SECTION 2. PHYSICAL AND GEOGRAPHICAL COASTAL PROFILE

2.7.1. General information about the mouth areas.

The mouth areas are the characteristic elements of Russian part of the coastal area of the Caspian sea. Some of the data about the mouth areas of Samur, Sulak, Terek and Volga (clockwise) are shown in table 2.7.1.1. All the given mouths belong to the delta type. [7].

Table 2.7.1.1. Modern morphometrical characteristics of the mouth areas of rivers according to [5, 7, 18].

Notes: 1) numerator – in 1978 (Before the raising of the sea level), denominator – in 1997; 2) numerator – before the artificial rectification of the river-bed in 1957, denominator – in 1997 ; 3) the square of the shoal zone of the mouth seaside 10000, ïëîùàäü îòìåëîé çîíû óñòüåâîãî âçìîðüÿ 10000, 28000 êì².

2.7.2. Mouth area of Samur

Delta of Samur has aligned sea boundary and two sleeves – Small Samur (northern, 24 km long) and Samur itself (southern).

As a result of artificial distribution of the flow in 50s Small Samur started to take about 90% of the river flow. In the mouth of that sleeve the deposit of the washout take place, while in the mouth of the southern mouth one can observe a wave washout of the shore, strengthened in the period of the top of the sea level.

2.7.3. The mouth part pf Sulak.

The mouth of Sulak consists of one sleeve delta and the shore.

Te modern delta of Sulak started to form on the open coast of the Caspian Sea in the beginning of the XIX century. In its development delta passed several cycles, including the ones on the break of the river-bed and the formation of deltas. The last natural break took place in 1929, in its result the new delta blade was formed, oriented onto the north. To the north from the seaside of delta it there is a long Sulak spit, formed of the products of the wave ruining, that separated the Sulak bay from the main coast. In 1957 the waters of Sulak were led out artificially. In the south-eastern direction. Here the “new” delta of Sulak started to get formed, while the old delta started to dry off and to get destroyed by the roughness even more severely. The washout of the delta increased after the immediate stoppage of the flow of alluvium as a result of the construction of the Chirkey water reservoir (1974) and during the period of the increased raising of sea level (sarting from 1978).

For the present moment part of Sulak delta is flooded in a result of the raising of the level of Caspian sea; the square of the delta from 1977 till 1993 became less for 36% (table 2.7.1.1). The head of the raised sea water level spread to the bed of Sulak for over several km. In the mouth of Sulak the pileups and sleeve vibrations of the level were penetrating more regularly [9]. In the conditions of the increased levels of the water the threat of river water’s bursting towards Sulak bay and Mekhbet lowering in the mouth part of Sulak remains potential.

2.7.4. Mouth part of Terek

The Terek mouth consists of vast delta (table 2.7.1.1), Agrakhan peninsula, parts of shallow Kizlyar and Agrakhan bays and open shore in the area of “new” delta.

Delta plain of Terek starts in the region of Stepnoye settlement (170 km of the sea). The mount of the modern delta is Kargalinsky hydrosystem, built in 1956. here the waters enter the main sleeve of the delta – the Kargalinsky break long as 106 meters and the system of water-dripping channels. There are a lot of freshwater lakes in the delta of Terek. Approximately 5,1 km3/year (61% of Terek flow) arrives into the low pool ; the size of the flow increases even more when reaching the mouth of Kargalinsky break (to 4,2 km3/year, 50% of the flow of the river). In the whole of Terek delta 1,7 km3/year of water (20% of river flow) is lost for good due to the evaporation from the surfaces of lakes, fluxes, watered lands.

Delta of terek was developing by means of breaks and formation of separate private deltas. The last break took place in 1914 having given the start to the formation of the new sleeve – Kargalinsky break.

The river formed an inner delta of 130 km2 in Agrakhan bay by 1977.

After the artificial leading out of river waters through the slit of Agrakhan bay (in 1973 and, later, in 1977) the “new” delta of Terek forms on the open coast of the Middle Caspian.

The attendant to the opening of the slit shortening of the length of the bed up to 28 km led twice (in 1973 and 1977-1978) to the massive scale erosion of the mouth part of Terek. The marks of the bottom and of the level decreased for 2-3 m; the wave of the regressive erosion spread for 50km [7, 9]. The low level of the sea these years became the reason for the erosion. The sea level raising that started in 1978 led to the opposite processes: the accumulation of pileups started on the mouth part, the marks of bottom and water level increased for 1-2 meters by 1993. The distance of the spread of the wave of the top and of the alluvium ended up with 50-60 km [9].

The increase of the marks of the water level in the mouth part of Terek creates prerequisites for the strengthening of delta flooding during the high water and new break of the bed. This kind of a break is much more possible in the direction of the southern part of former Agrakhan bay with the following exit of waters into the sea through the Mekhbetskiy shedding. The possibility of a break remains and it is not bound with the raising fof the sea water level. The upper part of the curve above the head of the channel named after Dzerjinsky is the most dangerous section. The breaks can be stimulated by the unsatisfactory condition of the defensive dams.

