Dhaka University Journal of Earth and Environmental Sciences, Vol. 2, 43-54, (July) 2011 Md. Ashraful Islam Mrinmoy Kumar Maitra Abdul Baquee Khan Majlis Sanzida Murshed Sunbeam Rahman
Spatial Changes of Land Use/Land Cover of Moheshkhali Island, Bangladesh: A Fact Finding Approach by Remote Sensing Analysis
Received : 4 February 2012
Abstract
Accepted : 3 November 2012
M. A. Islam () Geological Survey of Bangladesh Eimail:
[email protected] M. K. Maitra Weatherford Bangladesh E-mail:
[email protected] A. B. K. Majlis Geological Survey of Bangladesh E-mail:
[email protected] S. Murshed Department of Geology, University of Dhaka E-mail:
[email protected] S. Rahman Bangladesh Centre for Advanced Studies E-mail:
[email protected]
The present paper encompasses the study of Landuse/Landcover of Moheskhali Island and spatial changes of land with their most possible causes since 1972 to 2009. Using remote sensing, eight different land classes with their associated physical characteristics have been identified and quantitative analysis in order to find out the changes of each land class over forty years have been summarized in this work. Most alarming situation occured in the land class agriculture field which declined at a rate of 14.5 hectares per year since 1972 to 1989 and stands to increase 75 hectares per year in the next twenty years. The drastic increase of salt fields has been found at a rate of 108 hectares per year at the same time span. Anthropogenic activities together with some natural phenomena, i.e., cyclonic storm, fresh water scarcity for
1. Introduction Land use is defined as any human activity or economical function associated with a specific piece of land, while the term landcover relates to the type of feature present on the surface of the earth. (Lillesand and Kiefer, 2000). In other word, Land use is a process by which we can get maximum benefits from a land using it in terms of various types of activities, i.e., cultivation, residences, industries, forestation etc. by a systematic land use planning. This process is indispensable for such development works that is strongly involved with socio- economical growth of the particular area and to protect that area from any environmental and ecological degradation. A wide range of land type with their associated natural hazards, economical potency of each land type, biodegradation due to the impact of recent anthropogenic activities and versatile sedimentary depositional system have made the Moheshkhali Island unique, inasmuch to come in interest to the geologist as well as the other scientific community of Bangladesh since last one decade. Moreover, the land use and land cover mapping of Moheshkhali are essential from a different point of view.
cultivation etc. are responsible for the rapid encroachment of salt field to the cultivable lands. Recent sedimentation has formed huge landmass of tidal flats in last twenty years at the western part of Moheskhali that are mostly occupied by mangroves and the relatively older ones are used for salt cultivation. Although a considerable portion of mangrove at Sonadia has been lost for shrimp culture, the overall amount is increasing due to aforestation. Hilly region, a potential source of ground water, has been losing its area gradually due to illegal hill cutting and often deforestation. Keywords: Landuse Landcover, Remote sensing Agricultural land Salt field Change detection.
The coastal regions of Bangladesh including the Moheshkhali Island is a well known cyclonic path that have been suffering severe cyclonic winds, storm surges and tidal waves over many years, originating in the Bay of Bengal. Nearly one million people have been killed in Bangladesh by cyclones since 1820 (Talukder et al., 1992) and the after effects of this natural hazards are more common, i.e., loss of human life, their crops and houses, pollution of the drinking water due to the inundation of land and ponds by saline water. Land use and land cover mapping helps to identify the region that is stable and suitable for people to build permanent infrastructure that can prevent them from this kind of devastating tidal surges. Remote sensing and GIS techniques are becoming one of the most useful and influential analytical tools for resource planners and managers (FAO, 1988), as it interlinks spatial and attribute data for outputs in the form of maps, tables, and figures (Hossian et al., 2007). The integrated approach of remote sensing and GIS have used in this paper in order to study the morphological condition of Moheshkhali Island and to obtain other interpretative information that are essential for proper land use planning of that area. Knowing the present status of Moheshkhali land use, the sustainable utilization of
Islam et al. the lands and practices to avoid the endangering of the environment are the prime objectives for development work. To obtain a reliable output of this research, significant changes over forty years on land classes of Moheshkhali Island have been observed in order to find out the information about the preexisting land use patterns and changes in land use through time, together with their most possible causes.
