Hydrographically, the Republic of Azerbaijan belongs to the Caspian Sea basin. The water systems of Azerbaijan (rivers, lakes) were formed over a long geological timeframe and changed significantly throughout that period. This is particularly evidenced by remnants of ancient rivers found throughout the country. The country's water systems are continually changing under the influence of natural forces and human introduced industrial activities. Artificial rivers (canals) and ponds are a part of Azerbaijan's water systems.
Rivers form the principal part of the water systems of Azerbaijan. There are 8,359 rivers of various lengths within Azerbaijan. Of them 8,188 rivers are less than 25 kilometers in length. Only 24 rivers are over 100 kilometers long. Kur, Araz, Qanix (in Alazan), Qabirri (Iori), Samur, Terter, Turyan, Agstafa, Hekeri, Vilesh and others are the largest rivers that flow through the country.
Azerbaijan river systems are changing and evolving under the influence of various physiographic factors: climate, landscape, geological structure, soil and vegetation. The density of the river network increases, then gradually decreases later with higher altitudes. Except for the Talysh region (1.6-2.2 km/sq.km), the river system density is the highest (1-2km/sq. km) at 1,000-2,500 kilometers, while in the area of the Talysh mountains it peaks at 1.6-2.2 km/sq.km at 500-1,000 km. The average density of the river system of Azerbaijan is 0.39 km/sq.km. The density is even lower than 0.05 km/sq.km in the plains.
The country's rivers are divided into three groups:
The Kur basin rivers (Qanix, Qabirri, Turyan, Agstafa, Shekir, Terter, Khachin, etc.);
The Araz basin rivers (Arpachay, Nakhchivan, Okhchu, Hekeri, Kondelenchay, etc.);
3) Rivers, flowing directly into the Caspian Sea (Samur, Gudyal, Velvele, Vilesh, Lenkeran, etc.).
These three groups differ from each other for the volume of underwater supply to their streams. Perennial rivers are fed by a constantly flowing baseflow (groundwater). Seasonal rivers are fed by an elevated water table during the rainy period, while episodic rivers are not at all dependent on baseflow.
Like in all other countries, rivers have different feeding sources in Azerbaijan. Most rivers are fed by snow, rainfalls and ground waters. Snow is the predominant feeding source for the rivers of the Major Caucasus, while ground waters contribute the most to water supply of rivers in the Minor Caucasus. The Kur and Araz rivers pass Azerbaijan in their lower and middle courses.
The Kur river is the largest river of Azerbaijan. It stretches for 1,515 kilometers and covers an area of 188 thousand sq. km. The Kur originates from the Hel River in Turkey, passes through Azerbaijan and flows into the Caspian Sea in south-eastern part of the country. The Araz River covers an area of 86 thousand sq. km until its junction with the Kur River. It originates from the Bingol mountains in Turkey at the altitude of 3300 meters. On the whole, the Araz River forms Azerbaijan's border with Turkey and Iran. It passes through Azerbaijan in its lower 80 kilometers and joins the Kur River near Sabirabad. These two rivers belong to the group of rivers, flowing at full under the influence of snow and rainfalls in spring and rainfalls in autumn. The Kur River basin area (86,000 sq. km) up to the junction with the Araz River is smaller than the Araz water basin (101,937 sq.km). The river is still called Kur on the junction because the water level of the Kur is twice as high as that of the Araz River.
Weather produces the greatest impact on the river flow in Azerbaijan. Intensive rise in temperature causes melting of snow at heights of over 1500. The melting of snow further intensifies after heavy rainfalls of April and May. Snow melts more intensively in the high altitudes (over 2500-3000 meters) from early April through May until June. The melting process influences river flow even in summer time. Thus, melted snow water, absorbed by soil, emerges on the surface and raises water level in rivers. Low river basins (except for those of the Talysh region) are less influenced by the precipitation in spring and summer periods. Winter and autumn rainfalls account for the most part of precipitations in the Talysh region. Rivers are less full of water in summer in Azerbaijan. Heavy rainfalls that may from time to time occur in July and August, lead to floods, causing agricultural damages. Severe floods have been registered in the rivers of southwestern slopes of Major Caucasus Zengezur part. Rivers of the Major and Minor Caucasus mainly flow in hot seasons, while rivers of the Talysh regions flow in colder seasons of year. Rivers, flowing in hot seasons account for most part of all rivers (60-80%).
Such seasonal flows are difficult for industrial use. On the whole, rivers of the Azerbaijan Republic are divided into two groups, according to their water regime: 1) rivers of full-flowing regime; 2) rivers of flood regime. Flood rivers are the Lenkoran rivers and episodic rivers of Gobustan. Other rivers are included into the first group of rivers.
