Gravel Mining and the Garcia River

Sources of Information, Problems and Solutions

I.  Sources of Information:
         Local:
Fugro West, Inc. 1994.  Revised Draft Environmental Impact Report for Gualala Aggregates, Inc
Fugro West, Inc. 1995.  FEIR for Gualala Aggregates, Inc.
MCRCD (Mendocino County Resource Conservation District). 1995. Garcia Estuary Feasibility Study, Point Arena California.  Draft report prepared by Moffatt & Nichol Engineers.
MCRCD, 1992.  The Garcia River Watershed Enhancement Plan.
Philip Williams & Associates. 1996.  Garcia River Gravel Management Plan (GRGMP)
         General:
Philip Williams & Associates. 1997.  Upper Russian River Aggregate Resources Management Plan Mendocino County. (URRARMP)
Collins, B., and T. Dunne.  1990.  Fluvial Geomorphology and Gravel Mining: a guide for Planners.  California Division of Mines and Geology Special Publication 98.

II.  Problems:  Impacts of Instream Gravel Extraction

General Impacts of instream mining on cold water habitat;  as listed in the Upper Russian River Aggregate Resources Management Plan for Mendocino County:

A. Effects on River Stability -
Incision caused impacts - (Mitigations: M-1, M-2, M-5, M-6, M-8, M-14)
1. " Channel incision, or lowering of thalweg elevations.  This reduces diversity of aquatic habitat by reducing the relative elevation change between pools and riffles."

2. " Incision or headcutting in tributaries in response to a lower base level in the main channel."

3.  "Increased bank heights, bank erosion, and channel capacity due to channel incision."

4.  "Threat to infrastructure such as bridges due to incision that undermined bridge piers or supports.  ... (efforts may be made by the State to recover bridge repair costs from legally responsible parties)"

5.  "Exposure of clay substrate layer within or below gravel deposits dure to incision may remove gravel that is a necessary component of habitat."

6.  "Incision can cause a lowering of the groundwater table in the adjacent floodplain aquifer.  This may effect local wells, reduce the aquifer storage and impact riparian vegetation by isolating roots above the water table."

Morphological changes caused by changes to local morphology and hydrology - (M-1, M-2, M-3, M-5, M-6, M-7, M-8, M-9, M-11, M-14)
7.  "Local widening and flattening of the low flow channel in gravel extraction area where bar skimming occurs.  This leads to braiding of the low flow channel, and increased potential for bank erosion."

8.  "Downstream channel changes including reduced sediment supply to downstream bars, widening and flattening of low flow channel, and increased potential for braiding."

9.  "Upstream channel changes including incision or lowering of the thalweg elevation due to headcutting upstream of the mining area."

10.  "Removal of riparian vegetation reduces habitat and may cause channel instability and increase bank erosion."

11. "Degradation of habitat from the removal of the armor layer or coarse sediment from bars and release of fine material to the channel downstream."  This impact is reduced but not eliminated.

Two impacts listed for floodplain pit excavation are: potential for river capture and reduction in the filtering ability of the floodplain aquifer. M-F1 to M-F8, These impacts are reduced but not eliminated.

Floodplain skimming would result in temporary loss of riparian vegetation and the potential loss of stability.  M-F9, impact not eliminated.

B. Effects on Fishery Resources - This is a listing of the more direct impacts to fish.

1.  "A reduction in salmonid spawning gravel, protective cover, food resources and deep pools if gravel is depleted at a greater rate than it is replenished."  M-1

2.  "Increased proportion of fine grain sizes." (Relates to impact 11 above.)  not fully mitigated

3.  "Increased siltation."    M-6, M-9, M-10, M-11, M-13
         a.  "Increased sediment input due to construction of road crossings and spur roads."
        b.  "Increased erosion and sedimentation due to ... culverts in summer road crossings."
         c.   "Settling of fine-grained sediment could occur in fish food-producing areas, thereby smothering fish food organisms, if the streamflows are not adequate to move and deposit sediments to normal depositional areas."

4.  "Increased water temperatures, eroded banks, and reduced food availability, if the riparian habitat is altered and/or destroyed."  M-9, M-11, M-12

5.  "Decreased habitat for both fish and fish food organisms, if large woody debris and/or vegetation growing on gravel bars are removed during the annual gravel bar skimming."  M-9, M-11

6.  "Diminished habitat quality (reduction in pool size) and quantity, if the stream bed geomorphology is altered."   M-2, M-3, M-5, M-6

7.  "Direct kill, if any fish are present in the excavation area."  M-2, M-3

8.  Possibility of fish stranding in off-channel pools.  (paraphrased)  M-4

9.  "Blockage of migration of salmonids ... as a result of summer road crossings."  M-12

