The Curbside Bioswale

I · The problem

The problem.

Every street in this city is engineered around one unexamined assumption: that rain is a problem to be removed as fast as possible. On a residential block in Alamo Heights, the assumption had failed in the usual way. Stormwater sheeted off the pavement, collected against the curb, and sat — stagnant, mosquito-breeding, going nowhere a person would want it to go. The standard remedy is a larger pipe: move the trouble downstream and make it someone else's flood. The owners here wanted no part of that, and brought us in to find a better way.

The residential street before the swale — stormwater pooled across the road and against the curb with nowhere to drain. — The curb as it was: runoff with nowhere to go.

The completed stone-lined bioswale, planted with natives, holding water where the street used to flood. — The same ground, one season later: a planted channel that drinks the storm.

II · What they chose

What they chose.

What they chose instead is older than the pipe and smarter, and we were glad to build it. A bioswale — a thirteen-foot planted channel, stone-lined, cut along the curb exactly where the water already wanted to travel. It does not resist the runoff; it receives it. The same two hundred-odd gallons an hour of street drainage that used to pool and turn now enter the swale, slow against the rock, and sink. A little over two thousand square feet of chronic standing water, resolved — not by removal, but by absorption.

III · What it does now

What it does now.

A tall sunflower blooming at the edge of the stone-lined bioswale, which holds water while the street beyond floods. — A sunflower the height of a man, where the puddle used to be — and behind it, the street still doing what streets do.

The caliche — that hard, much-cursed Hill Country limestone soil everyone treats as a disease — turns out to be a perfectly good sponge if you give it a channel and a little time. The natives we planted along the bank do the rest: roots holding the soil, blooms feeding whatever flies. A sunflower the height of a man now stands where the standing water used to be, which is a more honest performance figure than anything a stormwater report has ever printed.

Field-observed at this site

Street drainage absorbed~200 gal/hr

Standing water relieved~2,000 sq ft

Swale length13 ft

Built / in service since2025

Observed figures from the installed swale — the absorption rate is field-observed, not a lab infiltration test. Performance varies with storm intensity and antecedent soil moisture.

How a swale is sized

First you size the storm you mean to catch. Rain volume on a contributing area:

V_gal = Area_ft² × Depth_in × 0.623

Then size storage to hold it — ponding depth plus the open void in the soil and stone (gravel ≈ 40% void). Example, for illustration only:

1,000 ft² × 1 in × 0.623 ≈ 623 gal
to manage in the first flush

Illustrative — the sizing method, not this site's measurement. Each property is sized on its own catchment, slope, and soil during the Site Read.

IV · The principle

The principle.

This is not innovation. It is memory. My people moved water this way for three centuries on the acequias that still run, quietly, beneath this city — slow it, spread it, let the ground drink, and hold to the old rule that water is a commons and not a nuisance. A residential bioswale is that exact logic, sized down to a single curb. Stop fighting the storm. Give it somewhere to go and it stops being a flood and starts, within a season, being a garden.

A swale like this only exists because an owner chooses it over the easy pipe. We read the ground, size the storm, and set the stone — but the decision to do right by the water is theirs, and we're grateful every time someone makes it.

Site: A residential street in Alamo Heights, San Antonio.
Built: 2025.
The swale: A 13-foot, stone-lined, curbside bioswale, planted with Hill Country natives.
Performance: Absorbs roughly 200 gallons an hour of street drainage; relieves about 2,000 sq ft of chronic standing water.
Purpose: Flood & stagnation mitigation — by absorption, not removal.

V · What it costs

What it costs.

Infrastructure should be priced like infrastructure: transparently, by what drives the number. A bioswale isn't a flat menu item — its cost is set by length, the soil you're cutting, the stone and plants it takes, and how much water it has to move. So the price comes from the property, not from a brochure. Here is exactly how it's built up.

How a bioswale is priced

Free to start. Quoted on the property. Often partly paid back by the city.

1 · Site ReadWe walk the property, find where water already moves, and size the fix. No obligation.

Free

2 · Design & sizingCatchment, slope, and soil worked into a sized section and plant plan — the drawing your build is priced from.

Per plan

3 · BuildPriced by what it takes: swale length, excavation through caliche, stone and bioretention media, native plantings, and the overflow. Quoted from your Site Read.

Quoted

The city often pays part of it back. SAWS rebates can offset turf-to-native and water-wise conversions — the WaterSaver Landscape Coupon runs $125–$150 per coupon (up to four, roughly $500–$600 total for qualifying SAWS residential customers), with additional outdoor-living and rainwater-harvesting rebates where they apply. We map the rebates you qualify for as part of the Site Read. Rebate values are seasonal — confirmed at the time of your Read.

The curbside bioswale.