Littérature scientifique sur le sujet « Sand borrow areas »

Movements of borrow sand replenished at two coasts of different configurations are investigated by analyzing the topographic data which were surveyed periodically after the beach fill placements. One is a long straight beach and borrow sand was placed behind a submerged breakwater. Another is a pocket beach which has an arcshoreline with a groyne at one end and a headland at another. It is found that the amount of borrow sand moved in the longshore direction surpasses the amount of borrow sand transported in the cross-shore direction regardless of the shape of the coast. A clear correlation is also found between displacements of shoreline and changes of sectional areas. These results imply that the deformation of the artificially nourished beach and the dissipation rate of borrow sand can be predicted by the so-called one-line theory.

The coastline of Panama City Beach, Florida (FL) has been stricken by several hurricanes during the last decades, especially after 1995. In 1998, beach nourishment projects started being implemented to address the impacts of the hurricanes on the coast. Sources of sand for that purpose are commonly from borrow areas located just offshore of the nourishment site. Impacts of these nearshore dredge pits on adjacent coasts will depend on incident wave conditions, nourishment sediment characteristics and some features of the borrow pit (distance from the shore, depth of cut, cross-shore extent, alongshore extent and orientation - Bender & Dean, 2003; Benedet & List, 2008). The practical goal of the current study was to mitigate for the negative potential effects by discovering the less impactful design of dredge pit geometries on the Borrow Area S1 in Bay County-FL. Five different cut widths and excavation depths within the permitted limits were herein evaluated. Evaluation of morphological impacts on adjacent beaches was carried with the processed-based morphodynamic model Delft3D, calibrated and simulated for a period of 13 years. Results were evaluated in terms of beach volume changes compared against a baseline simulation (no action).Switching from Alternative 1 (6,260,000 m³) to Alternative 2 (5,380,000 m³) does not result in a substantial reduction of the borrow area’s projected impact. The cut depth is still deep, and the surface area is unchanged. Alternative 3 (3,555,000 m³) is able to provide more substantial reductions in the borrow area’s impact. By reducing the acreage of the borrow area and switching to a uniform cut depth, the projected impact of the borrow area decreases 39% for 1.56 km along the downdrift beach. Under Alternatives 4 (3,060,000 m³) and 5 (2,755,000 m³), the impacts of the borrow area are projected to be less than 3.75 m³/m/yr. While both alternatives are viable, Alternative 5 minimizes potential impacts, and has a uniform cut depth and a volume that still satisfies the project’s requirements. Given these considerations, Alternative 5 is the preferred alternative. Additionally, all the alternatives increase the net-accretion along 6.5 km of Shell Island between 0.25 to 1 m³/lm/yr., a valuable side effect in a region with high net erosion. By conducting various simulations an optimal borrow area design has been identified that reduces its effects on the adjacent beaches.

Various solutions, which consist of numerous techniques, technologies and planning measures, are testing for reduction shoreline erosion, precisely for protection shore against waves attack. These methods may affect the site's geology and geomorphology, involving changes of the habitats in the site. Coastal defense projects and ideas must take into account the structure and functions of protected natural areas and their conservation objectives in order to avoid threatening the species and/or habitats on the site. The ecological impacts expected from coast protection structures on short-term are mostly negative, may disturbance the birds from their habitat, and destruct the marine coastal habitats with their own flora and fauna. In this study, we are indicating the effects of coastal protection measures on the ecosystem. Therefore, we present a part of methods applied or which will be apply on the Romanian shoreline and the effects that have an impact on the species and/or habitats on the site. The methods referred to “hard” methods so to harder the shore with fixed structure (bulkhead, seawall, revetment, breakwaters, sills or groins) or “soft” methods like beach nourishment that is not a sustainable method in time. The protection structures like breakwaters and groins trap or add sand and will change the beach geometry this means that can introduce new artificial material, which is extensively and rapidly colonized by algae and marine animals. In the cases of beach nourishment, under water sand nourishment and mudflat recharge, there are impacts both at the borrow site (the sediment source) and the target site. In the zone of extraction of borrow, sediments appear a damage and mortality to the benthos. Finally, it can conclude that some of the effects are beneficial for socio-economic aspect, but it is important also, the environment, which can bring bad consequences for earth landscape and make the ecosystem, be unbalanced.

Beach nourishment is a common strategy for erosion mitigation that also increases coastal resilience to storm impacts, provides habitat, and supports the economy. Regulations often require that placed sediment closely match the native grain size distribution and composition, however characteristics can vary based on the borrow site. Certain sediment properties will also influence beach slope and other critical beach functions. This study evaluates the 3-dimensional sediment properties and beach morphology of nourished and non-nourished barrier island beaches in northern Palm Beach County, Florida, USA. Surveyed beach profiles were compared with predicted slope based on median grain size. The inlet-adjacent beach managed with annual placement of beneficial use of dredged materials consisted of poorly sorted coarse sand and the steepest measured slope. Sediment was progressively finer and better sorted downdrift with decreasing foreshore slopes. Although sediment near the shoreline is typically the coarsest, clasts were finer than the mid-beach location suggesting that the sampling period coincided with beach recovery and onshore sediment transport of finer material. Sediment at the surface differed from sediment at depth, likely due to the frequent introduction of sediment from various borrow areas compared to the dominance of weathered coquina at depth. The non-carbonate, siliciclastic fraction was primary quartz with few other minerals. The estimated beach slope at the location with the coarsest sediment matched the measured slope. A lower beach slope was predicted for the other locations with finer grain sizes at the shoreline that was attributed to slightly steeper slopes associated with beach accretion. Therefore, complicated spatio-temporal morphodynamics of beaches should be considered when using median grain size from only one sampling event.

