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Aquatic Procedia 4 ( 2015 ) 1514 – 1521

INTERNATIONAL CONFERENCE ON WATER RESOURCES, COASTAL AND OCEAN ENGINEERING (ICWRCOE 2015) Impact of Mudbanks on Coastal Dynamics

Parvathy K. G.a*, Noujas Vb., Thomas K. V. b, Ramesh H.a

aNational Institute of Technology Karnataka, Surathkal, , 575025 bCentre for Earth Science Studies, , India, 695031

Abstract

Mudbanks are a major morphological feature which has a very close and direct impact on coastal dynamics. This paper is an attempt to study the impact of mudbanks on coastal dynamics. The coastal stretch of south of Alleppy coast extending from inlet to Alleppy Pier is considered. Over the past so many decades this coast has been witnessing the formation, dissipation, migration and disappearance of mudbanks continuously at several locations along the coast. Local information on the appearance/disappearance of mudbanks at various locations along the coasts during the recent years has been collected and discussed. The impact of mudbanks on the coastline dynamics along selected locations of Alleppy coast has been studied through GPS shoreline mapping, satellite images and presented. The study discusses the recent mudbank occurrence along Alleppy coast against those reported in the past and their significance in coastal dynamics. It is understood that the shoreline changes and erosion/accretion process are significantly controlled by the occurrence, non-occurrence mudbanks that form along the coastal sector. If mudbanks occur constantly for a few years at a particular location beach continuously accretes and disappearance /migration of mudbanks accelerates erosion. It is also observed that the beach sediments accumulate in the mudbanks region and its north and severe erosion is found along the coastal stretch south of the mudbank. Developing a solid knowledge of this local phenomenon would benefit in positioning fishing harbours and implementing coastal protection measures effectively.

© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license © 2015 The Authors. Published by Elsevier B.V. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review-review under under responsibility responsibility of organizing of organizing committee committee of ICWRCOE of ICWRCOE 2015 2015.

Keywords: Mudbanks; Coastal Dynamics; Shoreline Change; Alleppy coast

* Corresponding : E-mail address: [email protected]

2214-241X © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of ICWRCOE 2015 doi: 10.1016/j.aqpro.2015.02.196 K.G. Parvathy et al. / Aquatic Procedia 4 ( 2015 ) 1514 – 1521 1515

1. Introduction Coastal zone is the triple interface of land, ocean and atmosphere. Any developmental activity along the coastal zone requires a clear understanding of the dynamic processes controlling its very existence. When most of the processes, which are common to all coastlines are quite well known, there are some localised, but important processes requiring further research for developmental planning. [Joseph Mathew 1992]. Mudbanks are such an inquisitive coastal phenomenon which occurs only at a few locations in the nearshore waters of the world ocean. Mudbanks are defined as distinct patches of calm, turbid water with high load of suspended sediment, appearing close to the shore with a clay substratum during the rough monsoon season (Kurup 1977, Silas 1984, Mallik et al 1988, Ramachandran 1989).

The occurrence, non-occurrence and migration of mudbanks influence the coastal dynamics significantly along mudbank influenced coastal stretch of . According to the study (Parizanganeh 2008) mudbanks are associated with recurring episodes of erosion and accretion. This paper throws light into present mudbank occurrence along Alleppy coast against those reported in the past. This paper also details the mud banks impacts on coastline morphology along Alleppy coast.

2. Study Area Alleppy coast is best known for the occurrence of unique mud banks. The coastal stretch which extends from Kayamkulam inlet (9° 8'18.35"N 76°27'41.09"E) to Alleppy Pier (9°29'31.83"N 76°19'2.01"E) is considered for the present study in which and is a part. The coastline is nearly straight and has approximately NNW-SSE trends. Over the past so many decades this coast has been witnessing the formation, dissipation, migration and disappearance of mudbanks continuously at several locations along the coast.

3. Materials and Methods Shorelines digitised from geo-referenced imageries of 2006, multidated GPS shoreline mapping during 2013 and Google Earth satellite imageries of the study area acquired in 2013 were used in the study.

GPS survey has been conducted for measuring the positions of occurrence of mud banks and various other morphological signatures like present and earlier shoreline positions, old seawalls, berm crests, etc. These are supplemented with local information collected on the appearance/disappearance of mudbank at various locations along this coast and previous studies.

The satellite images were acquired from Google Earth and due care has been taken to download every images at same projection. Google Earth satellite imageries are not used as such. The datasets are suitably geo-referenced and rectified with maximum control points from the field in Arc GIS software. The accuracy of using georeferenced Google Earth satellite images has proved to be satisfactory by the works carried out by National Centre for Earth Science Studies, Thiruvananthapuram. The past shoreline has been digitised from geo-referenced satellite images to compare the erosion-accretion status of the present and previous mudbank locations. GPS survey was relied upon to get the latest shoreline.