cliff coast of Bangladesh characterized by hilly topography surrounded by coastal plain exhibiting unique geologic, tectonics and as well as geomorphologic peculiarities. The island is divided into four subdivisions i.e., active coastal plain, young coastal plain, old coastal plain and hilly areas with piedmont plain. Landforms are very much associated to the geological depositional system. Two different depositional systems prevail in Moheshkhali Island- closed to semi closed system in southern part and open to semi closed system in northern part (Majlis et al., 2011). Moheshkhali is in accretionary phase with a rate of 1.2 sq.km. per year since 1972 ( Islam et al. 2011). Southwest coastal plain and western coastal plain accreted huge landmass which eventually contribute to the land classes of this island directly or indirectly associated with the changes of Landuse/Landcover pattern in this area
Study area The Moheshkhali Island including the Materbari and Sonadia lies within 2120/N-2150/N latitude and 9145/E9200E longitude and bordered by Chakoria and Cox’s Bazar in the north, northeastern eastern and southeastern part across the Moheshkhali channel. The Kutubdia channel separates Moheshkhali Island from Kutubdia in the northwestern side and extreme western and southwestern part is open to the Bay of Bengal. Moheshkhali islands exhibits rather complex geological system on the eastern
Fig. 1 Location Map of the Study Area.
44
Spatial Changes of Land Use/Land Cover of Moheshkhali Island, Bangladesh different resolution problem in the present analysis. Numerous spectral analyses of different objects have been observed for identification of different landclasses.
2. Materials and Methodology Materials and Methodology in remote sensing and GIS involve several interrelated tasks. Regarding the present research work, methodology has been divided in to three stages. Image processing is the vital one, having multiple steps i.e image pre-processing stage, and processing stage and finally the post processing stage. All these necessary tasks are being prepared with the help of Erdas imagine9.1 and the final derivative maps are generated in ArcGis10.
Processing After all the above procedures, the assessment of land use and land cover was done by adopting an unsupervised classification scheme of Landsat images for the years 1972, 1989 and 2009. There was no alternative other than applying unsupervised classification technique since supervised classification was inexecutable due to some constraints. One of the essential steps in supervised classification of a satellite image is to select several ground control points in the corresponding area. But such control points were unattainable in Moheshkhali Island and its surrounding areas, where most of the mountainous parts had limited accessibility due to poor transportation route. Moreover surrounded landmasses are mostly tidal flat (intertidal zone), inundated twice in a day and were also inaccessible even by foot. Therefore the best that could be done was peripherally observing the area from boat to understand the status of various land classes.
Preprocessing Landsat MSS of year 1972 and Landsat TM image of year 1989 and 2009 have been used for Landuse/Landcover mapping. Table 1 shows the basic information of different satellite Imagery. Individual bands are stacked to get the combined image for the analysis. Only the Moheshkhali and its surrounding areas have been taken as the island fall under a single scene of landsat image. Landsat of 1989 has been set into UTM projection system which finally transform into Transverse Mercator with Everest 1830 datum. Landsat of 1972 has been resampled to common spatial resolution of 30 m using the nearest neighbor resampling method to solve Table 1. Satellite Images and their source Satellite imagery
Path and Row
Acquisition data
Resolution (m)
Landsat MSS
146 and 45
3-Nov-72
57X57
Landsat 5 TM
136 and 45
22-Feb-89
30X30
Landsat 5 TM
136 and 45
6-Dec-09
30X30
Source GLCF: Earth science data interface GLCF: Earth science data interface GLCF: Earth science data interface
been prepared for certain landclasses like shallow sea water, inland water body, agricultural land, dense hill forest, Mangrove forest etc. and then all this information together with field observation data have been incorporated in order to identify the landclasses. However, for the final evaluation of unsupervised classification several feature space layers were generated with the signature editor tools. Feature space layers are two dimensional scatter plots that show the reflectance values for any two bands of multispectral images. All objects were validating by plotting signature means of clusters onto feature space layers and thus finally separated different objects and identified the similar one as well.
Unsupervised classification groups the pixels with similar spectral characteristics into some unique clusters according to some statistically determined criteria, then systematic attempt to assign and finally transform the spectral classes in to thematic information classes of interest like agriculture, forest and wet land (Jason, 2005). In the first step of unsupervised classification 100 classes of spectral clusters with 98% convergence of threshold value, skip factors 1 of XY and 70 iterations of processing options, approximate true color and standard deviation 1 along the principle axis of clustering have been taken that eventually separates the whole image into desired hundred classes. In this case, the iterative self-organizing data analysis technique (isodata) algorithm has been used to perform the classification. To get the high accuracy result of Landuse/Landcover from image classification, several numbers of classes have been taken for this mapping though the study area is not intensely varied regarding the landclass.
