Pool Deck Drainage on Cumming Lots With Lake Lanier Water Tables

A Polo Fields homeowner called us after his second summer with a flooded pool deck — rainwater ponded against the house, and by spring, groundwater pushed up through the travertine joints from below. His deck wasn’t the problem. His lot was. He lived 0.6 miles from Lake Lanier, and nobody had told him what that meant for drainage.

We walked the site on a drizzly March morning. I pulled a 4-foot soil probe out of the turf next to the coping and hit saturated clay at 38 inches. Water wicked up the shaft within 90 seconds. The original builder — not us — had installed a standard 18-inch perimeter subdrain and a pair of surface-channel drains along the back edge. Code-compliant, technically. Useless on this lot. In Cumming, within a mile of the lake, you are not draining a pool deck. You are managing two water systems at once: the rain that falls on top and the groundwater that pushes up from below. Confuse the two, and you will be tearing out a deck within three years.

This post is for homeowners in Vickery, Hampton Park, St. Marlo, Lake Windward, and Windermere, and any of the Lake Lanier-adjacent parcels in Forsyth County. If your lot sits inside the seasonal high water table zone — and much of the land north of Hwy 20 and east of GA-400 does — your deck drainage system needs to cost more, dig deeper, and route farther than a standard Piedmont build. Here is exactly what that looks like, what it costs, and why cutting corners is the most expensive mistake you can make on a Cumming pool.

Why Lake Lanier Lots Have Two Water Problems, Not One

Much of the pool deck work we do in DeKalb, Gwinnett, or Walton County deals with one water source: rain. Rain hits the deck, rain runs off, rain goes somewhere. Size the slope, size the channel drain, route to daylight. Done. That math falls apart in Cumming anywhere within roughly a mile and a half of Lake Lanier’s shoreline, and in pockets along the Chattahoochee and its tributaries near Browns Bridge Rd.

The lake sits at a controlled pool elevation of 1,071 feet. Residential lots in the lake-adjacent zones of Forsyth County sit between 1,080 and 1,180 feet of elevation. That gradient — plus the saturated floodplain soils that extend inland from the shoreline — creates what hydrologists call a perched seasonal water table. From February through May, after the winter rain bank has saturated the Cecil-series clay, groundwater sits within 4 to 6 feet of the surface on lake-adjacent lots. On some parcels in lower-elevation coves, we have documented it at 3 feet 2 inches in late March.

That means your pool’s structural shell sits partially submerged in groundwater for roughly four months of the year. Your deck — poured on compacted stone above that saturated soil — is not just catching rain. It is the lid on a water reservoir that wants to push up.

The failure modes are distinct and they require separate engineering:

• Surface failure: rainwater ponding because the deck slopes wrong or the channel drain is undersized for summer thunderstorm bursts. Cumming averages 52 inches of rain per year, with single events regularly exceeding 3 inches.
• Subsurface failure: groundwater saturating the base course, lifting travertine or flagstone pavers, efflorescing grout joints white, and pushing hydrostatic pressure against the pool shell’s exterior.
• Combined failure: both at once, typically visible in April when rain rides in over already-saturated subsoil and the deck has nowhere to send the volume.

Standard Atlanta-metro pool deck drainage specs assume dry subsoil. They do not work here. The clay under your deck in Cumming is not the hard-packed high-density clay you find in older parts of Gwinnett. It is a Cecil-series Piedmont clay that holds more water, drains slower, and seasonally shifts up with the water table. Plan for it or pay for it later.

The 36-Inch Subdrain Rule and Why 18 Inches Fails Here

Standard pool deck construction across the Piedmont uses a perimeter subdrain — a 4-inch perforated pipe wrapped in filter fabric, bedded in washed #57 stone, tied to either a pop-up on the lawn or a catch basin that daylights to the property line. In Dacula, Lawrenceville, or Loganville, that drain sits at 18 to 24 inches below finish grade, runs along the back edge of the deck where it meets the retaining wall or house, and does its job.

In Cumming’s lake-adjacent zones, 18 inches puts the drain line above the seasonal water table. That is the opposite of what you need. A subdrain above the water table cannot lower the water table. It just collects whatever surface water seeps past the deck joints. Meanwhile the groundwater below it is still pushing up, still saturating the base, still finding its way through your grout.

Our spec on every Lake Lanier-adjacent Cumming project: perforated HDPE at 36 inches below grade, bedded in 12 inches of #57 washed stone wrapped in 8-oz non-woven geotextile. Two runs — one along the house side of the deck, one along the back edge — joined at the lowest corner and daylighted to a French drain exit within 30 linear feet. If the property topography won’t support a 30-foot daylight run, we add a dedicated sump basin with a 1/2-horsepower submersible pump on a mercury float switch, tied into the home’s interior circuit via Sawnee EMC’s required 240V service drop.