4. Results and Discussion Local information on the appearance/disappearance of mudbank at various locations along this coast during the recent years has been collected and discussed. The impact of mudbanks on the coastline dynamics along selected locations of Alleppy coast has been studied through GPS shoreline mapping, satellite images and presented. Morphological signatures like present shoreline old seawalls etc recorded are also used for studying shoreline variations and recurring episodes of coastal erosion and accretion along this coastal stretch.

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4.1. Mudbanks Location

4.1.1. History of Mudbank Locations The historical perspective of mudbank occurrence of past decades is detailed in Table 1

Table 1 Historical Perspective of Mudbank Formation

Year Reported Location Remarks 1678, 1725 Alleppy Location name not available 1860,1890 Alleppy Pier Northern Limit 1896 Alleppy Pier 10 km South 1902 Alleppy Pier 25 km South, Mudbank disappears 1924-1928 Aleppy Pier Moved southwards after it 1937 Alleppy Pier 8 km south of the pier 1950-1968 AlleppyPier,NorthPunnapra,South Punnapra 8 to 16 km south of pier, South Punnapra with its southern end at Nirkunnam

1966 Punnapra Before the onset of monsoon 1961-1968 Ambalapuzha 1969 Valanjavazhi Nirkunnam and Ayyankoil became respectively the northern and southern ends 1970 Alleppy Pier South of Alleppy pier 1972 Ambalapuzha, Kakkazham Extend adjoining the coast towards Purakkad. 1973 Between Ambalapuzha and Purakkad 1974-1975 Purakkad 1976 Between Purakkad and Thotapally Moved Southwards 1976-1980 Thottapally North of spillway 1981 Thotapally-, Punnapra Year not available Chethi, Omanapuzha, Thumboli Chethi-Omanapuzha mudbanks not occurring for many years

4.1.2. Recent Occurrences From the field survey and local information gathered mudbank was known to be formed in the following locations recently. Mudbank was formed during the southwest monsoon season of 2013 along the Alleppy coast. Mudbank was reported approximately at 3.5-4 km stretch alongshore from mid June to August in the Thykal and Punnapra region, Alleppy. These mudbanks continue to remain active and passive modes throughout the year contributing to more or less a stable beach throughout the year. The mudbank fisheries were found to remain active at Punnapra even during the fair weather season, but the mudbanks was seen a few metres offshore. During the southwest monsoon of 2012, mudbanks occurrence extended approximately 4 km stretch from Challi beach which is south of Punnapra to south Vadackal. In the recent years Thumboli-Ambalapuzha-Punnapra-Purakkad has become a mudbank belt during 2010 after a gap of 5-6 years. Around 10-12 years back mudbanks which were seen confined to Purakkad region has moved south towards Punnapra region and since then till now it is forming at Punnapra region repeatedly. The earlier and present mudbank locations are shown in Fig. 1. K.G. Parvathy et al. / Aquatic Procedia 4 ( 2015 ) 1514 – 1521 1517

Fig. 1 Mudbank locations along Kayamkulam-Alleppy coast, south of Alleppy

Mudbanks are characterized by spreading or growing to adjacent areas after their appearance. These sometimes disappear from one place after repeatedly occurring in the same area for years. These are very evident from the studies conducted along the Kayamkulam-Chellanam sector along southwest coast of India. According to Mathew (1992) the migration of mudbank is dominantly governed by seasonal variability in crossshore wave forcing. The same mudbank locations are found to be reported using different place names during the same year, for example the occurrence of mudbank at Kayamkulam and (Noujas et al 2010). In real situation the two place names pertain to the same location of Arattupuzha.

4.2. Coastal Morphology along Mudbank Dominated Coast The best known mudbank of the southwest coast of India is Alleppy mudbank as it occurs every year and shifts its position from Alleppy in the north to in the south. Mud banks have been reported in 1518 K.G. Parvathy et al. / Aquatic Procedia 4 ( 2015 ) 1514 – 1521

Arattupuzha (Kayamkulam), Thrikunnapuzha, Purakkad, Ambalapuzha, Punnapra along this study area. This coastal stretch has undergone noticeable variation in coastal morphology due to appearance/disappearance and migration of mudbank along this sector. The morphological variation of the past and present location of occurrence of mudbank is detailed in Table 2.

Table 2 Morphological Variation along Past and Present Mudbank Locations

Mudbank Location Lat Long Position Mudbank Status Morphological Observation Arattupuzha/Kayamkulam & 9° 8'18.35"N Not occurring since 1988. Severe erosion, Accreted beaches Thrikunnapuzha. 76°27'41.09"E started eroding, No beach in front of the seawall.

