Backyard Beauty in a Flood Plain: Challenges and Solutions

By Jolynn Bennett, Pavestone LLC

A nearby creek put the property on a 100-year floodplain map, requiring a retaining wall for the pool and deck addition. A three-piece ?EUR??,,????'??Anchor Diamond Pro Stone Cut?EUR??,,????'?? segmental wall (Pavestone) with geogrid soil reinforcement was selected for this 1,000 sq. ft. serpentine wall. During a 100-year storm, the creek water level could rise 6.7 feet above the wall toe (4.3-ft. below the top of the wall).

A swimming pool, fireplace, grill, deck, beautiful planting beds and a large play area were all part of the Baylin family?EUR??,,????'???s dream for a backyard living experience to complement their Sandy Springs, Georgia home.

The one impedance to the backyard project was the residence backed up to a small creek on a 100-year floodplain map. The homeowners were not initially aware of the issues presented by the stream buffer, but the homeowners soon discovered the project would be a larger, more complex undertaking than anticipated.

Sloping site grades and compliance with city requirements for a variance to build the pool and deck on the property were a few of the hindrances to creating the homeowner?EUR??,,????'???s dream backyard. More critically, it was necessary to build a retaining wall to elevate the pool and pool deck out of the flood zone, and support the pool deck on three sides because of the sloping grades. The challenge was undertaken by Ron Johnson of GeoServices Express, Ron Gudger of Site Works Surveys and Planning, and installer Chris Farr, ARC Outdoors, Inc. Teaming with hardscape manufacturer Pavestone helped formulate solutions the city would approve.

Ron Johnson described the situation: ?EUR??,,????'??The pool permitting and installation encountered a few obstacles. The city of Sandy Springs required mitigating the 100-year floodwater volume displaced by the pool and deck construction by removing an equal amount of earth volume from another location within the flood plain. In other words, the city required no net loss of flood water volume on the property.?EUR??,,????'??

A second retaining wall and four-ft. wide steps were installed in front of the 8.5-foot high embankment cut to stabilize the excavation, while creating an aesthetically pleasing look. Soil was installed in the wall geogrid reinforced fill zone. Concerned that high floodwaters could create a rapid drawdown loading condition and damage the wall, GDOT #57 crushed stone was installed behind the wall units at a minimum width of four feet. The stone allows water to drain rapidly and minimize rapid drawdown loading concerns.

The variance also required no nonpermeable surface installed within 75 feet of the stream on the property, and maintaining a 50-foot nondisturb buffer. The portion of the pool deck in the 75-foot permeable buffer was required to be a pervious paver installation, plus erosion control practices had to be maintained to protect the adjacent stream.

The hardscape design began with the selection of Anchor Diamond Pro Stone Cut to give structural integrity to the retaining wall, and Eco-Venetian Stone permeable pavers for the decking.

A second retaining wall and steps, constructed of 1,200 square feet of Anchor Diamond Pro Stone Cut units, were installed in front of the 8.5-foot high embankment cut to stabilize the excavation and create an aesthetically pleasing look.

The upper and lower deck was constructed using 2,200 sq. ft. of tumbled 80 mm
Eco-Venetian StoneTM pavers (Pavestone). The lower deck has a permeable construction to allow water to pass through the pavers. This was a code requirement, as no nonpermeable surface could be installed within 75 feet of the stream. Runoff on
the upper deck flows to collection drains.

?EUR??,,????'??The existing embankment above the second wall rises more than 30 feet, with an approximate 2 (horizontal) to 1 (vertical) slope,?EUR??,,????'?? explains Jones. ?EUR??,,????'??While wall two was primarily added to compensate for displaced floodwater, the wall also was used to enhance the beauty of the backyard. It was divided into two tiers to create an attractive raised planter area. The planter was raised approximately 3.5 feet above the lawn and is visible from most of the backyard, including the overlooking pool deck. The tiered wall was a more pleasing aesthetic for the homeowner.

Wall two had five site revisions to adjust for the flood area and site conditions. The neighbor?EUR??,,????'???s septic line ran through the wall and was relocated several times to allow for installation of the wall and the reinforcement zones. The site access and conditions required use of a rock hammer on a skid steer to bust out the rock to install the wall. Fifteen loads of rock were removed.

To comply with the requirements of the 75 ft. permeable buffer, the pool deck was lowered and separated into two different paver system installations. ?EUR??,,????'??To maintain a consistency both the upper and lower deck was constructed using 2,200 square feet of tumbled 80 mm Pavestone Eco-Venetian Stone pavers,?EUR??,,????'?? explains Chris Farr notes. The lower deck was a permeable construction that allows water to pass through the pavers while the upper deck was a nonpermeable construction; runoff goes to collection drains. The use of levels allowed for a consistent look and flow to the job.?EUR??,,????'??

The embankment above this two-tiered wall rises more than 30 feet, with an approximate 2 (horizontal) to 1 (vertical) slope. The wall was divided into two to create an attractive raised planter. The planter is 3.5 feet above the lawn and visible from most of the backyard, including the overlooking pool deck.