Mitigation for the Construction and Operation of Libby Dam

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Libby Creek Upper Cleveland Project Montana FWP completed the Libby Creek Upper Cleveland Stream Restoration Project in 2002 (approximate river mile 22), which restored approximately 3,200 feet of stream channel to the proper dimension, pattern and profile. This was conducted on Libby Creek located approximately 18 miles southwest of the town of Libby, Montana within Township 27 North, Range 31 West, Section 1 in Lincoln County (Figures 2 and 3). Past land management activities including logging, mining, riparian road construction, and stream channel manipulation have resulted in accelerated bank erosion along a number of meander bends, resulting in an over widened, unstable, and shallow channel (Sato 2000), which has resulted in low quality habitat for native salmonids including bull trout and redband trout. The existing channel prior to this restoration project was over-widened with frequent lateral migration of the active stream channel. These conditions resulted in frequent multiple channels within the project reach (Figure 4). Width depth ratios were high (ranging from 28-43 feet) and shallow mean bankfull channel depths ranging from 0.58 to 1.79 feet in depth (Table 1). We established design criteria for the channel dimensions according to reference reach criteria established by Rosgen (1996). Table 1 provides the design criteria and summary of existing conditions for several stream channel parameters. Stream restoration work began in September 2002 and proceeded through November 2002. During this period Montana FWP excavated approximately 3,200 feet of new channel according to the design criteria (Table 1) including an average design bankfull width and depth of 32 feet and 3 to 7 feet, respectively. We designed the channel pattern (Dunnigan et. al 2003) to utilize existing riparian vegetation in project reach wherever possible, in an attempt to maximize channel stability, and promote recovery of the riparian area. The resulting stream pattern design increased sinuosity (stream length divided by valley length) from 1.1 to 1.6, and subsequently increased total stream length from approximately 2,700 to 3,200 feet. During construction phase of this project, numerous structures were installed including 11 Cobble grade control structures for grade control and bank protection in pool tail-outs created by outside bends and rootwad complexes, 19 rootwad complexes for bank stabilization on outside bends of the newly constructed stream channel, 3 rock vanes to provide gradient control and pool habitat. Substantial effort was also expended to restore a healthy riparian vegetative community. These efforts included transplanting approximately 500 shrubs during construction and planting approximately 2,000 willow cuttings, 75 cottonwood poles, and 1,600 containerized native shrubs after stream channel construction. The stream channel profile prior to project construction contained few pools (Figure 5), and due to the limited geographical overlap with the newly designed channel thalweg could not accurately be displayed on the same figure as the new channel profile surveyed in 2002 and 2003 (Figure 6). The designed channel profile required excavation at numerous depositional areas throughout the project reach (Figure 6) and resulted in an increased quantity of pool habitat within the project area. Prior to project construction, the mean pool-to-pool distance was 325.4 feet. We resurveyed the project area in the summer of 2003 after the restoration work had been subjected to the first spring freshet after construction, and the mean pool 125
spacing was 172.8 feet, which represented a 46.9% reduction in the distance between pools. Pool spacing measurements in 2003 represented a complete sampling of all pools present during both years. However, the measurements collected in 1999 represented a sampling of the pools. We conducted a t-test and concluded that the distance between pools decreased significantly as a result of project construction (p < 0.05). In 1999, prior to project construction, we measured stream channel morphology at 5 cross-sectional survey locations in riffle habitat within the project area. After project construction in 2002 we established 9 permanent transects in riffle habitats. These same locations were surveyed again in the summer of 2003, after the project had experienced the first spring freshet. At each transect we measured mean bankfull width, depth, width to depth ratio, and cross sectional area. We used analysis of variance (ANOVA) and a subsequent multiple comparison test (Fisher’s Least Significant Difference; Zar 1996) to test for significant differences between years (alpha = 0.05; Table 2). Mean bankfull width, depth, and width to depth ratio were significantly reduced from 1999 to 2002 and 1999 to 2003. Comparisons for the three parameters between 2002 and 2003 were not significantly different (p > 0.05; Table 2). However, the associated variance for each of the 4 parameters decreased each year (Table 2). Due to the importance of pool habitat to rearing redband and bull trout within the project area, we devoted a substantial effort to monitor pool habitat after project construction to evaluate whether the pools maintained depth, width and length through time. After project construction in the fall of 2002, we measured mean bankfull depth, width, length and maximum bankfull depth of the 20 pools constructed in the project area. We repeated these measurements in the summer of 2003 after the project had experienced the first spring freshet. We did not perform a statistical comparison for these data because the pool measurements represented all pools within the project area (i.e. complete census), making statistical comparisons unnecessary. We observed a decrease in the mean values of each of the 4 parameters from 2002 to 2003 (Table 3). Mean bankfull depth showed the sharpest decline (18%) from 2002 to 2003, followed by pool length, which decreased by 17.7% (Table 3). The variance of each of the 4 parameters also decreased from 2002 to 2003 (Table 3). The mean annual variance for mean bankfull depth had the highest decrease (18%) between 2002 and 2003, followed by maximum bankfull depth variance, which decreased by 