FALL RIVER RESTORATION PLAN



Prepared by


THE FALL RIVER WILD TROUT FOUNDATION





OVERVIEW



The Fall River in northeastern California is a low gradient spring fed "meadow" stream that gently meanders across the Fall River Valley before emptying into the Pit River via the penstocks of PG&E's Pit 1 hydroelectric project. Channel morphology and current velocities are remarkably consistent for its entire 22 mile length with a complete absence of riffle and pool sequences. Since most of the year it is fed almost entirely by springs rather than overland flow, it runs crystal clear and virtually sediment free. The only tributary supplying sediment of significant quantity to the system is Bear Creek which enters just below Thousand Springs, the source of Fall River. After draining an area of approximately 95 square miles to the northwest, much of the flow of Bear Creek disappears several miles before entering Fall River as it infiltrates the porous lava bedrock. In most years, it is only during the spring and early summer that runoff from Bear Creek is great enough to enter the Fall River.

Today much of upper five miles of Fall River, from the inflow of Bear Creek just below Thousand Springs downstream nearly to the confluence with Spring Creek, is filled with a 2 to 4 foot thick layer of highly mobile sandy sediment. Prior to the sedimentation problem, this section of the Fall River was an outstanding wild trout fishery. Luxuriant aquatic vegetation and numerous moderately deep runs, cut-banks, sunken logs and other stream debris provided excellent fish habitat. As the mass of sand spread downstream much of the original cover of aquatic plants disappeared, the runs and cut-banks filled, and the sunken logs were covered. Today there is neither holding water nor the prolific insect hatches that made Fall River a world renowned dry fly fishing stream. The rainbow trout population is much smaller than prior to the sedimentation and has suffered a precipitous decline just in the past several years; angling, in particular fly fishing, has severely declined.

Farther downstream Fall River still supports a viable wild trout fishery between Spring Creek and Island Road Bridge, but there is concern that the mobile slug of sediment just upstream will also overwhelm this section. Two to three feet of sand has already accumulated in some reaches and over the past several years the aquatic vegetation cover has decreased significantly. Dry fly fishing is sporadic and undependable at best.

A detailed sediment monitoring program being conducted by the Fall River Wild Trout Foundation indicates that sediment volumes in the impacted sections have not decreased appreciably. Despite substantial winter flows the hoped for flushing did not occur. Clearly, the sediment problem is not getting better, and while wild trout fishery may not die, it is on the decline and may become so degraded that future rehabilitation could be jeopardized without timely action. Simply stated, we have an urgent situation that requires immediate and decisive corrective action in addition to long term restoration efforts.

The wild trout fishery of Fall River is world renowned for providing some of the finest dry fly fishing in North America. As such it is a unique recreational asset of the state of California and an irreplaceable natural resource that underpins the regional economy. Its loss could be potentially devastating to the Fall River Valley community. If both the sediment load already in the river and the current sources of new sediment are reduced to manageable levels the fishery can begin healing while long term restoration efforts and monitoring programs can be put in place to insure its future health. If interim efforts to remove the sediment and control additional inputs are delayed for too long the aquatic ecosystem that supports the wild trout fishery may become so degraded that a return to pre-1986 status will no longer be feasible.


WHAT IS THE SOURCE OF THE SEDIMENT?



In the past when erosion rates in the Bear Creek drainage basin were lower and the low gradient reach through the Bear Creek Meadow immediately above the confluence with the Fall River provided a natural sediment trap, the Fall River was probably relatively free of sediment from Bear Creek. Over the past century erosion rates in the Bear Creek drainage undoubtedly increased due to the usual list of possible sources that are found on most of our private and public western lands--logging, cattle grazing, and wild fires. In addition, the natural sediment trap provided by the Bear Creek Meadow was lost in 1960 when this reach of Bear Creek was artificially rechanneled, and the new channel subsequently suffered severe gully erosion through the late 1960's. Influx of sediment from the Bear Creek drainage basin (including gully erosion in the Bear Creek Meadow), as well as stream bank erosion on Fall River, probably has resulted in chronic low level sedimentation over the years; but even as late as the early 1980's Fall River did not have a serious sediment problem and, in fact, the amount of sediment deposition was considered rather small for a watershed of its size.

In 1977 a large wildfire locally known as the Pondosa Burn occurred in the Bear Creek drainage basin in the are known as Pondosa. Subsequent replanting efforts incorporating extensive soil disturbance have continued intermittently into the present further destabilizing the area. Sediment from the Bear Creek Burn began showing up in small quantities in Fall River by the late 1970's and early 1980's, but the problem became suddenly evident in February, 1986 when a dramatic storm event brought exceptionally high runoff from Bear Creek and with it a massive load of sediment which today has formed what is essentially a delta in the upper reaches of Fall River.

Since 1986, the sections of Fall River originally impacted with sediment from the Pondosa Burn have not flushed appreciably and the sediment slug, which consists primarily of sand, has spread farther downstream relentlessly destroying more and more of the aquatic ecosystem. Given the likelihood that the sediment will not flush naturally from the system in a meaningful time frame, mitigation measures should be seriously considered and carefully evaluated as soon as possible.

When evaluating various restoration alternatives it is important to distinguish between the present rates of sediment input from the various sources now operating in the watershed vs. the source of the sediment slug already in the river:



It is important to emphasize that the huge slug of sediment now spreading down the Fall River is primarily due to past conditions for the most part no longer active, and should be managed as a problem in itself that is distinct from those chronic low level currently active sources listed above.


WHAT CAN BE DONE TO CORRECT THE PROBLEM?



