1. “A DETAILED ANALYSIS AND ESTABLISHMENT OF EMPIRICAL
RELATIONS FOR ESTIMATION OF AFFLUX IN OPEN CHANNELS
CONSIDERING RECTANGULAR OBSTRUCTIONS”
AAKAAR 2013, IIT BOMBAY
PRESENTED BY:
KULDEEP KAUSHIK
RITUKESH BHARALI
STUDENTS, 6TH SEMESTER, B.E,
DEPARTMENT OF CIVIL ENGINEERING
ASSAM ENGINEERING COLLEGE, JALUKBARI, GUWAHATI, ASSAM

2. INTRODUCTION
 Afflux - defined as the elevation of the water level upstream of a body due to
the presence of obstructions in its flow.
 The local loss of energy due to fluid friction is compensated by an increase in
stream potential energy in the form of afflux upstream.
 In the fig: Picture depicting river afflux
Dashed line : normal water flow
Dotted line : flow of water in the presence of structures
Y4 - Y1 : Afflux height

3. OBJECTIVES
 As the water level varies due to civil constructions and banks breached in flood
times, the study basically deals in estimation of the water level due to
obstructions and approach in preventing the breaching of water in flood times
 The paper mainly focuses in developing an empirical relation for the estimation
of afflux upstream
 It basically enhances upon establishment of the optimized model keeping in
view of the safety and the economic factor of design.

4. THEORY
 Afflux – dependence on structural and flow variables
 Structural variables: opening ratio, skew, eccentricity, etc.,
 Flow variables: Froude’s number, sediment and debris
transport, choking.
 Dimensional Analysis – Buckingham Pie Method and
Graphical Analysis
 Analysis of variables –

5. PROCEDURE
 EXPERIMENTAL SETUP:
1) Rectangular open channel (5000 mm x 76mm
x 170mm) for the flow of water
2) Rectangular piers (25mm x 6mm x 200mm)
for the construction of the structure
3) Sheets of mica (1mm thickness) for the
variation of opening ratio accordingly
METHODOLOGY:
 After the set up water is allowed to flow
through the channel, keeping the blockage at
3.5 m
 Afflux is measured accordingly at various
points with the variation of opening ratio from
84% to 26%
 The data is then analyzed for developing the
suitable empirical formula for afflux
estimation.

6. OBSERVATIONS
Observations based on the experimental results:
 Plotting of graph with water level in Y-Axis and distance of the open channel in X-
Axis.
 Decreasing of opening ratio is inversely proportional to the afflux.

7. COMPUTATION FROM GRAPHS

8. DATAANALYSIS AND RESULTS
DIMENSIONALANALYSIS
•Graph 1 provides the flow pattern of
water for a variation of open ratio of
84% to 26% concluding O.R α
1/(Water Level Upstream)
•Graph 2 depicts the family of curves
between the water level and open ratio
for a specific L/B ratio signifying
Afflux α 1/ (L/B)
•Dimensional analysis computes the
relation between the estimation on of
afflux with parameters L/B and O.R
(constant Froude’s number 0.642) as
follows-
 dh/h = K. (0.642) (L/B) ̵ ͣ (δ) ̵ ᵇ
K, a, b are obtained from experimental data
 From graph 2 , the relation is obtained
for the best fit curve:
dh/h= -0.0065 δ + 0.795
 From the experimental results of table
2 , the best suited results for K and a is
obtained as:
dh/h= [0.89(-0.0065 δ + 0.795)] /

9. COMPARISION OF COMPUTED AND MEASURED dh/h AND
AVERAGE % ERROR

10. GRAPHICALANALYSIS

11.  No significant change in the
intercept
 Variation of slope (m) with L/B
ratio
 For L/B < 2.6: c= 0.792
 For L/B > or = 2.6 : c = 0.785

12. CONCLUSION
 Experimental results proves afflux to be a function of δ, Fr and
L/B ratio of the channel.
 Dimensional and graphical analysis resulted in two empirical
formulae. Maximum errors recorded were 6% and 8%
respectively.

13. THANK YOU