rip currents along the visakhapatnam coast

1. STUDIES ON BEACH PROCESSES AT VISHAKHAPATNAM
Dissertation submitted as partial fulfillment for the award of
MASTER OF SCIENCE IN PHYSICAL OCEANOGRAPHY
By
POTNURU GANAPATHI
Regd.No:711211428015

2. OBJECTIVES
 Analysis of surf zone currents a long the Visakhapatnam coast
 To identify the rip current features through the long shore currents and
 Identify the rip currents from Construction of wave refraction diagram

3. INTRODUCTION
Beach :
• The zone of unconsolidated material that extends from the mean low
water line to the place where there is a marked change in material or
physiographic form, or to the line of permanent vegetation
Beach Processes :
• Beaches constantly change. They may be high and wide during the
summer, then disappear during winter storms.
• Beach processes includesWaves ,Tides, Long shore currents, Rip currents,
, Sea level changes,Winds

4. WAVES:
• In fluid dynamics, wind waves or, more precisely, wind-generated waves
are surface waves that occur on the free surface of oceans, seas, lakes,
rivers, and canals or even on small puddles and ponds.
• They usually result from the wind blowing over a vast enough stretch of
fluid surface.
• Waves in the oceans can travel thousands of miles before reaching land.
Wind waves range in size from small ripples to huge waves over 30 m
high.

5. Wave Refraction:
• Refraction is the bending of waves because of varying water depths
underneath.
• The part of a wave in shallow water moves slower than the part of a wave in
deeper water.
• The part of the wave crest closer to shore is in shallower water and moving
slower than the part away from the shore in deeper water.
• The wave crest in deeper water catches up so that the wave crest tends to
become parallel to the shore.
• The water then moves parallel to the shore as an long shore current, carrying
sand and other sediments along the coast, changing the shape of the coast,
and forming and eroding the Beach

6. Rip Currents:
• Rip currents are generally strong shore-normal (jet like) flows that originate
within the surf zone and are directed seaward through the breakers.
• Rip currents typically reach speeds up to 1 m/s and some have been reported
as high as 2 m/s at Palm Beach, Australia (Short, 1985). Rip currents
influence the morphology of the shoreline and may be important for
transporting fine sediments offshore (Cooke, 1970; Komar, 1971; Short,
1999).
• The understanding of rip current systems is important in developing
accurate forecasts for predicting high-risk rip current events that are a public
safety hazard (Luschine, 1991; Short and Hogan, 1994; Lascody, 1998;
Engle et al., 2002).

7. • Rip currents are a common occurrence on many beaches. A rip is a discrete
seaward-directed current that can flow in excess of 2 m/s (Brander, 1999;
Brander and Short, 2000, 2001; Sonu, 1972). They are an important
geomorphic process that transports both water and sediment, and
consequently, they drive changes in beach morphology (Brander, 2005).
Figure: Arial Image of Rip Current System

8. Figure 2 : Aerial image of a rip channel at Woolamai with schematic diagram of the
structure of rip currents (824 Nat Hazards (2011) 59:823–832)

9. • Although rip currents are not caused by tides, the water level (tide elevation)
at the coast may have an impact on rip current speed and strength.
• Generally, rip current velocities increase as water levels (tide elevation)
decrease.
• Rip current velocities also typically increase as wave heights increase. An
increase in the height of incoming waves can result in sudden increases in
water depth and rip current velocities

10. STUDY AREA
Figure 3: Location map and study area

11. METHODOLOGY
• Wave induced long shore currents off Visakhapatnam coast have been
computed using the relationship given by Komar (1975). The equation
is as follows:
Where,

12. where is longshore current velocity in the mid surf zone,
is the maximum value of breaking wave orbital velocity which is
given by 2( )
• Eb is the wave breaker energy that can be evaluated from a knowledge of the
breaker height Hb, hb is the water at the wave breaking give by ( 4/3 Hb)
and  is the density of sea water.
• The drag coefficient Cf is 0.008 to 0.018 under normal filed conditions and rb
is the ratio of the wave breaker height to water depth with a value between
0.8 to 1.2.for Cf and rb are taken as 0.017 and 0.8 respectively the average
deep water wave steepness and Hb/y has been computed for different
zones along the coast from the calculated values of Hb.

