4
Challenges in Restoring Water Timing, Flow, and Distribution

As discussed in Chapter 2, Everglades restoration is premised on “getting the water right” by striving to reestablish the quality, flow, timing, and distribution of freshwater that characterized pre-drainage South Florida ecosystems. Addressing the disparate hydrological requirements of the diverse wetland communities that comprise the greater Everglades ecosystem demands highly integrated water resource planning and adaptive re-engineering and re-operating of the Central and South Florida (C&SF) Project.

Restoration at this scale involves many uncertainties, constraints, and tradeoffs. In the next two chapters, short-term priorities and longer-term plans for restoring surface flows and water quality are examined. The discussion of surface hydrology in this chapter focuses on the kinds of tradeoffs that are, of necessity, being made in re-distributing water to different parts of the Everglades, and considers the risks associated with incomplete restoration or long delays in providing storage capacity and additional water. The committee focused special attention on Water Conservation Area (WCA) 3 as an example of these challenges because it serves as the main flow-way of water through the remnant Everglades. WCA-3 provides habitat for important Everglades species and system features, and it is a nexus for many contentious Everglades water flow issues. Also, flows in Everglades National Park and WCA-3 are interdependent because of their adjacent geographic locations. Current water quality concerns and regulations, the cost and performance of source control and treatment alternatives, and the considerable technical and economic challenges of bringing existing and planned Comprehensive Everglades Restoration Plan (CERP) flows into compliance are summarized in Chapter 5.

PAST AND FUTURE CHANGES TO SOUTH FLORIDA’S WATER BUDGETS AND FLOW REGIMES

The hydrologic result of the Central & South Florida Project in the Everglades portion of the drainage basin south of Lake Okeechobee was a near-total



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 112
4 Challenges in Restoring Water Timing, Flow, and Distribution As discussed in Chapter 2, Everglades restoration is premised on “getting the water right” by striving to reestablish the quality, flow, timing, and distribution of freshwater that characterized pre-drainage South Florida ecosystems. Address- ing the disparate hydrological requirements of the diverse wetland communities that comprise the greater Everglades ecosystem demands highly integrated water resource planning and adaptive re-engineering and re-operating of the Central and South Florida (C&SF) Project. Restoration at this scale involves many uncertainties, constraints, and trad- eoffs. In the next two chapters, short-term priorities and longer-term plans for restoring surface flows and water quality are examined. The discussion of surface hydrology in this chapter focuses on the kinds of tradeoffs that are, of necessity, being made in re-distributing water to different parts of the Everglades, and con- siders the risks associated with incomplete restoration or long delays in providing storage capacity and additional water. The committee focused special attention on Water Conservation Area (WCA) 3 as an example of these challenges because it serves as the main flow-way of water through the remnant Everglades. WCA-3 provides habitat for important Everglades species and system features, and it is a nexus for many contentious Everglades water flow issues. Also, flows in Ever- glades National Park and WCA-3 are interdependent because of their adjacent geographic locations. Current water quality concerns and regulations, the cost and performance of source control and treatment alternatives, and the consid- erable technical and economic challenges of bringing existing and planned Comprehensive Everglades Restoration Plan (CERP) flows into compliance are summarized in Chapter 5. PAST AND FUTURE CHANGES TO SOUTH FLORIDA’S WATER BUDGETS AND FLOW REGIMES The hydrologic result of the Central & South Florida Project in the Ever- glades portion of the drainage basin south of Lake Okeechobee was a near-total 112

OCR for page 112
Challenges in Restoring Water Timing, Flow, and Distribution 113 transformation of the flow system (USACE and SFWMD, 1999). The impacts of these changes to the landscape and the ecosystem are described in detail in Chapter 2, but the quantitative changes in hydrology are discussed further in this section to provide a basis for additional discussion of improving water flow and distribution. A comparison between pre- and post-drainage water budgets of the Kissim- mee-Okeechobee-Everglades watershed (Figures 4-1 and 4-2) shows how the distributions of water storage and transfers are believed to have changed. Some of the key features of these modeled water budgets are summarized in Table 4-1 according to Natural Systems Model (NSM) version 4.6.2 and the South Florida Water Management Model (SFWMM) version 5.4 (see Box 4-1). Comparable water budgets based on the newer South Florida Regional Simulation Model (RSM) are not yet possible because of model development issues discussed in Chapter 6. The water budget models have considerable uncertainty associated with estimating evapotranspiration and specific values of water flows from one compartment to another, and the models are used here as generalizations rather than as exact accountings. According to the SFWMM, on average Lake Okeechobee discharges approx- imately 11 percent less water south under current conditions (554,000 acre-feet/ year) compared to pre-drainage flows (622,000 acre-feet/year; see Figures 4-1 and 4-2). Total inflow to the WCAs ranges widely with the models used. The SFWMM v. 5.4 calculates that current water inflows from the north to the WCAs (1.3 million acre-feet [MAF]/year) exceed that which would have occurred via sheet flow in the pre-drainage system (1.06 MAF per year; NSM v. 4.6.2). How- ever, the new Natural System Regional Simulation Model (NSRSM) depicts a wetter pre-drainage Everglades in which 1.5 MAF flowed from Lake Okeechobee into what is now the Everglades Agricultural Area (EAA) and at least 1.7 MAF flowed from the north into the current WCAs, across their northern boundaries (J. Obeysekera, SFWMD, personal communication, 2009). Roughly 1.9 MAF per year still enters the WCAs across the western, northern, and eastern boundaries under current conditions (see Figure 4-2), but inflow now occurs primarily through canal or stormwater treatment area (STA) discharges, unlike in pre-drainage conditions when direct precipitation and occasional overflows from Lake Okeechobee dominated freshwater inputs (Harvey and McCormick, 2009). Surface-groundwater exchanges were minimal in the rela- tively flat, peat-covered, pre-drainage landscape. In contrast, peat subsidence, canals, and levees have created local hydraulic gradients that increase seepage and surface-groundwater interactions. As a result, after losses by evaporation, the WCAs now lose nearly half their remaining water through seepage to coastal areas. In addition, the loss of peat through oxidation has accentuated ground- water losses by permitting movement of surface water downward. The thick

