6 Natural and Anthropogenic Lakes of River Valleys
101
Created as a result of closing the water space between the groynes
Construction of the groynes perpendicularly to the banks of the river bed changes
the existing hydrodynamic conditions as a result of a change in the course of the
bed and river streams. Near the groyne heads, river streams collapse and the dragged
debris is deposited in their “shade” [48]. Three mechanisms of this process can be
distinguished:
– natural accumulation of material. Sandbanks formed parallel to the shore separate
the water spaces cutoff from the main river bed. Gradually, the sandbanks are
fixed by vegetation, while the cutoff water surfaces are continuously reduced and
shallow.
– forced accumulation. It leads to a partial transformation of the spaces excluded
from the active river bed into the land area. This applies especially to sections
where the space between the groynes was large, and the dragged debris movement
is observed in the watercourses. In the space between the groynes, at different
distances from the shore, fascine mattresses or wicker curtains were usually placed
at the bottom of the rivers, which slow down the speed of the flowing water and
encourage the depositing of the retained material.
– artificial landing. When the space between the groynes is shallow, the land is
strengthened with vegetation planting, most often with willow seedlings.
Created as a result of the floodplain erosion
This process usually occurs during floods. When the water level in the river is high,
previously accumulated material is eroded and washed away. A basin is created in
the place where the material is eroded by the river, and it is filled with river water.
Taking into account the nature of the inflow or outflow to lakes in regulated river
valleys, a simple and complex hydrographic system can be distinguished [47].
The simple system includes single reservoirs (Fig. 6.8):
A flow lakes
A1 along the axis:
(a) with gravitational inflow and outflow,
(b) with regulated inflow and outflow,
(c) with gravitational inflow and regulated outflow,
(d) with regulated inflow and outflow.
A2 asymmetric, in close vicinity there is inflow and outflow of water:
(a) with gravitational inflow and outflow,
(b) with regulated inflow and gravitational outflow,
(c) with gravitational inflow and regulated outflow,
(d) with regulated inflow and outflow.
B lake with inflow in the form of a trench or channel from the flood plain
(a) gravitational inflow
101
Created as a result of closing the water space between the groynes
Construction of the groynes perpendicularly to the banks of the river bed changes
the existing hydrodynamic conditions as a result of a change in the course of the
bed and river streams. Near the groyne heads, river streams collapse and the dragged
debris is deposited in their “shade” [48]. Three mechanisms of this process can be
distinguished:
– natural accumulation of material. Sandbanks formed parallel to the shore separate
the water spaces cutoff from the main river bed. Gradually, the sandbanks are
fixed by vegetation, while the cutoff water surfaces are continuously reduced and
shallow.
– forced accumulation. It leads to a partial transformation of the spaces excluded
from the active river bed into the land area. This applies especially to sections
where the space between the groynes was large, and the dragged debris movement
is observed in the watercourses. In the space between the groynes, at different
distances from the shore, fascine mattresses or wicker curtains were usually placed
at the bottom of the rivers, which slow down the speed of the flowing water and
encourage the depositing of the retained material.
– artificial landing. When the space between the groynes is shallow, the land is
strengthened with vegetation planting, most often with willow seedlings.
Created as a result of the floodplain erosion
This process usually occurs during floods. When the water level in the river is high,
previously accumulated material is eroded and washed away. A basin is created in
the place where the material is eroded by the river, and it is filled with river water.
Taking into account the nature of the inflow or outflow to lakes in regulated river
valleys, a simple and complex hydrographic system can be distinguished [47].
The simple system includes single reservoirs (Fig. 6.8):
A flow lakes
A1 along the axis:
(a) with gravitational inflow and outflow,
(b) with regulated inflow and outflow,
(c) with gravitational inflow and regulated outflow,
(d) with regulated inflow and outflow.
A2 asymmetric, in close vicinity there is inflow and outflow of water:
(a) with gravitational inflow and outflow,
(b) with regulated inflow and gravitational outflow,
(c) with gravitational inflow and regulated outflow,
(d) with regulated inflow and outflow.
B lake with inflow in the form of a trench or channel from the flood plain
(a) gravitational inflow