Beach Type

Beach type refers to the prevailing nature of a beach, including the waves, tides and currents, the extent of the nearshore zone, the width and shape of the surf zone, including its bars and troughs, and the dry or subaerial beach (Short, 2006).

New Zealand’s numerous beach systems can be classified into 14 beach types. These include six wave dominated, three tide-modified, five tide-dominated.

Wave-dominated

Wave-dominated beaches are those that are exposed to persistent ocean swell,waves and low tides (range <2m). Wave-dominated beaches consist of three types: Reflective, Intermediate and Dissipative with the intermediate having four states (Short, 2006).

Reflective

Reflective beaches have the lowest wave energy of the wave-dominated beaches (breakers 0-1 m high). They are characterised by a relatively steep narrow beach face, composed of coarse sand, a narrow surf zone and often cusps on the upper part of the beach. They are relatively short in length in comparison to the other beach types because they tend to form in sheltered pockets in lee of rocks, reefs and headlands. Waves break close to the shore on a reflective beach with little prior loss of energy, this is a result of the steep beach face and deep nearshore zone. Reflective beaches are generally safe for bathing apart from the deep water close inshore and the high energy shore break during higher wave conditions. Also note that the steep beach and abrupt drop off from shallow water to deeper water can be a problem for the elderly and children.

Typical relective beaches: Port Jackson (West), Tuparoa Beach, Mahia, Westshore, Kaiteriteri, Okiwi Bay, St Andrews Beach

Intermediate beach types

Longshore bar and trough

Longshore bar and trough beaches consists of a shore parallel bar separated from the beach by a deep trough. Breakers are typically 1.5-2.0 m high and rip currents are moderate. The beach is generally straight composed of medium sand with a moderate to steep beach face. Cusps are also often present on the upper beach. At a Longshore bar and trough beach the deep trough and distance to outer bar generally restricts most bathers to the swash zone and inner trough.

The safest bathing area at a Longshore bar and trough beach is in the swash zone and in the inner trough away from rips.

Typical longshore bar and trough beaches: Mokau, Tomahawk Bay, St Kilda Beach, Football field Brighton

Rhythmic bar and beach

Rhythmic bar and beach are high energy beaches that consist of a rhythmic (undulating) bar, trough and beach. They have distinct rip troughs that are separated by detached bars. Breakers are generally 1.5-2.0 m high. They have cusps (in lee of bars) and are typically composed of fine-medium sand. The pronounced changes in depth and current between bars and rips make these beaches hazardous for children and the inexperiences during high waves and high tide.

The safest bathing on these beaches is on or behind the bars during lower wave conditions.

Typical rhythmic bar and beaches: Summer Hill Beach, North Clutha mouth, Taupirikaka Point at Ship Creek, Bruce Bay

Transverse bar and rip

Bars transverse (perpendicular) to and attached to the beach separated by distinct rip troughs at 150-300 m spacing. Breakers are typically 1.0-1.5 m high. The surf zone is 50 -150 m wide with cellular circulation pattern. The beach is undulated with cusps on the upper beach and is composed of fine to medium sand. These beaches are relatively safe during low waves however the pronounced changes in depth and current between bars and rips can be hazardous for the young and inexperienced.

The safest bathing on a Transverse bar and rip beach is on the bars and well away from the rip channels and their side feeder currents.

Typical transverse bar and rip beaches: Whangaparaoa Bay, Gisborne - Midway SLSC, Opunake, Kiritehere Beach, Curio Bay, Rapahoe, Morpeth Street

Low tide terrace

Low tide terrace beaches are composed of fine to medium sand and have a moderately steep beach face joined to an attached bar or shallow terrace that is often exposed at low tide. The bar extends alongshore, is flat and featureless, or maybe cut every several 10’s of metres by small rips. Breakers are generally 0.5-1.0 m high and these beaches generally occur in areas sheltered from direct wave attack. Low tide terrace beaches are generally safe for bathing, however they can be hazardous at mid to high tide when waves exceed 1m. Also note that at spring low tides waves may plunge heavily on the outer bar, behaving more like a relective type beach creating a hazard. Safest bathing at these beaches is at low tide when the waves are small.

Typical low tide terrace beaches: Matata, Ohope, Hicks Bay, Te Awanga, Bell Block, Okains Bay, Moeraki Beach

Dissipative Beach

Dissipative beaches are characterised as being high energy beaches with a wide surf zone (300-500m) including two to three shore normal bars and troughs, and a low-sloping and wide beach face consisting of fine sand. Breakers are typically 2-3 m high. On a dissipative beach wave break further offshore, waves then lose energy (dissipate) as they travel as a breaking bores across the wide surf zone. At a dissipative beach high waves and a wide surf zone restrict most bathers to the inner swash zone. Safest bathing at a dissipative beach is in the swash zone, however be aware that water levels will vary considerably between set-up and set-down. This is particularly a concern for young children who may be knocked over by the incoming set-up, or dragged seaward by the set-down.

Typical dissipative beaches: Oreti Beach, McCrakens Lookout, Orepuki beach

Tide-modified

Tide-modified beaches occur in areas of high tide range and usually lower waves. Tides usually range between 3 and 15 times the wave height and the wave height is <0.3m. There are 3 types of tide-modified beaches; Reflective + low tide terrace, Reflective + bars and rips, Ultra dissipative.