After the confirmation of all the class types the next and final work was recoding and masking to purify the land classes prior to analysis. Recoding undoubtedly needs to conform to the present classification scheme. This function assemblages 100 classes to desired 8 land class by combining several groups of clusters that represent the same land cover. Moreover, some additional functions were run over the last output images. As salt field and tidal flats give the same spectral response, it is hard to identify them distinctly. On the other hand, the settlement areas, adjacent to the piedmont plain, are difficult to recognize from image.
The next step was evaluating the classified clusters and assigning them in proper land class. In this regard firstly, 100 class classified raster image was geolinked to the raw images, highlighting the pixel locations of each of the 100 clusters and then trying to find those locations on the raw imageries. After doing this few typical spectral curves have 45
Islam et al. Salt fields and settlement areas have been digitized and overlaid on the final recoded image with the help of raster fill tool to avoid these misinterpretation, other mix classes have been corrected with the same option. More importantly, it was necessary to collect relevant data i.e historical data (collected from oral interviews of local people, they described the land status in some particular time period) required for classification of 1972 and 1989 images. For the change monitoring of specific classes, a GIS model has been run among three images with the help of
spatial model tool of Erdas imagine 9.1 using various conditional statements. Post-processing After doing all the above necessary functions, the derivative maps have been prepared by arcgis10. For the statistical analysis and graphs of different land classes of both the images have been prepared with the help of Microsoft excel.
Fig. 2 Flow chart of the working procedure.
3. Result and Discussions
Land class (1): Water body
Landuse/Landcover classification
Major channels, a number of charas, numerous khals and lagoons are grouped under this class.Two major channels, i.e., the Materbari in the West and the Moheskhali in the East, connected with a number of sub channels and creeksdrained through the coastal plain, are tidal in nature, whereas most of the charas in the hilly region, maximum are found in Saflapur union, are perennial in nature used as a
Eight different landclasses have been identified from the images of three different years i.e., 1972, 1989 and 2009 (figure 5) that are briefly described in the following sections with a ordered way. 46
Spatial Changes of Land Use/Land Cover of Moheshkhali Island, Bangladesh
good source of surface drinking water during the monsoon. In Sonadia island one prominent lagoon was identified in southeast (locally name Pubpara), whereas in southwest few prototype lagoons were reported during the field investigation.
increases day by day the settlements, along the foothills (piedmont area) and in the plain lands (tidal flats and old dunes), extends very fast. Land class (7): Sand dunes Beaches, old and new dunes and barrier beaches are grouped under this land unit km sandy beach and ridge extends along the length of onadia sland from north-west to southeast. This class is significant because it provides an excellent staging area and wintering ground for migratory waterfowl and shorebirds and provide nesting grounds for marine turtles. Dunes in this island are so far the largest in Bangladesh that are strong barrier for cyclonic damages and this features protected Sonadia island from devastating cyclone in the year 1991. Some of the seasonal people cultivate watermelon in the dune sands. In recent days, this class is very much significant for the probable development of the largest deep sea port in Bangladesh.
Land Class (2): Tidal flats This landclasss is found along the periphery of Moheshkhali island, especially outside of the protected Supratidal flat in Moheskhali, Materbari and both inner and outer side of Sonadia islands. A narrow strip of the intertidal deposits was found in the eastern tidal flat of Moheshkahli Island. Considerable part of Sonadia Island and northwest and northeast of Moheskhali Island gain huge intertidal flat if compare with the year of 1972 and 1989. Storm surges are the main hazard and cause serious damage in this region. Landclass (3): Mangrove Mangrove forests, the natural safeguard of Moheskhali, are categorized in this class. This landclass is sparsely distributed throughout Moheskhali, but the major portion is present in the southwestern part of Sonadia Island. Mangrove plantations are also scattered in Koriardiar and Matarbari islands as well as on the southeastern coast of Moheshkhali island. In recent years, however, the mangrove forest of Sonadia Island has been encroached, mainly for shrimp farming. This class is very crucial for the coastal ecosystem and more significant for saving life and properties of the people living in this area from cyclones and tidal surges.