13. Results and Discussion
Figure 4: Wave Refraction diagram from East, Period 8sec Figure 5: Wave Refraction diagram from East, Period 10 sec

14. Computations of the wave induced currents for East waves
Period 8 sec Period 10 sec
Statio
n
Breaker
height
Hb(m)
Currents
due to
oblique
V1
(m/sec)
Currents
due to
height
variation
V2(m/sec)
Resultant
current
V(m/sec)
Breaker
height
Hb(m)
Currents
due to
oblique
V1
(m/sec)
Currents
due to
height
variation
V2(m/sec)
Resultant
current
(m/sec)
A 1.20 0.6401 0.3027 0.3374 1.20 0.9912 0.4758 0.5154
B 1.04 1.4046 -0.0793 1.4839 1.04 0.474 -0.0306 0.5046
C 1.05 -0.1614 0.1253 -0.2867 1.05 -0.0807 0.0530 -0.1337
D 1.20 -0.276 -0.0510 0.3270 1.20 -0.3682 0.06809 -0.4362
E 1.25 0.666 0.26804 0.3779 1.25 -0.2880 -0.0985 -0.1895
F 1.15 0.6988 -0.4085 1.10732 1.15 0.3528 -0.25072 0.60356
Table 1: Computations of the wave induced currents for East waves

15. Deep water waves from East:
• Wave refraction diagrams have been constructed for wave period 8 and 10
sec four directions.
• These diagrams show the refraction patterns to the north side of the port.
The distribution of wave rays along the coast is by no means uniform and
do not show any regular pattern.
• Maximum current of about 1.48 m/sec is generated near station B, towards
north of Vishakhapatnam port for 8 sec waves.

16. • However, for 10 sec. waves the occurrence of maximum current
shifted to the station F north of the Vishakhapatnam port.
• The contribution due to variations in the long shore current
velocities is positive at some stations and negative at some other
stations.
• Finally rip current is observed between the stations B&C (Fig. 1)
due to convergence from deep water waves from the East.

17. Fig.6: Wave Refraction diagram from East Southeast, Period 8 sec Fig.7: Wave Refraction diagram from East Southeast, Period 10 sec

18. Computations of the wave induced currents for East South East waves
Period 8 sec Period 10 sec
Statio
n
Breaker
height
Hb(m)
Currents
due to
oblique
V1
(m/sec)
Currents
due to
height
variation
V2(m/sec)
Resultant
current
V(m/sec)
Breaker
height
Hb(m)
Currents
due to
oblique
V1
(m/sec)
Currents
due to
height
variation
V2(m/sec)
Resultant
current
(m/sec)
A 1.20 0.3682 0.1153 0.2529 1.20 0.5501 0.1443 0.4058
B 1.04 0.7803 -0.0104 0.7907 1.04 0.3175 -0.0064 0.3239
C 1.05 -0.3220 -0.0945 -0.2275 1.05 -0.6377 -0.0947 -0.543
D 1.20 -0.1845 -0.0375 -0.1475 1.20 0.459 -0.03757 0.4965
E 1.25 0.1922 0.1042 0.08806 1.25 0.7597 0.1107 0.6489
F 1.15 0.3528 -0.0996 0.4524 1.15 0.527 -0.11788 0.6448
G 1.30 0.10002 0.1027 -0.00268 1.30 0.10003 0.1027 -0.00269
Table 2: Computations of the wave induced currents for East South East waves

19. Deep water waves from East Southeast:
• Wave refraction diagrams have been constructed for wave periods 8 and 10
sec in four directions.
• These diagrams show the refraction patterns to the north side of the port.
The distribution of wave rays along the coast is by no means uniform
and do not show any regular pattern.
• Maximum current of about 0.7907 m/sec is generated near station B,
towards north of Vishakhapatnam port for 8 sec waves. But for 10 sec
waves the occurrence of maximum current shifted to the station E
north of the Vishakhapatnam port.
• The contribution due to variations in the long shore current velocities is
positive at some stations and negative at some other stations.
• Finally rip current is observed between the stations B&C (Fig. 3) due to
convergence from deep water waves from the East Southeast.

