Water-use planning faces uncertainty

http://www.newschief.com/news/20170520/water-use-planning-faces-uncertainty

One of the big issues is how the increased withdrawals affect lakes and streams, and water bodies connected to them such as springs, as well as the aquifer in general.

One of the big issues in addressing future water demands in Florida is how the increased withdrawals affect lakes and streams, and water bodies connected to them such as springs, as well as the aquifer in general.

Although water plans are increasingly including so-called “alternative water sources,” the fact is that all of these sources except conservation involve eating a different piece of the same pie.

The current drought provides tangible evidence of why this is so.

A 1972 state law required water management districts to set minimum flows for surface water bodies and the aquifer, though the actual implementation lagged for decades.

Setting the minimum flows, which the law says is the minimum level “at which further withdrawals would be significantly harmful to the water resources or ecology of the area,” has been controversial.

The controversy arises because of disagreements over whether the effects of past water permitting decisions was guiding low-ball minimum flow recommendations by the agencies’ staffs.

That wasn’t a matter of dispute in Polk County. It is well documented that in some cases actions that occurred decades before 1975 when major wells first had to get withdrawal permits were a factor. By then water levels had already dropped below historic minimums, both below and above the ground.

That was the reason the Southwest Florida Water Management District had to spend millions of dollars of taxpayer money to turn Lake Hancock into a reservoir to maintain a minimum flow in the Upper Peace River, though the current drought has made even that effort challenging.

Elsewhere in the state the case for human-caused water level declines has been more contentious as water managers recommend allowing lower flows.

Some facts are indisputable.

We live below what is known as a hydrologic divide that runs roughly across the peninsula around Gainesville south of the Suwannee River Basin.

It is an area in which all the water in rivers, lakes and the aquifer is totally dependent on local rainfall.

We all know that rainfall varies from year to year, but a little more than a decade ago scientists produced some research papers documenting the connections between streamflow and something called the Atlantic Multidecadal Oscillation (AMO).

At its most basic, this refers to the contention that there are some periods of recent history when rainfall was more plentiful than others and that directly affected surface water flows.

The high flow period was defined as from 1940 to 1969, which was the period in which a combination of high rainfall and some major hurricanes led to the establishment of Florida’s first water management districts.

They were originally intended to be flood-control districts. Nevertheless, if was also the period when overpumping of the aquifer caused Kissengen Spring near Bartow just west of the Peace River to quit flowing just two years after the area experienced one of the wettest years on record.

Between 1940 and 1970, Florida’s population grew from 1.9 million to 6.8 million.

The low flow period was defined as from 1970 to 1999, which was when Florida legislators set up a system for water management districts statewide, required major water users to apply for permits for their wells and when water management districts for the first time told everyone they were going to have to cut back on everything from crop irrigation to lawn irrigation.

From 1970 to 2000, Florida’s population grew from 6.8 million to 16 million.

In the past 17 years, water supply issues have become challenging as we’ve experienced a mix of extremely wet and extremely dry years.

The latest estimated state population is 20.6 million with no decrease projected. Meanwhile, the first in-depth regional water supply study for Central Florida has concluded that sustainable withdrawals from the aquifer have reached their limit — there’s still a lot of water down there, but if you pump too much too fast, salt water will replace fresh water.

That means major water users have to look for “alternative″ sources to feed their growth ambitions, which brings us back to the AMO.

In some of the recent debates over minimum flows for some Florida springs, water management staff has used the AMO to argue that all of the decisions to pump billions of gallons out of the ground are irrelevant; it’s just a lack of rain.

Not everyone’s buying it because critics contend it doesn’t tell the whole story.

A 2004 scientific review of the concept concluded it is unknowable what the future wet and dry cycles will be because scientists don’t really understand how this all works, but instead have merely been able to document what happened in recent history as well as anyone can piece together from what little long-term streamflow data are available.

Since then there has been more discussion of the uncertainties associated with climate change. This is projected to affect rainfall, including hurricane activity, which affects water supply and temperature, which affects water demand as well as water supply to some extent because of the effects of evaporation.

Additionally, the amount of sea level rise associated with climate change will affect the rate of salt water intrusion into portions of the fresh water aquifer.

The biggest issue is whether the rate of withdrawal from any source — lake, river, Upper Floridan Aquifer, Lower Floridan Aquifer — will exceed the rate at which rainfall will replenish it.

Anything beyond that is unsustainable.

No one can answer when we’ll reach that point and that uncertainty should be part of future water planning.

Tom Palmer is a longtime environmental writer. He can be reached at tomp47@yahoo.com.