Site Characterisation and Assessment of Sediments For Beach Renourishment

Marsden Point, Northland, New Zealand, is a Holocene, prograded barrier spit at the tidal inlet to Whangarei Harbour. The development of the Northport timber export port at Marsden Point in late 2000 modified the tidal inlet dynamic equilibrium due to a large reclamation (32.6 ha) and dredged turning basin (31.8 ha to 13 m below Chart Datum). The effects of the Northport development on the inlet morphodynamics and the potential use of dredge sediments as beach nourishment fill are the foci of this study. Regional sediment transport patterns adjacent to the Northport development were inferred and documented through the interpretation of sediment grain size distributions, geomorphic analysis of historical shoreline and bathymetry data, analysis of beach profiles, identification of seabed sediment transport pathways, and calculation of potential sediment transport vectors from hindcast wind-wave and current meter data. Sediments found in the lower harbour are consistent with Schofield's (1975) Hauraki (B) facies. Shelly lag sediments, which armour and stabilise the bed, were observed in similar locations to those present in 1983. Sediment transport directions inferred from sediment textural analyses were generally in agreement with directions found from beach profile analysis, morphologic interpretation and calculation of potential sediment transport vectors. Analysis of thirteen rectified and geo-referenced vertical aerial photographs of the Marsden Point region over the period 1984 to 2001, indicated a general reduction in dry beach widths within the harbour, and an increase in beach width at Marsden Point, where opposing sediment transport vectors meet and the ebb tidal delta of Mair Bank became 'welded' to the shoreline. This area exhibits highly variable beach profiles and offshore bathymetry, indicative of the relatively large potential sediment vectors meeting at this location. Comparison of digital bathymetric surveys, sediment transport pathways and bedform locations both pre and post-development, indicates changes have been limited to the local reclamation and dredge basin areas. Reduced post-development sediment transport potentials were found in the northern areas of the dredge basin. There is potential for scour and the development of a shell lag at the dredge basin's eastern edge. Small-scale (-1,000m³yr¹} accretion has been observed against both western and eastern edges of the Northport reclamation. Accretion is occurring due to dominant longshore sediment transport patterns (western edge) and the creation of a 'current transport shadow zone' (eastern edge). Dredge basin sedimentation is expected to increase over the next 5-10 years to reach 15-20,000 m³ yr¹ as the beach profile against Northport's western edge 'fills' with sediment. Sediment grain size comparisons and sediment transport patterns have been used to develop an effective beach nourishment plan for Marsden Bay (West and Central) using sediments sourced from Northport's dredge basin. The Northport development has caused only local modifications to sediment transport processes operating within the lower Whangarei Harbour. There have been no largescale changes in sediment transport patterns or morphology observed postdevelopment

Making space for shellfish farming along the Adriatic coast

This work focuses on the selection of new areas for shellfish farming along the coast of the Northern Adriatic Sea (Italy). Shellfish site suitability was assessed by means of a methodology based on Spatial Multi-Criteria Evaluation (SMCE), which provided the framework to combine mathematical models and operational oceanography products. Intermediate level criteria considered in the analysis included optimal growth conditions, environmental interactions, and socio-economic evaluation (e.g. organic carbon deposition; distance to harbour). Results showed that the whole coastal area comprised within 0 and 3 nm is highly suitable for farming of mussel, while the area comprised between 3 and 12 nm is divided between a highly suitable northern part, and a less suitable southern one. Seven different scenarios of development of shellfish aquaculture industry were explored. The introduction of a new species, and the assessment of the exposure to storm events are specific aspects taken into account in development scenarios. Results show that the degree of suitability for shellfish aquaculture in this area would not change dramatically with the introduction of oyster farming. Furthermore, results highlight that: (i) the growth potential in this area is high; (ii) the space with suitability index >0.5 increases when prioritizing the optimal growth condition criteria, and (iii) the socio-economic is the most restrictive Intermediate Level Criteria. Results were discussed by deriving general lessons concerning the use of SMCE in aquaculture space allocation, from the specific application in the Northern Adriatic Sea. Challenges and opportunities related to the proposed methodological framework, with particular reference to the use of resources provided by remote sensing and operational oceanography by means of mathematical models, were also discussed. Results can support a science-based identification of allocated zones for aquaculture in order to avoid conflicts, and promote sustainable aquaculture in the Mediterranean Sea, where the space for these activities is becoming increasingly limited

Aquaculture Site-Selection and Marine Spatial Planning: The Roles of GIS-Based Tools and Models

Around the globe, increasing human activities in coastal and offshore waters have created complex conflicts between different sectors competing for space and between the use and conservation of ocean resources. Like other users, aquaculture proponents evaluate potential offshore sites based primarily on their biological suitability, technical feasibility, and cost considerations. Recently, Marine Spatial Planning (MSP) has been promoted as an approach for achieving more ecosystem-based marine management, with a focus on balancing multiple management objectives in a holistic way. Both industry-specific and multiple-use planners all rely heavily on spatially-referenced data, Geographic Information System (GIS)-based analytical tools, and Decision Support Systems (DSS) to explore a range of options and assess their costs and benefits. Although ecological factors can currently be assessed fairly comprehensively, better tools are needed to evaluate and incorporate the economic and social considerations that will also be critical to identifying potential sites and achieving successful marine plans. This section highlights the advances in GIS-based DSS in relation to their capability for aquaculture site selection and their integration into multiple-use MSP. A special case of multiple-use planning—the potential co-location of offshore wind energy and aquaculture—is also discussed, including an example in the German EEZ of the North Sea

