1.4.2. Rivers and streams
A. The Southern Caspian Sea Watershed
The southern Caspian Sea watershed is one of the largest
water basins in the country. It extends as a narrow strip from the northeast of Azerbaijan
province to the northeast of Khorasan Province.
The Sefidrood River basin is the only basin that extends
south to the Zagros mountain range. This basin comprises areas whose waters empty into the
Caspian, and contains about 864 large and small rivers and streams. Most of these rivers,
originate in the northern slopes of Alborz mountain range, are short with small watersheds
and are characterized by mountainous, meandering and steep courses, interspersed with
several waterfalls and deep valleys. Their water source during the summer and autumn are
rain and natural springs and during the winter and spring melting snow.
The southern Caspian watershed covers an area of 177,000
km2 (11% of the total national land area) and consists of 7 main basins and 11 sub-basins.
The different provinces’ shares in the Caspian watershed are shown in Table 4 and
Figure ?. The total watershed of the Caspian is estimated at 3.6 million km2.
The annual surface water flow in this watershed has been
calculated at 14,650 million m2 (from statistics over a 24-year period) and is 21% of the
country’s total annual water flow.
Thirteen large rivers, with a basin area of more than 1000
km2, and 24 small rivers with a basin less than 1000 km2 are in this catchment. The
Sefidrood river with an annual average of water volume equal to 5,200 million m3, is the
outstanding source and accounts for 30% of the whole southern Caspian water flow. In Table
3 the specification of the main rivers and their basins are shown.
B. Rivers
The descriptions of the most important rivers along the
Caspian coastline from west to east are as follows:
Gilan Province Rivers
Astara River: Originates from the heights of the Republic of
Azerbaijan, is 30 km long and enters the Caspian through the city of Astara.
Gorganrood River: Originates from Talesh Mountain, enters the
sea through Hashtpar city, is 72 km long with an average annual flow of 217.5 million m3.
Sefidrood River: The largest and most important river in the
Southern Caspian basin with many tributaries is the major spawning ground for many
commercial migratory fish (except salmon). It is 780 km long with a basin of 65,000 sq.
km. After passing many cities and urban areas, it enters the sea at Kiashahr city at an
annual average of 154 m3/sec. Construction of three dams during the past years has
decreased the amount of biogene material in the water. This has also blocked the fish
migration route for spawning upstream, specially sturgeon and white fish. As this river
passes many populated areas, it carries a considerable amount of pollutants into the sea,
particularly urban sewage and agricultural outflows.
Paulrood River: The most important river on the east side of
the province with a basin of 1800 km2, 80 km long and an annual average flow of 400-500
million m3.
Anzali Lagoon rivers: 12 rivers with a capacity of 2 billion
m3 per year enter this lagoon, all through very high dense populated areas (rural, urban
and industrial). They carry a considerable amount of pollutants into the lagoon and then
into the sea. These rivers are considered the most polluted rivers along the southern
Caspian coasts.
Mazandaran Province Rivers
Hazar River: Originates from Lar Mountain and enters the sea
through the city of Amol. This river is the best-nourished river in the eastern side of
the province. Its upstream course runs through a very deep and steep valley, which is
covered by a dense forest and is regarded as one of Iran’s leading tourist attraction
sites. Its length is about 185 km with a basin area of 4,100 km2 and an average water flow
of 1072 million m3 per year. It is frequently given to flooding and has destroyed Amol on
its estuary several times.
Neka River: Originates from Shah-Koh Mountain and enters the
sea through Neka city. It is one of the important and nourishing rivers. Its length is
about 180 km with a basin area of about 3000 km2. It is a permanent river with an annual
average flow of 148.2 million m3.
Tajan River: Babolrood and Sajadrood rivers:
Golestan Province Rivers
Gorgan River: One of the most important rivers the
southeast of the Caspian for agricultural purposes. It runs through the Gorgan Plain and
Voshmgir Dam, which has been constructed for increasing the potential of water resources
in the area. The length of this river is about 350 km with a basin of 12000 km2. It
considered a permanent river. Although the river dries out during the hot season and dry
years, it runs for at least 10 months per annum. The average water flow of this river is
about 447.8 million m3 per year.
Ghareh-su River (Ooghan River): This river is one of
the main branches of the Gorgan river that originates from the Gorgan Plain and flows
mostly through the plain. Its length is 73 km with a basin of about 400 km2 and an annual
average flow of 29.2 million m3. The Ghareh-su River is a very important river from the
fishery point of view and is a spawning ground for migratory fish species, such as
sturgeon and white fish.
C. Water Quality
From the standpoint of water quality, the concentration of
suspended matter in water fluctuates according to the season. Water quality depends
primarily on the following factors: water flow intensity, distance from its origin, type
of bedrock, presence of salts on its course, basin type and finally on the nature of
ground water. As a rule, the more distant from its origin and the slower it flows, the
amount of anions CO3H- and CO3- would be reduced but the amount of Cl- would increase.
Regarding observed measurements done by the Ministry of
Power, the quality of surface waters along the Caspian coast is suitable and there are no
restrictions in using it for different purposes.
In Table 4, the water quality of some major rivers
is presented.
D. Sediment Load
Regarding the water fluctuations of rivers, the amount of
suspended matter changes accordingly, but apart from seasonal changes, the amount of
sediment load increases in wet years and decreases in dry years. Besides suspended
sediment load in the water column, some suspended solids also are carried away on the
riverbed as bottom load. Its amount is estimated about 10% of the suspended matter. In Table
5, the calculated suspended solid load of several important rivers is provided.
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SECTION 5
    
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