The coastal classification system constitutes the foundation for the CHW methodology. It is developed particularly for decision-support but includes many components of previously published coastal classification systems. The following sections outline the revised classification system used by the CHW 2.0 and the content is based on the original description published in Rosendahl Appelquist (2012).
The coastal classification system is based on the bio-geophysical components that are considered most important for the characteristics of a particular generic coastal environment. The components included are geological layout, wave exposure, tidal range, flora/fauna, sediment balance and storm climate, and each generic coastal environment has a specific combination of these variables. As the bio-geophysical variables can change significantly over short spatial distances, a generic coastal environment will according to the classification system theoretically apply to a particular spot along a coastline. For practical application, however, a generic coastal environment should be considered to extend longshore until any variables included in the system changes significantly.
In order to avoid a disproportionate large number of categories, the system applies an “Any” phrase in cases where a particular classification parameter is of minor importance. Variables such as local isostatic uplift/subsidence and sediment grain size have not been included as these to some extent are indirectly covered through other parameters. This is to achieve an appropriate balance between classification simplicity and correctly reflecting natural conditions. The different classification components have been clearly defined in order to differentiate the generic coastal environments and to make the classification system practical applicable. The definitions and assumptions for the different classification components are outlined below.
Geological layout
The geological layout constitutes the basis on which the dynamic processes act. It has been created by various past dynamic processes including glacial, fluvial, marine, volcanic and tectonic (Davis and Fitzgerald 2004). The coastal landscape continues to be modified by these processes over different timescales and making an assessment of a particular geological layout will therefore be a snapshot that will change gradually over time. However, as most major changes in geological layout take place on timescales of decades or more, the effect of these changes on the classification is limited. Furthermore, the subsequent layers in the classification system include the major short-term coastal processes, meaning that most gradual natural changes are handled by the system.
The geological layouts included in the classification system are defined based on a thorough analysis of the world’s costal environments and are framed in a way so they cover all major types of geological layouts worldwide. They are defined to include important generic characteristics while still maintaining an appropriate simplicity. The geological layout categories included in the CHW 2.0 are: sedimentary plain; barrier; delta/low estuary island; sloping soft rock coast; flat hard rock coast; sloping hard rock coast; coral island; tidal inlet/sand spit/river mouth. The first four categories are sedimentary geological layouts generally found on trailing edge coastlines such as the Atlantic coast of North- and South America whereas the sloping hard rock coast, is commonly found on leading edge coastlines such as the Pacific coast of North and South America. The flat hard rock coast can appear in various settings e.g. as raised coral reefs, whereas the coral island category is largely depending on tectonic and climatic conditions (Davis and Fitzgerald 2004; Masselink and Hughes 2003). The final category tidal inlet/sand spit/river mouth constitutes a group of specially dynamic geologic environments.
The sedimentary plain category is defined as coasts with average slopes of less than 3–4 % at least 200 m inland of the MSL, and which are composed of sedimentary deposits such as clay, silt, sand, gravel, till or larger cobbles. If coastal dunes are present, the slope may locally be higher than 3–4 % where the backbeach meets the dunes, but the coast will still fall into the sedimentary plain category. Sedimentary plains are often formed by glacial and fluvial processes or through coastal progradation (Davis and Fitzgerald 2004; Masselink and Hughes 2003).
The barrier category is defined as coasts that consist of non-sloping/low-lying, shore parallel sedimentary bodies with cross distances ranging from less than 100 m to several kilometres, and lengths ranging from less than 100 m to over 100 km (Davis and Fitzgerald 2004). Narrow barriers often exist where the sediment supply is or has been limited, while broad barriers are formed in areas with sediment abundance (Masselink and Hughes 2003). The seaward side of a barrier often contains a wave dominated beach environment, while the landward side consists of protected lagoons and estuaries with various kind of marsh or mangrove vegetation, depending on climatic conditions and tidal range. In meso- and macro-tidal environments, barriers are frequently cut by tidal inlets. In the classification system, a barrier can occur in parallel to coastlines of other geological layouts, located landwards of the barrier. This would e.g. be the case where a sedimentary plain or sloping soft rock coast is located landwards of a barrier.
