Saied Choopani, Hossain Hossaini Pour, Mahmood Damizadeh
Agricultural & Natural Resources Research Center of Hormozgan Province
P.O.Box 79145-1577 Bandar Abbas – Iran
Mohammadreza Gharib Reza
Soil Conservation and Watershed management Research Institute
P.O.Box 13445-1136 Tehran – Iran
Coastline changes are the most important and common processes in coastal zone. These changes were occurred in coastline of Kouhestak- Karian area in the Persian Gulf coasts in which terrestrial processes directly affect oceanic processes and vice versa. Coastline changes in Karian area contain sedimentary and geomorphologic unit’s transformation, subversion, erosion and substitutions to each other, sedimentation and occurrence of other ones.
The main scopes of this project are determination of the rate of coastline changes in short period (26 years) and long period (quaternary) and determination of effective factors in these phenomena. This research is based on GIS investigations, field operations and laboratory Studies, Preparation of orthophotos for two periods of aerial photo (1967, 1993), GIS studies.
Initial recognition of coastal features, investigation of maps exactness, and sampling of fossils from pale shorelines were done by field operations. Fossil samples were tested by 14C method at Jaber-Ebn-Hian laboratory in Iran. The main achievements are as follow:
1- Sedimentary unit’s polygon maps 2- Coastal landform unit’s polygon maps 3- erosion and sedimentation maps 4- Pale shorelines maps 6- superficial and vertical coastal changes rates and amounts 7- effective factors in coastline changes. Other achievements of this research were obtaining the best method for investigation of coastline changes in the Iran coastal zones, and late quaternary history of coastal Makran zone and coastal Zagros folded zone and areas of Karian area, which need coastal protection.
Coastal shorelines worldwide are changing rapidly as a result of natural physical processes and human activities. Natural factors such as sediment supply, wave energy, and sea level are the primary causes of coastal changes, whereas human activities are catalysts causing disequilibrium conditions that accelerate changes.
Coastal features susceptible to change through external forcing usually represent the integrated responsible, the shore zone to a number of interacting environmental variables operating across a broad spectrum of time scale. Whereas the interactive forces and geological and hydrodynamics processes and climate condition causes changes of coastline situation and create transgression and regression coastlines.
The investigation of changes in coastline position or morphology can aid in predicting the life expectancy of coastal infrastructure, but may also point to more complex trends in coastal stability, sediment supply, and crustal movement. It may be difficult to isolate the particular cause of a change is coastal position, morphology, or other properties; or a change in the rate, frequency, or intensity of coastal processes.
The study area is part of the Persian Gulf and is located in North of Hormuz strait, in Hormozgan province, Southern Iran. The total length of area is about 40 km, from east of Bandar-e-kouhestak to west of Bandar-e-Karian. This investigation is based on GIS method Applications, aerial photographs and supported by, topographical maps, Aster Images (2001).
The objective of this research may be summarized as follows:
- Preparing of sedimentation and erosion maps in the coastal zones using GIS
- Superficial and vertical coastal changes rates and amounts
- Preparing of Paleshorelines maps
- Determination of effective factors in coastline changes
- Prediction of future coastline behavior
- Protection of coastal resources, management of coastal development, reduction of coastal hazards.
The study area is part of coastline of Hormozgan province in the Persian Gulf and it lies between longitude 56° 52´ – 57° 5´ and Latitude 26° 45´ – 27° and is located in North of Hormuz strait, Southern Iran (figure 1). The coastline of Iran along the Persian Gulf has a total length about 2440 kilometers. Whereas the Hormozgan province is a coastal region in southern Iran with 1100 kilometers coastlines in Persian Gulf and Oman sea coasts.
Figure 1. Location map of the study area
Investigation of Coastline Changes on Short period (26 years)
This research focuses on coastal zone and is based on aerial photographs and supported by topographical maps, Aster Image satellite (2001) and GIS Applications. The image processing was to prepare a false color composite Aster Image of bands 321 which emphasize geology, irrigated area, land use and shoreline. The main part of study area is covered by Quaternary Formations and Pleistocene conglomerate deposited in the basin.
In this research two series of aerial photographs (1967&1993) and several steps were used to prepared final maps as follows:
1). Aerial photos has been scanning with gray scale shape by 300 dpi and mosaics for two different years using Adob Photoshop software by jpg format and were carefully checked and corrected where possible and created a false color composite Aster Image 3 2 1 bands (fig.2) for new investigation and filed work.
2). Digital photographs have been converted into ILWIS GIS package and georeferenced using digital topographic map (1: 50000) and standard ILWIS image to image method. The most important Coordinate systems useable in this step are LatLon and UTM Coordinate systems. Due to the accurate necessary of area was used UTM Coordinate System.
3). Delineation of coastal zone units by visual interpretation and were digitized on screen (on screen digitizing method) using landform concept of each coastal units (boundary of landform units) for two different years (1967 and 1993) and preparing maps of Coastal landforms for each year (Fig.3) using ArcGIS Program.
Fig.2. Aerial photos of study area (1967 & 1993) and FCC of bands 321(RGB) of Aster Image (2001)
The coastal landform of the study area can be grouped as follows (see Fig. 3).
- Land units (Qts, Qlt, Qssh, Qsp, Qm, Qal1, Qal2, Qal3, Qt2, Plm5)
- Estuary and coastline units (Qes, Qtb, Qtf, Qbsh, Qbm)
The berm crest was selected to comparison of shoreline changes and coastline profile. The berm crest usually represents the average sea level and is shown emergent of fluctuations of sea level in short and middle terms and wave performance .
