Project Number: 6408-13000-018-33
Project Type: Reimbursable

Start Date: Oct 01, 2007
End Date: Jun 30, 2010

Objective:
The primary objectives of the proposed study are to enhance and further validate the predictive, numerical models CONCEPTS and BSTEM to fully realize their potential as state-of-the-art tools for stream management, in the Lake Tahoe Basin and elsewhere. Specific objectives are: (1) Quantifying the effects of riparian vegetation and bio-engineered treatments on the resistance of bank materials to hydraulic erosion and bank undercutting for inclusion into both models; (2) Developing near-bank groundwater models to integrate with CONCEPTS and BSTEM for the purpose of simulating spatial and temporal variations in pore-water pressure; (3) Developing algorithms for CONCEPTS to simulate lateral migration of meandering channels in a deterministic fashion by accounting for hydraulic and geotechnical controls; and (4) Validating the use of the CONCEPTS and BSTEM models at the project-scale for existing and restored reaches of selected Tahoe basin streams using time-series historical data on flow, sediment transport and channel geometry.

Approach:
To accurately evaluate the susceptibility of root-permeated and bio-engineered streambanks to erosion, channel widening and lateral migration, the hydraulic and geotechnical resistance of these features must be quantified. A series of field experiments will be conducted using a root tensile-strength testing device in conjunction with root mapping to quantify root reinforcement of meadow and other riparian vegetation throughout the bank profiles. Submerged jet-test devices will be used to determine hydraulic resistance (critical shear stress and erodibility) of bank sediments with and without riparian roots as well as bio-engineered treatments. Laboratory and numerical experiments will be conducted to determine the variability in the fate of failed bank materials with and without roots. Sub-models will be developed or enhanced for BSTEM and CONCEPTS to simulate the spatial distribution of pore-water pressure in a streambank and along a stream-riparian corridor. Data will be collected at selected sites on Trout Creek and the Upper Truckee River to determine: permeability, soil texture, soil-water retention curve, above- and below-ground plant biomass, volumetric soil-water content, pore-water pressure, and groundwater table elevation. Pore-water pressure data for model validation will be obtained using digital tensiometers installed at various depths and distances from the channel along selected reaches representing a range of riparian-buffer systems. To accurately predict channel evolution in sinuous streams and to evaluate restoration strategies that include re-meandering of channels, a sub-model will be developed for CONCEPTS to simulate the lateral migration of meandering streams. The approach of Kean (2003) that extends the meandering-flow model of Smith and McLean (1984) to streams of arbitrary cross section geometry will be used. The model will be tested and validated against observed morphological changes over a range of spatial and temporal scales. BSTEM simulations will provide site specific predictions of appropriate streambank design and performance criteria using selected geometry, vegetation or other treatments. In contrast, CONCEPTS simulations will provide quantifiable evaluations of the cumulative impact of all treatments within the reach on fine-load reduction as well as any downstream impacts on channel processes and morphology.