Progress Toward Restoring the Everglades The Third Biennial Review - 2010 (2010) / Chapter Skim
Currently Skimming:
4 Challenges in Restoring Water Timing, Flow, and Distribution
4 Challenges in Restoring Water Timing, Flow, and Distribution
Pages 112-148
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 112... ...
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 112
|
From page 113... ...
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)
|
From page 114... ...
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.
|
From page 115... ...
. 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.
|
From page 116... ...
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)
|
From page 117... ...
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 rainfall in the dry season associated mainly with frontal passages, and that rain can lead to rising rather than falling water levels (i.e., "reversals")
|
From page 118... ...
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)
|
From page 119... ...
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 hydrology of the remnant Everglades ecosystem.
|
From page 120... ...
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)
|
From page 121... ...
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)
|
From page 122... ...
. The bitmap numbers in rectangles represent mean annual flow volumes in 1,000 acre-feet/year.
|
From page 123... ...
Performance measures are arranged in rows from north to south starting with Lake Okeechobee and the northern estuaries and ending with Florida Bay. The table also includes modeled ecological performance in 2015 assuming construction of the 1-mile bridge on the Tamiami Trail, new L-29 Canal stage constraints (8.5 feet above sea level)
|
From page 124... ...
Storage Reservoir Phase 1 • Lake Okeechobee Watershed Plan • Rain-driven operations in Rotenberger Wildlife Management Area • C-43 Basin Storage Reservoir Phase I TABLE 4-2 Selected Features of the Everglades Water Budget and Regional Performance ITABLE 4-2 Selected Features of the Everglades Water Budget and Regional Performance Indicators ndicators Restoration Future w/o Band 1 Projects SFWMM Future w/ Target Existing Project CERP 5.4.6 NSM v. 4.6.2 SFWMM Variable Water budget (KAF)
|
From page 125... ...
. In the Band 1 scenario, which was based on a different lake regulation schedule than is currently in use, unwanted high lake stages could increase in order to achieve other systemwide benefits such as reduced flood discharges to the estuaries and increased dry-season releases to Everglades National Park while avoiding additional cutbacks in water supply to the Lake Okeechobee service area (RECOVER, 2010c)
|
From page 126... ...
. Band 1 projects, which begin to reconnect WCA-3A, WCA 3B, and Everglades National Park, introduce increased risk of extreme high water events in WCA-3B, leading RECOVER scientists to recommend careful adaptive management of the transition to a wetter hydrologic regime in that area (RECOVER, 2010c)
|
From page 127... ...
indicate that the benefits of hydrologic restoration of the South Florida ecosystem will accrue mostly to the northern estuaries, southern WCA-3A, Everglades National Park, and eastern Florida Bay, areas where hydroecological conditions are currently far from desired conditions (Table 4-2)
|
From page 128... ...
Improved conveyance and better distribution of water in southern WCA-3A and Everglades National Park will be at the expense of shorter hydroperiods and increased risk of severe dry-down events and wildfires in northern WCA-2A and northern WCA-3A until storage is increased and water quality concerns are mitigated so that more water can be moved south from Lake Okeechobee and the EAA. It is important to recognize that it will be many years before the storage (and, by necessity, the associated water quality treatment and/or source control; see Chapter 5)
|
From page 129... ...
CASE STUDY: RESTORING WATER FLOWS IN WCA-3 The challenges of balancing competing objectives and the tradeoffs inherent in restoration are well exemplified in WCA-3. WCA-3 is central to the Everglades restoration, because it contains extensive and relatively intact Everglades landscapes, such as tree islands and ridge and slough, and it provides critical habitat for endangered species such as the snail kite and wood stork as well as nonthreatened wading birds.
|
From page 130... ...
Conflicts in the early to mid-1980s centered around the benefits of increasing flows to Shark River Slough and Florida Bay to restore ecosystem processes and recover wading bird populations (including the endangered wood stork) , and the resulting negative effects of lower water levels in WCA-3A on the
|
From page 131... ...
. Recent Water Management in WCA-3 Inflow and outflow of water in WCA-3 are regulated under the IOP by the water level targets and conditions in both WCA-3 and Everglades National Park (see also Box 4-2)
|
From page 132... ...
to prevent excessive flooding of nesting habitats for Cape Sable seaside sparrows. At lower water levels releases are determined by the amount of rainfall in WCA-3A using a simple linear regression model relating flow outflow to rainfall and evaporation.
|
From page 133... ...
© International Mapping Associates. bitmap dries out every year, water levels in the southern end have not reached average ground level since the mid-1990s.
|
From page 134... ...
Gage locations shown in Figure 4-6. bitmap top, vector bottom Major water management regimes are indicated at the top of each hydrograph and aver age ground elevation by the dark horizontal line.
|
From page 135... ...
IOP-CSOP Water Water Water Water Water Water Figure 4-8.eps FIGURE 4-8 Daily annual average and average annual minimum and maximum water levels for gauges GA-63 (northern) , GA-64 (central)
|
From page 136... ...
First, temporarily holding water behind the S-12 structures from November to April to accommodate the breeding season of the Cape Sable seaside sparrow in Everglades National Park has prolonged high water events in WCA-3A in some years, which can reduce the number of kites using this wetland and their nesting and foraging success (Darby et al., 2008; Martin et al., 2008; Zweig and Kitchens, 2008)
|
From page 137... ...
FIGURE 4-9 Relationship between water levels, nesting success, and juvenile survival of snail kites nesting Figure 4-9.eps in WCA-3A: (A) annual minimum water levels versus proportion of nests that successfully fledged at least one young (nesting success)
|
From page 138... ...
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)
|
From page 139... ...
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)
|
From page 140... ...
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)
|
From page 141... ...
Several CERP and non-CERP projects aim to improve the hydrologic conditions in WCA-3, although benefits from the largest projects (i.e., Decomp, L-31N Seepage Management) are roughly a decade away.
|
From page 142... ...
, 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.
|
From page 143... ...
. 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)
|
From page 144... ...
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.
|
From page 145... ...
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 decompartmentalization of WCA-3A and the new water sources and storage options to provide the flows needed for restoration.
|
From page 146... ...
. 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.
|
From page 147... ...
Hydrologic interdependencies of regions within the Everglades and the associated ecological tradeoffs that result from restoration and water management 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.
|
From page 148... ...
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.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.