoral zone;
Renourishes beach; Decreases nearshore wave heights reducing damage from
erosive waves and storms;
Reduces use of limited-capacity upland and offshore
disposal sites;
Decreases mobilization/demobilization costs; …
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Nourishment approach and model types should be considered (e.g. dune nourishment , nourishment of subaerial beach; profile nourishment; bar or shoreface nourishment); Basic steps for nearshore placement of mixed dredged material projects should include: Beach stability characterisation Receiving beach characterisation (physical, chemical, biological) Mixed dredged sediment characterisation (physical, chemical, biological) Beach monitoring/maintanance plan to evaluate project impacts, and whether the project is performing as designed and identify re-nourishment requirements
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Figure 10. Figure 10. Sampling stations in Lido di Dante.
Transect 1 Transect 5 Transect 4 Transect 2 Transect 3
5 profiles spaced 100 m apart alongshore m apart alongshore were surveyed were surveyed seaward seaward
Beach dune
Mid-
Shore
Shoreface: depth 0.5 m : depth 0.5 m
Shoreface: depth 1 m : depth 1 m
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Sampling plan: 5 cells (100 x 100 m)
1 composite sample for each cell
A total of 5 composite samples within CDF
Figure 11. Figure 11. Confined Disposal Facility and sampling plan.
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Figure 12. Figure 12. Grain-size analysis curves.
Mixed dredged sediments Grain size (mm) 0,01 0,1 1 % passing 25 50 75 100 Nourishing beach
Grain size (mm) 0,01 0,1 1 % passing 10 20 30 40 50 60 70 80 90 100
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448 448 400 400-
487 354 354 234 234-
794 P (mg/kg) P (mg/kg) 0.23 0.23 0.20 0.20-
0.31 0.07 0.07 0.05 0.05-
0.09 N ( N (‰ ‰) ) 2.13 2.13 1.20 1.20-
2.78 5.28 5.28 0.02 0.02-
29.76 Sand Sand (0.500 (0.500-
0.800 mm) % 2.71 2.71 1.89 1.89-
3.61 6.96 6.96 0.01 0.01-
43.19 Sand Sand (0.8 (0.8-
2 mm) % 0.21 0.21 0.17 0.17-
0.30 0.07 0.07 0.04 0.04-
0.12 TOC (%) TOC (%) 22.90 22.90 9.74 9.74-
46.22 0.34 0.34 0.00 0.00-
1.15 Silt Silt-
clay (< 63 mm) % (< 63 mm) % 30.07 30.07 21.21 21.21-
38.11 1.02 1.02 0.00 0.00-
6.20 Sand Sand (0.63 (0.63-
125 mm) % 35.58 35.58 12.48 12.48-
55.39 33.44 33.44 1.06 1.06-
68.68 Sand Sand (0.125 (0.125-
0.250 mm) % 6.61 6.61 3.77 3.77-
10.27 52.95 52.95 27.87 27.87-
74.08 Sand Sand (0.250 (0.250-
0.500 mm) % Average Average Range Range Average Average Range Range Mixed Mixed dredged dredged material material (CDF) (CDF) Nourishing Nourishing Beach Beach (Lido di Dante) (Lido di Dante)
Table Table 2.
dredged material.
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The grain-
size distributions of the source material should
be be compared to compared to grain grain-
size distribution at the proposed proposed placement placement site to determine sediment compatibility. site to determine sediment compatibility.
Mixed dredged sediments stored in the CDF indicates that sediments ts consist of fine sand, finer than consist of fine sand, finer than nearshore nearshore, mid , mid-
shore, and dune sediments found at the nourishing beach in Lido sediments found at the nourishing beach in Lido di di Dante. Dante.
Ideally, the grain size of the source material should be the , the grain size of the source material should be the same size same size than the native beach sand than the native beach sand to to minimise minimise erosion erosion. .
Physical separation processes are generally technically are generally technically simple methods for separation of particles on the basis of simple methods for separation of particles on the basis of size, density or surface chemistry differences (Olin size, density or surface chemistry differences (Olin-
Estes and Palermo, 2001; Myers and Adrian, 2000), that can be and Palermo, 2001; Myers and Adrian, 2000), that can be taken to produce material suitable for various beneficial taken to produce material suitable for various beneficial uses (e.g. beach nourishment), and should be evaluated uses (e.g. beach nourishment), and should be evaluated together with other alternatives to determine the most together with other alternatives to determine the most suitable approach for a given site. suitable approach for a given site.
