EFFECT OF RECENT CRUSTAL MOVEMENTS
ON THE SHAPE OF LONGITUDINAL PROFILES
AND WATER LEVELS IN RIVERS
N . G. VOLKOV, I . L . S O K O L O V S K Y , and A . I. S U B B O T I N
Institute of Geological Sciences, Academy of
Sciences of the Ukrainian SSR (Kiev),
USSR Hydro meteorological Centre (Moscow)
SUMMARY
1. The longitudinal profiles of river beds have the shape of a broken curve, as a
rule, and approach a parabola only in their general outlines,
2. The presence of breaks (deformations) in the profiles is due to variations in the
water discharge of the river at the confluences of tributaries, the heterogeneous
lithological composition of the river bed rocks and the effect of local tectonic activity
of structures crossed by the river.
3. To obtain quantitative characteristics of neotectonic movements, the deviation
(with positive or negative sign) from a specially calculated theoretical profile (geometrical analog , which the river would have under comparatively stable tectonic
conditions, is determined at each point of the profile. A procedure has been elaborated
for constructing the geometrical analog, applying nomograms and introducing
corrections for fluctuations of altitude of the mouth of the principal river, which
flows into the sea, and its tributaries.
4. The values of the deformations thus obtained are generalized by the isolines
method, and an isoder map is compiled characterizing the summary amplitudes
of
neotectonic movements in the Holocene (during the last 10-12 thousand years 1 .
5. The basic method of studying recent crustal movements consists of repeated
levellings and depth gauge observations; however, a procedure based on the study of
natural processes conditioned by recent movements is also of great scientific and
practical importance. One such method is the study of variations in time of the ratio
of discharges to water levels in rivers. These variations depend on the direction of
development of erosive processes. In uplifting areas scour of the river bed occurs and
a fall in the water level (without change in discharges); in subsiding areas there is a
tendency for river beds to fill with alluvium.
An analysis of the data on discharges and levels obtained by over 130 water gauge
stations shows that the raie of subsidence of river levels with constant discharge is
fully commensurate with that of recent crustal movements.
RÉSUMÉ
1. Les profils longitudinaux des lits de rivières ont la forme d'une courbe brisée,
en général, et ils ne s'approchent de la forme parabolique que dans leur ensemble.
2. L'existence des ruptures dans les profils est due aux variations du débit de la
rivière aux confluents des tributaires, à la composition Hthologique hétérogène du
lit de la rivière et à l'action de l'activité tectonique en certains points.
3. Pour obtenir les caractéristiques quantitatives de mouvements tectoniques, la
déviation (positive ou négative), à partir d'un profil théorique spécialement calculé,
que la rivjère prendrait sous des conditions tectoniques relativement stables, est
calculée en chaque point du profil. Une méthode a été mise au point pour construire
l'analogue géométrique, en utilisant des nomogrammes et en introduisant des corrections pour les fluctuations d'altitude de l'embouchure de la rivière principale, qui
s'écoule à la mer, et de ses tributaires.
4. Les valeurs des déformations ainsi obtenues sont généralisées par la méthode
des isolignes et une carte a été établie caractérisant les amplitudes des mouvements
tectoniques récents dans l'Holocène (au cours des 10 ou 12 derniers millénaires).
5. La méthode de base pour l'étude des mouvements récents de l'écorce terrestre
consiste en des nivellements répétés et des observations d'échelles de profondeurs :
cependant une méthode basée sur l'étude des processus naturels conditionnés par les
mouvements récents est aussi de grande importance scientifique et pratique. Une
méthode de ce genre est l'étude des variations dans le temps des rapports entre les
105
débits et les niveaux d'eau. Ces variations dépendent de la direction du développement
de l'érosion. Dans les régions qui se relèvent, une érosion du lit se produit et provoque
une baisse du niveau d'eau (à débits égaux); dans les aires de subsidence, il y a une
tendance au relèvement du lit par alîuvions.
