Learn More: River Reach

What does this mean?

Streams are the heart of drainage basins and their watersheds. Water that falls to Earth or surfaces from the ground is collected by watersheds and fed into streams. Streams, whether the tiny creek in your neighborhood park or the great Mississippi River, carry life-sustaining water to wildlife, farms, towns and cities. In Florida, thousands of lakes are maintained by a combination of stream flow and groundwater upwellings called springs. Streams also replenish our groundwater. Without natural stream flows, neither our ecology nor economy could survive.

The amount of water moving in a stream is referred to as the discharge or flow. "Discharged" is preferred, as "flow" is often used as a general term when discussing the movement of water (e.g., "Did you see any flow in the creek?"). Factors that affect stream discharge include: drought; thunderstorms; hurricanes; pumping for agricultural, municipal and industrial uses; dams; destruction of watershed and recharge zones by sprawl; and other land use changes. One of the lesser known, but critically important, functions of streams is that they convey great quantities of freshwater to bays and estuaries on both the east and west coasts of Florida. Without these constant deliveries to freshwater, Florida's bays and estuaries — the spawning and nursery grounds for virtually all near-shore fish species, as well as crabs, shrimp, oysters and scallops — would perish, along with it Florida's $140 million dollars/year commercial fishing industry and burgeoning aquaculture business.

In Florida, United States Geological Survey, water management districts, Florida Department of Environmental Protection (FDEP), as well as many counties and municipalities, measure stream discharge. These entities measure stream discharge for a wide variety of purposes such as wastewater permitting, flood control, flood prediction and warning, water resource management and conservation, and wildlife preservation. FDEP established Minimum Flows and Levels (MFL) for Florida's lake and streams in order to prevent significant harm as a result of withdrawals. The water management districts are required by S. 373.042, F.S. to develop a priority list of water bodies for which they will establish MFL. Each year the districts update their list and submit them to FDEP for review and approval. A map showing currently adopted MFLs can be viewed at: https://floridadep.gov/water-policy/water-policy/content/statewide-mfl-map

In addition to reviewing the districts' priority lists each year, FDEP Office of Water Policy also reviews MFL proposals for specific water bodies. The Office actively works with the water management districts to ensure that the proposed MFL is consistent with applicable rules, statutes, and other FDEP guidance.

How are the data collected? (Methods)

Stream discharge is determined by measuring water depth and current (or speed). The combination of a depth and current measurements allows hydrologists to calculate the volume of water passing by a given point. Discharge is reported in volumetric units, such as cubic feet per second (ft^3/sec or cfs) or cubic meters per second (m^3/sec or cms). To best determine stream discharge at a given point, depth and current measurements must be made at several points along a transect; this refers to a line across the stream's channel. Measurements made at each point across the stream are then combined to provide the total "instantaneous discharge". Instantaneous discharge can also be used for continuous calculation (estimation) of stream discharge.

At many locations, USGS and others have established gaging stations (Figure 1.). Gaging is the act of measuring stage (water level), and by mathematical extension, discharge. Gaging stations are physical structures that house instrumentation that measure, at a minimum, water level and by various means record those measurements continuously. The instantaneous discharge measurements previously mentioned are used to calculate discharge from the level measurements made at the gaging station. In other words, once instantaneous discharge has been determined, one can — with the correct formula — use water level measurements to closely estimate discharge at that location.

diagram and photo of gaging station

Figure 1. Gaging station configuration and a "gage house". From USGS Circular 1123, 1995.

The instruments used for stream gaging are collectively referred to as gauges, which can include a wide variety of devices including, but not limited to, floats; pressure sensors; radar transponders, and Doppler systems. The latter of which can not only measure water level, but also depth, current and water direction as well (Note: water current combined with water direction is referred to as water velocity).

The Water Atlas (www.wateratlas.org) presents all available discharge data for counties participating in the Water Atlas Program. Typically, these reports include discharge data from USGS, the County and the water management district within which the County resides. In many cases, county's Water Atlas will also provide a near-realtime window that displaces data live from gaging stations within the County.


Caveats and Limitations

Most discharge data that are posted by USGS, Water Atlas or a water management district are posted after quality control processing. Consequently, these data are not the most recent data available for a given location. Near-realtime data are typically current with in 15 minutes to one hour, but these data have not been through quality control processes. Therefore, it is advised that, prior to embarking on a water-related activity, you call reliable sources in the area that you intend to visit for water level and other meteorological and hydrologic conditions.

Additional Information