مجله مهندسی و مدیریت آبخیز
سال پانزدهم شماره 1 (بهار 1402)

Today, drought has become one of the hot topics of global concern, but its impact on the provision of services and functional health of watersheds in the face of this natural disaster has been less evaluated. Accordingly, in this study, the effect of drought on the Efin Watershed health has been evaluated based on changes in Reliability (Rel), Resilience (Res) and Vulnerability (Vul) indicators in the period 2005-2019. Based on this, the rainfall data of three rain gauge stations were interpolated using Inverse Distance Weighting (IDW) for the watershed and sub-watersheds. Standardized Precipitation Index (SPI) was then determined based on the mean and standard deviation of monthly data and was used to calculate the Rel, Res and Vul indicators. Finally, the overall health status of the watershed was determined by calculating the geometric mean of these indicators. The annual results showed that Efin Watershed in terms of Rel, Res and Vul indicators extends between 0.83-0.92, 0.17-0.33 and 0.24-0.54, respectively. The RelResVul index also has values between 0.37-0.53. The average watershed health indicator in this period was also calculated to be 0.42, which indicates mean watershed health condition. Spatial variations of watershed health also showed that Rel, Res and Vul indicators fluctuated between 0.85-0.86, 0.21-0.24 and 0.76-0.78 in different sub-watersheds. The results of rainfall analysis of the region, indicate that due to the relative stability of rainfall, the impact of human intervention and intensification of watershed health threatening factors, more than ever effect on the current situation and if not addressed will have harmful effects.

Sediment dams are built with multi-purpose goals including flood control, erosion, sedimentation and aquifer feeding. These dams, with the aim of controlling the sediment from transferring part of it to the reservoirs of the dams in the downstream, and by causing a delay in the surface runoff, they control a part of the flood and feed the aquifer of the area. Improper design or lack of optimal implementation of these structures causes the reduction of useful life and sometimes premature destruction of these structures. Evaluating the function and technical performance of such plans with the aim of improving and managing the system is of special importance. For this reason, in this article, a number of sediment dams implemented in Abdanan City of Ilam Province were investigated and evaluated. This research was conducted in the form of hydraulic simulation and comparison of the current situation with the conditions before the implementation of the project, in a section of the waterway about seven kilometers long. It should be mentioned that six stone and mortar dams have been built during the last decade. The results of the hydraulic simulation of the flooding of waterways and constructed structures showed that, based on the discharge with a return period of 100 years, the average overflow width of the construction dams is about 25% larger than the required value and the length of the stilling basin is about 40% less than the required value. In general, in all construction dams, the length of the stilling pond is not chosen correctly, so that the short length of the stilling pond has caused the hydraulic jump to leave the pond or to form at its end. Due to the high flow speed in the area of the hydraulic jump, erosion and destruction in the end zone of the calm pond has intensified, which has been extended to the upstream side and the main structure of the sediment dam. Based on the hydraulic simulation of the flood and the relative comparison of the results in the conditions before and after the construction of the dams, it was found that the constructed dams have a positive effect on the parameters of flow speed, flow strength and flow shear stress, which are all factors that aggravate erosion in the waterway. So that for discharge with a return period of 25 years, the speed, power and shear stress parameters of the flow have decreased by 23, 29 and 27%, respectively, during the research period. Therefore, the average reduction of these parameters locally and at the construction site of the six dams was estimated as 73, 85 and 82%, respectively. In general, according to the field visits and investigations, the implementation of the plan has been effective in controlling floods and sediments, and in case of annual protection and repair, its effects will be doubled.

