1122-3957-1-SM

Comments

Transcription

1122-3957-1-SM
1
Erosional Impact on Caspian Sea Coasts Stability Capacity
2
Homayoun Khoshravan
3
1
Head of coastal management group, Caspian Sea national research center, water research institute, Iran
4
5
Abstract:
6
Stability capacity determination of beach against marine erosion forces in the southern coasts of
7
the Caspian Sea (Babolsar to Noor) is the main target in this paper. By dividing study areas to 14
8
zones, shoreline displacement rate, land covering deformation and sand dune erosion
9
vulnerability tendency have been measured with remote sensing and the geographical
10
information system. In field monitoring, the geometric structure of the beach was mapped and 42
11
sediment samples have been obtained from the beach zone (Berm, shoreline, 0.5 meter depth).
12
Then the beach stability capacity levels that due to several criterions such as: (sediment texture,
13
geometry structure, sand dune accumulation, and land use development and land cover changes)
14
have been calculated by GIS in universal ranking system model (URSM). Results showed that
15
the highest stability capacity rates belong to Talar beach (zone 1) and Arabkheil beach (zone 2)
16
and the eastern part of Mahmoodabad beach (zone 9). By contrast, Mahmoodabad (zone 10) and
17
Noor (zone 14) were the most unstable regions against sea-levels and hydrodynamic forces.
18
19
Keywords: Caspian Sea; Stability capacity; Erosion; Beach; Morphodynamic
20
21
1- Introduction:
22
Nowadays stabilizing beach conditions against marine erosion forces is the first priority in
23
coastal management planning and coastal engineering function (Horikawa, K 1988). Usually
24
erosion vulnerability degree assessment of coastal zones is done by damage potential evaluation
25
and stability capacity calculation (Horikawa, K 1988). The hazardous conditions associated with
26
the rise of the Caspian Sea levels (between 1975 and 1996) had caused several problems in the
27
surrounded coastal zone and its damage impact has been observed as erosional and destructive
1
28
processes around the beach (Khoshravan, H 2011). Previous results show that the degree of
29
damage correlates with the natural stability capacity of the coastal zone (Khoshravan, H 2007).
30
For instance beaches with natural land coverings such as regions in pristine condition and
31
insulated beach structure have been less damaged (Khoshravan, H 2011).
32
rate of stability capacity of beach zones from the eastern part of Babolsar to Noor have been
33
evaluated and proven to be highly susceptible against marine erosion hazards. Previously the
34
southern Coasts of the Caspian Sea have been classified into five morphological zones
35
(Khoshravan, H 2000) and its morphodynamic classification could be described as having
36
sedimentary erosion and moderate condition (Khoshravan, H 2011). The most unstable beaches
37
are located in the western part of Mazandaran and central Gilan (Khoshravan, H 2011). And
38
eastern part of Miankaleh spit is proven to have the highest vulnerability to sea level rise hazards
39
(Khoshravan, H. Rouhanizadeh, S. 2011). However, high slope beaches in western Gilan and
40
Mazandaran have less vulnerability to sea level changing (Khoshravan, H 2007). High damage
41
potential near Babolsar-Noor is associated with its municipal urban and agriculture lands and
42
industrial unit abundance. Common effects of natural forces and man induced function resulted
43
in a fluctuation of erosion vulnerability hazard rates in this area. The real aim of recent
44
researches has been to control and accurately evaluate the stability capacity degree of beach
45
zones.
In this research, the
46
47
2- Study area:
48
The study area was located in the southern coasts of the Caspian Sea in the Mazandaran central
49
morphological zone (Khoshravan, H 2000) and it was elongated from Babolsar to Noor with 70
50
kilometer length (Fig 1). This part of the Caspian Sea contains a variety of morphological
51
shapes. For instance in perpendicular direction of the eastern beaches, we could observe sand
52
dunes and relatively wide berms and low shore steepness and a gradually change with a decrease
53
of berm width and increase of shore slopes by going westwards. Suitable geographical condition
54
in parts of the study area has caused those coastal constructions to develop urban centers and
55
ports among which Babolsar and Feridounkenar harbors are the most important traditional and
56
fishery locations in this region. There are several cities, tourism villages and small urban centers
2
57
along the study area which put up damage during the last Caspian Sea level rise (1978- 1996).
