Changes of Shoreline from 1977 to 1995
The most recent lowest sea level was recorded in 1977 (-29.04 meters above oceanic sea level),
which was followed by a continuous rise in sea level (Figure 3). With this rise in sea level the shoreline in
the study area has moved landward toward the north (Figure 6). This gradual rise in sea level extends as
much as 25 kilometers, maximum, in the vicinity of the Ural River mouth, and 35 kilometers to the
south-southeast of Atyrau from 1977 to 1995. Due to a 2.42-meter rise of sea level during the past 18 years
(Figure 3), two near-shore terrace zones (slightly elevated) in 1977 have gradually been submerged and
changed into very shallow water areas (Figure 5). An elongated peninsula near the Ural River mouth also
has become narrower and narrower. Then the peninsula has changed into isolated islands from 1988 and
finally disappeared in 1993 (Figure 5).
Depth of Water in 1998
Recognizing the rise of sea level from previous shoreline positions in 1977, 1979, 1984, 1986, 1988
and 1989, respectively, the depth of water in 1998 can be calculated. This can be done on the assumption
that there were no significant changes through erosion or sedimentation in submarine topography of the
submerged area during the 21 years since 1977. Based on this principle, depth of water in 1998 was
obtained using a curve showing recent changes in sea levels. Thus depth of water in 1998 was recognized
through image interpretation by up to approximately 35 kilometers from the shoreline.
1998 Bathymetric Map
Prior to the generation of a base map covering the entire study area, six submarine topographic
profile lines were set up with almost an orthogonal direction to the shoreline in 1998. Subsequently,
profiles were drawn considering partial changes of sea bottom gradient created by two terrace zones (slightly
elevated). A 1998 bathymetric map (Figure 7) was generated, expressed in isobaths of 50-centimeter
intervals, using these profiles as well as actual depths of water measured during the field verification survey
conducted in June, 1998. As a result, a submarine topography was obtained in the present offshore area
including two terrace zones mentioned above. The sea bottom gradients from 2.0-meter isobath southward
are steeper than shallow areas of less than 2.0 meters deep. The previous peninsula near the Ural River
mouth has also steep submarine topography (Figure 7).
Generation of a Base Map for Seismic Survey Planning
The above bathymetric map was further interpreted and land cover units were also added as
supplementary information. Finally, four zones are highlighted on the seismic base map (Figure 8) as those
to be sources and receivers for seismic data acquisition. The following methods of measurement were
designed respectively in three zones of the very shallow water area among four zones shown in Figure 8.
(1)Zone A: Approximately less than one meter deep. Explosives and geophones should be applied
respectively as source and receiver. A cable or radio telemetry system is preferable as a receiving system.
(2)Zone B: Depth of water exceeds one to six meters, maximum. Air guns and hydrophones should be
applied respectively as source and receiver. A bottom cable or radio telemetry system is preferable as a
receiving system.
(3)Zone R: This is a reed zone along a shoreline. Although depth of water is approximately one meter, a
seismic survey could not be conducted by any kind of method during 1998 because deforestation was
prohibited within this zone.
Conclusions
(1)When extracting “the shoreline at annual mean sea level” from satellite images, the landward limits of
the reed zone along the shoreline can be applied for the definition of the shoreline. The previous land area
of more than 35 kilometers wide has been submerged by a rise in sea level during the period from 1977 to
1995 (18 years) to the south-southeast of Atyrau.
(2)The bathymetric map in the very shallow water area was generated through drawing submarine
topographic profiles, and thus the complicated submarine topography was obtained in detail. The land
cover units were added to this bathymetric map and finally four zones are highlighted on the seismic base
map as those to be the source and receiver.
(3)It is very difficult to conduct a seismic survey in a reed zone along the shoreline without deforestation.
On the other hand, a shallow water-seismic survey can be conducted in the offshore area, on the basis that an
appropriate method of measurement is selected according to the depth of water.
Acknowledgements
The authors are grateful to Mr. Yuichi MARUYAMA, General Manager of the Department of
Research and Development of the Earth Remote Sensing Data Analysis Center, for permission to present
this paper. They also are much indebted to Dr. Oleg A. FEDORENKO, Yuggeo Co. Ltd. who kindly
provided technical support during the field verification survey and Dr. Shunji SATO, General Manager of
the Exploration Department of Japan Energy Development Co., Ltd., for critical reading of the manuscript.
Selected References
- Nakayama, Y., 1997: Monitoring Changes of Lakes in Central Asia by Satellite Data. Proceedings of the
Nihon University International Symposium on Global Environmental and Human Living, p.271-283.
- Sydykov, J. S., Golubsov, V. V. and Kuandykov, B. M., 1995: Caspian Sea and its Coastal Zone. National
Scientific Academy of Republic of Kazakhstan, Institute of Hydrogeology and Hydrophysics,
Ministry of Science and Technology, Government Company “Kazakhstan-Caspi-Shelf”, 211 pp. (in
Russian).