OCR for page 112
114 Progress Toward Restoring the Everglades FIGURE 4-1 Estimated annual water budget for the Kissimmee-Okeechobee-Everglades Figure 4-1.eps drainage basin, 1965–2000, under pre-drainage and pre-development conditions, calculated bitmap using the Natural System Model (NSM) version 4.6.2, which simulates regional hydrology in the absence of existing control structures. The numbers in rectangles represent mean annual flow volumes in 1,000 acre-feet/year, based on model simulations using a 36-year precipita- tion data set. Change in storage, shown in circles, represents the net inflows minus outflows over the period of record. SOURCE: J. Obeysekera, SFWMD, personal communication, 2009.

OCR for page 112
Challenges in Restoring Water Timing, Flow, and Distribution 115 FIGURE 4-2 Estimated annual water budget for the Kissimmee-Okeechobee-Everglades Figure 4-2.eps drainage basin under post-drainage and post-development conditions, calculated using a 36-year simulation using the SFWMM bitmapwith structures in place as of 2000 (usually consid- ered the typical “current” situation). The numbers in rectangles represent mean annual flow volumes in 1,000 acre-feet/year, based on model simulations using a 36-year precipitation data set. Change in storage, shown in circles, represents the net inflows minus outflows over the period of record. SOURCE: J. Obeysekera, SFWMD, personal communication, 2009.

OCR for page 112
116 Progress Toward Restoring the Everglades TABLE 4-1 Total Flow Volume of Freshwater Inputs and Outflows from Four of the Regions Shown in Figures 4-1, 4-2, and 4-5 Pre-drainage (KAF) Surface Precip./ET water Groundwater Total Lake Okeechobee Inputs 1,671 1,641 0 3,312 Outflows 2,338 980 0 3,318 Everglades Agricultural Inputs 2,635 942 0 3,577 Area Outflows 2,450 1,122 7 3,579 Water Conservation Areas Inputs 3,475 1,467 6 4,948 Outflows 3,007 1,916 23 4,946 Everglades National Park Inputs 2,776 1,752 8 4,536 Outflows 2,629 1,856 50 4,535 NOTE: The numbers represent total inflows and outflows calculated using the data provided in the figures, which were generated by the NSM v. 4.6.2 and the SFWMM v. 5.4. ET = evapotranspiration; KAF = thousand acre feet. peats of the pre-drainage system isolated the surface water from the ground- water. These changes also have important implications for water chemistry, as will be discussed in Chapter 5. Everglades National Park has also experienced substantial changes in flows as a result of the engineered systems upstream. Under the pre-drainage conditions, the area that is now Everglades National Park received roughly 1.3 MAF of water per year (according to both the NSM and the NSRSM) as overland sheet flows from the land that is now WCA 3, with total inflow of 1.7-1.8 MAF from all sources (Figure 4-1). Under present condi- tions the same park area receives about 0.8 MAF in surface flows from WCA-3 through culverts beneath Tamiami Trail (Figure 4-2). On average 1.1 MAF flows into the park from all sources (or 61-64 percent of pre-drainage flows), and seepage to the east removes an additional 0.2 MAF of this total. As a result of these adjustments, the park area that once discharged approximately 1.9 MAF per year through coastal ecosystems to the Gulf of Mexico (NSM 4.6.2; or 2.1 MAF per year according to the NSRSM) now only discharges about 1.1 MAF per year (see Figures 4-1 and 4-2). In addition to changes in the overall volume and distribution of water dis- cussed above, the Everglades landscape has also experienced substantial changes in the timing, duration, velocities, and directions of flow. Although no stage data for South Florida exist prior to the construction of the Tamiami Trail and associated levees, hydroperiods historically were thought to be tied to seasonal variation in regional rainfall and secondarily to the slow drainage into and from the region (Duever et al., 1994). Florida has a five-month “rainy season” (mid-May to mid-