Reflective + Low tide terrace

This is the lowest energy of the tide-modified beaches and also has the coarsest sand. Reflective + Low tide terrace beaches have a steep cusped high-tide beach composed of medium to coarse sand, which changes at an abrupt break in slope into a low-gradient wide (av.120 m but can range 20-1000 m) low tide terrace composed of finer sand. Typical breakers are 0.5-1 m high. At high tide waves surge at base of the steep beach face and there is no surf zone. At low tide there is a flat sand bar exposed, waves of > 0.5 m height plunge on the outer end of bar, and waves >1 m height may cut rip channels across the terrace. At high tide the deep water close inshore and steep beach face may cause a problem for the elderly and young children. At low tide stay on the bar inside breakers, if rip channels are present be aware of the seaward moving rip currents, also plunging waves can dump heavily on bar at low tide.

Typical reflective + low tide terrace beaches: Langs Beach, Tapapakanga Regional Park (Derry), Papa aroha, Cable Bay, Boulder Bank, Little Akaroa

Reflective + bars & rips

Reflective + bars & rips beaches have a relatively straight, moderately steep, narrow, and coarser sand, cuspated high-tide beach, fronted by a lower gradient, relatively featureless intertidal zone. they have a wave dominated low-tide surf zone usually characterised by bar and rip morphology. Breakers are typically 0.5 to 1.5 m high (height increases with onshore winds). At high tide waves break across a narrow continuous surf zone. At low tide a wider surf zone has rips (spacing 100-150 m). At high tide for safetst bathing stay inshore of the breaker zone. At low tide waves may plunge on shallow bars and deeper rip channels may present stronger seaward flowing rip currents.

Typical reflective + bars & rips beaches: None classified in New Zealand yet.

Ultra dissipative

Ultra dissipative beaches have a relatively straight, steeper, cuspated high tide beach, with a low gradient concave, featureless, wide (averages 400-500 m) intertidal zone. They occur on the higher energy, tide modified coasts with waves averaging 0.5 m, and are favoured by higher tide ranges and fine sand. They have a wide zone of spilling breakers of 0.5-1.5 m height (height increases with onshore wind velocity) at high tide and low tide. At high tide and low tide stay inshore of breakers zone for safest bathing because water depth increses gradually beyond breakers.

Typical ultra dissipative beaches: Orewa (Marie Place), Rabbit Island, Tahunanui Beach

Tide-dominated

Occur in areas of high tide range and usually lower waves. Occur when the tide range is between 10 and 15 times the wave height and the wave height is very low. Consists of 5 types Reflective + sand ridges, Reflective + sand flats, Reflective + tidal sand flats, Reflective + tidal mud flats, Reflective + rock flats.

Reflective + sand flats

Reflective + sand flats beaches have a small steep (3-10°), low-gradient, very low-energy high-tide beach composed of coarse sand, fronted by flat featureless sand flats up to several hundred meters wide composed of finer sand. there are no waves at a Reflective + sand flat beach unless strong onshore winds. At high tide there is deep water off beach. At low tide the tidal currents may parallel the low tide shoreline and its a long distance from dry beach to the low tide level.

Typical beach + sand ridges beaches: Shelly Bay, Omana Beach, Long Bay, Oamaru, Tapu Bay

Reflective + sand ridges

Reflective + sand ridges beaches have a steep (3-10°), narrow high-tide beach composed of coarse sand, fronted by an abrupt break in slope and a wide (several hundred metres) low gradient, usually finer sand intertidal zone containing shore parallel, numerous low amplitude sand ridges and runnels. At high tide there are no waves unless strong onshore winds, and relatively deep water off high tide beach. At high tide there is deep water off the beach. At low tide tidal currents may parallel the low tide shoreline and its a long distance from dry beach to low tide level.

Typical beach + sand ridges beaches: Wenderholm (Centre), Onahau Road, Fenwick Road, Liger Bay, Takapou Beach (East).

Reflective + tidal sand flats

Reflective + tidal sand/mud flats

Reflective + tidal sand narrow reflective high-tide beach composed of coarse sediments, fronted by wide (hundreds of metres) low gradient (<1°) sand flats, that become muddy on lower intertidal with tidal draining channels. Mangroves or other vegetation may grow in the higher intertidal zone. Entire tidal flat is covered at spring high tide. Usually calm, only low wind chop during strong onshore winds. At low tide its a long distance to tide shoreline; also possible deeper tidal channels and currents.

Typical Reflective + tidal sand flats: Kelleys Bay, Koputauaki, Miranda, Motueka Spit.

Reflective + tidal mud flats

Tide-dominated system with narrow reflective high-tide beach composed of coarse sediments, fronted by wide (100’s to several 1000’s of metres), low gradient (<1°) mud flats with tidal draining channels. Mangroves or other vegetation may grow in the higher intertidal zone. Usually calm, only low wind chop during strong onshore winds. Occur where there is a source of mud nearby and where waves are insufficient to remove muds. At low tide its a long distance to tide shoreline; also possible deeper tidal channels and currents.

Typical beach + sand ridges beaches: Tatapouri, Kina Beach

Reflective + rock flats

Tide-dominated system with steep reflective high tide beach fronted by rock extending seaward as an intertidal rock platform and/or rock flat. Bedrock control in the form of reefs and headlands means the beaches are short and waves average only 0.5 m height. Hazardous beaches where swimmers and waders in moderate to high waves need to beware of submerged rocks in the sub- to intertidal zone.

Typical reflective + rock flats: None classified in New Zealand yet.

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