The San Juan Bay Estuary Program and the Corporation for the Conservation of the San Juan Bay Estuary, intends to develop a cost-effective and environmentally acceptable plan for water quality improvement and seagrass restoration in the Condado Lagoon. One of the principal challenges associated with this Project is evaluating options for dredge material sources (borrow sites), transport, and placement in the Condado Lagoon to achieve the ecological restoration goal. A potential borrow site has been identified in the northwestern side of San Juan Bay near La Esperanza Peninsula. The accretion of sediment near the Peninsula has inhibited tidal flushing to this area from San Juan Bay. The implementation of this Project would support the beneficial use initiative by dredging the shoaling material at La Esperanza Peninsula and filling the artificial depressions in Condado Lagoon to improve water circulation at both the dredge and fill sites; as well as providing habitat for epibenthic growth in the Lagoon. In March 2011, Tetra Tech performed baseline investigations in Condado Lagoon, Puerto Rico in support of the San Juan Bay Estuary Program’s Water Quality Improvement and Seagrass Restoration Project. Field investigations included a bathymetric (multibeam) survey, benthic community data collection and sediment sampling. The results of the surveys were used to characterize benthic habitats in the Lagoon and to assist in evaluating alternatives for restoring the Lagoon to a gradient that supports a diverse epibenthic assemblage of Lagoon and estuarine species, specifically seagrass communities. In addition to the above mentioned investigations, Caribbean Oceanography Group deployed GPS-tracked lagrangian drifters in the lagoon in order to gather current data for the calibration of a hydrodynamic model of the Condado Lagoon. The intent of the multibeam survey was to map the existing depths and bathymetric features within Condado Lagoon, with an emphasis on detailing the extents of seven artificial depressions. The results of the survey determined a minimum depth of 0.8 m and maximum depth of 10.4 m (2.6 to 34.1 ft) in the Lagoon. Maximum depths were recorded in the center of the dredge holes, which are located in the center and eastern end of the Lagoon. The results of the multibeam survey were also used to support depth-based in situ data collection of the benthic community. The results of the benthic survey indicate a regional separation in benthic community diversity and abundance. The south-central and southeastern sides of the Lagoon support low to no biotic cover. This is contrary to the biotic diversity and abundance at the western, north-central and northeastern sides of the Lagoon. The benthic data also showed a segregation of benthic community assemblages between three depth ranges (shallow 1.8 to 2.4 m [6.0 to 8.0 ft]; mid (2.7 to 5.8 m [9 to 19 ft]); and deep 6.1 to 9.1 m [20 to 30 ft]). The benthic community in the mid depth range supports the greatest diversity and abundance of organisms. The areas with little to no biotic cover correspond to the dredged areas of the Condado Lagoon. Typical of low energy environments, finer grained sediments are located in the central and eastern regions of the Lagoon. Grain size analyses reported coarse material at the La Esperanza Peninsula sample site and the western end of Condado Lagoon, which are indicative of currents and regular water exchange in these locations. Organic content decreases from west to east in the Lagoon which supports the observations of lower benthic cover in the south-central and southeastern Lagoon compared to the western region. Based on the 2011 baseline investigations, H. decipiens was determined to be the most prevalent seagrass species in the Lagoon, followed by T. testudinum. Fill volume calculations based solely on the bathymetric survey results, estimate between 132,211 and 488,719 cy of fill material needed to support a water depth gradient (2.7 to 5.8 m [9.0 to 19.0 ft]) conducive to H. decipiens and T. testudinum growth in the central and eastern portions of the Lagoon. More specifically, the baseline results suggest a preferred depth of 4.05 m (13.3 ft) for H. decipiens, which would require between approximately 317,629 and 336,504 cy of fill material to restore a portion of the Lagoon. Caribbean Oceanography Group (with the support of Tetra Tech) has modeled the circulation within the Lagoon using the Environmental Fluid Dynamics Code (EFDC) hydrodynamic model. Modeling results reveal a complex circulation within the Condado Lagoon that is largely wind driven. A statistical analysis of the wind record for NOAA’s U.S. Coast Guard Station ID 9755371, located at the western end of the model domain was carried out, and 70%, 80%, 90%, 95% and 98% exceedance levels were determined. Model results show that under the 98% wind speed exceedance scenario, two of the examined locations within the dredged area of the lagoon experience a shear stress large enough to trigger a minimum sand grain diameter requirement for stability through the Shields relation. The locations and their minimum sand grain diameters are: A-2 with 0.46 mm and A-3 with 0.21 mm. These grain sizes correspond to Medium Sand and Fine Sand, respectively (after Wentworth (1922)). Evaluation of the direction of the shear at the above mentioned locations reveals that a portion of the material eroded from location A-2 (the medium sand) will be deposited at location A-3, and the rest (the fine sand) will be deposited at some combination of locations A-4, A-5, A-6 and A-7. Likewise the material originally eroded from location A-3 (fine sand) will be deposited at some combination of locations A-4, A-5, A-6 and A-7. Therefore, any unstable material placed at locations A-2 and A-3 will merely be shifted to another location within the fill area with a lower shear stress where it will become stable. Therefore the requirements for fill stability in the Condado Lagoon in terms of grain size are: 1) In order to remain stable under a 98% exceedance wind event, fill at location A-2 should be composed of sand with a grain diameter greater than 0.46 mm. In other words, Medium to Coarse sand should be used to fill location A-2. 2) In order to remain stable under a 98% exceedance wind event, fill at location A-3 should be composed of sand with a grain diameter greater than 0.21 mm. In other words, Fine to Medium sand should be used to fill location A-3. Of note is the finding that any material too fine to remain stable at either A-2 or A-3 will be deposited at some combination of the remaining fill locations, and thus will not be lost from the fill area, nor will it be unstable and cause problems elsewhere in the lagoon. It should be kept in mind that the lower exceedance levels (95% or less) did not present any minimum sand grain size requirements for stability. For those cases, sand fill of any grain size remains stable. Likewise, a higher exceedance level than 98% would require coarser fill at A-2 and A-3 than that discussed above. In either case, however, the eroded material would remain within the fill area, being deposited the downstream at a more sheltered location

Abstract The paper deals with a sandy shore located on the open sea side of the Hel Peninsula in Poland (the south Baltic Sea coast). The study site displays a cross-shore profile that intensively dissipates wave energy, mostly due to breaking. The theoretical modelling of wave transformation at this site reveals specific distributions of wave heights and bed shear stresses. The sediment borrow areas, presently used and identified for future exploitation, are located inconveniently far from the periodically re-nourished shores. The paper presents the possibilities of dredging works in the coastal zone that would not disturb the natural nearshore motion of water and sediments. The results of the study can be helpful in formulating generic safety standards, at least with respect to dissipative shores of non-tidal or micro-tidal seas, like the Baltic Sea.

