مجله مهندسی و مدیریت آبخیز
سال چهاردهم شماره 2 (تابستان 1401)

This study aims to determine the design strategy of a nuclear power plant near the river by assessing flood risk as a design precondition and the Darkhovin Nuclear Site near the Karoun River in Khuzestan Province was considered as a case study. In this study, by sampling the probabilistic space fitted to the flow rate and by filtering and removing flood flows that does not overflow from the river to the flood plain, the two-dimensional HEC-RAS hydraulic model was used to determine the depth and flow velocity within the power plant site. Frequency analysis of flood depth simulated by the model for different discharges showed that the frequency distribution of flow depth and the generating flood are different from each other. The safe design of a power plant site requires consideration of the many uncertainties that make it difficult to use conventional methods. In this research, for the first time, the Rosenbluet technique was used to evaluate the uncertainty and finally to determine the maximum possible water level for locating the reactor core. The results show that to create the maximum probable depth with a return period of 100 years, there should be a flood with a return period of 10,000 years in Karoun downstream of Ahvaz. The method presented in this research can be the basis of a standard for the safe design of nuclear power plants in the vicinity of rivers considering flood hazards.

The morphological and geomorphological characteristics of rivers are constantly changing due to their continuous nature. In this research, the geomorphology of a part of Karun River in relation to the changes leading to meandering has been studied using satellite data and with a "descriptive-analytical" methodology. For this purpose, first the cell values of different bands of TM images (related to 1991) and ETM (related to 2002 and 2010) were weighted using fuzzy hierarchical analysis method to detect the bands showing the most changes compared to other bands. Then, from the weighted bands, the main components of the corresponding bands TM 1991 and ETM 2010 (as the beginning and end years of the studied period) were extracted and finally, by defining the fuzzy membership of the changes, the regions with the highest amount and intensity of changes in five The floor is provided. The results show that bands 7 and 5 show the most weight changes (river area) among the other bands for the images of 1991, 2002 and 2010, respectively. On the other hand, the fuzzy membership function of the changes showed that the maximum changes with intensity of zero to 20%, with values of 149 square kilometers including 48.3% and also the minimum changes with intensity of 80 to 100% with values of 8.2 square kilometers including 2.6% of the total study area. Therefore, from the study area of Karun, an area of eight square kilometers (about 3% of the total area evaluated) has experienced the intensity of changes above eighty percent and about 20% of the area with an intensity factor of fifty percent or more, prone to meandering or about to.

Understanding the interaction of drought phenomenon and hydrological response of catchments can lead to obtaining some information for optimal water resource management. The aim of this study was to investigate the temporal relationship between drought and groundwater contribution to stream flow, in Kaka–Reza Sub-catchment. In this study, the common period of 1382-2017 was considered for the corresponding hydrometric and rain gauge stations. The Standardized Precipitation Index (SPI) was then calculated at time scales of three, six, nine, 12, 18 and 24 months. Base flow and related index were calculated by B-Flow-Line and Halick digital filter method in monthly, annual and total time bases. Then the Standardized Base Flow Index (SBFI), the Base Flow Duration Curve (BFDC) and the base flow duration curve shape index (SBFDC) was calculated. Changes in BFDC and the corresponding shape index and the relationships between SPI and SBFI were investigated and analyzed using the correlation method. The results showed that the average Base Flow Index during the research period was equal to 0.52 and its minimum and maximum were equal to 0.46 and 0.57, respectively. Also, the trend of bas flow changes is a decreasing trend with a low slope. The trend of changes SBFDC decreases over study period with a low slope. The rate of slope change is also from one to three percent, and close to the straight line, which indicates the tendency for base flow to be stable in the long time. The greatest impact of the drought phenomenon on the river base flow is in the time step of nine and twelve months. The correlation between SPI and SBFI with a coefficient of determination 0.87 confirms the increase in the groundwater contribution to base flow, with a delay of nine to twelve months.

The formulation of strategies for sustainable groundwater resources needs an integrated view of land-use, climate changes, social system, and the response of the hydrological system. Negligence in creating a balance between these variables in charging and discharging groundwater resources has led to problems such as land subsidence, saline water advancement, reduced water quality, increased pumping costs, etc. in most of the country aquifers. In this study, the Lenjanat region was selected as a case study and one of the important regions of the Zayandehrud Watershed due to its interaction with the river, the existence of land-use changes, and increasing harvest from the regional aquifer. The results of temperature and precipitation prediction in an optimistic and pessimistic scenario until 2035 by the LARS Model and the results of examining past and future land-use changes and calculating the impact factor (adjustment coefficient) using IDRISI SELVA, ENVI, and CA-Markov were included in the study model (a combination of WEAP and ANFIS) to investigate future runoff and its contribution to aquifer recharge. The results showed that both climate and land-use changes have some impacts on water resources. In the case study, the amount of runoff decreases due to the decrease in rainfall and increase in temperature, and runoff infiltration, and subsequent feeding and groundwater level decrease due to land-use changes and increase in groundwater abstraction. The average rainfall volume was estimated at 194.17 million cubic meters in the observed years, of which 99 million cubic meters rechrged the aquifer. The average volume of groundwater supply after the effect of an adjustment coefficient of 1.051 was predicted in the optimistic scenario of 10.09 and the pessimistic scenario of 93.72 million cubic meters, respectively.

