Fall River Wild Trout Foundation

PILOT DREDGING PROJECT

The purpose of a dredging project would be to remove the highly mobile recent sandy sediment that has decimated the Fall River aquatic vegetation and insect ecosystem and severely impacted the wild trout fishery that depends upon it. The goal would be to restore the channel to conditions found in the early 1980's prior to the sedimentation problem.

The objective of a pilot project would be to demonstrate that sediment removal with a modern suction dredge is a feasible method of rehabilitating the Fall River. Specifically, to be judged a success, the pilot project should demonstrate (1) that it is technologically and economically feasible to remove the sediment by dredging, (2) that it can be done in an environmentally sensitive manner that will produce no significant unforeseen adverse effects that can not be successfully mitigated by project design changes, (3) that once the sediment is removed the aquatic ecosystem will rapidly recover to a permanently sustaining level, and (4) that a return to the preexisting channel morphology would be beneficial without any adverse effects.

1. WHAT TYPE OF DREDGE WOULD BE USED?

The sediment would be removed from the river with a floating suction dredge about the size of a small houseboat. The sediment would then be pumped from the dredge as a slurry through a portable pipeline to the disposal site to be stored. Booster pumps can pump the material through the pipeline as far as necessary, with cost being the only limit to the distance pumped. Several systems have been developed that could handle the job, but our first preference is the self-propelled IMS Model 5012 suction dredge with cutter head and Star Wheel TM Drive System, equipped with a floating hose and a 12 inch pipeline with booster pumps.

Please see Appendix I for equipment descriptions and specifications.

2. WHERE WOULD THE DREDGED MATERIAL BE PUT?

The dredged sediment first would be contained at a disposal site in settling ponds behind berms. The water would be allowed to return to the river either as groundwater through the porous basalt or as overland flow after appropriate measures are taken to insure that suspended materials have settled out. A weir box structure would allow decanting of the clear water, with hay bale filters incorporated if necessary. These are simple cost effective methods that have been proven to work on numerous dredging projects and will ensure that all water returning to the river as a result of project operations will be of the same quality as when it entered the dredge.

Several disposal sites have been secured where the pumped sediment slurry could be dewatered and stockpiled for permanent storage.

3. HOW MUCH OF THE CHANNEL WOULD BE DREDGED?

The overall strategy would be to remove approximately 75% of the recent (post early 1980's) sediment without disturbing the preexisting stream bed. We propose removing most of the recent sand and sandy fines in the main part of the channel and leaving the recent fines that have accumulated along the banks, except where the recent fines extend well out from the bank (please see Appendix II for sample channel x-sections). The goal is to remove the highly mobile substrate that has decimated the aquatic vegetation and to restore the channel morphology to conditions found in the early 1980's. Flushing spawning beds is not a goal (most are upstream of the section to be dredged) nor is artificially reestablishing undercut banks (the river will do this naturally).

Not having to remove the material close to the banks will increase the dredger production rates and lower cost, and reduce to potential for unintended negative impacts. The river should naturally redistribute and stabilize the remaining sediment over time, ultimately doing a better job than trying to second guess where it should be. If some sediment is left in the main channel the river will naturally flush it over time. The fines left along the banks should stabilize, since the Fall River has a low rate of lateral erosion. Historically, the stream banks in the upper river have been stable, except where the combination of burrowing muskrats and grazing cattle are found and much of this section of the river already has been fenced. Ultimately, the stabilized deposits of fines along the banks will narrow the channel, and this channel narrowing, along with the reestablishment of the original depth by removal of the recent sediment from the main channel by suction dredging will decrease the width to depth ratio of the channel X-section.

4. HOW WOULD THE "ORIGINAL" BOTTOM BE DEFINED?

The Fall River has cut its channel into lake bed deposits consisting of a series of soft, but cohesive clay and diatomaceous earth layers, intermittently interbedded with resistant silica cemented layers. In some areas a resistant iron cemented hardpan has formed on the original lake bed deposits. Where the river is adjacent to the laterally confining lava beds, scattered basaltic cobbles often are found. Two distinctly different layers of sediment have subsequently been deposited. The lower, older sediment is composed of coarser sand of mixed mineral composition and particle size with a large proportion of small gravel which often forms an armor layer. This older layer is consolidated to the degree that it is very difficult to hand probe. It has a distinct bluish color (indicative of anaerobic conditions), and does not appear to be mobile. The overlying younger sediment is composed of finer sand with a homogeneous mineral composition and particle size distribution and no gravel content. It is very loosely consolidated and can be very easily hand probed. Usually a distinctive reddish color, especially if it is a very recent slug, it often displays ripple marks and dune features indicating it is highly mobile.