A study was carried out to determine the knowledge, attitude and practices of grooms towards brucellosis in Kaduna State, Nigeria. Structured questionnaires were administered to 40 horse owners and grooms’ men in three Local Government Areas (LGAs); Sabon Gari, Zaria and Igabi; of Kaduna State, Nigeria to access knowledge, attitude and practices towards brucellosis in horses. Results from structured questionnaire showed only 37.50% (95% CI) of the respondents were aware of brucellosis, of this 22.50% (95% CI) ascribed their sources of information on the disease to be the media, 10.00% (95% CI) from experienced grooms while 5.00% (95% CI) said they heard of the disease from professionals who attended to the veterinary care of their horses. Of the respondents, only 15.00% (95% CI) were aware that brucellosis is zoonotic and mentioned that it could be contracted via ingestion of contaminated material (12.50%) and contact (2.50%). On attitude of respondents towards brucellosis, 15.00% (95% CI) reported lending out their stallions for breeding to other stables. Only 2.50% (95% CI) did not borrow stallions for breeding because they considered brucellosis and trichomoniasis as reproductive diseases that could result from the use infected stallions. The study also reported 52.50% (95% CI) and 40.00% (95% CI) of the respondents were in the habit of lending and borrowing out grooming tools respectively. They lend and borrow out tool despite mentioning that such acts are capable of leading to diseases such as ulcerative lymphangitis (95.00%), ringworm (72.50%), dermatophilosis (5.00%) and thrush (7.50%). 67.50% (95% CI) of respondents mentioned that they participated in durbars and other tournaments with their horses and reported such participation could result in diseases like ulcerative lymphangitis (25.00%) and wounds (27.50%). 50.00% (95% CI) of the respondents grazed their horses where other animals grazed and reported that even where there were reports of abortions by such animals their horses did not come down with brucellosis. All the respondents reported giving their horses’ routine veterinary medical care, especially against babesiosis. The implication of this finding is that Brucella organisms may be spread among horse handlers and the grooms due to inadequate knowledge on brucellosis. The findings revealed poor knowledge attitude and practices towards brucellosis on the part of horse handlers and grooms. It was concluded that there is a need to create awareness amongst groomsmen and horse owners on the presence of brucellosis in horses as well as the dangers of zoonotic infection.

This brief survey of 19th century Latin America countries economy offered for reader’s attention represents the second article within a series of papers thought by the author in order to follow historical genesis of economical complex of regional states. The indicated period is to be of special interest due to the fact that within it happened development of its specialization accompanied by fundamental processes in commodity production based on destructing of communal Indian land ownership, abolition of slavery and stimulating of European immigration. The experience obtained during application of liberal conceptions in Latin America’s states at the beginning of capitalist economy clearly showed senselessness to borrow alien ideology without taking into consideration local specifics, because this fact frequently contradicted the needs of authentic development in the receiving countries. As a rule these conceptions represented requirements of foreign agents as well as interests of small part of local society aimed at intensification in exploitation of labour and natural resources. Moreover, its implementation led to strengthening of financial and political dependence, imposing rapid economic transformation and converting young creole republics into pseudo-state political formations («banana republics» in Central America, Puerto Rico, Cuba). Submitting more advanced South American areas (La Plata, Brazil, Peru) neocolonial methods have been tested: ruinous foreign loans, direct and indirect control of local industries and change of its structure in the interests of overseas investors. Here could be mentioned artificial boom of raw material export, control and destruction of local processing works. The said economic paradigm conditioned convulsive forms of social life: appearance of caudillos, dictatorships and authoritarian regimes as well as interregional conflicts (Pacific «Salitre» War between Chile, Peru and Bolivia, intervention of Triple Alliance in Paraguay, separation of Panama for constructing of interocean channel etc.). In particular, dynamics and correlation of these events in context of struggle for real national emancipation laid foundations for contemporary state of economic situation in each country including its alliances and determined its peripheral position in international division of labour. This phenomenon should be considered for building effective cooperation with the most of regional partners.

This pioneer study unravelled the economic implications of Senior High School (SHS) curriculum to parents in the rural area of Jolo and the urban center of Zamboanga City. Finding out the significant difference of said implications to parents clustered according to: Area Status, and Children’s Grade Level and Children’s School Type, and SHS-Associated Factors causing financial difficulty to them in both areas are also within the confine of this endeavour. As an expose facto cross-sectoral and evaluative survey, this research employed a qualitative descriptive approach. One hundred twenty seven (127) respondents comprising of parents and senior high principals/coordinators/directors were determined through a Purposive sampling method. Weighted Mean, t-test (Independent Sample-Test), and Ordinal Scales were utilized in analysing the data. The findings are forwarded - The economic implications of the curriculum to parents in both areas are as follows: more spending for school and non-school needs of children, compromised other household expenses and needs of the family, difficulty to support the education of senior high and non-senior high children, compromised expenses on non- senior high children, increased in educational expenses, costly secondary education, increased of daily expenses, financial burden, difficulty to manage income, difficulty to deal with tuition and miscellaneous fees, difficulty to save money, compromised personal and social expenses, need to generate extra income and borrow money to support the education of children, difficulty to extend financially assistance to needy relatives and friends (rural respondents), and difficulty to attend to social obligations on regular basis (rural respondents). As to the extent/intensity of the implications, parents in SCT-SHS and NDJC-SHS in rural area are more affected by the curriculum than the rest. While in urban center, parents in DPLMHS-SASHS and TTNHS-SHS are more affected than those in the four senior high schools. Generally, the extent/intensity of the economic implications of the curriculum to parents in both areas is slight. Income and tuition fee are among the top-ranking pre-determined SHS-Associated Factors causing financial difficulty to parents in rural area and urban center, and in the twelve senior high schools in both areas. Specifically, parents are shelling-out an average of PhP35,000 to 45,000 every year for the senior high education of their children. From the study findings, the researcher developed a model dubbed as Cycle of Despondency. The curriculum increases the private costs of education and burgles effluent family of two years of indispensable child’s contribution in terms of labor opportunity cost. Above all, it is taxing to parents beyond their financial capability to cope. Scrapping it, however, is indubitably not an astute plan. Instead, immediate and sweeping review and modification are prudent stratagems to undertake since it is already running for four years now. Program mitigating its pecuniary repercussions to parents have to be devised, along with inflexible regulation of school fees and charges. The Civil Service Commission (CSC) and corporate entities have to amend some job “educational requirements” to accommodate senior high graduates in the labor market. Studies on the economic aspect of the curriculum must be launched by various social divides - to spot genuine recommendations in aid of legislation and curriculum planning in general and map out alternative methodologies to minimize its impacts to family in particular. Otherwise, the curriculum will completely end up in fiasco.