10.  De-watering of stream channel or inadequate water depths due to water use in gravel washing and processing.  (This impact was not considered in the management plans but was an issue in the Gualala Aggregates EIR.)  M-15

C.  Effects on Riparian Habitat - Coho salmon are dependent on riparian habitat.

1.  "Bar skimming disturbs the existing riparian vegetation, providing opportunities for invasion by non-native species ..." Mitigatable with buffer and revegetation/irradication program.  M-9, M-11

2.  "Bar skimming mechanically removes habitat at the early to mid-successional stages, interrupting the natural formation of landforms which develop habitat complexity and a diversity of age classes."  Even with a buffer the opportunity to build a higher bar and establish a more complex habitat is gone.  May be unmitigatable.  M-9, M-11

3.  "Downcutting of the river channel ... can increase stream velocity and bank erosion, resulting in impacts to all habitat stages."  Mitigatable, perhaps, by limiting extraction to recruitment. M-1

4.  Modification of the substrate within the zone of seedling establishment.  "Substrate modifications of most concern are those which result in loss of gravels and exposure of the clay layer." Largely mitigatable by extraction limitations but there still is an unavoidable change to the substrate.  M-1, M-2

5.  "Terrace pit development impacts riparian habitat by removing vegetation - often for the long term.  Pits may  constrain the channel, reducing the area in which a diversity of riparian habitat stages may develop." May be possible to mitigate through appropriate design and conservation easements , however stream capture must be anticipated.  M-F1

Observed Gravel Extraction Impacts in the Garcia from the Garcia River Gravel Management Plan:

Five sites are listed as having extensive erosion during the 1995 floods.  The two areas chosen to show historic changes through sequential photographs, indicate a shifting of the low flow channel and braiding which, it is noted, may occur because of local impacts such as removal of vegetation or gravel.  Specific examples of degradation caused by instream mining are cited that  indicate instability:  "Downstream changes such as braiding on Bar 12 resulting from gravel skimming on Bar 11 were documented by Fugro West, Inc. (1994)"  (page 6), "The Baxman mining operations on Bar 30 resulted in reduced pool habitat quality along two stream reaches, as well as the elimination of the natural pool-riffle sequence.  (Matthews, 1990)" (page 7)

 "Incision in the thalweg that extended through the estuary suggests that sediment supply is insufficient to maintain the current channel bed elevation.

"If extraction continues, incision of the thalweg is to be expected."

Other limiting factors effecting gravel mining in the Garcia from the Garcia River Gravel Management Plan and other sources

Temperature Impairment:
Other studies conducted on the Garcia River (MCRCD 1992, Gualala Aggregates EIR, MCRCD 1995) show that temperatures above 60=B0F (15=B0C) are considered stressful and temperatures above 70=B0F (21=B0C) are considered lethal.  Optimal rearing temperature range for Coho is 53=B0F - 58=B0F (12=B0C - 15=B0C). (Gualala Aggregates EIR, page 5.4-13)  Mainstem temperatures are consistently above 60=B0F (15=B0C).  (Frog temperature data and daily mean water temperature data collected from 1964 to 1979 at the USGS gauging site at Conner Hole which showed an average mean of 15.3=B0C and the maximum temperatures exceeding 18=B0C an average of 106 day= s per year, EarthInfo 1994, page 27 of GRGMP)  Mainstem temperatures are stressful for Coho rearing.  Riparian cover must be protected and enhanced and gravel bars should be allowed to stabilize and vegetate to promote a greater depth to width ratio and a more complex riparian canopy.

III.  Solutions: Mitigation for Instream Gravel Extraction

Solution 1:  Cease Instream Mining
 "All instream gravel mining methods effect channel stability, riparian habitat, and fish, primarily through channel destabilization, substrate modification and direct loss of riparian vegetation.  The best way to reduce these impacts to channel stability and habitat is to minimize or cease instream mining." (URRARMP, page 60)

Both management plans recommend this final solution for solving the impacts of instream mining.  The plans recommend a phase out, but it is clear that these rivers do not have the resources to maintain a viable extraction industry.

