نشریه پژوهش های حفاظت آب و خاک
سال سی‌ام شماره 1 (فروردین و اردیبهشت 1402)

Floods are one of the natural events that cause significant morphological changes in riverbeds and adjacent lands, which result in financial, human, and other losses. When a flood occurs, the interference of the flow in the main channel and the flood plain causes the transfer of movement and complexity in the flow pattern from the main channel to the flood plain. Due to the dynamic nature of these events, statistical, experimental, and semi-experimental criteria are used to determine the dimensions of stable regime channels. Nowadays, the use of two-dimensional models to study the behavior of the regime channels has a superior advantage over the empirical and theoretical approaches, which are based on one-dimensional. There haven't been many numerical studies done on the flow pattern and sediment transport in alluvial channels, but there have been a lot of experimental studies. In this study, the behavior and hydraulic geometry of the trapezoidal compound channel have been investigated using MIKE21software for type of steady and unsteady overbank flow and Finally, the results of modeling in steady flow conditions showed less difference with real values than in unsteady flow conditions.In order to study the behavior of the main channel in the flood flow, the flow has been selected in such a way that the flood plain are in the state before the movement threshold. First, the compound trapezoidal channel section with fully losses boundaries/ with fully mobile boundaries was developed under bankfull flow, and then the behavior and geometry of the developed trapezoidal channel (regime channel) were evaluated under type of steady and unsteady flows. In the first step of permanent steady flow modeling, the flow conditions in the channel at a certain point are constant with respect to time, which means that the speed along the flow and the average depth of the flow are the same. In the second step of the modeling, the unsteady flow along the channel was checked with the same conditions as the first step, with the difference that the input discharge is variable in time.The results showed that when the cross-section of the main channel is full of water, there was no significant change in the width of the main channel, but the width of the main channel in overbank flows is higher than the full section and increases rapidly. The mean relative differences obtained at upstream and downstream width trapezoidal section, and flow depth in steady flow conditions are0.96, 0.88, and0.98,respectively, and in unsteady flow conditions, the average relative difference obtained at parameters upstream and downstream width trapezoidal section, and flow depth in steady flow conditions are1.12, 1.15and1.05,respectively. According to the sediment transport equations available in the software, the England-Hansen sediment transport relationship chosen as the appropriate relationship for the parameters of the channel dimensions, which can be more predictable to laboratory values.An stable alluvial channel with a bankfull, when subjected to flooding, tilts towards a new stable channel.Under steady flow conditions, estimating the results of the depth and width of a stable alluvial channel in the MIKE21model is more accurate than the results obtained from unsteady flow. Also, the values of width, depth and sediment concentration predicted by the above software are better estimated than the sustainable channel design methods such as brownlie, vanrajin and WBP. In all models, the width of the channel increases rapidly over the first 3hours, and then approaches the balance stage and the channel erosion rate decreases. As the discharge increases up to 15liters per second, the depth and width of the channel is more severe and then these changes are almost constant.

The physical properties of the soil, which cannot be easily measured, play an important role in the design of irrigation and drainage systems. Since the direct measurement of these characteristics is time-consuming and expensive, therefore, to estimate these parameters, most researchers use indirect methods such as transfer functions. This research aims to investigate and determine the best model for estimating soil moisture content in Field capacity (FC) and Permanent Wilting Point (PWP) using easily measured soil characteristics and pedotransfer functions in the R software environment and choosing the most suitable model for the soils of the Ravansar region in Kermanshah province.

In this research, the easily measurable properties of soil were used as input variables for five transfer functions of the multivariable linear, artificial neural network, Cubist, random forest, and support vector machine. At first, in the study area, the location of 120 profiles was determined using the Latin hypercube method. In these observation points, soil profile was dug and studied and samples were taken from its horizons. Then, laboratory analysis including measurement of electrical conductivity, pH, calcium carbonate equivalent, organic carbon, and percentage of sand, silt, and clay was performed on soil samples. Based on the range of changes of these characteristics, especially the soil texture, 75 surface soil samples and 33 soil samples from ten different soil profiles were selected. PWP measurement was performed on 33 samples and FC measurement was performed on surface and depth samples, i.e., 108, and then modeling operations were performed on them. Root mean square error (RMSE), mean absolute error (MAE), and R2 indices were used to evaluate the models.

