Mitigation for the Construction and Operation of Libby Dam

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85 83 81 79 77 75 73 Elevation (ft) 71 69 67 65 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Station (feet) As Built Existing Figure 10. The longitudinal profile of the reach of Young Creek located within the State Lands Restoration Project. The survey was completed before (2002; existing) and after (2003; post-construction) project completion. The station (longitudinal location measured at the channel thalweg) begins at the upstream boundary of the project. The as built stream channel was approximately 250 feet longer due to the increased meander frequency that resulted from constructing the new stream channel. 143
Discussion The Grave Creek Phase I and Libby Creek Upper Cleveland Restoration Projects maintained the designed channel dimensions after each stream experienced the spring freshet after project construction. Streams with C3 channel types should have width/depth ratios >12 and typically range from 10-37 (Rosgen 1996). Both the Libby and Grave Creek restoration projects were designed within this criterion and continued to meet it after the channel forming flows that occurred during the first spring freshet following project construction. The stream channel dimensions measured at the crosssection surveys on both the Libby Creek Upper Cleveland and Grave Creek Phase I Restoration Projects did not significantly (p > 0.05) change after the first spring freshet. Mean bankfull width, depth, maximum depth, width to depth ratio and cross sectional area all remained similar between years. Pool dimensions within both projects were similar between years. However, mean and maximum depth decreased after each project was subjected to bankfull channel shaping flows during the spring freshets. Although we did observe a decrease in pool depths after project construction, pool depth, quantity and quality still exceeded conditions that existed prior to project construction. We believe the observed changes in the pools that occurred as a result of the spring freshet on both Libby and Grave Creeks had relatively minor effects on the quantity and quality of juvenile salmonid rearing habitat, and that overall the stream channels are existing at a state near dynamic equilibrium. In addition to the minor changes in pool depth, we did observe an overall decrease in riffle slope after the spring freshets that were common for both the Grave and Libby Creek projects. The changes were primarily associated with the cobble gradient control structures that were placed in the pool tail out areas. These were the first two stream restoration projects that the cobble gradient control structures were utilized, and help point out that the science of natural channel design is still evolving, with improvements in structure design occurring in this relatively new science. We believe that these particular structures can serve a useful purpose, but that design modification could improve their function. We currently recommend designing these structures between 1.25 to 1.5 times the mean bankfull riffle width. We further recommend the run width below the cobble gradient control structures be designed at 0.8 to 1.0 times the mean bankfull riffle width. The cobble gradient control structures were constructed with material that was between D90 to D100 sized substrate within each particular stream. We will continue to monitor the performance of the cobble gradient control structures and modify their design criteria accordingly. We monitored the benthic macroinvertebrate and fish communities at the Libby Creek Upper Cleveland Project in order to evaluate the ecological response the restoration activities (see Chapter 1). Our results were somewhat counter intuitive. Of the seven metrics selected before the study, 3 had values in 2003 that were significantly different from the values attained from the 2000 sampling. However, they were all in the opposite direction expected. That is, we expected the samples to reflect an improvement after restoration, but the directions of change for the three significantly different metrics were consistent with disturbance. Similarly, redband trout abundance decreased by an average of 33.5% the first year after project completion. However, bull trout abundance within the project area increased by 80% compared to data collected three years prior to 144
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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
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Table 4. T-test results. This table
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Figure 19. Montana Mountain Metrics
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Table 5. T-test results. This table
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Juvenile Salmonid Population Estima
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Grave Creek Juvenile salmonid monit
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Number Fish per 1000 Feet 100 80 60
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Libby Creek Section 1 of Libby Cree
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Figure 28. Rainbow trout, brook tro
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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 and 120: Methods and Results Eureka Pond The
Page 121 and 122: spacing was 172.8 feet, which repre
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: Table 7. Mean cross sectional area,
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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