OCR for page 112
Challenges in Restoring Water Timing, Flow, and Distribution 117 Current (KAF) CERP flows (KAF) Surface Surface Precip./ET water Groundwater Total Precip./ET water Groundwater Total 1,667 1,660 0 3,327 1,667 1,820 0 3,487 2,140 1,211 0 3,351 2,130 1,374 0 3,504 2,635 497 34 3,166 2,635 614 26 3,275 1,917 1,243 3 3,163 2,025 1,244 3 3,272 3,475 1,915 0 5,390 3,475 1,899 0 5,374 3,333 1,163 891 5,387 3,301 1,485 592 5,378 2,776 1,087 87 3,950 2,776 1,898 5 4,679 2,469 1,124 355 3,948 2,572 1,597 503 4,672 October) that is typically accompanied by increasing water levels, and a less rainy or “dry season” (November to April) that is typically associated with stable or falling levels (Obeysekera et al., 1999). The reproductive success and survival of Everglades flora and fauna are linked to these seasonal cycles. For example, many wetland species such as apple snails, alligators, wading birds, snail kites, and Cape Sable seaside sparrows time breeding to coincide with the dry season, expecting water levels to recede slowly. Yet the area still receives significant rain- fall in the dry season associated mainly with frontal passages, and that rain can lead to rising rather than falling water levels (i.e., “reversals”), which can result in reduced reproductive success for many wetland birds (discussed in more detail later in the chapter). Reversals during spring likely occurred in the pre-drainage Everglades, but two factors probably have increased their frequency and mag- nitude recently. The first is the reduced water-storage and hydrologic buffering capacity associated with the reduced spatial extent of the Everglades. The second is current water management, which can contribute to increased annual changes in water levels, as has occurred on Lake Okeechobee (Beissinger, 1986; NRC, 2007). While the Everglades has been described by some as a “hyperseasonal savanna” (Kushlan, 1987; Duever et al., 1994), its inter-annual (between-year) rainfall variation actually is much smaller than that of other lowland neotropi- cal wetlands with similar flora and flora (Beissinger and Gibbs, 1993), such as the Llanos in Venezuela and the Pantanal in Brazil (Kushlan et al., 1985). Thus management activities that increase intra-annual (within-year) variation in water levels will likely adversely affect the Everglades.

OCR for page 112
118 Progress Toward Restoring the Everglades BOX 4-1 Modeling the Hydrology of the Historic South Florida Ecosystem An understanding of the water flows of the pre-drainage system is essential for resto- ration project planning. Comprehensive Everglades Restoration Plan (CERP) agencies presently use two models to estimate pre-drainage water flows: the Natural System Model (NSM) and the Natural System Regional Simulation Model (NSRSM). These models use similar platforms as hydrologic models of current conditions but without the water control infrastructure and with different land cover and land use. The NSM uses the same climatic input, model parameters, grid spacing (2 mile by 2 mile) and computational methods as the South Florida Water Management Model (SFWMM), but physical features, such as topography, vegetation type, and river locations are adjusted to represent the pre-drainage condition. As more paleoecology data became available that provided important insights into historic hydrologic conditions (e.g., Willard et al., 2001; Winkler et al., 2001; Saunders et al., 2006; Bernhardt and Willard, 2009), the NSM progressed through a series of revisions. Version 4.6.2 is the latest version of the model in use, although Everglades National Park has worked on its own revisions to the model code (called ENP Mod 1) based on paleoecology data that were not well simulated in prior versions of the NSM. ENP Mod1 simulates a much wetter system that that of NSM 4.6.2. The NSRSM is an entirely new fully coupled surface-groundwater model with a system of triangular cells ranging in size from 0.1 to 2 miles on a side. Compared with earlier modeling efforts for the pre-drainage system, the NSRSM covers a larger pro- portion of the entire watershed (and some areas outside the watershed), and it uses improved data sets, particularly for land cover and land use and topography. The South Florida Water Management District (SFWMD) is currently developing the South Florida Regional Simulation Model (RSM) designed to extend the NSRSM to describe present conditions. Generally, NSRSM model runs describe a natural system that is wetter than the system described by NSM 4.6.2 model runs. These three model-generated descriptions of the pre-drainage system are each different, and there is uncertainty inherent in such hind-casts of hydrologic conditions of a century ago. Despite these reservations, the committee sees some convergence among the recent pre-drainage model output (NSRSM, ENP mod1) suggesting a wet- ter pre-drainage system than prior NSM output, with total inputs from the north to the current Everglades Protection Area averaging 1.9-2.1 million acre-feet (MAF)/year. This amount can be contrasted against current flows of approximately 1.4 MAF/year across the same boundaries (Wilcox and McVoy, 2009). The inter-annual variation of flood and drought events is another impor- tant feature of the pre-drainage Everglades. Floods and droughts are recurring pulse events in many wetlands (Odum et al., 1995; Dong, 2006) including the Everglades (Thomas, 1974). The life histories of many plants and animals have evolved and been shaped in the Everglades by these hydrologic events (Davis and Ogden, 1994), which may have occurred on long-term rainfall cycles of 4-7 years in south Florida (Thomas, 1974; Beissinger, 1986; Duever et al., 1994),

