APPLICATION OF THE HYDRO-MORPHOLOGICAL THEORY OF CHANNEL PROCESSES FOR
ACCIDENT PREVENTION IN SOCIAL AND INDUSTRIAL COMPLEXES IN
State Hydrological
Institute (SHI),
23 Second Line,
Fax (812)
433-93-54, Е-mail: shi:@ sp.ru
In the hydro-morphological theory, the use of the system-structure approach allows investigation of the channel process patterns, development of its study methods, as well as solutions for the practical problems, while adhering to the same methodological ground. From this point of view, the channel process investigation of some section of a river equals to examination of an object of the nature in whole, and such an object represents a combination of a number of interlinked discrete morphological elements. Each of these elements consists of smaller components of another structure and genesis, and, at the same time, is a part of an element of higher structural level. Theoretically, the are six structural levels of the channel process: the level of the separate sediment fraction, the level of the bedload and suspended sediments of the channel microforms, of the channel mesoforms, of the river macroforms, the level of the morphologically homogeneous sections (by levels) of a river, and the level of the whole stream (fig. 1).
The methodology of study and monitoring of the channel process phenomena consists of identification and estimation of all characteristics which determine the channel process factors and also of the means and methods applicable for the assessment of their measurement, differentially for each structural level. For this purpose, the so-called “System of the channel prognoses” was developed by the State Hydrological Institute. This System consists of the four sub-systems, or the system-based scientific classifications, which are linked together following the principal of prognosis object, i.e., the channel process. The System includes the four sub-systems:
I. Classification of the forecasted principal elements and characteristics of the channel process.
II. Classification of engineering actions and constructions in accordance with the character of their interaction with the channel process.
III. Classification of the channel prognoses.
IV. Classification of data (fig. 2).
The Sub-system I shows the main features of the channel process which are expressed through the channel process elements and characteristics, such as discretization of the channel forms (on the six structural levels), direction of the channel deformations (reversible, irreversible, coexistent), interconnection of the channel forms (on the same structural level and on the different structural levels) (fig. 3).
The
fig. 3 illustrates the eleven components and characteristics of the
channel process. The models of the way of their behaviour
and the methods of their calculation and prognosis are being researched. For
example, for the meso- and the macroforms,
the author introduces a quantitative classification of the discrete morphological
formations (fig. 4). This classification expands the well-known
classification by Kondratyev and Popov.
Figure 1. Structural levels of the channel process
According to this scheme of the macro- and the mesoform types, the A type criterion has the energy value and shows the distribution of floodflow energy losses between the floodplain and the channel. The transformation of the big values of A into the smaller ones corresponds to reduction of hydraulic resistance for the floodplain λn and to increasement of the role of hydraulic resistance of the channel, λp. At the same time, the amount of the sediments to be transported by the channel increases; the minimal units of the bedload sediment discharge are observed in channels of the meandering type, while the largest units are seen in the alternate bar and the middle bar channels.
The Sub-system II displays the objective principal of the prognoses, i.e., the engineering actions, which are aimed at water withdrawers and water consumers and are carried out through any construction in the river channels or the floodplain.
Figure 2. The system of channel forecast. Each sub-system is illustrated below.
Figure 3. Classification of the forecasted principal elements and characteristics of the channel process
Figure 4. Classification
of the channel process of lowland river types
(according to B.Snishchenko)
2. The active structures are divided into two categories. When a first category structure is built, it leads to the one-way irreversible changes of the major part of the features which belong to the determinative factors of the entire river.
Building
the first category structures is practically always followed by reorganization
of the channel forms on all structural levels.
However,
every structure affects the characteristics of the determinative factors
differently. That is why a unitary scheme of these structures’ influence on the
determinative factors and the channel processes cannot be figured out. Such
schemes (and the corresponding normative documents) are to be worked out
separately for every type of the structures or influences. This fundamental
statement is also valid for the structures of other types. The body of the
first category structures, as well as of those of any other category, can be
enlarged with the help of the engeneering objects
which are similar to those mentioned above, in the terms of the character of
their influence on the channel process.
Figure 5. Classification of engineering structures and arrangements according to the type of their interaction with the channel processes
The second
category structures create local changes in some characteristics of the
determinative factors. As a rule, it does not mean a radical alteration of the macroforms, but only affects development of the bedload formations on the meso-
and the macroform levels. Many structures of this
category are being built with the purpose of regulation or stabilization of the
channel process.
