Natural System Models: NSM and NSRSM

The Natural System Model (NSM) and Natural System Regional Simulation Model (NSRSM) simulate the hydrologic response of a pre-drained Everglades system. The NSM and NSRSM do not attempt to simulate the pre-drained hydrology; the data necessary to perform such a simulation are not available. Rather, the use of recent climatic data (e.g., rainfall, potential evapotranspiration, tidal and inflow boundaries) allows for meaningful comparisons between the current managed system and the natural system under identical climatic conditions.

Prior to major drainage activities in south Florida that began in the late 1800s, the Everglades (south of Lake Okeechobee) consisted of approximately 4 million acres of subtropical wetlands and slow sheetflow that covered much of south Florida. This immense wetland system spread from the south shore of Lake Okeechobee to the mangrove estuaries of Florida Bay and the Gulf of Mexico. The Immokalee Ridge to the west and the coastal ridges to the east generally mark the hydrologic boundaries of the historic Everglades, although numerous connections through the coastal ridge overflowed from the Everglades to the Atlantic Ocean.

In the early and mid-1900s, construction changes in the Kissimmee basin removed significant regional storage upstream of Lake Okeechobee. Regional drainage improvements reduced the lake's surface area and lowered the depth. South of the lake, construction of the East Coast Protective Levee system in the Everglades (Water Conservation Areas) reduced the overall natural area by one half and constrained water flow south from the lake. Today, water managers are challenged with moving vast volumes of water within a much smaller, managed system.

Natural system modeling, in combination with other adaptive management tools, is being used to formulate restoration plans. Recent technological advances and improved knowledge of the natural systems have resulted in the implementation of the "next generation" Natural System Model (NSM) called the Natural System Regional Simulation Model (NSRSM). More details on the NSRSM can be found in the links below.

Summary of the NSRSM

Technological advances in hydrologic modeling at the South Florida Water Management District resulted in the development of the Regional Simulation Model (RSM). The RSM is a finite-volume based computer model that simulates multidimensional and fully integrated groundwater and surface water flow. The RSM Hydrologic Simulation Engine (HSE) is proven highly effective in modeling the processes influencing natural system hydrology in south Florida – a rainfall-driven system characterized by slow overland flow through flat but microtopographically varied landscapes, prolonged recession associated with storage and seasonally fluctuating water levels tuned to south Florida's subtropical climate. Application of the RSM to south Florida's Kissimmee-Okeechobee-Everglades and adjacent Big Cypress Predrainage watersheds is referred to as the Natural System Regional Simulation Model (NSRSM).

A comparison of input and output for the NSM and NSRSM was performed. The document can be downloaded under "Key Links" at the bottom of this page.

Using model results

Careful consideration should be exercised when applying model output. It is recommended that output be used in conjunction with other models, studies and information to suggest how depths, flows and hydroperiod patterns may have changed. The changes in depths, flows or hydroperiod patterns should be reported as a range of values, not as a single value.

The NSRSM is not designed or intended to be used in isolation to make future water management decisions. The model is primarily designed for use within an adaptive management framework to help understand the conditions and factors that gave rise to predrainage soils and plant communities. It is a guide to restoration planning and a means to help predict outcomes of restoration activities.

A Peer Review Panel was convened to review the technical basis and appropriate use of the NSRSMS. The panel indicated that one of the most useful applications of the NSRSM is as a tool to help guide future inquiries about the Everglades system. This would occur when model results do not coincide with an evaluator's preconceived notions of the condition(s), thus stimulating investigation. The NSRSM should be used in an adaptive management framework to help guide management experiments aimed at restoring hydrologic regimes and ecological function.