جستجوی مقالات مرتبط با کلیدواژه "مخزن سد" در نشریات گروه "آب و خاک"

reservoirs are very important for storing rainwater and floods, and water shortage management. In nearly all reservoirs, storage capacity is steadily lost due to trapping and accumulation of sediment. Sediment deposition in water reservoirs has major implications for storage capacity, reservoir lifetime and water quality. The present study aimed to evaluate the temporal dynamics of water stored and sedimentation rate in a reservoir using remote sensing data. For this purpose, the study was carried out in O. H. Ivie reservoir located in the America country. The techniques used to carry out this study have been pre-processing of Landsat 8 images, modeling and identifying water pixels using MNDWI index, evaluating reservoir capacity, and compression of results with recent bathymetric survey data to assessment sedimentation rate. According to the results, the average errors of computing the volume of water stored in the reservoir was about 9%. Based on this, the storage capacity of O. H. Ivie reservoir has decreased from 695 million cubic meters at the beginning of operation (1991) to 472 million cubic meters in 2019. The results showed that the lost storage capacity of the reservoir due to sedimentation is about 32% of the original volume and the annual sedimentation rate is 1.4%. Also, by evaluating the obtained results, the average height of sediment deposited in the reservoir between 2004 and 2019 was estimated to be about 9 meters. This research confirmed that remote sensing can estimate storage capacity and sedimentation rate in the reservoir with minimal cost and time.

This paper presents a novel technology for desilting dam reservoirs in a continuous and controlled manner. The proposed technology utilizes a suction system that incorporates two pumps: a dredge pump for removing and transporting sediments, and a high-pressure submersible pump for generating water jets to create turbulent flows in the bottom sediment layers. To evaluate the effectiveness of the proposed technology, local experiments were conducted in two cases: with the suction pump alone and with the addition of water jet flow. These experiments were conducted at the end of the reservoir of Zenouz Dam, which serves as a case study. The collected sediment mass was measured over time, and the resulting mass-time graphs revealed three distinct phases: ascending, descending, and constant. Based on the local conditions, soil properties and dredging system, the maximum sediment mass removal rates by the pump were 100 g/s for the case without water jet and ranged from 200 to 430 g/s for the case with water jet. Dimensional analysis was performed to determine the relationship between sediment yield and parameters such as sediment volumetric flow rate and sediment mass flow rate. The results showed that the variations of sediment discharge followed the same characteristic curves (discharge - height) of the pump. The average de-sedimentation efficiency was found to be 7-14% and 2-3% for the experimental pump modes with and without the jet flow, respectively. This indicates that the water jet flow has a significant influence on enhancing the de-sedimentation efficiency, and without it, the sediment removal would not be feasible.

This research, using the CE-QUAL-W2 hydrodynamic model, investigates and simulates the dissolved oxygen (DO) parameter in the Ekbatan dam reservoir under the influence of thermal stratification and temperature changes. Ekbatan Reservoir plays an important role in providing drinking and agriculture water in Hamedan city, so checking its water quality seems essential. The results show that the CE-QUAL-W2 model simulates well the temperature changes of the reservoir by considering the volume and geometry of the reservoir and meteorological parameters. Due to the fact that dissolved oxygen is affected by thermal stratification, the relationship between these two parameters has been investigated and the possibility of evaluating water quality through thermal stratification of the reservoir has been presented. The results show that thermal stratification in Ekbatan reservoir has periods of thermal stratification change and is complete in summer, while complete mixing occurs in autumn and early winter. These changes also affect the DO stratification in the reservoir. With a 68 percent increase in temperature, the DO concentration decreases by about 37.5 percent, and with a decrease in temperature, the DO concentration increases in the same proportion. In addition, the research results show that changes in air temperature have a significant effect on the concentration of DO in the reservoir. The change in temperature leads to a decrease in the density of water and a decrease in the solubility of oxygen in water, which in turn leads to a decrease in the concentration of DO in the reservoir water, and this issue is widely considered in environmental studies and water resources management.

So as to conserve and manage reservoirs effectively, a comprehensive awareness is necessary for the spatial and temporal pattern of water quality.  