The U.S. continental shelf is an important sediment source for beach nourishment and restoration efforts that mitigate erosion, increase resilience to storm impacts, provide habitat, and support the economy. The continental shelf is the preferred source for borrow sediment to closely match the native grain size distribution and composition of the site being restored. However, spatiotemporal variability of continental shelf sediment ranges in size and composition, resulting from previous sea levels and contemporary variability such as normal shelf processes, storm waves, and anthropogenic activities. Understanding the nature and distribution of continental shelf ridge sediment changes over time should reduce costs of efforts required to explore offshore sediments for coastal restoration projects. This review examines the present state of knowledge on the availability, distribution, and characteristics of continental shelf sediment under normal conditions and potential variability after storms and dredging. Under normal conditions sediment on the shelf is easily located and characterized as potential borrow areas. However, storms can induce enough sediment transport to change the boundaries of sediment borrow areas and the location of known sand ridges. Dredging can also influence sediment infilling of the dredged borrow areas, which impact benthic infauna and introduce potential onshore impacts depending on the geometry and nearshore proximity of the excavation. The results of this summary have identified gaps in the present knowledge such as a need for additional sand searches in under-investigated regions, a better understanding of storm impacts on hydrodynamic-driven ridge migration and continuing to review best management practices when new research of dredging practices and impacts are presented. A brief review of the present state of knowledge on the distribution and dynamics of continental shelf sedimentology and morphology are presented here to aid in advancing the scientific and coastal management community’s knowledge of shelf sediments and dynamics as well as highlight potential future research needs.

2006/2007
ITALIANO Nel corso degli ultimi 20 anni, intensi fenomeni erosivi hanno interessato gli arenili situati lungo l’arco costiero nord adriatico e tra le soluzioni impiegate per contrastare tali fenomeni la pratica del ripascimento è stata largamente utilizzata, in quanto permette di riportare le spiagge ad un nuovo equilibrio evitando di provocare impatti significativi sul sistema litoraneo. La problematica maggiore connessa a questo tipo di intereventi è legata alla necessità di ingenti quantità di sabbia dalle caratteristiche granulometriche compatibili con quelle delle spiagge in erosione, con il duplice scopo di ridurre gli impatti negativi sul sistema spiaggia e di minimizzare i costi legati alle operazioni di estrazione e sversamento. Le strategie di gestione delle risorse sabbiose vanno assumendo una notevole importanza all’interno degli strumenti di gestione costiera (Finkl, 1994) e tali strategie, oltre a dover essere basate su estese competenze nel campo della geologia e della sedimentologia, devono prendere in considerazione tutti i fattori ambientali che influenzano il sistema e ne sono influenzati. Problematiche attuali quali l’innalzamento del livello marino e gli effetti sui sistemi costieri, i fenomeni erosivi, la progressiva diminuzione di aree utilizzabili come cave di prestito (sia onshore che offshore) e la creazione di impatti conseguenti alle diverse misure di protezione dei litorali richiedono un approfondito interesse e la ricerca di soluzioni innovative. A partire dalla seconda metà degli anni novanta, ingenti quantitativi di sabbia, pari a 8×106m3 (Consorzio Venezia Nuova, 2006), sono stati sversati sulle spiagge presenti lungo l’arco costiero nord adriatico. Gli interventi, attuati tramite il prelievo di sedimenti presso le coltri sabbiose che ricoprono gli alti fondali delle aree residuali di piattaforma, hanno interessato ad esempio le spiagge di Jesolo, Sottomarina, Pellestrina, Isola Verde. Attualmente, secondo quanto previsto dal Magistrato alle Acque di Venezia tramite il suo concessionario Consorzio Venezia Nuova (2006), è previsto l’utilizzo di circa 3×106m3 di sabbia per interventi di mantenimento, tramite ricariche più frequenti e di minore entità. La pratica di approvvigionamento di sabbie presso le aree relitte di piattaforma ha tuttavia lo svantaggio di essere onerosa, a causa dell’impiego di grandi draghe o di lunghe pipeline per coprire le distanze dalla costa. In tale contesto, un’alternativa vantaggiosa può essere rappresentata dalla ricerca e dall’utilizzo di sabbie dai rialzi morfologici associati alle bocche tidali o eventualmente in alternativa dagli apparati di foce fluviale. Le bocche tidali costituiscono le principali vie di comunicazione marittime da e verso le lagune e necessitano di ordinaria manutenzione nei casi in cui il trasporto longshore sia tale da occludere il canale. In questi contesti uno studio morfodinamico rappresenta una base indispensabile per una corretta pianificazione degli interventi finalizzati al mantenimento dell’ officiosità delle bocche lagunari; la funzionalità e la navigabilità possono essere garantite attraverso le operazioni di dragaggio periodico, con prelievo mirato di sabbie nelle aree di accumulo del delta di riflusso (barra lineare di margine di canale e lobo terminale).Questa operazione si configura dunque come soluzione vantaggiosa per le operazioni di ripascimento di litorali in erosione, in quanto i depositi di ebb-tidal delta generalmente presentano caratteristiche granulometriche compatibili con quelle dei litorali adiacenti. La pratica di escavazione dai bassifondi marini o “ebb-shoal mining” viene largamente effettuata negli Stati Uniti, in Florida e New Jersey ad esempio (Cialone & Stauble, 1998). A seguito della raccolta di dati batimetrici e sedimentologici, in parte forniti dal Magistrato alle Acque - Consorzio Venezia Nuova ed in parte acquisiti attraverso ricerche