58
59
3- Materials and Methods:
60
Satellite images from 2004 and aerial photos related to 1983 were georeferenced by using a
61
remote sensing software (Erdas imagine) and coastal structures information layers (shoreline
62
location, berm width, sand dune accumulation, land use development, sedimentary environment
63
and coastal constructions) have been evaluated in separated fourteen zones in 5*5 Km dimension
64
with the help of the ArcGIS 10 software (Fig. 1). Then with the use of spatial analysis methods,
65
different layers were processed during the above mentioned period and shoreline displacement
66
range and land covering changeability condition were determined. After that, the beaches
67
geometry condition was mapped and important indexes such as back shore steepness, shore face
68
slope, width and elevation of berm, and shoreline strike were measured along the 14 stations.
69
Then 42 sediment samples have been taken from berm zone (from a depth of 0.5 m relative to
70
the shoreline surface) and their textural and compositional condition were studied in laboratory
71
tests. After that mean of sediments grain size, d50, skewness, kurtosis, standard deviation and
72
dry density have been calculated in analytical software. So different information layers of
73
sediments, natural protection structures, land use and beach structure geometry was produced
74
with the transmission, storage, and processing of all obtained data in the geographical
75
information system. Then with synthesis URSM model (Khoshravan, H 2007) on each
76
information layers in GIS, the main results of this research have been obtained. In the universal
77
ranking system model (URSM) each category of main indexes due to their significance degree
78
has been weighted (table 1) and with use of the Fuzzy mathematical theory, they were compared
79
to each other and quantity degree of stability capacity of beach zones associated to the above
80
mentioned information layers were calculated by adding the total number of each zone.
81
Ultimately with the compilation all obtained stability numbers for all information layers in GIS,
82
the overall rate of stability capacity has been determined in all 14 zones of the study area. Dry
83
density, mean, and sorting for sedimentary index stability capacity determination could be named
84
among the subcategories used. Also for the determination of the stability capacity of the beach
85
geometry structure index, important sub indexes such as: slope and height and width of berm
3
86
have been used in URSM. Frequency and presence of sand dunes and river sediment loads
87
were other sub categories which have been studied in the natural coastal protection stability
88
layer. Also land covering deformation and alteration and shoreline displacement associated to
89
sea level fluctuations and human activities were important sub categories which were used in
90
URSM. Finally by using popularization and incorporation sum in all indexes of each zone, the
91
overall stability capacity of the study area was determined.
92
93
4- Results:
94
4- 1- Shoreline displacement rate and beach deformation:
95
Obtained result from satellite images and aerial photos comparing during two periods (1983 and
96
2004) shows that shoreline displacement rates in the several zones of the study area are different.
97
The most significant relocation has been observed in (zone 7) and (zone 1) with 119 – 116 m
98
displacement (table 1). The lowest displacement has been measured in (zone 6) and (zone 9) with
99
33- 49 m changing (table 1). The vulnerability tendency of coastal regions submerged increased
100
in (zone 7) with 637058 square meters and also in (zone 1) with 598814 square meters and it
101
predominately decreased in (zone 5) with 171235 square meters (table 2). Also it was determined
102
that pristine beaches with natural conditions were located in the eastern and central part of the
103
study area (zone 1, 2, 6, 7, 8 and 9) (table 2). Evident municipal urban growth near west of
104
Babolsar (zone 4, 5) and west of Mahmoodabad (zone 10, 11, 12, 13 and 14) can be noted (table
105
2). Agriculture lands were dominant in (zone 2, 6, 7 and 8) (table 2). The most abundant of sand
106
dunes have been observed in the (zone 1 and 2) with 1142888 and 982596 square meters (table
107
1) which are absent in other coastal region such as (zone 5, 6, 10, 12, 13 and 14).