. In this research, a three-dimensional EFDC dynamic environmental model has been utilized, for the assessment and simulation of the thermal-regime and quality parameters of the Mamloo-Dam Reservoir. The information required for the calibration and validation of the model in the 12 months of the year of 2019, has been taken from 6 stations.

The thermal stratification has prolonged, for several months. Stability in stratification has obstructed the transfer of oxygen to the lower layers and the dissolved oxygen (DO) concentration in the hypolimnion, decreases intensely, in to less than 2 mg/L. In the entire seasons of the year, the highest concentration of Chlorophyll is relative to photic zones (with highest concentration 35.6 µg/L in august). The phosphorous factor restricts the growth of algae in the reservoir; and a high correlation between the modifications in total phosphorous concentration and chlorophyll was observed. The trend of modifications in total nitrogen illustrates its control by external input loads. Furthermore, the results attained in comparing the simulated and real values (R2 and RMSE values), display that the EFDC model has the capacity to simulate the hydrodynamic and qualitative parameters of the Mamloo-Dam Reservoir. Moreover, provided appropriate statistical indicators (RMSE=0.15, R2=0.72) in water level simulation.

Obstacle usually blocks the current and it has been found by other researchers an obstacle with a height more than two times of body height of flow is necessary to fully block the density current. The construction of an obstacle with this elevation creates problems in terms of performance and sustainability as well as the accumulation of sediments behind it.Rottman et al. (1985) solved the analytical solution of the two-phase current in a horizontal slope with an obstacle in the steady and unsteady flow and concluded that if the height of the obstacle is twice the body height of the density current so the density current is completely blocked. Prinos (1999) conducted studies on the effect of the shape of the obstacle on the current control. In his experiments, he used two semi-circular and triangular obstacles with the same height and concluded that the shape does not have a significant effect on the control of high current. Also, in the range of densimetric Froude number, 0.7 < Frd < 0.8 if the height of the obstacle is twice the height of the body of the density current, the current will be fully restrained. As it has been stated, for a complete block of density current, based on the results of previous investigators, the height of the obstacle should be at least twice the height of the body.The purpose of this study is to use successive obstacles with lower height, with greater sustainability and lower cost, in controlling density current. For this purpose, in different conditions, in terms of slope and concentration, three rows of obstacles with different heights and also different distances were used to control sedimentary and salty density current.

Pressurized flushing is one of the techniques for evacuating sediments from reservoirs. In this study, the impact of submerged vanes on performance of pressurized flushing were investigated. For this purpose, submerged vanes with convergent, divergent and combined arrangements in three distances from the bottom outlet (), three middle distances () and three heights above the sediment bed () were used and the results were compared with the non structural test (reference test). The results showed that the submerged vanes by creating rotational flow and turbulence, enhanced the performance of flushing and also by evacuating much sediment below the bottom outlet, the amount of evacuated sediments increased in all experiments. As, in the convergent and divergent arrangements, the volume of evacuated sediments increased respectively 6.5 and 48 times compared to the non structural test. Also, in the combined arrangement with two-row divergent of submerged vanes, in 0.5, 0.3 and 1, the volume of flushing cone increased 51 times compared to reference test. Finally, by using a polynomial correlation with vane spacing, a non-dimensional equation for estimating the scour cone volume was proposed.

One of the most important problems arising after the construction of a dam is sedimentation in the dam’s reservoir. In turn, one of the phenomenon that may affect the sedimentation is density currents. A density current is, indeed, the movement of a fluid through another one that has a different density. If there was saline stratification in the vertically downward direction in the reservoir of the static fluid, density current occurs as interflow. Kao (1977) derived the flow diffusion velocity along a common surface between two homogeneous fluids based on Bernoulli's theory. Likewsie, Ungarish (2012) and Sahuri et al. (2015) conducted studies on the interflow density current.

The experiments were conducted in a flume of 8 meters long, 34 centimeters wide and 70 centimeters high. To that end, a solution of water and salt was used to form the ambient fluid with saline stratification and a mixture of water and sediment particles as the dense fluid. 48 experiments were, then, carried out with 4 discharges (1, 1.5, 2, and 2.5 l/s), 3 slopes (2.5, 3.25, and 4 percent) and 4 concentrations (5, 10, 15, and 20 g/l). The motion of the interflow density current in a layered fluid is like that the flow entering the reservoir first expands as an underflow current and after moving a distance, it enters through saline layers of the fluid with saline stratified layers. The current, then, separates itself from the bed at a location in the reservoir where the density of the dense flow equals to that of the layered one. This way, the current finds the suitable density in its environment and moves in a horizontal layer (Fig.1).

