3-D Floodway Design Methodology Presentation

This presentation discusses the challenges faced by floodways due to extreme weather changes and the need for more structurally resilient infrastructure. The methodology involves dimensional analysis and 3-D design modeling to establish efficient and effective flood control structures. The design considerations include open channel flow characteristics, hydraulic shocks, frictional factor, and Froude number. The presentation also includes a theory model, design of experiment, and a procedure for designing the channel. The conclusion highlights the increase in velocity when a sluice gate is placed instead of the free fall over-fall case.

3-D FLOODWAY DESIGN
METHODOLOGY PRESENTATION
Flow Channel Development

INTRODUCTION
Problem Statement and Objectives
Major challenge with floodways is that they are often affected by
extreme weather change such as heavy downpour.
 Public safety is therefore at risk
Economic significance of such structures also diminishes
Hence aim is to develop a more structurally resilient
infrastructure that would serve the public in a safe fashion

Background
Structural resilience in critical infrastructure such as
floodways is essential as it greatly contributes to public safety
and institutional confidence (Javernick, Redolfi, and Bertoldi,
2018)
Extreme climatic change may alter the normal functioning of
these structures
Design engineers must look at the entire design architecture to
ensure resilience is restored especially in extreme weather
conditions
The biggest concern in major cities is the rapid urbanization

AIM
The project aims at establishing more
efficient and effective flood control structure
to improve public safety
It is assumed that the flow is open channel
hence various factors at play
Dimensional analysis and 3-D design
modeling
is utilized

LITERATURE REVIEW
According to Lokuge et al (2014), floodway
damage is mainly due to large boulders on
the channel bed.
Categorization of the damage include:
-Washout
-high water damage
-Rock structure damage (the latter is more
pronounced in most floodway channels

METHODOLOGY OF DESIGN
Problem Solving
Dimensional analysis would involve deriving
mathematical formulation using the
expression provided:

In Designing the channel
Parameters involved include: coefficient of
friction, density of flowing water, size of
channel and velocity of flowing water

Design Considerations
Open channel flow characteristics in
floodway design involves:
Considering hydraulic shocks for impact
loading and scouring
The frictional factor along the channel
The flow is also described using Froude
Number such that turbulent regimes are
distinct from streamline flow

Theory Model
To consider the components of Dimensional
Analysis : Viscosity, frequency, velocity
Sluice gate verses sharp crested weir
comparison
Flow characteristics
The developed floodway is trapezoidal in cross
section

Algorithm
Procedure Description
Firstly, I assume the flow s constant along the channel hence the following governing equation (based on energy and
mass conservation) to describe the various profiles given the conditions (Defna, and Bxo No “page”):
Dy/dx= 1/cos ϕ {(So-Sf)+ αV2/gAxdA/dx}/1-F2…(1)
Where F s Froude number given by F= {αV2/gD cos ϕ}1/2
To find the water profile y, can integrate equations 1 wth respect to x (n other words depth to vary with the
horizontal distance)
y= ∫ 1/cos ϕ {(So-Sf)+ αV2/gAxdA/dx}/1-F2dx…(2)
But since consider a prismatic channel, equation (2) bolts down to:
y= ∫ 1/cos ϕ {(So-Sf)/1-F2dx…(3)
Equation (3) which is further written as:
Dy/dx= (So-n2Q2/A2R4/3)/ 1-F2 … (4)
Now, using equation (4) above and the fact that the channel is trapezoidal, can undertake various calculations to
arrive at the profile:
The trapezoidal section:

Design of Experiment
Use of Gantt Chart for planning purpose
The experiment to be performed would be
time-based such that the extremity of the
condition is varied in steps until the
demolition state is attained
This would be repeated for three differently
designed floodways to check on structural
resiliency

THE MODEL
The channel cross section is
trapezoidal. The selected cross
section provides the most efficient
flow rate regime.

The Model
The channel cross section is
trapezoidal. The selected cross
section provides the most efficient
flow rate regime. Below is the
lengthwise channel (side view)

The model
The channel cross section is
trapezoidal. The selected cross
section provides the most efficient
flow rate regime. The lengthwise
section provides the breadth details

Procedure
Given side slope: 1.5:1, can actually obtain dimensions such as the breadth
and depth accordingly and ths s done as follows:
From the triangular part, hyp= (1.52+1)0.5= 1.80
And tan ϕ= 1.5, ϕ = Tan-1(1.5)= 56.31o
Hence dimensions are: b= 3.75m, h= 1.5m, and a= 3.75+2= 5.75m
The wetted perimeter, P= (2+3.75+3.75+1.8x2= 13.1m
wetted area A= ½(3.75 +5.75)x1.5= 7.125m2
Hydraulic radius, R= A/P= 7.125/13.1= 0.5439m
From Manning's Equaton, fnd the average velocty:
V= R2/3S1/2/n
Hence substituting when n=0.06: v= 0.54392/30.00051/2/0.06= 0.2483=
0.25m/s
And when n=0.02, v= 0.54392/30.00051/2/0.02= 0.7449 = 0.74m/s
Froude Number, Fr= αV2/gR cosϕ
= 1.1 x 0.252/9.81 x 0.5439x1 = 0.01289 (this is in turbulent regime)

Procedure…
From the flow rate, determine the net flow rate by considering the hydraulic loss
due to seepage hence:
Qnet= 14.5- 0.01x1.5-0.015x4.5= 14.4475 and this s what used for calculation of
the profile:
Hence the slope of the profile is determined using equation 4:
Hence: (0.0005-0.062x14.44752/7.1252 x 0.54394/3)/ 1-0.012892
= -0.0335m/m and can then determine the specific sections profiles as given the
excel sheet.
For the friction slope, Sf, I can determine from equation 3
Hence: dy/dx= 1/cos ϕ {(So-Sf)/1-F2=0.033006
5x10-4- Sf= -0.033006(1-0.012892)
Sf= 0.033499
And the available head for the free fall, only velocity head s assumed available
H=v2/2g= 0.252/2x9.81= 3.186x10-3m
Finally, I can replicate the procedure for the three special cases with a slight
modification on the flow rate equations. (Note that hydraulic power is dependent
on the flow rate)

Conclusion
There is often a marked increase in velocity
when sluice gate is placed instead of the free
fall over-fall case. This is due to the narrow
construction considering the area of the
sluice gate making velocity to increase given
flow rate is constant (Lokuge, Weena,
Setunge, Sujeeva and Karunasena, Warna,
2014).

REFERENCE
Javernick, L., Redolfi, M. and Bertoldi, W., (2018).
Evaluation of a numerical model's ability to predict
bed load transport observed in braided river
experiments. Advances in Water Resources, 115,
pp.207-218.
 Lokuge, Weena and Setunge, Sujeeva and
Karunasena, Warna (2014) Investigating the
performance of floodway in an extreme flood event.
In: First International Conference on Infrastructure
Failures and Consequences, 16-20 Jul 2014,
Melbourne, Australia