**KRISTIN
E. KASPER **

**PLAN B REPORT TITLE:**
ACCURACY OF HEC-RAS TO CALCULATE FLOW DEPTHS AND TOTAL ENERGY LOSS WITH AND
WITHOUT BENDWAY WEIRS IN A MEANDER BEND

**ABSTRACT:** River systems
are interconnected waterways that often change to reach a state of dynamic
equilibrium. Dynamic equilibrium is a fragile balance between flow conditions,
sediment transport, and environmental habitat in a river system. To study
river systems in detail, complex hydraulic models have been developed. Hydraulic
models calculate flow depths and energy loss through a river system and are
defined as 1-, 2-, or 3-dimensional models. Differences between each model
type depend on assumptions used to build the model. A 1-dimensional model
assumes the primary component of a 3-dimensional velocity profile is along
the x-coordinate axis. Therefore the velocity components along the y- and
z-coordinate axis are assumed insignificant. Positive velocity components
along the y- and z-coordinate axis refer to lateral flow to the right bank
looking downstream and the vertical direction while positive velocity component
along the x-coordinate axis refers to the flow direction. In 2- and 3-dimensional
hydraulic models, the 1-dimensional assumption for the y- and z-coordinate
axis does not hold true.

In 1-dimensional analysis, HEC-RAS is a common hydraulic model to study flow
depths and total energy loss along a study reach of a river system. HEC-RAS
is a 1-dimensional model that performs calculations for steady or unsteady
flow in gradually-varied or rapidly-varied flow analysis. Even though HEC-RAS
is a 1-dimensional hydraulic model, it is commonly used to model flow patterns
where the velocity along the y- or z-coordinate axis are significant. For
instance, HEC-RAS is used to study meander bends. Meander bends are undulating
segments in a river system where the dominant direction of velocity is not
necessarily along the x-coordinate axis. An added level of complexity develops
when bank stabilization features such as bendway weirs are added to a HEC-RAS
model. Bendway weirs are bank stabilization features built of local rock material.
Bendway weirs are constructed along the outer bank of a meander bend in order
to reduce bank erosion by directing high velocities along the outer bank to
the center of the channel. While protecting the stream bank, bendway weirs
support viable aquatic habitats, and riparian vegetation along a meander bend.

Since HEC-RAS is often used to model 3-dimensional velocity profiles with
and without bendway weirs, research needs to be completed to determine the
accuracy of HEC-RAS. Included in this study was an analysis to determine the
accuracy of HEC-RAS to model flow depths and total energy loss along a meander
bend with or without bendway weirs and a methodology to best estimate total
energy loss given HEC-RAS output.

**GRADUATION DATE:
**Fall 2005

**RESUME** (pdf)