APPLICATION OF GEOGRAPHIC INFORMATION SYSTEMS TO CHANNEL MIGRATION ZONE ANALYSIS FOR SECTIONS OF THE PUYALLUP, CARBON AND WHITE RIVER SYSTEMS, PIERCE COUNTY, WA; A TOOL FOR WATER AND LAND RESOURCE MANAGEMENT

Management of water and land resources associated with migrating river systems has generally proved challenging due to constantly changing river dynamics and channel location. Delineating and mapping zones of past and future channel migration can provide an effective tool in evaluating and implementing in-channel and flood plain resource management plans and strategies.

The Pierce County Department of Public Works and Utilities, and GeoEngineers, Inc., both located in Washington State, conducted an analysis of past and potential channel migration for portions of three major rivers running through the county: the Puyallup, Carbon and White Rivers. Geographic Information Systems (GIS) was chosen to manage a complex set of spatial and temporal data dating back to the 1880’s. Existing GIS data layers (roads, levees, etc) were projected into a common coordinate system. Historical maps and aerial photos were scanned, geo-rectified to current orthophotos and added to the database. The resulting data layers, including aerial photos from 1931 to 1998, were then used in various combinations to provide insight to channel behavior.

GIS applications were implemented to develop an understanding of changes in migration through different geologic substrates. Use of geologic and soils data layers, combined with scanned photos, helped identify cause/effect relationships between various geologic units and migration rates, as well as the response of channel dynamics to confining structures such as levees and hardened banks. The GIS product was also used as a tool to identify geologic and geomorphic field verification sites, and areas for detailed reconnaissance.

The results of the analysis and the channel migration zone maps identify channel sections that are sensitive to channel erosion, migration, and possible breaching of existing levees. Study results can be used to help identify and reduce flood related hazards, and better manage the adjacent flood plains.