OCR for page 112
Challenges in Restoring Water Timing, Flow, and Distribution 119 as well as associated cycles in the timing and extent of wildfires (Beckage and Platt, 2003; Lockwood et al., 2003). Over the past century, the transformation of the Everglades landscape through compartmentalization and canals has partly decoupled the occurrence of droughts and floods from rainfall variability, sometimes shortening or lengthening the intervals between drought and flood events or changing their duration. Restoration of natural hydrologic variation is needed to maintain ecological communities in the Everglades. For example, the reduction of droughts that cause dry-down events can cause a loss of tree islands (Willard et al., 2006), while too-frequent droughts can cause snail kite populations to decline (Beissinger, 1995; Martin et al., 2008) or reduce fish populations so that they can no longer adequately support large predators such as alligators (Mazotti et al., 2009). Finally, the magnitude and directions of flow have significantly changed as a result of engineering works as shown in Figure 4-3. Among the most important engineering changes was the creation of the WCAs, which interrupted and re- directed the sheet flow that formed and maintained the distinctive features and ecological functions of the Everglades. The effects of the water management structures on water depths are illus- trated in Figure 4-4, in which water depths during the midst of the rainy season are compared to those near the end of the dry season. Figure 4-4 captures a wet year (2006) and shows the extensive ponding that occurs in WCA-3A behind the L-67 levees, which prevent flow from moving southeast into WCA-3B, and above the Tamiami Trail (and its associated levee), which limits the flow of water into Everglades National Park. Similar effects can be seen in the southern ends of WCA-1, WCA-2A, and WCA-2B. Figure 4-4b shows the extent of extreme dry conditions that now occur during drought years, particularly in northwestern portions of the WCAs and Shark River Slough in Everglades National Park, and the persistent ponding in the extreme southern portions of the WCAs and behind the L-67 levees in WCA-3A. PARTIAL HYDROLOGIC RESTORATION AND SPATIAL TRADEOFFS Reduced spatial extent, extensive peat loss, and large urban and agricultural demands for water and flood control make it infeasible to fully restore the hydrol- ogy of the remnant Everglades ecosystem. Thus constrained, CERP and related projects have aimed at partial restoration toward pre-drainage depths, hydro- periods, and flow regimes. Some of the major features of hydrologic restoration under the CERP are summarized in Figure 4-5. By comparing Figure 4-5 to Figure 4-2, one can see that a fully implemented CERP is expected to lead to large reductions in flood discharges to the northern estuaries, moderate reductions in flood discharges to the WCAs, and significant increases in freshwater inputs to

OCR for page 112
120 FIGURE 4-3 Simulated mean annual overland flow based on climate data for the period 1965-2000, comparing the system under pre-drainage Figure 4-3.eps conditions as modeled by the NSRSM v. 3.3 (left; Said and Brown, 2010) and the present managed system using the Glades-Lower East Coast Service Area (LECSA) model (right; Senarath et al., 2008, 2010; see also Lal et al., 2005; SFWMD, 2006b). The color of the arrows is scaled to reflect landscape the magnitude of flow. bitmap SOURCE: L. Gerry, SFWMD, personal communication, 2010.

OCR for page 112
Challenges in Restoring Water Timing, Flow, and Distribution 121 a b FIGURE 4-4 Example of hydrologic extremes now characteristic of WCA-3 and Shark River Slough: (a) wet conditions observed on September 30, 2006 and (b) extreme dry conditions observed on April 20, 2008. Figure 4-4.eps SOURCE: Johnson (2009) generated using the USGS Everglades Depth Estimation Network (EDEN). bitmap with vector labels a & b Everglades National Park (see Table 4-1). These and other changes depend on new surface storage, aquifer storage and recovery, wastewater reuse, and other CERP elements described in Chapter 2. One of the consequences of reduced spatial extent and reduced storage in the modern system is that it may be impossible to get the water “right” or even “better” everywhere at all times. CERP planners have always recognized that restoration benefits would be unequally distributed across the Everglades landscape and that hydrologic conditions might even worsen in some areas in order to achieve desired outcomes in others (USACE and SFWMD, 1999). It is important to understand these tradeoffs and interdependencies when evaluating the design and staging of CERP projects, especially given the kinds of lengthy delays and design changes that have characterized restoration efforts to date. The extent to which one area is impacted to achieve benefits elsewhere depends on the amount of new storage and changing constraints on water distribution such as flood control, seepage management, and water quality.

OCR for page 112
122 Progress Toward Restoring the Everglades FIGURE 4-5 Estimated annual water budget for the Kissimmee-Okeechobee-Everglades drain- Figure 4-5.eps age basin under full CERP implementation, calculated using a 36-year simulation using the SFWMM v. 5.4.3. Model run CERP A shown simulates the CERP preferred alternative (D13R). The bitmap numbers in rectangles represent mean annual flow volumes in 1,000 acre-feet/year. Change in storage, shown in circles, represents the net inflows minus outflows over the period of record. SOURCE: J. Obeysekera, SFWMD, personal communication, 2009.

