The first mention of a bunker was thought to be in 1636 in the context of a “bunkard club” – bunkard being the Scots word meaning a seat or bench “also serving for a chest”. I believe that many golfers are still of the opinion that bunkers should be places of repose where a consistently comforting lie can be found. These days, increasing demands for uniformity and consistency of quality are perhaps nowhere better expressed than in the standards expected of the modern bunker. Golf greens may be the primary focus of attention, but bunkers often receive criticism regardless of the ability or error of the golfers’ ways.
It is worthwhile remembering the origins of the bunker on our links courses where “nature was the contractor” and bunkers were formed due to a combination of the attritional effects of animals sheltering and grazing within hollows, exposing the sand beneath the closely cropped and weakened turf. These areas were subsequently expanded by the scouring effect of the winds. There was no design to this process, or formula for the placement of bunkers, they simply evolved. The modern bunker is a stylised version of these early sandy hollows, but it is important to remember that the bunker is still a hazard in accordance with the rules of golf and the golfer has to accept a degree of variability between bunkers.
Bunkers may only cover 1% to 2% of the total area of the golf course but can require 20% to 25% of the available resources to maintain. Therefore it makes sense to take a long, hard look at the contribution of the bunkers before ploughing investment into renovating obsolete bunkers. As with many aspects of golf course architecture, it is an art not a science. Rational argument is required in order to determine which bunkers are valid and which require removal. Engaging a professional golf course architect to arbitrate makes sense as a holistic approach is adopted, avoiding the trap of decisions being made on the basis of one particular category of golfer.
Bunkers that only serve to punish the weakest should be removed. The significant advances in golf equipment have had a profound effect on the majority of our golf courses and bunkers, which previously influenced the low handicap golfer, thereby serving to ensnare the less able player who perhaps has the armoury to reach the hazard, but not sufficient skill to avoid it! This is contrary to the principal aim of the bunker to positively influence play and not to punish the weakest. Different golfers will have a range of views as to what constitutes a valid bunker; therefore an independent assessment by a qualified golf architect is the sensible way forward.
Bunker showing ravages of wear and tear
It is difficult to be too prescriptive as the location and popularity of the bunker has a major influence on its life cycle. Cleaning out contaminated sand and replacing with new may be required every five to seven years. At the same time, bunker drainage should be reviewed to determine if there has been any silting up of drainage lines or major contamination of stone backfilling.
The ravages of time are also seen in the condition of bunker faces that may have been repeatedly cut back to a sharp precipice (and occasionally may be convex rather than the conventional concave shape). As a consequence, bunkers tend to expand over time and bunker faces, which may
Links bunker face restoration
have been set back comfortably from the edge of greens, encroach excessively near. Sand build up beneath adjoining surrounds not only alters the profile over time – creating ridges on leading edges and accentuating mound heights – but also produces drought-prone areas of turf.
Bunkers which are subject to intensive wear and tear may require a face-lift every three to four years.
There is not a “one size fits all” solution for bunkers as site conditions, type of course and resources all have a profound effect on the most appropriate type of bunker. For example, large, shallow bunkers would be rapidly depleted of sand on windswept sites. Equally, small, deep pot type bunkers on clay-based courses are likely to resemble small ponds due to restrictions on drainage.
Figure 2 provides an indication of the best fir for specific circumstances although by necessity it is a simple table as no two golf courses are alike.
Example of deep inland bunker
Bunker face grassed down
There are different schools of thought regarding the use of a turf or sand face. Turf faces have the advantage of mitigating most of the effects of sand washout down slopes (which often brings with it finer soils which can clog sands and underlying drains) and reducing the commitment to raking. On the negative side, they can lack the visual (and psychological) impact of sand faces and the maintenance of the steeper turf slopes can be equally demanding of labour. There is always the hybrid option of rolling turf partially down the face, the extent of which is determined by the height and severity of slope. On wider, shallower bays, the sand can be swept up higher compared with the steeper “noses” where the turf can be brought down further. This provides a pleasing, undulating outline to the bunker providing both a manageable solution and one that works aesthetically.
Of course, for links and possibly heathland courses a revetted face is the first choice in most circumstances. This requires a ready supply of fibrous turf with good mechanical strength. Clay-based, thin turf will simply deteriorate too rapidly. Revetting is a laborious process but the end product provides a durable, attractive finish. There are a few commercial suppliers of bespoke revetting turf, but the majority is cut too thin for the obvious reason of conserving soil resources. Occasionally sea-washed turf is specifically imported for revetting purposes, cut to the requisite depth, i.e. around 37-50 mm.
Shallow revetted lip
A shallow wall of stacked turf also provides an effective means of creating a distinct bunker edge. This needs to be established prior to turfing of the surrounds. Another advantage is that soil contamination is minimised at the interface of the sand and turf edge. Usually only five or six courses of turf are required to provide a stable lip around the edge of the bunker of approximately 150 mm depth in total. Turf from the surrounds can often be salvaged for the purpose.
