Environmental effects

Major marine infrastructure can create positive economic and social benefits, through enabling transport and trade, and facilitating public access to, and enjoyment of, the marine environment. At the same time, because of the large scale of many of these projects, there can be significant adverse environmental effects on the marine environment which need to be addressed.

The following sections discuss the potential environmental effects in more detail.

Degradation of natural coastal landscapes

The placement of large structures into the marine environment, and changes to the natural form of the coastal edge through the construction of reclamations and seawalls, can have a major impact on natural coastal landscapes. Such human-made elements can create a significant visual impact (depending upon perception), replace natural rounded shapes and forms with straight lines and hard edges, and disrupt natural coastal patterns and processes. Many of the impacts are irreversible in practical terms.

Large single structures, such as wharves and boat ramps, may be intrusive when seen from both the land and from the sea. They are also likely to bring with them increased activity in the form of cars, boats and people. But it is the cumulative effect of many structures along the coastline that can have the most detrimental impacts on natural coastal landscapes.

Ports and marinas, in particular, often require reclamations and numerous structures to be placed within the coastal marine area. Some are occupied by a high density of boats and supported by a wide array of facilities. Container terminals at ports are often dominated by a combination of container cranes, stacked containers and vessels. They are commonly accompanied by commercial or residential development. Most ports have historically been developed in city centres or near major land-based infrastructure that supports the effective distribution of imports and exports. Natural landscapes in such locations are often already highly modified and urbanised, and this can reduce the landscape impacts of further expansion.

Canal developments also have a major impact on natural coastal landscapes, through the creation of canals, high density housing, numerous boats and floating pontoons and commercial facilities. The marine area and coastal edges within these developments are often entirely artificially created.

Because of the major impact that these kinds of developments can have on natural coastal landscapes, and the irreversibility of such impacts, it is important that the developments which do occur are carefully located, and that where possible they are confined to areas where natural coastal landscapes have already been compromised, such as disused port areas.

Damage to marine ecosystems

Reclamation causes the direct loss of coastal habitat in the marine area that is reclaimed. It can also disrupt the sensitive ecosystems of transitional zones between the land and the sea which, in their undisturbed state, contain a diverse range of organisms and are very ecologically productive. These areas can provide important nursery areas for marine life and habitat for seabirds. Natural systems in these transitional zones can also be important for trapping sediment runoff and controlling erosion. For these reasons, reclamations and major structures should be located away from ecologically important inter-tidal and marine habitats such as salt marshes, shell banks, sea grasses, shellfish beds, mangroves and major fish habitats. They should also be located away from bird roosting, feeding and nesting sites.

Causeways can result in the direct loss or relocation of marine habitat through burial. They can also reduce wave action and the amount of flushing on the inland side of the structure, resulting in the build-up of sediment, and sometimes eutrophication. This can create new coastal wetland habitat, but if the trapped sediments are contaminated by land-based discharges, the resulting habitat can be of poor quality. The amount of flushing will be affected by the size of the culverts built under the causeway. ²⁷⁶⁶  Bridges allow much freer flushing to occur and therefore should be used instead of culverts where possible.

Construction of offshore wind farms would disturb the seabed in the immediate vicinity of the structures. However, the structures can also provide new habitat for marine life by creating shelter and surfaces on which vegetation and benthic communities can establish themselves. Large fixed structures such as wharves and breakwaters may shade areas of water. The impacts of such shading will depend on the habitat affected, but most plants such as mangroves, sea grasses and sea weeds will deteriorate or die if shaded for significant periods. 

One of the main concerns associated with carbon sequestration is the potential for leakage of CO2 both during transportation and after storage. These leakages could be either abrupt or gradual. Their environmental impacts are not well understood, but is believed to be dependent upon the scale of the sequestration, and the location, geographical extent and prevailing conditions within the local marine environment. ²⁷⁶⁷

Dredging and marine disposal

The main environmental impacts from dredging and marine disposal are related to the: ²⁷⁶⁸

• Direct disturbance and physical changes to the seabed
• Suspension of sediment and associated changes in water quality
• Release and remobilisation of contaminants on or in the seabed
• Changes in local hydrodynamics and settlement patterns of sediment

Capital dredging necessarily removes flora and fauna from the seabed and increases its depth. With the exception of deep burrowing animals, the activity will completely remove all life from the sea floor for a period of time. The recovery rate of the benthic communities will depend on the particular nature of the ecosystem: some ecosystems dominated by opportunistic species may recover in only a few months, whereas those populated by slow growing, sensitive species may take years, or may never recover. 