Une analyse des données relatives aux débits et niveaux de 130 stations de jaugeage
montre que le taux de descente des niveaux d'eau pour des débits donnés est en pleine
concordance avec celui des récents mouvements de l'écorce.
investigations of recent decades have made it possible not only to establish the
presence of ubiquitous signs of Post-Alpine or Neogene-Quaternary crustal movements, but also to obtain numeric characteristics of these movements, both in the sum
for the entire neotectonic period and for its separate stages. On studying the neotectonic
movements and the structures created by these movements, the most diversified
methods are applied, including the investigation of the longitudinal profites of river
beds, which has proved to be very effective for the study of Holocene movements (for
the past 10-12 thousand years). The Holocene movements are characterized by the
totalized amplitudes rather than by rates, which is due to the fluctirationai nature of
these movements, the superposition of the fluctuations of the various periods and
amplitudes, the repeated alternation not only of rates but also of the signs of movements, in view of which the quotient obtained by dividing the amplitude by the time
cannot be regarded as the rate of movement.
As a rule the longitudinal profiles of river beds have the shape of a broken curve,
which approaches the parabola in its general outline. The breaks in the profile are due,
above all, to the change in the water content of the river at the junctions of tributaries,
the varying resistance to scour of the river bed rocks, the effect of the tectonic activity
of the given region and the local structures crossed by the river. Only the deformations
(breaks) of the longitudinal profile of the river due to the primarily differentiated neotectonic movements are considered. Deformations, due to other causes, are excluded on
the basis of a detailed study of the changes in the river discharge and in the geological
structure of the bed.
The topographic longitudinal river profile is compared with an analytically calculated profile, in order to obtain quantitative characteristics of the deformations,
which can be considered, with a certain degree of approximation, as proportional to
the totalized amplitudes of neotectonic crustal movements during the Holocene. The
analytically calculated profile is the profile of the river under consideration if this river
is flowing through a technically stable area in a bed of homogeneous rocks. There are
several methods of constructing such analytical profiles; but, the most applicable one
is the construction of the so-called geometrical analog of the topographic longitudinal
profile—a smooth line generalizing its shape, calculated with definite morphometric
criteria, inscribed in an actually existing topographic profile.
Numerous experimental investigations on the construction of theoretical longitudinal profiles of rivers by various mathematical methods show the simplicity and convenience of P. V. Ivanov's formulae, which offer a very uncomplicated method of calculating and expressing in symbolic form the outline of a longitudinal profile of any
shape, through the index of the shape of the river's longitudinal profile n, determined
for each river individually.
To exclude the effect of neotectonic movements on the altitudinal and linear (by
the profile line) position of the mouth of the principal river flowing into a body of
water with a shore-line displaced during the Holocene, we propose that the calculation
of a geometrical analog for rivers with mouths in subsidence regions, a geomorphological sign of which is the presence of drowned river bed sections at the mouth (estuaries)
•—as, for instance, in the case of the Black Sea depression rivers—should be carried out
with the correction l", the geometrical essence of which is shown in figure 1.
106
To make possible an unambiguous correlation of the real and calculated profiles,
giving an idea of (he deformation of the topographic profile, the altitudinal position
of the tributary mouths is correlated with the geometrical analog of the main river by
means of correction ± do when constructing geometrical analogs for each investigated
river basin.
After introducing the indicated corrections the line of the geometrical analog will
coincide with the topographic profile in the upper part or highest point of the characterized part of the profile and will be displaced at the mouth for the main river by a
value Ah (and along the profile line by !°) or for tributaries by the value ± do.
After constructing the geometrical analog of the profile, the relative deformation on
the longitudinal profile, ± d, the deviation of the topographic profile from its analog
(at every given point) is determined graphically or analytically. It is positive if the line
of the topographic longitudinal profile of the river is situated above the line of its
geometric analog and is negative with the inverse relation.
The values of the relative deformation of the longitudinal profiles of rivers thus
obtained are entered on a map of definite scale and are generalized by the isoline
method, which permits the compiling of a map on which points with equal deformation
values are connected by isodefs. At the given stage of investigation the isodef map
(fig. 2) is considered by us in its first approximation as a map of totalized amplitudes
of recent tectonic movements.
The application of the described quantitative method of analysis of the shape of
longitudinal profiles of rivers with the aim of neotectonic analysis in the practice of a
number of research and industrial organizations has led us to seek ways of improving
and simplifying it.