The cost delta versus a standard install is real. A typical Piedmont pool deck in Lawrenceville carries a drainage line item of $2,400 to $3,600. On a lake-adjacent Cumming lot, we bid that same line item at $6,200 to $10,000 — a premium of $3,800 to $6,400 that reflects the deeper trench (sometimes requiring a mini-excavator with a 36-inch thumb attachment), the larger stone envelope, the extended daylight run, and, on about 40% of these sites, the sump-pump redundancy.

Here is the reality: if your drainage contractor quoted you $3,000 for a pool within a mile of Lake Lanier, they are quoting a Dacula drain on a Lake Lanier lot. You will pay the difference later in deck repair, and that repair will cost $18,000 to $32,000 because the crew will need to demo the travertine to reach the failed subdrain underneath.

Surface drainage sizing is the second half of the equation, and Cumming’s Sawnee Mountain topography drives a specific summer storm pattern. Warm, moisture-loaded air pushing up the mountain face generates localized thunderstorm cells that regularly drop 1.5 to 3 inches of rain in under 45 minutes. The Big Creek gauge near the Forsyth County Administration Building has logged multiple 2.8-inch burst events in the last three summers.

Surface drainage designed for a coastal-plain average rainfall rate will flood every time one of those cells parks over your subdivision. We size Cumming pool deck channel drains to handle a peak flow rate of 8 gallons per minute per linear foot of deck edge — roughly twice the standard Piedmont calc. That means specifying NDS Dura Slope or ACO KlassikDrain 8-inch channel systems instead of the 4-inch residential grade most general contractors install. On decks above 800 square feet, we run dual channel lines — one at the house edge, one at the deck-to-lawn transition — to split the load.

The discharge side matters just as much. A 6-inch channel drain discharging into a 4-inch pop-up emitter will back up the second it hits capacity. Our spec: 6-inch SDR-35 PVC discharge to a daylighted outlet or a 24-inch diameter dry well with 18 cubic feet of capacity, lined with filter fabric and capped below turf grade. The dry well is critical on lots where the property line sits too close to allow a daylight run.

On a St. Marlo project last summer, the existing deck had a builder-grade 4-inch channel drain tied to a 3-inch PVC discharge that ran 48 feet to a pop-up. During a late-July storm, the homeowner watched the channel drain back up and overtop within eight minutes. We replaced the entire surface system with an 8-inch ACO channel, 6-inch discharge, and a dedicated dry well. Cost: $4,800 in materials and labor above the standard system. Warranty claim avoided: deck tile demo and replacement at $24,000.

Grading a Lake-Adjacent Deck Backward — and Why It Works

Counterintuitive point that trips up even experienced hardscape crews: on Lake Lanier-adjacent pools, we often slope the deck toward the pool, not away from it, at the outer perimeter. The reason is mechanical. Sloping outward toward the lawn sends surface water across the full width of the deck before it hits a drain. On a 14-foot-wide deck, that is a long trip through paver joints that have already absorbed groundwater from below. The water hits the outer drain but leaves a wet trail the whole way.

Sloping inward toward the pool — at a 1/4-inch per foot pitch — routes surface water to an interior channel drain set just outside the coping, which then dumps into the subdrain system below. The travertine stays drier. The grout stays intact. The pool’s built-in gutter overflow handles the minor volume that bypasses the channel.

This approach is not right for every pool. If your pool is a gunite shell with a conventional perimeter overflow, the inward slope works cleanly. If you have a vanishing-edge or perimeter-overflow system, we split the deck into wedges and route each wedge to a dedicated channel line, because a uniform inward slope will overload the pool’s overflow gutter during a burst event.

The grading plan also has to coordinate with the house. The Forsyth County Department of Planning and Community Development at 110 E. Main St., Cumming enforces a requirement that positive drainage must move surface water away from habitable structures. On a deck that slopes inward at the pool edge, we still have to carry surface water outward at the house edge — usually with a French drain set 18 inches off the foundation, tied into the main stormwater system. Permit reviewers in Cumming specifically look for this detail; two of our permit revisions last year came back asking for the foundation-side drainage plan to be drawn explicitly.

A subdrain is only as good as its exit. The pipe can be perfectly installed, at perfect depth, in perfect stone, and if water has nowhere to go it will sit in the pipe and eventually seep back out through the perforations. On Lake Lanier-adjacent lots, we insist on one of two exit strategies, in order of preference: daylighted gravity discharge, or a dedicated sump with an alarmed pump.

Daylighted discharge works when the lot’s topography has enough grade drop that the subdrain outlet can exit above ground somewhere downhill of the pool. The practical threshold: a 2% minimum slope over a 30-foot run, which translates to about 7 inches of elevation drop. In St. Marlo, Polo Fields, and the golf-course communities, we can typically find that grade. On the flatter lake-shelf lots near Mashburn Plantation and parts of Three Chimneys, we sometimes cannot.

When daylighting fails, the backup is a 24-inch diameter, 48-inch deep sump basin with a Zoeller M53 or equivalent 1/2 HP submersible pump, wired to a 240V dedicated circuit from the Sawnee EMC meter panel with a battery-backup secondary pump on the same float tree. The battery backup is not optional on these installations. Storms that overwhelm surface drainage are often the same storms that knock out power — we have pulled a primary pump sump basin in April that failed during a four-hour outage and flooded the homeowner’s finished basement.

Cost on the full sump system, installed and tied into the electrical service: $3,200 to $4,800 on top of the subdrain itself. Annual maintenance (pump pull, float test, basin vacuum): $180. That maintenance cost is the line item homeowners forget about. A Zoeller pump with a jammed float in year four costs you the basin, the pump, and often the subfloor of whatever the water reaches. Test the float every March before the rain season.

Materials, HOAs, and What the Package Actually Costs

Material selection on a lake-adjacent deck matters more than on a dry-Piedmont deck. The freeze-thaw cycle in Cumming runs to roughly 22 freeze events per year, and when the deck sits on saturated subsoil, every freeze-thaw pulse is amplified. Water that has wicked up into a paver’s pore structure freezes, expands, and spalls the face off in sheets. A deck that would last 30 years in Dacula fails in 8 years on a lake-adjacent Cumming lot if the wrong material is specified.

What we use:

• Travertine: unfilled, honed, 1.25-inch thickness minimum (not the builder-grade 3/4-inch or 1-inch tile). Sealed every 18 months with a penetrating siloxane sealer, not a topical acrylic. The pores stay breathable but repel water.
• Natural flagstone: Pennsylvania bluestone or Tennessee crab orchard, 1.5-inch thickness minimum, polymeric-sand joints, not mortar. Polymeric sand flexes with freeze-thaw. Mortar cracks.
• Concrete pavers: we use Techo-Bloc or Belgard only. Both manufacturers publish freeze-thaw performance data meeting ASTM C1645 for our climate zone. Cheaper pavers from big-box suppliers do not.

What we do not use on lake-adjacent lots: poured concrete deck slabs without a carefully engineered joint pattern (they crack at the first winter), porcelain tile on thinset over concrete (the substrate cracks and the tile follows), and any paver thinner than 1.25 inches.

The sealer question trips people up. Big-box stores sell topical acrylic sealers that leave a glossy finish. On a lake-adjacent deck, they trap moisture inside the stone. The first freeze-thaw cycle after application, you get milky white efflorescence under the sealer — which is permanent, because you cannot strip the sealer without damaging the stone. Use a penetrating siloxane. Prosoco SLX100 is our standard. Apply every 18 months. Cost per application on a 900-sq-ft deck: $340.

Beyond materials, you have to survive the permit and HOA gauntlet. Forsyth County’s permit process for pool deck drainage is not difficult, but it is specific. County permits are reviewed by a staff engineer, typically within 10 to 14 business days. The review is strict about foundation-side drainage, as noted above, and about stormwater discharge to neighboring parcels — you cannot dump a French drain outlet across a property line without an easement.

The HOAs are another layer. St. Marlo, Polo Fields, Vickery, and Windermere all have architectural review boards that approve pool and hardscape plans independently of the county. Turnaround on these is 2 to 3 weeks on average, longer in spring when volume spikes. They will require elevation drawings, material specifications, and drainage exit plans. Some HOAs (Vickery in particular) require that the drainage discharge be invisible from neighboring lots — which rules out above-grade pop-up emitters and forces you to spec a dry well or daylighted outlet into a planting bed.

Line-item breakdown on a typical 900-sq-ft pool deck drainage package in a Lake Lanier-adjacent Cumming neighborhood, based on our 2025-2026 bid data:

• Excavation and trenching for 36-inch subdrain, two runs, approximately 180 linear feet: $2,400
• Perforated HDPE pipe, #57 washed stone, 8-oz geotextile, fittings: $1,800
• Surface channel drains (ACO KlassikDrain 8-inch, two runs, approximately 60 linear feet): $2,200
• Discharge piping (6-inch SDR-35), fittings, daylight outlet or dry well: $1,400
• Sump basin and submersible pump (when daylight isn’t possible) plus battery backup: $3,800
• Electrical — Sawnee EMC-compliant 240V dedicated circuit for sump pump: $900
• Engineering and drainage plan for HOA and county submittal: $600

Total range: $9,300 to $13,100 for the drainage package alone, before any deck material, coping, or structural pool work. That is the real cost of doing this right on a Lake Lanier-adjacent lot, and it is $3,800 to $6,400 more than the equivalent drainage package on a dry-Piedmont Dacula or Lawrenceville lot.

The math homeowners need to hear: the delta is roughly 4% of a $250,000 pool project. Skipping it does not save you 4%. It costs you the deck eight years in, which at current Cumming labor rates means $18,000 to $32,000 to demo and rebuild. Properly engineered drainage is the cheapest insurance you will ever buy on a lake-adjacent build.