Hydrologic Data Summary for the St. Lucie River Estuary, Martin and St. Lucie Counties, Florida, 1998-2001

A hydrologic analysis was made at three canal sites and four tidal sites along
the St. Lucie River Estuary in southeastern Florida from 1998 to 2001. The data
included for analysis are stage, 15-minute flow, salinity, water temperature,
turbidity, and suspended-solids concentration. During the period of record, the
estuary experienced a drought, major storm events, and high-water discharge
from Lake Okeechobee.

Flow mainly occurred through the South Fork of the St. Lucie River; however,
when flow increased through control structures along the C-23 and C-24 Canals,
the North Fork was a larger than usual contributor of total freshwater inflow
to the estuary. At one tidal site (Steele Point), the majority of flow was
southward toward the St. Lucie Inlet; at a second tidal site (Indian River
Bridge), the majority of flow was northward into the Indian River Lagoon.

Large-volume stormwater discharge events greatly affected the St. Lucie River
Estuary. Increased discharge typically was accompanied by salinity decreases
that resulted in water becoming and remaining fresh throughout the estuary
until the discharge events ended. Salinity in the estuary usually returned to
prestorm levels within a few days after the events. Turbidity decreased and
salinity began to increase almost immediately when the gates at the control
structures closed. Salinity ranged from less than 1 to greater than 35 parts
per thousand during the period of record (1998-2001), and typically varied by
several parts per thousand during a tidal cycle.

Suspended-solids concentrations were observed at one canal site (S-80) and two
tidal sites (Speedy Point and Steele Point) during a discharge event in April
and May 2000. Results suggest that most deposition of suspended-solids
concentration occurs between S-80 and Speedy Point. The turbidity data
collected also support this interpretation. The ratio of inorganic to organic
suspended-solids concentration observed at S-80, Speedy Point, and Steele Point
during the discharge event indicates that most flocculation of suspended-solids
concentration occurs between Speedy Point and Steele Point.

[Summary provided by the USGS.]