ﻋـﻠـﻮم ﻣﺤـﯿـﻄﯽ ﺳﺎل ﭘﻨﺠﻢ، ﺷﻤﺎره دوم، زﻣﺴﺘﺎن 1386 ENVIRONMENTAL SCIENCES Vol.5, No.2 , Winter 2008 65-86 South Caspian River Mouth Configuration Under Human Impact and Sea level Fluctuations 1 ,1,2 2 Vahid Tavakoli , Abdol Hossein Amini , ٭Hamid Alizadeh Ketek Lahijani 1- Iranian National Center for Oceanography 2- Department of Geology, Faculty of Sciences, University of Tehran Abstract Rivers that flow from the Iranian coast to the Caspian Sea encompass 135,000 km2 of that ﻣﺮﻓﻮﻟﻮژي دﻫﺎﻧﻪ رودﺧﺎﻧﻪﻫﺎي ﺟﻨﻮب ﺧﺰر در ﺷﺮاﯾﻂ اﺛﺮ ﻋﻮاﻣﻞ اﻧﺴﺎﻧﯽ و ﻧﻮﺳﺎن ﺗﺮاز آب catchment’s basin and supply 40 million ton sediment to the Caspian coast annually. The ﺣﻤﯿﺪ ﻋﻠﯿﺰاده ﮐﺘﮏ ﻻﻫﯿﺠﺎﻧﯽ ٭1، وﺣﯿﺪ ﺗﻮﮐﻠﯽ1و2، ﻋﺒﺪاﻟﺤﺴﯿﻦ اﻣﯿﻨﯽdynamics of river mouths and deltas are studied 2 using hydrological data of the rivers, air photos, 1- ﻣﺮﮐﺰ ﻣﻠﯽ اﻗﯿﺎﻧﻮس ﺷﻨﺎﺳﯽ اﯾﺮان satellite images and geological and 2- ﮔﺮوه زﻣﯿﻦ ﺷﻨﺎﺳﯽ، داﻧﺸﮑﺪه ﻋﻠﻮم، داﻧﺸﮕﺎه ﺗﻬﺮان geomorphological maps as well as field observations and sediment sampling. Results from ﭼﮑﯿﺪه this study show that the morphology of the river رودﺧﺎﻧﻪﻫﺎﯾﯽ ﮐﻪ از ﺳﺎﺣﻞ اﯾﺮان ﺑﻪ ﺧﺰر ﻣﯽرﯾﺰﻧﺪ ﺑﺎ ﻣﺴﺎﺣﺖ ﺣﺪود ﯾﮑﺼﺪ و mouths and deltas are mainly controlled by marine ﺳﯽ و ﭘﻨﺞ ﻫﺰار ﮐﯿﻠﻮﻣﺘﺮ ﻣﺮﺑﻊ، ﺳﺎﻻﻧﻪ ﺣﺪود ﭼﻬﻞ ﻣﯿﻠﯿﻮن ﺗﻦ رﺳﻮب وارد ware-induced currents and sea level changes) and) ﺧﺰر ﻣﯽﮐﻨﻨﺪ. دﯾﻨﺎﻣﯿﮏ دﻫﺎﻧﻪ رودﺧﺎﻧﻪﻫﺎ و دﻟﺘﺎﻫﺎ ﺑﺎ اﺳﺘﻔﺎده از دادهﻫﺎي fluvial processes. Among these factors, sea level آبﺷﻨﺎﺧﺘﯽ رودﺧﺎﻧﻪ، ﻋﮑﺲﻫﺎي ﻫﻮاﯾﯽ، ﺗﺼﺎوﯾﺮ ﻣﺎﻫﻮارهاي، ﻧﻘﺸﻪﻫﺎي and riparian sediment supply have great variability. Analysis of hydrological data revealed زﻣﯿﻦﺷﻨﺎﺧﺘﯽ و رﯾﺨﺖ ﺷﻨﺎﺧﺘﯽ و ﻫﻤﭽﻨﯿﻦ ﻣﺸﺎﻫﺪات و ﻧﻤﻮﻧﻪﺑﺮداريﻫﺎي that, during the past few decades with increasing ﻣﯿﺪاﻧﯽ ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﻗﺮار ﮔﺮﻓﺖ. ﻧﺘﺎﯾﺞ اﯾﻦ ﻣﻄﺎﻟﻌﺎت ﺣﺎﮐﯽ اﺳﺖ ﮐﻪ رﯾﺨﺖ- human activities, the sediment supply of the rivers - ﺷﻨﺎﺳﯽ دﻫﺎﻧﻪ رودﺧﺎﻧﻪﻫﺎ و دﻟﺘﺎﻫﺎ ﻋﻤﺪﺗﺎً ﺑﻪ وﺳﯿﻠﮥ ﻓﺮاﯾﻨﺪﻫﺎي درﯾﺎﯾﯽ (ﺟﺮﯾﺎن reduced from 10 to 40 %. The Caspian sea level ﻫﺎي ﻧﺎﺷﯽ از ﻣﻮج و ﻧﻮﺳﺎن ﺗﺮاز آب) و رودﺧﺎﻧﻪاي ﮐﻨﺘﺮل ﻣﯽﺷﻮد. در ﺑﯿﻦ has changed over a range of 3 m during اﯾﻦ ﻋﻮاﻣﻞ، ﺗﺮاز آب درﯾﺎ و ﻓﺮآوري رﺳﻮب رودﺧﺎﻧ ﻪاي داراي ﺗﻐﯿﯿﺮات instrumental measurements. The rivers are زﯾﺎدي اﺳﺖ. ﺑﺮرﺳﯽ دادهﻫﺎي آب ﺷﻨﺎﺧﺘﯽ ﻧﺸﺎن داد ﮐﻪ در ﭼﻨﺪ دﻫﮥ اﺧﯿﺮ ﺑﺎ classified into three groups based on the morphology of their mouths and the nature of اﻓﺰاﯾﺶ ﻓﻌﺎﻟﯿﺖﻫﺎي اﻧﺴﺎﻧﯽ، ﻓﺮآوري رﺳﻮب رودﺧﺎﻧﻪاي از 10 ﺗﺎ 40 درﺻﺪ river/sea dynamics: Type 1 is rivers that enter to ﮐﺎﻫﺶ ﯾﺎﻓﺘﻪ اﺳﺖ. ﺗﺮاز آب ﺧﺰر در ﻃﯽ اﻧﺪازهﮔﯿﺮيﻫﺎي دﺳﺘﮕﺎﻫﯽ ﺣﺪود the sea through lagoons and lowlands. They have 3 ﻣﺘﺮ ﻧﻮﺳﺎن داﺷﺖ. ﺑﺮ ﺣﺴﺐ وﯾﮋﮔﯽ رﯾﺨ ﺖﺷﻨﺎﺳﯽ دﻫﺎﻧﻪ رودﺧﺎﻧﻪ و gained an ephemeral nature due to increasing دﯾﻨﺎﻣﯿﮏ ﻣﺤﯿﻂ درﯾﺎﯾﯽ و رودﺧﺎﻧﻪاي، ﻣﯽﺗﻮان دﻫﺎﻧﮥ رودﺧﺎﻧﻪ را ﺑﻪ ﺳﻪ ﮔﺮوه water consumption recently. Type 2 rivers have a ﺗﻘﺴﯿﻢ ﮐﺮد: ﻧﻮع 1: رودﺧﺎﻧﻪﻫﺎﯾﯽ ﮐﻪ از ﻃﺮﯾﻖ ﺳﺮزﻣﯿﻦﻫﺎي ﭘﺴﺖ و ﺗﺎﻻب- normal flow into the Caspian Sea. They are common in steep slope coasts, where they are ﻫﺎي ﺳﺎﺣﻠﯽ وارد درﯾﺎ ﻣﯽﺷﻮﻧﺪ. اﯾﻦ رودﺧﺎﻧ ﻪﻫﺎ ﺑﺎ اﻓﺰاﯾﺶ ﻣﺼﺮف آب، ﺑﻪ rarely affected by human activities and sea level رودﺧﺎﻧ ﻪﻫﺎي ﻓﺼﻠﯽ ﺗﺒﺪﯾﻞ ﺷﺪ هاﻧﺪ. ﻧﻮع 2: ﺷﺎﻣﻞ رودﺧﺎﻧﻪﻫﺎﯾﯽ ﺑﺎ ورودي changes. On moderately sloping coasts, they are ﻣﻌﻤﻮﻟﯽ ﺑﻪ درﯾﺎ اﺳﺖ. اﯾﻦ رودﺧﺎﻧ ﻪﻫﺎ در ﺳﻮاﺣﻞ ﭘﺮﺷﯿﺐ ﮐﻤﺘﺮ ﺗﻮﺳﻂ ﻋﻮاﻣﻞ .slightly affected by long-shore currents of the sea اﻧﺴﺎﻧﯽ و ﺗﺮاز آب ﺗﺄﺛﯿﺮ ﭘﺬﯾﺮﻓﺘﻪاﻧﺪ. در ﺳﻮاﺣﻠﯽ ﺑﺎ ﺷﯿﺐ ﻣﺘﻮﺳﻂ، دﻫﺎﻧ ﻪ اﯾﻦ Some distributaries of the rivers enter into the sea رودﺧﺎﻧ ﻪﻫﺎ ﺗﻮﺳﻂ ﺟﺮﯾﺎن ﻃﻮﻟﯽ ﺳﺎﺣﻠﯽ ﻣﻨﺤﺮف ﺷﺪه اﺳﺖ. در اﯾﻦ ﺣﺎﻟﺖ independently. Some bars and lagoons are ﺑﺮﺧﯽ از ﺷﺎﺧﻪﻫﺎي ﻓﺮﻋﯽ آنﻫﺎ ﺑﻪ ﻃﻮر ﻣﺴﺘﻘﻞ وارد درﯾﺎ ﻣﯽﺷﻮد. ﺑﺎرﻫﺎي developed in the vicinity of the river's mouth, most commonly since the last sea level rise. Type 3 رﺳﻮﺑﯽ و ﺗﺎﻻبﻫﺎي ﺟﺎﻧﺒﯽ در ﻃﯽ اﻓﺰاﯾﺶ ﺗﺮاز آب در دﻫﻪﻫﺎي اﺧﯿﺮ در represents the great rivers with a significant دﻫﺎﻧﻪ اﯾﻦ رودﺧﺎﻧﻪﻫﺎ در ﺳﻮاﺣﻞ ﺑﺎ ﺷﯿﺐ ﻣﺘﻮﺳﻂ ﺗﻮﺳﻌﻪ ﯾﺎﻓﺘﻪاﻧﺪ. ﻧﻮع sediment supply (Sefidrud River in the West and :3 رودﺧﺎﻧﻪﻫﺎي ﺑﺰرگ ﺑﺎ ﻓﺮآوري رﺳﻮب زﯾﺎد (ﺳﻔﯿﺪ رود در ﺑﺎﺧﺘﺮ و Gorganrud River in the East), producing deltas and ﮔﺮﮔﺎﻧﺮود در ﺧﺎور) ﮐﻪ اﯾﺠﺎد دﻟﺘﺎ و ﺑﺎرﻫﺎي رﺳﻮﺑﯽ دﻫﺎﻧﻪاي ﮐﺮد هاﻧﺪ. اﯾﻦ mouth bars. They have high sediment discharge رودﺧﺎﻧ ﻪﻫﺎ دراراي آورد رﺳﻮﺑﯽ ﻗﺎﺑﻞ ﺗﻮﺟﻪ ﺑﻪ درﯾﺎ ﻫﺴﺘﻨﺪ و ﻫﻢ از ﻓﻌﺎﻟﯿﺖ- into the sea and are more greatly affected both by human activities and sea level changes. ﻫﺎي اﻧﺴﺎﻧﯽ و ﻫﻢ از ﻧﻮﺳﺎن ﺗﺮاز آب ﺗﺄﺛﯿﺮ ﭘﺬﯾﺮﻓﺘﻪاﻧﺪ. Keywords: river delta, south Caspian sea, sea level ﮐﻠﯿﺪوا ژهﻫﺎ: دﻟﺘﺎي رودﺧﺎﻧﻪاي، ﺧﺰر ﺟﻨﻮﺑﯽ، ﻧﻮﺳﺎن ﺗﺮاز آب، ﻃﺒﻘﻪﺑﻨﺪي دﻟﺘﺎﻫﺎ. .change, delta classification * Corresponding author. E-mail Address: [email protected] ﻋـﻠـﻮم ﻣﺤـﯿـﻄﯽ ﺳﺎل ﭘﻨﺠﻢ، ﺷﻤﺎره دوم، زﻣﺴﺘﺎن 1386 ENVIRONMENTAL SCIENCES Vol.5, No.2 , Winter 2008 65 ¡ ¡ Introduction run off compared to the time when the river flow was The morphology of transitional depositional systems not regulated (Zonn, 1996). It accounts for a one meter (especially deltas) depends on both basinal and sea level fall since the 