Drainage on Flat Coastal Lots: Where Gutter Water Should Go

Why flat lots are tricky

Much of the Coastal Bend sits only a few feet to a few dozen feet above sea level. Wikipedia's town data lists Port Aransas and Rockport at 7 feet (Wikipedia: Port Aransas; Wikipedia: Rockport), and describes Flour Bluff as mostly flat at about 13 feet (Wikipedia: Flour Bluff). On land that level, water does not run off quickly. A downspout that empties at the base of the wall creates a puddle that spreads along the slab instead of draining away.

Soils add another layer. Island lots tend to be sandy and absorb water fast until the water table rises during long rainy spells. Inland areas often have heavier soils that drain slowly. Either way, concentrated roof water needs a plan.

How much water a roof sheds

Texas A&M AgriLife's rainwater program calculates catchment area as the building footprint plus overhang (Texas A&M AgriLife Extension, Rainwater Harvesting: Catchment Area). Every inch of rain on a 2,000-square-foot roof is a lot of water, and NOAA normals put the annual total at the Corpus Christi airport around 31.7 inches (NOAA NCEI 1991–2020 annual normals, Corpus Christi International Airport). Gutters gather all of that into a few points. Each downspout concentrates the runoff from hundreds of square feet into one spot.

Options, from simplest to most involved

Extensions

Rigid or flip-up extensions carry water several feet from the wall. They are inexpensive, easy to move for mowing and often enough on lots with even a slight slope away from the house.

Splash blocks

A concrete or plastic pad at the end of a downspout or extension spreads the stream and stops erosion. Splash blocks work best paired with an extension rather than directly at the wall.

Pop-up emitters

A buried pipe carries water to a spring-loaded cap in the lawn that pops up when water flows. They keep yards tidy, but they need enough fall between downspout and emitter to drain completely. On very flat lots, water can sit in the pipe, collecting debris and breeding mosquitoes.

Daylighting to a lower point

If part of the lot is noticeably lower, such as a swale toward the street, a buried line can carry water there. Avoid sending water onto sidewalks, across a neighbor's property or onto a driveway that slopes toward the garage.

Rain barrels and tanks

AgriLife describes rainwater harvesting as capturing, diverting and storing rainwater for later use, which also reduces runoff and erosion (Texas A&M AgriLife Extension, Rainwater Basics). Barrels and tanks fed by downspouts store water for landscape use. AgriLife recommends painting exposed PVC to reduce UV breakdown (Texas A&M AgriLife Extension, Rainwater Harvesting: Conveyance (gutters and downspouts)). Every barrel needs an overflow route sized for heavy tropical rain.

Rain gardens and beds

A planted low area away from the foundation can absorb downspout water. It should sit well away from the slab and be planted with species that tolerate both wet spells and dry summers.

Placement principles

• Discharge at least several feet from the slab, onto ground that slopes away.
• Avoid discharging into flower beds right against the house.
• Keep water off walkways and entries.
• Do not concentrate all downspouts in one corner of the lot.
• Consider neighbors: do not move your problem onto their lot.

Planning the layout on paper

A simple sketch helps more than any product. Draw the house outline, mark each downspout, and draw an arrow showing which way the ground slopes at each corner. Circle spots that puddle after rain. Mark patios, walkways, the driveway and property lines. Patterns appear quickly: one corner that collects water from two downspouts, a patio that sits lower than the lawn, a side yard that never dries out. Bring the sketch to the estimate so the discussion covers where each outlet should go and how water will leave the lot.

Maintenance

Downspouts, extensions and buried lines all clog with leaves, catkins and seed pods, especially after the spring live oak drop. Flush buried lines with a hose at least once a year. Check that extensions are still attached after mowing or storms. In Corpus Christi, the city lists yard waste in the brown or green cart with weekly collection (City of Corpus Christi, Solid Waste Services), which handles the debris you pull out.

Signs your drainage plan is not working

• Puddles along the slab or patio a day after rain.
• Bare, eroded soil under downspouts.
• Water stains on the lower wall.
• Mosquitoes concentrated near the house.
• Pop-up emitters that never pop up.

Making drainage part of gutter work

The easiest moment to fix drainage is when gutters are being installed or replaced, because outlets can be placed where discharge works best. On existing systems, adding outlets, upsizing downspouts and adding extensions are common upgrades. See downspouts and drainage and the estimate factors page.

Planning a barrel or tank? See rainwater harvesting from gutters.

Sources: Texas A&M AgriLife Extension, Rainwater Harvesting: Conveyance (gutters and downspouts); Texas A&M AgriLife Extension, Rainwater Harvesting: Catchment Area; Texas A&M AgriLife Extension, Rainwater Basics; NOAA NCEI 1991–2020 annual normals, Corpus Christi International Airport; City of Corpus Christi, Solid Waste Services.