The response of river mouths to large-scale variations in sea level and river runoff: Case study of rivers flowing into the Caspian Sea

Abstract

Regularities in the response of the mouths of major rivers, flowing into the Caspian Sea, to large scale variations in its level and river water runoff and sediment yield are considered. Changes in the morpho logical structure and hydrological regime of the Volga, Terek, Sulak, Ural, and Kura mouths have been ana lyzed in both geological past and separately for three modern periods: a considerable drop in Caspian Sea level before 1978, its abrupt rise in 1978-1995, and a relative stabilization in the subsequent years. Specific features were identified in the hydrological-morphological processes in different mouths, caused by the dif ferences in river sediment yields, and the slopes of delta surface and mouth nearshore beds. Some theoretical and methodological approaches were verified in the analysis and evaluation of the processes under consider ation. The obtained results of studies of the mouths of rivers flowing into the Caspian Sea can be regarded as examples and analogues in the assessment of processes, which take place at the mouths of other Russian and world rivers at present and can take place in the future under anticipated natural and anthropogenic variations in sea level and river runoff. MIKHAILOV et al. 59], State Hydrological Institute (SHI) [62], and Astrakhan Reserve [10, 11] collected a vast body of data on this object; the late XX-the early XXI, when studies were carried out by Geographic Faculty, MSU; SOI, and Water Problems Institute, RAS (WPI RAS) [3, 20, 21, 27, 33, 36, 41, 43, 47, 50-52, 57, 61, 64, 65, 68]. Extensive investigations were also carried out (mostly by SOI, MSU, and WPI RAS) at the mouths of the Terek and Sulak rivers [1,2,4,9,12, 17,24,28,35,38,40,[44][45][46]. Less studied are the processes in the deltas of the Ural [25,26,51,60] and the Kura [1,16,19,34,63]. The results of studies at the mouths of the Volga, Terek, Sulak, Ural, and Kura were reviewed and generalized in [30,36,37,68].

Landscape evolution in orogenic plateaus: Insights from quantitative morphotectonic analysis of the Turkish–Iranian Plateau and Caucasus regions

“…The Kura is the main stream with almost trellis pattern and the Arax is its major tributary with mainly dendritic pattern and confluence in the Azerbaijan Plain. The Kura-Arax has a catchment area of $193 577 km 2 (Table 1), and the average water and sediment discharges into the Caspian Sea during the last 40 years have been $16 km 3 y À1 and $17 million tons y À1 , respectively (Mikhailov et al, 2003(Mikhailov et al, , 2012.…”

Variability in fluvially‐dominated, fine‐grained, shallow‐water deltas

“…The Volga Delta plain has a distributive channel pattern with numerous active channel threads (Olariu & Bhattacharya, 2006). The channel pattern developed during forced regression from the late 1800s to the 1970s (Mikhailov et al ., 2012; Chen et al ., 2017) accompanied by deposition of a series of elongate sub‐deltas, themselves composed of stranded terminal lobes (Fig. 14).…”

“…(A) Satellite view of the Volga Delta showing a distributive channel pattern. The graph (based on Chen et al ., 2017) shows how Caspian sea level fell for around a hundred years, resulting in forced regression recorded by historical shoreline positions (simplified from Mikhailov et al ., 2012). Satellite image from Google Earth, Image Landsat/Copernicus.…”