The basic restoration strategy of the Fall River Wild Trout Foundation is to correct the immediate threat to the wild trout fishery by removing the sediment slug in the river utilizing environmentally sensitive modern suction dredging technology while simultaneously arresting the input of new sediment in order to buy time for the long term restoration of the watershed. How a pilot dredging project fits into the context of this basic strategy and overall restoration plan is outlined below.


IMMEDIATE MEASURES



1. Remove the bulk of the recent sediment

Phase I: Conduct a pilot suction dredging operation to assesses the feasibility of a full scale project.

Phase II: If deemed appropriate, conduct a full scale dredging operation to remove approximately 75% of the massive slug of sediment (approximately 200,000 yd3) that has come into the upper Fall River above Spring Creek Bridge (5 1/2 miles) since the early 1980's while leaving pre-existing sediment undisturbed.

Phase III: If deemed appropriate, continue the full scale dredging operation to remove approximately as much sediment volume in the 8 miles of river from Spring Creek Bridge downstream to the confluence with the Tule River.

2. Reduce Sediment from Bear Creek Burn by constructing low cost sediment traps in the Bear Creek Burn and at other locations known to be active sediment sources, thus effectively minimizing the current influx of sediment from the Bear Creek drainage basin while long term restoration efforts proceed.


LONG TERM MEASURES



1. Assess the Bear Creek drainage basin to identify any additional sediment sources and take corrective action to minimize them.

2. Restore the riparian corridor and stabilize the stream banks along Fall River by controlling the muskrat population, installing cattle exclusion fences, and replanting the stream bank vegetation.

3. Evaluate the feasibility of reestablishing the natural function of the Dana Meadow as a natural sediment trap, further minimizing the influx of sediment from the Bear Creek drainage basin.


A strategy of physically removing as much of the sediment from the river as is practical utilizing modern suction dredging technology should be seriously considered and carefully evaluated. Presently, it would be feasible to use suction dredging because much of the sediment is still in the upper reaches where it is concentrated and near workable disposal sites. Once the sediment extends much farther downstream it will be so dispersed and distant from the disposal sites that removal efforts will be much more difficult and expensive probably rendering the project economically unfeasible.

Currently, there is considerable opposition to a large scale dredging operation. A variety of concerns have been expressed--some are justified, others are not and most are due to a lack of understanding of the capabilities of modern suction dredging technology. Nevertheless, the reality of the present situation dictates that a pilot project be first successfully completed before a large scale effort to effectively correct the problem can begin. If so demonstrated, a full scale project can then be considered.


WHAT ARE THE ALTERNATIVES TO DREDGING?



When evaluating various restoration alternatives it is important to distinguish between the present chronic low level rates of sediment input from the various sources now operating in the watershed vs. the source of the massive sediment slug already in the river primarily due to past conditions no longer active. Possible restoration alternatives that have been suggested include:

(1) Doing nothing:It is highly unlikely that the sediment will flush naturally or stabilize to allow recolonization by the critical aquatic vegetation. As time goes on the problem will probably get worse not better, with the system further degrading and the cost of restoration increasing.

(1) Stream bank erosion control: Cattle exclusion fences, muskrat control programs, and riparian vegetation replanting are worthy projects which are currently underway and should be encouraged, but they will have little affect on reducing the amount of sediment already in the river. It is well documented that stream bank erosion was not the source of the sediment slug currently choking the river, nor is it currently a significant input of sediment. Restoring the riparian corridor and the previous channel geometry with its cut banks are important steps in restoring the wild trout fishery but stream bank erosion control will do little to mitigate the existing sediment slug.

(2) Sediment traps: As with stream bank erosion control, establishing sediment traps would do little to mitigate the existing sediment slug since less than 1,000 cubic yards of bed load sediment enters the Fall River via Bear Creek annually according to a recent study (Bear Creek Monitoring Program). However, since construction and maintenance of sediment traps in the Bear Creek drainage, especially in the Bear Creek Burn, would be relatively simple and inexpensive this method of reducing current sediment input to the Fall River should be encouraged. The probability for success is high and the risk of negative impacts minimal. On the other hand, reestablishing the natural sediment trapping capability of the severely gullied Dana Meadow by reengineering the original distributary system would be complex and expensive, and runs a very high risk of releasing large amounts of new sediment into the Fall River. The gully erosion occurred long before the current sediment problem began in the early 1980's; it was not a significant source of the sediment slug in the Fall River and is not currently contributing a particularly large amount of new sediment. Considering the relatively small volume of sediment contributed by the Bear Creek drainage, it is questionable whether the potential benefits of restoring the meadow as a sediment trap would outweigh unintended negative impacts.

(3) Instream structures: Instream structures designed to increase current velocity and accelerate downstream sediment transport have been employed with varying degrees of success in other watersheds, but probably do not offer a viable solution here. On a stream the size of the Fall River they would be prohibitively expensive and if successful would simply move the sediment downstream where it would create additional problems. In addition, this represents a heavy handed solution which at best would result in channel geometry vastly different from pre-problem conditions only 10 years ago. It must be emphasized that we are dealing with a massive amount of sand, much more than the system can absorb. It is questionable that trying to flush it through is a viable solution; given the huge volume of sediment and the very low gradient it would take an unacceptable length of time, and there is nowhere to flush it to, only additional downstream sections of the river would be impacted.

(4) Sediment stabilization: The desirable aquatic plant (Zannicellia palustris) requires a stable substrate for its roots to successfully anchor against the currents. In a loose sandy substrate it is subject to "blow-out" and effectively eliminated. Trying to reintroduce the aquatic vegetation after stabilizing the sediment instream is not practical; sand is simply too mobil to stabilize. Also, if the sandy sediment were somehow stabilized, the natural functioning of the river to adjust channel morphology would be severely hampered, and the present channel geometry with an undesirable large width to depth ratio would be come permanent.