نشریه تحقیقات مهندسی سازه های آبیاری و زهکشی
سال بیست و چهارم شماره 91 (تابستان 1402)

Determining the discharge in rivers using the cross-sectional area-velocity method, especially under flood conditions, is associated with serious challenges. Due to advances in measurement techniques, many researchers have strongly suggested the use of non-contact methods. The non-contact method that use surface velocity radar to determine the discharge are becoming more and more popular especially in flood conditions. This method is to use the concept of index velocity based on the generalization of surface velocity to mean velocity and discharge. Also index-velocity method was used for discharge monitoring or recording at streamflow- gaging stations with flow reversals, backwater effects, hysteresis effects and channel-roughness changes that the use of conventional "stage-discharge rating" method impractical or impossible. During floods, natural rivers appear in the form of a compound cross-section in their middle and end sections. Due to momentum exchange between main channel and flood plains, the flow hydraulic in compound channels is complicate. Most studies in index-velocity method are focused on prediction of the discharge in simple channels. Due to the hydraulic difference between the flow of simple and compound cross-sections, the velocity index (ratio of surface velocity to average velocity) for compound channels is still unknown.

The purpose of this study is how to apply the index velocity method in flood conditions (compound sections) and actually determine the optimal velocity index in compound sections and the highest percentage of its location in the width of the compound section. Also, by performing dimensional analysis, the influence of relative roughness parameters, Froude number, relative depth and relative width on the velocity index in compound channels was investigated. In order to build a laboratory compound channel, a channel with a rectangular cross-section with a width and height of 60 cm with a metal frame and glass walls was used. The height of the flood plain in all tests is constant and equal to 7 cm and three different widths of the flood plain 40, 45 and 50 cm in the smooth state and also one state of the flood plain with a width of 40 cm with metal mesh in compound form was made. Velocity distribution measurements were made in the compound channel, in the main channel and floodplain at 7 or 8 transverse points. In the present study, the velocity index in compound channels at a fixed bed slope of 0.1% and for the relative depth of the main section is 4.2-6.12 relative roughness 0.0003-0.0031 and Froude number 0.14-0.79 has been studied.

By examining the velocity index values across the compound cross-section it was found that the range of average of the velocity index in the width of the compound channels is 0.76-0.98 and with 63% relative frequency is in the range of 0.87-0.93. By fitting between all surface velocity and average velocity data in the entire compound cross-section, it was determined that the optimal value of the velocity index (with R2=0.95) for compound channels is 0.88 with value of absolute relative error of about 0.01-10.06% and an average relative error of 3.3%. The results showed that the increase in the relative roughness and Froude number of the approaching flow and the decrease in the relative depth in the floodplain cause a decrease in the velocity index. The relative error values of discharge estimation showed that in flood conditions (overbank), the velocity index value is different from the normal conditions (inbank) of the river and considering the same velocity index value for both normal and flood conditions will cause more error in the discharge estimation. By examining the location of the optimal value of the velocity index of 0.88 in the entire width of the compound section, it was determined that 71% of the density of points is located on the border of the compound channel and in the last quarter of the flood plain and the first half of the main section. Also, the velocity index is 0.92 in the main channel and 0.86 in flood plain, and if use them, a better estimate of the discharge in the compound channel is obtained. Analytical models of velocity distribution also showed that the velocity power law provides the best estimation of the velocity index than other models if the power index is chosen correctly.

The results showed that the use of the velocity index value of 0.88 for compound channels has an average relative error of about 3.3% in flow estimation. Therefore, by adjusting the default value, it is possible to improve the accuracy of flow estimation in flood conditions. In situations where the possibility of direct measurement in open channels (flood conditions) is not available, it is possible to use the cross section, the surface velocity at the border of flood plain and the main channel and the optimal velocity index of 0.88 can be accurately estimated.

