USING BEAVER DAM ANALOGS TO REDUCE DOWNSTREAM SEDIMENT LOADS A Pilot Project in California Creek, Spokane, Washington, USA Sue Niezgoda, Ph.D., P.E. Associate Professor of Civil Engineering Gonzaga University
Beaver Optimum Habitat Requirements WATER!!! Small- to medium, lowgradient streams (<6% slope) Lakes, wetlands, estuaries, off-channel tribs, etc. WOOD!!! Developed riparian areas that contain (1) vegetation for food, and (2) potential construction materials to build dams and lodges.
Beaver Dams! Created to impound water around lodge Dam location / repair cued by running water Dams constructed of wood and available debris (e.g., plastic, metal) Where palatable species are rare, conifers are used more in dams, with hardwoods saved for the food cache (Barnes and Mallik 1996)
World s Larger Beaver Dam Found in Alberta, Canada (2007) using Google Earth 850 m; longer than Hoover Dam
Benefits of Beaver Dams Bouwes et al. (2015)
Beaver Dam Viability Pollack et al. (2015) Beaver Restoration Guidebook
What are Beaver Dam Analogs? Structures completely or partially built by humans that mimic many of the functions of natural beaver dams
BDA Materials and Equipment Materials-similar to beaver dams Willow branches Herbaceous vegetation Rocks, mud Wood posts (typically non-treated) Equipment needed Chainsaw-to cut and sharpen posts Hand saws to cut willow Post pounder/power source (hydraulic or pneumatic) Material cost and labor = $500-$5000/structure Size of structure (length) Size of stream (depth of posts) Source distance of building materials Labor costs Students FREE LABOR!
Sediment Trapping in Hangman Creek Watershed, Spokane WA, USA Facts 1780 sq. km. 1112 sq. km. of dryland agriculture 358 km of perennial streams Issues Major changes in vegetation Altered hydrology - flashy Easily erodible soils Ag Lands Glacial Lake Deposits Human impacts Q 2 = 184 cms Q 10 = 370 cms Q 100 = 600 cms
Hangman Creek Flashy Hydrology Large Sediment Supply Nine Mile Dam Spokane River Spokane River
Hangman Creek - California Creek BDA Pilot Study Research Goal Examine effectiveness and sustainability of BDAs to enhance ecosystem benefits and reduce sediment loads and erosion in California Creek and the Hangman Creek Watershed. Research Objectives Collect preliminary monitoring data in California Creek to help establish a long-term intensely monitored watershed (BACI) study to test sediment trapping hypotheses in the larger Hangman Creek Watershed Develop structural design guidelines for BDAs in a variety of stream reaches with varying stream power
California Creek BDA Locations installed Sept 2016
California Creek Monitoring Plan Set Hypotheses Sediment Trapping Water Storage Reduced Erosion Develop Monitoring Plan Methods, Equipment, Personnel QA/QC Implement Monitoring Plan Analyze and Synthesize Results Adaptively Manage Monitoring Feedback into Adaptively Managing BDAs 1 st round of data collected Fall 2016 Drum roll please....
Spring Flood Feb 16-17, 2017 Rain on Snow Event Hangman Creek 10,000 cfs 5-year Event California Creek Landowner haven t seen flows this high in 30 years! Drone Video
BDA Adaptive Management - Extend width of each existing BDA and reinforce/rebuild - Use hydraulic modeling and drone footage: - Adjust BDA angles to be more effective - Add in 2-4 additional BDAs Yellow existing Red proposed Blue newly installed
New BDA Installation Sept 2017
Preliminary Conclusions and Lessons Learned Hypothesis Testing: BDAs maybe trapping sediment behind their structure Preliminary estimates 10-16 cu.meters/year (rough estimate, more data needed) BDAs raise ground water levels and store water longer Observational evidence only of this over first year (more data needed) Lessons Learned Not built wide enough into floodplain and several were flanked significantly Drone footage during floods can help with redesign (location and orientation) Structure is quite stable even under high flows Channel substrate material is important to BDA stability Inexpensive to build and modify, low risk
Questions?
Monitoring Results Repeat RTK Surveys Comparison of 2016 and 2017 Erosion Deposition Tolerance 0.2 ft
Monitoring Results RTK Comparison 2016-2017 Avg, Deposition Upstream of BDA (m) Volume of Deposition Upstream of BDA (cu. m) 0.15 10