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Rebirth of a River

The Big Wood River Better the Second Time Around

(page 2 of 3)

History of the Big Wood and human impact on the river.

The Big Wood is a fantastic river to fish in part because it is free-flowing for approximately 62 miles until it reaches Magic Reservoir south of Bellevue. Dams do not exist on the river above Magic Reservoir. Yet, its status as a wild section of river has encouraged efforts to control it around existing infrastructure and developments. However, the river’s ability to move within the floodplain is key to its health. Healthy rivers move in a sinuous S-shaped pattern, meandering back and forth across the floodplain to achieve an energetic equilibrium. Past efforts at flood control have resulted in diking along the river banks, filling in the floodplain, and installing riprap (large, angular rock along the banks), to limit the river’s ability to meander in the floodplain. Over time, these actions have straightened out the river channel, stretching the S-shaped curve the river follows over a greater distance. This straightening is known as “channelization.” Channelization permanently restricts the river to one channel, eliminates the natural meandering of the river, and effectively cuts the river off from its floodplain.

This year’s flooding has countered some of the effects of past efforts to control the river. According to Doug Megargle, Regional Fisheries Manager with the Idaho Department of Fish and Game, “the channel could have swung up to half a mile or more in one direction or the other,” prior to development in the floodplain. Dr. Bruce Lium of American Water Resources, a Hailey river contractor for more than 30 years, says that the spring flooding accomplished great things in terms of restoring the river’s natural functions. “The biggest benefit,” Lium notes, “is that the carrying capacity of the river has definitely increased.” According to Lium, the 2006 flood “probably has taken some of the channelization away.”

Removal of in-stream wood (logjams, cottonwood trees, rootwads, and woody debris jams that pile up in the river) that has occurred over the years negatively impacted fish habitat and flooding patterns. In-stream wood introduces bugs and other nutrients into the system which fish and other aquatic creatures need. It also plays a key role in slowing high flows and trapping sediment. As late as 1984, the Army Corps of Engineers spearheaded a “clear and snag” project which cleared 10 miles of the river channel in the Big Wood River of the many logs, rootwads, and woody debris jams that gave the river its name. Removal of the instream wood compromised the ability of the river to form pools crucial to healthy fish habitat.

Restoring the river that runs through it.

In recent years, efforts by local organizations such as Wood River Land Trust have improved the health of the river. Wood River Land Trust has completed restoration projects at different sites along the river including Lions Park, Bullion Bridge, and Riverside Pond in Hailey, as well as Boxcar Bend just south of Ketchum.

The restoration projects were designed to bring back a more natural function to the river and floodplain. The projects shared some common goals: restoring a more natural grade to and stabilizing riverbanks, allowing the river to flood and function more naturally by reconnecting it to its floodplain and preventing unnaturally large amounts of sediment from entering the flood waters.

In May and early June of 2006, the efforts paid dividends, assisting with flood control, protecting water quality, and preventing erosion. Plantings along the restored slopes at Bullion Bridge, Lions Park, and Riverside Pond stabilized the banks during high water and prevented sediment from entering the river. These restored banks demonstrate the greater stability of natural banks in comparison to banks where vegetation has been removed and shows one way to address future flooding with greater success.

At Riverside Pond, the pond itself acted as a sediment cache as sheet flooding entered the pond, slowed, settled out dirt and sediment, and returned to the river. During the flooding, the City of Hailey cleared the entry point for the pond to enable the maximum volume of sheet flow to enter the pond and protect neighbors from flooding. >>>

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