Course officials at TPC Potomac at Avenel Farm, a professional-caliber golf course in Montgomery County, Md., had seen their share of rain-soaked playing conditions since Avenel began hosting PGA tournament events in 1987. Still, little could prepare them for the flooding conditions that arose during the 2006 Booz-Allen Classic, which almost resulted in cancellation of the tour event.
Rock Run, a main tributary of the Potomac River that cuts through the course, had quickly filled during a period of heavy rain, submerging the fairways and greens and rendering the course largely unplayable throughout much of the tournament weekend. The flooding conditions were not new; Avenel officials had frequently dealt with damaging stream overflow through the years. However, conditions during the 2006 tournament were nearly catastrophic, with one official reporting that course clean-up even included tracking down port-o-johns that had floated away and become entangled with trees.
“Rain events in the one- to five-year range should not be producing flooding, but they were at TPC Potomac at Avenel Farm,” said Milan Moore, a designer with PGA TOUR Design & Construction Services, Inc. “After the 2006 Booz-Allen Classic was almost lost due to flood damage, it was clear that the future success of the golf course, from a functionality standpoint, depended on the stream restoration aspect.”
From gold to golf
TPC Potomac at Avenel Farm closed in 2007 to undergo a major renovation that would address the chronic flooding problems along with an extensive course redesign. PGA Tour Design & Construction Services contacted Dewberry, which had performed previous work at Avenel, to help engineer the renovation. Dewberry provided civil engineering, permitting, and surveying, and teamed with LandStudies, Inc., for environmental consulting. The centerpiece of the renovation was restoration of Rock Run, which runs along seven holes of the golf course. Engineers soon determined that the stream had suffered such extensive modifications since the 19th century that very little of the original stream corridor was still intact.
“The flooding situation at TPC Potomac at Avenel Farm was unique,” said Moore. “First, during the late 19th and early 20th centuries, the site’s stream system was the center of a major gold mining operation. The mining and the associated excavation significantly altered the system by removing or crushing the natural quartz gravel bed material that helped to prevent incision and protect the bedrock from weathering.
“Then, the golf course was built in the early 1980s,” Moore said. “It was designed to handle a quantity of runoff from surrounding developments, which were primarily rural at the time. Over the next 25 years or so, there was a significant increase in nearby development. All together, it created the foundation for major flooding during rain events.”
The mining operation and subsequent development had removed the bed material that was capable of preventing bed and bank erosion. Floodplain encroachments and channel straightening had caused increased velocities during higher flows. “Over time, the stream had become very narrow with a high velocity. Much of the bedrock was gone,” said Michael Sullivan, general manager of TPC Potomac at Avenel Farm. “Our intention was to restore the stream valley to a condition similar to that of 200 years ago.”
Creating a functional floodplain
Using the principles of fluvial geomorphology, engineers assessed the proper dimension, pattern, and profile for the stream system — consisting of approximately 3,600 feet of Rock Run and 3,200 feet of three unnamed tributaries. Initial investigations, which included extensive soil borings, trenches, and field visits, confirmed that very little of the original material that formed the stream valley was present. The field work helped to identify the thickness and type of material forming the floodplain, including the “legacy sediment” that had developed as a result of adjacent hill slope erosion, as well as spoil material from gold mining and fill material from previous agricultural practices and golf course construction.
Resources included software tools such as TR-20, developed by the U.S. Soil Conservation Service and required by the state of Maryland for hydrologic analysis of a watershed, and the U.S. Army Corps of Engineers’ HEC-RAS program for hydraulic analysis. Both programs provided a detailed model of existing stream corridor conditions as well as a model of the proposed design that could then be manipulated to determine the best parameters for the proposed condition.
The engineering team sought to reduce course flooding by restoring the stream channel to its original path and reconnecting it with a functional floodplain to increase flood flow capacity and storage. The fluvial system was designed to minimize flow near the course features and infrastructure, which required close coordination with the course architects to identify the “playable” and “non-playable” zones along the different watercourses. The number of golf cart and pedestrian bridges were minimized and designed to reduce the amount of backwater and frequency of flooding in areas identified as playable.
“The streams were drastically renovated to ensure that playable corridors would remain above water during a 100-year rain event,” said Moore. “The streams remain on the same golf holes as prior to the renovation, but that’s where the similarities end. The stream beds were rebuilt on new gravel layers, the floodplains were widened and regraded, and the channels were rerouted to slow water velocity and minimize impact to the surrounding banks.”
Moore also pointed to the extensive plantings in and around the floodplain to help stabilize banks and filter runoff. “Many species of trees, shrubs, grasses, and aquatics were planted,” he said, “and the restoration added over 12 acres of new wetlands, providing habitat and refuge for the wildlife native to the site.”
Following the natural course
According to Sullivan, there has been no recurrence of the flooding that plagued Avenel for years. “Now, the flow follows the natural course of the stream,” he said. “There is a floodplain buffer that is very effective.”
The ambitious project also incorporated the addition of 15 acres of forest, a course redesign, a new irrigation system, a new practice facility, and new stone walls and landscaping. “The reception has been great,” said Sullivan. “The state of Maryland is now looking at Avenel as a prototype for similar stream restoration projects.”
Moore confirms the positive outcome of the renovation, pointing to Tropical Storm Hanna as an example: “Hanna was a 100-year rain event that had periods of intensity that reached that of a 500-year event,” she said. “Prior to the stream restoration, such an event would have inundated the golf course and caused major erosion, loss of turf, and fallen trees. This time, the floodplain neared capacity and the water velocity was high, but the new streams were intact.”
The success of the transformation recently led to the announcement that Avenel would soon host another professional tour event: the Constellation Energy Senior Players Championship in October 2010. The project has also been recognized with a 2009 Merit Award from the Maryland Chapter of the American Society of Landscape Architects, which applauded the project’s environmental focus.
“PGA TOUR has taken an active role in environmental stewardship on many fronts, and the project at TPC Potomac provided the first of many large-scale opportunities at the design level to show our commitment,” said Moore. “Working in a responsible manner with the environment is a win-win situation.”
Joanne Cheok, P.E., is a senior associate and Mike Snyder, P.E., is a senior vice president with Dewberry. Both are based in the firm’s Gaithersburg, Md., office and can be contacted at firstname.lastname@example.org and email@example.com, respectively.