Presentation is loading. Please wait.

Presentation is loading. Please wait.

Preliminary Considerations for Nearshore Placement of Mixed Dredged Sediments on a North Adriatic shoreline (Italy) Contact: ROBERTA GUERRA University.

Similar presentations


Presentation on theme: "Preliminary Considerations for Nearshore Placement of Mixed Dredged Sediments on a North Adriatic shoreline (Italy) Contact: ROBERTA GUERRA University."— Presentation transcript:

1 Preliminary Considerations for Nearshore Placement of Mixed Dredged Sediments on 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

2 2Index I - Background  Area description  Relevant physical process  Water Quality II – Problem description  Coastal erosion: causes & effects  Natural forces  Land subsidence III – Solutions/Measures  Coastal defence: hard & soft measures  Beach nourishiment  Nearshore placement of mixed dredged material  Sediment sampling  Pre-nourishment conditions III- Effects and lessons learnt  Placement site factors  Planning and designing  Conclusions

3 I - Background

4 4 Area Description  Lido di Dante is a seaside resort located 7 km from Ravenna town, in Emilia-Romagna region (Italy)  The area is on the West side of the North Adriatic Sea, and is bordered by the mouths of the rivers Fiumi Uniti and Bevano. Figure 1. Location map of Lido di Dante.

5 5 Morphology of the coast  Lido di Dante is characterised by a beach stretching 3 km from the edge of coastal protection structures to the Bevano river mouth;  In the area outside the tourist facilities it is still possible to find natural dunes in the back of the beach. Nowadays this system is pretty narrow due to the development of tourist facilities and erosion problems;  Since the submerged breakwater has been built, the North part of the littoral has remained stable whereas the South part has undergone increasing erosion, particularly during winter storms. Northern beachSouthern beach Submerged breakwaters Beach dune Figure 2. Figure 2. Hard defence structures and natural dune in Lido di Dante.

6 6 Landscape features  The site includes the mouths of the rivers Bevano and Ghiaia, the related coastal area, the natural dune system, small brackish wetlands, a pinewood Pinus pinea, and cultivated land. Natural Park of the Po River Natural Park of the Po River National Nature Reserves National Nature Reserves Wetlands of international importance (Ramsar Convention) Wetlands of international importance (Ramsar Convention) Special Protection Area (SPA) & Site of Community Importance (SCI) Special Protection Area (SPA) & Site of Community Importance (SCI) Aerial view of the Bevano River mouth & protected wetlands. Figure 3. Aerial view of the Bevano River mouth & protected wetlands.

7 7 Relevant physical processes  Winds & Waves Lido di Dante is exposed to winds coming from NE (Bora), ESE and SSE (Scirocco) and NW (Maestrale). Lido di Dante is exposed to winds coming from NE (Bora), ESE and SSE (Scirocco) and NW (Maestrale). The strongest winds occur during winter from NW-N-NE. The strongest winds occur during winter from NW-N-NE. Summer is characterized by high frequency of southern winds. The different distribution and intensity of the winds are due to the different dimensions of the fetch area characterising the two main wind directions. Summer is characterized by high frequency of southern winds. The different distribution and intensity of the winds are due to the different dimensions of the fetch area characterising the two main wind directions. Wind directions and wave time series analysis showed that the most frequent storms come from Scirocco, but the strongest ones from Bora (Ciavola et al., 2007). Wind directions and wave time series analysis showed that the most frequent storms come from Scirocco, but the strongest ones from Bora (Ciavola et al., 2007). Figure 4. Figure 4. Wind rose offshore and wave climate offshore, 2002-2004 (data from www.idromare.com/index.php).www.idromare.com/index.php

8 8 Water quality  Water monitoring for bathing in the area of study, as well as in 92 sampling points of the regional shoreline, is carried out by the Environmental Protection Agency of Emilia-Romagna Region (ARPA) from April to September on a year basis.  Monitoring parameters are pH, dissolved oxygen (O 2 ), transparency, coliforms, etc. (data from www.arpa.emr.it/balneazione). www.arpa.emr.it/balneazione Figure 5. Figure 5. Water monitoring data, 2002-2004.

9 II – Problem description

10 10 Coastal Erosion: causes and effects Coastal erosionfactorsnatural and human-induced Coastal erosion results from a combination of various factors, both natural 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). 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 ).

11 11  Sea-level rise  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  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). Natural forces 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 ). http://www.regione.emilia-romagna.it/wcm/geologia/canali/ costa/progetti/02_analisi_pericolosita.htm

12 12 Land subsidence: a combination of natural and man-made processes   Coastal areas have experienced an increasing trends in subsidence over the years with a reduction around the 1980s due to regulations on 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).

13 III – Solutions/Measures

14 14 Coastal defence: hard and soft measures 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 offshore sands dredged materials 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 ongoing erosion problem, and periodic replenishment is usually be required. Sands sources for the nourishment of beaches along the Emilia-Romagna coast (northern Adriatic Sea) come from: (i) mainly offshore sands formed during the last Adriatic post-glacial transgression (Preti, 2006); and (ii) dredged materials from ports (Peretti, 2006). Groyne 1978 Groins 1983 Semi-submerged breakwater 1995

15 15 Beach nourishment at 7 regional beaches from offshore sand deposits  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;  Average beach accretion: 40 m. Table 1. Beach nourishment data (Regione Emila- Romagna, 2007) Figure 9. Map of Emilia-Romagna costal area (ARPA, 2002).