The most laborious process, with regard to definite difficulties and considerable
expenditure of time, is the calculation of geometrical analogs from the formulae of
a truncated parabola (P.V. Ivanov, 1951):
'""ft"
+a
*-"© #
where h is the height of the profile point above the lowest point (the river mouth);
h' is the corresponding value for the tributaries; / is the distance from the given point
to the mouth; L i s the length of the river; Hi = L-Ialfo's the dip of the main river at
its confluence with the given tributary; B% — H~HilH is the excess of the head of the
river over the mouth; n is the index of the longitudinal profile shape.
The heights above the lowest point of the profile calculated analytically {hi, As,
H,... h„) permit the construction of a theoretical curve, consisting of one branch of
a parabola, which generalizes the real, topographic profile. These calculations may be
considerably simplified by applying the method of nomograms.
The dependence h/H = (//£}" makes it possible to construct a nomogram of the
calculation of geometrical analogs of longitudinal profiles, the ratio l/L being plotted
along the axis of abscissae, and h/H along the axis of ordinates (the values of l/L and
h/H vary within limits from 0 to 1). The aggregate of branches of parabolas with
power indices varying from 0.5 to 10 permit the characterization of practically any
shape of profile (within the given limits of variations in «),
107
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Fig. 1 — Construction of longitudinal profiles of the Southern Bug, the Sobya arid the
Mertvovod rivers:
1. topographic longitudinal profile of principal river;
2. the same for the tributary;
3. geometrical analogs of longitudinal profiles after introducing correction P
and ifcrfo;
4. mouth of tributary;
5. ancient river mouth.
108
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analog of principal river at confluence with tributary; L present length of river;
1° length of section of river bed at mouth drowned by the sea; L' length of river
before drowning of section at mouth; ±do value of relative deformation of tributary
mouth; All excess of present river mouth over ancient one; ±d value of relative
deformation at given point of profile; o present sea level,
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The application of the method of nomograms introduces a definite systematic error.
However, this error does not exceed the graphic precision of construction of longitudinal profiles in the scale required for morphometric analysis.
Recent vertical crustal movements are studied by means of repeated levellings, which
permit the establishment of changes in the altitudinal position of bench marks during
the time elapsing between the levellings (usually 20-30 years 1 , taking into consideration
depth gauge observations as well. These methods are the most perfect ones at present;
however, they require a fairly dense network of highly precise levelling lines and considerable expenditures of money, and the first results can be obtained only several years
after the first levelling. These considerations force us to seek other methods for detecting recent crustal movements, which are perhaps less precise, but considerably more
feasible.
One such method, sufficiently reliable in our opinion, is the investigation of the
corrélation between discharges and water levels in rivers of low water content. Scour of
the beds and subsidence of underground water levels in welis, located on flood-plain
terraces formed by recent uplifts, may give the impression of progressive aridization
of rivers.
A tendency toward the filling up of river beds with alluvium and toward the gradual
upward displacement of discharge curves is manifested in areas of recent subsidence.
As a rule this process is less pronounced than the erosive alteration of beds in regions
undergoing elevation.
On the basis of an analysis of the data on discharges and levels obtained from 130
water gauge lines it was found that the rate of subsidence of river levels at constant
discharge is quite proportional to the rates of recent crustal movements established by
means of repeated levellings.
Figure 4 shows the change in the water level at the water gauge station with a constant discharge of water at this water gauge line, in order to illustrate the nature of the
variation in the ratio between the level and the discharge of the river.
In the Dnieper at Kiev, for instance, the discharge in 1885 was 500 m 3 /sec with the
water level 0.9 m above the station zero, in 1927, with the same discharge, the water
level was only 0.2 m. Thus, during 32 years the water-level of the Dnieper sank by
70 cm. During the period from )943 to 1954 the water level sank by another 17 cm.
This process continued further until the Kiev Hydroelectric Station dam was built on
the Dnieper.
Scour of the bed occurs still more intensely in the neighbouring Don River basin.
Here at Kazanskaya Station the water level, corresponding to a discharge of 140 m 3 /sec,
fel! by almost 70 cm from 1946 to 1962.
The scour of the Don tributaries—the Khopor, Medveditsa and other rivers—is
also intense.
In other regions the inverse process is observed. Figure 4 shows as an example the
graphs of multiannual variations in the water level in some rivers of the Volga basin. In
the Unzha River at the village Makaryevo, for instance, the discharge curve rose by
40 cm during the period from 1936 to 1961 (fig. 5). It is true that in the past two years
the level dropped slightly, but such temporary fluctuations have been observed previously.
