Littoral and Shoreline Processes in Large Man-Made Lakes
211
bars, single tombolos and spits are fixed here too and in doing so many bars and spits
extend in the direction opposite to the general direction of channel flows. The shorenormal sediment transport gives rise to more or less stretched sites of the accretive
terrace bordering the nearshore zone; the terrace face typically has a slope of 9-10°
exceeding 2.5-3 times the averaged slope of the bottom within the nearshore.
During the initial filling of the Novosibirsk Reservoir and just after its
formation, the rate of coastal erosion within the wave-dominated area was the highest
and on some sites it was as great as 25-30 m/yr. Terrigenous material entering the
nearshore zone as a result of bluff erosion was transported mainly in the offshore
direction, because of rather high steepness of original slopes. As the nearshore zone
width increases and the beach slope decreases due to cliff recession and sediment
accretion at the periphery of the offshore area, the erosion rate began to reduce. At
present the eroded shores recede at the mean rate of 4.5 m/yr and, in places, the
erosion has been terminated.
Within 15-20 years the position of brow of the accretive terrace bordering the
nearshore zone was relatively stabilized though casual fluctuations of the brow take
place even nowadays. It marked the change of prevailing tendencies in sediment
transport, that is the longshore sediment transport began to prevail over the cross-shore
one. Similar to the wave-dominated shores of seas, natural and other man-made lakes,
the shoreline of Novosibirsk Reservoir at the wave-dominated area represents a series
of bow-shaped terrestrial patches and therefore the longshore sediment transport
usually occurs as two-way migrations, the rate of which may be as great as 60,000Owing to the combination of the processes of erosion, sediment transport and
accretion, diverse landforms are being formed in the coastal zone. Among these
features the wave ripples, megaripples, antidunes, both longshore and transverse bars,
cliffs, benches and accretive terraces bordering the nearshore zone, barrier beaches,
spits, baymouth bars, cuspate bars, both single and double tombolos, etc., should be
mentioned.
Conclusions
Any one of large man-made lakes shows similarities to the type of lakes studied and it
is not a unified depositional sedimentary environment. These reservoirs represent a
complicated complex of different environments, such as fluvial-dominated and wavedominated ones as well as a transition environment, where both wave-induced and
fluvial processes take place. It is felt that certain of the environments are present
within the basins of most man-made and natural lakes. Probably, the exception are
lakes marked by a significant magnitude of the water level fluctuations and/or absence
of conditions for windy wave formation.
Within the basins of man-made lakes, along the lake fetch, a sequential
substitution of the fluvial-dominated sedimentary environments by predominantly wave
ones is observed. The substitution of environments is caused by diversified
geomorphic, geological and physical factors, and in turn drives the littoral and
211
bars, single tombolos and spits are fixed here too and in doing so many bars and spits
extend in the direction opposite to the general direction of channel flows. The shorenormal sediment transport gives rise to more or less stretched sites of the accretive
terrace bordering the nearshore zone; the terrace face typically has a slope of 9-10°
exceeding 2.5-3 times the averaged slope of the bottom within the nearshore.
During the initial filling of the Novosibirsk Reservoir and just after its
formation, the rate of coastal erosion within the wave-dominated area was the highest
and on some sites it was as great as 25-30 m/yr. Terrigenous material entering the
nearshore zone as a result of bluff erosion was transported mainly in the offshore
direction, because of rather high steepness of original slopes. As the nearshore zone
width increases and the beach slope decreases due to cliff recession and sediment
accretion at the periphery of the offshore area, the erosion rate began to reduce. At
present the eroded shores recede at the mean rate of 4.5 m/yr and, in places, the
erosion has been terminated.
Within 15-20 years the position of brow of the accretive terrace bordering the
nearshore zone was relatively stabilized though casual fluctuations of the brow take
place even nowadays. It marked the change of prevailing tendencies in sediment
transport, that is the longshore sediment transport began to prevail over the cross-shore
one. Similar to the wave-dominated shores of seas, natural and other man-made lakes,
the shoreline of Novosibirsk Reservoir at the wave-dominated area represents a series
of bow-shaped terrestrial patches and therefore the longshore sediment transport
usually occurs as two-way migrations, the rate of which may be as great as 60,000Owing to the combination of the processes of erosion, sediment transport and
accretion, diverse landforms are being formed in the coastal zone. Among these
features the wave ripples, megaripples, antidunes, both longshore and transverse bars,
cliffs, benches and accretive terraces bordering the nearshore zone, barrier beaches,
spits, baymouth bars, cuspate bars, both single and double tombolos, etc., should be
mentioned.
Conclusions
Any one of large man-made lakes shows similarities to the type of lakes studied and it
is not a unified depositional sedimentary environment. These reservoirs represent a
complicated complex of different environments, such as fluvial-dominated and wavedominated ones as well as a transition environment, where both wave-induced and
fluvial processes take place. It is felt that certain of the environments are present
within the basins of most man-made and natural lakes. Probably, the exception are
lakes marked by a significant magnitude of the water level fluctuations and/or absence
of conditions for windy wave formation.
Within the basins of man-made lakes, along the lake fetch, a sequential
substitution of the fluvial-dominated sedimentary environments by predominantly wave
ones is observed. The substitution of environments is caused by diversified
geomorphic, geological and physical factors, and in turn drives the littoral and