Lexington, Virginia • September 12, 2011
A team of Washington and Lee students, staff, and professors worked together to install a new stream gauge in Woods Creek during the 2011 Spring Term. The instrument is located on the W&L campus behind the Woods Creek Apartments and replaces one that was washed away in a flood a number of years ago.
Meredith Townsend, of the Class of 2011, and W&L Environmental Management Coordinator Chris Wise came up with the idea to try to reestablish a gauging station on Woods Creek as a work study project. Geology professors Paul Low and Dave Harbor, geology technician Emily Flowers, and Elizabeth George, Class of 2012, with the Environmental Studies Service Learning program all helped make it a reality. The group planned the installation, purchased the needed equipment, built the structure and installed the gauge.
There are two primary reasons for having a stream gauge on Woods Creek. First, the U.S. Geological Survey (USGS) monitors stream flow conditions on three larger streams in Rockbridge County, but only one other small stream, Kerrs Creek, is monitored. Data from smaller streams is just as important to research efforts.
These streams behave differently than larger waterways, especially during flood events. In smaller streams, flood levels are much higher and rise (and fall) more quickly because the creek is unable to accommodate the large influx of water. The new gauge will contribute to understanding the behavior of smaller creeks, both locally and nationally.
Another reason for having a gauge on Woods Creek is the unique nature of its watershed. While most of the watersheds in Rockbridge County consist primarily of undeveloped land, the Woods Creek watershed has a large portion ( between 30 and 40 percent) of developed land and is the only local stream that is affected by urban development. Development usually means a loss of canopy cover and vegetation and an increase in impermeable surfaces such as roads and roofs. This results in less soil absorption of rain, quicker runoff into streams and higher water temperatures as well as more pollutants.
The newly-installed stream gauge will provide additional data on water quality in Woods Creek. These data allow for comparisons between a more developed watershed and the undeveloped watersheds like Kerrs Creek elsewhere in the county.
The new gauging station consists of a thermometer, a pressure sensor and a conductivity meter. The pressure sensor is used to measure stage (i.e., height of the water surface) and to calculate water discharge (i.e., the volume rate of water flow). As the stage rises, more water presses down on the sensor, indicating a higher water level and thus greater total discharge. The conductivity meter measures total dissolved ions, which is an indicator of overall water quality.
W&L's Low is particularly interested in how the water quality in Woods Creek will change seasonally and with various flow, pressure, and temperature levels. Monitoring how discharge and conductivity are related, as well as the frequency of large discharge events, will allow insight into factors affecting water quality in smaller streams.
The exact relationship between water pressure, stage height, and discharge for a gauging station is determined through the development of a rating curve. In order to create a rating curve, water discharge is measured during different flow levels in the creek by measuring both the cross-sectional area of the stream and the average velocity of the flow. By correlating water discharge levels with certain pressures, the rating curve allows discharge data to be determined from the gauge's pressure readings.
George has already been completed some of the rating curve, but measurements will continue to be made as an ongoing project for the department of geology in the fall of 2011. The gauge takes readings every four to five minutes, and data will be downloaded and analyzed once a month.
The stream gauge will also be used as a hands-on tool to educate students of all levels. Most professors in the geology department do a few introductory laboratories on water dynamics, often using Woods Creek as an easy-to-access laboratory. The data from the gauge will be eventually made accessible to the entire W&L community, as well as the general public.