rip currents along the visakhapanam coast

STUDIES ON BEACH PROCESSES AT VISHAKHAPATNAM

Dissertation submitted as partial fulfillment for the award ofMASTER OF SCIENCE IN PHYSICAL OCEANOGRAPHY

ByPOTNURU GANAPATHI

Regd.No:711211428015

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

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 includes Waves ,Tides, Long shore currents, Rip currents,

, Sea level changes, Winds

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.

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

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).

• 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

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)

• 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

Figure 3: Location map and study area

STUDY AREA

• Wave induced long shore currents off Visakhapatnam coast have been

computed using the relationship given by Komar (1975). The equation

is as follows:

METHODOLOGY

Where,

where is longshore current velocity in the mid surf zone,

is the maximum value of breaking wave orbital velocity which isgiven 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.

Figure 4: Wave Refraction diagram from East, Period 8sec Figure 5: Wave Refraction diagram from East, Period 10 sec

Results and Discussion

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

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.

• 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.

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

Computations of the wave induced currents for East South East waves


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

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.

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

Computations of the wave induced currents for South East


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

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.

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

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

velocity(m/sec)

0.155 0.22 0.115 0.04 0.085 0.155 0.224 0.18

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

(m)

0.6 0.6 0.6 0.6 0.65 0.5 0.7 0.6

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 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) 16:00 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

velocity(m/sec)

0.13 0.26 0.095 0.117 0.08 0.095 0.204 0.23



Wave height(cm) 60 50 40 80 55 80 70 40


Breaker depth (m) 0.8 0.8 0.4 0.8 0.6 0.7 0.8 0.5

Surf zone

width(m)

30 28 15 10 20 20 30 30

Wave period(sec) 10.72 9.63 8.54 11.27 11.54 11.4 15.7 8.3

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) 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



Wave height(cm) 100 50 80 55 65 60 80 40


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 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) 15:00 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

velocity(m/sec)

0.237 0.53 0.042 0.237 0.07 0.127 0.133 0.54



Wave height(cm) 80 40 80 60 50 70 70 55


Breaker depth

(m)

1.2 0.4 0.7 0.65 0.7 0.8 0.7 0.5

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

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) 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

velocity(m/sec)

0.087 0.27 0.07 0.155 0.066 0.255 0.095 0.22

High/low water Low water High water Low water Low water High water High water High water Low water


Wave height(cm) 80 30 60 70 80 52 60 50


Breaker depth (m) 0.8 0.8 0.6 0.7 0.6 0.5 0.6 0.5

Surf zone

width(m)

40 30 15 30 25 20 25 45

Wave period(sec) 10.54 7.63 9.09 13 16.54 9.55 16.3 6.5

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) 17:30 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

velocity(m/sec)

0.092 0.62 0.085 0.293 0.08 0.07 0.185 0.5

High/low water Low water Low water High water Low water High water Low water High water Low water


Wave height(cm) 70 60 80 75 100 70 80 40


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

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) 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

velocity(m/sec)

0.1 0.68 0.086 0.1 0.09 0.08 0.15 0.17

High/low water Low water Low water High water Low water High water Low water Low water Low water


Wave height(cm) 90 65 50 40 80 80 60 50


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

Station 7: AU LADIES HOSTEL BAY-2 (170 42’25.4’’ N & 830 18’47.5’’ E)

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.

• 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.

• 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.

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rip currents along the visakhapanam coast

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