Climate change can lead to changes in the frequency, intensity, and duration of extreme climate events in different parts of the world. The purpose of this research is to investigate temperature and precipitation extremes in Lorestan Province. The data used in this study included precipitation and the maximum and minimum daily temperature of nine synoptic stations in Lorestan Province during a 28-year (1990-2017) common period. The matrices of minimum and maximum temperatures and precipitation daily data for each station were prepared and used to compute the extreme climate indices (26 precipitation and temperature extreme indices based on the recommendation of CLIVAR \ CLL expert group) using the R programming software. The results of studying the trend of cold and hot extreme weather indicators during the period 1990-2017 in the province using the Mann-Kendall trend test showed that for all stations, the hot indices have increased and more cold indices have decreased. In different regions of the province, positive and negative trends of hot and cold indices with different intensities have occurred. The highest upward trend of the warm extreme indices has occurred for the hot night’s index. Among the cold indicators, the greatest decrease occurred for several frost days and cold days indices. The decreasing trend of ice days is significant for 45% of stations at 99% level and the decreasing trend of cold days for 77% of stations at different levels of 90, 95, and 99%. The results of the study of the frequency of occurrence and trend of precipitation extreme indicators in Lorestan province showed that the total rainfall of this province, like many regions of the country, has decreased. In contrast, the occurrence of maximum rainfall in addition to being significant in the province has an increasing trend during the period 2017-1990. These conditions can indicate an increase in the number of occurrences of heavy and short-term rainfall events and, shorten the period of the rainfall season in the region.

Many of the environmental problems are caused by the changes in the main components of the hydrological cycle. However, water balance modeling can help to better understanding the components of the hydrological cycle in order to develop appropriate management options. The purpose of this study is to calculate three important components of surface water balance using the WetSpass model and evaluate the model in Hamadan-Bahar Watershed located in Hamadan Province on a monthly time scale. The results of the model evaluation in the study showed that the coefficient of determination between the observed and simulated runoff in the calibration and validation period is equal to 0.79 and 0.83, respectively. Groundwater nutrition assessment was also performed according to manual calculations of the variable for 2012-2013. Then, the results of Kramer correlation coefficient between spatial distribution maps of runoff, actual evapotranspiration and groundwater recharge were investigated with input maps of the model. In general, due to the importance of evapotranspiration in water balance calculations, the evaporation and transpiration maps of the model were evaluated separately for different uses. The evaluation results confirmed the capability of the WetSpass model in simulating runoff, evapotranspiration and groundwater feeding with an acceptable accuracy. The results of spatial distribution maps of runoff, actual evapotranspiration and groundwater recharge indicate a high correlation between evapotranspiration component with land use (0.54), soil texture (0.45), evapotranspiration potential (0.42) and temperature (0.31). Also, these results indicate a high correlation between runoff components with land use (0.62) and soil texture (0.58), and average correlations between groundwater recharge component with land use (0.32) and soil texture (0.34). Therefore, land use and soil texture were the first and second factors affecting the distribution of surface balance components, respectively.

Recently, the effects of climate change on the hydrological cycle and regime have become an important research topic. The results of atmospheric general circulation models (GCMs) together with hydrological models are used to determine the impacts of climate change on hydrologic regime. The daily minimum and maximum temperatures, rainfall and sunshine hours of the Shiraz synoptic station were simulated using the LARSE_WG6.0 statistical model. The efficiency of the model for simulating climate variables was determined using historical data of Shiraz station. To investigate climate change on runoff, two scenarios of the HadGEM2-ES model for two periods were downscaled using the LARSE_WG model. In the next step, runoff was simulated using the SWMM model and its results were compared with the measured runoff. For this purpose, 2 events were used for calibration and one event for validation. Based on coefficient correlation (R), root mean square error (RMSE) and Nash-Sutcliffe efficiency (NSE), the model has a suitable efficiency for simulating runoff. Then, LARSE_WG downscaled data were used in SWMM model and the runoff changes in future periods compared to present. According to RCP4.5 and RCP8.5 climate scenarios, precipitation will increase from 16.10 to 8.88% in 2021-2040 and 14.49% and 19.73% in 2061-2080. Therefore, assuming no change in landuse in Shiraz district 8, the volume of runoff will increase from 13.35 to 21.48 percent.

