Data Collection at Data Collection at U.S. Geological Survey U.S. Geological Survey

Stream GagesStream Gages

Antietam Creek nr Sharpsburg, Md.

The first USGS gaging station was established on the Rio Grande near Embudo, New Mexico in 1889.

Embudo trainees dispersed to collect data in other locations

Streamflow Measurements in the East

“Flood Crest March 18, 1936”

Potomac River at Chain Bridge nr Washington, D.C.

Potomac River at Point of Rocks, Md.

1889

1994

The Embudo LegacyData collected using nationally consistent, prescribed

standards

. The U.S. Geological Survey currently collects

streamflow data at over 7,000 sites

Potomac River at Little Falls nr Washington, D.C.

Minebank Run at Loch Raven, Md.

Data from over 18,500 locations can be analyzed with confidence

The basic piece of data collected at gaging

stations is stream STAGE (water level)

Stage can be sensed usingSTILLING WELLS

Outside reference gages

Intakes

Little Patuxent River nr Guilford, Md.

Stage can also be sensed using PRESSURE TRANSDUCERS

Orifice LineOrifice Line

Gwynns Falls at Washington Blvd. at

Baltimore, Md.

Stage is usually:

•Measured to an accuracy standard of:

“either 0.01 ft or 0.2 percent of the effective stage being measured” -- Office of Surface Water memorandum 93.07

•Recorded every 15 minutes

Basic Data Recorder

Most users of streamflow

information need to know the

DISCHARGE of the stream

Discharge usually measured using the

velocity-area method

Channel Cross Section

Discharge= Velocity x Depth x Width

1

10

100

1 10 100 1000 10000 100000

Discharge (cfs)

Sta

ge

(ft)

Rating Curve

Discharge Measurements

Discharge measurements are used to develop rating curves

Discharge must be measured at all stages

1

10

100

1 10 100 1000 10000 100000Discharge (cfs)

Sta

ge

(ft)

Discharge measurements during high stages are particularly important

Indirect measurement

To maintain ratings,

discharge must be measured

regularly

1

10

100

1 10 100 1000 10000Discharge (cfs)

Sta

ge

(f

t)

For example: rating changes as channel fills.

Staff gages can be damaged

Datum must be checked regularly

Benchmark at a station

Surveying crew from Utah District Gage houses settle

Jack DoyleBoise Field Office

By local office personnel

All gaging station data are checked and reviewed regularly

And by national review teams

Data from USGS gaging stations can be used to meet a variety of needs

Data from Thomas and Wahl, 1993

Current needs

Modeling and floodforecasting

Chesapeake Bay inflow

Susquehanna River at Conowingo, Md.

Long-term needs

Regional relations

Uses of Streamflow Information:Flood Frequency Analysis

Rank Year Peak 1 1993 10,500 cfs 2 1995 3,200 3 1988 2,340 4 1989 1,850 5 1997 1,230 6 1990 948 7 1992 550 8 1996 320 9 1991 200 10 1994 163

100

1000

10000

100000

0.010.1110100

Exceedance Probability

Dis

char

ge,

in

cfs

100-yearflood

Data dissemination

http://water.usgs.gov

http://md.usgs.gov

Data dissemination

Hydrologic Stations

GOES

Wallops, VirginiaCommand and DataAcquisition Center

DOMSAT

User Operations

( Internet )

Stage

http://water.usgs.gov

Post-mounted gage houseand sattelite antenna

USGS continues to pursue use of new technology

Acoustic doppler currentprofiler being used in Idaho

Aquacalc being usedto collect discharge information