Paleoclimatic investigation of the Quaternary period reflects fluctuation in climatic conditions during geological periods. Abrupt climatic changes, viewed as problem causing global incidents bring about adverse side effects in sensitive climatic zones such as Iran. Droughts and unpredictable floods that damage natural resources as well as human life become common yearly occurrences. Apart from influences of natural physical factors, human activities, if not properly controlled, add to the destructive power of the floods too. This happened in the Nekaroud basin mainly due to deforestation and damaging changes in landuse during the last century. The huge magnitude flood of summer 1999 which caused irreparable downstream damage and death of citizens is a sad incident of such environmental changes. The present study is an investigation into some characteristics of Nekaroud basin, an analysis of the reasons behind the occurrence of the catastrophic flood, ways to predict and prevent similar disastrous incidents in other catchments basins in Mazandaran as well as in other regions with similar conditions in Iran.

Among the various natural hazards, floods may be considered as the most devastating factor that inflicts great damage on human societies. Therefore, the importance of estimating flood damage and its scope in planning to reduce damages and determine points with high risk is very important. The aim of this study is to determine the extent of flood hazard using OLI satellite data. For this reason, a window of OLI satellite images of Landsat 8 was acquired before and after the Dezful flood of April 25, 2016. First, preprocessing operations include radiometric and atmospheric corrections of images were done, and the principal component analysis was then used to reduce the correlation of the data. Data processing was performed using a Support Vector Machine algorithm with linear and polynomial kernels. In order to train the Support Vector Machine algorithm, training samples for each class (agricultural land, flood extent, water resources, settlement areas, and recreational areas along the river boundary) were harvested at the user level. In order to evaluate the similarity of the classes and the degree of correlation between the samples, the quantitative assessment method of the Jeffries Matusita was performed. The results showed that the flood area was 11593. 26 ha, the highest damage was due to agricultural land with a destruction of 8467. 45 ha and recreational and tourist areas along the riverbank with a destruction of 2659. 14 ha.

Global climate change leads to an increasing in the number and severity of weather events such as floods. floods have been reported one-half of all weather-associated disasters with high impacts on countries. Global warming causes a different pat-tern of rainfall in Iran caused long-term drought since 30 years ago and recent heavy raining which lead to a massive flood in this country. It is predicted that health subsequences of Iran 2019 flood such as communicable diseases vary due to the geo-graphical extent and different climates of flooded areas. However, observing long term and short term preventive measures can be effective to reduce the high impact of flood in Iran.

Natural disasters threatening and endangering human communities has resulted in the study and research of such disasters through the related sciences and present methods of forecasting their behavior with time and place and also from a qualification and quantity viewpoint. To this end, numerous methods for the determination of the maximum flood in various return periods has been made available which can be refered to as flood frequency analysis methods. One of these methods is the regional flood frequency analysis in which instead of using the data from a single station, it considers the data and characteristics of a group of similar stations. In the case under the research this method uses L-Moments and Index flood in North, Razavi and South Khorasan water basins and MATLAB software. Maximum annual flood statistics were used from 68 Hydrometric stations with minimum and maximum statistical periods of 6 and 39 years. Using Cluster analysis the region under study was divided to 7 partitions. Discordance test has conducted and only one station in region C was found as discordance station. Because of knowing the homogeneity of the regions, the parameter of Kappa distribution were estimated and with using the simulation method of Monte Carlo with 500 times, the homogeneity measure was tested in 7 regions. Using homogeneity test all regions was found homogen. Using goodness-of-fit measure z and Kolmogrove-Smirnov the Log normal 3 parameters distribution were selected for two regions of A and B, GEV for C, Generalized Pareto for D and E, Generalized logistic for F and Pearson III for G. Besides, GEV distribution was found appropriate for all of the regions, only their parameters are different in any regions. For estimating of index flood a logarithmic model has found for each region with 4 variables of area, height, average slop and form factor. Using of these models, the index flood can be estimated in each region and it can be used for standardize the statistics of maximum flood values.

The frequency and severity of floods has increased globally. However, in many parts of the world, especially in developing countries, there is no accurate data for estimating the probable of flood risk. In this research, flood risk zonation has been done for delineation of flood fringe in Gamasiyab River (south of the Sahneh city, east of the Kermanshah province). The simulation of the flood has been carried out based on the HEC-RAS (one-dimensional hydrodynamic model), and the geometric data has been processed in the GIS by the HEC-GEORAS extension. Also peak discharge in diffrence return periods has been calculated using SMADA software by Type III Pearson distribution. The study area has been divided to four reaches based on river patterns and then manning's roughness coefficient has been calculated for each reach. The results show that 23. 78 km2 and 42. 1 km2 of the river floodplain have been inundated by 25-year and 100-year return periods respectively, so that amount of damage from the 100-year flood was higher than the 25-year flood. Also the width of inundation area in the reaches 2, 3 and 4 indicated that 25-year return period was not good criteria for flood fringe. It is necessary to study the other features of the river, including bed morphology, river depth and river pattern.

