فصلنامه حفاظت منابع آب و خاک
سال دهم شماره 3 (پیاپی 39، بهار 1400)

Apart from the understanding of the impact of land use and climate changes on the water cycle and hydrology regime, hydrological models are effective tools for designing and managing water resources. Currently, many hydrological models have been developed to simulate the basin, though choosing the right model is a challenge. To this end, a correct understanding of the model, its advantages, and limitations is necessary. In this regard, several studies have been conducted to evaluate the hydrological models performance in different regions and conditions. In the present study, the performance of two integrated hydrological and conceptual rainfall-runoff models of AWBM and MIKE NAM in the simulation of the average daily runoff in Gonbad Hamedan basin was investigated. Although both models are lumped models for rainfall-runoff process, the MIKE NAM model has a more complex structure compared to the AWBM. In addition to considering the initial conditions, MIKE NAM model is also capable of simulating snowmelt. The results of the runoff simulation during the calibration and validation periods were evaluated using two statistical indicators of the Nash-Sutcliffe efficiency (NSE) and percent bias (PBIAS). The NSE and PBIAS during the calibration and validation periods for the MIKE NAM model were 0.8, 6.3 and 0.71, -4.2; and 0.6, 14.33 and 0.55, -9.2 for AWBM model, respectively. The results showed that MIKE NAM model has a better performance in simulating daily runoff in Gonbad Moarref basin compared to the AWBM model.

Understanding and studying the river flooding, which in most cases is density current, can help to reduce adverse effects of sedimentation. To this end, the creation of obstacles in the bed of stream will be effective. In this paper, the effect of thickness (dimension) and the second layer of permeable obstacles on the control and trapping of density current is investigated experimentally. For this purpose, two types of groove and cavity obstacles with grooves and cavity diameters equal to 3 mm and made of plaque glass were used. Density currents were created by adding an insoluble, suspended polymer of expanded polystyrene with a mean diameter of 1.15 mm and a density of 1.155 g / l. The experiments utilized two different concentrations (10 and 20%), five different porosities, four different angles, four different thicknesses and two barrier layers. The results showed that the density current process with 10% porosity of the groove obstacle increased with increasing thickness. The second layer of obstacles have increased the material passage through both groove and cavity obstacles. This increase was recorded in the groove type of 1.96 and the cavity type of 2.34. Investigations showed that the optimal distance of the second obstacle from the first was 2.25 meters. According to the results, under similar conditions, cavity obstacles always perform better than groove ones.

 To deal with different water conditions, a model was developed to determine the optimal irrigation level and the optimal cropping area for major agricultural crops in lands of Moghan irrigation and drainage network in downstream of Aras Dam. In this model, in the stochastic conditions, with considering the uncertainty of required water supply, decision variables (optimal irrigation levels and optimal planting area in certain time steps) are obtained using stochastic dynamic programming (SDP) method. Expected value of the maximum profit from planting crops is considered as the return function. Also in deterministic conditions, the model was run by considering 4 scenarios. The results show the superiority of cropping pattern and optimal irrigation levels (even in water deficiency conditions) in terms of all studied factors compared to the common cropping pattern (even without water deficiency) in the region. Minimum value for factor of the required water per hectare is related to scenario 2 (cropping of low water requirement crops with pressurized irrigation in deterministic conditions) which is equal to 5368.14 m3. This factor in scenarios 1, 3 and 4 is 9079.78; 13496.25and 9211.73 m3 respectively and in the common cropping pattern in the region is 10900m3. Maximum value for factor of profit per hectare is related to scenario 2, equal to 102 million Rials. The mentioned factor for scenarios 1, 3 and 4 are 96.5, 73 and 89.5 million Rials, respectively.

Actual Evapotranspiration is one of the effective components in the hydrological cycle. Therefore, accurate estimation of this component at the watershed scale has an important role in the management of available water resources. In this study, the accuracy of actual evapotranspiration product values of five global terrestrial databases including MOD16, MYD16, SSEBOP, GLEAM, GLDAS was compared to the evapotranspiration values predicted from the SWAT model simulation in the Karkheh dam watershed in 2006, 2008 and 2011 which are low/high and medium rainfall respectively on a monthly scale. Then, the feasibility of improving the accuracy of evapotranspiration values obtained from these databases was investigated in eight different scenarios using simple averaging, M5 and SVR models as ensemble methods. The results showed that although actual evapotranspiration products are able to explain the trend of time changes of actual evapotranspiration in catchment, they are significantly different with the output values of the SWAT model as observation values at a significant level of 5%. The results also indicated the use of simple averaging has no effect on improving the results at the Karkheh dam watershed. However, the use of the other two ensemble methods improves the accuracy of actual evapotranspiration and the ensemble method explains 80% of the SWAT-derived actual evapotranspiration variations. Moreover, the ensemble model derived from SVR fed by the attributes of the superior data combination scenario, reduced the estimation error by about 44% compared to that derived from the best global terrestrial product which was GLEAM in this study.