The delta/low estuary island category is defined as coasts composed of fluvial transported sediment that is deposited in front of a river mouth. These landforms form in the coastal-fluvial interface where riverine sediment supplied to the coastline is not removed by marine processes. The formation of deltas/low estuary islands is therefore strongly dependent on the fluvial sediment discharge as well as the waves, tides and currents of a particular location. Plate tectonics and regional geological conditions also influence delta formation. Larger deltas are generally found on trailing edge and marginal sea coastlines, where large drainage basins provide a high fluvial discharge, and wide continental shelves provide a relatively shallow depositional area (Schwartz 2005). Small deltas might form along leading edge coastlines but their extension is limited by the smaller drainage basins and steep coastal gradient that does not allow significant sediment accumulation.
The sloping soft rock coast category is defined as coasts comprised of soft rock material with average slopes greater than 3–4 % at least 200 m inland of the MSL. Coastal cliffs with a steep cliff gradient combined with shore platforms or a landscape flattening landwards of the steep cliff also fall into this category. Sloping soft rock coasts can be comprised of a range of different sedimentary deposits such as chalk, moderately cemented laterite, clay, silt, sand and till with larger pebbles or cobbles. Hard sedimentary rocks are not included in this category and it can therefore be necessary to assess the level of sediment cementation in order to determine whether a particular coast should be classified as soft or hard rock. In the classification system, a rock will fall into the soft rock category if the sediment is poorly cemented, and as a general rule, it should be possible to push a knife some centimetres into the rock material without using excessive force. However, the simplest way to determine whether a coast consists of soft rock material is by using a basic geologic map. Sloping soft rock coasts can exist as both coastal cliffs and gently sloping vegetated hills.
The flat hard rock coast category is defined as coasts consisting of igneous, sedimentary and metamorphic rock with average slopes of less than 3–4 % at least 200 m inland of the MSL. Igneous rocks are formed from magma and are comprised of a range of different minerals and grain sizes depending on their chemical composition and solidification process. Sedimentary rocks consist of sediment that has undergone different stages of diagenesis, where the sediment has been compacted and cemented under increased temperature and pressure, creating a solid rock structure. Metamorphic rocks have formed from both igneous and sedimentary rocks when they have undergone recrystallization under high temperature and pressure (Press and Siever 2001). The specific physical and chemical rock properties influence the weathering and erosion processes, but for the coastal classification system, hard rock material is considered as one uniform group. Flat hard rock coasts can be present in different forms such as rocky coastal plains, islands and archipelagos.
The sloping hard rock coast category is defined as coasts consisting of igneous, sedimentary or metamorphic rock with average slopes greater than 3–4 % at least 200 m inland of the MSL. Sloping hard rock coasts can be present in different forms such as coastal mountain chains, headlands and archipelagos.
The coral island category is defined as low-lying coral islands in the form of tropical atolls and coral cays. Tropical atolls are open ocean coral islands that rest on a subsiding volcanic foundation. Atolls have a round shape with diameters ranging from a few kilometres to more than hundred (Schwartz 2005). Coral cays are younger islands formed on top of coral reefs or adjacent to atolls due to the accumulation of reef-derived sediment in one location as result of to wave action. These islands can rise up to three meters above high water level and can be composed of coarse reef fragments or fine carbonate sand. The beaches of both atolls and coral cays can have cemented to form beachrock and coral sandstone that help stabilize the islands (Haslett 2009).
The tidal inlet/sand spit/river mouth category is established as a separate grouping in the classification system as these environments can be highly morphologically active and respond quickly to changes in other coastal processes (Mangor 2004). In the classification system, tidal inlets are defined as the coastline of a tidal inlet itself and one kilometre parallel to the shore on each side of the inlet. Tidal inlets are found along barrier coastlines throughout the world and provide water exchange between an open coast and adjacent lagoons and estuaries. Their morphology depend on a range of different parameters such as tidal range, wave climate and sediment availability (Davis and Fitzgerald 2004). In special cases, where the inlet side consists of a hard rock headland, the inlet side should fall into one of the hard rock categories of the CHW classification system. Sand spits are elongate sedimentary deposits that are formed from longshore currents losing their transport capacity and subsequently depositing sediment at particular locations. They can be present in different shapes and are generally classified into simple linear spits, recurved spits with hook-like appearances, and complex spits with plural hooks (Schwartz 2005). River mouths are defined as the coastline one kilometre on each side of a well defined river mouth. Tidal inlets, sand spits and river mouths are assigned high priority in the CHW classification system, meaning that e.g. a sedimentary plain will fall into this category if it is located less than one kilometre on each side of a tidal inlet or river mouth.
