Flood Zone Investigation by using Satellite and Aerial Imagery Younes Daneshbod Islamic Azad University-Arsanjan branch Daneshgah Boulevard, Islamid Azad University, Arsnjan, Iran Email: daneshbod@gmail.com ABSTRACT Flood is one of the natural disasters that the control or decrease of its damages needs a special planning. The first step in flood control is to recognize flooding areas and flood risk zones, so based on this study, the flood damages could be reduced to its minimal amount. In this research the Baron dam watershed located in north west of Iran is studied. By using Landsat TM, Google earth images and the geomorphologic and physiographic studies, the flood zones were classified into 4 zones of sever, moderate, low, and non-hazardous. Results of satellite image interpretation show that there are 2754.8 ha of sever zone, 5292 ha of moderate zone, 3041.85 ha of low zone, and finally 87482 ha were classified as non-hazardous. The results show the fact that, the use of satellite images in the areas which lack terrestrial data is very useful and interpretation of such images is a fast and economical solution to recognize and classify flood risk areas or it can be used to estimate the flood damages in the shortest time. INTRODUCTION Most countries deal with the flood phenomenon and have caused lots of damages. They all have tried to reduce this damage to minimal. Flood as a natural catastrophe has caused lots of economical, social and human damages and has destroyed the existing infrastructure of the country. The damages are of the two kinds, direct and indirect such as destroying houses, roads, crop fields and pasture and even death of villagers of flood plain regions, it erodes the soil and in general destroys the ecosystem. Nowadays, modern techniques and tools especially remote sensing help the planners to evaluate the potential of natural dangers caused by flood in the least time and its a good method to evaluate the damages. Aerial imagery and satellite images are used widely to investigate the flood zone of hazardous regions. Nawaz has used remote sensing and GIS software to analysis flood danger, the aim of his research was to develop a map for crop fields of mozafar abad, and developing a GIS based database for damageable regions and to show the highlighted installation which is exposed to flood [1]. Kimitra and Monriul islam in a peper entitled flood hazard map and land development priority map developed using NOAA AVHRR and GIS data have develop flood hazardous maps [2]. Sharma in a paper, used the GIS related technologies to investigate the flood disasters in india, according to this investigation about 40 million hectars of India s fields are categorized as flood hazardous zones which 18.6 million hectars of it are exposed to the flood [3]. Balaj, sanakar, Karthi have evaluated disaster management as important task. They have concluded that the most important technique to reduce damages due to natural catastrophes such as flood is to investigate thoroughly the influenced regions [4]. ITC (International Institute for Geo-Information Science and Earth Observation) has proposed a method to appoint and categorize the flood zones. This research is more coincidence with local area. This proposal is based upon geomorphology observations of the area marks and topology. The category proposed by ITC is presented in Table 1 [5]. Table 1 The flood risk category according to ITC Earth surface Description Flood risk montinous only in valleys no risk high terrains valleys on huge floods low risk low terrains river banks culverts moderate risk sedimented deserts multiple culverts, high flood and sedimentation high risk flat terrains flooded high risk alluvial terrain erosion, sedimentation, flood high risk The experiences by other countries has shown that the first step to reduce the flood damages is to investigate the flood hazardous zones and classify them as different hazardous degrees, so from the outcome, one can decide how to take advantage of regions for different applications such as agriculture, manufacturing, commercial, new cities, villages
and industrial. With such knowledge we can reduce the damages caused by flood in the hazardous zones. This research has done by use and explaining satellite and aerial images. METHOD This research starts after physiographic and climatology based studies and uses Google Earth, Landsat TM satellite and aerial images. Some modifications from scaling, trigonometry and atmospheric georeferences has been done. Satellite images are explained and observed manually so the first surface map or topographic up and downs base on table 2 is prepared. This is the topographical map legend. This map is prepared from local watershed situation. In order to categorize the floodplain regions into different hazardous regions, the information provided in table 3 has been used and the flood plain hazardous map is prepared. Table 2 The Flood zone plains according to shape and flood risk property Earth type Symbol Description montinous M only in valleys high terrains T1 valleys on huge floods low terrains T2 river banks culverts sedimented deserts P1 multiple culverts, high flood and sedimentation flat terrains P2 flooded alluvial terrain R1 erosion, sedimentation, flood low terrains R2 river banks culverts sedimented deserts F1 multiple culverts, high flood and sedimentation montinous F2 flooded high terrains F3 erosion, sedimentation, flood flat terrains L1 river banks culverts alluvial terrain L2 multiple culverts, high flood and sedimentation Table 3 Flood zone category legend Earth surface Map Symbol Flood risk mountainous M,T1,T2,P1 no risk only in valleys P2 no risk sedimented desserts R1 low risk R2 moderate risk flat terrains L1 high risk L2 high risk alluvial terrain F1 high risk F2 moderate risk F3 low risk FINDINGS The flood risk zones at the Baron watershed is investigated by eye inspecting of Google earth and Landsat TM satellite images and rendation of 1:50000 aerial images by using the information provided in table 2, and after in-situ check. The results are shown in fig. 1 and table 4.