A rise in the water discharge curves has also occurred in other tributaries of the
Volga, for instance at the Klyazma River and in some left tributaries of the Don (the
Sosna, Podgornaya and other rivers).
The cited examples indicate that it is impossible to make use of data on river water
levels only for judging the nature of multiannual fluctuations of the water content. On
the basis of data on the water levels erroneous conclusions may be drawn as to progressive aridization or, on the contrary, as to increase in the water content of the area
under consideration. It is obvious that a change in the water level in the principal river
111
Fig. 3b— Map of rates of recent vertical crustal movements of the western half of the
European part of the USSR.
A. From data of repeated levellings:
1. lines of equal values of rates; uplifts;
2. over 10 mm per year;
3. from S to 10 mm per year;
4. from 6 to 8 mm per year;
5. from 4 to 6 mm per year;
6. from 2 to 4 mm per year;
7. from 0 to 2 mm per year; subsidences;
8. from 0 to 2 mm per year;
9. over 2 mm per year.
B. From data of multiannual displacements of river discharge curves:
1. districts of uplifts of earth's surface and predominant fall in water discharge
curves ;
2. districts of subsidences of earth's surface and predominant rise in discharge
curves.
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Fig. 4 •— Multiannual changes in level at constant river discharge.
1. Don — Kazanskaya (i>Qonst = 140 m s /sec);
2. Medveditsa — Arcliedinsky (Ôeonst = 20 m 3 /sec);
3. Khopor — Besplemenovsky (goonst = 32 m 3 /sec);
4. Dnieper — Kiev <2eoost = 560m 3 /sec);
5. Klyazma — Pavlovsky Posad (Qeonst = 15 m 3 /sec);
6. Unzha — Makaryev (Qeonst = 70 m 3 /sec).
se ion im m
no HO
m
30
60
70
40
Sir
Fig. 5 — Displacement of discharge curves during multiannual period.
A. Don — Kazanskaya.
B. Unzha — Makaryev.
115
involves a change in the intensity of erosive processes in the riparian area. On subsidence of the base level, there occurs intensification of the erosive activity of small
tributary streams and a more rapid development of ravines. As a consequence the
ground water level begins to fall, which may also lead to the erroneous inference that
the climate is changing.
An analysis of multiannual displacements in water discharge curves of rivers of
the European part of the Soviet Union shows that large areas exist within which the
process of a fall—or, on the contrary a rise—in the discharge curves predominates
(fig. 3b). A comparison of maps compiled on the basis of geodetic data (fig. 3a) and
hydrological observations (fig. 36) shows that a fall in the discharge curves—i.e. river
bed scour—occurs chiefly in areas of slow surface uplift and, on the contrary, in subsidence areas an upward displacement is observed in the curves.
The signs of rises, established on the basis of an analysis of the changes in multiannual discharge curves, are associated with relatively elevated regions—the Central
Russian elevation, the Donets Ridge, etc.—while the signs of falls are associated with
relatively low areas—the Tambov and Meshchera lowlands, etc.—which indicates that
the basic features of the relief of these elevations and lowlands are tectonically conditioned, and that spatially differentiated neotectonic movements are hereditary.
On studying multiannual fluctuations in discharges and water levels of rivers with
the aim of neotectonic analysis, it is essential to take into consideration the fact that
in long rivers we usually observe alternation of areas with signs of subsidences and
uplifts, which is explained as differentiation of movements and by the fact that scour
or intense accumulation in. the given area depends not so much on the absolute uplifts
or subsidences of the given area, as on the geomorphological effect of these movements
—'the lag in elevation of some parts of the area relative to others gives rise to signs of
subsidence, a rapid elevation of local structures causes backing up of rivers before the
structure, and so forth.
The somewhat greater races of scouring of river beds, as compared with the rates
obtained as a result of repeated levellings, is explained by the fact that rivers, after
formation of their levelling profile, continue to form a more gentle longitudinal profile,
and this natural process is superimposed on the activation of erosion as a result of
uplifts.
Highly precise hydrometric observations conducted within the framework of the
International Hydrological Decade may be applied not only to the study of discharges,
but to investigations of recent crustal movements as well.
116