Wave exposure
The wave exposure is the dominant energy source in the nearshore environment and a highly important parameter for the coastal morphodynamics. Although some incoming wave energy is reflected by the shoreline, most energy is transformed to generate nearshore currents and sediment transport and is a key driver of morphological change (Masselink and Hughes 2003).
For most coastal systems, gravity waves generated by wind stress on the ocean surface are the main source of energy. The restoring force for this wave type is earth’s gravity, and gravity waves are generally composed of sea- and swell waves (Masselink and Hughes 2003). Sea waves are formed under direct influence of the wind on the ocean surface and have peaked crests and broad troughs. They are often complicated with multiple superimposed sets of different wave sizes and whitecaps can be present during high wind speeds. Swell waves develop after the wind stops and where the waves travel outside the area where the wind is blowing. They have a sinusoidal shape and commonly have long wavelengths and small wave heights (Masselink and Hughes 2003). The wave height is the generally applied measure for incoming wave energy and is defined as the difference in elevation between the wave crest and wave trough (Davis and Fitzgerald 2004). Since the wave energy increases as the square of the wave height, coastal environments with high wave heights have relatively high energy intensity compared to protected coasts (Thieler et al. 2000).
The coastal classification system distinguishes between exposed, moderately exposed and protected coastlines. The distinction between these categories is based on the significant wave height, HS, that represents the average wave height of the one-third highest waves in a wave record and corresponds well to the visual wave height estimates (Masselink and Hughes 2003). To ensure consistency, the classification system uses the HS 12 h/yr, which is the nearshore significant wave height exceeded for 12 h per year (Mangor 2004).
The wave exposure level is determined based on the coastline geography and wind climate. All coastlines located in areas with swell waves are in the classification system defined as moderately exposed (Mangor 2004). These coastlines can be indentified based on Fig. 1, where coasts falling into “West coast swell”, “East coast swell” and “Trade/monsoon influences” are categorized as moderately exposed coastlines. It should be noted, however, that backbarrier and inner estuary coastlines in these regions are not swell wave coasts.
If the coastline is located outside the swell regions, the wave exposure should ideally be determined based on the S-B-M method. This method uses a nomogram to predict HS by input of wind speed, wind duration and fetch length and the nomogram is included in the paper for the CHW 1.0 (Rosendahl Appelquist 2012; Coastal Engineering Research Center 1984). If the HS 12 h/yr is determined as more than 3 m, the coast is considered exposed, while it is considered moderately exposed with an HS 12 h/yr of 1–3 m. If the HS 12 h/yr is determined as less than 1 m, the coast is considered to be protected.
Since it in many cases can be difficult to obtain the necessary wind data to apply the S-B-M method, the free fetch can be used to roughly estimate the exposure levels of non-swell coastlines. This is therefore the standard methodology applied in the CHW system. Coasts can be considered exposed if they border waterbodies larger than 100 km, while they can be considered moderately exposed if they are associated with waterbodies of the size of approximately 10–100 km. Protected coasts are generally restricted to inner waterbodies in the order of less than 10 km, but can also be seen along larger waterbodies with shallow nearshore zones or mild on-shore wind climates (Mangor 2004). When estimating the exposure levels, it is therefore important to be aware of physical conditions such as coastal reefs, tidal flats or wind conditions that cause the coast to fall into the protected category even when the water body is larger than 10 km. Ice affected coastlines may have seasonal fluctuating wave exposures due to presence of winter sea ice. As sea ice is expected to be highly vulnerable to climate change, however, the same approach as for ice free coasts should be applied. Only in locations where the sea ice is expected to be very stable, the fetch length has to take into account the ice cover.
Tidal range
Tides can have major impact on shoreline processes and on the development of coastal landforms. They are a manifestation of the moon’s and sun’s gravitational force acting on earth’s hydrosphere and are present in the form of oceanic waves with wavelengths of thousands kilometres, resulting in periodic fluctuations in coastal water levels (Davis and Fitzgerald 2004). Tides fluctuate on a daily basis following diurnal, semidiurnal and mixed tidal cycles (Davis and Fitzgerald 2004). Diurnal tides exhibit one tidal cycle daily whereas semidiurnal tides exhibits two cycles daily. Mixed tides have components of both diurnal and semidiurnal tides varying throughout the lunar cycle (Davis and Fitzgerald 2004). Globally, semidiurnal and mixed tides are dominating coastal areas (Haslett 2009).
