https://orcid.org/0000-0001-5154-0849
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ABSTRACT
The Nile River is considered one of the most important rivers in the world. The scouring of such a river must be comprehensively studied. Therefore, studying the general scour of the Nile River and adjusting the relevant scour equations are very important. Field data were collected (bathymetric, hydrological, and hydraulic) for several years in the selected study area (a river reach with a total length of 54 km). A geographic information system (GIS) database application was established to determine the scour hole characteristics. The scour equilibrium state (active, stable or passive) was classified according to the field observations. A numerical model was developed to calculate the hydraulic characteristics of the Nile River. Seven equations were selected to evaluate the general scour depth. The predictive performances of these equations were assessed using field data and computed scour depths. Four statistical tests were performed to evaluate the performances of the scour equations. The results showed that the equations are inadequate and can potentially lead to underestimation of the scour depth. The Lacey Natural Resources Conservation Service (NRCS) equation performs better than the other equations considered. The selected equations were modified to improve the prediction of the general scour depth of the Nile River. A new general scour equation was derived to simulate the Nile River general scour. Compared to the previously discussed equations, this new equation provided the most accurate prediction of general scour in the Nile River.
Abbreviations: The following abbreviations are used in this paper. AHD = Aswan High Dam; ASCII = American Standard Code for Information Interchange; CAD = Computer-aided design; FESWMS = Finite Element Surface Water Modelling System; GIS = Geographic information systems; MAD = Mean absolute deviation; MAE = Mean absolute error; MKS = Metre-kilogram-second; NRCS = National Resources Conservation Service; NRI = Nile Research Institute; R2 = Coefficient of determination; RMSE = Root mean square error; SMS = Surface Water Modelling System; SPSS = Statistical Package for the Social Sciences; USBR = United States Bureau of Reclamation; UTM = Universal Transverse Mercator; WGS84 = World Geodetic System; 2D = Two-dimensional
Notation
The following symbols are used in this paper:
| D50 | = | = Median size of bed material |
| df0 | = | = Water depth for zero bed sediment transport |
| e | = | = Error between the measured and calculated scour depths |
| Fb0 | = | = Blench zero bed factor |
| f | = | = Lacey silt factor |
| g | = | = Gravitational acceleration |
| H | = | = Water depth |
| HU | = | = Unit flow rate in the x-direction |
| HV | = | = Unit flow rate in the y-direction |
| n | = | = Number of samples |
| Oi | = | = Observed values |
| = | = Mean of observed values | |
| Pi | = | = Predicted values |
| = | = Mean of predicted values | |
| Q | = | = Designed discharge |
| q | = | = Discharge per unit width |
| q | = | = Mass inflow rate (positive) or outflow rate (negative) per unit area |
| Se | = | = Energy slope (or bed slope) |
| T | = | = Top width at the designed discharge |
| U | = | = Horizontal velocity in the x-direction |
| V | = | = Horizontal velocity in the y-direction |
| Vc | = | = Competent mean velocity |
| Vm | = | = Average velocity of flow |
| Ymax | = | = Maximum depth of flow |
| ym | = | = Hydraulic mean depth of flow |
| ys | = | = Scour depth below the streambed |
| Z | = | = Factor for regime equation, |
| z | = | = Vertical direction |
| zb | = | = Bed elevation |
| ρ | = | = Water mass density |
| Ω | = | = Coriolis parameter |
| β | = | = Isotropic momentum flux correction coefficient that accounts for the variation in velocity in the vertical direction |
| τby | = | = Bed shear stresses acting in the y-direction |
| τbx | = | = Bed shear stresses acting in the x-direction |
| τsy | = | = Surface shear stresses acting in the y-direction |
| τsx | = | = Surface shear stresses acting in the x-direction |
| τxx, τxy, τyx,and τyy | = | = Shear stresses caused by turbulence |
Disclosure statement
No potential conflict of interest was reported by the authors.
Correction Statement
This article has been republished with minor changes. These changes do not impact the academic content of the article.