Monitoring the quality of water resources and reservoirs is very important however water sampling is a very time consuming, costly and sometimes dangerous task. Satellite and aerial images from surface water could be applied to monitor water quality parameters of different water bodies effectively. In this research the possibility of estimating and monitoring chl-a concentration in Ekbatan reservoir is evaluated using Landsat 7 images. Different conversions were applied to bands reflectance and the relation between chl-a concentration with reflectance were examined and derived. Then the best model for estimating the concentration of chl-a was selected. The results of study showed that the equation based on the band ratio have the most precise estimate between all models. The value of R2Adj and SE were 0.91 and 0.04 respectively. The results show that using Landsat 7 images the concentration of chl-a could be estimated accurately.

Turbidity currents are the main process for the transport and deposit of sediments in reservoir, especially in the deepest part near the dam, where vital structures such as power intakes and bottom outlets are located. The existence of an obstacle in such current can cause a decrease in the velocity and thickness of the second turbidity current which, occurs after the obstacle. In this study that was carried out as a two-dimensional experimental study, the effect of a solid obstacle, its height on the vertical distribution profiles of the velocity, when there is an abrupt decreasing in the bottom slope, was investigated. Separate non-dimensional equations for the vertical distribution of velocity in different cases were developed. The coefficient of the non-dimensional equations were compared with each other. Results indicated that the existence of an obstacle can reduce the velocity of the turbidity current, which passes the obstacle, about 20%-50%, and also can reduce the discharge of the current by increasing the relative height of the obstacle from 0.0091 to 0.273 by about 20% -60%, respectively. This effect on turbidity current’s velocity and discharge would be increased by the increasing the height of the obstacle. The results also indicate that the highest change in the current discharge occurred in the jet region of the velocity profile.

Reservoir storage is essential for developing dependable water supplies and is a major component of the river system water budget. The storage contents of reservoirs fluctuate greatly over time with variations in water use and hydrologic conditions that range from severe multiple-year droughts to floods. Water surface evaporation typically represents a major component of the reservoir water budget. Estimates of the amount and rate of evaporation from open water surfaces are required in water resource management for a variety of purposes, such as the design of storage reservoirs, catchment water balance studies, municipal and industrial water supply, irrigation of agricultural lands and management of wetlands. The impacts of reservoir evaporation on water management vary greatly based on location with differences in climate, reservoir characteristics, and water management and use practices. Determining evaporation rates is essential for efficient management of reservoirs and water resources, particularly in water-scarce countries such as Iran. It is estimated that open water reservoirs in Iran lose high volume of their total water storage capacity per year by evaporation. For example, this loss is around 13% of the volume of inflow to KHARKHEH Dam per year. While this loss is of significant concern, the threat of a changing climate has been directing greater focus to how much water will be lost from Iran’s reservoirs in the future. As a result of the change in climate, particularly the increase in surface air temperatures, evaporation is also expected to increase throughout Iran. This paper analyses evaporation rates from Dez dam reservoir for the two periods (2021-2050 and 2051-2080) under modeled climate change conditions using five General Climate Models (GCMs) with A2 emission scenario. Global climate models, also known as general circulation models (GCMs), are models which solve the primitive equations of mass, momentum and thermodynamics to generate a description of the state of the atmosphere, and produce most of the meteorological variables, such as wind speed, relative humidity, rainfall, surface air temperature and solar radiation. The GCMs are typically used together, as a multi-model analysis, where long time series into the future and different GHG emission scenarios are used in order to create climatic statistics. Inherent to GCMs, however, is their coarse spatial resolution which amongst all the available models varies from 200 to 500 km. With this resolution, albeit GCMs incorporate the important large-scale atmospheric circulation, they are unable to capture local-scale factors such as the orographic elevation, proximity to water bodies and local winds. Therefore, the outputs of GCMs need to downscale for applying to modeled evaporation. Daily meteorological prepared using K-NN downscaling model to estimate evaporation rate from open surface water using equations derived from penman equation. The K-NN downscaling model is a nonparametric resampling method for generating new data series. This method simulates daily precipitation for a weather station by combining a stochastic weather generator model (based on non-parametric K-Nearest Neighbor approach) with future climate scenarios that are established based on projected monthly. In this study, an equation based on penman equation for situations where no wind data are available is used to estimate evaporation rate. The equation is validated by compared to the penman equation in estimating the evaporation rate in a meteorological station that has the same climate as DEZ dam. Then, evaporated volume, which is estimated using area-capacity relations of Dez dam, were compared with observed meteorological variables for the period of 1982–2011. Area-capacity curves are usually used for reservoir flood routing, reservoir operation, determination of water surface area, and capacity corresponding to each elevation, reservoir classification, and reservoir sediment distribution. In this study, a dimensionless curve is used to estimate the changes of capacity in relation to the changes of evaporation rate. Results of the application of the presented model for downscaling monthly precipitation outputs of GCMs show that the model has a high capability for downscaling precipitation. So, the used equation to estimate the evaporation rate is suitable for applying in DEZ dam station. Also, the results showed that the volume of average annual evaporation from the study reservoir will increase about 7% in 2021-2050 and 10% in 2051-2080 more than base period. The main reason of this increase can be global warming in the future. According to the modelling results, the mean annual air temperature will be increased by 1.3C and 3C in 2021-2050 and 2051-2080 respectively. This will have a significant impact on the evaporation rates, especially in spring and summer which the increases in temperature will be too high.