Landclass (8): Agricultural field Agricultural fields are grouped in this class. In Moheshkhali major agricultural field located in the piedmont plan and southern hilly region. Hilly valleys are extensively used for irrigation practice especially the paddy cultivation. Betel leaf cultivation is one of the most significant occupations in Moheskhali Island which are practiced in dominantly in side of the valley floor and to some extend in piedmont areas. Piedmont area has been identified along the foot of hills which extend up to 1.45 km in the west direction and 0.97 km in the east direction, eventually merges in to tidal flat plains, the boundary between piedmont plain and tidal flat plains are not identified clearly, it varies from place to place.
Landclass (4): Salt field Salt fields are assembled under this land class and covers significant portion of the tidal flats of Moheshkhali Island, especially in the major part of the protected supratidal zone of Materbari and Dhalghata union, mixed tidal flats along the western coast of Moheshkhali and sparsely distributed in the intertidal zone along the northeastern coast. Although, some salt production fields are converted to shrimp /fish farming and fish drying, eventually increases year to year.
Quantitative analysis of change detection Statistics regarding aerial coverage of landclasses and differences of aerial extend over forty years in Moheshkhali Island (shown as bar diagram in figure 3), demonstrates an overall scenario of the eight classes that are briefly described in the text based on the specified unsupervised classification showing in figure 4, prepared on the basis of table 2, have focused only those five classes that are facing the most alarming situation in the present time and their drastic changes are directly related to each other.
Land Class (5): Hilly forest This land unit has been used mainly for forestation where both the local forest department and the local people are engaged planting a variety of trees. This class is significant for the local communities who have come to depend upon the forest for many household necessities, such as firewood, housing materials and boat making materials, herbal plants for traditional medicines, honey and other minor products.
Significant changes in Land use/Land cover have been occurring since recent past. Anthropogenic activities are to blame the most for physical as well as the environmental changes of this area. The change detection of different Land use/ Land cover classes of Moheshkhali Island with their most possible causes has been described briefly in this study. Special focus has been given to the land class agriculture (8), salt field (4), mangrove (3), hilly forest (5) and tidal flats (2) and to a lesser extent, sand dunes (7) and settlement (6).
Land Class (6): Settlement This class contains the settlement area. Union Boro Moheshkhali, Choto Moheshkhali, Gorakghata, Kutubjom, located southeastern part of Moheshkhali, are densely populated compared to the northwestern part - Dhalghata and Materbari. The settlements are located sparsely at Hoanak, Saflapur and Kalarmarchhara. As the population
47
Islam et al.
Fig. 3 Diagram shows the area of different land classes of three time period.
Although the most common practice in this area is salt cultivation, some people use piedmont and valley floor for agricultural practice. The change detection between two Landsat images of 1972 and 1989 has found decrease of agricultural land at a rate of 0.21%, where it changed abruptly at a rate of 1.07% in between the years 1989 and 2009. At the same time increasing rate of salt field was
about 0.5% and 2.12%, respectively. Quantitative data from table-2 shows total individual land for agriculture in 1972, 1989 and 2009 is about 3056.2, 2794.9 and 1219.7 hectares respectively, of which only 26.5 hectares are common in each year. Salt fields on the other hand, is about 1402.8, 1844 and 4110.2 hectares in respective years, where 1136.3 hectares are common for each (table-2)
Table 2. Areas of different land classes in three different time periods (1972-1989-2009) considering only five classes which have major significance in the present analysis. Total Area in hectares
Changes of area in hectares
Land Class
Common
1972
1989
2009
1972-1989
1989-2009
1972-2009
Agricultural land
26.5
3056.2
2794.9
1219.7
261.3
1575.2
1836.5
Salt fields
1136.3
1402.8
1844
4110.2
-441.2
-2266.2
-2707.4
Mangrove
454.9
715.7
1376.8
2512.2
-661.1
-1135.4
-1796.5
Tidal flats
282.9
3991.5
957.7
3874.8
3033.8
-2917.1
116.7
Hill forest
5007.6
8408.4
5355.9
5126.2
3052.5
229.7
3282.2
Fig. 4 Diagram showing the differences in individual total area for five major land classes in three different time periods (1972-1989-2009).