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Figure 13. Figure 13. Metal Metal concentrations concentrations in in mixed mixed dredged dredged sediments sediments (CDF) and (CDF) and pre pre-
nourishing beach beach vs vs PELs PELs and and TELs TELs (Pellegrini (Pellegrini et et al., 2002). al., 2002).
CDF T 1 T 2 T 3 T 4 T 5 Ni (ppm) 10 20 30 40 50 60 70 80 TEL PEL CDF T 1 T 2 T 3 T 4 T 5 Pb (ppm) 10 20 30 40 50 60 70 80 TEL PEL CDF T 1 T 2 T 3 T 4 T 5 Cr (ppm) 50 100 150 200 250 300 350 400 TEL PEL CDF T 1 T 2 T 3 T 4 T 5 Cu (ppm) 10 20 30 40 50 60 TEL PEL
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According to Sediment Quality Guidelines (SQGs SQGs) set by ICRAM ( ) set by ICRAM (Pellegrini Pellegrini et et al., 2002), mixed dredged sediment is not likely to pose adverse al., 2002), mixed dredged sediment is not likely to pose adverse effects on the effects on the resident biota on the nourishing beach, except for Cr, and could resident biota on the nourishing beach, except for Cr, and could be suitable for: be suitable for:
Construction of fillings within ports;
Coastal defence defence structures; structures;
Recovery of coastal natural structures;
Open sea disposal.
Further investigation on physico physico-
chemical and biological properties to track provenance of material, plus toxicity testing and analysis of be provenance of material, plus toxicity testing and analysis of benthic community nthic community is necessary to determine suitability for beneficial uses (e.g. is necessary to determine suitability for beneficial uses (e.g. nearshore nearshore placement) and assess potential environmental impacts ( placement) and assess potential environmental impacts (Colosio Colosio et al., 2007). et al., 2007).
Source material
PEL ≤ Cr <TEL Cu < PEL Ni < PEL Pb < PEL
Pre-nourishing beach
PEL ≤ Cr < TEL Cu < PEL Ni < PEL Pb < PEL
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Mixed dredged sediments at the dredging site/confined disposal facility must be characterized to determine type of material and if it is contaminated. Bathymetry of the proposed placement site defines the placement site location and boundaries; Knowledge of the hydrodynamic climate (wind, waves, and currents) is necessary to assess the potential physical behavior of dredged sediment and to properly site a berm to optimize stability, wave breaking, or nearshore/beach feeding benefits. Physical model investigations of mixed sediment movement, improvement of existing numerical models determining the fate of dredged material, and environmental effects of material placed in the nearshore. Numerical model (e.g. profile evolution, shoreline evolution, multi- layer, quasi-3D) to predicting the effect of beach nourishment and sediment variation on beach morphodynamic assessment (Capobianco et al., 2002; Zanuttig, 2007);
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Planning and designing nearshore placement alternatives of mixed dredged material first require knowledge of the physical and ecological environment; Engineering decisions can then be made to determine potential placement alternatives that provide a basis for decisions driven by economic factors. The results of such decisions may then provide a beneficial, economically feasible nearshore placement alternative. Assessment of benefits and risks to submerged coastal habitats for shellfish, fisheries resources, endangered species, bottom habitats is necessary to determine short- and long- term environmental impacts.
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Nearshore placement of uncontaminated sand/silt mixtures placement of uncontaminated sand/silt mixtures has applications as a beneficial use approach, but… has applications as a beneficial use approach, but… Alternatives for disposing mixed sediments are limited by State and
local regulatory requirements that restrict the percentage of fines allowed to be placed directly on the beach;
The only alternatives available, offshore disposal or upland placement
sources from the local littoral zone, but can also be more expensive and time-consuming than nearshore placement.
Nearshore placement of mixed dredged material is often undesirable
because of the environmental impact of smaller grain size and/or darker colour may have on the beach or beach habitat.
Research on nearshore nearshore placement of mixed sediments is placement of mixed sediments is needed to develop to tools that will assist (i) to predict the needed to develop to tools that will assist (i) to predict the ability of a mixed ability of a mixed-
sediment placement to enhance the nearshore nearshore area, (ii) to assess physical and environmental area, (ii) to assess physical and environmental benefits/impacts, (iii) to justify projects, to promote cost benefits/impacts, (iii) to justify projects, to promote cost-
sharing and to address regulatory agency concerns.