Case Study: Drainage Problems on the Greens |
Locating drainage, irrigation and utility lines without as-built drawings can be a time consuming and expensive task. Several man-hours of labor can be spent probing and digging trenches to try to locate just one line. Then, of course, some more time and money is needed to restore the site to its original condition. This is especially difficult when existing conditions limit access to a particular site. Sites that typically places limits on unnecessary excavation are the greens on a golf course. Simply put, a golf green is a “layer cake” of sand, gravel, drainage pipes, soil and turf. The integrity and thickness of these layers is crucial to the health and well being of the turf on the green.   Comparing a photograph of the site, (below), with the point cloud model (above), demonstrates how the laser scanner captures everything within its line of site and converts it into a dimensionally and spatially accurate model. If one layer is too thick or thin, the turf on the green can become unhealthy. Inequalities in these layers will cause water to percolate through the green at an uneven rate, resulting in areas that are either too wet or too dry. Obviously, these types of conditions can cause maintenance problems for the superintendent and other turf professionals. Understanding the conditions underlying a green could help make the golf superintendent’s life easier, as they are constantly working to maintain the proper balance of water and fertilization. Drainage pipes below the green can fail, which would lead to obvious problems for the health of the turf. Unfortunately, like most construction projects, the as-built drawings for the under green drainage system may or may not be an accurate representation of site conditions. Disturbing these layers with unnecessary excavation can cause all sorts of problems, creating imbalances in the layers and their percolating abilities. The Atlanta Athletic Club was experiencing such a problem on two of its greens. Two small sinkholes had formed, leading to the conclusion there was a drainage problem the maintenance staff had to locate and repair. The repair was especially critical as the course was preparing to replant the grass on all its greens in preparation for hosting the PGA Championship.  The model was then exported into AutoCAD to create a traditional two-dimensional survey of the site that the superintendent and maintenance staff could use to locate and repair the drainage problem in the field. TC and its partners, LandAir Surveying of Georgia and Wolverton Engineering, were called in to employ their expertise in laser scanning and ground penetrating radar to help the club zero in on the sinkhole problem and resolve the problem. As mentioned in the Aug. LASN Technology column, “An Introduction to High Density Laser Scanning” www.landscapeonline.com/research/article/12295, laser scanning is a method of obtaining an incredibly accurate survey of a site’s existing conditions. Laser scanning collects millions of points, known as a point cloud, which is then assembled to create a digital model of a site. The data points are accurate to a quarter of an inch over 300 yards. Comparing a photograph of the site with the point cloud model demonstrates how the laser scanner captures everything within its line of site and converts it into a dimensionally and spatially accurate model. Ground penetrating radar (GPR) is a method for collecting information about objects below the surface of the ground. A GPR unit is walked or driven over the surface of the ground, and a technician uses the signals from the GPR to determine the location and depth of objects underneath. The GPR unit consists of a sending antenna that broadcasts radio waves into the ground, and a receiving antenna that reads the reflected signals. These signals are then displayed on an LCD screen, which tells a GPR operator where the objects are located. More sophisticated GPR systems exist that produce a three dimensional image of underground objects, much in the way that an MRI is used to look into human bodies.  This photo shows the GPR in action along with the laser scanner set up At Atlanta Athletic Club, our mission was to try to create an as built drawing of the existing drainage and irrigation lines adjacent to and underneath the greens in question. The superintendent and maintenance staff could then use these drawings to pinpoint and correct the causes of the sinkholes. First, a GPR technician pushed the GPR unit across and around the green, marking the location of the lines with orange pin flags. He continued to walk the unit across the green surface and surrounding areas, adjusting the location of the pin flags each time. Eventually, the pin flags were lined up in a fashion that resembled the alignment of the irrigation and drainage lines under the green. We asked the superintendent to verify the alignment corresponded with his understanding of the drainage and irrigation systems. Once the superintendent was satisfied, the GPR technician recorded the location and depth of each object underneath the flags. The laser scanner was then used to record the position of each of these flags in space. Technicians converted the raw laser scanner data into a point cloud model. The point cloud model was then combined with the depth readings from the GPR. This enabled us to construct a digital model of the above and below ground conditions. The model was then exported into AutoCAD to create a traditional two-dimensional survey of the site that the superintendent and maintenance staff could use to locate and repair the drainage problem in the field. Digital point cloud information was also provided to the maintenance staff, along with the necessary software to allow them to view and measure the site without leaving their office. The GPR/point cloud analysis of the green complexes at Atlanta Athletic Club revealed that an old drainage line on one green was seeping water, and on another line there was a potential irrigation leak. This analysis allowed the golf course maintenance department to know exactly where to dig to locate and make repairs, saving them untold man hours and expense in “chasing pipe” to find the problem. Furthermore, it enabled them to meet their deadline for replanting the turf on the greens for the big tournament. This technology can not only be used to locate problems, but could also prove to be an effective way to create accurate as-built drawings of irrigation, drainage and utility lines for sites that are in need of such information. As of this writing, DTC and its partners at LandAir Surveying and Wolverton Engineering were working on a proposal to use this system to help locate a rainwater catchment system in an urban area. |