OR - Solution 2: If mining continues, the following mitigations will reduce most, but not all, of the above mentioned impacts:  (all quotes are from the 7.1.1  and 7.1.2 of the URRARMP pages 61 to 66,  (GRGMP pages 87 to 93 is similar),  unless otherwise noted)

M-1  Permit mining Volume Based on Measured Annual Replenishment -This should be based on 50% or less of transport rate AND the actual replenishment at the site.  The Gualala Aggregates EIR explains it this way. "In many cases of instream gravel management, an estimate of average annual bedload transport is used to define a "safe yield" or the volume of gravel that can be safely extracted without depleting the gravel supply in the stream and causing channel changes and negative environmental effects and other impacts.  This concept is not accurate in many cases, particularly on the Garcia River, where a significant volume of bedload is not available for extraction and must move through the project reach to retain equilibrium channel morphology and substrate conditions.  In these cases, the actual gravel replenishment rate at a particular bar or for the entire project reach may be calculated with the sediment transport continuity equation: ...  Unless the sediment trap efficiency of the extraction site is 100% (not the case with bar skimming operations), then the bedload transport rate will always exceed actual replenishment with the latter defined as the volume actually deposited on the extraction site."  (page 5.2 -43, emphasis added)  The Gualala Aggregates EIR further states; "A key concept of gravel replenishment is that it must originate from sources upstream of the project reach in order to avoid depletion of local supply.  If, for example, flood conditions are hydraulically adequate to scour the low water channel and riffles, but not substantial enough to mobilize upstream sources, then gravel deposited on bars which appears as replenishment may have come from the low water channel and riffles in the immediate reach.  Extraction of this gravel would cause a net depletion of gravel supply in local reach.  Therefore, new gravel deposits on the bar in this case would not represent actual replenishment.  Actual replenishment on gravel bars must come from upstream sources in order to add material to the gravel bars while maintaining gravel supplies and related environmental quality in the low water channel and riffles."  (pages 5.2-43, 44)  Finally this quote from the same source sums up the need for cross sections and a maximum limit to yearly extraction that is a fraction of bedload;  "Estimates of bedload transport provide only a rough estimate of the maximum volume of aggregate available each year on average, and as explained above, do not account for storage effects nor year-to-year variability in flow and sediment transport.  Because future flood events during the project life cannot be accurately predicted, use of bedload transport as a "safe yield" is a flawed concept.  Over-extraction within one reach or within the river over an extended period without floods and replenishment can cause the greatest response and possible harm.  Consequently, it is preferable to extract gravel at the actual rate of replenishment as measure by volumetric changes between adequately spaced topographic cross sections of the affected portions of the river, while not depleting local supplies.  Therefore, the extraction rate should  only be a fraction of the estimated annual bedload yield."  (5.2-55)
"It is important for the County and the Data Evaluation Team to develop a system to allocate the total estimated annual replenishment between all of the operators (and individuals extracting their one-time 1000 cu yd) on the Upper Russian River."

M-2  Establish an Absolute Elevation below Which No Extraction May Occur - This is known as the "redline" and it is a permanent line drawn in the gravel it does not change from year to year.  "A redline elevation should be at least one foot above the low flow water surface elevation (at the edge of the bar closest to the low flow channel) during the first year following adoption of the gravel management plan..." To be effective, this line should have some hydrologic reasoning with the intent of retaining the structure of the low flow channel and bar rather than an arbitrary low flow measurement.  "A one-foot minimum elevation as a buffer with a 4% grade toward the bank or a two-foot minimum elevation with a 2% grade is consistent with that recommended by the National Marine Fisheries Service."

M-3  Limit In-channel extraction methods to "Bar Skimming" or an Alternative Method Recommended by the Data evaluation Team
bar skimming - limited to the downstream end of the bar with a riparian buffer on both the channel and hillslope (or floodplain) side.
excavation of trenches or pools in the low flow channel - is discouraged because of associated incision, widening and braiding, and because of direct disturbance of the low flow channel substrate, it also is found to have little habitat benefit because artificially constructed pools, not associated with hydraulic factors such as large woody debris are temporary and fill in during subsequent floods.
trenching on bars - may or may not be beneficial and only for severely aggraded, flat, shallow, and braided streams with few invertebrates

M-4  Grade Slope of Excavated Bar to Prevent Fish Entrapment - 2 to 4 % depending on the height above the lowflow channel

M-5  Extract Gravel from the Downstream Portion of the Bar - "Retaining the upstream one to two thirds of the bar and riparian vegetation while excavating from the downstream third of the bar is accepted as a method to promote channel stability and protect the narrow width of the low flow channel necessary for fish."

M-6  Concentrate Activities to Minimize Disturbance and Avoid Expansion of Instream mining Activities Upstream of River mile 3.7- mining should be concentrated to a few, already mined bars because "skimming decreases habitat and species diversity - these effects should not be expanded over a large portion of the study area.". (GRGMP)  In the GRGMP, Sensitive Habitat Areas were defined and identified in section 4.26 (page 28):  "Those areas which had both high habitat values and steelhead abundance (>100 fish) were chosen as the most sensitive areas which and are depicted in Figure 4.12.  These reaches included River Miles 3.9-4.4, 5.3-6.7, 7.1-7.2 and 7.5-8.0."  This study also states that the mainstem upstream of Windy Hollow Road (RM 3.7) is significant to spawning.  A study completed by CDFG in 1966 found that the "lower river" (below Eureka Hill Bridge) to be among the least damaged reaches of the Garcia.

