Monitoring a Wadeable Stream at Chattahoochee River National Recreation Area

Chattahoochee River intern Louisa Markow and hydrologic technician Daniel McCay stretch the tape across the stream while physical scientist Stephen Cooper records the channel width. Photo by Mark Hynds, National Park Service.

Surveying wadeable streams — ones that can be studied without a boat — is part of the National Park Service Inventory and Monitoring Division's work to track the condition of park resources. In May 2021, a writer who edits the program's reports joined a Southeast Coast Network team surveying a stream at Chattahoochee River National Recreation Area and described the day.

Why the streams change

The recreation area's thousands of acres of pine and hardwood forest and wetlands buffer 48 miles of the Chattahoochee River, from Buford Dam at Lake Lanier down to Atlanta. Hydropower releases from the dam and runoff from surrounding development strongly shape the flow of the river and its tributaries. Roofs, streets and parking lots change the quality, timing and duration of water reaching streams, which become "flashy": higher, faster surges in storms and lower flows in dry spells. Bigger peaks and changing water quality can destabilize banks and vegetation, and as banks erode and shift sideways they can threaten parking lots and bridges and the plants and animals living in the streams.

A natural, stable stream is in rough balance, carrying away about as much sediment as it receives. Too much or too little sediment alters aquatic habitats; excess sediment can smother them. Littering and heavy use of bike and foot trails also do harm. The network resurveys streams every few years to see what has changed.

The survey

The site was Gunby Creek, near the Cochran Shoals unit, just off a trail — its easy access was one reason it was chosen. Heavy rain had already cost the team days, since surveys need low flows. Each site has permanent benchmarks at its upstream, downstream and middle points on both banks, and 11 evenly spaced transects, imaginary lines across the stream. Finding and flagging the benchmarks came first.

The big picture. Stephen Cooper measured the tree canopy with a mirror-like densiometer upstream, downstream and on each bank, and estimated the share of each type of habitat, or geomorphic channel unit: runs (slow and shallow), riffles (fast water over rocks and other obstructions) and pools. Pools and riffles dominated. He took compass bearings between transects and four photos of each. For the pebble count, 100 randomly chosen particles of the streambed were measured in a representative riffle, which tells managers about the character of the stream bottom.

Wood. Fallen trees and branches change how water and sediment move. Pieces at least 10 centimeters (3.9 inches) thick and 1 meter (3.3 feet) long were recorded; the largest was just over 7 meters. Most were in jams or ramps leaning on the bank, which can trap sediment and change habitat for fish and insects.

Protocol author Jacob Bateman-McDonald measures a detailed transect with a total station. Photo by Mark Hynds, National Park Service.

Transects. At all 11 transects the crew took measurements with tape and stadia rod, slogging through the water and up and down muddy banks with deep water creeping toward the tops of their waders. They measured widths at four points on the bank, heights at two — where the stream fills its natural channel and at the lowest flat surface above that — and bank angles including undercuts, and noted bank sediment, vegetation, erosion, the dominant streambed particle size and features such as sand bars. At three detailed transects, Jacob Bateman-McDonald, the protocol's lead author and an assistant professor at the University of North Georgia, used a Trimble S6 robotic total station, the kind of instrument land surveyors use, to record points from beyond one bank, through the stream, to beyond the other, from which widths, heights and channel area can be calculated.

Measuring the bank: Daniel McCay, Louisa Markow and, kneeling, Stephen Cooper. Photo by Mark Hynds, National Park Service.

What the data are for

The site was finished by about noon, and the team moved on to the next. The measurements will be compared with the 2017 survey and combined with data from the wider watershed in a summary report. Changes since the last survey will show the effects of upstream land use, help predict future problems, and reveal habitat conditions for the stream's plants and animals — whether aquatic habitats are improving or declining, whether park structures are at risk, and whether visitors' experience could suffer — so park managers can better protect these resources.

Sources

• National Park Service, Southeast Coast Inventory and Monitoring Network: "Wadeable Stream Monitoring at Chattahoochee River National Recreation Area." The first-person account is retold in the third person.