1950s. Dam construction, terrestrial factors, such as sea level changes, wave and irrigation, sand and gravel excavation from rivers have wave induced currents, tidal ranges, and sediment reduced river loads to 40 %. This culminates in river supply (Coleman and Wright, 1975; Elliott, 1986; mouth erosion and retreat of seaward edge of deltas. Galloway, 1975). River mouths as a place of sediment Moreover, these changes have caused significant input to the basin play a significant role as sink basins ecological impacts in the river mouths and the Caspian and produce a special coastal morphology. These Sea. A sharp decrease in the fish stock of the Caspian processes involve a variety of interaction between Sea during the past few decades can be attributed to a riverine and basinal waters (Wright, 1977). They reduction in the fish migration into the river mouth in contribute to delta formation if the sediment supply to spawning period (Saiko, 1996) the receiving basin is sufficiently large. Delta plains, All 61 rivers that flow from Iranian coast to the as the gift of rivers to the basin are important features Caspian Sea are subject to intensive human activities. in coastal region (Saito, 2005) and play important role A densely populated coastal area (7 million 2 in human civilization (Wright, 1978). settlements in 15000 Km ) and distribution of high Morphology of river mouths that enter the Caspian water consuming crops such as rice and cotton makes Sea as a closed basin with a maximum 12 cm tidal the Iranian coast of the Caspian Sea different from range (Terziev, 1992) are mainly affected by fluvial other parts of the sea (Lahijani, 2004). The human and basinal processes. Wave and wave-induced regulation of the rivers has affected not only the total currents, rapid sea level changes and fluvial sediment mass of the water and sediment discharge but also its supply are controlling factors that modify the Caspian distribution throughout the year (Voropaev et al., river mouth configuration (Azimov et al., 1986; 1998b). Under the natural conditions of the past, Mikhailov, 1997; Voropaev et al., 1998b). The north spring floods had a slow start and a slow cessation. By Caspian deltas are developed on a gently sloping near- contrast, floods occurring nowadays are distributed shore and continental shelf, experiencing a low wave over the spring and autumn months. All changes in energy condition