STACK THE ODDS IN YOUR FAVOR: Taking advantage of USGS river-flow information can help paddlers plan safe and enjoyable trips

Canoe and Kayak Magazine
2002
By Jeffrey R. Deacon, Richard G. Kiah, and Michael J. Brayton

For more than 100 years, scientists have been measuring and recording the flow of water in the nation's rivers. The United States Geological Survey (USGS) is the principal federal agency providing water information to manage the nation's water resources. In 2001, more than 7,000 streamgages were operated and maintained by the USGS on rivers and streams across the United States. In New Hampshire and Vermont, the USGS continuously monitors streamflow at 97 locations. Streamflow information is used by federal and state agencies for a number of purposes including:
• forecasting floods and droughts;
• managing and operating dams and reservoirs;
• and protecting water quality.

The information is also useful for kayakers, canoeists, rafters, and fisherman.

The USGS streamgaging network provides information that can make for safer and more enjoyable outings. River-sports enthusiasts always want to know the conditions of the river when planning an outing. Streamflow data obtained and evaluated before a river trip can prevent the disappointment and loss of time associated with a long drive to a favorite spot, only to find it unwadeable for fishing or too low for a canoe trip. On the other hand, an adventurous canoeist may be willing to travel farther for a river outing, knowing that flow conditions on his favorite river are optimal. By using available information on current river flow, recreationists can plan safe trips to match the conditions of the water or to match their own abilities or skill levels.

How are Streamflow Data Collected?
Streamflow data are most commonly collected by the USGS at a streamgage along a river or stream. A streamgage house is constructed to hold equipment that measures and records the height of the water surface (stage or gage height). Stage and discharge (the rate water is flowing, reported as cubic feet per second, or ft 3 /s) are the most common ways that streamflow data are presented. The use of stage alone, however, can be misleading. Stage refers to the water-surface elevation above a fixed reference point near the streamgage. Stage readings are unique to each stream-gaging site and may not correspond directly to water depth. Never assume a stage reading is the equivalent of the distance between the water's surface and the streambed. Discharge is a more reliable indicator of the conditions that river recreationists will encounter. The discharge of the river is determined by measuring the width, depth, and velocity of the stream. To make a discharge measurement, streamgagers will often wade across small streams or larger streams at low flow. During high-flow conditions or on larger rivers, measurements are usually made from boats, cableway cars, or bridges.

Discharge values from each measurement are plotted on a graph against river stage recorded at the time of measurement to develop a stage-discharge relation, known as a rating curve, for each streamgage. A sample rating curve is shown in the graph below. In this rating curve, when stage is three feet, the corresponding discharge is 500 ft³/s. By relating stage to rating curves, a continuous record of discharge can be maintained.

Paddlers and fisherman who only monitor river stage could be misled because the stage-discharge relation changes over time. For example, a beaver or debris dam downstream from the streamgage can result in a rise in stage at the streamgage without any corresponding change in flow. Likewise, erosion of a stream channel can result in a localized lowering of stage for a given discharge. In this case, there may be enough water for a particular recreational use in spite of the low stage at the gage site. The USGS makes frequent discharge measurements to update and maintain the accuracy of the rating curves; therefore, river recreationists should learn to relate river conditions to discharges reported at streamgages.

Streamflow Data Online
Currently in New Hampshire and Vermont, all of the 97 continuous streamgages transmit near real-time data through a satellite or telephone network directly to a computer Web site. Streamflow data are updated at intervals of four hours or less and are available to the public on the Internet at: http://nh.water.usgs.gov.

Select the river of interest to determine its flow conditions. The recreationist should consider keeping notes or a logbook on conditions at various discharges on a particular stretch of the river to learn the river and plan future trips to match the skill level of interest. Learning the river by examining conditions over a range of stages and discharges helps the user to visualize the entire flow regime of the river.

Using Streamflow Information
Streamflow information available on USGS Web sites also allows river recreationists to project likely conditions of the river over several days. For example, fishermen may be interested in knowing when it is safe to wade a river after flows decline following a heavy rainstorm or snowmelt. By monitoring near real-time hydrographs (a plot of discharge in relation to time) on the Internet, fisherman can determine if the river flow is rising or falling and make more informed decisions on when it would be safe to wade the river. Paddlers who are interested in high flows can also monitor changing conditions to determine when the water is ideal for their skill level.

Streamflow data at certain streamgages can often be used as an index to determine the likely conditions on other nearby streams in the area. However, the recreationist must recognize that river drainage areas differ in size, elevations, and other characteristics. Generally, the farther away a streamgage is from the river reach of interest, the less reliable the data may be as an index. Also keep in mind that river systems change rapidly because of intense precipitation or the release of water from upstream dams. USGS real-time streamflow data on the Internet is provisional and subject to change after verification and approval by USGS personnel. It is important for paddlers and fisherman to realize that streamgages can malfunction for a number of reasons, including equipment failure, ice jams, and vandalism. Although the USGS closely monitors the data for problems with the streamgage readings, recreationists should always scout river conditions carefully upon arrival as a safety precaution. When used properly, USGS streamflow information can greatly benefit river recreationists.

Jeffrey R. Deacon, Richard G. Kiah, and Michael J. Brayton are USGS hydrologists in the New Hampshire/Vermont District who kayak, canoe, and fish for recreation in New England rivers.

E-mail contacts: jrdeacon@usgs.gov, rkiah@usgs.gov, mbrayton@usgs.gov

Related web pages:

Streamflow gaging station map and data (NH and VT)
More on how and why the USGS collects streamflow data