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Geomorphic Factors (geomorphic + factor)
Selected AbstractsGeomorphic and riparian forest influences on characteristics of large wood and large-wood jams in old-growth and second-growth forests in Northern Michigan, USAEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2007Arthur E. L. Morris Abstract Large wood (LW; pieces with diameter greater than 10 cm and length greater than 1 m) and large-wood jams (LWJs; two or more pieces of LW in contact with each other) are important components of stream ecosystems that are often distributed along stream channels in response to geomorphic and riparian forest factors that interact hierarchically. As a result, information on these relationships is valuable for predicting patterns of wood accumulation and characteristics of individual pieces of wood. We studied relationships between geomorphic and riparian factors and LW and LWJ structure in different geomorphic settings associated with old-growth and second-growth settings in Upper Michigan. We used redundancy analysis (RDA) and regression tree analysis to evaluate changes in LW and LWJ structural characteristics among geomorphic and riparian forest settings. Geomorphic factors explained 38·5% of the variability in LW and LWJ characteristics, riparian forest factors uniquely explained 18·4% of the variance and the intersection of the two categories of environmental factors (i.e. the redundant portion) was 29·8%. At the landscape scale, our multivariate analyses suggest that the presence of rock-plane bedding was an important predictor of the number of LWJs and the percent of channel spanned by LWJs. Our analyses suggest differences in relationships between geomorphic factors and LW and LWJ structure. Channel width, distance from headwaters, gradient and sinuosity were identified by regression tree analyses as the most important variables for predicting LW characteristics, while channel width and confinement were the most important variables for predicting LWJ characteristics. Old-growth settings generally contained a higher proportion of conifer and LW (both in and out of LWJs) with greater diameter and volume than in second-growth settings. Our study supports the view that restoration of wood to streams will benefit from considering the associations of wood structure with landscape and reach-scale geomorphology. Copyright © 2007 John Wiley & Sons, Ltd. [source] A study of Holocene floodplain particle size characteristics with special reference to palaeochannel infills from the upper Severn basin, Wales, UKGEOLOGICAL JOURNAL, Issue 2 2001Mark Patrick Taylor Abstract Multiple sedimentary units from floodplain reaches at Welshpool on the upper River Severn and at the confluence of the Afon Tanat and Afon Vyrnwy (mid-Wales, UK) were examined to ascertain if they have distinctive particle size characteristics. Changes in particle size characteristics and their possible relationship to known human and climatic impacts are also discussed. Ellipse plots of particle size characteristics from the River Severn floodplain at Welshpool show that coarse-grained outwash deposits can be clearly discriminated from channel margin or palaeochannel sediments. In contrast, at the Afon Tanat,Vyrnwy study reach, this discrimination is not seen so clearly. The relationships between age and particle size characteristics from the most sampled sedimentary environment, palaeochannel infills, were also examined. The data from the River Severn floodplain at Welshpool show that palaeochannel sediments reveal a gradual but clear increase in particle size from the mid- to late Holocene towards the present day. Sediments deposited in the period 90,160 years BP are markedly coarser. It is suggested that these changes may be related to the combined effect of land-use changes, metal mining impacts and changes in flood frequency and magnitude that occurred at this time within the upper Severn basin. In contrast, the particle size characteristics of post Late Devensian/Early Holocene units from Tanat,Vyrnwy palaeochannels were random with no discernible age,size patterns. It is suggested that the non-systematic grain size distribution may be due to the steeper valley gradients of the Tanat,Vyrnwy system (and by inference higher stream powers) and its relatively narrow valley form enabling more effective coupling between coarser outwash deposits found on and at the edges of hillslopes and the valley floor. Although the two study reaches have undergone comparable environmental change during the Holocene and lie in the piedmont zone of their catchments, palaeochannel units of the same age possess distinctly different characteristics. Intrinsic reach-scale geomorphic factors would appear to preclude the uniform application of particle size characteristics to determine alluvial response to environmental change. Consequently, care needs to be applied to the use of such data for environmental discrimination because the phenomenon of equifinality means that a specific set of sediment characteristics is not necessarily exclusive to specific fluvial environments in either space or time. Copyright © 2001 John Wiley & Sons, Ltd. [source] FLOW ANALYSIS OF LANDSLIDE DAMMED LAKE WATERSHEDS: A CASE STUDY1JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2006Kwan Tun Lee Abstract: The Chi-Chi earthquake, which occurred on September 21, 1999, and had a magnitude of 7.3 on the Richter scale, resulted in an extensive landslide that blocked the Ching-Shui Creek in Taiwan, forming a large lake with a storage volume of 40 million m3. This paper describes an analytical procedure used to perform flow analysis of the Tsao-Ling watershed, which includes the new landslide dammed lake. In this study, a digital elevation model was applied to obtain the watershed geomorphic factors and stage-area storage function of the landslide dammed lake. Satellite images were used to identify the landslide area and the land cover change that occurred as a result of the earthquake. Two topography-based runoff models were applied for long term and short term streamflow analyses of the watershed because the watershed upstream of the landslide dam was ungauged. The simulated daily flow and storm runoff were verified using limited available measured data in the watershed, and good agreement was obtained. The proposed analytical procedure for flow analysis is considered promising for application to other landslide dammed lake watersheds. [source] Climatic and geomorphic factors affecting contemporary (1950,2004) activity of retrogressive thaw slumps on the Aklavik Plateau, Richardson Mountains, NWT, CanadaPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2010Denis Lacelle Abstract The climatic and geomorphic factors affecting retrogressive thaw slump initiation and activity on the Aklavik Plateau (Richardson Mountains, NWT) were examined using historical air photographs over a 54-year period (1950 to 2004). In this region, thaw slumps include a near-vertical headwall, a floor of low gradient (2,10°) and a steeply sloping evacuation channel (15,25°) that connects the floor of the thaw slumps to Willow River located 60,150,m below. All thaw slumps on the Aklavik Plateau are located within the glacial limit of the Laurentide Ice Sheet and the majority developed on the western side of the valley on gently sloping terrain. Aerial photographic analysis showed an increase in thaw slump initiation from 0.35 new thaw slump yr,1 over the 1954,71 period to 0.68 new thaw slump yr,1 over the 1985,2004 period. This increase follows the pattern of the 10-year running mean summer air temperature record over the 1950,2004 period. However, the total number of active mature thaw slumps on the Aklavik Plateau decreased from a maximum of 46 in 1950 to a minimum of 24 observed in 2004, which follows, to a certain extent, the 10-year running average of rainfall. Both these trends may relate to the influence of climate on the erosional processes that are thought to initiate thaw slumps and keep them active in regions of highlands. Copyright © 2009 John Wiley & Sons, Ltd. and Her Majesty the Queen in right of Canada. [source] | ||||||||||