20. Fig.8: Wave Refraction diagram from Southeast, Period 8 sec Fig.9: Wave Refraction diagram from Southeast, Period 10 sec

21. Computations of the wave induced currents for South East
Period 8 sec Period 10 sec
Statio
n
Breaker
height
Hb(m)
Currents
due to
oblique
V1
(m/sec)
Currents
due to
height
variation
V2(m/sec)
Resultant
current
V(m/sec)
Breaker
height
Hb(m)
Currents
due to
oblique
V1
(m/sec)
Currents
due to
height
variation
V2(m/sec)
Resultant
current
(m/sec)
A 1.20 0.0923 0.1601 -0.0678 1.20 0.4594 0.1311 0.3283
B 1.04 0.0796 -0.0081 0.0877 1.04 -0.2384 -0.00817 -0.2302
C 1.05 -1.0143 -0.1035 -0.9108 1.05 -0.7914 -0.11303 -0.6783
D 1.20 -0.184 -0.0450 -0.139 1.20 -0.3682 -0.0375 -0.3307
E 1.25 -0.096 0.08936 -0.1853 1.25 0.09618 0.08530 0.0108
F 1.15 0.088 -0.1125 0.2005 1.15 -0.0884 -0.1438 0.0554
G 1.30 -0.199 0.1084 -0.3074 1.30 -0.4977 0.1085 -0.6062
Table 3: Computations of the wave induced currents for South East

22. Deep water waves from Southeast:
• Wave refraction diagrams have been constructed for wave period 8 and 10
sec in four directions. These diagrams show the refraction patterns to the
north side of the port.
• The distribution of wave rays along the coast is by no means uniform and
do not show any regular pattern. Maximum current of about 0.2005 m/sec is
generated near station F, towards north of Vishakhapatnam port for 8 sec.
waves. But for 10 sec. waves the occurrence of maximum current shifted to
the station A north of the Vishakhapatnam port.
• The contribution due to variations in the long shore current velocities is
positive at some stations and negative at some other stations.
• Finally rip current is observed at the station D (Fig. 8) due to convergence
from deep water waves from the Southeast.

23. Measurements of long shore currents at the time of field work:
• Along the Vishakhapatnam beach, long shore currents are measured. a
bottle half filled with wet sand is thrown into the surf zone and the time
taken by it to reach the shore is measured with the help of a stopwatch.
• The distance traveled is measured with the same staff that is used to
measure the sand levels. the distance divided by the time gives the current
velocity.
• In addition to it, the direction of the current and the breaker heights,
breaker types, the time period and the direction of the of the wave
reaching, the coast are also observed visually and tabulated

