Impact of Peak Flashes from Volgograd Hydropower Station on North-West Caspian Environmental Conditions

Impact of Peak Flash from Volgograd Hydropower Station on North-West Caspian Sea Environmental Conditions


P.V. Lyushvin, NTs OMZ, Moscow,
V.N. Zyryanov, IVP RAN, Moscow, S.N. Egorov, KASPNIRKh, Astrakhan, A.V. Kukharsky. NITs PLANETA, Moscow, V.F. Polonsky, A.N. Korshenko. GOIN, A.L. Lobov, Hydrometcenter of Russia, Moscow. 

ÐThe paper is based on the interpretation results of pollutant discharge into the Russian seas and of floods in the Lower Volga. Of total pollutants including petroleum hydrocarbons that enter into seas, more than 80% comes with runoff and waste water and above 90% of them arrives with river runoff (Fig.1a, [1]). Satellite data enables estimating the extent of these waters. The estimation is based on the analysis of satellite SST maps, chlorophyll and hydrosol content in surface water, and by use of radar images. There are observed some pollution traces on ice.

Hydrosol albedo, 19.09.2004	Hydrosol albedo, 28.09.1999	SST near the Volga delta, 27.05.2002

ÐRadar image, 29.09.1999 [17]	Radar image of the Bakhtemir arm with wave train from it, 14.07.2003 [17]	30.12.2004 (Trains of circular waves), a slick over the Ural Borozdina – does it oil spillage or calm? There is a windless region behind the Kulaly Islands, 30.12.2004	Left — 09.03.04 (arrows show slicks nearby melting ice. It might be oil products from the Kazakh oil fields)

With putting into operation the hydropower station in the Lower Volga, the hydro-ecological conditions of the Lower Volga and the North Caspian Region changed drastically. The winter runoff was trebled and the spring-and-fall flood decreased by the appropriate runoff value and its duration was halved. (Fig.1b).

Fig.1a: Petroleum hydrocarbon discharge (thousand tons) into the North Caspian Sea (Volga, Verkhneye Lebyazhie gauging station) and petroleum hydrocarbon concentrations (mg/l) in the North Caspian Sea and in the abyssal sea over the period 1977-1992 [1].

Fig1b: Left – Water stage in Astrakhan in 1947, (left scale in cm) and daily variations in water stage (right scale in mm). Centre – discharge water from the Volgograd GES (left scale) and water stage in Astrakhan. Left – discharge water from GES and water stage variation in Astrakhan in 1999 with no time shift and the 4- and 7-day time shift

ÑThe Volga runoff undergoes considerable annual variations (Fig.2). According to regulations the flush designed for spring flood simulation and fish reproduction is made by discharge water at the rate of 2.2km per day for first several days and then while there is enough water in reservoirs the transition of discharge water level to „shelf“ at the rate of 1.7km per day takes place. In non-dry years such a regime of discharge water is favorable for the 40-60-day flood that is considered to be environmentally allowable. However the period of water level below the maximum by 0.2m and even by 0.5m during flood is less than 3-4 weeks that is critical for the period required for baby fishes to be vigorous. When deficiency in water the floodplain is partially submerged for less than 2-3 weeks so a part of larvae or baby fishes either is washed away without being vigorous or dried out together with fish roe. Thus in dry 1975 a mass dry-out of fish roe and larvae was observed resulted in a minimum amount of baby fishes. When the Volga flow had been regulated near Volgograd, normal conditions required for reproduction of semi-anadromous and river fish in the Volga delta have been kept for the period 1967-1980 i.e. only 4 years [4-6].

Fig2: Left – multiyear variations in mean annual discharge in the Volga’s head of delta near the Verkhneye Lebyazhye gauging station (1) and in the Volga discharge at moving 6-year averaging (2) during the period 1890-2003 [3]. Centre — the layout of gauging stations in the Lower Volga [4]. Right – flood duration (water stage of above 4.3m in blue), the period of water level below the maximum by 0.2m and 0.5m during flood (orange and yellow respectively, red – maximum level)

Since the Volga tandem reservoir system, the fish population has decreased tenfold in the Caspian Sea as the result of a poor anthropogenic simulation of flood (Fig.3). In particular, Fig.3 (centre) shows that there is the tendency for an increase in bream baby fish population when flood duration is rather long. It is therefore concluded that the normative documents on spring flood simulation from GES should be corrected for extension of flood time from 2-3 to 4-6 weeks to the detriment of spawning area, otherwise fish roe and larvae will be dried out [4]. Such a correction of discharge and response of water stage to it in the delta is shown by dotted line in Fig.3 right.
The period from the spawning season to vigorous baby fish appearance should be more or equal to 3 weeks! Fish spawns at different times and therefore, the flood period should be extended for 4-6 weeks.

