Umatilla River Floodplain Assessment and Action Plan

The Umatilla River is 89 miles long and drains a watershed area of about 880 square miles. Some of the most prevalent human influences in the subbasin are associated with agriculture, exotic weed introduction, forest practices, livestock grazing, transportation, urbanization, and water development. The result of these activities have led to negative physical impacts, which include stream channelization, reduced instream water volume, high water temperatures, riparian vegetation loss, increased erosion and sedimentation into streams, and land conversion and degradation. The ecological effect of these negative impacts include increased flood frequency, reduced water quality, separation of stream channels from floodplains, loss of exchanges between the hyporheic zone and river flow, and loss and degradation of habitat for aquatic and terrestrial wildlife species.



This project was designed to develop a floodplain-scale, geomorphic-based assessment of current habitat conditions, identify necessary data gaps, and develop an action plan for the Upper Umatilla River Subbasin (Figure 1, attached proposal file). Given the dramatic differences in management in the sections of river, the additional municipalities included, and the previously identified boundaries that have been established by a variety of projects, it was decided to include that portion of the Umatilla River Watershed from the city of Nolin to the headwaters of the North and South Fork of the Umatilla River. This assessment and Action Plan is floodplain centric and includes the mainstem of the Umatilla River and the connectivity to the mainstem of the confluences of the upper tributary streams.



The CTUIR UAFHP successfully completed the development of the Umatilla River Assessment. Our Riverine Ecosystem Planning Approach is founded on comprehensive subbasin, subwatershed, and reach-based level assessments and strategic restoration action plans (scaled up to 20-years) with appropriate levels of agency and public scoping, technical input and buy-in. PCSRF dollars were used to develop vision statements, goals, objectives, restoration and passage priorities are established with measurable targets for watershed and floodplain function to improve fish populations. This includes the prioritization of focal areas and management practices based on key species utilization of existing and historic available habitat, and limiting factors with a mechanism for riverine planning that utilizes scientifically defensible techniques. Assessments developed and supported by the CTUIR are process-based (generally following the guidance of Beechie et al. 2008, Beechie et al. 2010, Beechie et al. 2012, Booth et al 2016, Castro et al. 2019, Palmer et al. 2005, Roni et al. 2017, Wohl 2019, among others), with data collected and analyses conducted to inform priorities to restore watershed processes that support native fish species. The assessment methods are repeatable for appropriate intervals of review and re-assessment depending on levels of progress or watershed change (e.g. status of passage inventory, high level of work accomplished, significant flow event, etc.). Assessment outputs include identification and degree of fish limiting factors as per CTUIR River Vision touchstones and conceptual actions to address limiting factors.

The assessment will serve to explain stream conditions as related to fish habitat needs, water quality, hydrology, and land uses, and it includes compiling and reviewing summaries of existing data and conducting technical analyses to provide a summary of the geomorphic setting including historic and current conditions. The action plan element of the work will involve effective stakeholder communication of assessment outputs, systematically compile potential projects supported by assessment outputs, create potential new solutions, evaluate restoration alternatives, and document the preferred path to monitor physical and ecological function from implemented habitat and stream improvements. A primary goal of the planning effort is to attenuate the limiting factors/ecological concerns/nonfunctional River Vision Touchstones related to habitat. The assessment will also serve to characterize the non-point sources of pollution (NPS) issues identified in the Umatilla River Basin Total Maximum Daily Load (TMDL), and the restoration projects identified in the action plan will include how each project addresses NPS issues, in order to help support implementation of Section 319 of the Clean Water Act. It is hoped that through these actions, additional local concerns about flooding and management of the floodplain/stream channel can be addressed and resolved. Additionally, the Action Plan will identify long term management objectives for the floodplain.



The riparian quality varies from moderately or largely intact in the headwaters, to moderate or highly disturbed in the lowlands. The lower sections are dominated by agriculture and rangeland. Relative to historical conditions, the lower portion of the study area in the Umatilla River Subbasin is highly simplified, straightened, restricted from floodplains, reduced riparian zone, and impacted by irrigation withdrawals. There are a variety of passage barriers in the upper headwaters that currently limit anadromy that will be identified and evaluated for relative population level impacts.