A Comparison of the Benefits of Northern & Southern Everglades Storage

Thomas Van Lent, Ph.D.
Rajendra Paudel, Ph.D.

 

Introduction

In 2016, the Florida Legislature passed the “Legacy Florida Act” and it was signed into law on April 7, 2016, by Governor Scott. The law sets the floor for spending on Everglades restoration projects and requires agencies to prioritize spending in a particular way, stating:

The Department of Environmental Protection and the South Florida Water Management District shall give preference to those Everglades restoration projects that reduce harmful discharges of water from Lake Okeechobee to the St. Lucie or Caloosahatchee estuaries in a timely manner.

To date, the agencies have not published any data quantifying the reduction in harmful discharges of Everglades restoration projects being considered and, thus, have not established a basis for implementation of this new legal mandate. The Everglades Foundation has begun this quantification effort.

Given the universal recognition that storage is critical, we focused on elucidating what the effects for storage would be. In this analysis, we looked at what the benefits would be for storage located north of Lake Okeechobee versus storage south of Lake Okeechobee. Specifically, we took two projects that are in the Comprehensive Everglades Restoration Plan (CERP) – a reservoir north of Lake Okeechobee and a reservoir south of Lake Okeechobee – and looked at the resultant benefits if they were constructed today. The goal is get some objective information that should help determine the proper prioritization of projects based on the new Legacy Florida mandate.

Background

The CERP is general over-arching plan to modify the Central and South Florida Project (C&SF Project) in order to restore the Everglades. CERP was established by the Water Resources Development Act of 2000[1] and signed into law by the President in December 2000. The Plan is a framework for changes “that are needed to restore, preserve, and protect the South Florida ecosystem while providing for the other water related needs of the region.”[2] There are many different components of CERP, but probably the most important is storage. The National Academy of Sciences pointed out the importance of storage in one of the first reviews of CERP.[3] Storage is essential to get the timing of water right, to make sure water carries over from wet periods to dry. Additionally, human demand for water must also be accommodated and is essential economic activity in South Florida.

The University of Florida Water Institute also reiterated the importance of storage, noting that we need “enormous increases in storage and treatment of water both north and south of the lake”[4] and that existing and authorized projects were insufficient to meet the goals of sending water south and reducing the discharges to the St. Lucie and Caloosahatchee estuaries. They cited information from the South Florida Water Management District (SFWMD) calling for more than 1 million-acre feet (330 billion gallons) storage north and south of Lake Okeechobee, compared to the 10.7 million acre-ft. of storage that the National Academy’s report toted up based upon the projects in CERP.

Storage North and South of Lake Okeechobee

CERP has 68 separate components, though we focus on two important ones: above-ground reservoirs north and south of Lake Okeechobee. Picking these two largest components will give the best idea of how storage north and south of Lake will function.

The main storage component north of Lake Okeechobee is called the “Lake Okeechobee Storage Reservoir” and denoted as Component A of CERP, which is described as follows:[5]

This feature includes an above-ground reservoir and a 2,500-acre storm water treatment area. The total storage capacity of the reservoir is approximately 200,000 acre-feet and is located in the Kissimmee River Region, north of Lake Okeechobee. The specific location of this facility has not been identified, however, it is anticipated that the facility will be located in Glades, Highlands, or Okeechobee Counties. The initial design of this feature assumed a 20,000-acre facility (17,500- acre reservoir and 2,500-acre treatment area) with water levels in the reservoir fluctuating up to 11.5 feet above grade. The final size, depth and configuration of this facility will be determined through more detailed planning, land suitability analyses, and design.

The purpose of this facility is to detain water during wet periods for later use during dry periods and reduce nutrient loads flowing to the lower Kissimmee River and Lake Okeechobee. This increased storage capacity will reduce the duration and frequency of both high and low water levels in Lake Okeechobee that are stressful to the Lake’s littoral ecosystems, and cause large discharges from the Lake that are damaging to the downstream estuary ecosystems. Depending upon the proposed location(s) of this water storage/treatment facility and pollutant loading conditions in the watershed(s), the facility could be designed to achieve significant water quality improvements, consistent with appropriate pollution load reduction targets.

The main reservoir south of Lake Okeechobee is Everglades Agricultural Area (EAA) Storage Reservoir, or Component G of CERP, which is described as follows:[6]

This feature includes above-ground reservoir(s) with a total storage capacity of approximately 360,000 acre-feet located in the Everglades Agricultural Area in western Palm Beach County and conveyance capacity increases for the Miami, North New River, and Bolles and Cross Canals. The initial design for the reservoir(s) assumed 60,000 acres, divided into three, equally sized compartments (1, 2, and 3), with the water level fluctuating up to 6 feet above grade in each compartment. The final size, depth and configuration of this facility will be determined through more detailed planning and design.