M-7  Review Cumulative Effects of Gravel Extraction - "The cumulative impact of all mining proposals should be reviewed on an annual basis to determine if there are potential cumulative riverine effects and to ensure that permits are distributed in a manner that minimizes long-term impacts and inequities in permits between adjacent mining operations."

M-8  Establish a Long-term Monitoring Program - see monitoring program GRGMP, Chapter 8 and URRARMP Chapter 8.

M-9  Evaluate Need for In-channel Reclamation on an Annual Basis - "Currently, in-channel re-vegetation is not recommended, provided that skimming operations follow recommendations for a 2% to 4% slope (from bank to low flow channel edge) on the downstream third of the bar without depressions that could trap fish." ... "Revegetation with native species should be planted adjacent to access roads in the riparian zone to act as a buffer and to retain fine sediment.  Retention of all naturally recruited woody debris should be encouraged." In order to mitigate impact C-1 there should be included an irradication program for non-native, invasive species.

M-10  Minimize Activities that Release Fine Sediment to the River - "No washing, crushing, screening, stockpiling, or plant operations should occur at or below the streams 'average high water elevation', or in the Russian River, the top of bank (Macedo, 1995).

M-11 Retain Vegetation Buffer at Edge of Water and Against Bank - "CDFG frequently suggests a buffer of 100 feet back from the top of bank of the channel ( Cox, pers. comm., 1995)."  The plan also recommends a riparian buffer on the upper 1/3 to 2/3 of the bar, along the channel and the hillslope (floodplain) side.  (M-3 and M-5)

M-12  Avoid Dry Road Crossings - "Dry road crossings disrupt the substrate and can result in direct mortality or increased predation opportunity of fry.  The preferred type of crossing is the free-span seasonal bridge (Macedo, 1996)." ... "Any structure placed across a river or recreationally navigable stream should be designed and installed so as to proved sufficient overhead clearance to allow unobstructed and safe passage for small recreational craft (California State Lands Commission, pers. comm., 1996)."

M-13  Limit In-channel Operations to the Period Between June 15 (July 15)* to October 15 "Gravel extraction for outside this window may interfere with salmonid incubation and migration." *The GRGMP notes that spawning salmonids have been observed as late as June 2 and that the hatching period may extend for 40 to 50 days, it must be realized that there will be impact to salmonids with this extraction window.  The start date must be latter than June 15 to avoid impact to these late spawners.

M-14  An Annual Status and Trends Report Should be Produced by the County, the Data Evaluation Team or Agent of the County -  results of monitoring, extraction volumes, recommendations for reclamation. 

M-15  Maintenance flows - Establish minimum by-pass flow at mining and processing sites.

7.1.2  Floodplain (Off-Channel) Extraction Recommendations

M-F1  Floodplain Gravel Extraction Should be  Set Back from the Main Channel - The URRARMP recommends 1000 feet from the main channel and 400 feet from tributaries to avoid "river capture".  (The GRGMP recommends 400 feet.)  Many hydrologists agree that river capture in floodplain pits is inevitable and it is best to recognize this impact and mitigate for the worst case scenario. The plans also recommend (citing CDFG), that the pits should be designed to withstand a 100-year flood and to avoid fish stranding, the pits must be above the 25-year floodplain, however, "NMFS prefers 100-year isolation to minimize fish entrapment."

M-F2  Maximum Depth of Floodplain Gravel Extraction Should Remain above the Channel Thalweg - this reduces the impacts of potential river capture and reduces impact to groundwater quality

M-F3  Side slopes of Floodplain Excavation Should Range for 3:1 t 10:1

M-F4  Place Stockpiled top soil above the 25-year Floodplain

M-F5  Floodplain Pits should be Restored to Wetland Habitat or Reclaimed for Agriculture - "There are very few examples of successfully restored or reclaimed gravel extraction pits ...".  The importation of clean, similar material to fill a pit for agricultural reclamation is unlikely.

M-F6  A Plan Must be Submitted Which Accounts for Long-term Liability - The impacts of floodplain pits goes far beyond the economic life of the operation - the general public should not bear this burden.

M-F7  Establish a Long-term Monitoring Program - to monitor " impacts to river stability, groundwater, fisheries, and riparian vegetation" and assess "any reclamation or restoration attempted".

M-F8  Annual Status Report - Included in the above mentioned report.

M-F9  Floodplain Skimming Should only be Considered if Future Channel Incision Deepens the Low Flow Channel
It seems highly unlikely that sediment supply into the river from upstream sources will be so reduced as to cause significant natural incision.