Fig.3: Left – Commercial fishery in the Astrakhan Region since 1932 till 2004, thousand tons. Centre – the relationship between the number of flood days when water stage does not go below the maximum by more than 0.2m and baby fish amount (billion specimens) in the Volga delta at different volume of runoff (April-June) in 1978-1990 (data on baby fishes from [5], straight line is a linear trend). Right – a scheme of standard march in discharge water from GES during spring flood (in black lines), the response of water stage march in Astrakhan (in green lines). Variations in standard march of the GES discharge water for achieving the optimally feasible march of water stage in the Volga delta in dry years required for fish reproduction (spawning) are marked by black dotted line.

The irregularity of the Volga runoff during the low-water depends for the most part on a daily and weekly runoff control – the power grid loading and flush peak respectively take place in the morning and at the beginning of workweek and the decrease takes place in the evening and at the end of workweek (Fig.4) [3,7-10]. The Volga daily discharge during the low-water is more or equal to 0.5 cubic km and its daily variation by more than 10% that results in an increase in water stage in the Astrakhan gauging station by more than 10cm is a peak flush. Peak „discharges are especially considerable in the evenings when electricity consumption increases and therefore the Volga water stage rises by 1-2m and in one evening in January of 1967 there was observed a raising by more than 4m“ [10].

Fig.4: Right – the recording of water stage in the Astrakhan gauging station. On the lower right – an enlarged segment since 24 May till 7 June 1992. At the centre -water stage match in the Astrakhan gauging station in 1983 (at the top) and in 1999 (at the bottom). Right – spectral density of water level fluctuations over the period January 1992 – December 2003 as per measurements in Enotaevka gauging station [3]

Intensification of Salt Mixing through Peak Flushes and Its Effect on Marine

The salt mixing of river and sea water in the North Caspian Sea is governed by the conditions of runoff wave propagation from Astrakhan to the sea. These conditions vary with water level, flush intensity, aquatic vegetation overgrowing, wind, and wind-effected phenomena. The Volga west arm (Bakhtemir River) waves reach the sea for 1.5-3 days while the east arm waves – for 3-5 days [2, 11, 12]. Because of this, the determination of the relations between sea water salinity and flushes should uses the peculiarities of runoff wave propagation rather than the strict daily shifts of water running from Astrakhan to the sea. The comparison of the variations in sea water salinity and runoff wave height (Fig.5) suggests that there is the tendency for a decrease in water salinity in the sea part of the delta when peak flushes from the GES. The man-made mixing reaches the bottom. In the Eastern Mangyshlak Porog there is observed a different tendency – river runoff water presses sea water to the eastern coast that results in a decreased mixing and increased water salinity. Fig.6 and 6a show a detailed analysis of water salinity variation in point ¹2 whatever the hydrometeorological conditions.

Fig.5: Left upright – extreme daily variations in water stage in Astrakhan, mm (for point 3 and 4 – 1-4 days prior to sea salinity measurement; for point 1 and 2 – 4-7days prior; the points corresponding to maximum daily increments in level are in black, maximum decrease in level – in purple). Across – salinity in ‰. Insert at the top [12].

Intensification of Salt Mixing through Peak Flushes and Its Effect on Marine Bioproductivity

The mixing rate of river and sea water is sometimes such that the near-bottom salinity varies by more than 2 ‰ for under half an hour (Fig.6, point ¹2 from Fig.5). In response of such a man’s impact the river biota attacks the marine biota and saltish water with marine biota goes back in several hours-days. Each biota can’t wait till its own water comes back because water salinity of more than 5-8‰ results in a change in osmotic pressure which is not compatible with life activity of many biota species, especially baby fishes and benthos [1,5,13,14]. For example, the boundary of mass spread of baby Caspian roach is limited by the 10‰ isohaline, bream and pike-perch — by the 7-8‰ isohaline [5]. In accordance with estimations [11, 12] the area the Volga jet flows in the North-West Caspian Sea (stress region) occupies approximately a third of the sea area.