We also investigated the costs in 2016 dollars in order to compare to the 2006 estimate $912,895,089.[7] Based on the description from the Component G, we estimated a cost of about $2.4 billion.

The purpose of this feature is to improve the timing of environmental deliveries to the Water Conservation Areas, including reducing damaging flood releases from the Everglades Agricultural Area to the Water Conservation Areas, reducing Lake Okeechobee regulatory releases to the estuaries, meeting Everglades Agricultural Area irrigation and Everglades water demands, and increasing flood protection in the Everglades Agricultural Area.

Analysis of Storage Benefits

To get an idea of the relative benefits of Lake Okeechobee Storage Reservoir (Northern) versus the EAA Storage Reservoir (south), we used the hydrologic model that was used to develop CERP, commonly known as the “2×2 Model.” In these simulations, we examined three scenarios:[8]

  1. the “Existing Condition Base,” which is a model representation of the current C&SF infrastructure and operating rules;
  2. the “Northern Reservoir” scenario, which is exactly the same as the Existing Condition Base, but with the addition of the CERP Component A, or North of Lake Okeechobee Reservoir; included.
  3. the “EAA Reservoir” scenario, which is exactly the same as the Existing Condition Base, but with the addition of the CERP Component G, or EAA Reservoir, included.

The analysis was intended to look solely at the relative benefits of these two elements of CERP so that a direct comparison between two options is possible. Undoubtedly, operational and structural improvements could be made that could increase benefits, but this direct comparison will give a better idea of the benefits that each of these two options produce and makes no assumptions about the project other than what is in the official plan.

The place to start with looking at the potential impacts is with Lake Okeechobee itself. The stage duration curve (Figure 1) indicates that with the EAA Reservoir, water levels in Lake Okeechobee are dramatically lower during wet periods. During these wet periods, water levels are between 0.5 and 1 foot lower, an extraordinary effect. On the downside, the Lake would see an increase in low water frequencies and durations, the consequence of lowering Lake stages during wet periods. The decrease in water levels in the Lake during wet periods with the EAA Reservoir is between 200,000 and 450,000 acre-ft. and sustained over a range of conditions, indicating that the EAA Reservoir is providing a benefit larger than its nominal size of 360,000 acre-ft.

The northern reservoir would have different effects. The biggest benefit is an increase in water levels during droughts, but would have only a marginal change in water levels during wet periods. Moreover, the net change to water levels in Lake Okeechobee with the Northern Reservoir is, on average, far less than the nominal size of the reservoir, which is roughly 0.4 ft of water in Lake Okeechobee. Clearly, the major benefits to Lake Okeechobee of a northern reservoir is for drought water supply, and not in lowering high water levels.

The outflows from the Lake also show the benefit of the EAA Reservoir in increasing the regulatory releases (excess flood waters) from Lake Okeechobee, which is shown in Figure 2. With a new outlet southward, operations are prioritized to move water southward into either the EAA Reservoir or into the Everglades itself. By adding the EAA Reservoir, the average annual volume of releases is increased from 660,000 acre-ft. to 870,000 acre-ft., an increase of more than 30%. That is why Lake Okeechobee stages decreased so significantly with the EAA Reservoir: the outflows increased.

To be clear, there was no attempt to change Lake Okeechobee operational rules, so it is very possible that, with the EAA Reservoir, estuary outflows could be decreased even further if the large decrease in Lake stages observed in Figure 1 were allowed to rise. Again, this analysis made no attempts to optimize performance of either reservoir beyond how it was described and modeled in CERP.

The Northern Reservoir has a very different function. It would likely have a very small change in the total outflow from Lake Okeechobee to the estuaries, increasing net regulatory outflows by about 1%. Also, there is a relatively small difference in high Lake stages with the Northern Reservoir. The explanation is that this reservoir is almost always full when Lake Okeechobee gets into a regulatory releases situation, as the volume sent from the Lake into the reservoir during regulatory periods is only about 25% of its nominal capacity. That is, the reservoir is typically at 75% of its capacity when harmful releases to the estuaries begin, so there’s not much room to store those releases. And given that the only outlet for the Northern Reservoir is Lake Okeechobee, there no ability to “make room” in the reservoir for additional Lake water.

