Dune Restoration vs Sand Stabilisation

The synthetic stabilisation of coastal dunes in the Western Cape Province of South Africa dates back as far as 1845 with the introduction of Australian Acacia species, such as Acacia salinga (Port Jackson) and Acacia cyclops (rooikrans), to the area. Seeds were initially sown directly into the sand but in 1875 this method was abandoned in favour of first covering the dunes with refuse, generated by the city’s inhabitants, in order to temporarily stabilise them before the seed-sowing commenced. After deeming this method uneconomical, the city introduced a French technique in 1896 whereby a foredune was formed at the source of the drifting sand through the construction of wooden barriers or propagation of marram grass (Ammophila arenaria). Invasive Acacia species were then introduced, either as seeds or as seed-bearing branches, to the area behind the constructed foredune. Even though it was realised in as early as the 1940s that invasive species out-compete their indigenous counterparts, extensively altering the natural ecosystem, it wasn’t until the mid-1970s that the use of these methods was eventually limited (Avis 1989). Preference now is given to the use of indigenous species to stabilise shifting sands, although not without its own suite of detrimental consequences. The use of invasive marram grass and Acacia species presented clear-cut effects on the dune ecosystem; producing dense monotypic stands that acted to crowd out the indigenous vegetation, altering nutrient cycling and the natural dynamics of the system and modifying fire regimes (increasing the frequency and intensity at which the fires burn). While the use of indigenous species may negate the aforementioned impacts, the synthetic stabilisation of large sand-drifts still results in not only the net loss of sand from beaches but localised changes, many as yet to be documented, in the geomorphological and ecological characteristics of such a sensitive and dynamic system.

Alexandria Dune Field - Maka (1)

Figure 1: Alexandria Dune Field (forming part of the Woody Cape Section of the Addo Elephant National Park) is a stunning example of a coastal dune field (Makabongwe Sigqala)

Alexandria Dune Field - Maka (6)

Figure 2: Vegetation found in the dune slacks of the Alexandria Dune Field (Makabongwe Sigqala)

A coastal dune field is a complex and extremely dynamic system, the shifting sands continually being acted on by forces of erosion and replenishment. Walking on the beach, the day-to-day changes in the shape and form of the dune backdrop are clearly noticeable and yet little acknowledgement seems to be afforded to their presence and these movements. I find this lack of interest alarming as these sandy hillocks also act as a natural buffer at the ocean/continental interface, one of increasing importance when confronted with climate change and the subsequent rising of sea-levels. Coastal dunes form as a result of an accumulation of sandy sediment, through aeolian (wind) transport, landward of a beach (Sloss et al. 2012a). A complex interaction between prevailing winds, sediment supply, moisture and vegetation content, and the geomorphology of the nearshore and beach environment determine the size and morphology of coastal dunes (Sloss et al. 2012b). This array of geomorphological features, environmental heterogeneity and species variability contribute to the high ecological diversity that characterises coastal dunes but in spite of their ecological significance, many of these systems have already been substantially impacted and severely degraded through human activities (Martínez & Psuty 2008).

Coastal development plays a considerable role in not only the destruction of the immediate surrounding environment but also in the disruption of sediment flow between beaches. The Hout Bay/Sandy Bay case study in Cape Town is a classic example of what not to do when developing and expanding the urban sprawl in a sensitive coastal environment. Aerial photographs from 1948 (Fig 3) show an unobstructed flow of sand between Hout Bay and Sandy Bay but by 1968 this sediment flow had been severely impeded by development and vegetative stabilisation and by 1989, the flow had been halted completely, the system ceasing to function (Low & van Eeden 2013). With unprecedented development occurring in the valley between 1989 and 2000, measures were put into place to prevent the accretion of sand on beachfront properties (Gosling 2013; Low & van Eeden 2013). These measures included the establishment of introduced vegetation, such as rooikrans and marram grass, and the erection of brushwood barriers on the mobile dunes with strategically-placed sand-trapping barriers near the river mouth (Gosling 2013; Low & van Eeden 2013).