108
The results of the ranking model of the beach deformation stability capacity indicated destructive
109
condition associated with land use development and land covering alteration in (zone 5 and 14)
110
and many coastal regions such as (zone 3, 4, 10, 11 and 12) are also in unstable conditions (Fig
111
2). The Stability condition of the beaches was relatively good in (zone 7, 8 and 9), (Fig 2). The
112
results of the ranking model of natural protection structure stability showed that the rate of
113
constancy of beach zones associated to sand dune abundance and river sediment regime near the
114
sea and the presence of marginal lagoons as defense structures to hydrodynamic impact
4
115
increased in (zone 1, 2 and 7) and other beach zones such as: (zone 10, 11, 12, 13 and 14) and
116
these are in unstable condition due to natural protection structure (Fig 3).
117
118
4-2- Beach structure geometry and natural sediments condition:
119
Obtained results from beach profiling showed that the maximum width of berm is seen in (zone
120
5) with 82 m width and the minimum expanse exists in (zone 12) with 15 m width (table 3).
121
There are no certain berms in (zone 4 and 10), (table 3). The uttermost berm height was
122
monitored in (zone 9) with 3.5 m height and the lowest berm height has been found in (zone 12)
123
with 1 m height (table 3). The maximum slope of berm has been record in (zone 9) with 0.11
124
degree and slightest steepness was detected in (zone 5) with 0.02 degree (table 3). The rate of
125
beach structure geometry stability predominately decreased in (zone 13, 10 and 4) and the
126
maximum endurance has been record in (zone 8 and 9), (Fig 4). The beach structure's constant
127
condition was relatively good in (zone 8, 7, 6 and 5) and other zone had moderate situations (Fig
128
4). Sedimentology records indicated that the grains mean sizes varied in those monitoring zones.
129
The finest particles with fine sand composition covered the eastern part of the study area (zone 2)
130
with 0.18 mm size and more coarser sediments have been found in (zone 11) with 1.8 mm size
131
(table 3). The maximum density of sediments has been determined in (zone 4) with 3.46 and the
132
lowest density of particles belongs to (zone 2) with 2.55 (table 3). The main results of the
133
sedimentary stability capacity ranking model showed that (zone 11 and 4) have the most stability
134
against marine erosion forces and coastal regions such as (zone 2, 3, 14, 13, 12, 5, 1 and 9) have
135
the lowest stability (Fig 5). Others areas are known to have moderate stability.
136
137
138
139
4-3- Overall beach zones stability capacity:
140
The overall results of the ranking model of stability capacity of beach zones that contains 4
141
information layers (sediments, beach structure geometry, beach deformation and beach
5
142
protection structures) showed that the most stable beach area is located in (zone 1, 2 and 9) and
143
slightly less constancy has been seen in (zone 14 and 10). Other beach zones are shown to have
144
low endurance against hydrodynamic impact (Fig 6).
