Flow velocities within most of the M akhool-Samaraa Reach of the Tigris River are considered high compared to the local and worldwide flow velocity ranges. Toffaleti sediment transport function with the Van Rijn fall velocity and the effective depthto-width computation methods are the most compatible and suitable methods for computing the Sediment Transport Potential (STP) in the M akhool-Samaraa Reach of the Tigris River. The computed STPs in the M akhool-Samaraa Reach of the Tigris River are considered high on local and global scales, especially during high flow. M edium gravel is the larger grain gradation class that can be transported. However, the suspended sediment is the dominant part of the Sediment Transport Capacity (STC), with a great majority of clay and very fine silt. This paper implemented an HEC-RAS-based steady two-dimensional hydrodynamic model to evaluate the hydraulic characteristics and Sediment Transport Capacity (STC) of the M akhool-Samarra Reach of the Tigris River, where this part is not already investigated. This model was prepared with the aid of topographical surveys, hydraulic measurements, and laboratory tests, as well as recorded data. The main findings show that the flow velocities within most of the studied reach are considered high compared to the local and worldwide flow velocity ranges in natural rivers. Also, the Toffaleti sediment transport function with the Van Rijn fall velocity and the effective depth-to-width computation methods are the most compatible and suitable methods for computing the Sediment Transport Potential (STP) in the studied reach.With the maximum flow, the computed STP was less than the average (5.7×10 6 tons/day) in 45% of the reach length, where the maximum STP is 8.7×10 6 tons/day. However, with the minimum flow, the STP intermittently fluctuates below the average (0.2×10 6 tons/day) in 48% of the reach length, where the minimum STP is 0.14×10 6 tons/day. Generally, these STPs are little more than the Tigris River in M osul and much higher than that in Baghdad. Also, these STPs are considered high on a global scale, especially during high flow. M edium gravel is the larger grain gradation class that can be transported. It constitutes less than 0.00005 % of the STP. Furthermore, the STC computations clearly show that the suspended sediment is the dominant part of the STC and the bed material constitutes less than 0.002% of the STC of the total load. However, most of the STC concerns the clay and very fine silt.
Worldwide and especially in less developed regions, process-based evaluations and/or geomorphological information on large-scale rivers are still scarce. Such investigation become of urgent need due to the climate change and expected occurrence of extreme floods and drought which may threaten the safety of nearby and downstream cities, especially in regions that are highly sensitive and affected by climatic changes. The Tigris River, in Iraq, is one such river that has undergone significant alteration to its flow and morphologic aspects due to climate change and the construction of many dams. However, morphology and its change for many reaches of this river are still uninvestigated. To this end, field and satellite-based investigations into the morphology of a reach located between Makhool District and Tikrit City have been conducted. In addition to the cross-sectional survey-based determination of the reach geometrical aspects, a sinuosity indices-based evaluation of the reach planform was implemented, utilizing a satellite indices-based approach. Furthermore, the characteristics of bed material were identified through field sampling. Investigation results show that the reach has a steep bed slope and many islands of low altitude with an elongated shape. The reach has a mild sinuosity with alternating bars. The dominant particle sizes of the bed material are coarse and medium gravel with a dominant particle shape of disc particles. Moreover, the satellite-based change detection indicated the fading out and disappearance of some secondary channels, the growth of many islands, and the movement of some bends downstream. The percentage of changing parts for the period 1975–2021 is 14%. Most of this change, 11%, occurred after the construction of the Mosul Dam. This reveals the sensitivity of reach morphology to flow change due to the construction of dams. The conducted fieldwork and the applied methodology contribute to supporting efforts to add knowledge worldwide about uninvestigated rivers. Doi: 10.28991/CEJ-2022-08-07-03 Full Text: PDF
A small aspect ratio of submerged vanes when used near the outer bank at the angle of attack between 10° to 20° and at the initial height above the bed between 20-40% of flow depth is considered one of the most successful river training structures. Vanes when located within the bends of river, produces helical swirls at inverse action with the centrifugally secondary current action. Accordingly, its existence leads to mitigate the influence of the secondary current, thus reducing the outer bank erosion. The present study aims to investigate the effect of distance which measured from the outer bank (δb) on the hydraulic performance of vanes when it arranged at a specified configuration within 180° bend. As a result, when the submerged vanes have been installed at δb/b = 0.25 within the third to the fifth sectors of bend and δb/b = 0.1 within the sixth sector at a zigzag pattern led to lesser outer bank scour with the Percentage Improvement (PIindicator) equal to 72.71%.
River engineering investigations require some level of hydrodynamic and morphologic analysis. The detailed of the hydraulic and morphologic features through meander evolution can be recorded by the numerical model spatially and temporally. The Center for Computational Hydro-science and Engineering, two- dimensional model (CCHE2D V3.29) was adopted to investigate the hydraulic and morphologic changes through meander’s evolution. Through the experimental work, a series of experiments runs were carried out through combining different geometric and hydraulic parameters to produce different experiment conditions. These parameters are flow rate, bed slope, and different initial incised and wide channels for both rectangular and trapezoidal sections. The CCHE2D model was calibrated and verified using two sets of experimental data. According to the computed values of statistical indicators, BIAS, NSE, and MAE of 0.0084, 0.96, and 0.0132 respectively for water level simulation, and 0.007,0.94, and 0.0182 respectively for bed level simulation, the calibrated Manning’s roughness which gives an acceptable agreement between simulated and measured water and bed levels was 0.029. The verification results were evaluated by the same statistical indicators of BIAS, NSE, and MAE of 0.09, 0.81, and 0.018, respectively, as evidenced by the statistical indicators, values that the CCHE2D model was reasonably capable of simulating the hydraulic and morphological changes through meander evolution.
Abstract:The experimental program of this paper was restricted to free vertical drop structure at the end of the rectangular channel. The roughness and slope of the bed of approach channel are the aim of this study to show their effects on End Depth Ratio (EDR). Three different roughness from smooth (n = 0.009) to rough (n = 0.019) with four-bed slopes from horizontal (S o = 0) to S o = 0.01 were adopted with total 72 runs. The analysis of experimental data was focused on the variation of EDR as a roughness and/or bed slope changed. Also, the design formulas have been derived statistically for numerous practical situations and recommended to be used as predictive equations for both EDR and discharge.
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