Hout Bay Dune Field - Cropped

Figure 3: Aerial comparison of the Hout Bay/Sandy Bay Dune Corridor – 1948 on the left and 2011 on the right (Low & van Eeden 2013)

Historically, sediment would be driven north by the prevailing south-easterly winds during summer, replenishing Sandy Bay, the cessation of this sediment supply has subsequently resulted in the denuding (pun intended) of Sandy Bay and the engulfment of municipal infrastructures in Hout Bay (Fig 4). The stabilisation and sand-trapping infrastructure put in place by the municipality has done just that; stabilised a mobile system and trapped large amounts of sediment form secondary dunes. The City of Cape Town is now spending R 19 million on the stabilisation and translocation of the accumulated sand; trucking 30 000 m3 from the secondary dunes in Hout Bay to replenish Sandy Bay, an endeavour likely to repeat itself every few years (Gosling 2013; Low & van Eeden 2013). Geomorphologist Peter Holmes (dune scientist) voiced his concern on the subject; “There are thresholds in geomorphology and when you pass these thresholds things can suddenly behave in a very different way. We may have reached the stage that the dunes are so high that they begin altering the wind regime off the beach. The physics behind it is quite complex and we don’t yet know what is happening there. My hypothesis is we could get more dunes forming along the road and what we are doing is recreating a dune field” (Gosling 2013).

Hout Bay - Nick

Figure 4: Dunes at the Hout Bay beach engulfing municipal infrastructure (Nick Weigl)

Dune restoration, as the term suggests, is a reactive exercise because historically protection was not afforded to these environments and therefore did not form part of town planning practices. Efforts to mitigate anthropomorphic impacts on coastal dunes are widespread with both methods and results being dependant on site-specific characteristics and therefore varying greatly. Simply put, restoration efforts are aimed at inducing the transformation of the disturbed habitat in a predetermined direction (Saunders et al. 1993; van Aarde et al. 1996). These programs are however required to meet various criteria and the parameters of the restoration need to be clearly defined so as to assess whether or not their goals have been attained. Rehabilitation has been defined as a modulated change in an ecosystem after a discrete disturbance event, with the explicit aim of improving ecosystem structure and function. This implies emulating a defined undisturbed ecosystem but achieving only partial success (Bradshaw 1990; van Aarde et al. 1996). Especially true when knowledge of the area prior to the disturbance event is limited. In such cases; undisturbed areas that are either neighbouring or matching in structure, function and dynamics would then serve as references to which the variables of the disturbed system can be compared (van Aarde et al. 1996).

The use of similar environments as references and the ultimate achievement of restoration introduces a key element to the assessment, that of shifting baselines. Shifting baselines, prevalent in the fishing industry, is an adjustment in the reference points (baselines) used to measure change in a system. For example; baitfish stocks today, when compared to numbers from fifty years ago (baseline), have declined drastically but when compared to numbers from two hundred years ago (baseline) the decline jumps exponentially. Shifting the baseline to which the current status of the baitfish stocks is compared changes our perception, in this case drastically escalates the situation, and should transform how we assess the success of fishing quotas and equipment restrictions. Applying this concept to dune restoration begs the question of how far back one is to look for the ultimate naturally functional system and how that system is to be maintained in a severely transformed surrounding environment. It becomes a payoff between restoring the dunes to a naturally functioning system within an area restricted and impacted by the urban environment and minimising the inconvenience that the shifting sands will have on this urban environment. It becomes a case, not of dune restoration but rather one of sand stabilisation; the glaring difference being the priorities of the urban environment being placed ahead of the integrity of a functioning ecosystem. Why not call a spade a spade?

