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​Debris, sediment

  A. Background

  1. Post-fire debris flows can cause acutely high sediment loading and deposition in streams.

  2. The most extensive potential damages to stream habitats likely are from wildfires, as stochastic (chance) events.

  3. Wildfire possibilities increase as climate change brings rising temperatures and serious stream and soil dewatering.

  4. Naturally occurring highly erosive soils also are sources of sediment transport to streams.

  5. High intensity storms, unusually high stream flows, and landslides can increase sediment load.

  6. Logging, road and trail installation and maintenance, off-road recreation can add to sedimentation [1].

  7. Nutrients and waste solids in runoff from pastures can result in streambed coverings, including algae growth.

  8. Lost streamside vegetation, from fire or trampling, for example, can increase erosion transport of soil into streams.​

    Limiting | Drought | Debris

No streambed sedimentation at large-flow tributary Bear

Bear_edited.jpg

  B. Consequences

  1. Accumulation of debris and sediments can stress and diminish trout populations.

  2. It can smother macroinvertebrates.

  3. This can diminish their diversity and density and decrease the food supply for trout [2-4]

  4. Sedimentation also can clog interstitial spaces in substrate harboring incubating eggs, at redds.

  5. It can suffocate embryos or block emersion of alevins, reducing reproduction [5-7].

  6. Post-fire debris flows are stochastic disturbances resulting from high-intensity rainfalls at burned areas.

  7. They can deliver sediment, and larger debris, to stream channels.

  8. In the short term, this may limit or eliminate trout presence within the affected area.

  9. This can result from scouring stream reaches to bedrock, especially in small headwater streams

  10. It can remove food and damaging other necessary features such as cover and connectedness [8-13].

  11. Over the long term and extending downstream, it can result in reconfigured stream morphology [9, 14-17].

  12. It includes reduced channel stability and increased sediment loads.

  13. This can reduce trout population persistence throughout the stream [18, 19].

  C. Conditions

  1. Slopes greater than 30 percent and at least 300 ft in length or adjacent to ravines are distinctive.

  2. They have high risk of post-fire debris flows [9, 20, 21].

  3. Slopes greater than 7 percent [22] and confined have high risk of producing sediment flow [23].

  4. Researchers have found a majority of post-fire debris flows associated with other particular characteristics.

  5. That would be watersheds or sections with drainage areas >640 acres and >20 percent slopes [24].

  6. The likelihood and extent of sedimentation depends primarily on fire severity [25].

  7. Also consequential are the post-fire timing, duration, and magnitude of precipitation events.

  8. Damage to the macroinvertebrate community from sedimentation can increase with elevation [26].

  9. Colorado describes measurement of the reduction in relative abundance of sediment-sensitive taxa [26].

  10. That and the increase in relative abundance of sediment-tolerant taxa [26].

  11. Combined, they enable judging risk to macroinvertebrates [26].

  12. This is based on methods recommended by the National Water Quality Assessment Program [27].

  13. Macroinvertebrate density may be a more sensitive indicator of sedimentation effects than diversity [28].

​​

References

  1. M. K. Young, "Colorado River Cutthroat Trout: a Technical Conservation Assessment," USDA Forest Service, Rock Mountain Station, Fort Collins, 2008.

  2. E. E. Wohl, "Virtual Rivers: Lessons from the Mountain Rivers of the Colorado Front Range, New Haven, CT: Yale University Press, 2000.

  3. J. M. Culp, F. J. Wrona, and R. W. Davies, "Response of Stream Benthos and Drift to Fine Sediment Deposition Versus Transport, Canadian Journal of Geology, vol. 64, pp. 1345-1351, 1986.

  4. P. J. Wood and P. D. Armitage, "Biological Effects of Fine Sediment in the Lotic Environment," Environmental Management, vol. 21, pp. 203-217, 1997.

  5. G. M. Kondolf, "Assessing Salmonid Spawning Gravel Quality," Transactions of the American Fisheries Society, vol. 129, pp. 262-281, 2000.

  6. C. D. Williams, "Summary of Scientific Findings of Road and Aquatic Ecosystems: Primary Research and Analysis, 1999, Available at http://lobby.la.psu.edu/068_Roads_in_National_Forests/Organizational_Statements/PRC/PRC_Effects.doc.

  7. J. P. McGee, T. E. McMahon, and R. F. Thurlow, "Spatial Variation in Spawning Habitat of Cutthroat Trout in a Sediment-Rich Stream Basin," Transactions of the American Fisheries Society, vol. 125, pp. 768-779, 1996.

  8. R. E. Gresswell, "Fire and Aquatic Ecosystems in Forested Biomes of North America," Transactions of the American Fisheries Society, vol. 128, pp. 193-221, 1999.

  9. E. R. Sedwell, R. E. Gresswell, and T. E. McMahon, "Predicting Spatial Distribution of Postfire Debris Flows," Freshwater Science, vol 34, no. 4, pp. 1558-1570, 2015.

