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Distorted Froude‐scaled flume analysis of large woody debris
Author(s) -
Wallerstein Nicholas P.,
Alonso Carlos V.,
Bennett Sean J.,
Thorne Colin R.
Publication year - 2001
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.271
Subject(s) - froude number , geology , flume , debris , channel (broadcasting) , debris flow , drag , geotechnical engineering , erosion , shear stress , open channel flow , geomorphology , bedform , hydraulics , large woody debris , sediment transport , sediment , hyperconcentrated flow , hydrology (agriculture) , flow (mathematics) , mechanics , bed load , engineering , physics , ecology , oceanography , aerospace engineering , riparian zone , habitat , electrical engineering , biology
This paper presents the results of a movable‐boundary, distorted, Froude‐scaled hydraulic model based on Abiaca Creek, a sand‐bedded channel in northern Mississippi. The model was used to examine the geomorphic and hydraulic impact of simplified large woody debris (LWD) elements. The theory of physical scale models is discussed and the method used to construct the LWD test channel is developed. The channel model had bed and banks moulded from 0·8 mm sand, and flow conditions were just below the threshold of motion so that any sediment transport and channel adjustment were the result of the debris element. Dimensions and positions of LWD elements were determined using a debris jam classification model. Elements were attached to a dynamometer to measure element drag forces, and channel adjustment was determined through detailed topographic surveys. The fluid drag force on the elements decreased asymptotically over time as the channel boundary eroded around the elements due to locally increased boundary shear stress. Total time for geomorphic adjustment computed for the prototype channel at the Q 2 discharge (discharge occurring once every two years on average) was as short as 45 hours. The size, depth and position of scour holes, bank erosion and bars created by flow acceleration past the elements were found to be related to element length and position within the channel cross‐section. Morphologies created by each debris element in the model channel were comparable with similar jams observed in the prototype channel. Published in 2001 John Wiley & Sons, Ltd.