Stakeless site grading with a GPS machine-control system helps carve out lakes, basins, and swales for large-scale land development.
BY RICHARD RYBKA
From its conception, the Metro Air Park project in Sacramento, Calif., presented many challenges. The project, on a site adjoining Sacramento International Airport, involves development of 20 million square feet of warehouse, retail, office, and hotel space with related infrastructure at a cost of $2 billion. A championship golf course will be included.
Zoning approval was received in 1993, and since that time, the owners have acquired 1,886 acres for the development. Environmental approvals, primarily focused on endangered species habitat issues, held back final approval and construction until October 2003.
Drainage was one of the major issues in designing the project. Prior to purchase for development, the site was used for agricultural purposes. It was suited ideally for growing rice because of its low elevation and minimal grade change. An irrigation canal traversed the site near the north end, and the site drained naturally to three locations. In order to meet development objectives, however, the canal will be removed and all drainage will be directed to the southeast corner of the site.
Stormwater management, a necessary component of site planning and land development, can be approached as a regulatory burden or as a creative opportunity. By integrating it with the planning, design, and engineering of a development site, good siteplanning practices can identify the extent and define the placement of stormwater-control features, which can contribute significantly to the visual quality and environmental value of a completed project.
The stormwater management plan for Metro Air Park is an outstanding example of creative engineering in response to land planning objectives. Hydrologist Patrick Stiehr, P.E., founder of Watermark Engineering, Roseville, Calif., developed the drainage plan for the project in 1993 while working for another civil engineering firm.
Subsequently, the land owners commissioned a golf course architect to design the course. When development plans finally came to fruition, the owner's construction manager called in Watermark to review the previously prepared drainage study and to make recommendations.
Dynamic modeling was advocated because the total storm volume was important, and there was significant backwater throughout the area that needed to be presented accurately. The shapes and grading of lakes, detention basins, and conveyances through the golf course were redesigned completely for functional and aesthetic compatibility.
Watermark's recommendations and revisions netted cost savings of $4 million compared with those of the original study.
Engineers with Watermark proceeded to complete the final drainage study for the project in 2002. This study prescribed the first phase of site preparation tasks, including constructing the stormwater-control infrastructure required for build-out of 30 percent of the project. Major tasks included the following:
- construct storm drainage systems for two major access roads;
- rough grade the golf course site for surface drainage;
- construct four detention basins to serve as water features within the golf course;
- construct two detention basins on other areas of the site; and
- generate and place excavated material at the southern end of the site to remove it from the Federal Emergency Management Agency designated floodplain and to change the surface drainage pattern.
Stiehr's final design includes many innovative features. Four lakes and grassy swales incorporated into the golf course provide detention, convey stormwater, and improve water quality. The grading of these features elevates tees, greens, and fairways above design storm levels.
Overland swales are designed to remain dry, except during rain events when they will function for overland conveyance. The lake edges are contoured for a natural appearance. Stormwater detained within the lakes will be used for irrigation purposes.
The scope of construction work under the original $11.9-million contract included moving 2 million cubic yards of dirt, laying 30,000 feet of storm pipe, grading 30,000 feet of v-ditch, and building the complex, meandering stormwater basins. Completion time for the project was a slim 120 working days, and contract terms provided for only one payment at the completion of the project. Construction began in October 2003.
From an excavation contractor's standpoint, the stormwater control and grading design for the site presented other challenges. Unlike typical detention basins, the four lakes within the golf course had contoured edges. The sides and bottoms were designed with varying slopes. But, conventional grade staking the entire project would be a time-consuming and expensive task, particularly for the lakes within the golf course. Additionally, by contract, construction layout services were the responsibility of the owners.
Faced with these contractual and site challenges, the contractor developed a strategy to eliminate much of the conventional survey requirements, resulting in a significant savings to the owner. Using Topcon System Five 3D-GPS+, fully automated machine-control systems on three dozers and two motor graders enabled operators to perform "stakeless" grading. The owners only incurred layout expenses for the storm drain lines and structures.
The Topcon GPS+ system offered key advantages compared with other available solutions. For example, GPS-guided, machine-control and survey systems require access to a minimum of five satellites to provide accurate horizontal and vertical control. GPS-only systems access the global positioning satellites launched and maintained by the United States. But, access to the minimum number of U.S. GPS satellites sometimes cannot be achieved because of their positions in the sky. Trees and structures also can obstruct access to satellites.
Topcon's GPS+ technology enables access to Russian GLONASS satellites as well as the U.S. GPS satellites. This provides more available satellites and improved sky distribution, which minimizes equipment operating downtime and improves horizontal and vertical accuracies.
Topcon also offers software that is specifically designed for construction/contractor applications. The Metro Air Park project's contractor prepared surface files required for the System Five equipment automation systems using Topcon's 3D-Office program.
Pocket 3D software was used in the field computer/rover system to verify positioning of drainage features and to check grades.
These programs, with user-friendly interfaces, are designed to work together and to be operated with a minimal amount of training.
Contractors can realize several benefits from using machine-control systems. Machine operations are controlled automatically to produce the correct design grades, eliminating costly reworking. Less experienced machine operators can perform efficiently with a minimum amount of training, and delays caused by waiting for survey crews to provide grade staking are eliminated. Using a GPS machine-control system, the contractor completed the Metro Air Park project on schedule and was able to create picture-perfect lakes that were a mirrorimage of the plans.
Richard Rybka, a photo journalist for Pleasanton, Calif.-based Topcon, is a Registered Landscape Architect and has 25 years of experience with site engineering, land development, and contracting. He can be contacted via e-mail at firstname.lastname@example.org.