48
Spatial Changes of Land Use/Land Cover of Moheshkhali Island, Bangladesh Destructive cyclones in 1991 and 1993 played a vital role for such noticeable encroachment of salt fields in western tidal flat. Most of the cultivable lands at western part of Moheshkhali became ineligible for use in agricultural purposes due to intrusion of saline water, as the area was inundated during strong tidal surges. Same condition occurred during the cyclonic storm in 1961 and 1963, by when the local people converted most of their agricultural lands for salt cultivation. Low budget along with limited installation setup encourages local people to engage in salt cultivation. In some particular areas, people entailing with this profession use the same land for shrimp culture during monsoon that brings double profit for them. Sweet water scarcity during dry months in the tidal flat area is another factor for forcing people towards salt cultivation. In fact rain water is the only means for irrigation in tidal flats. Sometimes people are being forced to cultivate salt in the fallow areas that are adjacent to salt fields because of the degrading fertility of that land. Moreover, a little amount of common field, i.e., 26.5 hectares (table-2), in the year 1972, 1989 and 2009 also indicates the shifting nature of agricultural practice. The other possible factors are, increasing salinity due to the high water level of spring tide during monsoon inundating the agricultural land by overflowing the coastal embankments and, to a lesser extent, degrading fertility as a consequence of cultivating the same
crops in same lands frequently. Flash flood often washes out and causes severe damages of crops on the valley floor and piedmont areas. Illegal hill cutting due to settlement and betel leaf cultivation in the western flank near Hoanok and Kalamarchara exposed sandy sediments (named as Tipam Formation by Aziz and Alam, 1979) that are washed away during rainy season and infill the adjacent hilly charas hindering navigability of waterways and are often responsible for triggering flash floods. Strong tidal surges make sand blanket over the cultivable land that reduces the soil quality for cultivation. However, in recent years, agricultural lands are increasing widely in the southern part of Moheshkhali, especially in Sonadia Island. After huge live losses and severe damage of properties at Gorakghata during the cyclone in 1991, people started migrating to Sonadia from that part. In some particular areas near dune sands, watermelon cultivation is exercised widely by the local people. Besides this, people cultivate some seasonal crops at the periphery of shrimp culture area due to the intervention of human activities, i.e., extensive and illegal hill cutting and slope modification, unplanned development for settlement and uses of adjacent lands for betel leaf cultivation, hill forest area has been reducing at an average rate of 90 hectares per year, where the amount reduced approximately 170 hectares per year in the first 18 years (1972-1989).
Fig. 5. Land use/ Land cover map of Moheshkhali Island based on unsupervised classification technique projected over the raw satellite images of respective time periods.
49
Islam et al.
Fig. 6 Spatial Distribution of land Classes in Three Different Time Period (Left- Changes in land Class Agricultural Field, Right-Changes in Land Classes Salt Field).
depositional phase, where the salinity is comparatively high and turbidity is relatively low due to less river activity, are used for salt cultivation. From the digital globe image and field checking, a number of localized embankments have been found on the newly emerging tidal flats outside of the main embankment that are occupied by the local land grabbers for salt/shrimp cultivation. Both the change detection map (fig-7) and quantitative data shows distinct differences in tidal flats over 40 years. The total land calculated for tidal flats in 1972 and 1989 is about 3991 and 957 hectares respectively that increased to 3874.8 hectares in the year 2009, where 622 hectares are common each year (table-2). Area of tidal flat in 1972 is little bit higher than 2009 as shown in the table-2 is somewhat contradictory though the rapid accretion of tidal flat in recent time. It might be a consequences of the fact that larger portion of the tidal flat in year 2009 is occupied by salt field and newly planted mangroves Coastal forestation by planting mangrove after 1971 and rapid conversion of tidal flats towards salt fields played a vital role in decreasing fresh tidal flat at a rate of 168 hectares in the first 18 years. However, during 1989-2009, tidal flats have increased dramatically. Cyclonic storms in 1991 changed the cox’s Bazar-Teknaf coast as well as the extremely southern part of Kutubdia eroding enormous amount of sediments; probably deposited in more or less semi-protected depositional system in the western part of Moheshkhali that are