The results showed that the accuracy of pedotransfer functions in estimating PWP is higher than FC (R2 and RMSE values of the Cubist model for PWP are 0.81 and 0.054 and for FC are 0.53 and 0.085, respectively). Also, the results for FC showed that between the models, the Cubist and the artificial neural network have low MAE (0.066 and 0.068) and RMSE (0.085) and high R2 (0.53 and 0.54) respectively, compared to other models.

The overall results showed that Cubist, Artificial Neural Network, and Random Forest models with lower error and higher R2 have higher efficiency for soil moisture estimation in FC than other models. The results showed that the Cubist and random forest models were the best models for estimating moisture at the PWP in terms of comparing the coefficient of determination. This research showed the importance of using new machine learning methods in studies related to soil transfer functions to estimate difficult-to-measure soil properties. Also, the results of this research are acceptable for a wide range of plains in Kermanshah province, which has similar soil formation conditions to the Ravansar region.

The ecosystem and equilibrium of rivers can be significantly affected by the river bank erosion which can also limit the human access to the rivers. Groyne is an important river restoration structure that prevents bank erosion through deviation of flow from the river banks to the main channel. From the permeability aspect, these structures can be classified into three types of permeable, impermeable, and bandal-like ( hybrid type which includes permeable and impermeable types ). Moreover, these structures can be categorized to straight, T-shaped, and L-shaped configurations. This research aims to investigate the local scour around a new type T-shaped bandal like groyne. The total number of 66 experiments were conducted through a straight flume ( 12 m length, 0.6 m width, and 0.6 m depth ) under non-submerged and clear water conditions. T-shaped bandal like and T-shaped impermeable groyne structures were fabricated in three web to wing length ratios of 0.5, 0.75, and 1. Also, three upstream to downstream wing ratios of 0.5, 1, and 2 and the permeabilities of 33%, 50%, and 60% were selected for the T-shaped banal like structure. The experiments were carried out at the flow discharge of 6 Ls-1, 9Ls-1, 12 Ls-1 and 15 Ls-1 in the presence of the T-shaped impermeable groynes and the T-shaped bandal-like groynes. It was revealed that, increasing the structure permeability resulted in decreasing of the maximum relative scour depth. Under 33%, 50%, and 60% permeabilities of the T-shaped bandal-like groynes, the maximum scour depth was decreased by 63%, 78%, and 83%, respectively compared to the T-shaped impermeable groynes. Moreover, it was observed that the maximum relative scour depth was increased by the average of 46% as for the greater values of structure length. The maximum relative scour depth was also increased for the greater values of flow discharge. It was found that there is no relationship between the maximum scour depth and the ratio of upstream wing length to the downstream wing length of groyne. Based on the results, the permeability and length of the groynes and the flow discharge are among the factors affecting local scouring around T-shaped bandal-like groyne. The significant decrease in the relative scour depth in T-shaped bandal-like groynes compared to T-shaped impermeable groynes indicates that the T-shaped bandal-like groynes have better performance than the impermeable ones in scouring control, structural stability and river bank protection.

The plant have a close relationship with the climatic conditions and their surrounding environment to go through the stages of growth and development. Therefore, the knowledge and understanding of the effect of atmospheric parameters on plant yield and production efficiency is very important.

The experiment was conducted in the form of a randomized complete block design in three replications with five experimental treatments including: no water deficit (control) (NWD), water deficit at the booting stage (WDB), flowering (WDF), milking (WDM), and doughing (WDD), in Varamin, Iran. Simulating the future climate, using the HadGEM general circulation model under the RCP4.5 and RCP8.5 climate scenarios in the three periods of 2025, 2055 and 2085, by the AgMIP model using long-term climate data related to the base period (1980-2009) was done. SSM-Wheat model was used to simulate wheat growth.