In general, the layer of sediment designated younger is the massive influx of sediment beginning in the mid 1980's, with the older layer resulting from the long term chronic input from the Bear Creek drainage basin and stream bank erosion along Fall River over the past century. It is important to emphasize that the very loose younger sediment to be removed is easily distinguished from the consolidated older sediment, and that the pronounced boundary between the two is remarkably level making the task of removing the younger sediment layer while leaving the older layer undisturbed very much less complex than in most river systems.

5. HOW PRECISE IS THE DREDGE?

For the project objective of reestablishing the original beds of aquatic vegetation to be achieved, the dredged channel must be left with a minimum of the recent sandy sediment, while the older layer of consolidated sediment underneath should be left as undisturbed as possible. Even several inches of loose substrate may effectively eliminate the critical aquatic plants. The suction dredge is technically capable of removing the loose recent sediment within this depth tolerance. The topography of the buried surface of the older sediment unit has very little relief; conforming to the variation in slope of this surface is a task well within the technical capabilities of the dredge. The depth of the cutter head can be set to a predetermined depth within the precision limits of one inch, and the suction action of the pump can efficiently remove on the order of six inches of the targeted unconsolidated recent sediment without the assistance of the cutter head thus effectively minimizing any significant disturbance of the older sediment. The desired depth can be laid out in detail by project personnel (the "grade setter") by setting an array of probes ahead of the dredge indicating depth to the bottom of the recent layer of sediment. The operator would then set the cutter head to those depths minus six inches more or less as determined by actual results. Collateral injury resulting from disturbing the older sediment can be kept to an insignificant level by following the procedure outlined above.

6. HOW WILL DREDGING REHABILITATE THE WILD TROUT FISHERY?

The primary benefits of removing the unstable sandy sediment would be the reestablishment of the original aquatic vegetation, particularly the desirable Zannichellea palustris (Z-Grass) and Myriophyllum sibiricum (Northern watermilfoil) along with the invertebrate communities they support. Once the sediment is removed the aquatic plants are expected to reestablish rapidly (the desired species are considered difficult to eradicate weeds in some watersheds!) along with the insect communities and the wild trout population. Assuming the current low rates of new sediment input continue and long term restoration projects to reduce those inputs even more are successful, the restoration results should be long lasting.

7. ARE THERE OTHER BENEFITS OF DREDGING?

An additional potential benefit of removing the unstable sandy sediment to the aquatic ecosystem is an increase in habitat for the endangered Shasta Crayfish (Pacifastacus fortis). Populations of the Shasta Crayfish have survived in the upper Fall River in several small areas of exposed lava cobble substrate found in the few places not inundated by sediment. Dredging should help flush the large areas of lava cobbles presently inundated with sediment thus providing expanded habitat for this endangered species.

In addition to restoring a more desirable width to depth ratio, the benefits of returning to a pre-sedimentation channel morphology are to mitigate the increased incidence of flooding and its attendant problems of stream bank destabilization and loss of income from curtailed farming and ranching activities. With the stream bed rising 2 to 4 feet due to the recent sediment accumulation and no significant widening, channel volume has been reduced by as much as 30% to 50% through many reaches. Any increase in current velocities to compensate for this decrease in channel volume has been minimal due to the low gradient of this "meadow" stream. Consequently, much less water can now be transported within the existing channel, so the adjacent lands, most often extensive low lying farmland and pasture, are now more prone to flooding. Particularly problematical since the sedimentation is the greater incidence of extensive shallow flooding of these adjacent lands during the relatively low flows in the summer and fall. The saturated conditions caused by this shallow flooding exacerbate the stream bank destabilization and erosion caused by muskrats and cattle and ultimately can restrict farming and ranching activities for some distance back from the river. Removing the recent sediment and reestablishing the previous channel depth is expected to mitigate this problem.

An additional benefit of removing the recent sandy sediment would be to reduce the cost of pump maintenance for domestic and agricultural water users. Damage to the impellers by sand and the need to remove sediment to keep intake pipes clear will be reduced.

Finally, given the high profile of the Fall River and the close scrutiny this pilot project would likely to draw, successful demonstration that modern suction dredging is both feasible and environmentally sensitive would have the benefit of facilitating the acceptance of this technology as a viable restoration tool for many of the similarly damaged watersheds throughout California, if not the United States.

