The focus of the modeling effort will be to inform on the two primary risk categories identified during the August 18, 2014, Buckmire technical workshop. These two risk categories are: 1) Flood risk management, and 2) Agricultural/Infrastructure risks due to changed hydrologic regime in the restored area.  

An existing USACE developed HEC-RAS model of the Columbia River below Bonneville Dam will be modified to provide additional detail in the project area. Overall domain of the Buckmire Slough existing condition model will extend from the Lake River confluence with the Columbia on the downsteam end to the Willamette confluence with the Columbia on the upstream including Lake River and Vancouver Lake at a minimum. Areas bounded by Lake River and Columbia, including Shillapoo Lake, are within the model domain, but will not be developed in detail or reported as no change to surface water flows are expected between existing and with project condition.

Model runs will include a typical winter and freshet season selected from observed data as well as a 1996 flood event run. Due to complicated overland flow patterns in the Buckmire project area, new 2-dimensional capabilities in HEC-RAS 5.0 beta will be used to model the phase 2 area. A 1-dimensional model developed by others in the Phase 1 area will be provided by and incorporated into the project area model. USACE personnel will calibrate the existing condition model to existing observed data.  USACE personnel will then run the existing conditions model for a single observed winter and spring freshet season as well as the 1996 flood event.  USACE will prepare a brief model letter report describing existing conditions, model development and calibration work activities.

Significant Assumptions:
-- Details of existing pumping or water control structure operations are not required to establish existing conditions related to the two identified risk categories.
-- The existing OTAK Consultants Buckmire HEC-RAS model and/or model data will be provided by others for incorporation into the existing condition and alternative models.
-- Risk item “Agricultural/Infrastructure risks due to changed hydrologic regime in the restored area” can be addressed by changes in surface water elevations within the project footprint. USACE does not propose to perform groundwater modeling within this scope.
-- Risk item “Flood Risk” will be addressed with modeling of the 1996 event and comparison of maximum water surface elevations between the existing and alternative condition within the domain. Modeling specific to address FEMA National Floodplain Insurance Program implications is not scoped.
-- No additional data collection is required (bathymetry, calibration data or otherwise). Where data is not available, best judgment is adequate for planning level model development and analysis purposes.
-- Details of project alternatives will be provided by others. USACE will participate in alternative design meetings, but iterative modeling work to refine alternative actions is not included in the scope.
-- Use of beta model software is acceptable for planning purposes. The existing HEC-RAS 5.0 beta is experiencing rapid development with a planned release in early 2015. Additional 2-D modeling features will become available intermittently during development and will be used to extent possible.
-- Scope does not include providing data for HEC Ecosystem Functions Model (EFM) use at this time. When EFM data needs are know, appropriate scoping can occur and get integrated into the modeling scheme.