TThe operations of cleaning, modifying, reconstructing and implementing concrete coating of the soil sections of the main water transmission channels with a flow capacity of more than 50 cubic meters per second in large modern irrigation networks, urban, rural, industrial water supply, etc. usually have allocated the largest share of investment costs. By considering the optimal hydraulic-economic technical principles, the use of the most effective and new technologies to achieve the goals of efficient and cost-effective technological development to reduce the investment costs of executive and current operations of exploitation to the minimum amount, are the goals of this research. In this regard, in the current research, a movable separating blade wall (with dimensions of 3*0.2*3 m) made of polyethylene or fiberglass materials, on a sled truss structure (with dimensions of 1*0.8*6 m) was installed and assembled and sealed for a length of 100-150 m. To prevent losses and wastage of water due to excessive leakage in earthen channels and without interrupting the flow of water to increase the transmission efficiency, with the recommended method, the necessary and optimal technical hydraulic and economic conditions were provided and made possible to perform concrete coating operations in the soil sections of the main water transmission channel during its exploitation.The operations of cleaning, modifying, reconstructing and implementing concrete coating of the soil sections of the main water transmission channels with a flow capacity of more than 50 cubic meters per second in large modern irrigation networks, urban, rural, industrial water supply, etc. usually have allocated the largest share of investment costs. By considering the optimal hydraulic-economic technical principles, the use of the most effective and new technologies to achieve the goals of efficient and cost-effective technological development to reduce the investment costs of executive and current operations of exploitation to the minimum amount, are the goals of this research. In this regard, in the current research, a movable separating blade wall (with dimensions of 3*0.2*3 m) made of polyethylene or fiberglass materials, on a sled truss structure (with dimensions of 1*0.8*6 m) was installed and assembled and sealed for a length of 100-150 m. To prevent losses and wastage of water due to excessive leakage in earthen channels and without interrupting the flow of water to increase the transmission efficiency, with the recommended method, the necessary and optimal technical hydraulic and economic conditions were provided and made possible to perform concrete coating operations in the soil sections of the main water transmission channel during its exploitation.TThe operations of cleaning, modifying, reconstructing and implementing concrete coating of the soil sections of the main water transmission channels with a flow capacity of more than 50 cubic meters per second in large modern irrigation networks, urban, rural, industrial water supply, etc. usually have allocated the largest share of investment costs. By considering the optimal hydraulic-economic technical principles, the use of the most effective and new technologies to achieve the goals of efficient and cost-effective technological development to reduce the investment costs of executive and current operations of exploitation to the minimum amount, are the goals of this research. In this regard, in the current research, a movable separating blade wall (with dimensions of 3*0.2*3 m) made of polyethylene or fiberglass materials, on a sled truss structure (with dimensions of 1*0.8*6 m) was installed and assembled and sealed for a length of 100-150 m. To prevent losses and wastage of water due to excessive leakage in earthen channels and without interrupting the flow of water to increase the transmission efficiency, with the recommended method, the necessary and optimal technical hydraulic and economic conditions were provided and made possible to perform concrete coating operations in the soil sections of the main water transmission channel during its exploitation.The operations of cleaning, modifying, reconstructing and implementing concrete coating of the soil sections of the main water transmission channels with a flow capacity of more than 50 cubic meters per second in large modern irrigation networks, urban, rural, industrial water supply, etc. usually have allocated the largest share of investment costs. By considering the optimal hydraulic-economic technical principles, the use of the most effective and new technologies to achieve the goals of efficient and cost-effective technological development to reduce the investment costs of executive and current operations of exploitation to the minimum amount, are the goals of this research. In this regard, in the current research, a movable separating blade wall (with dimensions of 3*0.2*3 m) made of polyethylene or fiberglass materials, on a sled truss structure (with dimensions of 1*0.8*6 m) was installed and assembled and sealed for a length of 100-150 m. To prevent losses and wastage of water due to excessive leakage in earthen channels and without interrupting the flow of water to increase the transmission efficiency,

Providing food security in scarcity conditions of water resources requires macro-planning for the supply, allocation and water consumption in different sections such as agricultural section. In Iran, like in other countries of the world, most fresh water resources are consumed in the agricultural sector. In this situation, one of the effective and practical solutions is the optimal use of irrigation water in the agricultural sector, which consumes the most water. The most basic component for optimal irrigation water management in Iran is the awareness of applied water in the production of various agricultural products under the farmers’ management conditions. Therefore, this study was conducted with the aim of appraising irrigation water management indicators such as seasonal applied water, yield , and irrigation water productivity, total water productivity (irrigation water plus plus effective rainfall ) in Azarbayjan Sharghi, Azarbayjan Gharbi, Ardabil, Alborz, Tehran, Chaharmahal and Bakhtiari, Fars, Qazvin, Markazi, Hamedan, Golastan and Mazandaran provinces as peach and nectarine production hubs in Iran.