8. WILL A DREDGED CHANNEL CAUSE NEW PROBLEMS?

Concerns have been raised that dredging the river will dramatically change its basic hydraulic character creating an unpredictable state that might somehow cause a worsening of the situation. That would be a well based position if the goal were to artificially design some theoretical "natural" channel configuration, but that is simply not what is proposed. It is extremely important to emphasize that this is a proposal to restore the channel morphology to what it was in the early 1980's prior to the sedimentation problem. The hydrologic results are predictable, the river will behave essentially as it did prior to the sedimentation problem only a few years ago. Fall River is a very low gradient stream, its erosive and or sediment transporting power will not suddenly change with the proposed channel deepening. The objective of the proposed dredging project is to reduce the width to depth ratio of the channel morphology to its pre-1980's condition, thus providing an environmental benefit rather than a liability.

Restoring channel depth can be expected to slow current velocity and lower water level for a given discharge. Neither is expected to cause any significant adverse impacts. On the contrary, as discussed earlier the drastically reduced cross sectional area of the present channel appears to be no longer capable of carrying even average summer discharges. Water levels in the summer and fall of 1994 were higher than at any time in recent memory with widespread flooding of adjacent agricultural land, despite the flows being below average (250-300 cfs compared to an average of 450 cfs). With the end of the drought and the return of normal precipitation and flows, flooding could be even more of a problem unless the sediment is removed. Slower current velocities would have a potential negative impact so far as bed load transport rates and consequently natural flushing rates are slowed. However, current velocities would not be reduced enough to significantly extend the time period necessary to naturally flush the sediment from the system.

Stream bank geometry would not be adversely affected by the project. As specified in the project description, only the main channel would be dredged. The predominantly finer recent sediment that has accumulated along the bank would not be disturbed, and the sides of the dredged channel would be sufficiently sloped to minimize sloughing of material.

9. WILL DREDGING HARM ANY PLANTS OR ANIMALS?

The potential for significant effects needs to be considered for (a) fish, fish eggs and yolk sac fry, (b) benthic and invertebrate communities, (c) all endangered species, (4) aquatic plant communities, (5) riparian habitat and dependent species, and (6) upland habitat at the spoil disposal site. Many of the observations listed below come from the 1994 California Department of Fish and Game publication Adoption of Regulations for Suction Dredge Mining.

The effects of suction dredging on fish eggs and yolk sac fry can be significantly adverse, but since the nearest spawning beds are over two miles upstream according to the CDFG no negative impact can be expected. Adult and juvenile fish, even small slow moving species such as sculpin, have no difficulty avoiding entrainment by a slow moving suction dredge. Physiological effects of elevated turbidity and suspended sediment can be expected to be negligible--only localized low levels are produced by modern suction dredges, especially when working in sediment predominately composed of sand.

Migration of fish through the project area will be unimpeded since the zone of disturbance caused by the dredging activity is a small proportion of full channel width. The presently low numbers of fish in the project area make issues of adverse affects on resident fish behavior and distribution a moot point. Suction dredges of the design specified for this project have been successfully employed to dredge commercial fish and shrimp farms with no adverse impacts noted.

Suction dredging can have short-term localized adverse impacts on existing benthic and invertebrate communities, but they can be considered insignificant. Few benthic organism inhabit the mobile sandy substrate, and even if present, it has been shown that areas disturbed by suction dredging can be completely recolonized within two weeks to two months.

Two aquatic endangered species are found in the Fall River . The Shasta Crayfish (Pacifastacus fortis) is listed at both the state and federal level, and the state has also listed the Rough Sculpin (Cottus asperrimus). Dredging procedures that will virtually guarantee no significant harm to these two organisms will be required to satisfy all concerns with this extremely sensitive issue.

In the upper river, only several small populations of Shasta Crayfish have been noted in isolated areas of bare lava cobbles. It is highly unlikely that they would venture onto the bare sandy flats to be dredged. The dredge is self propelled, therefore it can easily be maneuvered away from areas the Shasta Crayfish inhabit. No collateral damage is expected with this species, instead the project should result in a beneficial increase in their habitat.

The slow moving bottom dwelling Rough Sculpin offers some challenge to insure avoidance of incidental injury. If necessary, individuals could be shepherded from the area ahead of the slowly advancing dredge, a relatively easy task with a high expectancy of success considering the shallow depths and extreme clarity of the water. An alternative strategy could be to trap and relocate them out of the path of the dredger. The Rough Sculpin prefers a substrate of loose fine material, so exposure of the original bottom by dredging can be expected to result in a loss of preferred habitat.