As mentioned, site-specific characteristics define the parameters of the rehabilitation project and determine the eventual outcome; therefore, while restoration to a ‘former glory’ would be an ultimate goal in most cases, some situations are deemed too degraded, their functionality too compromised, and as such are merely granted a management status. One such example would be Witsand Beach (Fig 5). Situated on the western shores of the Cape Peninsula, Witsands forms part of the Soetwater-Witsand Coastal Conservancy (2009) and is home to the African black oystercatcher (Haematopus moquini) and the Cape clawless otter (Aonyx capensis – Fig 6), both classed as Near Threatened on the IUCN Red List. This wide, crescent-shaped beach is wedged in the midst of mountain peaks and is backed by rolling dunes, fringed by thriving indigenous vegetation. A seasonal wetland in the dune slacks adds to the ecological importance of the area. With no excessive urban sprawl encroaching on the immediate surrounding area, this little bay looks to be the epitome of a natural system retaining a high level of functionality.

Witsands

Figure 5: Witsand Beach

Cape clawless otter

Figure 6: Cape clawless otter on Longbeach, Kommetjie

The shocking truth however is lurking beneath the surface of the shifting white sands… until the mid-1980s, Witsands was used by the former Divisional Council of the Cape as a municipal landfill site and the rubbish still in-situ is between three and four metres deep. During the heavy winter rains; the water from the wetland erodes the dunes, the river scouring out waste-filled channels and spewing the decades-old rubbish into the ocean. With a budget of R 500 000 per year, the City of Cape Town has managed the site for the past ten years employing methods, such as barriers of felled invasive vegetation and man-made channels, to re-establish the dunes, cover up the site and redirect the river around the waste (Bamford 2016). Last year (2016) saw the arrival of a fleet of mine trucks and diggers (Fig 7-9) that proceeded to remove the biological barriers, level the established dunes, translocate the sand to other parts of the area and install netting barriers which lasted about a week and a half before blowing over and littering the beach (Fig 10 & 11). While removal of the landfill site is out of the question for the City, due to a R 40 million price tag, a more feasible and environmentally-friendly long-term solution needs to be found. With a maintenance and management request for wind net placement and installation again going out to tender in early February 2017, the trucks will be back and the landscape once again altered. The mere presence of the trucks in such a sensitive environment calls into question the validity of the Conservancy and highlights the fact that covering up the landfill site takes precedence over ensuring the integrity of a naturally functioning system.

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Figure 7: Mine trucks and excavators landscaping Witsand Beach

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Figure 8: This process of excavation and relocation is to occur every year at Witsands

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Figure 9: Large amounts of sand were translocated across the beach

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Figure 10: Netting and posts at Witsand Beach, as well as exposed rubbish from the landfill site

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Figure 11: The infrastructure did not withstand the first north-westerly winds

Witsands Dune Collage

Figure 12: Timeline of the Witsands landscaping

By reviewing the circumstances and taking past transgressions into account, it is clear that both the Hout Bay and Witsand situations are inherited problems with the authorities attempting to find a way to best manage a severely degraded and defunct system but with the urban aspect of the system being a priority. The Klein Slangkop Private Estate (shown in part in Fig 13), situated on a headland protruding into the Atlantic Ocean south of Noordhoek Beach and backing on to land protected by Table Mountain National Parks (a subsidiary of SANParks), is the location of the third case study and one with two very clear distinctions. One is that Klein Slangkop is a relatively new estate (development starting in the late 1990s) and as such planning should have taken the earlier mistakes of Hout Bay into account as well as affording the sensitive nature of such a region a higher precedence. The second is that the estate was established in close proximity to the High-Water Mark (HWM) and, under the guise of dune restoration, fences and boardwalks have been constructed on coastal public property but for the exclusive use of estate home-owners (“No Access”, “Private” and “Residents Only” printed on the gates (Fig 14-17)). Both aspects of the second point contravene sections of the Integrated Coastal Management Act. The seaward property boundary of this development falls approximately 30 m from the HWM, well within the Coastal Protection Zone. According to the Act, the Coastal Protection Zone in regions zoned as urban includes “any land unit that is situated wholly or partially within 100 metres of the high-water mark” (Act No. 24 of 2008, Section 2 (16.1 (e))). This 100 m reserve does not however prohibit development entirely, it is merely a trigger for an Environmental Impact Assessment (EIA) (Ramsaru 2011). I did not manage to track down the EIA but find it interesting that, given the issues in Hout Bay, development is still able to occur on sand dunes. The Act also stipulates that; “No person may construct, maintain or extend any structure, or take other measures on coastal public property to prevent or promote erosion or accretion of the seashore except as provided for in this Act” (Act No. 24 of 2008, Section 1 (15.2)).

