Selecting a bunker sand that is best suited for the site-specific conditions on golf courses is critical to producing and maintaining quality playing conditions and maximizing bunker longevity. The two properties of bunker sand that will most influence performance are particle size distribution and sand shape. These characteristics can be accurately defined in the laboratory. Additionally, there are many other factors to consider such as drainage, cost, vulnerability to wind and water erosion, crusting potential, chemical stability and color. All these characteristics will influence the quality of the golf experience and are key considerations in selecting sand for your golf course bunkers.
The intent of this article is to 1) summarize nine key bunker sand characteristics, 2) provide practical sand selection guidelines for bunkers given a range of architectural styles, climatic conditions, lining materials and golfer expectations, and 3) answer a few frequently asked questions regarding bunker sand.
Key Bunker Sand Characteristics
There are nine key bunker sand characteristics that can be tested in a laboratory: particle size distribution, particle shape, coefficient of uniformity, angle of repose, penetrometer reading, infiltration rate, crusting potential, chemical reaction and color. The soil moisture release curve (SMRC) and moisture column tests will also be discussed. The following text will summarize these characteristics and how they are tested, and offer new perspectives based on current challenges observed in the field.
1. Particle size
In 1985 and 1986, USGA agronomists cooperated with golf courses across the United States to assess bunker sand quality and collected a total of 42 bunker sands for laboratory testing. To this day, the results from this study by K.W. Brown and J.C. Thomas are regarded as the industry standard for bunker sand selection.
Brown and Thomas suggested that 78% of the particles in bunker sands should be between 0.1 and 1.0 mm in diameter. This range is broader than what is recommended for rootzone mixtures in the USGA Recommendations for a Method of Putting Green Construction, and for good reason. A narrower range may omit acceptable bunker sands and may result in a bunker sand with too many particles within only one or two size classes, which can lead to soft conditions. Less than 15% of the bunker sand particles should be in the very coarse fraction, between 1 and 2 mm. This is more than twice the percentage allowed in the putting green recommendations because drainage, not moisture retention, is paramount in bunkers and coarse particles tend to promote better drainage and are less prone to erosion. The Brown and Thomas guidelines limit material larger than sand – i.e., gravel-sized particles greater than 2 mm in diameter – to less than 2%. No golfer wants to ruin their new sand wedge hitting from gravel-filled bunkers. Given the importance of drainage, fine particles must be minimized. The combined silt and clay fractions must not exceed 3%. Excess silt and clay will cause crusting when dry, increase moisture retention and reduce drainage capabilities. Additionally, the very fine sand content – between 0.05 and 0.1 mm – should be less than 5%. The guidelines for fine material are more stringent than for putting green rootzones because of the importance of drainage and minimal moisture retention for bunker playability. Refer to Table 1 for the particle size distribution guidelines.