bibliografiche e due campagne di acquisizione di dati, sono state effettuate numerose elaborazioni con lo scopo di definire le potenzialità di prelievo di sabbie da alcuni apparati di delta di riflusso localizzati lungo l’arco costiero nord adriatico. La ricerca ha permesso inoltre di ampliare la base dati già esistente ed approfondire la morfodinamica delle bocche tidali presenti nel contesto ambientale nord adriatico, nonché le caratteristiche morfologiche degli ebb-tidal delta ad esse associati. Massicci interventi antropici, attuati a partire dallo scorso secolo, hanno portato alla modificazione dei litorali e dell’assetto delle bocche tidali, attraverso la costruzione di strutture permanenti a difesa degli arenili e per consentire la navigazione. Pertanto, le analisi sono state effettuate sia su apparati di bocca tidale in condizioni naturali che su bocche tidali stabilizzate da moli foranei. Infine, è stata analizzata l’evoluzione morfologica recente di alcuni apparati di foce fluviale (Adige, Piave e Sile), al fine di indagare l’eventuale possibilità di estrazione di sedimenti dagli scanni sabbiosi prospicienti tali apparati. Parte integrante del lavoro di ricerca è stata la messa a punto di una specifica procedura geostatistica in ambiente GIS (utilizzando il software ESRI ArcGis™), basata sul metodo elaborato in origine manualmente da Dean and Walton (1973). Una dettagliata analisi morfologica e morfodinamica degli apparati di bocca tidale e foce fluviale è stata effettuata attraverso l’elaborazione di modelli digitali del fondale marino (DEMs), consentendo l’elaborazione di alcune relazioni predittive relative a determinati parametri fisici quali prisma tidale, sezione della bocca e volume del delta di riflusso. Tali risultati sono stati messi a confronto con analoghe elaborazioni, relative a differenti contesti costieri come ad esempio le coste statunitensi e neozelandesi, in modo tale da evidenziare locali fattori morfodinamici responsabili dello sviluppo degli apparati di delta di riflusso. Le numerosi analisi metodologiche, condotte tramite l’estensione Geostatistical Analyst all’interno del software ESRI ArcGis™, hanno permesso di ottenere una valida procedura per il calcolo dei volumi di sabbia depositati nelle strutture di delta di riflusso. Infine, attraverso l’integrazione di tutti i dati raccolti, sia di nuova acquisizione che provenienti da fonti preesistenti, è stato predisposto un geodatabase in GIS, denominato Ebb-delta Geodatabase, che raggruppa tutte le potenziali cave di prestito individuate nonché le caratteristiche granulometriche dei depositi. Relativamente agli apparati deltizi del Piave e dell’Adige, dall’analisi è emersa una situazione critica di erosione dei fondali antistanti le foci, da attribuirsi con una certa sicurezza alla drastica diminuzione dell’apporto di materiale grossolano, avvenuta alla fine degli anni ’50 del secolo scorso e causata dagli interventi antropici sulle lungo le aste fluviali. I delta sommersi, privati di una parte consistente del contributo sedimentario, hanno subito un asporto di quantità significative di sedimento ad opera del moto ondoso e delle correnti marine e le occasionali ricariche, dovute agli eventi di piena, non sono sufficienti a riequilibrare il sistema. Su tale situazione insistono inoltre fenomeni puntuali, come nel caso dell’Adige, dovuti alla recente messa in opera di manufatti che hanno ulteriormente accentuato il processo di erosione dei fondali E’stato ritenuto pertanto che, in ragione di una dinamica sedimentaria legata ad eventi discontinui e a cicli stagionali di erosione-deposizione, ed essendo insufficiente l’apporto solido da parte dei corsi d’acqua, l’estrazione di materiale alle foci del Piave e dell’Adige non sia una soluzione praticabile ai fini del ripascimento di litorali in erosione. Diverso è il caso del fiume Sile, per il quale è stato verificato che l’apporto solido è per sua natura scarso, dunque insufficiente a creare significative anomalie deposizionali nell’area di foce. Gli apparati di delta di riflusso associati alle bocche tidali, sia naturali che stabilizzate, rappresentano al contrario significative trappole sedimentarie in ambiente sottocostiero, caratterizzate da volumi di sabbia compresi tra 270.000m3 e 10×106m3. La procedura geostatistica elaborata, definita procedura geostatica semi-automatica (Authomatic Detrending Procedure-ADP), si è rilevata un utile strumento analitico per la valutazione dell’estensione dei depositi sabbiosi e le elaborazioni effettuate hanno consentito di integrare dati provenienti da fonti non omogenee. Inoltre, lo studio della morfodinamica delle bocche tidali di Lido, Chioggia, Malamocco e Buso ha fornito un’interessante analisi relativa all’evoluzione dei delta di riflusso a seguito della costruzione di moli foranei. Come sottolineato da Carr and Kraus (2001), lo sviluppo verso mare e l’estensione degli apparati di delta di riflusso è determinato dall’ampiezza del prisma di marea, dalla pendenza della piattaforma costiera, e dal processo di confinamento del getto tidale da parte dei moli. Nonostante la casistica esaminata nel corso dello studio sia stata limitata a 11 bocche tidali, la correlazione riscontrata tra i valori di prima tidale ed i volumi ottenuti tramite la procedura geostatistica dimostra che nel caso di bocche tidali non armate i processi tidali siano prevalenti sull’azione del moto ondoso nell’influenzare lo sviluppo delle coltri deposizionali. La relazione V-P elaborata per l’area costiera nord adriatica risulta molto simile a quella ottenuta per le bocche tidali neozelandesi da Hicks and Hume (1996) mentre si discosta in maniera significativa da quelle elaborate per le coste statunitensi da Walton and Adams (1976) e Marino and Mehta (1988). L’utilizzo di una procedura standardizzata, come nel caso della procedura geostatica elaborata all’interno del progetto di ricerca qui presentato, ha permesso di ridurre la soggettività nella stima dei volumi che caratterizzava il metodo proposto originariamente da Dean and Walton (1973). Inoltre, tale