In this study, a field survey was conducted to measure applied irrigation water and yield under the gardeners’ management in peach and nectarine production hubs. This indicators was measured in 195 gardenes in Azarbayjan Sharghi, Azarbayjan Gharbi, Ardabil, Alborz, Tehran, Chaharmahal and Bakhtiari, Fars, Qazvin, Markazi, Hamedan, Golastan and Mazandaran provinces with different conditions of climates, irrigation methods (surface and drip), salinity of irrigation water and soil; and different peach and nectarine cultivars during growing season 2018-2019. To measuring irrigation water volume, after determining the inflow of water to the garden by carefully monitoring the garden irrigation time and measuring the irrigated area, the volume of irrigation water applied by peach and nectarine trees in each garden was measured. Crop yield was obtained in three consecutive years and their mean was used in the analysis. Irrigation water productivity (WPIrr) and total water productivity (WPIrr+pe) were calcucated as the ratio of yield to applied water and irrigation water plus effective rainfall, respectively. Then, the effect of modern irrigation methods (surface drip irrigation) on applied water, WPIrr and WPIrr+pe were investigated in the study areas. Analysis of variance was used to investigate the possible difference between yield, applied water and WP among the hubs. Data adequacy was assessed by using the method provided by Sarmad et al. (2001)

The results showed that the difference between average volume of water applied by gardeners, yield, WPIrr and WPIrr+pe, in the studied sites were significant at 5% probability level. The average amount of applied water by gardeners in Azarbayjan Sharghi, Azarbayjan Gharbi, Ardabil, Alborz, Tehran, Chaharmahal and Bakhtiari, Fars, Qazvin, Markazi, Hamedan, Golastan and Mazandaran provinces was 8617, 7178, 8140, 8137, 8568, 7763, 8814, 8675, 10806, 6428, 2842 and 2012 m3/ha, respectively, and the average was 6734m3/ha. The yield of peach and nectarine varied from 10 to 50 tons/ha with an average of 20 tons/ha. Irrigation water productivity (WPIrr) varied from 1.6 to 8.6 and its average was 3.06 kg/m3. The average WPIrr+pe for peach and nectarine was 2.44 kg/m3. The results showed that the average applied water for peach and nectarine orchards in the study areas except for Golestan and Mazandaran provinces for surface and drip irrigation methods were 9325 and 7098 m3/ha, respectively, (p<1%). Therefore, in drip irrigation method, applied water was 25% less and WPIrr was 34% higher.

In general, the results of this study provide useful information on irrigation water management indicators in peach and nectarine production to managers and water decision makers within Iran. Accordingly, in order to reduce the volume of irrigation water and improve peach and nectarine water productivity, it is recommended to use drip irrigation method in suitable climatic conditions where irrigation water is of good quality and the technical criteria of design, implementation, operation, and economic considerations are met. Also, training and application methods to improve the performance of surface irrigation to reduce evaporation and applied irrigation water is recommended.

Water management in the agricultural sector is very important as the largest consumer of water resources in the country. Estimation or determination of water use management indicators, including the amount of water consumed, irrigation efficiency and water productivity of various agricultural and horticultural crops in the country, is one of the most important key indicators in macro-planning related to supply of water, allocation and consumption in different sectors including agriculture. The volume of water used by agricultural crops as one of the indicators for evaluating the optimal use of water resources and plays a very important role in the management and macro-planning in the field of water management and engineering. Barley plant is cultivated and produced in almost all the countries of the world and it is considered as the fourth grain in the world in terms of production after wheat, corn and rice. In Iran, barley with a cultivated area (irrigated and rainfed) of more than 1,684,000 hectares and with a production of more than 3,176,000 tons, after wheat, it is the most important crop and is cultivated in most parts of the country due to its wide ecological compatibility. Due to the economic importance of barley production in the country, it is necessary to study the volume of irrigation water and water productivity to produce this strategic product.

In Khorasan Razavi province, 2 cities with the highest area under barley cultivation were selected for evaluation, Sabzevar and Neyshabur. To conduct this research, 12 fields in Sabzevar region and 12 other fields in Neyshabur region have been selected. The volume of irrigation water was measured in these 24 fields during the irrigation season. The measurements were carried out in different irrigation and planting methods, various soils, different salinity of irrigation water and soil and different barley varieties during the growing season of 2021-2022 without interfering with the farmer's irrigation management. The measured values were compared with the gross irrigation water requirement estimated by the Penman-Monteith method using the last 10 years meteorological data and also with the national water document values. Crop yield was recorded at the end of the growing season and water productivity was calucated as the ratio of yield to total water (irrigation applied water and effective rainfall).

