As a physical testing laboratory and agronomic consulting company, we spend a lot of our time helping people to build USGA golf greens, sports fields, and landscapes based upon the USGA concept. The USGA system (see picture), which was first released in the 1960s, utilizes a sand based rootzone layer placed over a gravel layer. The gravel layer is on top of a drainage system that is placed in the subgrade. These sand based turf systems are utilized because they provide an excellent medium for sports turf growth, superior water management capabilities, and can withstand high usage.
Perched Water Table
The USGA system provides maximum removal of water during heavy precipitation events, and it stores water above the gravel during periods when the ground is not saturated. How does it achieve this effect? Because the USGA system is based upon a concept known as the perched water table, which is also known as an inverted filter design. It is called an inverted filter because of the presence of the fine sand particles over the more coarse gravel. This design allows water to be held (or perched) in the rootzone layer. This perched effect occurs because the primary driving force for water movement during periods of unsaturation is the capillary effect of the particle voids.
The large voids of the gravel result in a reduction in the capillary effect. At the rootzone/gravel interface, these larger voids effectively create a barrier to further downward water movement during unsaturated times. As saturation is approached, additional pressure is applied allowing water to move into the larger voids of the gravel layer, and further down through the sub-surface drainage system.
The above summary only scratches the surface of the physics, construction and performance of a perched water table or inverted filter type system. The March/April 1993 USGA Green Section Record contains detailed information on this concept.
There are many other systems that can be utilized for the construction of high performance rootzones. Among these are sand caps, California greens, and native materials. Each of these will have advantages and disadvantages based upon site-specific conditions.
For more information on rootzone designs and evaluation please contact us by phone or e-mail.
Turf Diagnostics and Design is pleased to announce that Sam Ferro has been promoted to the position of President. Sam, who was previously the corporation's Vice President, will be responsible for the overall direction and operation of the company
Duane Otto has been promoted to the position of Vice President. Duane, who has been a consultant for the company since 1996, will be in charge of the company's technical efforts.
Turf Diagnostics and Design is an independent landscape, soil, and materials testing laboratory and agronomic consulting company. We feel that we offer service and quality that is unsurpassed in the testing industry, and we are very proud of the work we do. Among our customers are the finest builders, suppliers, owners, architects, designers, groundskeepers, and superintendents working in the landscape, golf course and sports field industries.
If you are one of our current customers, we would like to thank you for your business. We hope that we can continue to provide you with prompt service, high-quality lab data, and effective consulting recommendations. For those of you who haven't tried our services, we hope that you will give us the opportunity to provide support to your firm.
We want to be your testing laboratory. If there is anything we can do for you, please contact Duane or me. We will do our best to make you happy that you are using Turf Diagnostics and Design.
Turf Diagnostics & Design
Helping You Have Healthy Turf
Issue 2 2000
The Perched Water Table
While you can always contact us at Turf Diagnostics and Design to discuss the hows and whys of various rootzone systems, we feel that a review of the physics behind the USGA system will be helpful to many of our clients. Thus, presented below is a very brief summary of the science involved with the "perched water table" (also known as an "inverted filter").