Complex topography and other natural factors cause a non-standard flow across the country. The flow increases with altitudes and reaches its top at a certain height (2800, on the north-eastern slope of the Major Caucasus, 2000-2200-on its southern slope and 2200-2400 on the Minor Caucasus). The flow starts to decline from above the indicated height. Due to the orographic specifications of the Talysh mountains, the flow is inconsistent with the average height. It decreases with the increase of altitude in the Talysh mountains, while in Peshteser and Burovar mountains it rises with the altitude.
The full-flowing rivers of the Azerbaijan Republic mainly flow on the southern slope of the Minor Caucasus. The average flow of such rivers exceeds 45 l-cm. The flow falls to 5 l-cm till the Alazan-Ayrichay lowland. The flow module of rivers of the north-eastern slope of the Major Caucasus 18 l-cm. The increase of flow with the increase of altitude is relatively uniform in this part of the Major Caucasus. The intensive increase in the module of flow is registered on the area between the Yah mountain chains and the Major Caucasus mountains. (upper Qusar, Qudyal and other rivers.). The Average annual module of flow is from swings hesitates from 10 to 20 l-cm.
The flow of rivers, originating in the slopes of the Yah mountains, differs from that of the rivers, flowing from the Major Caucasus. The flow increases intensively and reaches from 6 to 18 l-cm at a height of 1000-2000 meters, due to high level of precipitation. The flow gradually decreases till the Caspian Sea shore down to 0.5 l-cm. the flow decreases beginning from the north-west of till south east of the seaside lowland and reaches zero level on the Apsheron peninsula. Compared with the Major Caucasus, the flow in the Minor Caucasus is more complicated, due to its orographic complexity and differing location of mountain chains. The highest flow has been registered in the rivers flowing from the slopes of Gamish and Qapidjic mountains (over 28 l-cm).
In the Karabakh plateau precipitation is absorbed by soil rocks, thus turning the region into the arid area, while in some places it bursts onto the surface thus increasing the water level in the rivers. That is typical of the upper Terter, Hekeri and other regions as under water provides 70-80% of water to them. The flow fluctuates from 0.8 to 22 l-cm in south east of the Minor Caucasus (rivers, originating in the Caucasus mountains) and from 0.5 to 10 l-cm in the Nakhchivan Autonomous Republic. The flow gradually decreases to the level even lower than 0.5 l-cm on the plains on the side of Araz. In the Talish region the flow increases in the direction from the north to south and from the west to east. The flow reaches its peak (over 25 l-cm ) in Tengerud and Astara river basins in the central part of the region, while it reaches its minimum north of the Vilesh river, as well as in the Lenkeran and Vilesh rivers. Gobustan, Nakhchevan and Kur-Araz plains account for the lesser part of water system in Azerbaijan.
Rivers of Azerbaijan carry large quantity of sediment, the result of erosion in the river basins. The rivers in Azerbaijan are the most polluted rivers in the world. Their average annual pollution rate changes from 0.07 to 9 kg-1 cubic mete per region. It reaches its top on the north slope of Major Caucasus and minimum-on the Karabakh plateau. The surface erosion is intensive in the north slope of the Major Caucasus(100-6800 t/sq/km) , and it becomes weaker on the Karabakh plateau (5-10 t/sq.km). The surface erosion in the rivers of the Major Caucasus (0.53 mm) is by 13 higher from that of the Minor Caucasus (0.03 mm per year) and Talish mountains (0.04 mm per year).
3-2- Hydrological system and its importance
The hydrological system of the Azerbaijan Republic contains 10.3 billion cubic meters of water reserves. These water reserves together with those, entering Azerbaijan from neighbor countries (20.6 billion cubic meters) make up 30.9 billion cubic meters. Each square meter of the country receives 90 thousand cubic meters of reserves, while the annual per capita volume of water reserves total 1270 cubic meters. The basin of the river Kur accounts from most part of the water reserves. The nonunifomal distribution of water reserves across the region and around the year hammers the utilization of these reserves and as a result of that the reserves are not able to meet constantly growing demands for fresh water. The situation requires the regulation of water flow. 60 water reservoirs of the country with the capacity of over 1 million cubic meters account for 21 billion cubic meters of water reserves. Most part of these reserves is used in different spheres (irrigation, water supply, industry, fishery, etc). The establishment of water reservoirs of the Middle Kur plays the important role to meeting demands for water. Currently, serious measures are undertaken to preserve pure water reserves and to prevent their polluting with communal and industrial wastes.
The Canals of the Azerbaijan Republic are the main source of irrigation. The canals used for the said purpose extend to 47058.8 kilometers., with canals, used by several farms, accounting for 8580.3 kilometers and those, used only by one farm-for 38478.5 kilometers. The amount of 11 billion cubic meters of water is used in irrigation each year. Irrigated area of Azerbaijan totals 1.4 million hectares.
