DOI: 10.7267/t722hg254
title: Willamette River Floodplain 100 Meter Slices Framework Tabular Attribute Data

description: The Slices Framework is intended for use in making decisions about conservation and restoration in the Willamette River floodplain. It makes use of distinct spatial units for tracking change in the floodplain. The first of these units are 1 kilometer long slices drawn at right angles to the floodplain, first put forward in the Willamette River Basin Planning Atlas (Ch. 8 pp. 131-147 in Hulse, Gregory and Baker 2002). The second of these units are 100m subdivisions of the original 1 km slices, with ten 100m slices in each 1 km slice. Together, they cover the entire pragmatic floodplain of the Willamette River. We define the pragmatic floodplain as the zone subject to periodic flooding that is bounded by significant infrastructure (e.g. highways, residential areas, etc.). This framework is intended to support the assessment, planning, and monitoring of conservation and restoration activities within the Willamette River floodplain. These activities may include reconnecting historical channels that have been blocked and allowing the river to flood certain locations from which it is now normally excluded. Since restoration activities that would require disruption of significant constructed assets, roads, residential and commercial areas, and others, are infeasible, the spatial extent of this framework is narrower, primarily in the section between Eugene and Albany, than the historical floodplain. The tabular attribute data reports amounts of key processes and patterns by slice and how they vary over time.
description: The 100 meter polygons are designed to be regular spatial subdivisions of a preexisting map that subdivided the Willamette River historic floodplain into 1 kilometer spatial reporting units called "slices" developed by the Pacific Northwest Ecosystem Research Consortium http://oregonstate.edu/dept/pnw-erc/ . The 1 km slices were created by a combination of automated and manual steps that relied on a series of scripts written in the ArcInfo command language AML. The principal script in this suite is called segment.aml, originally developed by John Gabriel at Alsea Geospatial, Inc. in 1999, and modified for use in creating this 100 m slice coverage. Primary inputs to the script are the name of a line coverage representing the principal axis of the River's mainstem and parameters defining the interval to be used in locating points along the axis and the length of lines subsequently to be drawn by the script at right angles to the axis through each of the points. The axis coverage NUAXIS was provided by the Department of Fisheries and Wildlife at Oregon State University. Prior to creating the 100 m slices map, we created a 1 km slices map and ensured that its lines were spatially coincident with those in SLICES_v21. Subsequent to the development of the 100 m slices coverage, a revised 1 km slices coverage, called V21E was created that, primarily for the reach south of Albany, reduced the width of the floodplain from the historic area of inundation to the narrower "pragmatic" floodplain defined as the area for which the 100 m slice spatial reporting units are intended to be used. The output of the segment script is a series of arcs intersecting the main stem centerline at 100 m intervals. Manual edits and assigning of slice numbers: Manual editing was required after the AML created the 100 m arc coverage. Where the centerline was predominantly north to south (for example, slices 8101 - 10010), the AML created arcs were evenly spaced and aligned as expected. Where the centerline contained a vertex to accommodate variations in the shape of the river (for example, slices 6401 - 7310), the 100 m arcs created by the AML were spaced and aligned in ways that were inconsistent with our nesting of 100 m slices within 1 km slices. Manual edits were done where required to correct spacing and to distribute arcs where there is a change in channel orientation. The primary guideline was to have each set of ten 100 m slices nested within its 1 km slice, i.e. the northern boundary of 100 m slice 8301 is coincident with the northern boundary of 1 km slice 83 and the southern boundary of slice 8310 is coincident with the southern boundary of 1 km slice 83. The 100 m arc coverage was converted to a geodatabase feature for manual edits in ArcMap. The 1km coverage was used as a background for editing to align 100 m slices and adjust spacing. A 100 m parallel spacing is not possible in locations where the channel changes orientation over a short distance (for example slices 3501 - 3510, 4601 - 4610). In these locations each set of ten 100 m slices was connected to a common vertex defined by its bounding 1 km slice. Where the common vertex occurs depends on the change in orientation (at 1 km slice 35 it is to the west, at 1 km slice 71 it is to the south, at 1 km slice 124 it is to the east). Where the bounding 1 km slice met at a vertex on the boundary (for example 1 km slices 72 and 112), the 100 m arcs were snapped to this same vertex. Where the 1 km slices did not have a common vertex at the boundary (for example 1 km slices 71, 73, 122), the 1 km boundary arcs were extended to create a common vertex outside of the boundary. The 100 m slice arcs were snapped to this newly created common vertex and then extended past the boundary on the opposite side. To create the 100 m polygons, the arc coverage was clipped to the boundary polygon and then appended to the boundary polygon. The assigning of 100 m slice numbers used the 1 km slice numbers as a starting place. For each 100 m slice nested within a 1 km slice, the identification begins with the 1 km slice number and is followed by 1 - 10 (1 is northernmost, 10 is southernmost). For example, the 100 m slices within 1 km slice 35 are 3501 - 3510. The assignment of 100 m slice numbers was accomplished with a combination of GIS operations (point on polygon overlay, joinitem) and manual inspection and editing. Where a slice is not contiguous (for example slice 22701 which has 3 polygons), the same slice number identifies all polygons of that slice.
description: Hydrologic Unit Code: 1709