296
R. Graf
regard through flood protection strategies, which, assigned until a flood occurrence,
were based on technical precautions through a system of flood control structures and
devices as well as immediate warning and response.
Most floods are caused by lowering valley retention with levees and increasing
maximum flows, or making the cross-section smaller and decreasing the river bed
flow carrying capacity, which further raises the maximum water levels. Levees which
protect flood-prone areas used by people during flood are often broken and destroyed
on stretches of many kilometres, which limits the possibility of controlling the course
of a flood and minimising the extent of the disaster with a technical flood protection
system (Fig. 15.10). Potentially, there is a risk of a higher rise, for which there are
designed facilities protecting against flood, and as a consequence, water overflowing
the levee or breaking it altogether. Too low flow carrying capacity of inter-levee
zones in urban areas, caused, e.g., by a low levee, without any possibility of making
it higher, requires the introduction of additional protections in the form of a flood
relief channel or polder upstream of the city. A flood protection system with a similar
scope and components whose purpose is to lower the flood wave is planned for the
city of Cracow [64].
The strategy “Moving flood away from the people” (Fig. 15.10) is a continuation of the traditional, technical mode of threat containment and flood protection. It
is implemented chiefly through: water storage reservoirs, levees, dry flood control
reservoirs, polders, flood relief channels, flood and storm gates, as well as measures
aimed at increasing natural retention (e.g. afforestation). Flood protection in a river
valley gives rise to the possibility of settling multiple areas, which, however, are
characterised by a high risk of flood occurrence, thus jeopardising society with great
losses.
The technical direction of protection entails eliminating or reducing flood damage
by the operation of a hydrotechnical system. An example is the complex of water
storage reservoirs in the Vistula Basin, whose purpose is outflow reduction and
maximal spacing of flood wave culminations. The reservoir functioning in the Goczałkowice system delays culminations on the Small Vistula, the Soła Cascades reservoirs distance Soła culminations from Skawa culminations, in a similar manner as
the ´
Swinna Por˛ eba reservoir on the Skawa River, which, by stopping about 60 million
m
3 of water even during the 2010 flood, delayed a culmination of the wave on the
Vistula [64].
To flood rise reduction, besides technical measures, also contributes to soil retention, which is lowered in urbanised catchments. For a leveed river, maximum flows
are regulated by active surface retention, which determines the space between levees,
whereas the land sides of levees provide for so-called ‘confined’ retention. Proper
management of urban space, biotechnical land development by forestation or limiting
surface sealing in urbanised areas (e.g. green car parks) and rational precipitation
water management can redound to increasing the active catchment surface area
regulating surface and groundwater levels [22, 65].
The unreliability of many technical infrastructure devices recorded during the
recent years’ floods [46], and the manifestation of the so-called apparent safety
syndrome in a leveed valley, have indicated to the need to introduce another flood
R. Graf
regard through flood protection strategies, which, assigned until a flood occurrence,
were based on technical precautions through a system of flood control structures and
devices as well as immediate warning and response.
Most floods are caused by lowering valley retention with levees and increasing
maximum flows, or making the cross-section smaller and decreasing the river bed
flow carrying capacity, which further raises the maximum water levels. Levees which
protect flood-prone areas used by people during flood are often broken and destroyed
on stretches of many kilometres, which limits the possibility of controlling the course
of a flood and minimising the extent of the disaster with a technical flood protection
system (Fig. 15.10). Potentially, there is a risk of a higher rise, for which there are
designed facilities protecting against flood, and as a consequence, water overflowing
the levee or breaking it altogether. Too low flow carrying capacity of inter-levee
zones in urban areas, caused, e.g., by a low levee, without any possibility of making
it higher, requires the introduction of additional protections in the form of a flood
relief channel or polder upstream of the city. A flood protection system with a similar
scope and components whose purpose is to lower the flood wave is planned for the
city of Cracow [64].
The strategy “Moving flood away from the people” (Fig. 15.10) is a continuation of the traditional, technical mode of threat containment and flood protection. It
is implemented chiefly through: water storage reservoirs, levees, dry flood control
reservoirs, polders, flood relief channels, flood and storm gates, as well as measures
aimed at increasing natural retention (e.g. afforestation). Flood protection in a river
valley gives rise to the possibility of settling multiple areas, which, however, are
characterised by a high risk of flood occurrence, thus jeopardising society with great
losses.
The technical direction of protection entails eliminating or reducing flood damage
by the operation of a hydrotechnical system. An example is the complex of water
storage reservoirs in the Vistula Basin, whose purpose is outflow reduction and
maximal spacing of flood wave culminations. The reservoir functioning in the Goczałkowice system delays culminations on the Small Vistula, the Soła Cascades reservoirs distance Soła culminations from Skawa culminations, in a similar manner as
the ´
Swinna Por˛ eba reservoir on the Skawa River, which, by stopping about 60 million
m
3 of water even during the 2010 flood, delayed a culmination of the wave on the
Vistula [64].
To flood rise reduction, besides technical measures, also contributes to soil retention, which is lowered in urbanised catchments. For a leveed river, maximum flows
are regulated by active surface retention, which determines the space between levees,
whereas the land sides of levees provide for so-called ‘confined’ retention. Proper
management of urban space, biotechnical land development by forestation or limiting
surface sealing in urbanised areas (e.g. green car parks) and rational precipitation
water management can redound to increasing the active catchment surface area
regulating surface and groundwater levels [22, 65].
The unreliability of many technical infrastructure devices recorded during the
recent years’ floods [46], and the manifestation of the so-called apparent safety
syndrome in a leveed valley, have indicated to the need to introduce another flood