whereas the western and southern forcing factors to the river months, both human- Caspian deltas experience high wave energy on the induced and natural factors, contribute to the change steeply sloping continental shelf (Azimov et al., 1986; and adjustment of the river entrance to the Caspian Mehdiev, 1966; Voropaev et al., 1998a). The Caspian Sea. Iran’s southern Caspian coast receives 61 rivers Sea deltas are exposed to a rapid sea level fluctuation of which only two of them (the Sefidrud and in a range 100 times greater than that which occurs in Gorganrud Rivers) have built deltas in the Caspian the oceans (Kroonenberg et al., 2000). The drainage Sea. The small rivers entering from the southern basin of the Caspian Sea covers an area of 3.5 million Caspian coast make simple river mouths that are Km2 (Mikhailov, 1997). In recent decades, human sensitive to forced factors. activities in the drainage basin of the Caspian Sea have In spite of a huge literature on the northern and changed the natural fluvial regime (Krasnozhon et al., western Caspian coast deltas, the southern Caspian 1999; Lahijani and Krasnozhon, 1999; Mikhailov, rivers and deltas are poorly understood. This paper 1997). The most prominent human impacts were aims at introducing southern Caspian river mouth reducing water and sediment discharge at a rate of 10 morphology based on natural processes and the impact % and 40 %, respectively. The Caspian Sea now of human activities. The major attention will be paid to suffers from an annual shortfall of around 40 Km3 of ﻋـﻠـﻮم ﻣﺤـﯿـﻄﯽ ﺳﺎل ﭘﻨﺠﻢ، ﺷﻤﺎره دوم، زﻣﺴﺘﺎن 1386 ENVIRONMENTAL SCIENCES Vol.5, No.2 , Winter 2008 66 ¡ ¡ the Sefidrud River delta, since it is the greatest river in age from the Precambrian to the Quaternary eras the south Caspian coast. (Nowroozi, 1971; Stocklin, 1974, 1977; Sussli, 1976). Around 130 rivers flow into the Caspian Sea The Caspian Sea and its Catchment Area through the northern, southern and western coasts The Caspian Sea is a semi-eclipse basin oriented in a (Terziev, 1992). The eastern coast is characterizes by N-S direction with a length of about 1,200 km and the lack of fluvial discharge. The northern Caspian width of about 400 km. The sea surface (at a 28 m rivers drain vast areas of the Russian plain and height) is around 360,000 km2 and the water volume encompass 90% of the freshwater discharge into the exceeds 78,000 km3 (Nikolaeva, 1971).