Klein Slangkop Boundaries - New Fenceline

Figure 13: Klein Slangkop Private Estate – Orange indicates property boundaries and black indicates the fence erected in 2015 (NGI)

Kommetjie - Megan (11)

Figure 14: Private access point on coastal public property

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Figure 15: Private boardwalks on coastal public property

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Figure 16: Only “Dune Restoration” signs as a deterrent

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Figure 17: Signs often just get washed into the ocean

In 2015, the fence (wire and posts with cement foundations that are already being undermined by wave action (Fig 18 & 19)) surrounding the estate was moved and the boardwalks extended further seaward so that it presently stands at approximately 6 m (at its closest point) from the HWM. Key to note is that the design does not correspond with the dune restoration measures used on the rest of the peninsula (and almost all dune restoration projects worldwide), including the measures recently introduced further down Longbeach. Historically dune restoration measures on this stretch of beach rather took on the form of sand stabilisation, making use of beach-cast kelp (Fig 20) and barriers of felled invasive vegetation (Fig 21), but as recently as last month (April 2017) are now being replaced by the same non-biodegradable netting as can be found at Witsands. Taken in the context of dune restoration, the sole purpose of the wire fence bordering the estate is to keep people off the dunes as opposed to re-establish the dunes, thus focussing on a single aspect of impact rather than taking a holistic view of the system. The newly extended fence and its overabundance of established estate access points now includes a more significant portion of coastal public property and it appears to allow estate home-owners exclusive access to the dunes; their children and dogs often seen playing in them (Fig 22 & 23). So why is the fence actually there? Yes, it has “Dune Restoration” signs every few hundred metres but it has already been established that this fence design cannot restore a dune system, especially when, after a few good winter storms the sea washes the infrastructure away.

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Figure 18: Fence erected in 2015 (foreground) and original fence (background)

Kommetjie - Megan (8)

Figure 19: Infrastructure at Klein Slangkop being undermined by wave action (Megan Sivewright)

Beach-cast kelp

Figure 20: Beach-cast kelp used to stabilise the dunes and prevent sand blowing into beach-front properties

Invasive vegetation barriers

Figure 21: Barriers of felled invasive vegetation

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Figure 22: Children and dogs from the estate are often seen playing in the dunes

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Figure 23: Estate home-owners enjoy exclusive access to the dunes

The fundamental question to ask is; to what structure is this dune system expected to be restored? In other words, what are the goals for this restoration project? Analysing aerial photographs of the Fish Hoek Valley Dune Corridor dating back to 1945, it becomes clear that this valley has undergone extensive development over the past seven decades. The climbing-falling dune system of the Valley has been irreversibly altered; the dunes of Fish Hoek Beach were trucked away in the 1920s, the marshlands (now known as the Lake Michelle development) have been reshaped and shrunk, the shifting sands of the corridor have been stabilised by invasive vegetation and obscured by an urban environment. The functioning of this system mirrored that of the Hout Bay/Sandy Bay system in that the prevailing south-easterly winds transported sand from one end of the corridor, replenishing the beach upwind. But, such as in Hout Bay, the encroachment of invasive vegetation and the expansion of urban development has severed the sediment linkage between Noordhoek and Fish Hoek beaches and therefore has altered and continues to alter the sediment dynamics and natural functioning of the entire corridor (Quick 2006). So why, if the system is no longer functional, is it imperative to “restore” a narrow fringe of dunes on a small headland, especially since they appear to have remained in the same state since the inception of the development of the valley? While it is important to protect the remaining few isolated pockets of dune ecosystem in this valley, in no way can this dune system be restored to a naturally functioning system without removing the urban development, which would include the Klein Slangkop Private Estate.

