by James C. Thomas C.P.Ag
Selection of the proper bunker sand for your golf course is no small task. Potential bunker sands should be carefully evaluated for particle size distribution, particle shape, performance in the fried egg lie test, color, crusting, set-up, carbonates, and saturated hydraulic conductivity. Doing your homework in testing and evaluating potential bunker sands prior to purchasing one will assure you and your club of getting the best product for your money and will provide a pleasurable playing experience for golfers.
An ideal bunker sand is a very clean washed sand containing 3% or less total silt plus clay. Greater amounts of silt and clay in bunker sands make them susceptible to crusting and set-up which increases the amount of maintenance required to keep the bunkers in playable condition. In addition, high amounts of silt and clay tend to make the sand slow to drain and may lead to ponding of water in the bunkers.
Since bunker sand is frequently blasted from greenside bunkers onto putting greens, an ideal bunker sand should contain less than 3% gravel and 7% very coarse sand particles. Bunker sands with higher amounts of gravel and very coarse particles may damage expensive greens mowers, reduce putting quality, and slow play on the golf course. In addition, an ideal bunker sand should contain 65% or more particles in the medium and coarse ranges (0.25-1.0 mm) and 25% or less in the total of the medium-fine, fine, and very fine fractions (0.05-0.25 mm).
The optimal particle shape for a bunker sand is very angular with a low degree of sphericity. The sharp angles and corners of an angular sand help the particles to interlock and increase the sands resistance to displacement by golf balls which land in the bunkers. Elongated and flatter shaped particles with low sphericity also increase the resistance to displacement by golf balls. Thus, angular sands with low sphericity have fewer buried balls making it easier for golfers to play out of the bunkers.
Generally, light colored sands are preferred for bunker use. The most commonly encountered bunker sand colors are white, light brown, yellowish brown, and light gray. Pure white sands are sometimes used for achieving a dramatic or contrasting effect, particularly at courses located near the ocean or other large bodies of water. Sands having a tan or light brown color are better suited to inland courses and tend to be more natural in appearance, are less trouble to maintain and are easier to play from due to the reduced amount of glare.
Sands high in carbonates and sands high in silt and clay tend to exhibit severe amounts of crusting and set-up. Crusting is the formation of a thin hard shell on the sand surface, while set-up is the formation of a thick crust which extends as deep as the water penetrates. Severe amounts of crusting and set-up require more frequent raking to keep the sand in playable condition. Probably the criteria most often used to select bunker sands is the “fried egg lie test”. This is a laboratory test designed to evaluate the potential for golf balls to partially bury in the bunker sand. The test involves placing a standard quantity of air dry bunker sand in a test vessel and stirring it to simulate raking. A golf ball is placed on the surface of the sand and a pocket penetrometer is used to press the ball half-way into the sand. The force required to press a golf ball half-way into the sand is measured and compared to a table of data allowing the sand to be rated as having a very low, slight, medium or high potential for burying golf balls. For the average golf club, a fried egg lie test score of 2.4 or greater will suffice, however, for championship play courses, a score of 2.6 or greater will provide ideal playing conditions.
The saturated hydraulic conductivity (also referred to as the infiltration rate) is a measure of the rate water will move through the sand. Since a major cause for bunker renovation is a lack of adequate drainage, it stands to reason that sands with high saturated hydraulic conductivity values are preferred. In addition, bunker sand from green side bunkers are often blasted onto putting greens surfaces. Unfortunately, there are no published standards for the conductivity of a bunker sand. Since the accelerated range for saturated hydraulic conductivity of a putting green root zone mixture is 12-24 inches per hour, we recommend a minimum conductivity of 20 inches per hour for a good bunker sand. Using a bunker sand with an initial conductivity of 20 inches per hour or greater will assure you that the sand will drain well provided that the bunkers are equipped with functioning under drainage systems. In addition, the high initial conductivity will minimize the effects of contamination by soil, dust and organic debris washed or blown into the bunkers.
Once you have done your homework and selected a sand for use, you may want to use this sand to renovate one or two of the most frequently played bunkers and then get player’s feedback on how well they like it. Once you are sure that the players will accept it and you have good test results on the sand, it is time to order the sand and renovate the bunkers. To be sure that you are receiving the same quality of sand as tested and ordered, a sub sample of the delivered sand should be collected and tested. As a general guideline, we suggest sampling after the delivery of each 20% increment of the total order.
Samples should be collected carefully by probing the stockpile at numerous locations with a length of PVC pipe or other suitable device. The samples should be combined in a bucket and mixed thoroughly. A one gallon size sample should be withdrawn from the bucket, packed in a zip-lock bag or other suitable container and shipped to the lab for evaluation. A complete bunker sand evaluation typically costs on the order of $250 which is a fairly small expense considering the investment in time and materials being made during bunker renovation.