40.4% (Table 3). Although mean pool length decreased by 17.7%, the total proportion of pool habitat (sum of all pool lengths divided by total project area stream length) within the project area decreased by 4%, from 22% in 2002 to 18% in 2003. In addition to a complete census of all pools within the project area, we also surveyed all 13 riffles within the project area to evaluate changes in riffle slope through time. The postconstruction mean riffle slope in 2002 was 1.95% (variance = 7.79*10 -5 ), which decreased by 33.3% in 2003 to a mean riffle slope of 1.30% (variance = 2.033*10 -5 ). We attribute the overall flattening of the riffles within this project to 2 factors. Further examination of our survey information revealed that the top end of our riffles generally incised within the channel (degraded) due in part to the scour achieved below many of the gradient control cobble structures installed at the tailout area of many of the pool structures. The lower portion of 126
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Mitigation for the Construction and
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MITIGATION FOR THE CONSTRUCTION AND
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depth of burbot that were relocated
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ACKNOWLEDGEMENTS We are thankful to
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Juvenile Salmonid Population Estima
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deviation from reference conditions
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Figure 46. Minimal detectible diffe
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Chapter 2 Tables Table 1. Design sp
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INTRODUCTION Libby Reservoir was cr
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PROJECT HISTORY Montana Fish, Wildl
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2002 - Montana FWP collaborated wit
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DESCRIPTION OF STUDY AREA Subbasin
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Table 1. Current relative abundance
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Similar impacts have been observed
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2460 2440 2420 2400 2380 2360 2340
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construction and operation of Libby
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Chapter 1 Physical and Biological M
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Biological monitoring data was prov
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Figure 1. An aerial photograph of L
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antenna located approximately 5 cm
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We compared samples collected in Se
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extends downstream 131 m. This sect
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and reduced again to 28 ganged floa
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Results Bull Trout Redd Counts Grav
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Table 1. Bull trout redd survey sum
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Quartz Creek Bull trout redd counts
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Bull Trout Redds 40 35 30 25 20 15
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Keeler Creek Bull trout that spawn
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Burbot Monitoring Below Libby Dam T
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Table 2. Summary information for th
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7000 6000 5000 Y = 45.246e 0.0055x
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The Libby FWP Mitigation Staff surg
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Table 2. (Continued) Capture locati
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Figure 18. Capture locations for a
Page 69 and 70: Table 4. T-test results. This table
Page 71 and 72: Figure 19. Montana Mountain Metrics
Page 73 and 74: Table 5. T-test results. This table
Page 75 and 76: Juvenile Salmonid Population Estima
Page 77 and 78: Grave Creek Juvenile salmonid monit
Page 79 and 80: Number Fish per 1000 Feet 100 80 60
Page 81 and 82: Libby Creek Section 1 of Libby Cree
Page 83 and 84: Figure 28. Rainbow trout, brook tro
Page 85 and 86: Pipe Creek Juvenile rainbow trout w
Page 87 and 88: Table 6. Average length and weight
Page 89 and 90: Catch per Net A. Mountain Whitefish
Page 91 and 92: Table 8. Kamloops rainbow trout cap
Page 93 and 94: 25000.0 20000.0 15000.0 10000.0 500
Page 95 and 96: Burbot per Trap Day 3 2.5 2 1.5 1 0
Page 97 and 98: Table 9. Average catch per net for
Page 99 and 100: Table 11. Percent composition of ma
Page 101 and 102: deviation = 0.052; Figure 43), with
Page 103 and 104: Table 12. Individual probability va
Page 105 and 106: Discussion Long-term monitoring of
Page 107 and 108: We believe that Libby Reservoir dur
Page 109 and 110: Figure 47. Minimal detectible diffe
Page 111 and 112: References Bahls, L., R. Bukantis,
Page 113 and 114: trout status report (below Kootenai
Page 115 and 116: Chapter 2 Stream Restoration and Mi
Page 117 and 118: food sources, as evidenced by the l
Page 119: Methods and Results Eureka Pond The
Page 123 and 124: Figure 2. Vicinity Map for Upper Li
Page 125 and 126: Table 1. Design specifications for
Page 127 and 128: 70 60 50 40 30 20 10 0 500 1000 150
Page 129 and 130: Grave Creek Phase I Restoration Pro
Page 131 and 132: Table 4. Design specifications for
Page 133 and 134: 190.0 185.0 180.0 175.0 170.0 165.0
Page 135 and 136: educed the mean width and width to
Page 137 and 138: Table 7. Mean cross sectional area,
Page 139 and 140: Discussion The Grave Creek Phase I
Page 141 and 142: References Chisholm, I.M., M.E. Hen
Page 143 and 144: Appendix 148
Page 145 and 146: Table A2. Lower Grave Creek Demonst
Page 147 and 148: Table A4. Libby Creek depletion pop
Page 149 and 150: Table A7. Mean zooplankton densitie
Page 151 and 152: Table A9. Mean zooplankton densitie
Page 153: Table A13. Yearly mean total zoopla
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Mitigation for the Construction and Operation of Libby Dam

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