OCR for page 112
138 Progress Toward Restoring the Everglades likelihood of localized drought in WCA 3A during dry years (Cattau et al., 2008), which has adversely affected kite populations because juvenile survival and nesting success are related to minimum annual water level (Figure 4-9b). Finally, the current water regulation schedule has the potential to shorten the number of months during which kites can breed (Mooij et al., 2002). Kite population growth is strongly positively related to the duration of the breeding season because long breeding seasons allow multiple nesting attempts that offset typically low prob- ability that any one nesting attempt will be successful (Beissinger, 1986, 1995). In conclusion, snail kite reproduction in WCA-3A now suffers from a water regulation schedule that appears to exaggerate the seasonal changes in water levels and does not mimic the seasonal patterns expected in a wetland driven by a natural hydrologic cycle and seasonal flows. Loss of Tree Islands Altered hydrology has produced myriad vegetation changes in the South Florida ecosystem. Drought-prone areas of northern WCA-3 have experienced peat loss, increased wildfire frequency, loss of tree islands, shrub invasion into emergent wetlands, loss of aquatic plants, sawgrass expansion into former slough wetlands, altered periphyton communities, and increased establishment of invasive exotic species (NRC, 2008; RECOVER, 2008). Tree islands may be consumed by fire, but trees may also die from excessive drought when water levels are more than 1 foot below ground for more than 30 days (Sklar et al., 2009b). At the other extreme, in areas such as southern WCA-3A where there is extended ponding of deep water, tree islands area has been accompanied in recent years by a lack of seedling establishment caused by stress from prolonged inundation (McKelvin et al., 1998; see Figure 2-13). Growth and survival of even the most water-tolerant species are inhibited or reduced when water depths on islands exceed 1 foot for more than 120 days (Wu et al., 2002). Tree islands cover less than 5 percent of the Everglades, but they number in the thousands, ranging in area from less than 10 m2 to more than 70 hect- ares (ha; 173 acres) (Sklar and van der Valk, 2002). The systematic loss of tree islands from the central Everglades is of special concern because of their long time to establish, their high species diversity, and the disproportionate role they play in nutrient cycling and in supporting wildlife populations (Sklar and van der Valk, 2002). Within WCA-3, there was a 67 percent decrease in total tree island area and a 45 percent decrease in the number of islands between 1940 and 1995 (Patterson and Finck, 1999; Sklar et al., 2005). Some tree islands have become “ghost islands” of standing dead trees or have disappeared altogether. The largest

OCR for page 112
Challenges in Restoring Water Timing, Flow, and Distribution 139 period of tree island loss occurred between 1950 and 1970, with slower rates of loss before and after. The most recent analysis shows that between 1995 and 2004 tree island area declined an additional 520 acres (6 percent), and the number of tree islands declined by 11 percent (Figure 4-10). Ridge and Slough Ridge and slough landscapes are characteristic of the Everglades. They are defined by long, regularly spaced ridges of sawgrass that extend across a marsh in a linear fashion and are separated by interconnected wet sloughs and scattered tree islands (SCT, 2003). Major changes in the conditions of ridge and slough pat- terns can occur surprisingly quickly—within a decade—in response to changes in water depths and flow if the surface retains its underlying microtopography (Armentano et al., 2006; Sklar et al., 2009b). For example, Armentano et al. (2006) showed that within Taylor Slough, vegetation transitions between ridge FIGURE 4-10 Tree island trends between 1940 and 2004. SOURCE: F. Sklar, SFWMD, personal communication, 2010. Figure 4-10.eps bitmap

OCR for page 112
140 Progress Toward Restoring the Everglades and slough communities occurred within a few years of building and operating the S-332 pump. The causes of pattern changes (Figure 2-13) are uncertain, but analyses suggest that local factors rather than regional factors are responsible, particularly water depth, flow, elevation and vegetation patterns, and the trans- port of sediment (Chapter 6). It can, however, take decades to centuries for flows across peatlands to rebuild the ridge and slough configuration of the topography (Willard et al., 2001). Long-Term Peat Loss Between 1950 and 2000 the Everglades Protection Area lost roughly 28 percent of its peat soils by volume due to drying, oxidation, and burning (Figure 4-11). That loss has been especially pronounced in northern WCA-3A, WCA-3B, and northeast Shark River Slough. As a result, soils in northern WCA-3A are now shallower (average depth <2 feet), denser, and have lower organic matter content than any other region of the WCAs (EPA, 2007). Even if the water flows were restored to these areas, rebuilding this lost peat and associated soil biogeochemi - cal and ecosystem properties would take centuries. These losses have important implications for the maintenance of landscape features and characteristic veg- etation in these areas. The loss of peat thickness has several important effects on Everglades landscapes, including increased exchange of surface water and groundwater with chemical and hydrologic consequences; and, as mentioned above, the loss of peat represents the loss of the substrate required to build and maintain the ridge and slough landscape. It also results in loss of elevation and therefore increases flooding depths and durations. Balancing Multiple Restoration Objectives for WCA-3 As is discussed previously in this chapter, managing water upstream of the Tamiami Trail in WCA-3 and downstream in Everglades National Park to promote the restoration of multiple species and multiple ecosystem restoration objectives in both areas has proven to be problematic over the past five decades. Excessive drying or flooding has resulted in peat loss from subsidence and wildfires, loss of tree islands and encroachment by shrubs into emergent wetland habitats, loss of characteristic ridge and slough topography, and declines in snail kites in WCA-3. Similar problems have occurred for these same ecological features and the Cape Sable seaside sparrow (see Chapter 2) in Everglades National Park. Restoration success for both units is inextricably bound because flows in Ever- glades National Park and WCA-3 are interdependent because of their adjacent geographic locations. In this section, the committee discusses ways to balance the multiple restoration objectives for both WCA-3 and Everglades National

OCR for page 112
Challenges in Restoring Water Timing, Flow, and Distribution 141 FIGURE 4-11 Soil thickness at 867 locations measured between 1995 and 2005, contrasted against thickness from 1946 as shown in inset map. SOURCE: Scheidt and Kalla (2007). Figure 4-11.eps bitmap Park by examining long-term and near-term implementation issues in relation to CERP and non-CERP projects and by articulating conflicts among the hydrologic needs of species that could be evaluated and tradeoffs that could be analyzed (see also NRC [2005] for discussion of tradeoff analysis). The committee also considers the prospects for making management operations more responsive to real-time ecological conditions. Several CERP and non-CERP projects aim to improve the hydrologic con- ditions in WCA-3, although benefits from the largest projects (i.e., Decomp, L-31N Seepage Management) are roughly a decade away. In Box 4-3 near-term