Environmentally Sustainable Aquaculture: An Eco-Physical Perspective

The New Zealand aquaculture industry during the late 1990s and early 2000s experienced a significant and sustained period of growth. Greenshell mussels (Perna canaliculus) are proving to be a popular and valuable cultured species, with large domestic and international markets. Traditionally, these bivalves have been farmed within enclosed embayments and on relatively small scales (~3 Ha). The recent expansion of the industry coupled with the near saturation of existing 'traditional' sites and new culture technologies has led the industry toward alternate environments, notably exposed offshore sites. Initial proposals within the Bay of Plenty have included multiple farms of ~4500 Ha each. This novel approach to shellfish culture created uncertainty with respect to potential environmental impacts, cumulative effects, and sustainable carrying capacities within these exposed open-coast locations. In zoning for Aquaculture Management Areas (AMAs), environmental managers must be informed of each of these aspects to ensure the rational and sustainable use of the coastal-marine space. The overall goal of this study is to determine the potential for environmentally sustainable large-scale offshore mussel culture within the Bay of Plenty marine environment. The long term sustainability of aquaculture development on an open coast is a function of many influences which can vary in both time and space. The benthic environments of the Bay of Plenty exhibit great variability in their ability to assimilate waste inputs from suspended mussel culture; a direct function of the variability in sedimentary environments and benthic habitats within the region. Specifically, silty sediments with low natural organic contents, generally found between 40 and 100 m depths are the most suitable locations for sustainable mussel aquaculture from an environmental impact perspective. Both observations and model predictions indicate productivity potential within the region to be greatest within neritic zones of the western Bay of Plenty. Local wind forcing is the predominant mechanism forcing local shelf currents. Current meter data and numerical modelling tests from this study indicate that local winds explain the majority of water current variability on the shelf, generate the delivery of new nutrients to the shelf through upwelling, and hence create the variability in productivity potential. Complicating the AMA zoning process for environmental managers, however, are existing uses of, and societal values toward, the coastal-marine environment. GIS planning tools have been shown to be effective at minimising conflicts and maximising sustainability potential through informed site selection. Within the Bay of Plenty, these preferential sites are located on the mid-shelf (60-80 m depths) offshore from Pukehina, Matata, and Whakatane. This study shows that the simulated cumulative lower trophic-level depletion impacts of two large (~5000 Ha) proposed offshore mussel farms vary seasonally as a result of subtle changes in ecosystem dynamics and mussel feeding patterns. At proposed stocking densities, largest relative impacts are expected during autumn and winter, when relative phytoplankton biomass is low and growth rates slow. During spring, while absolute impacts are greater than those during autumn/winter, greater phytoplankton-zooplankton biomass and faster growth rates result in quicker recovery times and reduced 'depletion halo' extents. Year-long predicted impacts are below those applied as 'acceptable limits of change', both within New Zealand and internationally, indicative of the ecological carrying capacity

Sediment dynamics surrounding a flood tidal delta adjacent to reclamation and a dredged turning basin

Field measurements of tidal current velocities are used to infer sediment transport characteristics in the lower section of a large, tidally dominated estuarine system at Whangarei Harbour, New Zealand. Recent (2002) developments at the harbour entrance included a 32.6 ha intertidal reclamation and a 31.8 ha dredged turning basin. Residual distance vectors indicate that the postdevelopment, large-scale pattern of sediment transport dynamics remains consistent. Minor, localised modification of transport potentials has been observed immediately adjacent to the developments, however. These modifications include a slight realignment of current flows near the reclamation wall and some leakage from a previously identified transport loop near the dredged basin. The potential for scour is identified along the eastern margin of the dredged basin, which could act to remove material moving downslope into the basin from its western edge. These data are consistent with numerical model results that predicted minimal consequences resulting from the developments. Lower harbour sediment dynamics are consistent with established patterns for tide-dominated inlets, with separation of the channel into areas of ebb and flood dominance, and typical transport patterns over the flood tidal delta. Broad-scale inlet geomorphology has been maintained, which is consistent with other dredged tidedominated inlets

An integrated GIS approach for sustainable aquaculture management area site selection

Within New Zealand, growth in the aquaculture industry has led to the diversification of aquaculture sites from more sheltered bays and harbours toward open coast locations. Coastal zone managers, along with the aquaculture industry, aim to ensure the long-term sustainability of any ‘new’ sites selected. Through targeted data collection programmes and the subsequent implementation of Geographic Information System (GIS) based models, the most suitable and sustainable locations for Aquaculture Management Areas (AMAs) can be identified. This approach is applied within the Bay of Plenty, New Zealand, with specific reference to suspended mussel (Perna canaliculus) aquaculture. Within the region, areas where maximum sustainability may be achieved make up 18% of the total area considered, with conflicting uses and other constraints accounting for 46%. Whilst further site and development specific studies are required to determine explicit carrying capacities, the effort required has been considerably reduced by eliminating unsuitable locations and identifying those where sustainability can be maximised

Integrated sediment habitat mapping for aquaculture zoning

The benthic environment of the nearshore to inner-shelf within the Bay of Plenty, New Zealand, was sampled and surveyed to classify sedimentary environments and benthic habitats. Reef and soft sediment habitats are characterised, delineated, and the potential impacts of suspended bivalve aquaculture considered. An integrated approach is used, utilizing a GIS database to combine remote sensing techniques such as multi-beam sonar and underwater video capture, with physical sampling of the soft sediments using sediment grab samples and infaunal organism identification. Soft sediment habitats, comprised of fine silty and muddy sediments with low organic contents, are determined to be the most suitable benthic environments above which to site suspended bivalve aquaculture. Transfer of knowledge from the study is maximised through the creation of a CD-ROM complete with hyper-linked analysed data and video files, thematic data layers and a freely available, query-able GIS viewer package