Based on the findings, the changes of maximum and minimum temperature compared to the baseline in the periods of 2025, 2055 and 2085 showed that the maximum and minimum temperature under RCP8.5 scenario increased more than RCP4.5. So that under the RCP8.5 scenarios, the maximum temperature increased by 2.1, 4.3, and 6.9 (ºC), respectively. and the minimum temperature increased by 1.5, 3.2, and 5.6 (ºC) respectively. The amount of precipitation in the periods of 2025 and 2055 under the RCP8.5 scenario increased by 4.9 and 5.9%, respectively. While the amount of precipitation in the period of 2085 under RCP8.5 scenario showed a decrease of 12.6%. The results showed that both in the no water deficit and the water deficit at the flowering stage in the periods of 2025, 2055 and 2085 under RCP4.5 and RCP8.5, the FASW by passing through The early stages of wheat cv. Mehregan growth were faced with water shortage stress and the need for irrigation was necessary from that time. Also, the length of the growth period of wheat cv. Mehregan in 2085 period was shorter compared to 2055 and 2025 periods, and this period reduction was much more intense than the growth season. The evaluation of grain yield in 2085 under the RCP8.5 scenario showed that the water deficit at the flowering stage significantly reduced grain yield by 16.8%.

In the climate change conditions, the maximum and minimum temperatures under RCP4.5 and RCP8.5 scenarios increased during the studied periods compared to the base period. This increase was more intense from 2025 to 2085 and also under the RCP8.5 scenarios. Based on the findings, the FASW in the no water deficit and the water deficit at the flowering stage at the 2025, 2055 and 2085 periods under both scenarios showed the absence of water stress. The results of the evaluation of the grain yield showed that the reduction of grain yield under the RCP8.5 scenarios was more obvious and more severe than the RCP4.5 scenarios. The water deficit both the booting and especially flowering stages caused a significant decrease in grain yield.

Planting the proper cultivar in the most optimal sowing date is very decisive in the management of environmental resources, including water resources, and leads to maximum water productivity of and energy efficiency for increasing performance. Therefore, this research was conducted with the aim of determining the most appropriate sowing date and water productivity for commercial cultivar of bread wheat under supplemental irrigation and water deficit conditions in the climatic conditions of Gorgan, Iran.

This experiment was carried out as split-split plots based on randomized complete block design (RCBD) with four replications, during the 2021-2022 cropping season. In this experiment, two moisture conditions (supplemental irrigation and water deficit conditions) were placed in main plots, seven sowing dates (from 1 November to 31 December, 10-day intervals) were placed in subplots and four bread wheat genotypes (including Arman, Araz, Taktaz and N-93-9) were placed as sub-subplots.

The analysis of variance for grain yield and water productivity showed that the effect of moisture conditions was significant at the 0.05 level and the effects of sowing date and cultivar were significant at the 0.01 level. The results of mean comparisons showed that the grain yield in water deficit conditions (5288 kg ha-1) was significantly lower than the supplemental irrigation conditions (5715 kg ha-1). Water deficit conditions caused a significant increase in water productivity (17.3 kg ha-1 mm-1) compared to supplemental irrigation conditions (16.1 kg ha-1 mm-1). The highest grain yield was obtained on the second (11 November, 6340 kg ha-1) and third (21 November, 6165 kg ha-1) sowing dates. Also. the highest water productivity was related to the second and third sowing dates (18.6 kg ha-1 mm-1). The results of mean comparisons for cultivars showed that in Taktaz (as an early-maturing cultivar) grain yield (5872 kg ha-1) and water productivity (17.8 kg ha-1 mm-1) were significantly greater than other genotypes.

The results of this research showed that water deficit conditions caused a significant decrease in grain yield and a significant increase in water productivity. The highest grain yield and water productivity were obtained on the second and third planting dates. Also, grain yield and water productivity in Taktaz cultivar were significantly greater than other genotypes. In general, it can be said that the planting of Taktaz cutlivar in the second and third sowing dates (11 and 21 November) has resulted in achieving the maximum performance and water productivity in both supplemental irrigation and water deficit conditions.