The likelihood that the reservoir will be nearly full when regulatory releases begin also explains why the Northern Reservoir has a limited impact on releases from Lake Okeechobee to to the St. Lucie and Caloosahatchee estuaries; the Caloosahatchee and St. Lucie volumes drop by only about 6% each. Again, the reservoir is typically full, and so the decrease in estuary discharges is limited by the available capacity in the reservoir because it does not present a new operational outlet for Lake Okeechobee.

If one uses as the criterion for prioritization of a project its ability to decrease harmful estuaries discharges, then an EAA Reservoir is clearly superior. In addition, an EAA Reservoir has better performance during wet periods in Lake Okeechobee, decreasing the failure risk to the Herbert Hoover Dike. The Northern Reservoir has superior performance in improving drought conditions in Lake Okeechobee.

The EAA Reservoir puts significantly more water in the Everglades when Lake Okeechobee gets high. This has two effects. First, there is an undesirable effect that the water depth in some regions of Water Conservation Areas become higher during wet conditions, as shown in the depth duration curve for southern Water Conservation Area 3A in Figure 3. This area already has unnaturally high water depths because of the artificial impoundments created by the C&SF Project levees. During wet periods, water levels could increase by as much as 0.2 feet. However, in Everglades National Park, water levels (Figure 4) are markedly improved under all conditions. In terms of flows, both the quantity and the timing of flows to Everglades National Park improved, as indicated by flows across Tamiami Trail in Figure 5. There is more water flowing in both the wet season and the dry season. Overall, total average annual volumes through the heart of the Everglades increased by about 21% with an EAA reservoir.

With a Northern Everglades Reservoir, there are no observed changes in flows or water levels in the Everglades. It improves the water supply in Lake Okeechobee, but none of that Lake Okeechobee water is sent to the Everglades under the current operational policies. Therefore, a Northern Everglades Reservoir shows no apparent effects in the Everglades. With a Northern Everglades Reservoir, there are no observed changes in flows or water levels in the Everglades. It improves the water supply in Lake Okeechobee, but none of that Lake Okeechobee water is sent to the Everglades under the current operational policies. Therefore, a Northern Everglades Reservoir shows no apparent effects in the Everglades.

Summary and Conclusions

In this analysis, we attempted to do a first-order analysis of a simple question: what are the benefits of building the CERP storage projects north and south of Lake Okeechobee? We applied the same tools used to develop CERP, and looked at what would happen if these projects were build on top of the water management system in place today.

We found that the EAA Reservoir reduced the volume of harmful discharges from Lake Okeechobee to the estuaries by nearly 50%, while the Northern Reservoir reduced the volume of discharges by about 6%. The main benefit of the Northern Reservoir is to provide more water supply benefits to the Lake. The EAA Reservoir had the additional benefit of increasing flows in the Everglades by about 26%, where a reservoir north of Lake Okeechobee did not show changes in flows or water levels in the Everglades.

 

stage-duration-curves-for-lake-o

 

mean-annual-flood-control-releases-from-lake-o

 

normalized-duration-curves-for-enp

 

annual-average-overland-flow-across-transects

 

[1] Public Law 106-541 Section 601. “Title VI — Comprehensive Everglades Restoration”

[2] PL 106-541 §601(b)(1)(A)

[3] Re-Engineering Water Storage in the Everglades: Risks and Opportunities

Committee on Restoration of the Greater Everglades Ecosystem, National Research Council (2005) page 1. Available at http://www.nap.edu/catalog/11215.html

[4] Options to Reduce High Volume Freshwater Flows to the St. Lucie and Caloosahatchee Estuaries and Move More Water from Lake Okeechobee to the Southern Everglades

An Independent Technical Review by the University of Florida Water Institute, March 2015, page 6. Available at http://waterinstitute.ufl.edu/research/downloads/contract95139/UF%20Water%20Institute%20Final%20Report%20March%202015.pdf

[5] Central and Southern Florida Project Comprehensive Review Study, Final Integrated Feasibility Report and Programmatic Environmental Impact Statement, US. Army Corps of Engineers and the South Florida Water Management District, April, 1999. page 9.2

[6] Central and Southern Florida Project Comprehensive Review Study, Final Integrated Feasibility Report and Programmatic Environmental Impact Statement, US. Army Corps of Engineers and the South Florida Water Management District, April, 1999. page 9.9

[7] http://141.232.10.32/pm/projects/project_docs/pdp_08_eaa_store/revised_draft_pir/022206_eaa_pir_mainbody.pdf

[8] All simulation codes, input decks, and output are available by contacting info@evergladesfoundation.org.

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