From a morphodynamic perspective, the tidal range influences coastal processes in many ways and is controlling the horizontal extent of the intertidal zone, the vertical distance over which coastal processes operate and the area being exposed and submerged during a tidal cycle (Haslett 2009). The tidal range is defined as the height difference between the high water and low water during a tidal cycle (Schwartz 2005) and the tidal range of a particular coastal location is controlled by a range of different parameters including the distance from an oceanic amphidromic point, the local bathymetry, the width of the continental shelf and the coastal configuration (Haslett 2009). The numerical value of the tidal range vary significantly between coastal locations and span from almost zero to about 16 m in funnel shaped embayments such as the Bay of Fundy, Canada (Davis and Fitzgerald 2004). Tides of a particular location also fluctuate on a daily basis depending on planetary positions.
For classification purposes, coastlines can be grouped into various tidal environments based on tidal range, and a generally used classification system operates with the three main categories micro-tidal, meso-tidal and macro-tidal (Schwartz 2005). Micro-tidal environments are defined as coasts where the tidal range does not exceed 2 m and can be found on open ocean coastlines such as the eastern seaboard of Australia and the majority of the African Atlantic coast (Haslett 2009). Meso-tidal environments are defined as coasts with a tidal range of 2–4 m and examples of these are found on the Malaysian and Indonesian coasts and on the eastern seaboard of Africa (Haslett 2009). Macro-tidal environments are defined as coasts where the tidal range exceeds 4 m which is the case along some of the northwest-European coasts and in parts of north-eastern North America (Haslett 2009). The global distribution of micro-, meso- and macro-tidal environments is shown in Fig. 2.
The effect of tidal range on coastal morphodynamics is largely influenced by the local wave conditions. Therefore, the relative size of tides and waves of a particular location is—seen from a morphodynamic perspective—more important than the magnitude of the tidal range itself (Masselink and Hughes 2003). This relationship is illustrated by the relative tidal range expression that states that the relative morphodynamic importance of the tidal range decreases with increasing wave exposure (Masselink and Hughes 2003). This principle is applied in the classification system that uses the three different tidal categories, micro, meso/macro and any that are applied in accordance with wave exposure. Where the coastline is exposed or moderately exposed, the classification uses the any tide category as these environments are considered to be largely dominated by wave processes. This may lead to some inaccuracies in the hazard assessment of coastlines with a very large tidal range but is considered a reasonable simplification taking the impacts of other classification parameters into account. At protected coastlines, the tidal range can have major impact on the coastal morphodynamics and the classification system therefore distinguishes between micro and meso/macro-tidal conditions. Under micro-tidal conditions, these coastlines will still be partly wave dominated whereas they will be largely tide dominated under meso/macro-tidal conditions. The merging of meso/macro tides is regarded as an acceptable simplification without major implications for a reliable hazard evaluation, except under extreme high tidal range conditions. Since the effect of tidal range on the inherent hazards of sloping soft rock coasts, flat hard rock coasts, sloping hard rock coasts and coral islands is considered to be minor, the any tide category has been applied to these layouts for simplification purposes. In the case of tidal inlets, tidal forces play a key role for their morphodynamics, but these environments are included in a separate category due to their special properties.
Flora/fauna
For some coastal environments, the local flora/fauna constitutes an important parameter for their morphodynamics and inherent climate change hazards. In the classification system, the flora/fauna has been included where it is considered to play an important role for the characteristics and inherent hazard profile of a coastal environment. The integration of the flora/fauna component in the classification system is complicated by its interdependence with other physical classification parameters and this is reflected in the application of the flora/fauna categories. In total, the classification system operates with nine different categories namely intermittent marsh; intermittent mangrove; marsh/tidal flat; mangrove; marsh/mangrove; vegetated; not vegetated; coral and any.
The intermittent marsh and marsh/tidal flat categories are applied to coastlines whose geological layout falls into the categories sedimentary plain, barrier and delta/low estuary island. The marsh is a grass-like vegetation of salty and brackish areas along protected, low energy coastlines. It colonizes higher parts of the intertidal environment, forming coastal wetlands that act as a sediment trap for fine grained sediment. Marsh areas gradually build up from continuous flooding and subsequent sediment deposition, which can be particularly large during storm events. Due to the continuous accumulation of sediment, marsh areas can to some degree follow sea level rise but will eventually drown if sea level rises too rapidly. In locations with a high tidal range, marsh areas are often continuous and combined with extensive tidal flats, and the classification therefore distinguishes between the intermittent marsh category applied to areas with micro-tidal conditions and the marsh/tidal flat category applied to areas with meso/macro-tides.