Any existing aquatic vegetation will of course be removed during the course of the dredging operation. However, this is again a moot point since few if any aquatic plants have been found in the upper river for nearly a decade, and it is unlikely that the detailed surveying and mapping of the aquatic vegetation to be done just prior to the initiation of dredging will find any revegetated areas.

The 12 inch pipeline can be placed in such a manner so no significant disturbance would occur where it passes through the riparian corridor. Also, it can be disassembled and moved in the same manner. The dredge would be launched at preexisting ramps, or if not available, with a crane that can be stationed so as not to injure the riparian vegetation or dependent communities such as nesting waterfowl.

That there are no occurrences of endangered plants or animals in either the disposal area or the area where the pipeline lies would have to be verified by on site inspection during the permitting process. In the event that Bald Eagle nesting sites are discovered, the requirement of a half mile exclusion zone during the spring nesting season will not present a problem because actual dredging operations would not be initiated until well later in the year.

10. WILL DREDGING AFFECT WATER QUALITY OR QUANTITY?

Some concern has been raised regarding the possibility that discharge from the many small springs which feed Fall River throughout its upper reaches might be diminished if the lava beds are used as a disposal site. Such a scenario is highly unlikely since the sediment consists mostly of sand size particles which are too large either to restrict surface infiltration of water or to be carried into the subsurface fractures. In addition, these springs are almost certainly feed by a very large area of the lava beds, so restricting surface infiltration on several hundred acres would be insignificant. Nevertheless, if the lava beds were used as a disposal site dye tests could be used to determine whether the disposal site is a significant source area for the springs and if judged unacceptable, an alternate location could be selected.

The dredge pumps 5,000 gallons per minute so would not drain the river capacity to any significant degree. Most of the pumped water would ultimately return to the river either as ground water inflow or overland return flow from the disposal site. Since the project would be in the winter months, only a negligible amount of the water removed from the river would be lost through evaporation.

Return of sediment back to the river will be relatively easy to contain in settling ponds. The sand will literally pile up at the end of the discharge pipe and only the water will run off, leaving the pumped sand in place. The effluent material pumped to the disposal site may be decanted naturally or by using a weir box structure and berm, and incorporating a filter structure if necessary. Utilizing these methods, the suspended solids can be removed and turbidity of all return flow will be kept to a level essentially the same as when it originally left the river.

Turbidity would be minimized at the dredger by the dedicated shroud on the cutter head. It would be up against the work face of the material and seal out most of the water, increasing solids pumped. Typically, the action of the pump will draw most of the disturbed material away and the rest will fall out within feet of the machine while it is operating. Turbidity levels within the immediate vicinity of the dredge will not exceed levels that could cause injury to biological systems, and will be at negligible levels beyond the project area.

Turbidity would be monitored both upstream and downstream of the dredge and disposal site to ensure that expectation of water quality standards are met. Suspended load and bed load transport rates will be similarly monitored to evaluate if project operation is causing a significant change. Other water quality parameters will be monitored if deemed necessary during the permitting process.

The contamination of the river with lubricants from the dredge would be minimized by the use of nylon bushings on the underwater cutter head. Spills of diesel fuel and oil are always a distinct possibility even when all appropriate care is used when operating heavy equipment. To minimize any such incident a boom device designed to contain petroleum spills would be in place at all times while the dredge is operating or being refueled.

11. WILL DREDGING AFFECT RECREATION USES?

Trout fishing, water fowl hunting, canoeing and bird watching are the most common recreational uses of the Fall River. The greatest potential for adverse effects from a dredger operation to these activities are those associated with hindering the passage of small motorized prams and an occasional canoe or other paddled craft. With many dredger projects ropes and cables are needed to propel the dredge or hold it in place against strong currents, as well as other equipment such as hoses and the dredge itself may interfere with up and downstream movement causing inconvenience at best and a serious safety and liability problem at worst. However, these are not expected to be problems with this pilot project. The dredge which would be used for this project is only 8 1/2 feet wide and by using a self propelled drive system is capable of holding a position in the slow current of Fall River so would not require cables to work off. Without an array of cables, boat traffic would be able to easily move around the dredge while it is operating. The floating discharge hose can be handled in such a manner that it will not interfere, as well, by using a shore man to rope off and tend it.