By determining the threshold of runoff and erosion by rain simulator, it can be determined rainfall amount that causes runoff in different conditions with more speed and accuracy and lower cost. After determining the threshold of runoff and erosion in each region, using biological methods and operations can prevent the conversion of runoff to flood. In this research, considering that the threshold of runoff and erosion occurs simultaneously and mistakenly only the term of runoff threshold is used in different researches and do care less about erosion threshold and in order to determine the most important factors affecting the simultaneous threshold of runoff and erosion of different land uses of Aghajari and Gachsaran formations, part of Margha and Kuhe Gach watersheds of Izeh city with an area of 1609 and 1202 Hectare selected. This study was conducted to determine the relationship between runoff and erosion threshold using a rain simulator with some soil physical and chemical properties such as very fine sand percentage, sand, clay, silt, pH, electrical conductance, moisture, calcium carbonate and organic matter in different land uses of Aghajari and Gachsaran formations. Then, sampling was done at 13 points and with three replicates in Aghajari and Gachsaran formations at different rainfall intensities of 0.75, 1, and 1.25 mm/min in 3 land uses of rangeland, residential area, and agricultural land using a rain simulator. SPSS and EXCEL soft wares were used for statistical analysis. The most important factors affecting runoff and erosion threshold were identified by multivariate regression. In general, in Gachsaran formation in all three land uses, clay and calcium carbonate showed the highest role in increasing the threshold of runoff and erosion. The most roles in reducing runoff and erosion threshold showed very fine sand and moisture content in Gachsaran Formation. However, in the Aghajari Formation, in all three land uses, the highest role in increasing the threshold of runoff and erosion, showed clay and organic matter. In addition, the most roles in reducing the threshold of runoff and erosion in the Aghajari formation showed very fine sand and soil sand and salinity.

In this study, the perspective of reference crop evapotranspiration (ETo) in the southern part of the Aras River Basin under climate change condition was drawn using SDSM downscaling. For this purpose, meteorological data of selected synoptic stations located in this basin were used and after receiving the downscaling outputs for the parameters required for estimating ETo by Penman-Monteith FAO-56, basin ETo was calculated for the near future (2021-2050). In this regard, daily reanalysis NCEP data and station daily data include: maximum and minimum temperature, wind speed, relative humidity and sunshine hours as well as output data on CanESM2 model under RCPs scenarios were used to generate future station data for estimate Aras Basin ETo. The studied stations included: Ahar, Ardabil, Parsabad, Jolfa, Khoy and Makoo and the base period for the data was considered 1985-2005. First, the efficiency of SDSM in simulating the parameters required for ETo estimation was evaluated by comparing NCEP simulated data with station data. Their comparison indicated the appropriate performance of the model in simulating data. Therefore, climatic parameters were simulated using the CanESM2 model under RCPs scenarios for the future. After calculating their monthly values, in CROPWAT was entered to estimate the basin ETo and trend of the variable for the next three decades were calculated. The results showed that the basin ETo in the future period compared to the base period will increase by an average of about 7 mm per year. In terms of stations, there will be an increase in Parsabad (102 mm) and Jolfa (66 mm). This increase also means an increase in the water needs of plants. Also, the future trends of ETo in Khoy, Makoo, Ahar and Ardabil will be decreasing.

Soil erosion and sedimentation is one of the main problems in most of watersheds in Iran and a fundamental limitation against sustainable development. The usage of vegetation cover is the cheapest and most suitable approach for soil conservation. In the present study, the height, vegetation cover and density of Vicia Dasicarpa and Villosa Vicia investigated on reducing runoff and sediment. The experiments conducted using standard plots with dimensions of 22×1.8 m, slope of nine percent and east direction; so that, nine experimental plots including three treatments and three replications installed and performed in the form of randomized complete block design. Runoff sampling was conducted from the tanks installed at the end of each plot, and the parameters of vegetation surface cover, vegetation density and plant height were measured at each sampling time. Then, the means of measured parameters were statistically analyzed and compared using Duncan Test. According to the results, the maximum runoff  (97%) and sediment (94%) reduction were observed for Vicia Dasicarpa during the experiment. Also, it was detected that plant properties such as vegetation cover and density have a great correlation with runoff and sediment reduction which means soil and water conservation. Therefore, selecting the cultivar and plant species is an important step to increase the efficiency of this biological method. Based on the findings, in order to conserve soil and water as well as assisting the livelihood of the watershed residents, the use of legumes compatible with rainfed conditions having appropriate properties such as strong root, stem system and coverage along with initial irrigation at important growth stages of the plant in drought conditions is recommended.