Fig. 1 The categorized area according to ITC Table 4. The flood zone Area according to shape map Map unit Area (hectars) Percent Dam s lake 511 0.5 F1 1201.7 1.2 F2 3936.5 4 F3 1383.3 1.4 L1 45.8 0.04 L2 398.1 0.4 M 85627.7 86.3 P2 494.1 0.5 P3 1417.9 1.4 R1 1196.5 1.2 R2 1508.9 1.5 T1 795.3 0.8 T2 646.4 0.6 Total 99160.7 100
In order to categorize the flood plain risk zones we have used the information provided in table 3 which is the category guide for the classified regions to the three zones of high, moderate and low hazardous risk. Fig. 2 is the flood plain risk zone category map. Fig. 2 Flood plain risk zones Upon the information extracted from the flood risk zone map. The total area of the region is 99160.7 hectares. The complete information is provided individually in Table 5. Table 5. The flood zone Area according to category map Flood risk category Area (hectars) Low risk 3141.85 Moderate risk 4894.12 Moderate risk with flooding 398 High risk 2709 High risk with flooding 45.77 No risk 87482
Fig. 3 Overall satellite image of studied area (Google Earth) Fig. 4 Satellite image of studied area north of chaldoran city (Google Earth)
THE CONCLUSION AND DISCUSSION Flood is the major problem in Baron Watershed which is influenced both by nature and human causes. The Natural cause of flood is related to topography and steep slope (The physiographic studies show that 61.5 percent of watershed area has steeps of 12 to 60 percent and 2.5 percent has slopes of greater than 60 percent) the impervious layers (most of the rocks in the watershed have no or little seepage). The watershed morphology (most watersheds are in compact form), high intensity with short duration rainfall, low vegetation cover and finally change of land use and poor management methods in watershed are of mankind cause of flood. The geographic location, low slope of plains is another reason for flooding. High topography variation in main branches and middle branches and low slope plains at the watershed outlet from mountainous region to flat terrains causes flooding. In low slope terrains because of low speed of flow, sediment will settle so the water flow keeps changing its path. By each flood the path changes and the damages will increase. The results described in this study should provide helpful information about flood risk management and should be useful in assigning priority for the development of very high risk and high risk areas. In addition, the study may have considerable management implications for emergency preparedness, including aid and relief operations in high risk areas in the future. Flood hazard and flood risk maps may also help the responsible authorities to better comprehend the inundation characteristics of the flood plains, the protection of which is their responsibility. In addition, the general public will be made aware of the imagery of flooding which helps in understanding the risk of flood. Finally, the outcome of this research shows the fact that, the use of satellite images in the areas which lack terrestrial data is very useful and interpretation of such images is a fast and economical solution to recognize and classify flood risk areas or to be used to estimate the flooding damages in the shortest time. REFERENCES [1] F. Nawaz, and M. Shafique data integration for flood risk analysis by using GIS & RS as tools. Proceedings of Map Asia 2003. [2] S. Kimiteru, and MD. Monirul islam, flood hazard map and land development priority map developed using NOAA AVHRR and GIS data. Proceedings of ACRS 2000. [3] V. K. Sharma Use of GIS related technologies for managing disasters in India: an overview GIS@development webpage, http://www.gisdevelopment.net/application/natural_hazards/overview/nho0003.htm (acc.04-09-12) GIS@development, India 2003. [4] D. Balaji, R. Sankar, and S. karthi, GIS approach for disaster management through awareness - an overview, Proceedings of Map India 2002. [5] H. T. Verstappen, Applied Geomorphology Elsevier, 1983.