Swale

Florida Statutes 403.803(13) defines a swale as a manmade trench and then sets four conditions. A trench has to meet all of them.

• Shape. It "Has a top width-to-depth ratio of the cross-section equal to or greater than 6:1, or side slopes equal to or greater than 3 feet horizontal to 1 foot vertical;" in other words, wide and shallow, or gently sloped.
• Water only after rain. It "Contains contiguous areas of standing or flowing water only following a rainfall event;" so it is dry the rest of the time.
• Vegetation. It "Is planted with or has stabilized vegetation suitable for soil stabilization, stormwater treatment, and nutrient uptake;"
• Design. It "Is designed to take into account the soil erodibility, soil percolation, slope, slope length, and drainage area so as to prevent erosion and reduce pollutant concentration of any discharge."

Two things follow from the wording. The word "manmade" means a natural dip in the ground is outside the definition however much it looks like one. And the last test is about intent as much as shape: the trench has to be designed around its soil, slope and drainage area, which is not something a glance at a lawn can confirm.

The section's own lead-in begins "When used in this part," so this definition governs that part of Chapter 403. It is the statute's meaning, not a rule for every use of the word in a county notice or a guidance document.

The everyday word is looser. Among the wastewater containment methods in its washing guidance, the Florida Department of Environmental Protection describes onsite swales as "shallow, grassy low areas designed to collect runoff and allow it to seep into the ground without discharging to a stormwater system".

That description keeps the grass and the purpose, soaking water into the ground, and drops the statute's ratio, its slope figure and its design test. It is also written into a document with a specific scope: FDEP's Recommended Best Management Practices for Mobile Vehicle and Equipment Washing. Its third recommended practice reads: "Identify all stormwater drains, grassy swales and ditches and locate sanitary sewer manholes at the proposed wash area." FDEP recommends those practices; the document does not make them rules.

Collier's archived NPDES Permit page uses the word in a third way, as a place pollution arrives. It says pollution "can come from pipes from homes or businesses dumping into swales or canals", and calls that kind of pollution an illicit discharge. In that sentence a swale is a place pollution arrives, named beside canals. FDEP's onsite swale, by contrast, soaks water in without discharging to the stormwater system of curbs, ditches and storm drains.

A swale is also different from a pervious surface. A swale is a shaped low area that gathers water; a pervious surface is any ground that lets water soak in, flat or not.

Put the two senses side by side and the gap is plain. FDEP's everyday swale is recognized by what it does with water. The statutory swale is recognized by measurements, by whether it holds water only after rainfall, by its planting and by how it was designed. A grassy low area that holds standing water between rains, or one too steep or narrow for the statute's ratio, can fit the first description and fail the second.

That is why no definition answers whether a low area at a particular address is a swale in the statute's sense, or who is responsible for maintaining it. The county or the city that governs the address answers that question.