At that time people shed plenty of trees for building their houses as these were available around. In the western flank Hoanok, Kalamarchara and Saflapur union suffer serious hill cutting in recent time. Qualitative data shows total individual lands in 1972, 1989 and 2009 are about 8408.4, 5355.9 and 5126.2 hectares, respectively, whereas 5007.6 hectares are common throughout the time span (table-2) which has a clear impression on the change detection map of hill forest (figure-7). Now-a-days both the Forest Department and local people are enthusiastic about planting a variety of trees. as they are concerned about protecting the lands from extensive soil erosion and destructive landslides; Thus the percentage of vegetation is increasing in some particular regions. However, the hilly area is a good source of ground water that is still in artesian condition. It is relevant to add that the demand of fresh water will highly rise during the implementation of the deep sea port and after the completion of this mega structure. As the tidal flat area cannot supply the huge amount of fresh water required due to the intrusion of saline water, the hilly areas have to be the main contributors to confront the crisis. As the tidal flats increases these are occupied by mangrove and to some extent, converted to salt field in recent time. Mainly the muddy tidal flats (a considerable portion) are occupied by mangrove during their young stage of formation; and older 50
Spatial Changes of Land Use/Land Cover of Moheshkhali Island, Bangladesh responsible for the huge formation of tidal flat in the next 20 years. Although major portion of mangrove forest at Sonadia Island has been lost ,distinctly identified from image of 2009,(figure-8) due to the local land grabbers before 2007 for shrimp cultivation, the overall percentage of mangrove of Moheshkhali has been increasing due to the newly born mangrove forests along the eastern and western coast of Moheshkhali and plantation of mangrove trees both by the Forest Department and local people as they became aware of protecting their properties from destructive cyclones and tidal surges. The total unchanged area has been calculated from change detection analysis for mangrove forest (table-2) is about 455 hectares in 1972, 1989 and 2009, whereas individually shows 715.7, 1376.8 and 2512.2 hectares, respectively (figure-8).Unlike the above land classes, less attention has been given on land class water body, settlements and dune sands. Changes in waterbody in 40 years have not been considered due
to the factor of open sea. Settlement areas can not be identified clearly, especially in Landsat 1989, as the settlements surrounded by trees are adjacent to the hill forests, giving the same spectral response as the hilly forest does. For the year 2009, settlements are clearly delineated from the Digital glove image due to its higher resolution. However, it is rather difficult to make distinct separation between the three satellite images i.e. Landsat TM 1989 and 2009, regarding the settlement class but from the population census data, a sharp increase of population and settlement areas are found over 21 years. Salt/shrimp cultivation and fishing are two factors that accelerated the growth of population in this area. People, who are migratory, incorporated themselves in those professions for better and cheaper facilities.
Fig. 1 Spatial distribution of land classes in three different time period changes in land class Hill Forest (left) changes in land class Tidal Flat (right).
51
Islam et al. Areas consisting of dune sands have experienced very little change. Dunes in Sonadia Island remain more or less unchanged but few paleodunes (Monsur and Kamal, 1994) in Western Moheshkhali are modified due to human interventions. The Sonadia sand dunes played an important role as a natural safe guard during the destructive cyclone in 1991, which is advocated by a fewer number of people died at Sonadia compared to Materbari area.
Fig. 8 Spatial distribution of land class Mangrove in three different time periods (1972-1989-2009).
With the help of change detection model, a land-water distribution map was prepared using the water class for both images. Spatial distribution of land-water in Moheshkhali Island gives six new classes exhibiting various combination of land-water condition which finally calculated total accretion and erosion in this area in different time periods. Areas containing sea water/channel water between 1972 and 1989 was about 4329.5 hectares that has accreted in year 2009. Major portion of western tidal flat, south east of Sonadia Island near Gorokghata and adjacent areas of Materbari and Moheshkhali channels fall in this class. About 1976 hectares area contained water in 1972, accreted in 1989 and was finally free from erosion in 2009. About 937.8 hectares area was land in 1972 that underwent erosional condition in 1989 and finally reached gaining phase in 2009. The area that was covered by water at 1972,
Fig. 9 Spatial distribution of land-water classes in three different time period (1972-1989-2009) (left); the horizontal bar diagram (lower right) showing the status of erosion and accretion (in hectares); and the pie diagram (upper right) showing the proportion of each land-water class (in %) throughout the studied area during the time period 1972-2009.