In the last century, dams have constructed with the objective of water supplies for agriculture, drinking water and industry. However, the results from the performance review of dams show adverse effects on the downstream environment and the availability of water resources. The purpose of the Chashm dam construction on the TalarRiver's tributaries is the water supply for Semnan city.
This study was conducted in TalarRiver watershed. TalarRiveroriginatesfrom AlborzMountains in Mazandaran province, in the southern Caspian Sea basin, in north of Iran and flows parallel with the Firouzkooh-Ghaemshahr road and it arrives to the Caspian beach area in the Malek Kala village. In order to supply the water requirements of Semnan city, the construction of Chashm dam on the TalarRiver's tributaries placed on the agenda of the Ministry of Energy. However, because of the uncontrolled exploitation of agricultural streams and invasion of privacy riverbed, the TalarRiver has acute and critical conditions from the point of hydrologic and environmental. To study the hydrological impacts of Chashm dam, Talar watershed was considered with an area of approximately 1057 square kilometers of the Pole Sefid gauging station using a rainfall-runoff model.
Simulation of the study area hydrological behavior shows that the Chashm Dam average water discharge is near to 8.6 million m3. This figure will be significant changes during wet and droughtperiods. The minimum and maximum monthly discharge of the Chashm Dam watershed in August and February is equal to 0.31 and 0.55 m3/s respectively. The minimum and maximum monthly water demand in turn in October and August is equal to 0.015 and 0.4 m3/s respectively and this shows that the river discharge in June is lower than the downstream water demand. Based on confirmed studies of the Kamandab Consulting Engineers, drinking water requirement of Semnan province, water rights user's requirement and downstream environmental requirements are 4.54, 2.164 and 2.448 million m3, respectively. This is despite the fact that the volume of annual input water is slightly lower than this figure in normal.
Simulation of the study area hydrological behavior shows that the Chashm Dam average water discharge is near to 8.6 million m3. This figure will be significant changes during wet and drought periods. The minimum and maximum monthly discharge of the Chashm Dam watershed in August and February is equal to 0.31 and 0.55 m3/s respectively. The minimum and maximum monthly water demand in turn in October and August is equal to 0.015 and 0.4 m3/s respectively, and this shows that the river discharge in June is lower than the downstream water demand. Based on confirmed studies of the Kamandab Consulting Engineers, drinking water requirement of Semnan province, water rights user's requirement and downstream environmental requirements are 4.54, 2.164 and 2.448 million m3, respectively. This is despite the fact that the volume of annual input water is slightly lower than this figure in normal. In addition, the Chashm Dam area is about 110 hectares and given the minimum annual actual evaporation equal to 700 mm, about seven hundred thousand cubic meters of water stored in the reservoir will be lost. Due to the simultaneous occurrence of the maximum water requirement, maximum evaporation and a minimum of water inlet to the Chashm Dam reservoir in warm seasons, it seemsthat, it is not possible to provide needs based on these studies and no doubt, in the case of water supply in Semnan province, we have to stop the flow of the river in downstream of the dam. The results of this study suggest that on many rivers large headwater dams have reduced the frequency and duration of floodplain inundation downstream and these changes lead to changes in downstream ecosystems. The results from the simulation and analysis of the Chashm Dam in downstream are as follows: a) stop of the river flow in downstream of the dam site, b) the sharp decline in river discharge in minimum (varied) flows, c) reduce in the rate and volume of maximum flows, d) changes in the hydrological regime of the river such as base flow, flow stop, the frequency of the river full section and competency which will make dramatic changes in the morphology of the river and downstream ecosystems. Note that is not verified by modeling and forecasting studies, is how to manage the reservoir. The amount of water stored in the reservoir and discharge to downstream is directly a function of the reservoir management.

