ALLIED ASSOCIATIONS
From the Ground Up: The Drainage System and Gravel Layer in a USGA Green Successful moisture management is essential for providing high-quality putting surfaces. In a USGA green, the drainage system and gravel layer help ensure that turf has enough water to be healthy while allowing excess water to drain quickly from the root zone profile. A subsurface drainage system is required in all USGA greens. Drainage lines should be laid out according to the unique contours of each green. Main drainage lines should be placed along the line of maximum fall. Depending on the contours of a green, it may be necessary to have more than one main drainage line. A perimeter drain – sometimes called a “smile drain” – should be installed wherever main drainage lines exit a green. It is essential that perimeter drains be installed against the cavity wall; if the pipe is even a short distance away from the edge of the green it may not provide adequate drainage and could cause serious turf issues in the future. The gravel layer in a USGA green helps the root zone mix retain sufficient moisture
Lateral drainage lines should be placed across the for healthy turf while allowing rapid drainage of excess water. slope of the subgrade and spaced no more than 15 feet apart. All lateral lines must extend to the edge of the green cavity to capture any water that may gather near the cavity wall. Lateral lines should always be laid out in a way that best captures water, which means that the pattern of lateral lines will vary from green to green. A “herringbone” design is not appropriate for all greens.
Drainage trenches should be at least 6 inches wide, 8 inches deep and must maintain a minimum slope of 0.5 percent to the outlet point. Each drainage trench should be filled with at least 1 inch of gravel before installing drainage pipes. After the pipes are installed and completely embedded in gravel, grade stakes should be placed at frequent intervals throughout the subgrade and marked with the height of the gravel layer and root zone mix. The gravel layer must be installed to a minimum depth of 4 inches. Greater depths can also be used without adversely affecting performance. Using some extra gravel to finalize putting green contours can be easier than performing this detail work in the subgrade. Keep in mind, however, that the final surface of the gravel layer should exactly mirror the proposed contours of the putting surface. The gravel layer serves several important functions in a USGA green. It creates a perched water table that helps the root zone mix retain sufficient moisture for healthy turf. It also allows for rapid drainage of excess water from the root zone profile and helps protect drainage pipes from being clogged by small particles. The USGA is currently updating its Recommendations for a Method of Putting Green Construction and the associated “Tips for Success” document. The revised Recommendations will account for current scientific research, modern construction techniques and technology, and current material testing methods. The revised USGA Recommendations will be released in early 2018.
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