Most areas in our country are subject to frequent flood damages and increasing loss of lives and properties. This research present a methodology, based on the use of mathematical hydrologic models simulating mutual interaction of effective factors, to study the spatial distribution of flood producing areas with in watersheds. The watershed of interest, Damavand, was divided into seven subwatersheds which were digitally characterized in a geographic information system (GIS). Subwatersheds flood hydrographs associated with design rainfalls were determined using HMS model and were routed in the stream network to yield the total hydrograph at the outlet. With successively eliminating subwatersheds from the simulation process, in a method titled "successive single subwatershed elimination method", flood hydrograph at the outlet was determined so that the contribution of each subwatershed in the flood peak at the outlet could be quantified. Then, all subwatersheds were ranked with respect to the order of contribution to the outlet flood peak. The routing results show that this contribution is not only a function of subwatershed discharge and size but also a function of other factors. Thus, any flood control measure must consider the flood area prioritization in term of contribution at the outlet.

Using of flood for identification of plant nessassary water for its growthing and decreasing of flood damages is possible in many different methods. By using of water spreading system, seasonal flood in susceptible land will be spreaded and, will have different effects on ground water tables, plant cover and soil on these lands. In order to measurement of physical soil properties variations in Delijan water spreading stations of Markazi province, seven channel water distributions (distribution area) and regions between those (wetness area) were selected and then each channel and wetness area after that were devided to three parts and at center of each parts one compined sample was obtained in two depths of soil (0-25 and 25-50 cm). Also, measuremant of soil infiltration rate in distribution and wetness area was obtained by double ring method. Soil physical properties in two these area and different channel was compared using tstudent and ANOVA method respectively. The results showed that the water Spreading activities has been significant decreasing about sand and infiltration rates at %1 level and about bulk density at %5 level. Also, about the amounts of clay, silt and Sp there have been significant increasing at %1 level.

flood is a sudden happening and quick and destructive event that causes death and financial sensible and unsensiable damages in different parts on the world and Iran annually. Control or decreasing these destructive impositions needs precise and accurate studies. So, recognition of the places with runoff generation potential is very important. In current study, two major aims of investigation of the application of distributed ModClark model in flood hydrograph simulation and determination of flood source area in distributed and sub-watershed condition were investigated in the Khanmirza watershed, Chaharmahal-e-Bakhtiari Province. For this reason, at first, inputs of model were extracted by ArcGIS 9. 3 and then model was calibrated and validated. In next step, in order to determine flood source area for cell units and sub-watersheds, by applying "Unit flood Response" method, at first, design rainfall with return periods of 25, 50, and 100 years at the Aloni station were extracted and then influence of each cell and sub-watershed on output hydrograph of the outlet watershed were obtained. The results of model based on comparison between equal-width discharges show that at validation step, the model was simulated the flood hydrograph with high precision with root mean square error, efficiency coefficient, and R2 of 1. 53, 0. 89, and 0. 74, respectively. Also, according to the results of current study, based on the flood volume relative error, peak discharge, base time, and time to peak, ModClark model had lower error in predicting the flood volume and peak discharge. The final results showed that flood source area increases in sub-watersheds from downstream to upstream, while it doesn’ t follow any distribution in cell units.

In this research, from data of 26 hydrometric station records and l-moment approach, regional and stational flood frequency of Dez basin was analyzed. For identifying homogeneous regions, Ward hierarchical cluster method was used. The appropriate number of homogeneous regions was determinate from nonhomogeneity test and discordancy measure. The Dez Basin was divided into three homogeneous regions. In these regions parameters of the regional frequency distribution were evaluated by the L-moment ratios. The L-moment diagram, goodness of fit test, and plotting position methods were used for the selection of appropriate distribution and plotting position formula. Generalized Extreme-Value distribution and Chegodieve plotting position formula is appropriate for region A, generalized logistic distribution and Greengurten plotting position formula for region B and Generalized Extreme-Value distribution and Greengurten plotting position formula for region C were selected. The relative root mean square error (rRMSE) between observed and estimated data, in all stations, in high return periods is small and in small return periods is vicversa. Regional models evaluated for determination of flood discharge magnitude in different frequency by linear and multiple regression method.