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waves in currents, where these waves can appear suddenly and subsequently grow
considerably, and they are mechanistically different to the smaller current ripples. He
attributes the origination of sand waves to a form of deposition-scour wave (identified
later by Inglis
1949
;Raudkivi
1963
,
1966
; etc.), where the initial waves extend
themselves laterally even more quickly than they grow vertically owing to near-bed
fluid dynamics. Growth is suggested to be limited by a combination of the water depth
and decreasing effectiveness of the lee vortex as the bedform grows. Cornish (
1908
)
further discusses the sizes of current ripples, sand waves, and upstream-moving
bedforms (antidunes in today's terminology).
Studies of ripples and larger sand waves to this time were based on observations
and sparse manual measurements of sizes and migration speeds. In a novel approach,
a sounding lead covered in tallow was used by Siau (
1841a
,
b
) to prove the existence
of oscillatory-flow ripple marks at depths of up to 617 ft (Johnson
1916
). 1910-1920
saw a notable increase in bedform measurements and experimental studies of
bedform dynamics, and a consolidation of understanding of current-formed bed
waves, notably through the German works of Blasius (
1910
) and Forchheimer
(
1914
), and the works of Gilbert (
1914
), Johnson (
1916
), and Bucher (
1919
).
The study of Gilbert (
1914
), carried out with the assistance of Edward Charles
Murphy, is recognised as a landmark experimental investigation (e.g. Bucher
1919
;
Kramer
1935
;Kondrat'evetal.
1959
;Raudkivi
1967
;Graf
1984
). Although the
primary aim of the study was to determine the laws governing bedload transport, the
tests of sediment diameters of 0.3-7 mm involved bedforms from threshold condi-
tions to antidunes occurring for supercritical flows. Gilbert (
1914
)providesdetailed
observations of bedform types, origination, growth, migration and speeds, sizes (and
relations to controlling factors such as sediment and flow depth and speed), transport,
shape and three-dimensionality, variation with discharge (including sizes, speeds, and
the dune-plane bed and plane bed-antidune transitions), interactions (including coa-
lescence, bedform dividing, generation on larger bedforms, and antidune cycling),
and associated sediment dynamics (including related actions of turbulent structures).
In regard to bedform types, Gilbert (
1914
) discusses dunes, plane bed, antidunes, and
shoals, commenting that antidunes were earlier noted by Cornish (
1899
), and also
Cornish (
1908
) and Owens (
1908b
) in the discussion and closure of Owens (
1908a
).
Bucher (
1919
) provides a review of the work to that time on the origin of ripples
and related sedimentary surface forms. He discusses current ripples (conventionally
parallel, but also rhomboid and linguoid, and having notable similarities to aeolian
ripples in terms of characteristics and origins), meta ripples and sand waves (deemed
a serious menace to navigation), related forms, and transitions between them. He
summarises data on bedform sizes and speeds of movement, suggests formation
mechanics (including a potential Helmholtz instability for dunes), and describes the
orientations, anastamosing hierarchy, shapes and three-dimensionality, migration and
speeds, sizes (including lengthening with time, and changes with increasing and
decreasing velocity), transport, controlling factors (including flow depth, fluid vis-
cosity and sediment size and density), and associated sediment dynamics (including
interactions with near-bed flow structures).
A review of European hydraulic research regarding transportation by traction
isgivenbyKramer(
1935
), who augments this with additional experimental