The SWAT Model has been accepted as a comprehensive surface water simulation model in estimating water balance components with the ability to study different management scenarios on water resources. In most studies, the SWAT Model is calibrated based on the accuracy of surface runoff estimation, and its comparison with field measurements in hydrometric stations. In a previous study, the performance of the SWAT Model in estimating runoff, evapotranspiration, and yield of wheat, barley, corn, sugar beet, alfalfa, apple, and grape crops in the Mahabad Plain was satisfactory and acceptable. The purpose of the present study was to use the SWAT calibrated model in estimating other components of water balance including deep percolation, lateral flow, return flow from the aquifer to the river in the same area. Assessing the components of water balance in the unsaturated zone, and its effectiveness in aquifer balance is important in managing the utilization of integrated water resources. The results showed that the calibrated model was able to estimate the difference between the deep percolation in the wetted year compared to normal years, and the difference in the infiltration in the wet year compared to the dry year under the influence of increasing rainfall. The results showed that the amount of deep percolation in the wetted year compared to normal and dry years has increased by about 23% and 43%, respectively. The average depth percolation is estimated 157.86 mm (17.1%). At the same time, the model has been able to estimate the difference in the amount of infiltration in different areas of the plain, and in different seasons of the year according to the type of land use and land management patterns. The amount of lateral flow has also increased in the wetted year compared to the dry year, so that the amount of this component has doubled. In this study, the average return flow from the aquifer to the river was estimated to be 20.9% (129.6 mm). Surveys have shown that the presence of shallow groundwater level has a significant role in creating surface return flow from the aquifer to the river. In general, the results showed that recharge due to rainfall and irrigation water from unsaturated zone is one of the most important input components of groundwater models such as MODFLOW in arid and semi-arid regions. The amount of recharge is important in more accurately estimating water level fluctuations. Given that the MODFLOW Model is not well able to estimate the recharge processes and lateral flow in the unsaturated zone. Therefore, the simultaneous use of SWAT and MODFLOW models in estimating the water balance components of the unsaturated zone and combining it with the groundwater model is important in studies and management of operation of integrated water resources.

Karkheh watershed is located in the western to southwestern region of Iran and in a dry to semi-arid region. The existence of different agricultural systems, including irrigated and rainfed agriculture, low water efficiency, the existence of production limitations (salinity and drainage management in the downstream), poverty and lack of livelihood of local communities (upstream), the issues of upstream-downstream impacts of the basin, environmental issues, etc., led to the proposal of the Karkheh watershed as a suitable model in the country for the CGIAR Global Water and Food Challenge Program (known as CPWF). Therefore, this basin was chosen as one of the representative watersheds among the other nine watersheds of this global program, as a model for arid and semi-arid regions of the world, and the program was implemented during phase one of the program (2004 to 2008). In the implementation of this program, approaches, organization and mechanism, management structure, technical and program criteria, basin management principles, stakeholders' participation, innovations and ways of presenting outputs, in different stages of basin selection, program start and during The implementation of projects approved by the program were adopted and used. The main objective of this article is to document the methodology used during the process of implementing the CPWF international research and development program in the Karkheh Basin, so that its hidden knowledge is revealed, related experiences and achievements are documented, and used for future uses in other similar projects in this or other basins in the country. The study method is mainly based and derived from the study and analysis of program documentation archives, reports, discussions held during the meetings, the results of workshops and national and international conferences and the reports of the field visits carried out during the implementation of the global CPWF program and the implementation of this program in Karkheh basin. Among the important achievements and methodologies and the documented indicators of the program, one can include the methodology of collaborative development of technologies, the examination of the paths of project results, the criteria for selecting research sites, and the methodology for determining the principles of integrated watershed management which are presented and explained in detail in this article.