[BrianL99]

After Milton, there's certainly a lot of discussion about how drainage systems work, but it seems that most people don't have a basic understanding of what a system is supposed to do, nor how and why it does.

Drainage 101.

When a developer buys and develops a parcel of land, the Clean Water Act and numerous other federal, state and county laws and regulations apply. All of those regs essentially require 3 conditions. The post-development conditions as it applies to “water”, must remain the same. At the perimeter of the parcel of the land, the developer must retain current water quality standards and cannot increase the rate, volume or quality of the water that leaves his property. This design is usually predicated on conditions that would exist, up to and including, a 100 year storm event.

Water (drainage) is controlled by a myriad of techniques. Channelling, detaining, retaining, sheet flow, piping, culverts, dams, ponds, infiltration, sedimentation basins, etc. There are lot of components to a drainage system.

The developer can do pretty much whatever he wants to control the water internally and he can store it or dump, wherever he wants … it’s his property.

Design within those property boundaries, is another other story.

There are various state and local regulations that control what happens within the subdivision. Usually, that system is designed for a 20 or 50 year storm. A design may cause flooding of roads, during events that exceed the design criteria.

Privately owned land might also “flood”, when a storm event exceeds the design criteria. Remember, the developer owns all the land when he designs his system, he can put the water wherever he wants and can continue to do it, if he put the proper easements into place before selling off homes.

In theory, property that is planned to be transferred to the Districts, should (IMO) be designed to withstand at least a 50 year storm event, without damage to infrastructure or public buildings.

In other words, when it’s said that The Villages drainage design is supposed to handle a 100 year storm event, that doesn’t mean there won’t be any flooding. It means at the property lines of the original development area, the volume, rate, and quality of the water that leaves the site, will be the same as it was before the development. You are allowed to flood interior lands.

On an individual neighborhood basis, things may be different. The regulations are always changing and becoming stricter. I suspect back in the 90’s, internal drainage was required to meet the 25 year/24 hour storm. I don’t know the design criteria that was use for the “infrastructure” land that is now owned by the District, but I suspect it varied through the years. It's probably a 50 year storm design, but could be 100 year. Whatever it is, it does not prevent “flooding”, it localizes and controls flooding.

If the internal drainage system was designed for a 100 year storm event (which I doubt), that doesn’t mean there’s never going to be any “flooding”. It means that the regulatory agency in charge of approval, was satisfied that any area that may flood, can withstand the amount of flooding that’s likely to occur.

Most communities in the USA, don't require a drainage plan for individual homes, unless they're located near a water body or in the Flood Plain. There really isn’t any criteria, other than the home is above or below the 100 Year Flood Plane, as shown on FEMA maps. Other than that, it’s up to the builder to grade a lot or building area, in a way that keeps water away from the foundation. It’s no more complicated than that.

"Drainage systems" do NOT prevent flooding, they control water.

I’m sure we have Registered Professional Engineers or Hydrologists on TOTV, that can explain this better than I, but the above are the basics.

[Stu from NYC]

Still amazing to me that we had a huge storm and the villages is designed to handle it with no flooding

[BrianL99]

Originally Posted by Stu from NYC

Still amazing to me that we had a huge storm and the villages is designed to handle it with no flooding

We have the best and one of the most sophisticated drainage system of this sort, in the USA. Anyone who knows anything about drainage will tell you, it's an engineering masterpiece.

(I do think we need better maintenance of the ponds and culverts, though.)

[Altavia]

Thanks fur there overview.

I thought this is clear as to the design intent?

https://www.districtgov.org/PdfUpload/Storm%20Water.pdf

[BrianL99]

Originally Posted by Altavia

Thanks fur there overview.

I thought this is clear as to the design intent?

https://www.districtgov.org/PdfUpload/Storm%20Water.pdf

That's an excellent document, although I doubt many folks take the time to read it.

I just read it and as I suspected, the design criteria has changed through the years and some areas are designed for a 25 year storm and others for a 50 year or 100 year storm.

I understand drainage pretty well from a conceptual standpoint, but without seeing the design intent, the specifics are semi-guesswork. Thanks for posting this!!