Application of Natural Systems Models in Estuaries
The natural systems models may not initially provide flow rates for precise locations.
Therefore, we here provide a process for using the natural system model output to estimate
freshwater releases to estuaries.
Schedule water releases according to a rain-driven water inflow formula that
establishes a time series of daily average flow rates whose frequency distribution has the
same general characteristics as flow rates simulated by the natural systems model with the
same time series of rainfall.
Calibrate the raindriven formula so that (1) the distribution of wet season daily
average flow rates is centered around the flow that creates salinities naturally prevalent
in the particular estuary during the wet season and (2) the distribution of dry season
daily average flow rates is centered around the flow rate that creates salinities
naturally prevalent in the particular estuary during the dry season. For most South
Florida estuaries, natural wet season open water salinities probably were centered around
a spatial gradient across the estuary from 18-30 ppt and natural dry season open water
salinities probably were centered around a gradient across the estuary from 25-36 ppt. In
the natural system, salinities in the mangrove zone probably graded from 0-18 ppt to 10-24
ppt during the wet season and 0-25 ppt to 10-30 ppt during the dry season.
When the information becomes available, one can use the output of the natural system
model to determine the modes (in terms of cubic feet per second) of wet season (June-Nov)
and dry season (Nov-May) frequency distributions of daily average flow rates. An estuarine
salinity and circulation (hydrodynamic) model driven by the output of the natural system
model, could approximate natural salinity patterns in an estuary as a function of current
rainfall.