Over the last two decades, the need to restore rivers to the natural and near-natural state has become noticeable. One of the most important tools to achieve this goal, is to assess the hydromorphological changes of the river due to human intervention. In the present study, in order to evaluate the hydromorphological conditions of the Tajan River along the middle to lower parts (city of Sari) the Morphological Quality Index (MQI) and Hydromorphological Quality Index (HMQI) has been used. Seven reaches in 50 m riparian buffer width were selected and three quality main indicators including geomorphological, artificial, and channel adjustment were studied using satellite images of Landsat 4 in 1975 and Landsat 8 in 2019, aerial photos in 1960 and 2006, hydrological data, and data collected during the field surveys. The results showed that the studied reaches of Tajan River mainly classified as the moderate-quality class for the MQI, while it is classified as one quality class lower for HMQI, mainly as the poor-quality class. The main reason is that all the studied reaches (except reaches 1 and 7), located downstream of the Shahid Rajaee Dam, within the 30 km, which change considerably the river discharge and sediment transfer, also the extreme human impact and anthropogenic stresses in the catchment, such as land-use change. The results also showed that the method, which was used in this study, is effective, in general, index-based assessment, diagnosis of the hydromorphological problems, and an exact comprehensive realization of the response to the mentioned stresses.

Using one or some specific property to discriminate the sediment of different sources is impossible. Therefore, properties were selected with attention to the type and properties of sedimentary sources. Thus, the efficiency of tracers for identification of sedimentary sources should be evaluated and obtained results should be recommended for similar areas. Therefore, in this study, the efficiency of rare earth elements in discrimination sediments of lithological units has been investigated. 69 samples collected from surface soil and active walls of channels in 10 lithological unites of the Chandab watershed basin. The amount of rare element earth was determined by using the neutron activation analysis method. Then, the assumptions of discriminant analysis method (1- the variables are distributed normally, 2- the within-group covariance matrices are equal  3-There is no multicollinearity between variables) were evaluated and then were applied. Based on the results, lithological unites fo Chandab Watehrshed classified into five groups and Yb, Sc, Sm, Th and Eu were selected as sedimentary tracers. According to the F method, for coefficients of discriminate functions, the selected elements can discriminate sediments of lithological groups at 95% confidence level. The ability of Sm, Eu, Yb and Sc to successfully discriminate different sources are the same and more than Th.

Sediments can be sensitive indicators for monitoring contaminants in aquatic environments. Therefore, understanding the mechanisms of accumulation and geochemical distribution of heavy metals in aquatic systems and providing basic information for judging environmental health risks, spatial study of metal concentrations in sediments and their comparison with non-contaminated bases is of great importance. One of the common methods of soil pollution assessment is the use of pollution factor index (CF). The calculation of this index requires determining the background of the elements under study. For this purpose, statistical methods based on mean and standard deviation of data are commonly used. Due to the skuwness of the distribution of geochemical data, the use of this parametric method is limited, so the use of methods resistant to outlier data can be proposed as an alternative approach. In the last two decades, the fractal method has been used to separate communities in data related to many disciplines of earth sciences. In order to evaluate the two mentioned methods, 770 samples of waterway sediments containing six metal elements of As, Cr, Cu, Ni, Pb and Zn were collected in an area that is located in the north of Khorramabad. The background of the elements was determined by both methods (statistical method resistant to outlier data and fractal method) and finally the CF index was calculated. This index based on statistical methods assessed at the intermediate level for arsenic, chromium, copper, nickel, lead and zinc 7.5, 0.8, 5.5, 0.5, 4.7 and 9.2 percent, respectively. For the mentioned elements based on fractal method, the medium level of contamination were 39%, 28.9%, 88.6%, 39.4%, 45.7%, 73.4% of the total sample, respectively. In addition, with the second method, 3% (copper), 0.1% (lead) and 4.3% (zinc) of the number of samples have been evaluated at a considerable level. The results showed that the use of statistical methods in determining the background of the elements, despite the selection of a statistical method appropriate to the distribution of data, has reduced the sensitivity of the pollution index and reduced the efficiency of the index in the separation of pollution classes. While the use of fractal method due to considering the spatial dimension (area) in separating different background communities from anomalies leads to better efficiency of CF index and thus improves regional pollution estimates.

