Caspian Rapid Sea Level Changing Impact on Estuaries Morphodynamic Deformation  

Homayoun Khoshravan , Masoumeh Banihashemi
Caspian Sea Research Center, Water Research Institute, Km 8 Khezerabad, Sari, Mazandaran, Iran
Author    Correspondence author
International Journal of Marine Science, 2013, Vol. 3, No. 32   doi: 10.5376/ijms.2013.03.0032
Received: 05 May, 2013    Accepted: 03 Jun., 2013    Published: 02 Jul., 2013
© 2013 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Khoshravan and Banihashemi, 2013, Caspian Rapid Sea Level Changing Impact on Estuaries Morphodynamic Deformation, International Journal of Marine Science, Vol.3, No.32 253-257 (doi: 10.5376/ijms.2013.03.0032)


In this paper, the evaluation of sedimentary-morphodynamic deformation of main estuaries of rivers in the southern coasts of the Caspian Sea is main target. With selecting, eight main rivers and by sampling of sediments on them in the beach zones, geometry of surrounded beach structure, morphodynamic condition and sedimentary deposition processes were analyzed. with interpretation satellite and aerial images of study area along the period between 1983 till 2004 that correspond to last progression phase of Caspian sea level arise (+ 2.5m), the effect of rapid sea level changing of the Caspian Sea on beach and mouth of rivers have been measured. The results show that there are different type of the estuaries in the study area and the last sea level arise has caused morphdynamic deformation (trait inclination of rivers, inflation of mouth and it’s widen) on the beach zone and the rivers mouth condition. Therefore as conclusion, the rivers of the Caspian Sea southern coasts have different behavior against rapid sea level changing in the coastal zones and they are classified to three statements: erosion, accretion and transition.

Caspian; River; Sediment; Morphodynamic; Fluctuation; Estuary

Morphodynamic structures figures in the estuary area were associated to sedimentary depositional processes and hydrodynamic of sea and hydraulic of river (Lichter and Viely, 2010). The protection and remediation of rivers in the coastal zone against to erosion and destructing events and preventing of environmental disturbances development on there have required enough understanding on natural condition of marine forces (waves, currents, storms) and river discharge amount (Wright and Thom, 1980). So in this research recognition and classification of sedimentary-morphodynamic condition of rivers mouth and its deformation situation against rapid sea level changing is the main problem. Previous studies results show that hydrodynamic and hydraulic effects have special trait in study area (Alahmad, 1996). As the annually regime of prevailing winds is very different. So physical condition of wind-induce wave in the coastal area is complex and different (Alahmad, 1996). This agent caused the energy of the breaking waves would be dissimilar in the different part of the southern coasts of the Caspian Sea (Alahmad, 1996). Therefore wave dominated area has been spread along the West part of Mazandaran province beach and East of Gilan province shore. At the other hand the South-Eastern coasts of the Caspian Sea (Bandar e Torkaman) and the coasts in the West part of Gilan have low energy statements (Alahmad, 1996). Other coasts along the West part of Mazandaran central zone have transition condition of energy level (Alahmad, 1996). Also the statement of hydraulic forces of rivers is similar to hydrodynamic of sea. The rivers of study area were classified to permanent and temporary conditions considering the amount of water and sediment discharge to the Caspian Sea (Khoshravan, 2001). From morphological point of view the southern coasts of the Caspian Sea has been classified to five zones (Khoshravan, 2000). Each of them has special condition related to beach structure geometry and morphodynamic and sedimentary condition (Khoshravan, 2000). as result of the beach response to environmental forces. Therefore the shape of estuary and river mouth completely was associated to surrounded morphological zone. As previous research showed that the Southern coasts of the Caspian Sea has been classified to three hydrodynamic condition (dissipative, reflective and transition) (Khoshravan, 2007). Also past study on Sefidrood River delta shows that rapid sea level changing have direct influence on its evolution along the Quaternary period (Alizadeh, 2007; Jedari, 2005). It was determined that many rivers of study area were connected to the Caspian Sea through marginal lagoon and some of them enter to the sea directly (Alizadeh, 2007). So there are different conditions of estuaries shapes, sedimentary depositions and morphodynamic structures in the study area. So in this paper with emphasis to geometry of beach structure, sediment size distribution and morphodynamic formation we want to compare main rivers of the study area together and then their behavior would be controlled against rapid sea level changing through satellite image interpretation.