procedura si è rivelata particolarmente utile nei casi in cui l’assetto morfologico risulti particolarmente complesso, come nel caso delle bocche tidali armate con moli fortemente aggettanti (Lido, Chioggia, Malamocco, Buso). In questi casi infatti è stata verificata una significativa discordanza tra i valori ottenuti tramite l’applicazione delle relazioni predittive e i risultati delle elaborazioni geostatistiche. Prima degli interventi di stabilizzazione, la maggior parte delle bocche tidali nord adriatiche presentava una configurazione marcatamente asimmetrica, dovuta all’ingente contributo del trasporto litoraneo che ha contributo in numerosi casi alla costruzione di lidi sfasati nella direzione sopraflutto (i.e. Punta Sabbioni; Alberoni; etc). A partire dal diciannovesimo secolo, a seguito delle difficoltà riscontrate per la navigazione dovute all’interramento e/o alla migrazione del canale principale, diverse foci lagunari sono state armate e tale intervento ha comportato una drastica modificazione del regime deposizionale nell’area sottocostiera. Di conseguenza, in relazione alla lunghezza dei moli foranei, la struttura deposizionale di delta di riflusso ha subito un processo di riconfigurazione, generalmente attraverso una traslazione verso mare a maggiori profondità, accompagnata da una parziale erosione dell’accumulo pre-esistente. In numerosi casi inoltre la presenza dei moli ha funzionato come sbarramento per il trasporto litoraneo il quale, prima di venire catturato dal getto tidale ed entrare nel by-pass sedimentario della bocca, ha alimentato l’accrescimento dei litorali posti sopraflutto, come ad esempio nel caso del litorale di Punta Sabbioni adiacente alla bocca di porto di Lido. Ciò ha portato alla formazione di differenti tipologie di delta di riflusso, pesantemente influenzate dall’intervento antropico, per le quali il volume di equilibrio teorico potrebbe essere raggiunto solamente a seguito di un ingente contributo del trasporto longshore, in un arco di tempo considerevole. Uno dei risultati di maggior interesse del presente lavoro risiede dunque nella verifica di uno “stato di immaturità” dei delta di riflusso associati alle bocche tidali stabilizzate, come nel caso della bocca di porto di Lido in cui la costruzione dei moli risale a circa un secolo fa. Come evidenziato da Hansen and Knowles (1988), il processo di confinamento da parte dei moli porta il flusso tidale ad abbandonare il canale principale naturalmente scavato, i canali marginali di flusso e la piattaforma di swash, con effetti sulla pre-esistente struttura deposizionali paragonabili a quelli osservati nei processi di rottura naturale dell’ ebb-tidal delta (ebb-tidal delta breaching; Fitzgerald et al., 1978). Al Lido a seguito della costruzione dei moli la maggior parte dei sedimenti in transito nell’area sottocostiera sono stati depositati sulla spiaggia di Punta Sabbioni, con una conseguente diminuzione del carico sedimentario disponibile per la costruzione del delta di riflusso. Poiché il volume stimato a seguito delle recenti indagini risulta corrispondere a solamente il 10% dell’ipotetico volume di equilibrio, il caso del Lido può essere considerato come un caso di delta “immaturo”, in quanto solo dopo l’esaursi dell’ingente fenomeno di accrescimento dell’arenile di Punta Sabbioni (che risale alla fine degli anni ’60) ha potuto intercettare la gran parte del carico sedimentario associato al trasporto longshore. Numerose incertezze permangono allo stato attuale delle indagini per quanto concerne l’effettivo raggiungimento del volume di equilibrio teorico; le annuali operazioni di escavazione effettuate per mantenere l’officiosità del canale, potrebbero difatti portare ad una configurazione stazionaria del deposito, che potrebbe essere confermata solamente attraverso uno specifico piano di monitoraggio. Gli studi effettuati sulle altre bocche tidali armate localizzate all’interno del contesto in esame hanno in ogni caso evidenziato un comportamento morfodinamico simile; i risultati delle elaborazioni confermano una estensione dei delta di riflusso inferiore a quanto previsto dalle relazioni predittive anche alle foci di Malamocco, Chioggia, e Buso. Per concludere, si sottolinea come la messa a punto di uno specifico database in GIS delle caratteristiche sedimentologiche delle morfologie oggetto di indagine costituisca un efficace strumento di gestione, che permette di associare ai diversi tipi di deposito le informazioni più significative riguardanti la localizzazione; i volumi utilizzabili, etc. Conoscendo le caratteristiche granulometriche dell’arenile da sottoporre all’intervento di ripascimento, un’interrogazione al database permette di identificare le potenziali cave di prestito compatibili, per poi progettare gli interventi più idonei, come ad esempio il prelievo di sedimenti dal canale principale nei casi in cui vi sia un surplus che provoca intralcio alla navigazione, oppure l’estrazione di sabbia nelle aree del delta di riflusso a maggior tasso di crescita (canali marginali flusso e/o lobo terminale). In ogni caso, l’estrazione deve essere limitata sia in estensione che per quanto riguarda lo spessore, per evitare effetti negativi e significativi disequilibri sui fenomeni di rifrazione delle onde e sulla dinamica sedimentaria. Non vi è alcun dubbio che un’attuazione sconsiderata della pratica di estrazione di sabbie dai delta di riflusso possa comportare conseguenze negative sui fondali ed i litorali adiacenti, d’altra parte come suggerito da Hansen and Work (1999) se gli interventi vengono pianificati in modo tale da rimuovere una frazione ridotta del deposito mantenendo così i naturali processi di scambio sedimentario, gli impatti sui litorali adiacenti possono essere di minima portata. La preservazione dell’assetto generale del delta, attraverso l’escavazione di sedimento nella parte terminale verso mare su un’area più estesa in superficie e meno in profondità, può efficacemente ridurre l’alterazione dei pattern di rifrazione delle onde e dei meccanismi di trasporto dei sedimenti.
