Hydrogeomorphic linkages of sediment transport in headwater streams, Maybeso Experimental Forest, southeast Alaska

Abstract

Abstract:Hydrogemorphic linkages related to sediment transport in headwater streams following basin wide clear-cut logging on Prince of Wales Island, southeast Alaska, were investigated. Landslides and debris flows transported sediment and woody debris in headwater tributaries in 1961 , 1979 , and 1993 . Widespread landsliding in 1961 and 1993 was triggered by rainstorms with recurrence intervals (24 h precipitation) of 7Ð0 years and 4Ð2 years respectively. Occurrence, distribution, and downstream effects of these mass movements were controlled by landform characteristics such as channel gradient and valley configuration. Landslides and channelized debris flows created exposed bedrock reaches, log jams, fans, and abandoned channels. The terminus of the deposits did not enter main channels because debris flows spread and thinned on the unconfined bottom of the U-shaped glaciated valley. Chronic sediment input to channels included surface erosion of exposed till (rain splash, sheet erosion, and freeze-thaw action) and bank failures. Bedload sediment transport in a channel impacted by 1993 landslides and debris flows was two to ten times greater and relatively finer compared with bedload transport in a young alder riparian channel that had last experienced a landslide and debris flow in 1961. Sediment transport and storage were influenced by regeneration of riparian vegetation, storage behind recruited woody debris, development of a streambed armour layer, and the decoupling of hillslopes and channels. Both spatial and temporal variations of sediment movement and riparian condition are important factors in understanding material transport within headwaters and through channel networks.

Willingness to pay for ecosystem conservation in Alaska’s Tongass National Forest: a choice modeling study

“…River and stream degradation stemming from timber production adversely affect many other ecosystem services, beyond those just associated with consuming, viewing, or knowing that wild salmon exist in historically abundant levels. For example, documented examples on the Tongass include the degradation of nutrient cycling (Tiegs et al 2008), water regulation (Gomi et al 2004), and erosion control services (K. Kahklen and W. Hartsog 1998, unpublished manuscript).…”

Hydrogeomorphology: overview of an emerging science

“…Gomi et al (2004) assess the occurrence, distribution, and downstream effects of landslides and debris flows in a previously glaciated catchment in southeast Alaska, including controls by landform characteristics. Three papers on sediment sources and suspended sediment transport in small catchments of Peninsular Malaysia and Sabah contribute to the scant literature on managed tropical forest ecosystems.…”

Landslides and Rockfalls

“…In a study of the bedrock topographic signature, Korup (2006a) uses plots of probability distributions of two slope metrics, slope angle (b) and slope gradient (tanb) to identify median slope angles across a region of variable uplift, erosion, landsliding density, precipitation and glaciation, with the only unifying variable being rock type; the suggestion arises that local hillslope evolution adjusts to rock mass strength irrespective of the intensity of tectonic and climatic forcing (Figure 3.9). Korup (2006a) cautions that apparent correlations between the density and location of contemporary landsliding may not be indicative of the long-term erosion rates particularly in small catchments where the frequency of one geomorphological process in small (<100 km 2 ) catchments greatly affects yield (Gomi, Sidle and Swanson, 2004). This is supported by observations of exponential growth of landslide density of earthquake-triggered landslides with mean slope angle in post-Niigata Earthquake, Japan (Yamagishi and Iwashashi, 2007), as opposed to a more linear increase with rainfall-induced failures.…”