In some
cases, building of such structures as cofferdams, the alluvium pits in channel,
and the offtake water diversion with dams can cause
noticeable changes in the determinative factors of the channel process and the
flowing forms on all structural levels. This happens when several
morphologically uniform river sections are dammed, when, while taking alluvium
out of an open pit, its amount significantly exceeds the volume of natural
sediment discharge, and when there is a long time accumulation of the bedload sediments in the offtake
water reservoirs. In all these cases, all the mentioned structures of the
second category can be defined as the engineering structures of the first
category.
Building of the passive structures on a river does not change the determinative factors of the channel process. Their constructive features, dimensions, locations, and exploitability are such that they cannot change neither noticeable amount of hydraulic parameters of the flow, nor the sediment transport regimes, nor the restrictive factors of the channel process. In this context, all these are the antipodes to the first category structures. In some cases of the mass building of such structures on a river, the result of their influence on the determinative factors can be the very same as that of the active structures. For instance, this can occur when there are too many small-scale offtake water diversions on a river.
Contrary to the first category structures, the passive ones are influenced by all types of the channel forms. Like in the case of the active structure groups, the interaction of the channel forms and the passive structures should be examined differentially, i.e. separately for every type of construction.
Reorganization of the macro- and the mesorforms can cause imbalance in any type of the passive structures shown in fig. 5. The microform movements do not have to influence such structures as power transmission line posts, siphons, embankments, but such movements become the key points in the silting process of submarine trenches, bulkheads, dissipate spillways waste discharges, and offtakes.
Therefore, taking into account the channel process during the passive structure engineering means defining of those channel forms which will influence this very structure, and also estimating the diapason of the channel deformations. If the structure cannot be placed beyond the established borders of deformation, its placement problem is solved by any of following methods:
- Stabilization of the flow with the help of the channel improvement structures of the second category.
- Discovering new, more suitable for such deformations, location.
- Designing a radically different construction which permits to avoid the channel deformation influences.
The Sub-system III shows the classifications of channel prognoses.
Their types are categorized in accordance with the prognoses features (tab. 1).
The channel prognosis is prediction of any change in the structure of the morphological channel or floodplain in either spatial or temporal interval. This prediction is based on the knowledge of development laws of the channel processes. Such laws determine these changes in specific conditions of any particular stream.
Table 1 illustrates the special features along with the corresponding types of prognoses. As a rule, the channel prognosis must be complex and take into account several types of particular prognoses
The Sub-system IV classifies the necessary data, the computation and prognosis of the determinative factors characteristics. The data requirements should not be of a general character, but must have a well-defined aim, in accordance with the content of the Sub-systems I, II, and III.
With the help of the ‘Channel Prognoses System’ the large-scale practical investigations of the channel process were performed. The investigations dealt with the single structures (hundreds of oil and gas pipeline crossings over the rivers and the reservoirs, dozens of offtake water diversions and spillways waste discharges, many bridges over rivers, etc.), and also with large and extensive energy lines which cross hundreds of rivers (The Caspian Pipeline Consortium, The Sakhalin II oil pipeline, the Baltic Pipeline System, and the like). Besides, the state specifications for uniform mass structure systems (spillways waste discharges, oil and gas pipeline crossings, power transmission lines, etc.) have been developed.
Table 1. Classification of the channel prognoses
|
Features of the prognoses classification |
Types of prognoses |
|
By general target basis |
Scientifically
cognitive |
|
Engineering
|
|
|
Environmental
|
|
|
By the stream genesis |
Prognoses
for the natural streams |
|
Prognoses
for the artificial streams |
|
|
By the stream (river) type |
Prognoses
for the plain rivers |
|
Prognoses
for the mountain rivers |
|
|
Prognoses
for the rivers flowing in specific conditions (permafrost, karst, etc.) |
|
|
By the type of interaction between the engineering structures and the channel forms |
Prognoses
for the first category structures |
|
Prognoses
for the second category structures |
|
|
Prognoses
for passive structures |
|
|
Prognoses
for the urbanized sections of the rivers |
|
|
By
the forecasting period |
Prognoses
for the stages of the channel forms development |
|
Prognoses
for the cycles of the channel forms development |
|
|
By the prognosis methods |
Hydro-morphological
|
|
Hydraulically
morphological |
|
|
Modeling |