ENGLISH Beach erosion has strongly affected a large number of beaches along the northern Adriatic coastal area over the past 20 years. Among the different engineering solutions available to contrast coastal erosion, the soft-engineering practice of beach re-nourishment is widely recognized to be a good compromise between desired outcomes and negative environmental impacts. One of the major issue concerning beach nourishment activities is the necessity to find suitable sources of sand, with the purpose of both reducing costs and minimizing environmental impacts. As stated by Finkl (1994), strategies for sand management are becoming increasingly more important as a coastal management tool. Also, the same author suggests that new sand management strategies, based on sound geological principles, must reflect sensitivity to environmental concerns. Rising sea levels, increased shore erosion, decreasing supplies of suitable fill materials (both on-and off-shore) and increasing concerns over environmental impacts associated with coastal protection measures (Finkl, 1994), are some of the reasons for a significant interest in these coastal problems. Along the Venice lagoon barrier islands and adjacent beaches (i.e. Jesolo, Sottomarina, Pellestrina, Isola Verde), 8×106m3 of sand have been extracted and placed for nourishment projects starting from the 1990s. Nowadays the Venice Water Authority (Magistrato alle Acque through its concessionary Consorzio Venezia Nuova, 2006) plans the placement of a total volume of 3 x 106 m3 of sand for beach maintenance, suggesting that critical beach erosion can be mitigated by smaller but more frequent nourishments. Previous re-nourishment projects were carried out through the utilization of sand borrow areas located offshore, at a distance of approximately 20km from the coast, a solution that has high operational costs. An alternative solution may be represented by the use of nearshore sand deposits, located in the proximity of tidal inlets or within the delta front area outside river mouths. Since inlets are the only access pathways between a lagoon and the sea, one of the major problems in terms of navigability is their intrinsic incapacity to maintain a predetermined configuration. Due to the longshore drift, the channel can shift and cause continuous filling of abandoned routes. Moreover, during storms landward pushes can increase the natural rise of the terminal lobe of the ebb delta, enhancing the phenomenon of shoaling at the channel entrance. During the last decades, the practice of ebb-tidal delta mining (Cialone and Stauble, 1998) has been progressively increasing, with the rising demand for suitable beach fill material along barrier islands. Ebb-tidal delta mining gives a new outlook on beach re-equilibrium projects since a large amount of sand, well compatible to native adjacent beaches, is stored by the ebb-tidal delta and easily mined at low cost. Dredging of an inlet opening and channel may also represent a good compromise between navigational needs and the rational use of dredged material. Several potential borrow areas were analysed in the present study, focussing on the evaluation of sand volumes deposited outside tidal inlets and river mouths, as a consequence of existing local hydrodynamic conditions. The coastal area object of the investigation is the northern Adriatic coastal area between the Isonzo and Po rivers, consisting of lagoon-river delta systems fronted by barrier islands and sandbars fed by tidal inlets. New data were collected through bathymetric surveys and sediment sampling and integrated with data from older surveys, thus obtaining a rather complete and uniform catalogue of sand resources. The development of a specific geostatistical procedure was also a main objective of the research, aimed at obtaining reliable results concerning ebb-tidal delta volumes. Considerable changes on the northern Adriatic barrier island systems and associated inlets have occurred over the last century as a result of intense human activity, including construction of permanent structures on both the barriers and the inlets. Those structures are mainly seawalls and groins designed to fix the shoreline and jetties to keep inlets from migrating and to maintain a given channel depth. Both natural and stabilized inlets were investigated, leading to a specific analysis concerning the morphodynamics of stabilized inlets. The present research has been developed through several phases. A detailed analysis of the overall morphology of different nearshore features such as natural and stabilized inlets and river mouths has been conducted, mainly through ESRI ArcGIS™ software, followed by elaborations of predictive numerical relationships concerning inlet parameters (i.e. tidal prism, cross-sectional area and ebb-tidal delta volume). The results obtained were then discussed and compared with analogue relationships elaborated for other environmental settings (i.e. the U.S.A and New Zealand coasts), highlighting the influence of local morphodynamic factors in determining ebb-tidal delta growth along the northern Adriatic coastal area. Methodological analyses concerned a large number of geostatistical tests through ESRI ArcGIS™ Geostatistical Analyst extension, that allowed to obtain a specific procedure for calculating ebb-tidal delta volumes. Finally, with the aim to provide a useful and agile tool for sand resources management, all results were integrated into a GIS geodatabase, named Ebb-delta Geodatabase, which includes the individuated potential sand borrow areas with associated grain size characteristics. The major outcomes of the research are the followings: 1) the seafloor morphologies facing the Piave and Adige river mouths exhibit strong erosional patterns over the last thirty years, possibly as a consequence of a decrease in sediment supply from rivers. Therefore, these areas were not considered suitable sand resources for beach nourishment projects, whereas their morphological evolution testifies that a disequilibrium in sediment supply and deposition is occurring; 2) ebb-tidal deltas represent significant sand sinks along the northern Adriatic coastal area, both the natural and the stabilized ones, with volumes comprised between c.a 270.000m3 and c.a. 10×106m3. 3) the newly-developed semi-authomatic procedure (ADP) provided to be a useful analytical tool for the evaluation of ebb-tidal delta volumes; the development of agile geostatistical procedures allowed the integration and processing of newly collected and older bathymetric and grain size data. Additionally, the study of the morphodynamics of Lido, Chioggia, Malamocco and Buso inlet, provided an analysis of ebb-tidal delta volumes and jetty effects. According to Carr and Kraus (2001) the offshore extent and dimension of the ebb-tidal delta is in great part determined by the magnitude of the tidal prism, the slope of the nearshore shelf, and the ebb-jet confinement caused by jetties. Notwithstanding the limited statistics, the direct proportionality between tidal prism and ebb-tidal delta volumes obtained from the application of the ADP on the bathymetric dataset, as well as the high correlation coefficient, demonstrates that natural or almost natural inlets in the northern Adriatic tend to build ebb-tidal deltas which are strongly influenced by tidal processes. Thus the effects of storm induced wave winnowing and longshore sedimentary drift may be considered uniformly distributed, since scattering in the prism vs. ebb-tidal delta volumes relationship is negligible. The V-P relationship of ebb tidal delta volumes in the northern Adriatic is very similar to that obtained by Hicks and Hume (1996), but significantly different from that found by Walton and Adams (1976) and Marino and Mehta (1987) in the United States. The use of a standardized procedure, as in the case of the geostatistical application here proposed, reduces the subjectivity in the calculation of the ebb-tidal deltavolume which occurs when using