2.7.5. Mouth area of Volga

The uniqueness of the mouth area of Volga provides the presence of one of the most complicatedly broken deltas of the world and the huge shallow seaside. The delta of Volga is the oasis among the dry steppes and semi-deserts. The hydrographic net of delta is represented by numerous currents (sleeves, channels and erics) and the imen lakes. The general number of currents is about 1000 [18]. The length of the sae boundary is as long as 175 km. The shallow indelta zone is of the mouth seacoast has the extent from the north to south for 30-50 km and is as deep as 2,5 m (with the sea level –27 BC). This part of the sea coast is cut by the net of natural furrows and artificial navigable channels and fishing channels. The total amount of channels is 28, 3 of them are nvigable channels, 8 are arterial and 17 are additional fishing channels. Volgo-Caspian channel (86 km long, 5 m deep), Belinsky channel (42 km long, 3 m deep) and lagan (30 km long, not bound with the delta) belong to the navigable channels. In the beginning of 90s the depth of arterial fishing channels was 1,5 m [18].

The shoal part of the mouth coast is grown by water flora.

The area of the mouth coast consist of bent platform wide as 70 m and deep as 3-7 m (between the isogypsum –30 -- -34 v BC) and of the è èç ñâàëà ãëóáèí ñ ðåçêèì óâåëè÷åíèåì ãëóáèí îò 7 äî 13-15 ì (ìåæäó èçîãèïñàìè -34 è -40 - -42 ì ÁÑ ïðè óðîâíå ìîðÿ -27 ì ÁÑ).

In the delta of Volga the flow of the river is distributed according to the schemes of five main sleeves (table 2.7.5.1), of which Buzan (the most left one) and Bakhtemir (the most right one) are the most water-bearing. When decreasing the size of the flow of the river the portion of Bakhtemir’s flow increases noticeably (table 2.7.5.1) and this fact testifies the tendency of this sleeve to the energezation (it is stimulated by the deep marine exit through the Volgo-Caspian channel).

Table 2.7.5.1. Modern distribution of the Volga flow through the current of delta (in%) according to [18].

Note: the summary flow of Volga into the upper deltas results from the flow in the main river-bed, along Akhtuba and Volgo-Akhtubinsky source.

For the past 50 years the portion of Bakhtemir’s flow increased from 24 to 31 % of the middle flow of the Volga, the portion of Buzan increased from 31 to 34 % while the portion of other sleeves either decreased or remained unchanged [7, 18].

When the water level is high during the high waters the part of delta of Volga gets flooded. The area of flooding can be 50-70% of the whole square of the delta [18]. 8-10 km3 of water is evaporated annually from the surfaces of lakes and flooded area at present and that is not compensated.

The raising of the Caspian Sea level for 2.35 m during 1978-1995 led to the increase of bottom depths in coastal and shoal areas, to the flooding of some islands nearby the coast, of the narrow band (several km wide) in the low coastal zone of delta. In the lowers of the sleeves the raising of the sea level, when the flow was not massive, started only after 1988-1990, that is 10-12 years later that in the sea. The parameters of the increase of the level in the currents of delta (table 2.7.5.2) happened to be not very big and appeared to be absolutely inadequate to the parameters of the raisings of the sea level itself. If in the shoal (island Iskusstvenniy) the water level raised for 0,9 m by 1995 when the water flow was low then at the point Olya (24 km from the sea boundary of delta) it raised only for 0,4 m. In high waters there was almost no level raising to be observed. .

The distance of the spread of the backwater in the deep sleeve of Bakhtemir in a low flow of the river did not exceed 90 km (table 2.7.5.2), and in other sleeves it did not exceed 30-40k. Such a weak reaction of the water levels in the seaside part of the delta of Volga on quite a reasonable raising of the level of the Caspian Sea (in contrary to the processes in deltas of Sulak and Terek is explained by the blocking role of the “buffer zone”, which is the wide and shallow mouth seaside.

Table 2.7.5.2. Estimation of the effect of the increase of the level of Caspian sea up to 2.35 m during 1978-1995 on the level of the water in the mouth area of Volga [8].

Notes: 1) the distance of the points island Iskusstvenniy (shoal zone of the seaside) and Olya (lower of the sleeve of bakhtemir) from the top of delta are 187 and 136 km accordingly, and 27 km (towards the sea) and 24 km (towards the land) accordingly; 2) Q_c – the summary of water use of Volga at Verkhniy Lebyajiy (bed, Akhtuba, flood-lands).

On the background of high sea levels the danger of penetration of strong pileups increases.

The average growth of the square and the length of Volga delta during the fall of the sea level in 30s were 180 km2/year and 1km/year accordingly. [18]. Starting from 1960 the condition of the sea boundary of the delta was mainly stable.

SECTION 1

SECTION 2

SECTION 3

SECTION 4

SECTION 5

SECTION 6

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