Assessment of flow patterns and morphological changes in Nile river bends (Damietta branch)

ABSTRACT

The river’s bends are a major feature of rivers as a result of their hydraulic and morphological characteristics where the flow pattern has a three-dimensional (3D) nature. The aim of this research is to study the flow pattern induced morphological changes in river bends, evaluation of secondary currents in the different scenarios of flow, and develop a new equation for estimating the bend scour depth for the Nile River. Twenty bends in the Damietta branch (Nile River) in Egypt were selected where the study was done by conducting a bathymetric survey and 3D velocity measurements by an ADCP. A numerical model (Delft 3D) was applied to simulate the flow pattern in different flow scenarios. In addition, a Geographic information system (GIS) was used to analyze the morphological changes and bend scour depths. Statistical correlation between morphometric and hydraulic characteristics and morphological changes ratios was determined, as the results showed a significant correlation between these parameters. Four equations were selected for predicting bend scour depths. The results showed that the agreement between equations values and measured values is not reliable. Therefore, a new equation was derived to predict bend scour depth in the Nile River where it provides a more accurate prediction.

KEYWORDS:

• River bends
• secondary flow
• bend scour equation
• ADCP
• Delft3d model

Abbreviations
The following abbreviations are used in this paper.	=
GIS	=	Geographic information systems
MAD	=	Mean absolute deviation
MAE	=	Mean absolute error
NRI	=	Nile Research Institute
R2	=	Coefficient of determination
RMSE	=	Root mean square error
SPSS	=	The Statistical Package for the Social Sciences
2D	=	Two-dimensional
3D	=	Three-dimensional
BTI	=	Bend tightness index
SI	=	Sinuosity index
STD	=	Standard deviation
VMT	=	Velocity mapping tool

Disclosure statement

No potential conflict of interest was reported by the author(s).