Maintenance dredging usually involves frequent removal of material and the amount removed differs considerably depending on the site and type of development. For example Pine Harbour maintains the channel by dredging 3000m³ per year, Westpark Marina dredges up to 10,000m³ per year and the Lyttelton Port maintenance dredging has varied between 290,000m³ to 800,000m³ per year over the past 10 years.

The impact of maintenance dredging on the seabed is usually less severe than capital works, because the activity is taking place in an area which has already been disturbed, and the organisms that have recolonised the area are likely to be more resilient.

Dredging and disposal can also discharge sediment into the water column:

• As the seabed is disturbed by the dredge
• When sediment overflows from hoppers and barges carrying the dredged material
• As the sediment is dumped at a marine disposal site
• By re-suspension of material at the disposal site

Disposal of the dredged material has a number of environmental impacts. There are generally limited opportunities to dispose of dredged material for beneficial reuse, such as beach re-nourishment or in reclamation, land disposal is typically too costly and impracticable which means that marine disposal is often the option of choice. When dredged material is disposed of in the marine environment it can smother the benthic fauna in the immediate disposal area, as well as lead to an increased water turbidity. It is important that disposal sites are chosen to ensure that the impacts are isolated to these locations and the plumes are generally localised. For example, the Ports of Auckland disposes of some dredgings from its dredging programmes, including from the Port of Onehunga, in the Fergusson reclamation where the dredged material is mixed with cement to make mudcrete for the reclamation. ²⁷⁶⁹

There are concerns over the re-suspension of sediment and impact on local ecosystems from the disposal sites in the inner harbour areas. Historically, dredged material from the Pine Harbour Marina in Auckland Harbour has been disposed of locally. In 2009 the marina sought a resource consent to dispose of 3000 metres3 annually off Motukaraka Island nearby the marina. Local concern about the impact of the disposed sediment on cockle and pipi beds and sea grass played a part in the consent being declined. The marina now has permission from Maritime New Zealand to dispose of the sediment off Great Barrier Island in deep water. ²⁷⁷⁰

Where sediment is released into the water column, it can affect the clarity and turbidity of the water, potentially reducing light penetration. The suspended material may eventually settle on  areas around the dredged site, blanketing the benthic animals and plants that live there. The effects of this will vary, depending on the resilience of the communities, and the conditions that they are used to, but may cause stress, reduced rates of growth or fatalities. Suspended sediment from maintenance dredging is likely to have less impact than that from capital dredging, due to the already disturbed nature of the site. ²⁷⁷¹

Some animals are more sensitive to siltation than others. Shellfish, which have delicate feeding and breathing apparatus, may be affected by increases in sedimentation. Similarly, sediment can become trapped in the gills of young fish causing increased fatalities, and smothering of spawning or nursery areas for fish can result in the death of eggs and larvae. This could potentially reduce the level of recruitment for harvestable fisheries such as snapper. Lastly, smothering of intertidal areas may result in decreased availability of food for the birds and fish that feed there. 

In some areas where dredging is commonly undertaken, such as at the entrances to ports and marinas, the sediment on the seabed can often have an elevated level of contaminants. Dredging can remobilise contaminants accumulated in these areas and potentially re‐disperse them further away. The level of risk from this is based on the: ²⁷⁷²

• Degree of remobilisation
• Patterns of dispersal
• Sediment size and quality
• Bioavailability and toxicity of the contaminants
• Sensitivity of species in the downstream area

The potential for dredged sediment to cause toxic effects was assessed in 2012. ²⁷⁷³ This research reviewed monitoring and assessment data on sediment concentrations of five heavy metals (arsenic, chromium, copper, lead and zinc) in seven representative sites around the Auckland region (including two marinas, a port approach and a port area). The work highlighted that dredging material in this region ranged from low contamination to extremely contaminated. It concluded that the extent of contaminant dispersal is expected to be similar to sediment dispersal, being localised, but cautioned that care was needed with extremely contaminated sediments adjacent to sensitive areas. ²⁷⁷⁴

Changes to coastal processes

Structures such as jetties, breakwaters, seawalls, reclamations and groynes may alter wave energy, currents and tidal flows. This, in turn, has the potential to change the transport of sediments along the coast, resulting in coastal erosion in some areas and higher levels of sedimentation and accretion in others. Reclamation inside harbours and inlets also reduces water space, and consequently the volume of water that moves in and out of the area on each tide, thereby affecting tidal flows and flushing. This is sometimes referred to as the tidal compartment. 