OCR for page 112
142 Progress Toward Restoring the Everglades non-CERP and CERP projects affecting WCA-3 and Shark River Slough are sum- marized. As described in Chapter 3 and above, these near-term projects will shift more water flow to the east, allow increased conveyance from WCA-3A into northeast Shark River Slough (NE-SRS), and increase the capacity for fresh- water inflows to NE-SRS via the Tamiami Trail road raising and 1-mile bridge construction. These projects will thereby improve hydrologic conditions in NE-SRS and will partially mitigate flooding problems in southern WCA-3A and western Shark River Slough. In addition, Taylor Slough wetlands should experi- ence improved hydrologic regimes, and damaging flood releases to Florida Bay should be reduced. Discharging more water south of Tamiami Trail into NE-SRS could increase the frequency and intensity of drought, peat loss, and vegetation change in northern WCA-3A, if these near-term projects are not accompanied by increased inflows into WCA-3. Even assuming that the current Integrated Delivery Schedule can be maintained and that water quality issues can be addressed (see Chapter 5), it will be at least 10 and possibly 25 years before significant new water can be provided through WCA-3 or via an eastern flow-way. In the meantime, the Florida snail kite population appears to be at high risk of extinction (Martin et al., 2007), precipitating a management crisis before CERP restoration measures are in place. In the interim, it is important to find near-term ways to improve water BOX 4-3 Near-Term CERP and Non-CERP Projects Affecting WCA-3 and Shark River Slough Projects currently scheduled for completion by 2013 will • restore flow connections between Water Conservation Area (WCA)-3A and northeast Shark River Slough (NE-SRS) by bridging and raising the Tamiami Trail (Mod Waters 1-mile bridge, under construction); • degrade L-67 and L-67ext levees in WCA-3 and NE-SRS (Mod Waters, partially completed) to re-connect WCA-3A and -3B and improve surface-water distribution in NE-SRS; • install new conveyance and seepage control structures in L-29 and L-67 levees to manage flow connections between WCA-3A, WCA-3B, and NE-SRS (Mod Waters, partially completed); • provide flood control in the 8.5-square-mile area (Mod Waters, completed); • manage eastward seepage with the S-356 and S-357 pump stations (Mod Wa- ters, completed but not operating); and • develop and implement an operating plan for moving water from WCA-3A to NE-SRS (Combined Structural Operational Plan).

OCR for page 112
Challenges in Restoring Water Timing, Flow, and Distribution 143 management practices, where practicable, to maximize restoration benefits and minimize further long-lasting impacts to these areas. These near-term efforts should make use of quantitative tools to estimate the likely reproductive success, survival, population size, condition, or extent for critical ecosystem components (e.g., snail kites, cape sable seaside sparrows, tree islands, ridge and slough patterns) under current and near-term projections of hydrologic conditions and should use the results of such analyses to inform management decisions. Near-Term Operational Improvements Examples of management refinements that could benefit WCA-3 are the implementation of a new rainfall-driven flow formula for Zone E releases (see Appendix D) to Everglades National Park and more flexible scheduling of S-12 gate closures under the IOP. These alternatives, described in more detail below, are being considered as part of the Everglades Restoration Transition Plan (ERTP), a multi-agency effort3 to improve water management operations concurrent with the November 2010 expiration of the biological opinion that imposes the current IOP regulation schedule (see also Chapter 3). Since 1985, Zone E water deliveries from WCA-3A to Shark River Slough have been managed to mimic pre-drainage flow timing and volume expected from rainfall based on a simple linear regression model. This “rainfall formula” operates once water levels in WCA-3A fall below flood control levels. The allocations are based on observed flow responses to rainfall and evaporation in WCA-3A during a 1941-1952 reference period. The formula is calculated weekly, and water is released through the S-12 structures to northwest Shark River Slough (NW-SRS) or via the S-333 gated spillway to the L-29 Canal and southward via culverts under the Tamiami Trail. Recently, hydrologists at the SFWMD have developed a non-linear neural network model that outperforms the existing regression model in forecasting stage response to rainfall in WCA- 3A and allows managed flows that are much closer to pre-drainage hydrology (Neidrauer et al., 2007; Ali, 2009). Even using existing control structures and operating constraints, the new rainfall formula provides improved stage forecasts that allow more rain-driven flow to Everglades National Park, resulting in a 10 percent increase in total flow to Shark River Slough and a 34 percent increase to Northeast Shark River Slough compared to the existing formula, mostly in the dry season from November to January (Neidraurer, 2009). These changes come with a slight increase in duration of low stages in The main participants have been the SFWMD, U.S. Fish and Wildlife Service, the USACE, Ever- 3 glades National Park, the Florida Fish and Wildlife Conservation Commission, and the Miccosukee Tribe.