4- Raster polygon maps with 0.5 * 0.5 meter pixel size were generated using polygon to raster option for each year (1967 & 1993). The output raster map always uses the same domain as the input polygon map. The secondary step in raster operation was to prepare a cross map 1967 and 1993 by standard ILWIS cross option. These combinations give an output cross map and a cross table.
Fig.3. Polygon Maps of Coastal landform for each year
5. The Final step was prepared map of coastline area changes (Fig. 4) using cross table and attribute map operation and prepared final map of coastline area changes by ArcGIS Program (Fig. 4).
Fig.4. Coastline changes map of the study area
Investigation of Coastline Changes on long period (Quaternary)
The investigation of paleoshorlines is based on field observations, fossil sampling and supported by aerial photographs (1993), Aster image (2001), topographical map (1:50.000) and GIS applications. The image processing was to prepare a FCC of bands 321 (RGB) of Aster image, for preliminary investigations and prepare paleoshorlines map. According to aerial photographs and image satellite several paleoshorlines were shown in the study area that results of regression final of sea water in the Holocene.
In this part of research several step were used to prepared final map and determination of coasts uplift rates as follows:
1) Prepared paleoshorline map using aerial photographs (1993) and update by Aster image (2001) and supported with field work (Fig.5).
2) Paleoshorline survey and fossil sampling
In order to sample points and direction of survey were distinguished on aerial photographs and map and then a long transect about 6 km, from oldest paleoshorline (Fig. 7) toward sea and prepared a cross section of survey direction. Several transverse dunes or paleoshorlines at various elevations could also be seen from near sea to about 6 km far from them in the study area. The fossil sampling was done from oldest to newer paleoshorlins along of survey direction (24 samples). Two samples were selected (S4 & S24) for radiocarbon test. Location and accurate elevations of 2 points (S4 & S24) were measured using DGPS.
3- Correlation and Dating of former Coastlines
Two fossil samples were tested by 14C method at Jaber-Ebn-Hian laboratory in Iran (S4 & S24). The results of absolute age determination of samples selected were shown in table 1 and calculated uplift and regression rate of coast.
|Fig. 5: Location of Paleoshorlines in the study area||Fig. 6: Fossils of S4 Pleo shorline in the study area (1850 ± 30 Yr BP)||Fig. 7: Location of S24 Pleo shorline in the study area (3890 ± 40 Yr BP)|
Table 1: Results of radiocarbon-dated samples from pleoshorelines on the study area.
Discussion and Conclusion
To comparison between units of coastline changes map (Fig.4), can shows, that coastal accretion area is more than the coastal erosion area. The coastal accretion areas are located in eastern part of the study area where wind sediments are exposed and the mouth of river with more sediment.
The geological and hydrodynamic factors play an important role in the transportation and movement of sediments. In the western and eastern parts of Zarani river important sedimentary process is erosion, particularly which waves are dominant (wave dominated shorelines).
However, due to about 30 years time interval, the results can be based for regional planning and coastal constructions by 50 years return period in the study area.
The use of aerial photographs with digital format and GIS coverage’s for mapping Coastal provides a number advantages over conventional aerial photographs interpretation and other data including timeliness, synopticy, and reduced costs.
The investigation of coastline behavior can be beneficial for hazard reduction.
Based on superficial and vertical coastal changes rates of study area (fig.8) and dating of former coastlines by 14C method (table 1) the regression rate can be calculate relatively. Sediment yield recharge, wind sediments transport and coastal profile slope are influences on dominate coastal processes in the study area and can be change in place by place.
According to distance of paleishorlines from recent coastline and age of them (table 1), coastline regression rates is 0.27 m/year and 1.17 m/year respectively S4 and S24 samples. Whereas uplift rate is 0.6 mm/year duration between 3900 to 1850 years ago that indicated of increasing of sediment yield recharge, inland upward or sea level downward in a 2050 years period.
Important results of sea level changes are formation of coastal sedimentary sequences in Quaternary time. Coastal sedimentary sequences in the study area are shown retrogressive coastline and respectively from base to up including Plioplistocene conglomerates, high and low level alluvium terraces, sand ridge that are components of wave dominate deltas, tidal flat, supra tidal, river alluvial deposits considered: river channel deposits, river bar deposits and flood plains and evaporate deposits (sabkha).
Fig. 8: superficial and vertical coastal changes rates and amounts in the study area
We acknowledge financial support for the research project of An Investigation of Hormozgan province Coastline Changes from Agricultural and Natural Recourses Research Center of Hormozgan province and Soil Conservation and Watershed Management Center.
- Bird, E. 1997. Coastal Geomorphology an Introduction. Department of Geography, University of Melbourne, Australia, John Wily & Sons, LTD.
- Bart Makaske and Pieter G.E.F.Augustinus, 1998. Morphologic Changes of Micro-tidal, low wave Energy beach Face during a Spring Neap Tide Cycle, Rhone-Dlta, France, Journal of Coastal Research, No.14, pp 632-645.
- Gharibreza M.R and Jalali N. and Moatamed A. 2003. Investigation of coastal area changes of Sistan and Balochestan Province ran. Soil Conservation and Watershed management Research Center.
- Kraus N, C. and Rosati J, D. 1997. Coastal Engineering Technical Interpretation of Shoreline-Position Data for Coastal Engineering Analysis. Note CETN II-39 (12-79).