Fig.6: The march of water stage in the Astrakhan gauging station and its variations per day (at the top), of water temperature (centre), and salinity near the bottom (at the bottom) during the period 18 September – 10 November 2004 in point ¹2. A temporal correspondence of runoff wave passing through the Astrakhan gauging station and variations in the marine near-bottom salinity are indicated by red arrows (the diagram of water stages is shifted by 4 days relative to lower diagrams). The inserts show an average wind speed by pressure field, in September and November – calm weather, in October (7-10, 15-18, 22-25) – pressure field alteration, wind, roughness 15,21], the Volga water is mixed near bars. Right – data obtained when light wind is marked by blue, when fresh wind – by orange (the tendency line is given for light wind conditions)

Fig.6a: Extreme variations in sea near-bottom salinity when runoff wave passing across the North Caspian Sea for point ¹2 of Fig.5. Left – with no filtering of storm events; right – with filtering of such events in October 2004 (7-10, 15-18, 22-25) [15, 21]. Under storm conditions (Fig.6b) the Volga water is mixed completely near bars and the salinity in the sea is 9-11%.

Fig.6b: The left radar image [17] shows two wave structures (the upper insert — small runoff wave early the third decade of October is indicated by arrow) in the Central Caspian Sea, 24 October 2003. One short-wave structure comes from the Volga while the other structure with wave length of by order greater than that of the first structure, goes along the Volga delta; this is likely to be a manifestation of pressure waves over the Caspian Sea (the lower insert). The right radar image dated 30 December 2004 [17] shows the wave structures which are evidently caused by a rapid change in pressure field over the sea with the passage of anemo-pressure wave (the bottom insert [15]) which coincided with that of runoff wave across the sea (see the upper insert)

Satellite Images of the Northern Caspian Sea. Typical Event Outside Intensive Man-Made Flushes from GES on 19 September 2004

Fig.7a: Radar image of the North-West Caspian Sea (the last on the left) dated 19.09.2004 [17] does not show a pronounced wave structures during the period of no peak flushes under gentle and moderate wind conditions (water level is given by black heavy line, daily fluctuations of water level in the Astrakhan gauging station since 1 September till 1 October 2004 – by thin line are shown in the second left figure, the wind characteristics are presented in two right figures [15, 21]). A dark strip stretching from the Agrakhan Peninsular seen in the radar image is wind attenuation under semitransparent cloud; this cloud is seen in Fig.7b on the left

Fig.7b: The AVHRR/NOAA images (maps) of the North Caspian Sea; centre – SST map, °Ñ; right – hydrosol albedo, %. Behind the Volga bars and sandbanks at depths of more than 3-5km there are generally observed the monotone changes in SST field; the shallow water temperature is higher or lower than that of the sea depending on the season and local insolation conditions. The hydrosol content in water column (water column albedo) is maximum in Kazakh Karman, in the Volga sandbank and bar region, and in river water filaments (the technique hydrosol albedo and SST calculation is given in [16, 22]).

Fig.8a: Radar image, 21.01.2005 [17], wave trains coming from the Volga arms and channels are encircled, an enlarged segment of the upper wave train is given in insert

Fig.8b: Radar image of marine part of the Bakhtemir Arm with wave train from it, 14.07.2003 [17]. It seems to be the passage of daily runoff wave (peak flushes were not observed – the upper insert from 1 July to 1 August; a weak wind – the lower insert [15])

Satellite Data and Information on the North Caspian Sea when Runoff Wave Enters the Sea

The consequences of runoff wave passage across the Caspian Sea may be seen from the analysis of chlorophyll fields in Fig.10 [23], namely, the increased chlorophyll content in the sea is generally observed in on the beam of the Volga canals. Runoff waves spill out river water passed rapidly through the delta biological filter, over the Volga bars. This results in man-made increased pollution (chlorophyll, hydrosol, biogen, and petroleum hydrocarbon) in the sea and this pollution moves towards the region of future LUKOIL oil derricks.

Fig.10: The upper row — chlorophyll content in the upper water column beyond the time of runoff wave front passing across the sea ±1-4 days. The dates of runoff wave reaching Astrakhan are 25.03.1999, 25.09.1999, 06.04.1998, and 26.04.2000 from left to right [23]. The lower row – difference between the maximum chlorophyll content in the water column 2-3 days after the date in the upper figure and the minimum chlorophyll content).