A “myriad of contradictions” is the best way to describe the Klein Slangkop, and in part the Longbeach, situation. Described as an “Eco Estate” and boasting the presence of a number of elusive creatures, Cape clawless otter and Cape porcupine (Hystrix africaeaustralis), it would stand to reason that the state of the natural environment in which they have developed would be of a high priority. Why then are dogs allowed by their owners to roam unsupervised (Longbeach is an off-lead beach but responsibility for one’s pets is of utmost importance if the off-lead status is to continue to be enjoyed) from beach-front properties, often chasing and attacking wildlife? Why are non-biodegradable materials (Fig 24) being used in such a sensitive and exposed environment, especially when winter storms wash the infrastructure into the ocean contributing to marine debris (Fig 25-27)? Why is irrigation being used to water plants adept at surviving in a harsh, water-scarce environment (Fig 28)? Freshwater, especially in a semi-arid country, is a limited resource; a fact all the more important in the current drought situation. To see the sprinklers running in a howling south-easter defies logic! Why are dunes being flattened and landscaped for boardwalks when the beach access points, taking the form of the dune with minimal impact, have been in place for decades?

Kommetjie - Megan (2)

Figure 24: Non-biodegradable netting (Megan Sivewright)

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Figure 25: Fence posts washed out of the structure

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Figure 26: More debris being added to the coastal environment

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Figure 27: Cape of Storms

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Figure 28: Irrigation of the dunes defies logic

The problem is urban development in a coastal dune ecosystem; a situation that cannot be solved by the mere erection of an inadequate fence that’s only accomplishment is that of injuring animals (the wire used is thin and not at all conducive to an environment that facilitates frequent movement of animals between the ocean, the dunes and the pockets of coastal vegetation) and incapable of restoring any form of sand dune. There needs to be a clear distinction between the terms “dune restoration” and “sand stabilisation” because it has become apparent that in the case of the coastal dune ecosystems of the Cape Peninsula, “dune restoration” is a misnomer. Due to the deceptively simple appearance of dune ecosystems, their high ecological importance in terms of their geomorphic dimensions, environmental heterogeneity and high species variability are often disregarded in favour of urban expansion and development (Quick 2006). As the Hout Bay/Sandy Bay and Witsands cases show, we are sometimes stuck with managing unwanted situations; the harsh reality being that actions from the past often have irreversible consequences that are still evident, more often than not magnified, in today’s setting. No event occurs in isolation, our actions have repercussions that transcend space and time and as such should form an integral part of the decision-making process in current situations because the outcomes of these form the foundations of future scenarios.

Explore. Dream. Discover.

In wake of the recent storms lashing the Cape recently (7 & 8 June 2017), I thought it pertinent to add an addendum to this article in order to highlight the impact that such weather could have on the inadequate dune restoration efforts and their subsequent contribution to the issue of marine debris (as mentioned in the article). Water tends to follow the path of least resistance; add to this 12-15 m swells, a close-to-spring high tide, 50+ knot winds and the landscaped dune paths are transformed into a canal, channelling the water into the very areas that intact dunes would do a better job of protecting. The photos below were supplied by Janet Sivewright, unless otherwise stated.

Cape Storm 2017 (3)

The remnants of the Klein Slangkop dune restoration efforts

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The LongBeach netting did not withstand the storm and now adds to marine debris

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Infrastructure at Klein Slangkop now litters the beach

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Remnants of the Klein Slangkop Dune Restoration Fence

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Remnants of the Klein Slangkop Dune Restoration Fence

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Water is channelled through the landscaped pathway and into the car-park behind the dunes

Cape Storm 2017 - Julie Phillips

Water channelled along to boardwalks at Klein Slangkop (Julie Phillips 2017)

ACKNOWLEDGEMENTS

I would like to thank the awesome people who contributed photographs to this article; Makabongwe Sigqala (Alexandria Dune Field), Anthony Sivewright (Kommetjie), Janet Sivewright (Kommetjie), Megan Sivewright (Kommetjie) and Nick Weigl (Hout Bay).

