Investigation the Cause of instability in Kol Delta Rivers (A Case Study: Westhern Bandarabbas)



Extended Abstract

River instability needs to be evaluated on spatial and temporal scales. It must be recognized that rivers differ among themselves, and through time, and one river can vary significantly in a downstream direction. Morphology and behaviour of drainage network, to change from neotectonic is sensitive. Meanwhile meanders of delta levels are the most unstable areas of the rivers. Tectonic deformation causes change in channel slope, which in turn is responsible for variations in channel morphology, fluvial processes, and hydrological characteristics of a river system. River responses to active tectonics produce characteristic geomorphological features revealing surface deformation in any area. The study area is located in Hormozgan province and north coastal of Hormoz strait. Kol River with the formation of a relatively large delta, flows from north to south and arrive to the Strait of Hormoz. The purpose of this study is recognition evidence and evaluation of neotectonic in Kol river drainage network. In this paper rely on results based on field survey and index of geomorphic, morphology and riverbed changes, Kol River has been studied.

For achieving results, geodynamic data National Cartographic Center related to Bandar Abbas station, index geomorphic such as drainage density (P), asymmetric factor (AF), sinuosity (S) and hypsometric integral (Hi) & time of concentration (Tc), topographic and geologic maps, aerial photos related to year of 1957 and satellite images of this area related to years of 2005, 2001, 1989 and 1977, as the main research tools and conceptual and model techniques were used. Methods are based on analytical and experimental method and technique of work is comparison during the transformation sequence of times. In the present work, first the morphometry of delta environment is investigated with considering the shape and the other main factors which control the morphometry of the river. At the second stage the data were imported in GIS environment to show the change model in the different places and times in a period of 50 years. To find out changes in the river bed, aerial photos and satellite images related to the study area in different time periods were examined. Then the data through field works by GIS (Arc Gis & ilwis) analysis and effect of tectonic analyzed. In this view, between redirected drainage and morphological feature and neotectonic affects has been relationship.

Results and Discussion
Range studied is located in south Zagros unit and fault existing in the region, are buried under the coastal sediments during the quaternary. Considering the evidence as changes multiple paths in different time periods, crossing the fault line, broad and narrow riverbed, It seems that under the influence of neotectonic active in the region. Sandstone and marl formations and very low slope of delta, caused the river does not have much stability and has repeatedly redirected during the past 50 years. Factors such as high slope of the upstream basins, plant cover poverty, low permeability formations of delta, being short time of concentration, precipitation intensity and the nature of showery precipitation, have caused occurrence of periodic floods in this region. These issues caused the river was not much stability and during the past half-century repeatedly to change the path (Figure 6). Based on data of geodynamic, displacement and tectonic activities of region is toward the north-eastern. This information indicates faults activity and tectonic movements in the region. Finding indicates continuity of the last neotectonic activity in the study area. Amount of activity is not the same everywhere, and upstream part of more than downstream of these activities is affected. Existing anomaly in the river, such as high density network of drainage, local development of meanders, being broad and narrow river bed and sudden redirects in different periods of time, including signs an active zone. Thus between neotectonic movements and changes in drainage network is a kind of interaction and reaction river systems is strongly influenced by this activity.

Results of research show that river still gain dynamic balance and is changing and transferring and create new screws. In general, changes are toward downstream. Management, set privacy and channel control, especially at the time of the occurrence of floods, is the most effective way to stability of river. also results from geomorphic indices and geodynamic data show that study area entirely influenced by neotectonic activities, But amount of influence is not the same in all region, as in the north-eastern part is higher. The present approach may be considered as an extended behaviour oriented approach for predicting morphodynamic evolution of rivers. The findings of this research can be useful for the study of impact of neotectonic on riverbed changes, the planning of construction, landuse planning, environmental protection, stability of river bed and generally sustainable environmental management. If we understand the various processes of change, prevention through good management and application of mitigation measures can be appropriately applied to the problem. Continued field measurements are the key to improving upon these procedures and add to the collective understanding of these complex and valuable river systems.