52
Spatial Changes of Land Use/Land Cover of Moheshkhali Island, Bangladesh Unpublished report of Geological survey of Bangladesh, Peoples of Republic of Bangladesh.
accreted in 1989 and eroded again in 2009, is about 191.4 hectares. On the other hand, about 288.7 hectares area was a part of land at 1972 which eventually eroded in 1989 and still in erosional phase till 2009. Very little portion of this island, about 478.6 hectares was land in both 1972 and 1989 but now is in erosional phase. Both the classes are covering the coast of Materbari and Sonadia islands and a very little portion has been found scattered throughout the area. Devastating cyclone in 1991 together with wave action might be the major controlling factor for such erosional activities. It is evident from the image analysis and change detection model that Moheshkhali Island is in gaining phase; approximately 7242 hectares of land have been accreted since 1972 whereas only 958.7 hectares of land have been eroded.
Bay of Bengal. The Jounal of NOAMI, Vol. 11(1): 15-21, Dhaka, Bangladesh. FAO. 1988. Aspects of FAO’s Policies, Programmes, Budget and Activities Aimed at Contributing to Sustainable Development. Document to the 94th session of FAO council, Rome, 15-25 Nov. 1988. Rome: Food andAgriculture Organization of the United Nations. Hossain, M.S., Chowdhury, S.R. and Chowdhury, M.A.T. 2001. Integration of Remote Sensing, GIS and Participatory Approach for Coastal Island Resource Use Zoning in Bangladesh, Songklanakarin Journal of Social Science and Humanities 13(3) Jul. - Sep. 2007 : 413-433. Islam, M.A, Majlis, A.B.K and Bazlar,R, 2011. Changing face of Bangladesh Coast. Abstract volume. National seminar on Bangladesh Coast: Geology, Hazards and Resources. 29-30 Dhaka, Bangladesh, organized by Geological survey of Bangladesh,Peoples republic of Bangladesh.
4. Conclusion Using remote sensing analysis together with GIS modeling, the present study illustrated the spatial and temporal land cover changes in forty years time span. Salt field, agricultural land, hill forest and mangrove forests are the major land classes that have been changed distinctly over forty years. It is essential to know the up-to-date informations on various land classes of Moheskhali Island for evaluating and managing the proper land planning for any development work, improvement of socio-economic issues for the local people, assessment of various environmental impacts and the bio-diversity. Anthropogenic activities and to some extent, few natural phenomenon are the major controlling factors for physical as well as environmental changes on different landclasses of this area since 1971 to 2009. Rapid encroachments of salt field to the cultivable lands are declining food security of this area. In the near future, rest of the agricultural lands can also be affected due to the implementation of the deep sea port near Sonadia. Government should shoulder the responsibility to encourage the local people for agricultural practices to protect the remaining cultivable lands.Hill cutting is another major concern in some particular areas in Moheshkhali accentuating adverse effect on natural environment. There should be a vital role of local people as well as the local authority to prevent these illegal acts and proper regulatory laws and mitigation plans should be implemented for the protection of hill forest. Sonadia Island has a great prospect as a tourist spot, but it is essential to protect Sonadia beach for any environmental pollution and degradation as it is the only fresh and undisturbed natural beach in Bangladesh. More mangrove plantation is highly recommended in newly emerging tidal flats for the protection of Moheshkhali Island as it falls in a high cyclonic zone in the Bay of Bengal. Sand dunes should be kept unhampered in place which acts as natural safe guard to protect the Sonadia Island and more awareness about the coastal ecology should be grown among the tourists.
Jensen, J. R. 2005. Introductory digital image processing: A remote sensing perspective. New Jersey: Prentice Hall, Englewood Cliffs. Lillesand, T.M., Kiefer, R.W. 2000. Remote sensing and image interpretation, John Wiley and Sons, New York. Majlis, A.B.K, Islam, M.A, Khasru, M.A and Ahsan, M.K 2011. Protectred to open basin depositional system: An Appraisal for the Quaternary Evolution of the Moheshkhali-Kutubdia Coastal Plain, Bangladesh, Abstract volume. National seminar on Bangladesh Coast: Geology, Hazards and Resources. 29-30 Dhaka, Bangladesh, organized by Geological survey of Bangladesh, Peoples republic of Bangladesh. Monsur, M.H and Kamal, A.S.M.M.1994. Holocene Sea-level Changes along the Moheshkhali and Cox’bazar Teknaf Coast of the Talukder, J., Roy, G.D. and Ahmed, M. (eds.). 1992. Living with cyclone: Study on storm surge prediction and disaster preparedness. Dhaka: Community development library.
5. References Alam, MK., Azim, MA, 1978. Geological report on the Moheshkhali Island, Cox’s Bazar District, Bangladesh.
53