Soil erosion is an important subject in water and soil conservation researches which is influenced by natural and anthropogenic factors. Hence, knowledge on soil erosion amount enables the identification of critical areas and prioritization of measures. One of the effective factors in the evaluation of soil erosion is slope and length (LS) which could be calculated using different methods and algorithms, so the selection of the best method to provide proper estimation is important. However, the comparison of the performance of the different estimation methods has not been sufficiently considered. Therefore, the present study was conducted to calculate the LS factor and evaluate its effect on estimations of soil erosion in the Shazand Watershed using four common algorithms viz. Renard et al. (1997); Desmet and Govers (1996); Moore et al., 1991, and Böhner and Selige (2006) in geographical information system. The results of this study while confirming the difference of about 15 times among performances of various algorithms, indicated that the mean soil erosion using the algorithm of Renard et al. (1997); Desmet and Govers (1996); Moore et al. (1991), and Böhner and Selige (2006) were 4.95, 19.47, 1.73, 1.34 t ha-1 yr-1 in case of the stability of other factors of RUSLE model. Considering the calculated amounts of slope length on the topographic map, the Desmet and Govers (1996) algorithm performed better than other algorithms in LS calculation for the study watershed. It clearly verified the necessity of selecting pertinent procedures for the calculation of input factors for the precise estimation of soil erosion.

Landslide is one of the natural hazards in watersheds that cause a lot of damage every year. Neotectonic activity plays an important role in increasing the occurrence of landslides. The purpose of this study is to investigate the relationship between active tectonics and landslide inventory using morphotectonic indices in the ​​Fahlian River Basin. For this purpose, landslides distribution in the region were first mapped out and stored with the help of Google Earth images, LANDSAT-8 images, aerial photographs and field visits. Next to the extraction and calculation of four morphotectonic indices; volume to basin surface index (V/A), bifurcation index (BR), surface canal density index (P) and relative relief index (Bh). Morphotectonic indices were measured in each sub-basin. Preparation of these indicators has been done using topographic and geological maps, satellite images, field visits and using geometric and mathematical principles with the help of the features available in ArcGIS10/4. Each index was divided into three categories in terms of tectonic activity, and finally, based on the segmentation of each index, the level of tectonic activity of the region was determined on the basis of the index of relative tectonic activity index (Iat). Finally, by cross ovrlaying of the landslide inventory map to the relatively active tectonic zonation map, the percentage of landslides occurred in each tectonic zone was determined. The results showed that 67.34% (428.34 ha) of landslides occurred in the area with high tectonic activity, which covers only 45.73% of the total area of ​​the study basin. This result indicates the role of active tectonics in increasing landslide occurrence.

Shortage of rainfall and drought are among the factors affecting the water shortage crisis in arid regions due to the high rate of evaporation in these areas, while reducing the amount of water productivity, it reduces soil moisture. Therefore, the application of conservation methods by reducing the rate of evaporation and maintaining soil moisture in addition to improving plant growth and yield increases water productivity. The aim of this study was investigation of the effect of sand mulch and nano-clay in buried clay pot irrigation on temperature and humidity changes in one of the wind erosion centers of Sistan region. For this purpose, wind sediments accumulated in Sistan plain as well as flood sediments of Helmand riverbed (sediments transported during floods entering from Afghanistan) were sampled. By determining the particle size of sediment samples, the largest particle size of wind sediments was separated to prepare a sandy cover using a sieve. To prepare clay nanoparticles, Flood sediments were also pulverized using ball mill by examining the particle size and determining the main elements (using the XRF method). By preparing treatments including sand cover, nano-clay and control by installing thermometers and probes at depths of 10, 30 and 50 cm Soil temperature and humidity were measured (using TDR) for a period of 186 days. Also, at the end of the test period to evaluate soil stability indices by sampling from different depths, the mean weight diameter (MWD) and geometric mean index (GMD) of aggregate diameter were measured based on dry sieving method. The results showed that there was significant different at 5% level on soil moisture and temperature distribution between treatments. In depth 10 cm, the highest amount of retained moisture were measured in sand mulch treatment (1.2 and 1.4 times retains moisture compared to nano-clay and witness treatments, respectively). The highest amount of retained moisture in depth 30 and 50 cm is related to nano-clay treatments (45 and 68% more maintain compared to sand mulch and witness treatments, respectively). The results also show that the highest and the lowest amount of soil temperature at different depths related to witness and sand mulch treatment respectively. Mulch cover by shaping temperature equilibrium in soil profiles, caused 17.2 and 33 % reduction of temperature compared to nano-clay and witness treatments. The results also showed that, there were significant differences between treatments in mean weight diameter (MWD) and geometric mean diameter (GMD) and the highest amounts of this index related to nano-clay treatment (p<0.05). Based on the results of this study, the use of sand mulch and nano-clay by reduces the temperature and improving the stability of aggregates, increases the volume of soil moisture in the subsurface layers by 30 to 45% and also increases the retention time in soil moisture and reduces irrigation frequency compared to the state without protective action in the soil. Therefore, the application of the methods used in this study, provides the required moisture to the plants to establish vegetation in the wind erosion centers of the study area.