OCR for page 112
144 Progress Toward Restoring the Everglades WCA-3A and an increase in loading of total phosphorus to Everglades National Park, once again pointing to the multiple tradeoffs associated with changes in water management. Analyses are not available to date, however, to determine whether the new rainfall formula will promote recovery of the most endangered species in WCA-3 and Everglades National Park (kites and sparrows) or how well it supports other Everglades wildlife and ecological functioning. Moreover, in the absence of historical stage or flow data for comparison, evaluation of the efficacy of the new rainfall formula is based on comparison with recent version of the Natural System Model, which has considerable uncertainty in performance as discussed earlier in this chapter. Nevertheless, the new approach to managing rain-driven flow may be a promising way to improve water management and to deliver restoration benefits quickly prior to full project construction. The new formula could yield even greater benefits with the completion of Band 1 projects (Neidrauer et al., 2007). Given the constraints, the proposed operational changes at minimum are not expected to perform any worse than the existing operations plan (IOP) (T. Hopkins, FWS, personal communication, 2010). Within the ERTP effort, water managers and biologists are also reconsider- ing the management of the S-12 structures that discharge water from southern WCA-3A into NW-SRS. As discussed above, the opening and closing of those structures has been on a rigid calendar schedule to avoid flooding Cape Sable seaside sparrows during the nesting season, but this schedule has seriously impacted southern WCA-3A through excessive high water and rapid draw-down. The ERTP team is considering a more flexible approach to S-12 operations that responds to the actual nesting behavior of Cape Sable seaside sparrows in Ever- glades National Park in a given year while also addressing resource concerns in WCA-3, such as those related to snail kites and tree islands. This more nuanced water management, combined with the new rainfall formula, could provide bet- ter water distribution and depths, balancing the needs of multiple species and ecological objectives. System operations is also being improved through continuation of biweekly phone consultations among scientists and managers. These operations consul- tations consider recent precipitation and water levels across the South Florida ecosystem as they relate to target species and ecosystems and provide for real- time adjustments to operations as needed to address flood control and water supply demands, while striving to maintain optimal water management for multiple species. The calls have become more formalized over time, and each participating agency4 now provides written recommendations for operations in advance of the call based on the specific needs of the target species or landscape Typically including, but not limited to, the U.S. Fish and Wildlife Service, Everglades National 4 Park, the USACE, the SFWMD, and the Florida Fish and Wildlife Conservation Commission.

OCR for page 112
Challenges in Restoring Water Timing, Flow, and Distribution 145 components. This information is then used by USACE and SFWMD operations managers in their water management decisions. The ERTP team has encouraged the USACE and SFWMD to document the water management decisions made, so that the results are available for analysis to learn about and improve upon system operations. These regular multi-agency consultations are a first step toward multi-species adaptive management, which is essential to restoration progress. They represent a change in the way the agencies have interacted in the past and especially in the consultation process for the U.S. Fish and Wildlife Service (FWS). Under the ERTP, consultation has moved from a retroactive process that often evaluates the ecological effects of proposed water management on listed species to determine if a jeopardy decision would occur, to a more proactive process that attempts to recover species before further population declines accrue. The committee commends this incremental multi-agency approach to improve water manage- ment and ecological conditions in WCA-3 during the transition period before significant new storage and conveyance features are built. This represents a form of incremental adaptive restoration, as proposed by NRC (2007). However, it is important that the CERP agencies seize the associated opportunities for learning from these flow modifications, so that the information can be incorporated into future system improvements. Tools to Support Multi-Objective Management and Tradeoff Analysis The efforts described in the previous section would benefit from a more rigorous basis for analyzing the species and ecosystem tradeoffs, which is dis- cussed in this section. The need to develop and use tools and analyses, including examples, was discussed in NRC (2005). However, currently there are no formal decision-making tools for managing multiple species in South Florida (NRC, 2008). Multi-species and multi-objective management appears to be limited to the aforementioned interagency phone consultations to discuss possible current and future improvements to water management operations. Missing from this process are decision support tools that integrate the effects of water management decisions on multiple species and ecosystem components such as tree islands. These tools will have an especially important role to play in planning water management over the next several decades, as we await the decompartmental- ization of WCA-3A and the new water sources and storage options to provide the flows needed for restoration. The process of consultation and decision making would also benefit greatly from a clear articulation of where the hydrologic needs of Everglades target spe- cies and ecological features conflict. Because these species have life histories that have been shaped by the seasonal rhythms of water level rise and fall in