145
146
5- Discussion:
147
The last phase of the Caspian Sea’s rapid sea level change from 1978 till 1996 with 2.5 meter
148
rise had caused coastal region destruction and its damage impact was of high grade. Tendency of
149
erosion varied in surrounded area and it depended on coastal structures and human activity
150
development (Khoshravan, H 2011). Therefore beaches of the southern coasts of the Caspian Sea
151
near Mahmoodabad – Ramsar sustained some damage and hazard risk levels in these regions
152
were of high grade. However other areas like the western parts of the Gilan province and eastern
153
regions of Mazandaran have been less damaged (Khoshravan, H 2011). This process is
154
correlated to beach stability capacity and its susceptibility to erosion phenomena and important
155
criterions such as: beach structures geometry, sediment size and composition, sand dune
156
abundance, land covering alterations and land use development which contributed to sea erosion
157
hazards (Khoshravan, H 2011 and Hatfield, R.G. and Cioppa, M.T. 2010). As the above
158
mentioned results showed, physical condition of the beach structure geometry is very important
159
for the stability capacity of coastal zones. This caused some beaches with high height and low
160
length of berm in the western part of study area to have lower susceptibility against marine
161
erosion impact. And other areas with low height of berm and wide berm are considered
162
susceptible zone. Therefore due to this criterion, the study area was classified into high (zone 14,
163
13, 12, 11, 10 and 9), Moderate (zone 8, 7, 6 and 5) and low steepness beach zone (zone 1, 2 and
164
3). Also the maximum rate of shoreline displacement happened in the eastern parts of study area
165
(zone 1 and 2) and the central region of study area is known to be in the same condition (zone 9,
166
8 and 7). The main submerged land parts were located in pristine beach areas where no human
167
activities occurred. Man induced impact such as port construction, beach material extraction,
168
tourism and urban implementation has caused the most instability in the western parts of
169
Babolsar (zone 4, 5 and 13, 14). The shorelines of these beach zones have been severely
170
damaged and would be restored by break waters. Changeable conditions of sediments size
6
171
distribution density caused different stability situations in the study area. For example (zone 4
172
and 11) have more stable condition due to this. On the other hand, the beach areas of (zone 2 and
173
3) are notably unstable. Finally we can deduce that the overall rate of stability capacity is of high
174
grade in (zone 1, 2 and 9) and beach zones in opposition to them (zone 14, 12, 5 and 4) are the
175
most unstable regions against marine erosion impact (Fig 6).
176
177
6- Conclusion:
178
The study areas have been classified into unstable beaches (zone 14, 5 and 4), stable (zone 1, 2
179
and 9) and moderate (zone 6, 8 and 11) using different criterions of stability capacity (sediments,
180
beach structure geometry, beach deformation and sand dune abundance). Human activities have
181
caused widespread deformations in coastal zones and destroyed an abundance of sand dunes and
182
berms in Babolsar, Feridoonkenar, Mahmoodabad and Noor and it ultimately led to high damage
183
impact and more vulnerability hazards. At the present time, sand exploitation and unauthorized
184
construction in beach zones are the most important factors in coastal zone erosion and
185
destruction and consequently it is essential to do sustainable management for natural restoration
186
to take place.
187
188
Acknowledgement:
189
The author would like to thank Seidmasoume Banihashemi and Zarbali Shabanian for their
190
dedication, time and scientific advice and Sourena Rahimi for his outstanding contribution to
191
editing and proofreading without whom this project could not have been completed perfectly.
192
193
194
195
196
197
198
199
References:
Horikawa, K. 1988. Nearshore dynamics and coastal processes. University of Tokyo press,
Tokyo, 522 pp.
Hatfield, R.G. and Cioppa, M.T. 2010. Sediment sorting and beach erosion along a coastal
foreland, sedimentary Geology, (3-4): 63-73.
Khoshravan, H. 2000. Caspian Southern coasts morphology zone, Caspain sea national
research center (CSNRC), internal report pages: 34- 48
7
200
201
202
203
204
205
206
207
Khoshravan, H. 2007. Beach sediments, Morphodynamics, and risk assessment Caspian Sea
coast, Iran, Quaternary international journal, 167-168, pages 35-39
Khoshravan, H. 2011, Caspian sea southern coasts classification on the basis of
morphodynamic record, earth and space physic scientific and research journal, jeophysic
society of Tehran university, No: 3, issue 37, pages 24- 27
Khoshravan, H. Rouhanizadeh, S. 2011. The impact of coastal modification and Caspian
rapid sea level change on the Amirabad coastal zone, International of natural resources and
marine science, issue 1 (2), Pages 1- 11
208
209
210
211
Fig 1- study area location map
212
213
8
214
Fig 2- beach deformation stability capacity of study area
215
216
Fig 3_ natural protection structures stability capacity of study area
217
9
218
219
Fig 4- beach structure geometery stability capacity
220
Fig 5- sedimentary stability capacity
221
10
222
Fig 6- overall beach stability capacity of study area
11

Similar documents