Citation
Ali, Hydar Lafta
(2019)
Modelling hydro-morpho dynamics of river junctions under the impact of unsubmerged vanes.
Doctoral thesis, Universiti Putra Malaysia.
Abstract
Controlling the flow and river bed morphology in the confluence and branching
junctions are important in rivers training and navigation works. The flow in a river
junction is highly complex, due to rapid changes associated with flow dynamics,
sediment transport, and geomorphology. Erosion and deposition zones are considered
as the main critical features that appear at the river junction and causing many
problems such as increasing the possibility of flood risks at the river confluence, on
the other hand, a shortcoming of the inflow discharge at the river branching which
effects different water supply projects. In this study, two cases have been selected
owing to their suffering from hydro-morpho dynamics issues. The first case is a
confluence of Kurau and Ara rivers located at tropical region Perak, Malaysia, while
the second case is a branching of Tigris river located at temperate region Missan, Iraq.
The aim of this study is to control the hydro-morpho dynamics features at the junction
of a confluence and branching rivers. Measured and acquired data were used to
investigate the scour hole that usually formed in the erosion zone and bar formed in
the deposition zone. The data of the confluence junction was acquired while for the
branching junction was measured. Garmin echoMap 50s device was used to measure
the bathymetry survey, while Son Tek River Surveyor device M9 was used to collect
discharge, velocity distribution, and cross-section geometry. In addition, Van Veen
Grab sampler was used to collect bed material sampling of the Tigris branching
junction. The results of data collection for the confluence of Kurau and Ara rivers
show that the velocity was ranged between 0.8 and 1.1 m/s at the location of the
maximum scour zone and between 0.1 and 0.3 m/s at the location of deposition zone,
while for the branching of the Tigris river the velocity was around 0.5 m/s at the
location of the scour zone and 0.1 m/s at the deposition zone. A 2D numerical model
of Mflow_02 solver was used to build, calibrate and validate the numerical models
using field data to simulate the selected river junctions before simulating various
arrangements of unsubmerged vanes as control structures. This solver was able to
calculate two-dimensional plane unsteady flow, river bed morphology and sediment transport by unstructured meshes of finite element method. The error of the model
output was found to be less than 20% in both cases. The simulations with different
arrangements of unsubmerged vanes were proposed as control structures to mitigate
scouring and deposition zones that usually occurred at natural river junctions. The
results revealed that the most effective size and location of unsubmerged vanes mainly
depend on their performance in deposition and scouring zones. For both cases,
simulation results show that a single unsubmerged vane can successfully control the
scouring and deposition zones. In the confluence junction, the third scenario of
installing a single unsubmerged vane with 10 m length at an angle of 30° gave the best
solution for diminishing the maximum scour zone and minimizing the deposition zone.
In branching junction, the results of the fourth scenario by introducing a single
unsubmerged vane with 50 m length, placed perpendicular to the flow direction of the
main branching river, show that the deposition zone was reduced to 82% when
compared with the simulation without vane. In summary, this study addresses the
applicability of using the 2D numerical model in complex riverine system for
predicting hydro-morpho-dynamics changes in junctions with and without vanes as
training structures. The significance of this study is attributed to the simulation of
various scenarios for controlling scour and deposition zones by using unsubmerged
vanes and recommended the best solution that provides minimum scouring and
deposition zones and thus may enhance river flow dynamics.
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