To further insure safety to boaters, warning signs and flags could be stationed both upstream and downstream of the work area. In addition, the project staff person acting as grade checker who would be stationed upstream of the dredge can also warn approaching boats and act as escort around the work area if necessary. On the downstream side, the boom device deployed to contain pollutant spills would also serve as an effective warning barrier to accidental entry into the work area. A flagman and escort could be stationed at each end of the project area if deemed necessary during the permitting process.

With a proposed start of November 16, the day after trout season ends, fishing activities would not be affected by a dredging project. Even if operation of the dredge were to begin earlier, fishing would not be significantly affected. Very few anglers now bother to fish the upper river, their main concern would be free passage to the still productive waters downstream. Impairment of fishing conditions caused by increased turbidity would extend only a very short distance downstream of the operating dredge and not be significant immediately downstream of the project area. The section of the Fall River still supporting a viable fishery begins below Spring Creek Bridge far enough downstream to not experience any negative effects to fishing conditions caused by elevated turbidity.

Fewer birds and water fowl will probably choose to be in the immediate vicinity of the operating dredger, but since most bird watching and water fowl hunting is done from "drift through" boats, overall these activities would not be significantly diminished.

Recreationalists expect quiet restful conditions and the noise and engine exhaust of a dredging operation is a potential negative impact. While the noise exhaust produced by the diesel engine on the dredge and booster pump might be considered irritating, even in the immediate vicinity of the machinery it is not exceedingly offensive. Few recreational users would be on the river at the time of year dredger operations would be scheduled, and those that are could quickly pass through the area. Only three permanent residences are along this section of the river and they are strong supporters of this project. The dredge should not have to run over 12 to 14 hours per day to achieve a 10 hour pumping regimen so late night operation is not anticipated. Noise and exhaust pollution constitute only minimal negative impact within the project area, and negligible impact beyond.

12. WILL NATIVE AMERICAN ARTIFACTS BE DISTURBED BY DREDGING?

Native American artifacts, consisting primarily of arrowheads, are very numerous in the older layer of sediment. Prior to the current sedimentation problem, these artifacts were commonly found on the surface of the older sediment layer and the areas of exposed clay lake bed deposits. Their occurrence in the newer sediment is rare and probably insignificant. Dredging methods that satisfy the concerns of the Native American community are being developed. A Native American observer would be on site during all operating times to ensure compliance with this requirement. The disposal site would also have to be approved with the same concerns in mind.

13. HOW WILL RESULTS BE MONITORED?

The rehabilitation of the wild trout habitat by successful reestablishment of the original aquatic vegetation would be measured, evaluated and reported by personal from the USDA National Aquatic Weed Laboratory who are currently conducting an extensive aquatic vegetation study in the impacted sections of the Fall River. As part of the pilot sediment removal project, the USDA team would fully document pre-project conditions within the project area in terms of the areal distribution and abundance of individual species of all aquatic plants of interest, and the characteristics of the existing substrate and aquatic environment in terms of those parameters potentially important to those plants. Post project conditions would be similarly monitored for a minimum of two years, and longer if deemed necessary to determine if exposing the stable substrate beneath the recent sediment will result in recolonization by the original aquatic plants. Also, propagules would be introduced to one or more test plots within the project area to remove the variable of successful recruitment. The criterion for success would be clear evidence of rapid and apparent long term recolonization of areas previously devoid of Z-grass and/or watermilfoil within the project area (including reseeded test plots).

Post-project changes in the extent of Shasta Crayfish habitat would be monitored by the Fall River Wild Trout Foundation. A detailed sediment inventory done in 1994 (Upper Fall River Sedimentation Study, Progress Report) delineated the areas of exposed lava cobbles. The Fall River Wild Trout Foundation is currently conducting a detailed sediment transport study which includes the monitoring of fluctuations in the distribution of the sediment slugs. The extent of the areas of exposed lava cobbles would be updated just prior to project initiation, and would be monitored during and after the project and for a minimum of two years after completion (and longer if deemed necessary). The criterion for success would be a measurable increase in the areal extent of exposed lava cobbles.

The Fall River Wild Trout Foundation would measure and report changes in channel morphology in the project area resulting from the removal of the recent sediment. The criterion for success would be reestablishment of the pre-sedimentation channel morphology with a decreased width to depth ratio, and one which is stable without unintended negative impacts such as accelerated lateral erosion. The Fall River Wild Trout Foundation has been operating a continuously recording gaging station in the upper Fall River and would continue this monitoring program after project completion for a minimum of two years (and longer if deemed necessary) to determine if the post-project deeper channel results in a change in water levels for given discharges. The criterion for success would be decreased water height for given discharges, particularly during summer and fall low flow seasons.