The intermittent mangrove and mangrove categories are applied to coastlines falling into the geological layout categories sedimentary plain, barrier and delta/low estuary island. Mangrove is a woody shrub vegetation that grows along protected, low energy coastlines forming a swampy environment. It is very dependent on air temperature and cannot tolerate a freeze and its geographical extension is therefore limited to low and moderate latitudes. The extensive root network of mangroves acts as an efficient trap for fine grained sediment and reduces wave erosion of the coastline. Like marsh areas, mangrove forests are rich ecosystems providing nursing grounds for many animals and in addition limit erosion and flooding from tropical storms. In the classification system, the intermittent mangrove category is applied to areas with micro-tidal conditions, while the mangrove category is applied to areas with meso/macro-tides, as they colonise the tidal flats. The combined marsh/mangrove category is applied to protected, flat hard rock coasts that have a narrow band of marsh/mangrove vegetation.
The vegetated and not vegetated categories are applied to the geological layout category sloping soft rock coast where vegetation of the coastal slopes plays an important role for the coastline characteristics. The vegetated category is applied when more than 25 % of the slope is covered with vegetation while the not vegetated category is used when less than 25 % is vegetated. Possible vegetation includes different grasses, scrubs and trees depending on the soft rock properties, slope and climatic conditions. Although some types of vegetation have a better stabilizing effect than others, the important criteria seen from a coastal classification perspective is whether the coastal slope is vegetated or not. Sloping soft rock coasts may be fronted by a narrow band of marsh or mangrove vegetation but this is not considered of major importance from an inherent hazard perspective. In cases where the fronting marsh or mangrove areas are more extensive, the coastline will automatically fall into one of the non-sloping geological layout categories.
The coral category is applied to flat hard rock coasts and sloping hard coasts where the corals have a firm substrate to thrive on. Corals are carnivorous suspension feeders, living in large colonies as polyps with an external skeleton of calcium carbonate (Masselink and Hughes 2003). Since they generally attach to hard substrates, rocky shorelines provide suitable coral habitats (Masselink and Hughes 2003). Reef building coral species only thrive in water temperatures between 18 and 34 °C and are thus limited to tropical and subtropical environments (Davis and Fitzgerald 2004). Reef building corals are very light sensitive and reefs are rarely being created at depths greater than 50 m. Locally, water turbidity and salinity can be important parameters for reef formation, and high turbidity can decrease light penetration and increase sedimentation, thereby inhibiting coral growth. Salinity levels outside the range of 27–40 ppt also limit reef formation, and low salinity combined with high turbidity often explain the reef openings found close to river mouths (Masselink and Hughes 2003). Corals can survive in high energy wave environments and even shows enhanced growth on exposed coastlines (Masselink and Hughes 2003). In the classification system, the coral category includes both fringing and barrier reefs fronting rocky coastlines. Since coral reefs often are backed by carbonate beaches and not bare rock, the special beach category available in the classification system for flat hard rock coasts and sloping hard coasts captures this condition. The separate geological layout category for coral islands is assumed to be associated with coral reef environments of various kinds.
The any category (also indicated with an A in the CHW) is used when the flora/fauna is not considered to play an important role for the coastal characteristics and/or inherent hazard profile. In some cases, the flora/fauna may have relevant functions such as the ability of lyme grasses to reduce aeolian sediment transport, but compared to the other classification parameters it is not expected to influence the included hazards significantly.
Sediment balance
The sediment balance is an essential morphodynamic parameter and particularly important for coastlines falling into the sedimentary layout categories. The sediment balance determines whether there is a net accumulation, removal or balance of sediment at a particular coastline over time and is largely determined by the sediment transport and availability.
