Zoning Flood Hazard in the GabrikDrainage Basin

Flood risks are considered as the most important and hazardous natural risks of Iran, which haveoccurred more and more severely in recent years. The severity of this risk in the Gabrik drainage Basin is more due to geographic position, special climate, and geology conditions and basin factors while a numerous volume of floodwater flow leads to destruction of residential places, agricultural lands, as well as human and financial damages every year. The target region was one of the main drainage basins of south east shoreline of Iran placedin the East of Hormozgan province. This study aims to decrease human and financial damages inducing floodwater hazards in the available residential places of the basin using statistical analysis, field survey, and evaluation resulting to detecting and providing zoning plan of floodgate regions. In this study, different techniques are recruited in a new form to detect effective parameters of floodwater occurrence, meanwhile their layers are combined using Geographic Information System and a highly accurate plan is illustrated. The results of this zoning indicate the regions with high and very high risk include, in sum, 23.4 percent of area meaning that flooding state of wide zones of this basin is the result of temporal raining, low permeability, critical slope, and erodibility. Therefore, executing watershedplans and constructing dams are very necessary to decrease and control this risk and improve the region conditions. Study AreaOne of the main drainage basins of south eastern of Iran is theGabrik drainage basin including an area of about4404square kilometers, which is placed between between 58° 06' 45" to east longitude of 58° 47' 48" and 25° 46' 27" up to north width of 26° 47' 34".This basin is placed in south eastern of Hormozganprovince, inJassktownship regarding political divisions. The target basin originates under the basins of Bandar Abbas-Saddijdrainage, and its output stream flow to Oman Sea located70 Km east of Jask Township, which is in north ofBeshagard Mountains, south ofOman Sea,east ofSaddij drainage basin and westof Jegin drainage basin.

The statistical analysis, field study, and assessment of remote sensing methods are used in this study. Different data are used to zone the Gabric drainage basin regarding floodwater hazards. Topography maps including maps in scale of 1:25000 covering all around of Iran, which were provided by IranianNational Cartographic Centre were used. The geological maps providedby Geological SurveyofIran and mining discoveries wereused to prepare geology map of the Gabric drainage basin in digits as well as evaluating available information.Its erodibility and permeability was measuredby ArcGIS 10 software package. The degree of erodibility and permeability was determined based on the geological instruction of counseling engineers in Iran. Satellite images of the ETM Imagery, Landsat 8 satellite in November 2014 wereused to analyze and evaluate the vegetation range of Gabric drainage basin. In order to measure the climatology of GabricBasin, the statistics available for the stations including climatology and Lir stations during 20 years and the close stations including Synoptic station of Jask, Minab with 30 years’ period, Totan climatology stations, Dahandar, Bikh, Dad Khodawell, Khomeini Shahr, Tidr and Kermestan with 20 years statistical period were used. For the field survey, the deposits of the studied region were detected and their height was measured by GPS. The floodwater hazard of the Gabric drainage basin waszoned using GIS. First, effective factors on creating flood water weredetected and selected; meanwhile, its layers wereclassified and prepared to provide this map by experts of soil in Hormouzgan Province. These layers are weighted based on their effectiveness. Then, the layers were weighted using AHP in Expert Choice Software Package and combined in GIS software leading to the final map. In addition, the potentiality offlooding of each basin in gabricwas determined based on Zonal Statistics and in order to prepare the layers, different methods such as statistical techniques, GS software for choosing the best torque, measurement of convergence and divergence, as well as other factors such as height by Simple Cokriging, and SAVI Index for examining the plant coverage of the basing with ENVI Software were used.

orderto combine nineeffective criteriato prepare the map of zoning of floodwater hazards in Gabrik drainage basin, the raster layer of each one of these criteria wasdivided and weighted into different parts with different values as well as a 50-meter pixel size. Then the weight value of these criteriaand accumulative weighting order of Raster Calculatorwerecombined using Geographic Information System and GIS Software and the final map for flooding prone regions in Gabrik drainage basin wasprepared. The flooding statues of each sub-basin using Zonal Statistics Method wasevaluated.The obtained results show that the regions with very high risks include 8.4 percent, the regions with high risk include15 percent, the region with mean risk include34.7 percentof the basin area. The regions with low risks include32.8 percent and finally, the regions with very low risk include9.1 percent of the basin area. In this region, 10 sub-basins are in danger of very high risk, 17 sub-basins are in danger of high risk, 16 sub-basins are in danger of mean risk, foursub-basins are in danger of low risk, and sevensub-basins are in danger of very low risk of floodwater hazard. Therefore,in sum, the main and most important natural hazard in Gabrik drainage basin is the floodwater hazard, which occurs due to special climate, geologicaland physiographical conditions.

The objective of this study is detecting the reasons of flooding and zoning of floodwater risks in Gabrik drainage Basin, which is one of the main drainage Basins of Oman Sea shoreline placing in the east of Hormozganprovince. Wide range of studies were conducted to recognize natural conditions of this basin byevaluating and analyzing its alluvial terraces sediments using field study during January 2014indicating the effect of different factors such as climate, basin, and physical factors withrespect toincreasing severity of basin flooding (SistaniBadooei, Negaresh and Fotoohi, 2014). These factors resulted inspecial geographic conditions of east south of Iran, which led to the development of flood risk and changing it to the most important natural risk of the region due to existence of insatiable geological and erosionable structures, as well as severe rainfall. Based on the statistics reported by HormozganProvinceNatural Resources and Watershed Department in 2011, there are 94 villages in the Gabrik drainage Basin and their overall population is 5926. Theymainly inhabit near the main river and floodplain and earn money from agriculture and animal husbandry, especially in the outer part of the basin. Therefore, the pan of flood risk in this basin is prepared to detect the risky regions and decrease human and financial damages. The effective factors and criteria of flood occurrence including temperature, annual evaporation, vegetation of basin, slope of basin, ground permeability, erodibility, ability of geological structures, the distance of the main river, the field of floodplain, detecting available alluvial terrace sediments in the basin, use of lands and geomorphology plans are detected and classified regarding their effects withrespect toseverity and weakness of flood risks based on the results of distributed questionnaires by the personnel of Land Protection and Watershed of Hormozganprovince. Different data including topography plans with a scale of 1:25000, geological plans, satellite pictures, field capture, and the statistics of climatology stations, rain measurement,and synoptic are recruited to prepare each of above mentioned criteria, which are analyzed using techniques like ground statistics, SAVI Indicatorprocessed, prepared and combined using GIS System. Thus,the final plan of zoning of the flood risk in this field is prepared. What obviously can be indicated in this plan is the severe state of flooding, in such a way that around 8.4 percent of the area includes the regions with very high risk, 15 percent with high risk, 34.7 percent with moderate risk, 32.8 percent with low risk and only 9.1 percent with very low risk, which do not result in a proper conditions of life. Peopleneed water resources based on the regional statistics, most of available sub-basins in this basin have very high flood risk indicating severe conditions of flood risk. In sum, several different climatic, physiographical and basin changes have all changedGabrik Basin to one of the most severe flood-causing basins in Iran. Since all of the connecting ways to the basin is at the time of low level of water in the river, the flooding could hinder passing and bring about so many problems for the people living in the villages. Hence, public informing and training aboutfloods, informing the inhabitants of the basin villages about hazardous regions, preventing people from constructing houses near to the river,and executing watershedplans and constructing dams are required to improve current state and decreasehuman and financial damage inducing of flood risk.