Downspout Erosion in Jacksonville: Why Your Downspouts Wash Out the Mulch and Soil, and How to Stop It

The short answer: one downspout releases its whole share of the roof in a single spot, and Northeast Florida's sandy topsoil over hardpan cannot soak it in fast enough, so the water runs and carries mulch and sand with it. Splash blocks only move the problem two feet. The lasting fix is an underground downspout drain: solid HDPE pipe that carries the water away from the house.

The 5 Causes of Downspout Erosion in Northeast Florida

Jacksonville gets about 53 inches of rain a year, most of it from June to October in short, violent bursts. Under that load a downspout outlet behaves like a hose.

1. Concentrated discharge from a single outlet

A 3x4 downspout collects an entire roof plane and releases it from one opening. The energy of the whole plane lands on a square foot of ground. Sandy topsoil has almost no cohesion, so the stream scours a channel, lifts the mulch and carries loose sand across the lawn. The bigger the roof plane a downspout serves, the deeper and faster the hole forms.

2. Splash blocks and short extensions that stop too close to the house

A splash block or a short extension usually ends about 2 feet from the wall. Beneath the sandy topsoil sits a hardpan or spodic layer, often 12 to 36 inches down, that stops water from draining. It cannot soak in, so it sheets across the surface, runs back toward the slab and undercuts the block. Within a couple of seasons the splash block is tilted or half buried.

3. Undersized or overflowing gutters

Not every washout starts at the outlet. Undersized 5-inch gutters overflow at the corners and over the front lip in a heavy burst, dropping water along the drip line and leaving a trench down the wall. If the erosion follows the gutter and not the downspout, the gutter is the cause. Either way the soil beside the slab stays wet. See our 6 vs 7 vs 8 inch gutter guide and the downspout sizing guide.

4. Landscape beds pitched toward the house and constantly wet soil

Many beds are mounded against the slab or built higher at the outside edge, so surface water drains back toward the foundation. Add irrigation that runs several mornings a week and the soil is already saturated when the storm arrives, so every drop from the downspout runs off and takes mulch with it. Saturated sand has nowhere to put more water.

5. Flexible recycled corrugated extensions from the home center

The flexible accordion hose from the home center is recycled corrugated pipe: made from recycled material with no exact resin mix, it crushes under a mower, clogs with sand and splits at the ribs. Soil and root intrusion then compromise the line, on average within 3 years, and the backed-up water lands right back at the wall, so a crushed hose is worse than none.

The 20-Minute Diagnostic Walk

One rainy afternoon and a walk around the house will tell you which cause you have.

1. Watch the outlet in a hard rain. A clean stream into a trench points to cause 1 or 2. Spilling from the gutter lip points to cause 3.
2. Probe the hole. Push a screwdriver into the washed-out spot. If it sinks easily, the sand is loose and saturated. If it stops short, you have hit hardpan.
3. Check the bed slope. Lay a straight board from the slab across the bed. If the bed rises away from the house, water runs back toward it.
4. Look for the stain line. A brown band on the stucco or siding just above the ground is splash-back from concentrated discharge.
5. Follow the extension. Check any recycled corrugated hose. Crushed, kinked or full of sand means it has already failed.

How We Fix Downspout Erosion

Underground downspout drains

We connect a downspout adapter to solid (unslotted) FDM heavy-duty HDPE, 3.5-inch or 4-inch, 100 percent virgin resin, rated for vehicle traffic, with snap-fit joints and no glue. The pipe runs underground to a pop-up emitter at the lawn edge, a catch basin, a dry well, or a tie-in to a French drain. No glued joints to crack as Florida soil swells and shrinks, and a 100-plus year design life. Details are on our underground downspout drains page.

Pop-up emitter, catch basin, dry well or French drain

The lot decides the outlet. A lower lawn edge takes a pop-up emitter, a low spot takes an NDS catch basin, and a lot with no outfall takes a dry well. If the yard is also soggy, we tie the line into a French drain so one system handles both.

Regrade the bed

Once the water has a pipe, we reshape the bed to slope away from the slab, replace the lost sand and restore the mulch.

Correct the gutter where the gutter is the cause

If the washout follows the drip line, pipe at the bottom will not fix an overflowing gutter. We install 6, 7 or 8-inch seamless 0.032 aluminum with hidden hangers at 24-inch maximum spacing and enough outlets that each roof plane has its own 3x4 downspout (4x5 on 7 and 8-inch).

The honest trade-off

Buried pipe needs fall, so the discharge point must sit lower than the downspout. On a flat lot the run may need to be longer than people expect to find that spot. We measure it on site and tell you before you commit.

What the Fix Costs

Downspout drains are priced per foot, so the price follows how far the water has to travel; see our drainage cost page. A French drain runs $2,500 to $6,500 for most Jacksonville yards ($25 to $60 per linear foot). The written itemized quote is the price the job is installed at.

Where Downspout Erosion Hits Hardest in Northeast Florida

Mandarin

Deep sand and big live oaks mean clogged downspouts that spill and dig; see Mandarin.

Nocatee and St. Johns

New sod over compacted fill sheds water instead of absorbing it. See Nocatee and St. Johns.

Fleming Island and Orange Park

Pine needles clog the gutters and clay pockets hold water on the surface; see Fleming Island and Orange Park.

San Marco and Riverside

Older homes with close setbacks leave little room to discharge a downspout; see San Marco and Riverside.

Ponte Vedra and the Beaches

Sand over a water table often within 24 to 48 inches fills fast and washes out; see Ponte Vedra and Jacksonville Beach.

Downspout Erosion FAQ

Quick Answers

Related Resources

• Underground Downspout Drains
• Dry Wells
• French Drain Installation
• Downspout Sizing Guide
• 6 vs 7 vs 8 Inch Gutters
• Drainage Cost
• Standing Water in Yard
• Soggy Yard After Rain
• Water Pooling Against the Foundation
• Water Pooling on the Driveway
• Side Yard Drainage
• Lanai and Patio Flooding
• Drainage Solutions Hub
• Drainage Pipe Spec
• Why Is My Yard Flooding