If bunkers are to perform with any degree of consistency, good drainage is essential. Bunker sands which are slow to dry out resemble a porridge and are difficult to recover from, regardless of ability. For most inland sites, internal bunker drainage is essential. Bunkers are formed with gently convex bases, therefore the main drain must be installed through the lowest point of the bunker. Additional drainage spurs may be needed on each side of the main drain depending on the design of the bunker and soil characteristics. A “blinding” material such as “Aquadyne” can be used over the drainage aggregate to minimise contamination of the drain and pin down the drainage stone, or it can be used to form a “box drain”, eliminating the need for stone. Alternatively, a conventional sand blinding layer is cheaper – possibly increasing the depth of bunker sand over the drain, provided that the sand is compatible with the drainage aggregate and does not migrate down into the stone.
Drainage in bunkers must be connected to a positive outfall where practical. External soakaways should be considered a last resort, as their effectiveness is limited in heavy soils. Indeed, even where a more permeable material is encountered, soakaways can be difficult to maintain due to silting up over time.
Flow of external water into bunkers can also be problematic. Diverting flow away from bunkers is the priority and this can be achieved by shaping surrounds using a combination of mounds, shallow ridges and swales, which need not be too intrusive. If this is not feasible, a perimeter “smile” drain around the top edge of the bunker base can intercept water before it builds up momentum and takes sand with it.
There is a huge range of liners both natural and man-made on the market, but no one perfect solution. Linings are used mainly to pin down stone within the underlying soils that can gradually break through into the bunker sand. They can also reduce contamination of the sand with finer soil particles. Conventional two dimensional geotextile membranes tend to form a “slippery” surface on which it is difficult to retain sand to a consistent depth, even on relatively gentle slopes. Therefore these materials are often exposed, with snagging of clubs and bunker rakes commonplace.
For steeper faces there are alternative products now available, e.g. “Sand Trapper” or “Bunker Mat” which are three dimensional, fibrous materials that hold sand in their matrix of fibres. They are expensive and require careful installation (notably thorough pinning down) to achieve success.
Engineered base layers utilising a specified aggregate bound together with a resin coat (e.g. Sportscrete) are also available, although they require installation by experienced personnel under the correct conditions to maximise their potential.
Bunker lined with turf being sanded
Upturned turf provides a lower cost and a more natural solution to bunker lining but eventually a turf layer will break down. On steeper faces there can also be problems with anchorage, even if the turf is laid the right way up and the grass killed off with a total weedkiller.
Lining the bunker with a deeper layer (around 150 mm) of a finer sandy, stone-free subsoil and compacting this to form a firm, clean base is more laborious but it does provide an effective barrier. With all these methods, effective drainage is still essential.
As part of the process of re-contouring bunker surrounds and stripping out significant quantities of sand accumulation, it is essential to provide a good foundation for the new turf. A minimum depth of 150 mm of topsoil should be the aim but if there is a deficit, additional soil may need to be imported to compensate.
Finally we come to the controversial subject of bunker sand selection, which is worthy of an article in its own right. There are several criteria for selection, the most important of which are the physical properties of the sand and related drainage performance (which influence playability), chemical reaction (pH) and the aesthetic appeal of the sand. The abundant fine sands found on links courses are ideally suited to pot bunkers where usually there are no issues of maintaining a good depth of sand or limitations on drainage. However, using fine sands on inland courses based on much heaver soils invariably results in failure due to rapid clogging of the fine sand particles with silt/clay particles, leading to poor performance and substandard playing conditions. Therefore, a “heavier” sand with a larger particle size is preferred which will perform better when wet as well as staying in place for longer. A medium to coarse grade sand with the majority of particles in the range 0.25-1.0 mm provides the initial selection criteria, usually with the majority of particles centred on the 0.25-0.5 mm range (medium grade), although too narrow a distribution can compromise the stability of the sand. Selection needs to be refined still further as rounded sand particles will act like marbles with limited opportunity for achieving firmness (with the liability for increased “poached egg” lies), whereas angular to sub-angular particles will lock together more effectively and create a firmer surface. Invariably there will be the usual cries of a bunker being too soft after re-sanding or perceived excessive amounts of sand. In reality, this is often due to the sand being new and not having sufficient time to weather and firm up. Compacting the sand when wet will reduce the tendency to plug, but occasionally the golfer has to “play the ball as it lies” and accept the challenges of golf, regardless of what is deemed to be fair.
Recommended sand depth is approximately 100 mm with approximately 50 mm on faces.
Bunker under renovation
There is much to be said for greenstaff carrying out their own bunker renovation programme as work can be dovetailed to appropriate conditions as well as there being ownership of the end product. With the tight financial restraints imposed on many golf courses, the economic advantage of constructing in-house also comes into the equation. Design guidance may be needed before embarking on a more extensive overhaul of bunkers. Engaging a man plus machine for the critical aspects of bunker shaping and drainage, with the greenstaff responsible for preliminaries and finishing works, can be a successful approach, dependent on the skill of the contractor to realise the design requirements of the club. The final option is to devolve all works and responsibility to a golf course contractor. This tends to be most relevant when timescales are limited and bunker renovation programmes more ambitious.
The following provides a brief resume of the main considerations:
This article originally appeared in STRI's Bulletin for Sports Surface Management, January 2011.