The data were collected primarily to support development of a quantitative classification that would be applicable to local floodplain environments. Secondarily and in support of the primary objective, data were collected to quantify the range of variability – both natural and human-caused -- of some natural features in the floodplain. Many of these features are believed to indicate the functional health of the floodplain and its wetlands. The collected data and the resulting classification scheme will be used, along with other tools and policies, for (a) identifying the most geomorphically and biologically degraded parts of the system, (b) specifying appropriate in-kind compensation for any unavoidable future alterations to floodplain wetlands, and (c) monitoring the functional recovery of the floodplain system as a result of future restoration projects.

CTUIR’s main objective for this study was to support development of a hierarchical numerical classification that could be applied to the floodplain environments of the lower Umatilla River, including but not limited to its wetlands. The classification is designed to be applied at the scale of an individual wetland (about 0.1-100 acres) located within a floodplain, rather than at the scale of an entire river reach or subwatershed. Ideally, the classification should not be used alone, but in combination with procedures for assessing other watershed components (e.g., channel stability) and wetlands at broader scales. Such an integrated approach is necessary for wetland restoration to succeed, because watershed components have numerous intricate linkages across multiple scales, with cumulative, non-linear interactions among components being common.

The entire lower Umatilla River system, rather than just the portion on CTUIR lands, was included in the study in order to provide the broad foundation necessary for developing a hierarchical classification. It was determined that the classification should be (a) defined by variables that can be readily assessed by resource technicians with minimal training, (b) based on hydrogeomorphic variables (and the vegetation variables that largely reflect them) so that the resulting categories are most pertinent to wetland function, and (c) be compatible with (i.e., represent a localized elaboration on) the HGM classes recognized statewide.

This project was completed under the 2000 EPA Wetlands Grant (CWA Sec. 104) administered through Yvonne Vallette, EPA Project Officer, Region 10.