Qualitative and quantitative management of water resources to meet the demand for different usages is the major approach in each country policy. In this regard, dam reservoirs water quality monitoring is an important step in the management of these resources. This study investigated the prediction of dissolved oxygen in a gauging station in the Boulder reservoir (USA) by artificial neural network, multi linear regression and conjunction of wavelet analysis and artificial neural network models. In the proposed wavelet analysis and artificial neural network model, observed time series of dissolved oxygen was decomposed at different scales by wavelet analysis. Then, total effective time series of this water quality index was imposed as inputs to the artificial neural network model for prediction of dissolved oxygen in one month ahead. Results showed that the wavelet analysis and artificial neural network combined model performance were better in prediction rather than the artificial neural network and multi linear regression models. Using wavelet analysis improved the modeling results considerably. In the combined model, determination coefficient, E, and RMSE is obtained 0.96 and 0.22 respectively. Artificial neural network and the combined wavelet with artificial neural network models produced reasonable predictions for the minimum values that lead anaerobic condition in reservoir.

In this article the new sediment module of WASA-SED that aims at simulating the process of sedimentation in reservoirs is developed and evaluated. To evaluate this new module of WASA-SED، the process of sedimentation in Barasona dam reservoir (Spain)، located in a region with high erosion، was examined. The most important parameter in the simulation of sedimentation in reservoirs is to determine the thickness of the active layer. Hence، for the calibration of the model، the relevant data of two time intervals when one was related to the period of normal operation of the reservoir (1986-1993) and another one to a period of the operation time along with the flushing (1995 to 1997) were used. After determining the active layer thickness، the sedimentation process was simulated for the period 1998-2006. The results of the simulation were compared with the dam reservoir hydrographic information. The results of the comparison showed that the new module of WASA-SED for simulation of sedimentation in dam reservoirs in regions with high erosion had a proper accuracy.

Pressurized sediment flushing is one of the methods for removing deposited sediment in reservoirs of dams. In this method, by opening the bottom outlet, deposited sediment in the vicinity of the bottom outlet is flushed out. In this study by performing experiments on a physical model, the effect of a semi-cylindrical structure in front of a bottom outlet on increasing pressurized sediment flushing capacity was investigated. The Semi-cylinderical structure used in the experimnts was closed at the upper side and had an opening width equal to the bottom outlet diameter at the upstream. Also in the all experiments the height of the structure was six times greather than the bottom outlet diameter and the level of the sediment layer was tangent to the bottom outlet. The experiments were conducted with four different discharges released from the bottom outlet, three water depths above the bottom outlet and four diameters of the semi-cylinderical structure. The results of the Experiments indicated that using a semi-cylinderical structure can increase sediment flushing capacity up to 10 times in contrast to nonstructured case. For a fixed depth of water, an increase in outflow discharge increased scour cone depth. Also for a fixed amount of outflow discharge and structure diameter, changes in water depth had almost no effect on scour cone depth. Also the results indicated that at a constant water level for each outflow discharge there was a proper diameter for the semi-cylinderical structure.