Azerbaijan has a total of nearly 250 lakes. Most of them are small, while Hadjigabul, Sarysu, Masazyr, Djandargol and others are relatively large. The lakes of the middle and high mountain areas (Goygol and Maralgol of the Kurekchay Basin, Major and Minor Alagoller of the Shamkir River Basin) are extremely aesthetically pleasing. The lakes of Azerbaijan have erosion-glacial, erosion-river, tectonic and abrasive origins. There is a number of standing and salt relict lakes in the Absheron peninsula. In the summer, most of the lakes dry up and become saline. Mountain lakes are used for the purposes of cattle watering, irrigation, fishing (Hadjikabul, Sarysu, Aggol and others), while the salt water lakes of the Absheron peninsula are used for the production of chemical agents as well as for medical treatment. The lakes of the upland stream of rivers: the Bababat group of lakes, Ganlygol (the Nakhchivan River Basin), Goygol (the Shemkir River Basin) and others have turned into water reservoirs. They supply additional volumes of water to rivers in the summertime.
Over 60 water reservoirs have been constructed in order to regulate the river flow in Azerbaijan. The formation of these reservoirs is one of the measures that has been undertaken in order to ration the utilization of water and energy resources. The largest water reservoirs (Mingechevr, Shemkir, Araz and Serseng Reservoirs) are designed to be utilized for various purposes, while most other ponds are used exclusively for irrigation.
Azerbaijan has several glaciers within its territory. They mainly span the Bazarduzu (with an area of 3.62 sq.km.), Bazaryurd (1 sq.km), Tufan (0.51 sq.km) and Shahdag (1.08 sq.km) peaks of the Major Caucasus Mountains. One can also come across other areas of eternal ice that can be found at a height of 4,000 meters above sea level.
3-6- The Caspian Sea
The Caspian Sea, largest enclosed water basin in the world is of great importance for Azerbaijani people. It has a unique physical and geographical properties.It should be noted that the flora and fauna of the Caspian Sea are rich in endemic species. For example, 90% of the total reserves of sturgeon, differing from other fishes by its antiquity, are found in this sea.
The specific geographical landscape created favorable recreational conditions. The sea stretches along a meridian in shape of Latin letter "S" and it locates between latitude 47'17" north and longitude 36'33"east.
The sea across the meridian stretches to nearly 1200 km, its average breadth is 310 the maximal and minimal breadth is 435 and 195 accordingly. As the level of the Caspian Sea changes periodically, the volume of water and its boundaries are also changeable. At present the level of the sea is 26.75 meters below sea level. At this level the area of the sea is 392600 km2 and the volume of water is 78648 km3. This volume makes up 44% of the total water reserves of all lakes in the world. Its maximum depth is 1025 meters and due to that the sea rivals the Black Sea, Baltic Sea and Yellow Sea and it is even deeper that the Adriatic Sea, Aegean Sea, Tiren Sea and Sulu Sea.
Caspian Azeri Sector occupies central and southern parts of the Sea. Caspian Sea water differs from that of the world ocean by its salinity. The salinity totals 5-6 ppm in the north and 12.6-13.5 ppm in south. 170 out of 300 mud volcanoes in Azerbaijan are located in the Caspian Azeri sector. The number of volcanoes is higher in the South Caspian Sea.
The uniqueness and color of natural conditions promoted the preservation of a number of rare flora and fauna species in the Caspian Sea up to present days.
The Caspian Azeri sector accounts for 171 species of phytoplankton, 40 species of animal plankton, 258 species of fitdentos, 91 species of macrozoodentos and 80 species and subspecies of fish belonging to 14 families. Carp-like fishes are the most numerous species-42 species, they are followed by gudgeons-31, herring-17, salmon fishes-2, sturgeon-5 species. The fish fauna of the Caspian Sea comprises 4 genuses, 31 species and 45 subspecies of endemic fishes. Most endemic fishes are registered in central part of the Caspian Sea.
Approximately 40 species and subspecies of fish play important role in fishing. Flock accounts for the biggest part of the total fish fauna (80%) the remainder part comprises herring, grey mullet, friar, argentine, and gudgeon.
The Red Book of the Azerbaijan Republic includes the following species of rare and endangered species: stone-eel, sig, Southern Caspian white-eye, chekhon, and sea pike-perch. In the last few years, the number of all kinds of sturgeon (beluga, spine, and long-nosed sturgeon), Caspian salmon, white salmon, khramulya, shamai fish, shibrit, garasol, is decreasing rapidly and these fishes are on the verge of extinction. The seal is the only mammal found in the Caspian Sea. It is the smallest kind of all existing seals. The number of Caspian seals decreased from 1.5 million in early 20th century down to 360-400 thousand in 1980th. The Caspian seal was included into the Red Book in 1993.
302 species of birds have been registered on the Caspian Sea and its coastal regions: these include 37 species of water birds, 109 species of birds populating areas around water basins and 156 terraneous birds.