1 Material and Method
1.1 Study area
Caspian Sea as the largest surrounded basin in the world is located between Eurasia Bridge and there are five marginal countries along its coastal area. Its watershed basin area is about 400.000 km square and the maximum length of it is 1200 km and with average wide approximately about 365 km. there are many important rivers around the Caspian Sea, that among them Volga is the vital river and it cover 75 percent of water entranced of the Caspian Sea (Khoshravan, 2001). After that, Omba, Solak, Samour, Atrak and Oral are important rivers in the Caspian region. The southern coast of the Caspian Sea as study area was elongated along the North-Alborz Mountain and it has 865 km length. There are more than 100 rivers in this region that they discharge water and sediment to the Caspian Sea (Figure 1).

Figure 1 Study area location map and main rivers of the Caspian sea south coasts

1.2 Methodology

the main rivers of study area have been studied from the amount of discharge of water and sediments to Caspian Sea and then eight rivers were selected in the southern coasts of the Caspian Sea: (Gorganrood, Neka, Larim, Sorkhrood, Nashtarood, Sefidrood, shafarood and Lisar) (Figure 1). They are covering all part of study area from East to West ward. The selection indexes of river depend on hydrological condition of rivers and hydrodynamical and morphological of the beach zones. In the second stage, with field survey monitoring and sediments sampling, all sedimentary–morphodynamic formation of beach zone and estuary of rivers were measured. Samples were collected from River mouth, around the beach and at the back of rivers. Then after laboratory test sediments grain size parameters were calculated with analytical software. So the sedimentary characteristic of rivers mouth were determined and classified by obtained results. Subsequently the estuary shape of main rivers of the Caspian Sea and river mouth deformation have been comparing with use satellite images associated to last Caspian sea level rise during 1983 till 2004. The images of 1983 year belong to the aerial photos with scale 1:10000 and the satellite images are from Landsat (TM), 2004 year were georeferenced with topography map with 1:25000 scale and with use GIS software (Arc- GIS 9-2), all vector data of rivers and estuary were prepared and finally with comparison of them, the estuary deformation along the above mentioned time was reconstructed.

2 Results
2.1 Sediments texture analysis
Comparing results of sediments grain size analysis and sedimentary parameter evaluation (d50, Mean, Skewness, Kurtosis, standard deviation) of all selected river of coastal stations show that sediments textural properties have varied between the mouth of rivers and the adjacent coasts area (Table 1).

Table 1 The sediment grain size mean of sampled points

2.2 Estuary shape classification
It was known that selected river could be classified from sedimentology index point of view. The kind of sediments of study area change from very fine grain sediments (clay to sandy clay) in the Gorganroud River to very coarse gravel (pebble and cobble) in the west of Gilan (Shafaroud and Lisar rivers). As expected the transition modes have been observed with fine to medium or coarse sand in the central of Mazandaran and Gilan coasts (Sorkhroud, Sefidroud, and Nekaroud Rivers). Also the comparing results of sediment size of rivers mouth and surrounded beaches determined that there is much dissimilarity between coastal sediments and estuary. For instance: in the Sefidroud estuary, all sediments in the beach belong to rivers and it could be covered vast area of beach zone. At the other hand shore sediments of the Caspian Sea have covered the rivers mouth in the Nekaroud and Larim Rivers. But there are transition condition near to Sorkhroud and Nashtaroud rivers that sea and rivers sediments cover the coastal zone together.
2.3 Estuary shape classification
On the basis of obtained results of field monitoring and satellite image analysis the rivers mouth of study area have been classified to the kind of barred, swollen, widen, inclination, tighten, deltaic and non deltaic estuaries (Figure 2). The rivers of south eastern of the Caspian Sea in the Gomishan-Badar e Turkmen and in the central part of Gilan coasts (Gorganroud and Sefidroud rivers) have certain developed delta. Instead of there is no delta in the West of Mazandaran and West of Gilan beach zones (Nashtaroud, Lisar and Shafaroud rivers. The traits of Rivers of central of Mazandaran have been inclined near to shore (Nekaroud and Larim Rivers). Also some mouths of rivers of West of Mazandaran and Gilan have been barred with fluvial coarse grain sediments (Nashtaroud, Lisar and shafaroud Rivers). And many of them have been widen in the central part of Mazandaran coasts (Larim Rivers).

