Nature of Things: With flood control, the devil's in the details

2020-04-11 | Laurel Leader

April 11-- Apr. 11--Last week I talked about the effects of droughts on water policy.

This week I'll discuss floods, which as I mentioned last week was the original intent of water "management" policy in Florida.

The issue could arise later this year if the predictions of an active hurricane season turn out to be accurate and any of those hurricanes drench us.

As many of you know, there were schemes dating at least to the 19th century to engage in major infrastructure projects to drain low-lying areas of Florida to make the land more useful for crops and cattle.

They included everything from Hamilton Disston's efforts to drain the headwaters of the Everglades to the Peace Creek Drainage District and obscure local flood control districts. One of those, the Peace River Valley Water Conservation and Drainage District, built the original control structure on Saddle Creek south of Lake Hancock. The Southwest Florida Water Management District, which was founded as a flood-control agency, inherited the structure and never saw fit to dismantle it. Instead, the agency rebuilt it to hold more water in the lake so it could replenish the upper reaches of the Peace River during droughts.

By the 1970s the idea of the so-called "structural" approach to flood control --canals and dikes--gave way to working with nature instead.

The most often cited example of that turnabout is the Four Rivers Basin Project.

That involved a plan to build reservoirs and to dredge stream channels in and around the Green Swamp, which contains the headwaters of the Peace, Hillsborough, Withlacoochee and Ocklawaha rivers. The idea was to hold back water that otherwise would have flowed toward Tampa and other urban areas as it did following Hurricane Donna in 1960.

Quite a few artificial drainage projects had already been undertaken in that part of the state by then, but the work directed by the U.S. Army Corps of Engineers was intended to "improve" it.

Eventually Swiftmud officials decided instead to simply purchase large tracts of land in the Green Swamp and let natural systems handle most of the water management, though they did build the Tampa Bypass Canal to divert floodwaters from the Hillsborough River.

When it comes to flooding, the issue that many people care about is more local than regional. That is, will their home, their yard or their street get flooded when there is unusually heavy rain.

This issue often arises when a new development is proposed next to existing homes and residents logically ask whether the runoff from the roofs, driveways and roads will end up on their property.

Although those concerns are usually brushed off by review panels, they raise valid issues.

One is that the cumulative impact of development runoff does sometimes alter regional drainage characteristics.

It not only increases the volume but also sometimes the velocity of the runoff. Faster moving water can scour stream banks and the soil around bridge supports and even cause localized flash flooding, according to reports I've received.

But there's something else.

The complaining residents are often reassured that any flooding issues will be handled by engineering to guarantee no more water flows from the property in the future than it does now. This is usually referred to as a "pre-post match."

That's somewhat true, but doesn't tell the whole story.

The whole story is that storm retention systems are engineered only to handle storm runoff from a specific intensity storm, and if they are properly designed and maintained, they will do that.

How big a storm the system is required to accommodate is the catch.

It will vary depending on how strict or permissive local development regulations are.

The reason for the discrepancy is simple. The larger, more protective stormwater systems take up larger tracts of land, which means there will be fewer residential lots or retail space to market.

This tug of war has been going on for a long time, and it has sometimes taken conditions in exceptionally wet years to strengthen the regulations.

Today there are generally good assurances that the design the engineer submitted is actually what's in place. That wasn't always the case.

In the end, though, what really counts is whether it's enough.

Water plan webinars

If you would like to keep up with water planning in this part of the state, the folks at the Central Florida Water Initiative are holding a series of online webinars in lieu of public meetings.

One involving rulemaking for water reservations in the Kissimmee River is scheduled for 10 a.m. Thursday.

A second involving an update and explanation of the regional water supply plan will occur April 23.

For details, go to

Waste dropoff site closed

The household hazardous waste dropoff site at the North Central Landfill has been temporarily closed to protect the health of the workers.

The site is the place where residents can take unwanted or unused materials such as used oil, solvents, herbicides, pesticides and old fluorescent light bulbs containing mercury for proper disposal because these materials should not be placed in household garbage carts. That's because the materials could pollute groundwater at the landfill and exposure could threaten the health of workers who unknowingly handle the material.

Meanwhile, residents are asked to hold on to the material until the dropoff center reopens. They can also call 863-284-4319 to get more specific information about what material is suitable for disposal in their garbage bins and which is not.

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