Mass erosion is the movement of rock and soil down the slope, mainly due to gravity. One of the most significant mass movements is debris flow. These are actually fast moving landslides and are a very dangerous natural disaster in mountainous areas. To control erosion and prevent sediment movement downstream, there are various biological and engineering methods available. Debris flow is most commonly controlled by check dams. The main purpose of building these dams is to control and reduce the amount of sediment entering the rivers. The backs of most dams may be filled with coarse-grained sediments and in areas with debris flows, so it is imperative to monitor how well these structures maintain different sediments. In some parts of the Nanor Baneh watershed and in the adjacent basins, there has been debris flow that has caused damage to the forests downstream. Consequently, there has also been a filling of the waterways and reservoirs of check dams. Therefore, the purpose of this study was to investigate the sedimentation granularity of check dams built in various parts of the watershed. Based on available sources, information, and maps of the basin, 58 points were identified, and their surface soil was sampled. To determine soil PSD, a hydrometry method using a 24-hour reading and sieve series was used. There are 88 gabions and masonry check dams evaluated in this research. Sediment samples were collected from each dam at two points and at two depths (a total of 57 sediment samples). After air-drying, the sediment samples were passed through a 2 mm sieve and the size distribution of particles smaller than 2 mm was determined using the hydrometric method (24-hour reading) and the same sieves as the soil samples. To determine the size distribution of particles larger than 2 mm, the sieve method (sieves with openings larger than 2 mm) was used. A comparison of the particle size distribution of soil samples upstream of the dams and the sediments behind the dams was conducted to investigate the effectiveness of these dams in trapping fine-grained and coarse-grained sediments. Finally, the gradation curves and D50 of the sediments behind the dams were examined. Based on the size distribution of particles smaller than 2 mm in the soil and sediment samples, the ratio of sand, silt, and clay in sediment samples (with mean values of 90.53, 5.45, and 4.02, respectively) varied significantly from those in the soil samples upstream of the dams. The results of D50 ratio (< 2 mm) of sediments to the soil sample upstream of check dams (average 25.92) revealed that most check dams were effective in trapping sand and larger particles, but they were less effective in keeping smaller particles in suspended sediments. Furthermore, the high D50 values for the total sediments (average 3.80) indicate that most sediments are coarse-grained. A number of check dams located in the path of the debris flow were also completely filled in one or two rainfall events, according to local evidence and field studies. Most check dams were highly effective at keeping coarse-grained sediments and preventing their movement downstream, according to sediment analysis behind them. But, these dams have little effect on trapping fine-grained sediments, and complementary methods for controlling and trapping them downstream of check dams may be needed. However, the role of these dams in reducing runoff intensity, reducing the peak flow of floods, protecting roads and residential areas downstream and many other effects cannot be ignored.

Soil organic carbon (SOC) is one of the most important components of soils that affects other characteristics of soil. SOC is also influenced by other soil characteristics. Studies showed that change in land use from pasture and forest to agriculture decreased SOC. However, this is not always true and it depends on various factors, especially the methods of organic matter management in the farm. This study was conducted with the aims of investigating the effect of changes in land use from forest and pasture to agriculture on the level of SOC and determining direct and indirect effects of soil characteristics on SOC in a bio-sequence of Sistan plain.

The studied bio-sequence was located in Jezink region, by the Hirmand river in the northeast of the Sistan plain and in the southwest of the border of Iran and Afghanistan. In November 2016, a total of 25 soil samples (5 soil samples from each vegetation) was collected by supervised randomized manner from the depth of 0-20 cm of each of places that had dense vegetation of Populus euphratica and Tamarix ramosissima (the forest covers), of Desmostachiya bipinnata and Suaeda vermiculata (the pasture covers), and the crop of Triticum aestivum ( with 15 years old land use change). Then, 28 physical, chemical and biological characteristics of the soil including percentage of SOC were measured and calculated. Statistical analysis of data in the form of completely randomized design, comparison of average SOC data with the least significant difference test, Pearson correlation between the measured soil characteristics, and stepwise regression analysis to identify significant effective factors on the changes SOC was performed by Statistix10 software. Then by path analysis the direct and indirect effects of those characteristics on the amount of SOC was calculated by Path 2 software.

