Hydrodynamic and Morphological Impact of Hydraulic Structural Interventions: An Investigative Case Study on Feni- Muhuri River System of Bangladesh

Abstract

This paper offers an analysis on Muhuri River in terms of change in velocity, water level,
scouring depth at different locations, thalweg shifting and afflux due to construction of structural
intervention on Feni-Muhuri river system. Primarily, Gumbel’s distribution approach was
adopted for fixation of the flood frequency analysis in terms of 25, 50 and 100 year return
periods for both Feni and Muhuri River. Due to prevailing lunar dominancy, historical (1968-
2009) tidal data had to be considered for estimating the design maximum and minimum water
level at the available stations within the study reach. Discharge and water level data of different
return periods were fed into the HEC-RAS 1D and 2D interface of Delft3D model as inputs of
boundary conditions for the supplementary hydrodynamic and morphological investigation.
Results on planform and thalweg analysis reveal significant siltation over the last decade in case
of both the rivers. To analyze the hydraulic impact of bridge, a 1.65 km long reach was selected
as the model domain. Velocity, variation in water surface elevation, scour depths have been
studied for 5 different planning scenarios of the bridge and bankfull discharge condition in terms
of variation in length and number of spans. General, Pier, Abutment, contraction, combined and
local scour depths have been computed for the bridge using available approaches integrated in
HEC-RAS.