24. Station 1 : PALM BEACH (17043’8.2’’N & 83020’7.3’’ E)
3-2-13 10-2-13 17-2-13 24-2-13 3-3-13 10-3-13 17-3-13 25-3-13
Time (24hours) 16:30 09:30 09:30 09:30 09:30 09:30 09:30 16:45
Current direction South east South North North south North North North
Current
0.155 0.22 0.115 0.04 0.085 0.155 0.224 0.18
velocity(m/sec)
High/low water High water High water Low water High water High water High water High water Low water
Wave direction South east South east South east South east South east South east South east South east
Wave height(cm) 50 40 60 50 60 50 60 45
Type of breaker Plunging Plunging Plunging Plunging Plunging Plunging Plunging Plunging
Breaker depth
0.6 0.6 0.6 0.6 0.65 0.5 0.7 0.6
(m)
Surf zone
width(m)
35 10 20 11 15 20 20 25
Wave period(sec) 11.81 6.27 8.72 12.63 10.56 8.1 15.7 9.3
Station 2 : VICTORY AT SEA (170 43’ 5.3’’ N & 830 19’ 57.2’’ E)
3-2-13 10-2-13 17-2-13 24-2-13 3-3-13 10-3-13 17-3-13 25-3-13
Time (24hours) 16:00 09:00 09:00 09:00 09:00 09:00 09:00 16:30
Current direction South east South North North south North North North
Current
0.13 0.26 0.095 0.117 0.08 0.095 0.204 0.23
velocity(m/sec)
High/low water High water High water Low water High water High water High water High water Low water
Wave direction South east South east South east South east South east South east South east South east
Wave height(cm) 60 50 40 80 55 80 70 40
Type of breaker Plunging Plunging Plunging Plunging Plunging Plunging Plunging Plunging
Breaker depth (m) 0.8 0.8 0.4 0.8 0.6 0.7 0.8 0.5
Surf zone
30 28 15 10 20 20 30 30
width(m)
Wave period(sec) 10.72 9.63 8.54 11.27 11.54 11.4 15.7 8.3

25. Station 3 : SUBMARINE1 (170 43’2.07’’ N & 830 19’52.2’’ E)
3-2-13 10-2-13 17-2-13 24-2-13 3-3-13 10-3-13 17-3-13 25-3-13
Time (24hours) 15:30 10:30 10:30 10:30 10:30 10:30 10:00 17:00
Current direction South east South North South North North South North
Current
velocity(m/sec)
0.042 0.2 0.11 0.177 0.085 0.102 0.325 0.3
High/low water High water High water Low water High water High water High water High water Low water
Wave direction South east South east South east South east South east South east South east South east
Wave height(cm) 100 50 80 55 65 60 80 40
Type of breaker Plunging Plunging Plunging Plunging Plunging Plunging Plunging Plunging
Breaker depth (m) 1.4 0.7 0.9 6.7 1 0.4 0.8 55
Surf zone width(m) 35 15 10 20 30 25 32 35
Wave period(sec) 13.63 6.63 8.72 10.54 11.87 10.64 13.6 6.7
Station 4 : SUBMARINE1 (170 42’58.7’’ N & 830 19’43.4’’ E)
3-2-13 10-2-13 17-2-13 24-2-13 3-3-13 10-3-13 17-3-13 25-3-13
Time (24hours) 15:00 10:00 10:00 10:00 10:00 10:00 10:30 17:15
Current direction South east South North North South North North North
Current
0.237 0.53 0.042 0.237 0.07 0.127 0.133 0.54
velocity(m/sec)
High/low water High water High water Low water High water High water High water High water Low water
Wave direction South east South east South east South east South east South east South east South east
Wave height(cm) 80 40 80 60 50 70 70 55
Type of breaker Plunging Plunging Plunging Plunging Plunging Plunging Plunging Plunging
Breaker depth
1.2 0.4 0.7 0.65 0.7 0.8 0.7 0.5
(m)
Surf zone
width(m)
40 15 25 15 20 20 30 45
Wave period(sec) 9.09 6.54 7.72 12.72 11.27 10.72 13 9.33

