Geoscience Reference
In-Depth Information
results. In discussing this paper, Straub (
1935
) presents the results of recent North
American experiments, providing measurements of ripple sizes and observations of
ripple formation, shape, movement, and variation with flow velocity. Kondrat'ev
et al. (
1959
) provide a later summary of research on the theory of sediment move-
ment, including discussions and analyses of theoretical, experimental, and field
investigations on the movement of sediment as bedforms. Regarding Russian
experimental studies of bedforms up to that time, they particularly highlight the
early work of Velikanov in 1923 and extensive investigations of Goncharov,
Lapshin, Roborovskaya, and Pushkarev in 1935-1936. In terms of experimental
methodologies, they note developing large-scale use of photography, high-speed
motion pictures, and special emulsion drops in numerous experiments over the
period 1936-1946 as turbulent flow structure was investigated in conjunction with
bedform and sediment dynamics under the guidance of Velikanov. Kondrat'ev
et al.'s summary of Russian experimental investigations finishes with the studies
of Kudryashov and Znamenskaya in the 1950s. They conclude that most investi-
gators to that time had ignored the internal flow structure and focused on determin-
ing empirical relations between bedforms and structureless-stream variables such as
mean velocity, depth, slope, sediment diameter, etc. They also note that the wide
variety of proposed relationships revealed the extent to which the nature of the
interaction between stream and channel was still obscured. In terms of Russian field
investigations of bedforms, Kondrat'ev et al. (
1959
) note the studies on the rivers
Volga, Mologa, Luga, and Kemka over the period 1934-1935 in which bedform
arrangements, sizes, speeds, transport rates, and superposition were linked to flow
and sediment characteristics. They also put forward a theory in which bedform
generation is linked to pressure variations at the bed surface and basic laws of
oscillation.
Inglis (
1949
) reviews work on fluvial ripples and dunes carried out in India over
the previous decade using sediments sizes of 0.2-19.4 mm. He provides obser-
vations regarding bedform types (principally ripplets, ripples, dunes, and sheet
movement) and transitions between them, mechanisms of formation (including
scour-deposition waves and viscous-turbulent sediment motions), controlling fac-
tors (including flow depth, velocity, discharge, sediment load, and sediment char-
acteristics, with cohesion and grain coarseness limiting or preventing ripple
formation), shapes and three-dimensionality, sizes, bedform superposition and
elimination, hydraulic resistance, and associated sediment dynamics (including
interactions with turbulent structures).
1.2 The Ultrasonic Depthsounder Revolution and Non-intrusive
Measurements of Bed Dynamics
In 1956, the US Geological Survey established a significant research project to
investigate roughness in alluvial channels. Because photographic recording and
manual measurements of exposed bedforms after the draining of a channel could