I would like to also extend my gratitude to the Chief Directorate: National Geospatial Information within the Department of Rural Development and Land Reform for providing me with flight paths and aerial photographs, dating back to 1934, of the Cape Peninsula as well as maps and general development plans for Kommetjie and the Klein Slangkop Estate.

REFERENCES

AVIS AM. 1989. A Review of Coastal Dune Stabilisation in the Cape Province of South Africa. Landscape and Urban Planning 18 (1): 55-68.

BAMFORD H. 2016. R500K a Year Spent on Dump Site. [ONLINE] Available at: http://www.iol.co.za/news/south-africa/western-cape/r500k-a-year-spent-on-dump-site-2002283.

BRADSHAW AD. 1990. The Reclamation of Derelict Land and the Ecology of Ecosystems (53-74) in Jordan WR, Gilpin ME & Aber JD (eds); Restoration Ecology: A Synthetic Approach to Ecological Research. Cambridge University Press: Cambridge.

GOSLING M. 2013. Grassing of Hout Bay Denuded Sandy Bay. [ONLINE] Available at: http://www.iol.co.za/capetimes/grassing-of-hout-bay-denuded-sandy-bay-1548015.

LOW AB & VAN EEDEN JD. 2013. Management and Rehabilitation Plan for the Hout Bay Dunes. Report PO 4501955067. [ONLINE] Available at: http://www.houtbayheritage.org.za/Hout-Bay-dune-management-report-Vol-2-final.pdf.

MARTÍNEZ ML & PSUTY NP. 2008. Coastal Dunes: Ecology and Conservation. Springer-Verlag: New York.

NATIONAL ENVIRONMENTAL MANAGEMENT: INTEGRATED COASTAL MANAGEMENT ACT. 2008. Act No. 24 of 2008: Section 1, Sub-Section 15.2 and Section 2, Sub-Section 16-17.

QUICK L. 2006. The Geomorphic Changes to a Dune System in the Cape Peninsula: Fish Hoek – Noordhoek Dune Corridor. BSc (Hons), University of Cape Town, Cape Town, South Africa.

RAMSARU R. 2011. Managing Coastal Development in Rapidly Developing Areas: The Case of Umhlanga Rocks. MSc Thesis, University of KwaZulu-Natal, Durban, South Africa.

SAUNDERS DA, HOBBS RJ & EHRLICH PR. 1993. Nature Conservation 3: The Reconstruction of Fragmented Ecosystems. Surrey Beatty & Sons: Chipping North.

SLOSS CR, HESP P & SHEPARD M. 2012a. Coastal Dunes: Aeolian Transport. Nature Education Knowledge 3 (10): 21.

SLOSS CR, SHEPHERD M & HESP P. 2012b. Coastal Dunes: Geomorphology. Nature Education Knowledge 3(10): 2.

VAN AARDE RJ, FERREIRA SM, KRITZINGER JJ, VAN DYK PJ, VOGT M & WASSENAAR TD. 1996. An Evaluation of Habitat Rehabilitation on Coastal Dune Forests in Northern KwaZulu-Natal, South Africa. Restoration Ecology 4 (4): 334-345.

4 thoughts on “Dune Restoration vs Sand Stabilisation

  1. Really interesting, Sally – and I’ll bet most property owners in those sensitive areas aren’t aware of the distinction between restoration and stabilisation! Makes me think of the road, and a house or two, in Betty’s Bay below Sandy Mountain (as we called it), that were constantly converted into sand dunes. Much smaller scale, of course, but now it’s obvious – the road and houses were built within the sand dune belt! I think my Dad will find this a fascinating read – I’ll take him a copy next time I’m there!

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