Ecologic and precursor success criteria for south Florida ecosystem restoration

A Science Sub-Group Report to the Working Group of the South Florida Ecosystem Restoration Task Force

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I. Team Members:

From the Corps of Engineers: Ron Hilton, Mike Choate, and Richard Punnett.
From the South Florida Water Management District: Jayantha Obeysekera, Cal Niedrauer, and Randy Van Zee.
From NOAA: Joan Browder.
From USGS: Aaron Higer.

II. General Rationale.

At the present time, the output from the Natural System Model (NSM) represents the best estimate of the hydrologic response to climate in South Florida under predrainage conditions. The NSM current period of record is 1965-1990. In order to accomplish the restoration success indices for reinstatement of natural hydropatterns1 and sheet flow throughout the system as approximated by the NSM, the SFWMD must update the NSM as soon as possible. At the present time, a score cannot be calculated for extraordinarily wet years such as 1994 and 1995. The SFWMD currently has plans to update the period of record to include 1994 and possibly 1995.

Since the restoration effort will affect several diverse habitats (e.g. sloughs, bays, wetlands, and uplands), the hydrologic indices for different geographical areas for potential restoration will likely be different. The Taylor Slough area is the first of the areas where restoration effects can be measured. Water releases into Taylor Slough will be scheduled on the basis of a rainfall driven formula for Taylor Slough that gives stages at selected locations. For comparison purposes, the NSM will be used to develop data for the rainfall formula. It is very important that the rainfall formula in the form of regression models include both daily rainfall and antecedent conditions. Monitored areas or cells will be selected where well data currently exists or where wells will be installed.

III. Recommended Specific Success Criteria:

Specific Indices:

Targets (i.e. preferred conditions) will be based upon a rainfall formula for Taylor Slough (recently developed by Tom Van Lent under contract by the NPS). Indicators will be used to compare observed data to modeled predrainage stages using a nearness of fit approach. Specific indicators for Taylor Slough that can be compared are as follows:

Index 1:
The hydraulic gradient within the ENP relative to ENP boundaries indicating the general direction of surface and groundwater flow. The index would be related to the number of days per year when the gradient is consistent with the predrainage pattern.
Index 2:
The rate of recession at selected sites during dry seasons.
Index 3:
Compare observed water levels (stages) and changes to those predicted by the rainfall formula. The index would be related to the number of days per year when water levels are consistent with historical hydropatterns.
Index 4.
Restore more natural flows across the L-28 levee. The index should be related to a rainfall formula which will replicate flows or stages consistent with the NSM.
Index 5.
Restore hydropatterns in northern WCA 3A. The index should be related to depth of water in the range and seasonally as indicated by the NSM. The index will have to be related to a rainfall index or else NSM will have to be updated to cover the monitoring period.
Index 6.
Restore hydropatterns in NE and Western Shark River Slough. The index should be related to depth of water in the range and seasonally as indicated by the NSM. The index will have to be related to a rainfall index or else NSM will have to be updated to cover the monitoring period.
Index 7.
Restore more natural flows to the Caloosahatchee and St. Lucie Estuaries. The index should be related to a rainfall formula which will replicate flows consistent with the NSM. Since the historical flow from Lake Okeechobee to the St. Lucie Estuary did not occur, the target could be zero. However, if attenuation facilities are developed in the St. Lucie basin, some lake releases could be beneficial.

IV. Supporting Information Needed

Each of the specific indices requires development of a suitable rainfall formula as the basis for comparison. It is assumed that these relationships will be possible. A scientific approach should insure that the relationships are also valid.

V. Other Potential Success Criteria

This section was divided into two subsections for indices that had a good probability for being developed, and indices that had no clear basis of establishing a target. All the indices listed were considered important, but the likelihood of establishing valid criteria was uncertain.

Potential New Indices:

Analyses of available data are needed to develop direct indices of freshwater flow to Florida Bay. It is recommended that freshwater flows into Florida Bay at Taylor, Alligator, and McCormick Creeks, as well as from Joe Bay, be used as indicators. The relationships must be developed between freshwater flow characteristics at these locations and upstream well stages. Then, standards or targets for the rainfall pattern of a given year, or set of years, can be developed based on modeled predrainage hydrologic conditions. It is further recommended that "annual number of days with zero flow, for each creek" be the statistic to be used as the basis of the index. Each index would then be closeness of fit to the standards or targets. In collecting field data, the salinity of creek flow is being measured to determine where there is any freshwater influence, because tides and winds influence flow through these creeks and flow can occur when there is no freshwater inflow. This must be taken into account when computing the index from actual data.

Changes made to WCA 1 and 2A as a result of regulation schedule changes should be evaluated. Since the changes were not a result of trying to meet specific targets, it is not clear what the target should be. Both elevation and fluctuations were not targeted to be "natural." However, it may be desirable to compare the results to a rainfall index derived from the NSM.

Future changes to the L-67 levees will result in changes in temporal and spatial stages within WCA 3A and 3B. If the changes are made to improve hydropatterns, then a rainfall index (based on the NSM) would be appropriate. If the changes are made to support flows into the Park, the same index may be useful but would not be sufficient in itself to indicate success since flows into the ENP need to be included.

Lake Okeechobee represents a case that will never be restored to "natural fluctuations." Water supply and flood control will always be important. An index needs to be developed which will indicate littoral zone success while allowing greater than historic fluctuations patterns.

Water Preserve Areas (a.k.a. Buffer Strip) are still in need of definitions of size and function. While seepage will probably be an important feature, there is an opportunity to create wetland functions. As these areas are being designed, hopefully environmental features will be planned and then success indicators can be developed.

Desirable New Indices:

S-65 releases (from Lake Kissimmee) should be regulated to mimic historic patterns. However, since the NSM does not cover that area, the index could be related to the "restoration criteria" used for the Kissimmee River restoration effort. The SFWMD is developing a plan to monitor restoration success.

Eastern discharges through LEC canals need to be evaluated for impacts on Biscayne Bay. Within the next few years, modeling information should be available for indices.

L-8 and Loxahatchee Slough areas should be considered for restoration. Since there is no plan to do so, success indicators cannot yet be developed.

VI. Scientific Support Required

For the potential indices listed above, it is uncertain that the data (available now and in the near future) and methodology will successfully produce a good basis for comparison. Until further testing of some of the hypotheses is performed, the need for future scientific support cannot be determined.

VII. Discussion

In applying rainfall driven formulas as a basis for comparison, the effect of changed boundary conditions should be evaluated. For example, flow across Tamiami Trail could be restored to historic patterns, but unless the eastern ENP boundary prevents unnatural seepage discharges to the East, ENP flows will not be restored throughout Shark River Slough. Likewise, any specific comparison should include boundary effects.

VIII. References

1. Perkins, W. A. and T. K. MacVicar. 1991. A Computer Model to Simulate Natural South Florida Hydrology, Draft report, South Florida Water Management District, West Palm Beach.

2. Van Lent, T. 1994. Calculation of a Rainfall/Stage Response Model for L 31W for the period 1970-1982, submitted to the National Park Service under contract CA5280-4-9040.

1Hydropattern includes quantity, timing, and distribution of freshwater flow.

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