the Dean and Walton method (1973). The ADP could also be a useful method for a step-by-step preliminary test on ebb-tidal delta structure determination as in the case of complicated bathymetric frameworks. Equilibrium conditions based on delta volume vs. tidal prism relationships constructed for natural or almost natural northern Adriatic inlets, may be used to infer the hypothetical delta volume also for jettied inlets. During the past, many northern Adriatic inlets were strongly asymmetrical, because of significant longshore transport processes that gave rise to large up-drift coastal offset. Since the 19th Century, owing to great difficulties in navigation through the main channel, some inlets were fixed by jetties. Depending on the jetty length, precisely on the offset between shoreline and jetty apex, the ebb-tidal delta may re-shape or completely erode, and thus begin to re-form offshore, shifting to a distance equal to that of the jetty length. This may cause a delay in ebb-tidal delta formation, since the longshore sediment input is not immediately captured by the inlet system and stored in the ebb delta. In fact, the up-drift beach will accrete until the sediments are able to by-pass the jetty, thus entering in the inlet sedimentary budget. What can be observed is a large variety of new “human-induced” ebb deltas, whose equilibrium volumes may be reached only when a large amount of transported long-shore sediment has been trapped for long time. The “immaturity” status of the new ebb-tidal deltas is a major result, for the case of Lido inlet, the largest in the north Adriatic, where jetties were constructed about one century ago. According to Hansen and Knowles (1988) confinement of the flow by jetty construction has resulted in tidal flow abandonment of the natural main ebb channel, swash platform and marginal flood channels, resulting in effects similar to those observed in natural ebb-tidal delta breaching (Fitzgerald et al., 1978). After jetty construction, sediments were stored in the up-drift area of Punta Sabbioni and caused the accretion of that beach, resulting in a starved status of the ebb-tidal delta potential area. Considering that the present ebb-tidal delta volume accounts for only 10% of the equilibrium hypothetical volume, Lido inlet can be seen as a typical case of immature ebb-tidal delta, which only recently has significantly grown offshore due to the jetty fixation. Some doubts arise from the possibility that the delta volume will increase, owing to the periodic dredging operations that are done for navigational improvement. This practice may lead to a stationary configuration of the ebb tidal delta, that can be tested only through a specific monitoring plan. Additional studies concerning the behaviour of jettied inlets provided similar results in the cases of Malamocco, Chioggia and Buso inlets. Data analysis confirms the limited ebb-tidal delta extension also in these latter cases, and a morphodynamic response comparable to the one observed at Lido. The ebb-tidal delta sediment inventory that was processed through GIS has very high versatility and can associate type of deposits (grain-size, sorting) with its location and volume “excess”. Once the required physical parameters of the material are known for a beach that needs to be re-nourished, a GIS query could identify different potential borrow areas and subsequent actions can be planned. The suitability of a morphological artificial re-shaping may be planned, by mainly using sand from growing areas, i.e. the channel margin linear bar and terminal lobe, as well as the sedimentary surplus from navigational maintenance located inside the outer part of the main ebb channel. In any case, dredging must be limited both in extension and thickness, in order to minimize the already cited effects on wave and sedimentary dynamics. The use of ebb-tidal delta sediment as a source for beach nourishment material has and will be controversial. However, as suggested by Hansen and Work (1999) there is a natural variability to these inlets systems, and if artificial bypassing practices mimic the natural processes by removing a small percent of the delta on an annual basis, there is likely to be minimal adverse impact to adjacent shorelines. Mining the seaward edge of the delta over a large area would maintain the overall geomorphology of the inlet and would reduce the possibility of severely altering nearshore refraction and sediment transport patterns
XX Ciclo
1976

Abstract Maintaining and retaining a quality sandy beach is a primary requirement for attracting people and tourists in any coastal country. Tourism Enterprises Company (TEC) in Kuwait owns 230 m long sandy beach in Ras Al-Ardh Sea Club, Salmiya, Kuwait. The beach has been eroding because of strong hydrodynamics forces from waves and currents. TEC wants to develop a stable sandy beach of 30 m wide. Kuwait Institute for Scientific Research (KISR), Kuwait is assigned to carry out the required scientific studies. In order to make sure a stable quality beach will exist, KISR has carried out the needed studies, which involves the field measurements such as bbathymetry survey, current and tidal variations, physical characteristics of beach soil, beach and sea bed profile, establishing the design parameters such as waves, currents, tide and wind. Hydrodynamic model study using DELFT3D model for the present and for the proposed extended groin conditions with beach nourishment were carried out. Also numerical modeling using GENESIS model to understand the future shore line changes due to the proposed development was carried out. Design of Groins to estimate the weight of armor units and weight of inner layers were carried out. The particle size and quantity of sand needed for reclamation of 30 m wide beach was estimated. Based on the study, it is recommended that the sandy soil to be used for 30 m wide beach nourishment should have D50 greater than 0.42 mm (say 0.5 mm) and D10 greater than 0.25 mm. The borrow pit much be selected by keeping this soil characters in mind. It is recommended to use a submerged offshore breakwater in order to retain the beach sand in place and for reducing the maintenance nourishment. Otherwise, large quantity of the capital nourished beach sand will escape into the deeper water due to strong current coupled with waves and steep seabed slopes. Environmental Impact Study was carried out as per Kuwait Environment Public Authority requirements to bring out the impacts due to beach filling and the construction submerged offshore barrier and extension of east groin for a distance of 30 m. TEC will implement the recommendations for developing the beach in Ras Al-Ardh sea club and will be useful to attract more people to use this beach.

This report documents a numerical modeling investigation for dredged material from nearshore borrow areas and placed on Folly Beach adjacent to Stono Inlet, South Carolina. Historical and newly collected wave and hydrodynamic data around the inlet were assembled and analyzed. The datasets were used to calibrate and validate a coastal wave, hydrodynamic and sediment transport model, the Coastal Modeling System. Sediment transport and morphology changes within and around the immediate vicinity of the Stono Inlet estuarine system, including sand borrow areas and nearshore Folly Beach area, were evaluated. Results of model simulations show that sand removal in the borrow areas increases material backfilling, which is more significant in the nearshore than the offshore borrow areas. In the nearshore Folly Beach area, the dominant flow and sediment transport directions are from the northeast to the southwest. Net sediment gain occurs in the central and southwest sections while net sediment loss occurs in the northeast section of Folly Island. A storm and a 1-year simulation developed for the study produce a similar pattern of morphology changes, and erosion and deposition around the borrow areas and the nearshore Folly Beach area.