Hydromet Frequently Asked Questions

Does LCRA use the Hydromet information to issue flood warnings?

No, the National Weather Service issues flood warnings. LCRA supplies Hydromet data to the National Weather Service's River Forecast Center in Fort Worth to help forecasters decide whether to issue flood and weather warnings.

How many gauges are in LCRA's Hydromet network?

There are more than 275 river and weather gauges in the Hydromet network. LCRA periodically adds new gauges to meet specific operational needs.

What do the gauges measure?

The gauges measure hydrological data, including river stages, lake levels and streamflows, and meteorological data such as rainfall, air temperature and humidity.

What is streamflow?

Streamflow is the rate at which water flows, measured in cubic feet per second (cfs). One cfs is equal to about 450 gallons per minute.

What is a river stage?

Stage a river’s height, though it usually doesn't correspond with the natural bottom of the river channel since the riverbed changes over time. Instead, the stage is determined from a benchmark where all measurements are taken. Typically, the benchmark is set below the natural bottom of a channel.

What is flood stage?

Flood stage refers to the height (or stage) of a river or stream at which the water begins to create a hazard to lives, property or commerce.

How do I find the flood stage at a given location?

Find the flood stage by selecting a Hydromet site on the map while looking at Stage and Flood data. Flood stage levels are determined by the National Weather Service and the local communities. Not all locations have a predetermined flood stage level.

How often is rainfall measured?

Each Hydromet gauge reports data every 15 minutes. The Hydromet displays rainfall for various time periods, from the most recent 15 minutes up to the past two weeks.

How is rainfall measured?

Many Hydromet gauges measure rainfall by using a funnel attached to a small “tipping bucket.” Each time one-hundredth of an inch of rain falls, the bucket tips. A computer records the number of tips or "counts."

On the rainfall pages, what does "count" refer to?

A "count" refers to one-hundredth of an inch of rain.

Counts accumulate over time at each gauge location until the count is reset. The count can be helpful in finding the amount of rainfall over a period of time by subtracting the count at the beginning of the time period from the count at the end of the time period.

What is "conductivity data" and "micromhos"?

Conductivity is one way to determine water quality and indirectly measure water salinity. The Hydromet includes instruments to remotely measure water conductivity, or the water’s ability to pass an electrical current. Higher conductivity readings can come from inorganic dissolved solids such as chloride, sulfate, sodium and calcium. LCRA installed the instruments to detect high levels of salt and other dissolved solids.

Conductivity is measured in micromhos or microsiemens per centimeter (µs/cm). At sites upstream of Lake Buchanan, normal levels are about 700 to 1,000 µs/cm, higher than in most of the lower Colorado River watershed.

Follow Gauge Data Records under Useful Links on the Hydromet page to view the Conductivity Data Report. LCRA also displays conductivity and other water quality data on the LCRA Water Quality Data page.

How often is the information updated?

Each Hydromet gauge reports data every 15 minutes. LCRA can configure gauges to report data more often during extreme conditions such as flood events.

How is the information transmitted?

The Hydromet gauges send a continuous stream of data over LCRA’s data collection network to central computers at LCRA's River Operations Center in Austin. LCRA hydrologists, engineers and other experts use the data to develop forecasts, analyze trends and share information with the public.

Have more questions? Contact LCRA through Ask LCRA.