26. Station 5 : RK BEACH (170 42’ 42.5’’ N & 830 19’ 13.4’’ E)
3-2-13 10-2-13 17-2-13 24-2-13 3-3-13 10-3-13 17-3-13 25-3-13
Time (24hours) 17:00 11:00 11:00 11:00 11:00 11:00 11:00 17:30
Current direction South east South North South North South North North
Current
0.087 0.27 0.07 0.155 0.066 0.255 0.095 0.22
velocity(m/sec)
High/low water Low water High water Low water Low water High water High water High water Low water
Wave direction South east South east South east South east South east South east South east South east
Wave height(cm) 80 30 60 70 80 52 60 50
Type of breaker Plunging Plunging Plunging Plunging Plunging Plunging Plunging Plunging
Breaker depth (m) 0.8 0.8 0.6 0.7 0.6 0.5 0.6 0.5
Surf zone
40 30 15 30 25 20 25 45
width(m)
Wave period(sec) 10.54 7.63 9.09 13 16.54 9.55 16.3 6.5
Station 6: AU LADIES HOSTEL BAY-1 (170 42’ 31.1’’ N & 830 18’ 54.8’’ E)
3-2-13 10-2-13 17-2-13 24-2-13 3-3-13 10-3-13 17-3-13 25-3-13
Time (24hours) 17:30 11:30 11:30 11:30 11:30 11:30 11:30 17:45
Current direction South east South North North North north South North
Current
0.092 0.62 0.085 0.293 0.08 0.07 0.185 0.5
velocity(m/sec)
High/low water Low water Low water High water Low water High water Low water High water Low water
Wave direction South east South east South east South east South east South east South east South east
Wave height(cm) 70 60 80 75 100 70 80 40
Type of breaker Plunging Plunging Plunging Plunging Plunging Plunging Plunging Plunging
Breaker depth (m) 0.7 0.6 1 0.8 1.2 0.8 0.8 0.7
Surf zone width(m) 20 15 10 20 10 10 20 30
Wave period(sec) 10.18 9.18 7.72 11.9 16.9 13.26 12.2 10.4

27. Station 7: AU LADIES HOSTEL BAY-2 (170 42’25.4’’ N & 830 18’47.5’’ E)
3-2-13 10-2-13 17-2-13 24-2-13 3-3-13 10-3-13 17-3-13 25-3-13
Time (24hours) 18:00 12:00 12:00 12:00 12:00 12:00 12:00 18:00
Current direction South east South South North South North South North
Current
0.1 0.68 0.086 0.1 0.09 0.08 0.15 0.17
velocity(m/sec)
High/low water Low water Low water High water Low water High water Low water Low water Low water
Wave direction South east South east South east South east South east South east South east South east
Wave height(cm) 90 65 50 40 80 80 60 50
Type of breaker Plunging Plunging Plunging Plunging Plunging Plunging Plunging Plunging
Breaker depth (m) 1.1 0.6 0.6 0.7 0.5 0.8 0.7 0.55
Surf zone width(m) 40 20 20 30 20 20 30 35
Wave period(sec) 8.63 9.08 7.9 8.45 11.45 10.9 13.8 15.7

28. CONCLUSIONS
• For the present study, seven stations are considered and the
observations are taken over the seven stations during the period of two
months from February 2013 to March 2013.
• It is observed that the current velocity is maximum at the station 7
with the value 0.68 m/sec and at station 6 with the value 0.62m/sec
during 10th February 2013.
• The observed current velocity is minimum over other stations when
compared with the above two stations.
• Here it is also observed that the water level is low, indicating the rip
currents but the intensity is less.
• This is due the wave height and other parameters are not sufficient.
The wave direction is southeast and the type of the breaker is
plunging, and both are same for all the stations during the observation
period.

29. • The observed breaker depth is maximum at the two stations 6 & 7 than the
other stations. The presence of the head between the station 6 &station 7 and
the bays of the two stations results the wave convergence. The convergence
between these two stations causes the rip currents to occur.
• From the wave refraction diagrams for the southwest monsoon, rip currents
are identified at the stations F & G due to convergence from deep water
waves from the South of Southeast direction.
• Rip current is also observed between the stations B & C, at the station D and
between the stations B & C due to convergence from deep water waves from
the East, southeast and East of Southeast respectively.

30. • The calculated values of long shore current velocities are positive and
negative, and The positive values represent the northward long shore
current direction while the negative values represent the southward long
shore current direction.
• At the stations B & C, F & G and at station D, the convergence of these
two opposite directed long shore currents is responsible for the formation
of rip currents at those stations.