Geomorphic Mapping of Fern Ridge Lake, Oregon, 2023

In cooperation with the U.S. Army Corps of Engineers, the U.S. Geological Survey evaluated geomorphic conditions within Fern Ridge Lake near Eugene, Oregon, to inform cultural resources management and other natural resources decisions. Reservoir erosion and deposition during seasonal flood-control operations have formed a diverse array of landforms that can impact water storage, aquatic and riparian habitats, cultural resources, and water quality, among other resources. Process-based geomorphic mapping of Fern Ridge Lake provides a basis for evaluating geomorphic processes and patterns of sediment transfer within the reservoir and provides an inventory of landforms from which to evaluate the geomorphic change over time.

This documentation describes a shapefile including process domains, landforms, and cover within the reservoir of Fern Ridge Lake. Mapping encompasses all landforms within a 30-square kilometer area upstream from Fern Ridge Dam approximately coinciding with the maximum pool elevation of 373.5 feet (113.8 meters; National Geodetic Vertical Datum of 1929 [NGVD 29]). Fern Ridge Lake includes submerged reaches of Inman Creek, Hannavan Creek, Long Tom River, Coyote Creek, Middle Fork Coyote Creek, West Fork Coyote Creek, and the Amazon Creek Diversion Channel of Amazon Creek. The dataset was mainly developed by digitizing from orthoimagery and digital surface models (DSMs) created from aerial photographs collected in January 2023 (Schwid and others, 2025). Mapping was conducted during seasonal low-pool conditions when reservoir lake levels are lowered to minimum conservation pool level to provide storage for incoming high flows and minimize downstream flooding; these conditions occur routinely each winter, revealing reservoir flood morphology and are referred to as “seasonal drawdowns.” The geomorphic mapping framework for Fern Ridge Lake was adapted from that developed for Fall Creek Lake, Oregon (Keith and Stratton Garvin, 2021; Keith and others, 2024). An associated data report describes the geomorphic mapping framework for the reservoir at Fern Ridge Lake in greater detail and provides mapping unit descriptions including delineation criteria, hypothesized formation processes inferred from remote-sensing datasets, field observations and literature, and descriptions of specific processes sharing each mapping unit during seasonal flood-control drawdown operations.