The coastal sediment transport can be divided into two main categories, namely transport of non-cohesive and cohesive sediment. Transport of non-cohesive, sand-sized sediment, termed littoral transport, plays an essential role for the sediment balance of exposed and moderately exposed sedimentary coastlines. This type of transport is mainly controlled by the wave height, wave incidence angle and sediment grain size, and large quantities of sediment can be transported down the coastline by this process (Mangor 2004; Davis and Fitzgerald 2004). Coastlines dominated by littoral sediment transport generally respond to physical changes by adjusting their theoretical equilibrium profile, which is the average characteristic form of a coastal profile, controlled by sediment grain size and to some degree wave conditions. Changes in sediment availability, storm conditions or sea level will cause the theoretical equilibrium profile to shift to a new equilibrium state that matches the changing framework conditions. Because of this mechanism, a coastal profile will require more sand to maintain its existing shoreline position if a new equilibrium profile is created due to sea level rise. This will lead to shoreline erosion if no net sediment supply is present.
Transport of fine, cohesive sediment or mud plays an important role in the sediment balance of protected coastal areas. Cohesive sediment particles have a relatively low fall velocity compared to sand grains and the individual grains have the ability to cohere to each other. These particles cannot form stable coastal profiles in exposed and moderately exposed coastlines since they easily go into suspension. Fine grained, muddy coasts are therefore only found in protected coastal areas where there is abundance of cohesive sediment. Such coastlines are generally vegetated with marsh or mangrove vegetation, sometimes combined with mud/tidal flats (Mangor 2004). Coastlines dominated by cohesive sediment can respond to rising sea level by growing vertically by increasing the sediment accumulation rate, but may also suffer from inundation and erosion depending on sediment availability and tidal dynamics.
In the classification system, the sediment balance section includes the two main categories balance/deficit and surplus and the two special categories no beach and beach that applies to the hard rock coastlines. It has been decided to group the balance/deficit categories together to simplify the classification system and to ease the difficult evaluation of the sediment balance on-site or remotely. Coastal areas that are currently experiencing sediment deficits or only have sufficient sediment to remain stable at current conditions are likely to suffer from sediment deficits with a rising sea level, unless new sediment sources emerge (Haslett 2009). Coastal areas that currently experience sediment surplus might suffer deficits at a later stage if sea level rises sufficiently or there is a change in local sediment dynamics. However, seen from a hazard perspective, these coastlines are less likely to experience severe sediment deficits in the near future.
For achieving an optimal accuracy of the hazard assessment, temporal data on sediment transport, erosion and accumulation would be valuable for determining the sediment balance of a particular coastline. As the CHW system is intended to be used in areas with limited data availability, however, it is designed to rely on a combination of remote sensing data and on-site assessments. Direct short-term observations are complicated by the fact that single storm and high-wave events can lead to temporal coastline erosion which is reversed during calm conditions, thus causing fluctuating erosion and accumulation patterns (Mangor 2004; Stive et al. 2002). This means that a particular coastal area may one day appear to erode while looking stable sometime later. For evaluation of the sediment balance, it is therefore recommended to make use temporal remote sensing techniques to evaluate coastal changes over several years. In case there is any doubt about the sediment balance evaluation, the user should assume a balance/deficit as this is the default category for the CHW system. This is also recommended where there are indications of short-term human alteration of the sediment balance.
For hard rock coastlines, the classification system does not require a sediment balance evaluation but simply apply a no beach category if the coast consists of bare rock and a beach category if some kind of beach environment is present.
Storm climate
In areas with tropical cyclones, coastal areas can experience extreme wind, wave, and precipitation conditions that significantly affect the coastal morphodynamics and inherent hazard profile. Tropical cyclones are generated over tropical seas where the water temperature exceeds 27 °C. They are normally generated between 5°–15°N and 5°–15°S and about 60 tropical cyclones are generated annually worldwide with peak periods in September in the Northern Hemisphere and in January in the Southern Hemisphere (Mangor 2004). Wind speeds in tropical cyclones exceed 32 m/s and can cause extreme wave heights, storm surges and cloudburst. Although tropical cyclones have a great impact on the coastal morphology when they hit, the general coastal morphology of an area is largely determined by the local wave climate (Mangor 2004).
The classification system distinguishes between locations with and without tropical cyclone activity, without considering their frequency. This is decided as tropical cyclones contribute to the inherent hazards in all areas where they occur regardless of their frequency. The classification system uses the map shown earlier in Fig. 1 to categorize the influence of tropical cyclones on coastal areas (Masselink and Hughes 2003). In areas indicated to be under “Tropical cyclone influence” the classification system applies a yes to tropical cyclone activity while it applies a no for locations outside these areas.