16 16 Nearshore placement of mixed sediments  Nearshore placement of uncontaminated sand/silt mixtures has applications as a beneficial use approach (US Army, 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; …

17 17 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 Planning and designing

18 18 Sampling for Pre-nourishing Conditions 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 were surveyed seaward Beach dune Beach dune Mid-Shore Mid-Shore Shoreface: depth 0.5 m Shoreface: depth 0.5 m Shoreface: depth 1 m Shoreface: depth 1 m  Sampling device: box-corer  N° samples: 20

19 19 Sampling for Mixed Dredged Sediments  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.

20 20 Pre-nourishment conditions: physical characteristics (1) Figure 12. Figure 12. Grain-size analysis curves.

21 21 Pre-nourishment conditions: physico- chemical characteristics (2) Nourishing Beach (Lido di Dante) Mixed dredged material (CDF) RangeAverageRangeAverage Sand (0.8-2 mm) % 0.01-43.196.961.89-3.612.71 Sand (0.500-0.800 mm) % 0.02-29.765.281.20-2.782.13 Sand (0.250-0.500 mm) % 27.87-74.0852.953.77-10.276.61 Sand (0.125-0.250 mm) % 1.06-68.6833.4412.48-55.3935.58 Sand (0.63-125 mm) % 0.00-6.201.0221.21-38.1130.07 Silt-clay (< 63 mm) % 0.00-1.150.349.74-46.2222.90 N (‰) 0.05-0.090.070.20-0.310.23 P (mg/kg) 234-794354400-487448 TOC (%) 0.04-0.120.070.17-0.300.21 Table 2. Table 2. Comparison of sediment characteristics: nourishing beach and mixed dredged material.

22 22 Compatibility – Grain size The grain-size distributions of the source material should be compared to grain-size distribution at the proposed placement site to determine sediment compatibility. The grain-size distributions of the source material should be compared to grain-size distribution at the proposed placement site to determine sediment compatibility.  Mixed dredged sediments stored in the CDF indicates that sediments consist of fine sand, finer than nearshore, mid-shore, and dune sediments found at the nourishing beach in Lido di Dante. Ideally, the grain size of the source material should be the same size than the native beach sand to minimise erosion. Ideally, the grain size of the source material should be the same size than the native beach sand to minimise erosion. Physical separation processes are generally technically simple methods for separation of particles on the basis of size, density or surface chemistry differences (Olin-Estes and Palermo, 2001; Myers and Adrian, 2000), that can be taken to produce material suitable for various beneficial uses (e.g. beach nourishment), and should be evaluated together with other alternatives to determine the most suitable approach for a given site. Physical separation processes are generally technically simple methods for separation of particles on the basis of size, density or surface chemistry differences (Olin-Estes and Palermo, 2001; Myers and Adrian, 2000), that can be taken to produce material suitable for various beneficial uses (e.g. beach nourishment), and should be evaluated together with other alternatives to determine the most suitable approach for a given site.

23 23 Pre-nourishment conditions: ranges of metals Figure 13. Metal concentrations in mixed dredged sediments (CDF) and pre- nourishing beach vs PELs and TELs (Pellegrini et al., 2002).

24 24 Compatibility – ranges of metals  According to Sediment Quality Guidelines (SQGs) set by ICRAM (Pellegrini et al., 2002), mixed dredged sediment is not likely to pose adverse effects on the resident biota on the nourishing beach, except for Cr, and could be suitable for:  Construction of fillings within ports;  Coastal defence structures;  Recovery of coastal natural structures;  Open sea disposal.  Further investigation on physico-chemical and biological properties to track provenance of material, plus toxicity testing and analysis of benthic community is necessary to determine suitability for beneficial uses (e.g. nearshore placement) and assess potential environmental impacts (Colosio et al., 2007). Source material PEL ≤ Cr { "@context": "http://schema.org", "@type": "ImageObject", "contentUrl": "http://images.slideplayer.com/12/3533812/slides/slide_24.jpg", "name": "24 Compatibility – ranges of metals  According to Sediment Quality Guidelines (SQGs) set by ICRAM (Pellegrini et al., 2002), mixed dredged sediment is not likely to pose adverse effects on the resident biota on the nourishing beach, except for Cr, and could be suitable for:  Construction of fillings within ports;  Coastal defence structures;  Recovery of coastal natural structures;  Open sea disposal.", "description": " Further investigation on physico-chemical and biological properties to track provenance of material, plus toxicity testing and analysis of benthic community is necessary to determine suitability for beneficial uses (e.g. nearshore placement) and assess potential environmental impacts (Colosio et al., 2007). Source material PEL ≤ Cr

25 IV – Effects and Lessons learnt

26 26   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); Placement site factors

27 27   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. Planning and designing

28 28Conclusions  Nearshore placement of uncontaminated sand/silt mixtures 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 of mixed dredged sediments, not only keeps much needed sand 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 placement of mixed sediments is needed to develop to tools that will assist (i) to predict the ability of a mixed-sediment placement to enhance the nearshore area, (ii) to assess physical and environmental benefits/impacts, (iii) to justify projects, to promote cost- sharing and to address regulatory agency concerns.


Download ppt "Preliminary Considerations for Nearshore Placement of Mixed Dredged Sediments on a North Adriatic shoreline (Italy) Contact: ROBERTA GUERRA University."

Similar presentations


Ads by Google