Large woody debris

Scientists who drafted the initial restoration plans emphasized the importance of placing the large pieces of wood in the streams to "jumpstart" natural dynamics. During the diversion period prior to the 1994 Water Board order, the streams lost riparian forests, the natural source of large wood. Today, the streams are clogged in some sections with small woody debris—remnants of desiccated willow—but there’s little large wood, and the forests that can provide it will take another 20 years to grow.

Termed "large woody debris" (LWD) in restoration lingo, hunks of wood in the stream help create habitat complexity. As soon as they are placed, they immediately create cover for fish and a substrate for invertebrates—all those bugs fish love to eat (see sidebar). In addition, trunks and rootwads deflect flows in complex ways, boosting the dynamics of scour and deposition.

"Woody debris may have been an important factor on these streams in creating the kind of channel and vegetation diversity that characterizes the Mono Basin streams," said Dr. William Trush, the scientist in charge of monitoring Mono Basin stream recovery. "Debris jams create backwater and inundate the bank areas, depositing sediment and affecting the riparian vegetation. They also might be an important factor in redirecting water into multiple channels."

Ideally, adding LWD involves placing logs, stumps, and rootwads along stream sections deficient of pools, meanders, undercut banks, and large boulders. LWD should be allowed to move with stream flow and lodge wherever it might. Once placed, the rootwads will give the streams something to work against during the years while the riparian forests recuperate.

According to scientists, the time required for the rootwads placed this year to increase habitat complexity will vary. "It depends on the magnitude and duration of flows sufficient to move bedload," said Trush.

In his two years’ work so far on the streams, work that DWP voluntarily initiated prior to the Water Board decision, Trush is beginning to see that channel roughness is as important as channel slope as a determining factor in how the streams respond to different flows. "I had thought that slope was a key determining factor, but I’m beginning to see that it’s roughness. The roughness provided by debris affects slope."

Getting the wood into the stream is a one-time action to be taken this year. If DWP finds other opportunities to add large woody debris—such as material made available during the upcoming Caltrans highway-widening projects—more might be added in the future.

As with all restoration, you have to strike a balance between the ideal and the practical. The ideal large woody debris would be a 20-foot trunk with rootwad attached. The rootwads being placed this year were left over from Caltrans highway work a number of years ago and stored at Cain Ranch. Their trunks were long ago taken to fuel local wood stoves. The reality is people in the area need fuelwood, so it’s hard to come by a trunk of any size.

According to Trush, the recovering streams are filled with small woody debris, as dead willow stems and sagebrush along the banks fall into the water. "Collectively, these small woody debris jams function something like big logs. And, as a practical matter, they might be what the stream has to work with until the streams develop their forests."

DWP’s efforts on the streams are part of a long-term restoration plan approved by the State Water Resources Control Board late last year. Restoration actions in the plan are designed to reinstate natural processes and habitat conditions, as opposed to specific former landscapes. The most important action is providing the streams with variable flows that simulate the streams’ natural fluctuations, including periodic flooding. These flows also will raise the level of Mono Lake, which will fluctuate during future wet and dry cycles around an average level of 6392 feet.

The LWD being placed in the streams in 1999 is only a fraction of the wood the streams will eventually carry when restored. Because natural large wood—large trees undercut in floods or toppling over in old age—will take some decades to grow and then fall, our children and our grandchildren will be the beneficiaries of today’s restoration.

According to local angler and outdoor news writer Marty Strelneck, woody structure makes the best places for fish to hide both in the stream and the undercut banks, whether from anglers or from the fierce dives of local osprey and kingfishers. In particular, tangled root wads and logs with pools scoured beneath them are the ideal place to find wild fish, the ones canny enough to know how to survive. Marty estimates that the large majority of fish you catch from these areas will be wild, not planted, trout.

Logs that have been in the water for a long time become host for numerous aquatic insects, another benefit for the sly fish that hide there during the day and emerge at dawn and dusk.

Of course, the woody structure that provides these angling benefits also presents the greatest hazard to lures and flies. "Bring along a good supply of lures and flies if you want to fish woody debris," advises Marty, pointing out with a smile that tackle shops—and the local economy—benefit from large woody debris too.