Lower Columbia River Watershed Council

I. Introduction to the Watershed Assessment

Purpose

A watershed assessment is a series of environmental evaluations on an area geographically bounded by the extent of the watershed. The definition of a watershed is an area of land in which all the precipitation and groundwater drain down slope to a common point within a stream channel. “Each watershed is drained by a hierarchical network of channels whose size increases downstream from small rills through gullies to small and large river channels as the amount of water and sediment they must carry increases (Dunne, 1978).” Topographical features called ridgelines separate watersheds forming boundaries conveniently mapped for management purposes. Within these boundaries the natural processes and human influences can be summed and analyzed to develop a characterization of watershed conditions. Watersheds are variable in size and within any one watershed a nested set of subwatersheds can also be defined. The practicality of delineating subwatershed boundaries is seen in management and habitat restoration where a large watershed is often partitioned into smaller units to provide a framework for summarizing and analyzing data.

A watershed assessment is the process of evaluating how well a watershed works, with a focus on evaluating the status or health of the aquatic resources. The process includes steps for identifying key issues within the watershed; examining the history of the watershed; describing its features; assessing human influences; and evaluating various resources within the watershed. The goals of the assessment are to identify features and processes important to fish habitat and water quality, determine how natural processes and human activities are influencing those resources, and evaluate the cumulative effects of land management practices over time.

Portland State University prepared this assessment for the Lower Columbia River Watershed Council. The primary goal of the watershed council is to evaluate the conditions within the watershed and develop habitat protection plans and enhancement and restoration projects. The information provided here will be used as a guide for the prioritization and design of restoration projects.

This watershed assessment follows the procedures and guidelines outlined in the Oregon Watershed Assessment Manual. The assessment manual provides a guide on how to compile and evaluate information about watersheds. The manual is organized into ten components: historic conditions; channel habitat types; hydrology and water use; riparian/wetlands; sediment sources; channel modification; water quality; fish and fish habitat; watershed condition evaluation; and monitoring plan. Components one through eight are summarized in the watershed condition evaluation with protection and restoration plans addressed in the monitoring plan component.…..

The entire assessment is available for download in Adobe pdf format in 10 sections available here, these files range in size from 500k to several meg !

 

1. Introduction to the Watershed Assessment 1.4meg
2. Historical Conditions Assessment 500k
3. Channel Habitat Types 1.2meg
4. Hydrology and Water Use 7meg
5. Riparian and Wetland Assessment 1.5meg
6. Sediment Sources 1meg
7. Channel Modification Assessment 5meg
8. Water Quality Assessment 900k
9. Fish and Fish Habitat Assessment 3meg
10. Watershed Evaluation 600k

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