The size, shape and orientation of structures relative to the shoreline and natural water flows will determine its hydrological and sedimentation effects. A notable example of how a structure can change sedimentation flows is the breakwater that was constructed as part of the Timaru Port in the late 1870s. This resulted in major erosion at Washdyke but also in the creation of a new beach at Caroline Bay. Before works to construct Timaru Port began, Caroline Bay was moderately deep, with narrow mixed sand. Now approximately 30,000 m³ of sand has accumulated annually in the shelter of the North Mole, and the shoreline has advanced seaward by more than 650 metres. ²⁷⁷⁵

Dredging can also alter the processes that govern the movement of sediments in the coastal marine area. Dredging for capital works has the potential to cause a significant change to the equilibrium of the system, depending on the circumstances. In some situations this can alter the bathymetry of the seabed, impact on the flow of sea water and have an effect on wave patterns with consequential effects on areas such as surf breaks (this is an issue that was raised in connection with the marina at Whangamatā).

There are concerns that the construction and operation of marine tidal turbines could impact on local tides. For example, it was estimated that in the Bay of Fundy, tidal power plants could decrease local tides by 15cm. However, the environmental impact assessments that have been completed indicate that impacts are site specific and depend greatly upon local geography. ²⁷⁷⁶

Degradation of water quality

During the construction phase of a marine development, developers are generally required, as part of their resource consent, to use best practice preventative measures including silt curtains, settlement ponds, temporary retaining walls, temporary dry docking and new technologies. These measures are intended to reduce the risk of sediment or any potential contaminants being introduced into the wider marine environment. Compliance with these consent conditions is managed by unitary and regional councils.

After construction has been completed, the potential for degradation of water quality surrounding the structure will depend on what it is used for. Wharves, jetties and marinas typically attract large numbers of people and boats that, in turn, have the potential for discharges into the marine area – including fuel spillage, sewage from boat toilets and rubbish. To help address this, Westhaven Marina has a ‘no discharge’ policy within the marina, which is discussed further in the case study at the end of this chapter.

The parking and boat washing areas found at marinas may also be a source of contaminated runoff into the sea if they are not appropriately managed. In 2012 a project was undertaken by NIWA for the Environmental Protection Authority (EPA) which looked at the levels of copper leaching from antifoul paints. This research indicated that, in many of New Zealand’s marinas, copper concentrations could be above guidelines for the protection of marine life. ²⁷⁷⁷  Since then, the EPA has carried out a reassessment of antifouling paints ²⁷⁷⁸  and the Ministry for Primary Industries has prepared draft antifouling and in-water cleaning guidelines ²⁷⁷⁹ .

When a marina or canal development site is located in a poorly flushing area, or the design of canals and structures prevent adequate flushing, the area can become a trap for sediment and pollutants causing the water and sediment quality of the area to be affected. ²⁷⁸³  A RAMSAR Convention report on canal estates highlighted that the majority of environmental problems arise from canal systems that are not designed to allow a certain amount of flushing, ultimately resulting in: ²⁷⁸⁴

• Additional nutrient loading in the water
• An effect on biological diversity

The problem can be minimised through the use of wide canals, which have good linkages, to allow a circular flow of water throughout the entire development. This helps to ensure that the development is well-flushed by tidal action and that any contaminated run-off is collected and treated. Ongoing vigilant management, is also required, to ensure that spillages into the marine area are minimised through the adoption of good practice.

Disrupting the relationship of tangata whenua with the marine environment

For Māori, the marine environment was traditionally a place to source food, as well as being fundamental to travel and communication. Inland tribes often accessed kaimoana by way of putanga, or corridors to the coast.

