The South Florida Water Management District operates one of the largest regional water management systems in the world. With more than 1,600 miles of canals and 1,000 miles of levees/berms, 60 pump stations, and more than 500 structures and 700 culverts, the District actively operates and maintains the water management system to protect regional water supplies and provide flood control for 7.7 million people – plus the environment, agriculture, businesses and visitors – in South Florida. Weather extremes, ranging from droughts to hurricanes, can dramatically affect South Florida's water supply and flood protection actions.
Engineers, meteorologists and water managers monitor weather and water levels 24 hours a day. They use data and computer models to determine optimal operation of the hundreds of water control structures thoughout the system.
Operational Planning includes the review and development of operating protocols and plans, coordination with District groups and the U.S. Army Corps of Engineers regarding Operating Manual review and development. Operational Planning uses the current state of the system (Lake Okeechobee levels and groundwater levels) as input to the South Florida Water Management Model (SFWMM). A suite of graphics are produced for the decision makers to analyze. The application involves the investigation of potential areas of flexibility in the South Florida Water Management District water control system operational guidelines and federal regulation water level schedules. The objective is to improve the water resource evaluation tools available to water managers to develop a comprehensive set of operational performance measures and to provide a forum for public input to operations.
Position Analysis is a special form of risk analysis evaluated from the "present position" of the system. Its purpose is the evaluation of water resources systems and the risks associated with operational decisions (Hirsh 1978; Smith et al., 1992). This evaluation is accomplished by estimating the probability distribution function of variables related to the water resources system, conditional on the current or a specified state of the system.
Interpreting the Quantile Graphics Produced by the Position Analysis Simulation
SFWMD produces quantile graphics for several significant water bodies, canals and gauge locations. The lines can also be called "iso-percentile lines". These graphics represent a statistical summary of the simulated stages for a given location. They provide the probability of the stage being below a given value, for every day of the year, based on a current initial stage and the rainfall regime experienced by that feature each year for the 41-year simulation period, running 365 days from initialization. For instance, for all the stages shown on the 80% line, the probability of being below that stage is 80%, while the probability of being above is 20%. The 50th percentile is the median stage each day, thus half the years on that day were above that value and half were below. One shouldn't expect that a given iso-percentile line comes from a single simulated year. They are usually formed with values coming from different years. This provides a useful probabilistic indication of where the stage level could go. It is reasonable to accept that above-average rainfall at a given location will lead to higher than median stages in that area, but there is no one-to-one relationship between rainfall and the stage values. Other factors are involved, not least of which is the management criteria for moving water through the system.
Climate prediction at extended range (beyond several days) is an emerging area of science. A basic goal of this science is to identify regions and time periods where climate shifts in terms of average conditions and the potential for extreme events is significantly increased (or decreased). In considering problems in weather and climate prediction, it is vital to recognize that weather is governed by chaotic dynamics, so that small differences in initial states, can eventually lead to large differences in the atmosphere's behavior.
As a consequence, the ability to predict the precise sequence of weather events is intrinsically limited. Tentative estimates place an average upper bound for skillful weather prediction at a few weeks, but exceptions extending beyond this range can be found.
But does this mean that beyond some time period, say a month, all hope for useful predictions is lost? Emphatically not, if instead of attempting to predict the precise sequence of events (today will be fair, tomorrow rainy, etc.), the goal is changed to attempting to predict the relative likelihood of various kinds of events. At the heart of climate prediction, then, is the problem of determining how the probability distributions of various quantities, such as temperature and precipitation, will change in a particular region given the initial state and trends of the global climate systems including the effects of interactions of various atmospheric and oceanograhic phenomena. Climate shifts may occur on many time scales ranging from one month to many centuries.
A new, interim regulation schedule for the management of Lake Okeechobee water levels was approved by the South Atlantic Division of the U.S. Army Corps of Engineers on April 28, 2008. The new Lake Okeechobee Regulation Schedule, named LORS2008, replaces the regulation schedule known as WSE (Water Supply/Environmental), which had been in effect since July 2000. One of the primary objectives of the new schedule is to manage lower lake elevations to reduce risk to the Herbert Hoover Dike and to lessen the likelihood of high damaging discharges to the Caloosahatchee and St. Lucie estuaries.
The LORS2008, like its predecessor WSE, incorporates tributary hydrologic conditions and hydrologic outlooks into the operational guidance using two Release Guidance Flow Charts. One flow chart guides the determination of discharges to the Water Conservation Areas (Part C), while the other flow chart helps to determine discharges to the estuaries and to tide (Part D). The operational flexibility of the LORS2008 schedule allows for adjustments to be made in the timing and magnitude of Lake Okeechobee regulatory discharges derived from hydrologic conditions in the lake tributary basins and based on climate and hydrologic outlooks.