2010 Annual Report 1a.Objectives (from AD-416) The overall objectives of the proposed study are to (1) determine critical shear stress and erodibility values for fine-grained materials comprising the channel boundary of selected tributaries of the Tualatin River, (2) use these results to estimate how potential changes in flow regime may impact the frequency and duration of sediment entrainment and bank stability, (3) test a new, smaller- version of the jet-test device being constructed by the USDA-ARS, and (4) determine the magnitude of root reinforcement provided by native riparian species in the basin. 1b.Approach (from AD-416) Reconnaissance of tributaries of the Tualatin River will be conducted to ascertain channel stability using Rapid Geomorphic Assessments (RGAs) and to select 50 sites for more intensive data-collection activities. An additional 250 sites will be selected for more limited erodibility testing. At each of the 50 intensive sites, a series of measurements will be conducted to provide the data to perform analyses of erosion potential and bank stability. For erosion potential, submerged jet tests will be performed to determine the critical shear stress and erodibility coefficient of bed and bank-toe materials. With these data, erosion rates under a given boundary shear stress and duration will be estimated. Resistance of streambanks to mass failure will be determined using a borehole shear-test device. Historical flow data will be downloaded from USGS Web sites and used to determine trends in mean-daily and peak flows over the period of record. Discharge data will be used to develop flow magnitude, frequency and duration relations using standardized techniques. Boundary shear stress will be obtained from the discharge data in combination with bed-slope information obtained during the RGAs. Flow and boundary shear stress data will be used in combination with critical shear-stress data to determine under which flows entrainment is predicted at each site. The frequency and duration relations for these discharges will provide an estimate of the percentage of time that erosion will occur. This analysis will be conducted for both existing conditions and for alternative flow regimes. The Bank-Stability and Toe-Erosion Model (BSTEM) will be used to evaluate critical conditions for bank stability. The frequency that critical hydrologic conditions occur will be evaluated from historical gage records and compared to the proposed alternative flow regimes to determine the potential effects of the proposed regimes on the volumes and frequency of mass failure. Tensile strength and root distributions will be determined in a trench or bank face at field sites for five native, riparian species. This will be accomplished by. 1)determining the root diameter – tensile strength relation;. 2)quantifying the number of roots and their size distribution; and. 3)quantifying the distribution of roots with depth. For each species at least three sets of field experiments, representing a range of ages will be conducted. A tentative list of native species has been developed from which five will be selected. Results of the field investigation will be used as inputs into the root-reinforcement model RipRoot to calculate the increase in shear strength due to roots. Simulations of bank stability conditions will be conducted using BSTEM with a range of measured bank-strength data from tests along tributaries of the Tualatin River. This will be accomplished by modeling different bank heights, bank angles and pore-water pressure conditions with and without the effects of vegetation. Comparisons between species and between non-vegetated and vegetated banks will be made. Species assemblages making up the greatest reinforcing effects will be tested and reported. 3.Progress Report Management of stream channels bounded by cohesive sediments is problematic because of the difficulty in quantifying the resistance of the boundary to erosion by hydraulic and geotechnical forces. Several instruments are available to test erosion resistance in the field but comparisons of results are not available. Submerged jet-tests and cohesive-strength-meter tests have been conducted at 50 sites in sediments comprising the channel boundary to determine the resistance of the materials to hydraulic forces operating at the bed and bank toe. The Borehole Shear Tester and Torvane-shear tests are being conducted to determine the resistance to geotechnical forces operating on the bank mass. All sites have been tested. Analysis of historical flow records (provides by CWS) have been analyzed with the jet-test data in one sub-basin (Cedar Mills-North Johnson) to compare critical shear stresses with those provided by existing flows. Flow data will also be used with the Bank-Stability and Toe-Erosion Model (BSTEM) to determine critical conditions for bank stability at the selected sites. Differences in results will be used to identify the net effects of the proposed flow regimes on bank stability. BSTEM will also be run iteratively over a series of annual hydrographs. Volumes of erosion by hydraulic forces and bank failures will be summed for each storm event comprising the annual hydrograph for both existing and proposed conditions. Differences in eroded volumes will provide information on the effects of the proposed flow regimes. A draft NSL Technical Report Results for the Cedar-Mills North Johnson sub-basin was provided to the cooperator for review. Project monitoring is conducted by conference calls and by meetings in the field area.