The impacts of marine development on the marine environment is a critical issue for coastal Māori. Gathering of kaimoana, both for sustenance and to provide for visitors, is an integral component of life. When those resources are compromised, such as when structures are placed over shellfish beds or in a place that obstructs access to them, the Māori way of life is also compromised.  Activities which contaminate water and sediment can result in kaimoana being unsafe to eat and in a reduction in the abundance and diversity of marine life.

The impacts of dredging and reclamation are identified by the Te Awanui Tauranga Harbour Iwi Management Plan 2008 as significant cultural issues, in  particular the impacts on traditional relationships in the area, disturbance to kaimoana and potential re-establishment of kaimoana. ²⁷⁸⁵

Coastal works such as reclamations and the construction of seawalls can result in the loss of intertidal areas, which reduces the areas where shellfish can be harvested. The Kāi Tahu ki Otago Natural Resource Management Plan 2005 identifies that such activities and structures restrict physical access to the foreshore and seabed for the collection of kaimoana. ²⁷⁸⁸  Construction activities can also result in the destruction of culturally important sites such as wāhi tapu and traditional waka linkages and mooring places.

The location of wastewater treatment plants in the coastal environment has caused much concern among coastal Māori. A Cultural Impact Assessment of the Matata Wastewater Scheme, prepared in 2014, identified significant concerns for Tangihia Hapū in regards to the Matata wastewater scheme in Whakatane. This included stating that disposing of partially treated wastewater in a wāhi tapu area where the bones of tupuna were buried is culturally unacceptable and that locating the treatment plant in proximity of the Rangitihi Marae is culturally unacceptable. ²⁷⁸⁹

Loss of public access

Structures built along and near the coastal edge can enhance public access (through boat ramps and jetties, as well as walkways around buildings) and also obstruct it (through restrictions to access) both to the marine area and to areas within it. Port developments typically exclude public access to the coastal edge for safety and security reasons. However, some ports provide organised educational tours for school groups and interest groups. Marina and canal developments vary in the extent to which they provide for public access.

Public access to marina berths is often excluded, particularly at night, for security reasons. The marina berths themselves are occupied by licencees, and are not freely available to other boat users, although some may be available to visiting boats for short-term periods. Some marinas incorporate public walkways, boat ramps, parking, picnic areas and cafes as part of the complex, and this enables members of the public to access and enjoy the coastal environment.

Public access is typically not available around the coastal edge of canal developments as privately-owned residential properties extend right down to the coastal edge. The waterways themselves are usually in public ownership and open to all users. Some canal developments also provide small public parks alongside sections of the canals. ²⁷⁹²  

There has been considerable controversy over the extent to which members of the public should have access to private wharves and jetties. The general legal principle is that unless a coastal permit expressly limits public access, and such a limitation is necessary to give effect to the permit, the permit holder cannot exclude the public from the coastal marine area. ²⁷⁹³ The situation in any specific case will be affected by the ownership of the seabed on which the structure is located and the conditions of the coastal permit authorising the use and occupation of the structure. Under the Marine and Coastal Area Act (discussed in Chapter 2: Marine management) no person owns or is capable of owning the common marine and coastal area, ²⁷⁹⁴ but this area expressly excludes freehold titles currently held over the seabed. ²⁷⁹⁵

Reverse sensitivity

The very nature of major marine developments, particularly ports and marinas, means that there are operational activities which result in issues beyond the immediate boundaries – such as noise and light from port operations. Adequate lighting is a necessary part of providing for a safe working port. In addition, many major marine developments require land-based transport links that can impact on the surrounding community. Such issues are often referred to as reverse sensitivity, which has been defined by the Environment Court ²⁷⁹⁶  as “the legal vulnerability of an established activity to complaint from a new land use. It arises when an established use is causing adverse environmental impact to nearby land, and a new, benign activity is proposed for the land. The ‘sensitivity’ is this: if the new use is permitted, the established use may be required to restrict its operations or mitigate its effects so as not to adversely affect the new activity”.

Degradation of marine heritage

Marine developments can negatively impact on marine heritage if reclamations or structures are built in the vicinity of, or over, archaeological sites, wāhi tapu and other sites of historical significance. As the location of many marine heritage sites is poorly recorded, research will often need to be undertaken in respect of individual marine development proposals, to determine whether a historical site may be impacted upon.

Last updated at 2:11PM on February 25, 2015