Figure 2 the Variety of Rivers mouth shape in the study area

2.4 Rapid sea level fluctuation and estuary deformation
Satellite images periodic comparing results show that the last sea level rose as 2.5 m elevation from 1984 till 2005 could be change the estuary condition and mouth of rivers shape in the study area. As related to steepness of beach and kind of sediments covering in the determined morphological zones, the shape of mouth of rivers has been changed at the different types. For instance territory of Gorganroud and Sefidroud Rivers near to beach zone have been limited by sea level progression. Also the rapid penetration of sea water to rivers has caused the several morphodynamic formation changing (widen and displacement of mouths). And in the other part of study area kind of estuary response is different and wider mouth could be observed on there. For instance in the Nekaroud estuary territory the mouth of river was displaced toward beach about 135 meters and the wide of mouth is increased along the sea level rise (Figure 3). Of course in the high steepness beach zone like Sorkhroud shore, the river territory could not be affected by sea level raised.

Figure 3 The rapid sea level changing impact on rivers mouth deformation in the study area

3 Discussion
Major coastal sediments of the study area were originated from the rivers, among them Sefidroud, Haraz and Gorganroud are very important rivers and have special significance. The Rivers of the Caspian Sea southern coasts were classified to two orders: Meandering and braided Rivers (Khoshravan, 2001). Field survey result determined that braided rivers usually have short trait and their mouth were covering with coarse fluvial sediments in the western part of Mazandaran and Gilan morphological zones. And meandering rivers at the near beach zone have long traits and they discharge fine sediments (sand, silt and clay) to coastal zone in the central region of Gilan and Mazandaran morphological zones. The Iranian Rivers which enter to Caspian Sea have watershed basin with 135,000 km square and annually they charge 40,000,000 tons sediments to the Caspian Sea. Hydrology data evaluation associated to rivers shows that during many recent decades, with human activity developed as dam making caused that the amount of sediments of rivers decreased about 10 to 40 percent (Khoshravan, 2001). Also hydrodynamic of Caspian Sea in the study area has no stable situation seasonally and it varied along the southern coasts of the Caspian Sea (Khoshravan, 2007). So this region of the Caspian sea from hydrodynamic effect to beach zone have been classified to dissipative, reflective and transition beach (Khoshravan, 2007). Also sediments of study area were breakdown to three type regime (coarse gravel, sand and very fine grain of clay) (Khoshravan, 2000). It is interesting that the beach zone sediments were following from nearshore morphodynamic and variety of rivers. As at the high slope shore, usually coarse grain of sediments was deposited and reversely at the low steepness beach, fine sediments have been dominated.
4 Conclusions
As conclusion there is real direct relationship between beach steepness and sediment size distribution. The comparing of sedimentary parameters data of selected stations show different result from natural condition of sediments point of view. And with apply sediments sorting, d50, mean, skewness, kurtosis as indicator the estuaries of the southern coasts of Caspian Sea have been order to:
Well sorted coarse grain sediments (Nashtaroud River)
Bad sorted coarse grain sediments (Shafaroud and Lisar Rivers)
Well sorted fine to medium sand (Sorkhroud, Neka and larim Rivers)
Bad sorted very fine sand and clay sediments (Gorganroud and Sefidroud Rivers).
The hydrodynamic and Hydraulic energy level is different between above classified estuaries. As in Nashtaroud and Sorkhroud waves and currents have been well developed and river effect is low to sediment distribution and here is wave dominated region. At the other hand in the Gorganroud and Sefidroud territory sediments of rivers cover all part of beach zone and there are active deltaic sedimentary deposition. So these areas are called to River dominated region. Hydrodynamic impact is very low degree around them. Of course the Lisar and Shafaroud Rivers are following as same statement. As the field monitoring and satellite image analysis results show that erosion processes associated to sea have caused estuaries shape deformation like: declination, tighten, widen, barred and inflation of the mouth of rivers. And at the other hand in accretion coastal zone with high hydraulic energy, other type of morphodynamic formation like Delta and sand bar have been created (Dan and Janr, 2011). In the transition beach zone the estuary shape could be change differently with common effect of rivers and sea forces. Usually at this place sand spits were originated by double impact of river and sea (Dan and Janr, 2011). Finally on the basis of morphodynamic index, the estuaries of southern coasts of the Caspian Sea have been breakdown to three types as following mentioned:
Erosion estuaries (Nashtaroud River)
Accretion estuary (Gorganroud, Sefidroud, Shafaroud and lisar Rivers)
Transition estuary (Sorkhroud, Larim, Nekaroud Rivers)
Therefore as final conclusion we showed that sediments size distribution and morphodynamic formation is a good indicator for estuary classification in the study area. Also rapid sea level changing of Caspian Sea has a direct influence on rivers mouth deformation and the tendency of changeable events associated to estuary depend on sea and river forces and type of beach zone from geometry of beach structure point of view.
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