Physical Stream Habitat Dynamics in Lower Bear Creek, Northern Arkansas
Abstract
This study evaluated the roles of geomorphic and hydrologic dynamics in determining physical stream habitat in Bear Creek, a 239 km2 watershed in the Ozarks in northern Arkansas. During a relatively wet 12-month period, Bear Creek was altered by a series of floods, including four with discharges exceeding a 1-year recurrence interval and one with an estimated 2- to 4-year recurrence interval. These floods eroded sediment from the study reach at rates in excess of other sites previously studied in the Ozarks. The 2- to 4-year flood scoured gravel from pools and deposited it in riffles (areas of swift, relatively shallow water). The smaller floods eroded gravel from the riffles and deposited it in pools. A two-dimensional hydraulic model was compiled to assess habitat variation with hydrology. Depths and velocities simulated for discharges of 0.1 to 556 cubic meters per second were classified into habitats using hydraulic criteria. Races (areas of swift, relatively deep water downstream from riffles) disappear completely at the lowest flows and riffles contract substantially in area. Pools also contract during low flow, but deep scours adjacent to bedrock outcrops sustain some pool area even at the lowest modeled flows. Magnitude and frequency of bed-sediment entrainment show that most habitat maintenance results from flows that occur about 4-7 days a year. The analysis documents the geomorphic and hydrologic dynamics that form and maintain habitats in a warm water stream in the Ozarks. The range of flows that occurs on this stream can be partitioned into flows that sustain habitat by providing the combinations of depth and velocity that stream organisms live with most of the time, and those flows that surpass sediment entrainment thresholds, alter stream geomorphology, and therefore maintain habitat. The quantitative relations show sensitivity of habitats to flow variation, but do not address how flow may vary in the future. (7 tables, 93 figures, 50 refs.)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 2003
- Accession Number
- ADA418479
Entities
People
- Caroline M. Elliott
- Joanna M. Reuter
- Robert B. Jacobson