Restoring Wet Meadows
Wet mountain meadows are some of the most productive habitats in the Southwest. They provide important habitat for endemic plants and animals such as the Arizona willow, Mogollon paintbrush, White Mountains clover, and Apache trout. Many meadows have been eroded and dewatered by channel downcutting, which can happen when flows increase due to road construction or wildfires and when the meadows have been weakened by animal trampling.
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A Meadow in Trouble
Pacheta Cienega was one of those meadows in trouble. It lies on the beautiful lands of
the White Mountain Apache Tribe in the high country of east-central Arizona.
When and how downcutting started in this meadow is not clear, but a culvert that was too small may have contributed to
the problem. The meadow may have been naturally vulnerable to coming out of
balance because it is located in a transition from steeply-sloping silicic
rocks to flat-lying basalt flows (see map). However, ungulates (wild elk and domestic
cattle) were clearly overusing the plants needed to keep the stream intact, and
they were damaging the channel bed and banks with their hooves. To address this
problem, Tribal managers changed their livestock rotation in the area and built
a fence around the most sensitive area to reduce impacts from the animals.
Tribal hydrologists also enlarged the capacity of the culvert crossing to
facilitate passage of bedload. However, drought conditions in 1996 constrained
the growth of stabilizing vegetation and encouraged elk to feed and walk along
the unusually shallow stream. Where the channel was becoming incised and
unarmored, an additional 4 to 8 inches (10 to 20 cm) of downcutting occurred by
1997. Once a channel starts to downcut, it usually does not stop until it has
caused a lot more erosion. Because this stream provided valuable habitat for
trout, we helped the Tribe design a treatment to restore stability.
The Treatment
We proposed placing "riffle formations" at places where natural riffle materials had been washed out of the stream. The formations help to dissipate the stream's energy by increasing the undulation of the channel bed, increasing the roughness of the channel, and spreading high flows into the floodplain. We recognized that we would have to bring in riffle-forming materials because, although the bedload of Pacheta Creek was dominated by fine gravels, this natural source was insufficient to replace the coarse gravel substrates that had protected the channel bed from erosion.
Placement of the formations took one day of intensive labor. A Tribal enterprise delivered 54.5 metric tons of large gravels and small cobbles (1-5 inches/25-125 mm) to the site. A work crew consisting of Tribal staff, RMRS scientists, and participants in the Tribe's summer youth environmental program transported the rock materials to each riffle site using wheelbarrows and a small trailer (photos). Workers placed the rocks at 25 riffles spaced along 558 feet (170 m) of the degraded reach. Each formation averaged 7.9 feet (2.4 m) in length. Some workers raked and stomped the rocks into the bed and under the banks to keep flows centered through the riffles. Meanwhile, others cut plugs of sedges from wet areas in the meadow and placed them among gravels along the sides of the riffles. The purpose of transplanting was to stabilize the riffles with a living fabric and to revegetate bare areas along the streambanks. We had also observed that water flowing over riffles in our reference streams was relatively quiet. This auditory clue helped workers build the riffles, since riffles that were built too high produced gurgling noises from the rapid flow of water over the formations. Workers repacked and raked the rocks toward the banks until the gurgling sounds subsided, indicating reduced velocities. Through an iterative process, we added rocks to raise riffles that became submerged as new ones were placed, until each riffle was at the desired height relative to the preceding and succeeding ones.
Results of Treatment
Monitoring showed that the treatment produced many favorable changes, such as:
- increasing bed undulation, which dissipates energy
- dispersing flood flows into the meadow
- capturing and retaining naturally occurring fine gravels, which creates spawning habitat for trout
- expanding trout habitat by increasing the water depth in pools
- repaving the streambed, making it less susceptible to erosion
- rewetting the meadow, helping native sedges to recolonize bare patches
- reducing animal damage to the channel by creating resistant areas where elk can cross and
- improving the attractiveness of the stream and meadow
Conclusions
The riffle formations proved to be a sustainable, low-cost approach for restoring a high-value pool-riffle systems where natural bedloads were insufficient to replace riffle materials lost to streambed erosion. This treatment should be applied only after treating factors that caused the degradation, which may include improperly designed road crossings and overuse by animals. Although it is a structural intervention, the riffle formation technique promotes recovery of the stream through natural processes.
For more information, please review our article on this restoration technique, which appeared in the June 2004 edition of Ecological Restoration. Please note that the article is under © copyright 2004 by the Board of Regents of the University of Wisconsin:
2004 Medina, A. L. and J. W. Long. Placing riffle formations to restore stream functions in a wet meadow. Ecological Restoration 22:120-125.
Full Text PDFAcknowledgments
We wish to thank the White Mountain Apache Tribe and its members who implemented this restoration project, permitted the publication of these findings, and continue to demonstrate leadership in the ecological restoration of their ancestral homeland.
Page contact:Al Medina | AWAE - Flagstaff-Rocky Mountain Research Station
