Geology topics

Kenneth F. Karle

Publications and source records attributed to Kenneth F. Karle.

3 recordsLinked to original sources

USGS2009

Flood effects on an Alaskan stream restoration project: the value of long-term monitoring

On a nationwide basis, few stream restoration projects have long-term programs in place to monitor the effects of floods on channel and floodplain configuration and floodplain vegetation, but long-term and event-based monitoring is required to measure the effects of these stochastic events and to use the knowledge for adaptive management and the design of future projects. This paper describes a long-term monitoring effort (15 years) on a stream restoration project in Glen Creek in Denali National Park and Preserve in Alaska. The stream channel and floodplain of Glen Creek had been severely degraded over a period of 80 years by placer mining for gold, which left many reaches with unstable and incised streambeds without functioning vegetated floodplains. The objectives of the original project, initiated in 1991, were to develop and test methods for the hydraulic design of channel and floodplain morphology and for floodplain stabilization and riparian habitat recovery, and to conduct research and monitoring to provide information for future projects in similar degraded watersheds. Monitoring methods included surveyed stream cross-sections, vegetation plots, and aerial, ground, and satellite photos. In this paper we address the immediate and outlying effects of a 25-year flood on the stream and floodplain geometry and riparian vegetation. The long-term monitoring revealed that significant channel widening occurred following the flood, likely caused by excessive upstream sediment loading and the fairly slow development of floodplain vegetation in this climate. Our results illustrated design flaws, particularly in regard to identification and analysis of sediment sources and the dominant processes of channel adjustment.

Alaska↗

USGS1999

Stream restoration at Denali National Park and Preserve

Placer mining for gold has severely disturbed many riparian ecosystems in northern regions. We are conducting a long-term project to test methods to promote restoration of a placer-mined watershed in Denali National Park and Preserve. The project included hydrological restoration of the unstable and excessively confined stream with heavy equipment. We stabilized the floodplain with bioengineering techniques, including alder and willow brush bars anchored laterally to the channel and willow cuttings along the channel. A moderate flood near the end of construction showed that the brush bars provided substantial protection, but some bank erosion and changes in slope and sinuosity occurred. Subsequent refinements included greater sinuosity and channel depth, pool/riffie construction with stone weirs, and buried alder and willow brush projecting from the bank. The reconstructed stream and floodplain have remained stable for five years, but have not been re-tested by a another large flood. The willow/alder riparian plant community is naturally revegetating on the new floodplains, but vigorous willows which sprouted from branches in brush bars and banks still provide the erosion protection.

Alaska↗

USGS1994

Stream and floodplain restoration in a riparian ecosystem disturbed by placer mining

Techniques for the hydrologic restoration of placer-mined streams and floodplains were developed in Denali National Park and Preserve Alaska, USA. The hydrologic study focused on a design of stream and floodplain geometry using hydraulic capacity and shear stress equations. Slope and sinuosity values were based on regional relationships. Design requirements include a channel capacity for a 1.5-year (bankfull) discharge and a floodplain capacity for a 1.5- to 100-year discharge. Concern for potential damage to the project from annual flooding before natural revegetation occurs led to development of alder ( Alnus crispa ) brush bars to dissipate floodwater energy and encourage sediment deposition. The brush bars, constructed of alder bundles tied together and anchored laterally adjacent to the channel, were installed on the floodplain in several configurations to test their effectiveness. A moderate flood near the end of the two-year construction phase of the project provided data on channel design, stability, floodplain erosion, and brush bar effectiveness. The brush bars provided substantial protection, but unconsolidated bank material and a lack of bed armour for a new channel segment led to some bank erosion, slope changes and an increase in sinuosity in several reaches of the study area.

Alaska↗