Changes in the population of phosphate-solubilizing bacteria 37%, phosphate-solubilizing fungi 44%, total phosphate-solubilizing microorganisms 39%, bacteria 51%, fungi 46%, total microorganisms 51%; and also the changes in the amounts of organic carbon 39%, clay 68%, silt 71%, sand 81%, electrical conductivity (EC) 37%, sodium 56%, potassium 81%, nitrogen 67%, calcium 56% and magnesium 37% were affected by vegetation covers. The highest SOC was measured in vegetation cover of P. euphratica with a value of 1.24%. P. euphratica had organic carbon 2.21, 1.69, 1.94 and 1.86 times more than that of T. aestivum, D. bipinnata, S. vermiculata and T. ramosissima respectively. However, there was no significant difference in organic matter between vegetation covers of T. aestivum, T. ramosissima, D. bipinnata and S. vermiculata. SOC had the strongest positive (r=0.63) and negative (r=-0.60) significant (P≤0.01) correlation coefficients with the population of phosphate-solubilizing fungi and the sodium concentration of the soil solution, respectively. Also, based on the results of stepwise regression analysis and path analysis, the population of phosphate-solubilizing fungi and cation exchange capacity (CEC) were, respectively, the most effective positive influencing factors. The population ratio of phosphate-solubilizing microorganisms on the total microorganisms, as well as soil EC, were respectively the most effective factors negatively influencing the percentage of SOC in the study area.

In general, the most sensitive land use to changes is P. euphratica forest. Therefore, in order to improve soil quality and increase carbon storage in arid and semi-arid regions, in addition to maintaining and developing P. euphratica forest cover, it is suggested that the management and improvement of soil characteristics include: the population of phosphate-solubilizing fungi, CEC, The population ratio of phosphate-solubilizing microorganisms and EC should also be considered.

Recently, conservation tillage (controlled) as a soil stabilization factor has been given much attention so that the soil is less disturbed and at least 30% of plant cover to remain on the soil surface. This greatly helps to maintain soil structure and moisture, especially in sloping fields. The fields of the Hezarjarib Behshahr region are steep, and due to the cold and dry climate and the wind blowing most of the year, it is very important to stabilize and maintain the soil moisture and structure and prevent it from being washed away by the wind. On the other hand, the sloping lands of this region are under dryland cultivation of wheat and barley, which have little income for farmers and require alternative crops. In this way, Black cumin (Nigella sativa) plant is a valuable substitute for them. Therefore, the purpose of this study was to investigate the effect of controlled tillage to cultivate black cumin plants on energy consumption, physical properties and soil protection, as well as plant performance in the sloping lands of Hezarjarib Behshahr region.

The investigated parameters included the required draft force by tillage tool, tractor fuel consumption, and changes in the degree of soil fragmentation and permeability before and after tillage. The input variables included root cutter supplement in two levels (without and with root cutter), tillage depth in two levels (35 and 28 cm for chisel) and forward speed in two levels (low gears 1 and 2). Considering 3 replications for each treatment, a total of 24 experimental plots with 2m width and 40m length were created with the random complete block design (RCBD) method and perpendicular to the slope. Regarding the yield and yield components of black cumin, after harvest, biological yield parameters, root weight, root length, root diameter, the width of root distribution, number of follicles per plant, number of seeds per follicle, thousand seed weight, plant height, stem diameter and performance were measured per unit area.

The results showed that the effect of the input variables was significant only on the required draft force by tillage tool and the tractor fuel consumption, in addition to the biological yield and the yield per unit area of black cumin. The use of a root cutter increased the required draft force by tillage tool and tractor fuel consumption, while harmed soil permeability and crushing, seed weight, biological yield and yield per unit area of black cumin. The use of higher forward speed leads to an increase in draft force and fuel consumption, and the absence of root cutter, leads to a decrease in soil permeability and fragmentation, biological performance and yield per unit area of the black cumin at a greater depth of tillage, while at a lower depth, no significant (5%) difference can be seen between the two speeds. Increasing the depth of tillage up to the range of vertical root growth due to the negative draft of the tillage tool has reduced the draft force and fuel consumption and had a positive effect on soil permeability and crushing plus crop yield.

The best-researched treatment was the used triple action tillage tool, without root cutter supplement, greater ploughing depth and forwarding with low gear 1. In this way, it will be possible to save 25% in fuel consumption due to the negative draft of the rotary plough, increase the depth of the plough and reduce the required draft force by 25%, increase the biological yield (straw) by 25% and increase the yield by 45%.