The results showed that the amount of applied water, the amount of barley yield and the water productivity in Sabzevar region were 4710 m3/ha, 2.86 ton/ha and 0.77 kg/m3, respectively. The amount of applied water, the amount of barley yield and the water productivity in Neyshabur region were determined as 4408 m3/ha, 2.54 ton/ha and 0.61 kg/m3, respectively. The volume of barley irrigation water in the studied areas varied from 2393 to 7911 and its weighted average (based on the cultivation area) was 4593 m3/ha. While the average gross requirement of irrigation water in the studied areas using the Penman-Mantis method using meteorological data of the last ten years and the national water document was 9111 and 8489 m3/ha, respectively. The average yield of barley in the selected fields varied from 1600 to 5600 and its weighted average was 2310 kg/ha. Irrigation water productivity in the selected farms varied from 0.24 to 2.34 and its weighted average was determined to be 0.58 kg/m3. The applied water productivity in the selected farms varied from 0.21 to 1.57 and its weighted average was determined as 0.45 kg/m3.

According to the results of this research, in the two regions of Sabzevar and Neyshabur, the weighted average (based on the area under barley cultivation in the two regions) of the volume of irrigation water and the irrigation water productivity in barley fields are 4593 m3/ha and 0.58 kg/m3, respectively. It was obtained. The amount of irrigation water in the production of barley in these two regions is about 5.8% less than the national average and the applied water productivity is about 35.6% less than the national average. The calculated gross irrigation requirement was obtained by using the national water document and the book "Estimation of water requirement of agricultural and horticultural plants of the country", respectively 9111.3, 8489 and 8566 m3/ha. In terms of the share of effective rainfall in irrigation water, the results showed that 37 and 27% of the amount of irrigation water was supplied through effective rainfall in Neyshabur and Sabzevar, respectively. By comparing the amount of irrigation water used by farmers in the barley fields with the gross irrigation requirement, the result was that the farmers did not have enough water for irrigation and Unintentionally, they have done deficit irrigation in the barley fields, and in fact, the farmers have done irrigation as much as they had water.

The fundamental principles of smart irrigation hinges upon precise assessments of soil moisture content within the root zone layer. Various techniques have been developed to ascertain root zone soil moisture content, such as using soil moisture measurement sensors or simulation models. Each one of these methods has its own distinct advantages and disadvantages. Data assimilation encompasses an array of approaches that combine model estimates with the corresponding observed data to derive a more precise estimations of the required data. The purpose of this research is to ascertain the feasibility of reducing the number of depths at which soil moisture measurements were taken and increasing the time interval between two consecutive soil moisture measurements using the Ensemble Kalman filter.

This study was conducted synthetically based on information collected from four farms in Jovein, Khorasan Razavi Province, cultivating sugar beets and corn. Data was collected from four farms during the period of April to November 2020. The numerical solution of the Richards equation with the inclusion of the sink term was used to simulate the soil moisture changes in the root zone layer. To mitigate data assimilation's vulnerability to potential result divergence among members, an identification and correction mechanism, along with handling divergent members, were integrated into the system. This mechanism was found on the sudden model result shift throughout the entire root profile between two consecutive days. Two indicators were used to evaluate the scenarios: a) the sum of covariance matrix diameters at the last simulation time step, and b) the normalized root mean square difference of the soil moisture content within the soil profile, comparing the scenarios with the scenario having the largest number of soil moisture measurement depths and the shortest time interval between two consecutive measurements.

The results indicated that with the application of Ensemble Kalman filter, it is possible to improve the accuracy of the results using a longer time interval between measurements. The Data Assimilation scenarios exhibited a remarkable capability in reducing the diameter of the covariance matrix. This reduction, ranging from 61% to 86%, compared to the open-loop scenario, emphasizes the ability of Ensemble Kalman filter to effectively mitigate uncertainty. The normalized root mean square difference , was notably improved by the Data Assimilation scenarios. The normalized root mean square difference of scenarios ranged from 0.03 to 0.11, while the normalized root mean square difference for the Open Loop was 0.15, highlighting the capacity of Ensemble Kalman filter to minimize discrepancies between simulated and observed soil moisture profiles. Such reductions in normalized root mean square difference values signify the model's improved ability to capture actual soil moisture variations, thus contributing to more reliable predictions and better decision-making in agricultural water management. The application of Ensemble Kalman filter helped to select the proper measurement depths and ultimately to reduce the number of required soil measurement points.

Data Assimilation successfully diminished the uncertainty of the soil moisture content results, even when utilizing the minimum number of soil moisture measurement depths and maximum time intervals between observations. Both of these findings—increasing the time interval between consecutive measurements and reducing the required number of measurement depths—indicate that with the application of data assimilation, it is possible to decrease the cost of the implementation of the smart irrigation.