OCR for page 112
146 Progress Toward Restoring the Everglades the Everglades, it has been suggested that the water management needs of key endangered species are compatible to the point that a single water management schedule would suffice for all (SEI, 2007). This might have been true before the Everglades was reduced in area and the flows were modified, but the popula- tion crash of snail kites, the fluctuations and recent expansion of wading birds, and the stability of Cape Sable seaside sparrows over the past decade suggest otherwise. Moreover, there is evidence that hydrologic needs of key Everglades species sometimes conflict. For example, nesting success of snail kites is nega- tively related to the rate of water recession during the breeding season, but water recession rates are positively related to the nesting success for wading birds (Frederick and Collopy, 1989). Initiating water recession in WCA-3 in October, which has been suggested to ensure the high concentrations of aquatic prey that are required by wood storks, would be unlikely to maintain the areas of flooded emergent vegetation that are required by snail kites for nesting from February through May (SEI, 2007). Conflicts between species’ hydrologic needs may also have a spatial dimen- sion that has been created by the damming effect of the Tamiami Trail. For example, opening the S-12 gates on the western side of WCA-3 earlier in the late fall or winter to release more water into western Shark River Slough would likely have adverse impacts on Cape Sable seaside sparrow subpopulation A, but it would likely reduce the degradation of tree islands and ridge and slough landscapes within southern WCA-3A that are used for nesting and foraging by wading birds and kites (SEI, 2007). Decision tools that create a common and comparable framework across species and Everglades ecosystem features are available in various forms, and they should be adapted as necessary and applied to more fully assess potential tradeoffs and to identify risks (NRC, 2005; SEI, 2007). These tools should support simultaneous evaluation of the effects of water management decisions on snail kites, Cape Sable seaside sparrows, tree islands, and other species or ecological processes of concern. To do so, these tools would need to directly or indirectly connect hydrology (e.g., water depths or stages, recession rates) to (1) habitat conditions (e.g., in the form of Habitat Suitability Index Models (HSIs). HSIs can be graphical, logical, or mathematical models based on species- habitat relationships that can be tested and continually improved; (2) specific demographic rates in the form of statistical models. For example, several snail kite demographic traits related to hydrology in WCA-3 that could form the basis of a demographic model are demonstrated in Figure 4-9; and (3) rates of population change in the form of population models that inte- grate the effects of hydrology on changes in population size or on multiple

OCR for page 112
Challenges in Restoring Water Timing, Flow, and Distribution 147 demographic traits that are used to calculate population change with matrix population models. Tools would provide ways to weight the relative values of performance met- rics, species, or features to quantify tradeoffs. While different kinds of decision support tools could be used for different species or processes, their results would be integrated. Using multiple models of differing complexity for the same species or features allows the triangulation of inference about management options and is increasingly seen as a useful approach to support decisions. Science managers and restoration decision makers should also take advantage of tools that already are in use, evaluate their relevance to this situation, and adapt them as needed. CONCLUSIONS AND RECOMMENDATIONS The reduced extent, altered topography, and reduced storage of the mod- ern Everglades make it infeasible to achieve the same degree of restoration throughout the remnant system. Hydrologic conditions may even worsen in some areas in order to achieve desired outcomes in others. In particular, northern WCA-3A and -3B have experienced substantial drying, peat loss, and subsid- ence, which makes it challenging to maintain suitable water flow, levels, and hydroperiods there. Hydrologic interdependencies of regions within the Everglades and the associated ecological tradeoffs that result from restoration and water manage- ment decisions need to be rigorously analyzed from a whole-system perspective and clearly communicated to decision makers and stakeholders. The CERP lacks a formal approach for evaluating in a transparent way the systemwide benefits of alternative restoration plans or policies, although RECOVER scientists have made good use of hydrologic models and performance measures to evaluate the design and staging of the CERP. RECOVER, in collaboration with water managers and decision makers, should develop evaluation methods to quantify and integrate across the tradeoffs required to sustain Everglades’ species and features to assess the systemwide restoration benefits. Any consideration of the ecological risks associated with water management should consider the timescales over which adverse ecological outcomes might be reversible, if they are at all. Increasing water storage (and associated water quality treatment) is a major near-term priority. Over the next 5–10 years, CERP and pre-CERP proj- ects will improve the conveyance and distribution of water in southern WCA-3A and Everglades National Park. But until additional water of sufficient quality becomes available, the restoration benefits will be modest and could result in shorter hydroperiods and more severe dry-down events in northern WCA-2A and northern WCA-3A. The IDS does not currently have a plan for water storage

OCR for page 112
148 Progress Toward Restoring the Everglades to support planned projects in the remnant Everglades ecosystem, aside from the stalled EAA A-1 Reservoir, and the benefits of the EAA A-1 Reservoir to the remnant Everglades remain unclear. WCA-3 is a growing focus of public controversy and management concern because of its location and the way the entire system is operated to manage water distribution and quality. WCA-3A supports extensive and relatively intact landscapes including ridge and slough patterns and tree islands and provides critical habitat for endangered species, such as the snail kite and wood stork. It is the homeland of the Miccosukee Tribe of Indians and supports the tribe mem- bers’ traditional and contemporary lifestyles. Over the past decade, however, there have been drastic declines in snail kite numbers and nesting success in WCA-3A, as well as continued slow declines in tree island size and number. The imminent loss of the snail kite from WCA-3A may precipitate a crisis in water management. To some degree, this situation has been exacerbated by the cur- rent operation of the compartmentalized Everglades that alters flows across the Tamiami Trail to restore Cape Sable seaside sparrows and ecosystem functioning in Everglades National Park. In light of the rapidly deteriorating conditions in WCA-3A, improvements in operations could lead to important near-term restoration progress. The committee commends the cooperative, multi-objective approach to improve near-term operations that is reflected in the ERTP and encourages continuation of this approach, supported by rigorous scientific analysis and decision tools, beyond the November 2010 end point. This process has the potential to align water management in the water conservation areas with a schedule that responds more flexibly to real-time conditions. Improved species models and multi-objective decision analysis tools are urgently needed to provide more rigorous scientific support for water man- agement decisions. Multi-objective decision tools can be used to help evaluate hydrologic effects and water-level management options on threatened species, ecosystem features such as tree islands, and critical ecosystem processes.