  10. M. A. Bozek and M. K. Young, "Fish Mortality Resulting from Delayed Effects of Fire in the Greater Yellowstone Ecosystem," Great Basin Naturalist, vol. 54, pp. 91-95, 1994.

  11. D. K. Brown, A. A. Echelle, D. L. Propst, J. E. Brooks, and W. L. Fisher, "Catastrophic Wildfire and Numbers of Populations as Factors Influencing Risk of Extinction to Gila Trout (Onchorhynchus gilae), Western North American Naturalist, vol. 61, pp. 139-148, 2001.

  12. P. J. Howell, "Effects of Wildfire and Subsequent Hydrologic Events on Fish Distribution and Abundance in Tributaries of North Fork John Day River," North American Journal of Fisheries Management, vol. 26, pp. 983-994, 2006.

  13. C. M. Sestrich, T. E. McMahon, and M. K. Young, "Influence of Fire on Native and Nonnative Salmonid Populations and Habitat in a Western Montana Basin," Transactions of the American Fisheries Society, vol. 140, pp. 136-146, 2011.

  14. J. R. Sedwell, G. H. Reeves, F. R. Hauer, J. A. Stanford, and C. P. Hawkins, "Role of Refugia in Recovery from Disturbances: Modern Fragmented and Disconnected River Systems," Environmental Management, vol. 14, pp. 711-724, 1990.

  15. G. E. Reeves, L. E. Benda, K. M. Burnett, P A. Bisson, and J. R. Sedwell, "A Disturbance-Based Ecosystem Approach to Maintaining and Restoring Freshwater Habitats of Evolutionary Significant Units of Anadromous Salmonids in the Pacific Northwest," in Evolution and the Aquatic Ecosystem: Defining Unique Units in Population Conservation, Bethesda, MD, 1995.

  16. L. Benda and T. Dunne, "Stochastic Forcing of Sediment Supply to Channel Networks from Land Sliding and Debris Flow," Water Resources Research, vol. 33, pp. 2849-283, 1997.

  17. C. L. May and R. E. Gresswell, "Spatial and Temporal Patterns of Debris-Flow Deposition in the Oregon Coast Range, USA, Geomorphology, vol. 57, pp. 135-149, 2004.

  18. L. D. Benda, D. Miller, P. Bigelow, and K. Andras, "Effects of Post-Wildfire Erosion on Channel Environments, Boise River, Idaho," Forest Ecology and Management," Vol 178, pp. 105-119, 2003.

  19. S. M. Wondzell and J. G. King, "Postfire Erosional Processes in the Pacific Northwest and Rocky Mountain Regions, Forest Ecology and Management, vol. 178, pp. 75-87, 2003.

  20. S. H. Cannon, J. E. Gartner, M. G. Rupert, J. A. Michael, A. H. Rea, and C. Parrett, "Predicting the Probability and Volume of Post-Wildfire Debris Flows in the Intermountain West United States," Geologic Society of America Bulletin, vol. 122, pp. 127-144, 2010.

  21.  J. E. Gartner, S. H. Cannon, P. M. Santi, and V. G. Dewolfe, "Empirical Models to Predict the Volumes of Debris Flows Generated by Recently Burned Basins in the Western US," Geomorphology, vol. 96, pp. 339-354, 2008.

  22. O. S. Hungr, S. McDougall, and M. Bovis, "Entrainment of Material by Debris Flows," in Debris Flow Hazards and Related Phenomena, Berlin, Germany, Springer Verlag Praxis, 2005, pp. 135-158 in M. Jacob and O. Hungr (editors).

  23. K. M. Moore, K. K. Jones, and J. M. Dambacher, "Methods for Stream Habitat Surveys: Aquatic Inventories Project," Oregon Department of Fish and Wildlife, Corvallis, Oregon, 2007.

  24. C. Parrett, S. H. Cannon, and K. L. Pierce, "Wildfire Related Floods and Debris Flows in Montana in 2000 and 2001," U.S. Geological Survey, Reston, VA 2003.

  25. Hyde, K., "The Use of Wildfire Burn Severity Mapping to Indicate Potential Locations for Gully Rejuvenation, Bitterroot Valley, Montana," University of Montana, Missoula, MT, 2003.

  26. Colorado Water Control Division, "Guidance for Implementation of Colorado's Narrative Sediment Standard, Section 31.11(1)(a)(i), 2014.

  27. D. M. Carlisle, M. R. Meador, S. R. Moulton, and P. M. Ruhl, "Estimation and Application of Indicator Values for Common Macroinvertebrate Genera and Families of the United States," Ecological Indicators, vol 7, no. 2007, pp. 22-223, 2007.

  28. T. F. Waters, "Sediment in Streams--Sources, Biological Effects and Control," American Fisheries Society, Bethesda, MD, 1995.

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