In recent decades and by beginning of new century, one of earth planet's inhabitant population's worries and particularly countries located in dry lands such as our country is water problem in a way that availability to water with appropriate quality and quantity has been converted to a challenge. Temperature related features and stability of reservoirs could be predicted by use of mathematical modeling and in case of environmental problem, can be taken remedial way for decreasing problems by various ways. A vertical two-dimensional laterally averaged hydrodynamic and water quality model (CE-QUAL-W2) was used to simulate the hydrodynamics, temperature, and water quality in the Shirin Darre Reservoir over the years 2011 through 2012.Considering that the eutrophication of the Shirin Darre reservoir have been increased since in early August and reached to thehighest level in September until that the reservoir entered in eutrophication condition, the calibrated model was then applied to simulate water quality response to various nutrient reduction scenarios. Results of the model reveal that a 60% to 70% reduction of phosphorus loads will improve the water quality from eutrophic to mesotrophic. Also that, in the long term, with proper management strategies of reducing watershed nutrient loads can improve the water quality of this reservoir. The modeling effort has yielded valuable information that can be used for decision makers for the evaluation of different management strategies of reducing watershed nutrient loads.

Density of deposits is bounded on different variables e.g. physical properties of sediment particles, rate of deposit's layer compaction and type of reservoir operation. These criteria have uncertainty and so the specific weight of deposits has the same problem. In this paper, the effective factors that influence the density of deposits in the reservoirs had been classified and then the basic concept of Delta method was stated as one of the popular techniques for analysis of uncertainties. Further, the case of Kenny reservoir in the White River basin at northern Colorado was selected to determine the specific weight of deposits in the reservoir and the coefficient of variation. The results of this investigation indicate that in the case of Kenny Reservoir the density of deposits is 1267 ± 125.6 (Mean ± SD) kg/m3, and the coefficient of variation of specific weight for accumulated deposits equals 9.9% for the period of 15 years of reservoir operation.

In this study، Doroodzan dam reservoir was sampled over 26-month period and twice per month at different depths and chloride concentration were measured. Based on the measured data، HEC5-Q model was calibrated and then used to simulate the reservoir. Mean Concentrations of observed and simulated chloride in the first year were 52. 9 and 55. 6 and in second year 79. 7 and 85. 8 mgL-1، respectively. The variations of measured and predicted Cl concentrations in the first year were between 33. 7-106. 4 and 33. 2 - 84. 9 mgL-1، respectively and in the second year 28. 4-177. 7 and 28. 6-169. 0 mgL-1، respectively. The maximum Cl concentrations in the first and second years were 106. 4 and 177. 7 mgL-1، respectively. Comparison of predicted concentrations and amounts of statistical parameters including d، RMSE، and MAE showed that predicted values in both years were in close agreement with observed data.

In this research the thermal stratification of the water in the Torogh Dam Basin and the resulted changes in its quality with respect to temperature, salinity and dissolved oxygen was investigated using the Dynamic Reservoir Simulation Model. The results indicated that in wet years such as 1998, when the average annual precipitation and the resulted inflows to the basin is higher than its long-term average, the water level in the basin reaches above 50 m. Under such conditions, thermal stratification starts from mid-spring and lasts to the end of summer, and establishes through the total depth of the basin. Consequently, considerable changes in water quality occur through the depth. However in dry years such as year 2000, the water level in the basin diminishes considerably (16 to 20m in depth) and thermal stratification either does not establish or if establishes, it is incomplete, starts much earlier and persists for much shorter periods of time. On the basis of the model’s results, the differences observed in the average temperatures of the surface and deep layers of the basin during the spring and summer seasons of 1998 were 10◦C and 11◦C, respectively while in the spring of 2002, the observed difference was only 1.5◦C. The results of the study also showed concurrent occurrence of salinity stratification with thermal stratification which results in increase in salinity with increase in depth. The difference between salt concentration of the surface and deep water layers of the basin was observed to be 43 mg/lit in the spring of 1998 and 10 mg/lit for the summer of the same year. In regard to the dissolved oxygen concentration, the simulation results showed a difference in the range of 0 to 9 mg/lit between the surface and deep water layers. With the start of stratification, oxygen concentration decreases gradually with depth., such that in July the lowest 10m layer of the basin becomes completely anaerobic, providing conditions for production of undesired odors, tastes and color. During the period of 1998 to 2004 (period of data analysis and simulation run), the water quality of the basin was observed to be uniform in autumn and winter months indicating a complete mixing condition in the basin.