Overflows play an important role technically and economically in optimizing the operation of water storage structures. Piano key weir is an advanced and developed type of spillway that can transfer large amounts of discharge by keeping executive costs constant. The aim of this study was to determine the parameters affecting the discharge coefficient, using nine physical models. The ratio of the width of the input keys (Wi) to the output (Wo) in the seven overflows were: 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 and 1.6 (PK1.0, PK1.1, PK1, PK1.3, PK1.4, PK1.5 and PK1.6 respectively) and the other two models included PKT (thicker-walled) and PKTP (thicker-walled and crown-enhanced). The effect of changing the width of the inlet (Wi) and outlet (Wo) keys on the discharge coefficient and stage-discharge curve, the effect of wall thickness and parapet wall were evaluated. Results showed that the best model for changing the inlet and outlet widths was the model of PK1.4, which resulted in 30% increase in discharge rate compared with the control. The increase in wall thickness led to an increase in the discharge at a 5% rate in comparison with control and installing parapet wall resulted in a 10% increase in discharge and a uniform distribution of flow lines on the weir. According to the results of this research, based on the superiority of three models of PK1.4, PKT and PKTP, the geometric properties of these models can be used as a model in optimizing the design of piano key weirs.

In this study, the Spatio-temporal performance of 5 global gridded precipitation datasets including GPCC V8, CHIRPS V2, ECMWF ERA5, NASA MERRA2, and PERSIANN-CDR (PCDR) in drought monitoring has been evaluated. For this purpose, the standardized precipitation index (SPI) and precipitation information of 13 synoptic stations of the Meteorological Organization of Iran during the thirty years of 1987-2016 has been used. Comparisons were carried out based on performance indices include correlation, mean square root error (RMSE), Nash-Sutcliffe efficiency coefficient, and modified agreement index (MAI) as well as drought detection accuracy metrics including False Alarm Ratio (FAR), probability of detection (POD) and the Critical Success Index (CSI). The results showed that GPCC, ERA5, PCDR datasets had a strong agreement with SPI observations so that they showed the drought trends and situations well and their R2 with observational SPI was

This study aimed to evaluate and compare the two water quality indicators NSFWQI and IRWQIsc on the rivers of the five basins of Khuzestan, namely Karun, Karkheh, Dez, Marun-Jarahi, and Zohreh-Hindijan using data recorded in the years of 1390 to 1396. This study shows the differences between the two methods as well as the validation of the water quality index developed in Iran. While according to the NSFWQI index, the rivers of the region are in average condition in terms of quality and there is no particular problem except for points on the Karun River, there is no particular problem; the IRWQIsc index evaluates the status of surface water quality in the province as moderate to poor. Examining the differences between the two indices, it was concluded that the use of the electrical conductivity parameter in the IRWQIsc index has led to the detection of bad areas in terms of quality. The NSFWQI index has been successful in identifying points of high pollution around Ahvaz, while the IRWQIsc index has been successful in identifying points of high salinity on the Zohreh and Jarahi rivers. In determining the spatial distribution of the indicators, three methods were used: spline, kriging, and inverse distance weighting method, which based on the evaluation of the results, the last one was selected.

The prohibition of the entire area of the plains of the Markazi province and the impossibility of a new water withdrawal and occurrence of subsidence has caused the importance of monitoring of subsidence. On the other hand, the Differential Interferometry SAR (D-InSAR) is an efficient way to continuously, accurately and in a wide range monitor land subsidence. In this research, the D-InSAR method was used in the study of land subsidence in Arak city. 14 single-look complex images were obtained in the range of C-Band by EOLi-sa software. Ten processing steps were done by the SARscape software based on the four interferograms which had both the time and space criteria. On the other hand, the National Cartography Center has repeated the observations of the first-class network of the country for the city of Arak, located on the BHBT route (Borujerd-Salafchegan) in 1985 and 2004 and it measured 190mm ± 0.8mm / km of subsidence in 19 years. Based on four geocoded reflated unwrapped interferograms, the subsidence rate was calculated about one centimeter at year, for the central regions of Arak (around the Shohada Square of Arak). The urban areas had also almost identical subsidence rate. Therefore, the results of validation of the D-InSAR method using the observations of the National Cartography Center confirmed appropriate accuracy of the D-InSAR method. The results of this study showed the impact of geological and water resources factors on subsidence and the necessity of protecting water and soil resources in development projects in Arak city.

Since the creation of green space depends on the availability of water and dedicated water for irrigation of urban green space, green belts and afforestation in arid and semi-arid climates. Water availability has great value and should be used optimally with high efficiency. For this reason, in order to save water, planting species that need less water and at the same time have optimal growth efficiency has always been as an executive policy. The aim of current study is to estimate the water requirement of tree species in the field and greenhouse under different water stresses in Robat Karim town of Tehran province. This research has been done in both space of greenhouse and field by saplings of Robinia pseudoacania and Ailanthus altissima Mill and it was done in a completely random design in the field and greenhouse. This research has two stages and each stage consists of several phases. In the first stage, respectively soil field capacity, determining of MAD, determining water requirement of saplings through evapotranspiration were examined and in fact, by determining the water requirement of saplings, the irrigation cycle was determined. In the second stage, the studied saplings were subjected to water stresses 2, 4 and 6 days after reaching MAD and at each period, the physical characteristics data of the saplings were collected. Generally, the results of this study have shown that Robinia pseudoacania has a higher water requirement and more irrigation cycles in the field and greenhouse than Ailanthus altissima Mill.