Not formed since 1988 Beach is accreting due to newly constructed groin field Purakkad Shifted further north to Erosion Punnapra Ambalapuzha 9°22'32.33"N Not formed at present Erosion 76°21'12.91"E Punnapra Present mudbank location Very wide beaches continue to exist with an accreting tendency Beach developed seaward of old seawall Alleppy Pier 9°29'31.83"N Not formed at present. Not Beach shows accreting tendency 76°19'2.01"E reported since 1970

The artificial structures along the coast include seawalls, groins and breakwaters. Construction of seawalls has been adopted to protect the major portion of the coast. Seawalls along most coastal parts have been constructed after Tsunami which struck the coast on December 2004. Old damaged gabion type seawall is observed south of Arattupuzha. Certain places like the Valiazheekal and Perumpally have groin fields, and these groins are in good condition. The groins are recently constructed and transitional in nature. An important fishing harbour on the seacoast side is at Kayamkulam. Breakwaters are constructed at Kayakulam and Thotapally inlet for developing fishery harbours and fish landing centres. Other than the fishing harbours there are numerous fish landing centres at Tharayilkadavu, Thottapally and Punnapra. Old seawalls exist along the coastal sector. During monsoon season severe losses is experienced to the south of Punnapra region. Coastal erosion is a major problem in Arattupuzha north of Kayamkulam breakwater. Due to heavy erosion frontal beach is almost absent at several locations. Between the Kayamkulam and Trikkunnapuzha sector there is no regular frontal beach except for few gaps in the sea wall. Seasonal beaches are present at certain other locations while beach is totally absent in various In most of the sectors beach is absent throughout the year. Due to the transitional groins at Valiazheekal (9° 8'57.12"N 76°27'32.30"E) and Perumpally beach (9°10'1.97"N 76°26'55.37"E) is accreted in this region.

4.2.1. Purakkad Punnapra Coast

The coastal stretch which extends from Arattupuzha (Kayamkulam inlet) to Alleppy pier is a major mudbank affected type of coast. The coastal stretch considered for the present study is a straight sandy coast in which Purakkad-Punnapra coastal sector is a part. The most distinctive trait of Alleppy mudbank is it is known to shift its position. It is observed that with the disappearance of mudbanks at Arattupuzha /Kayamkulam and Thrikkunnapuzha the accreted beaches started eroding. The occurrence, non occurrence and shifting of mudbanks influence the coastal dynamics significantly along Purakkad Punnapra coastal stretch. It is reflected in the shoreline change in mudbank location.

In the earlier times mudbank was reported at Purakkad but in the recent years it shows a tendency of appearing at Punnapra. To understand the shoreline dynamics due to the migration of mudbanks from Purakkad to Punnapra shoreline variation analysis were performed. For the past 10-12 years mudbanks are repeatedly occurring at Punnapra region. When mudbanks shifted from Purakkad to Punnapra, erosion at Punnapra disappeared and accretion was initiated. The Punnapra coast noted for its high erosion has wider beaches now westward of seawalls K.G. Parvathy et al. / Aquatic Procedia 4 ( 2015 ) 1514 – 1521 1519 which were constructed when it was eroding at the time of regular occurrence of mudbank south at Purakkad. The position of old seawall shows the beach is continuously accreting and a wide beach is formed in front of the old seawall approximately 300 m. The beach developed seaward of old seawall indicating morphological variation along Punnapra sector due to mudbanks is shown in Fig. 2.

Fig. 2 Beach developed seaward of old seawall indicating morphological variation along Punnapra sector due to mudbanks (2005-2013)

This can be particularly attributed to the formation of mudbanks in this region during the recent years. Very wide beaches continue to exist with an accreting tendency in the presence of mudbanks. During monsoon season the other sectors south of Punnapra region show erosion tendencies .As an effort to protect the newly accreted beach at Punnapra beach vegetation and trees have been planted a few metres away from the shoreline by Kerala Forest Research Institute (KFRI) with the help of local community. The prograding shoreline at Punnapra and eroding shoreline at Purakkad is shown in Fig. 3(a) and 3(b) respectively. The statistical analysis of erosion-accretion episodes for Purakkad –Punnapra sector for the year 2013 is detailed in Table 3. 1520 K.G. Parvathy et al. / Aquatic Procedia 4 ( 2015 ) 1514 – 1521

Fig. 3 (a) Shoreline Variation at Punnapra (2006-2013) (b) Shoreline Variation at Purakkad (2006-2013)

Table 3.Statistical Analysis Purakkad –Punnapra Sector for the year 2013

Location Quantity (square kilometre) Status

Purakkad 0.2857 Erosion

Punnapra 0.1288 Accretion

Shoreline from Kayamkulam (9° 8'18.35"N 76°27'41.09"E) to Alleppy pier (9°29'31.83"N 76°19'2.01"E) is found to be undergoing recurring episodes of erosion and accretion for past years due to appearance/disappearance and migration of mudbanks. The beach width of the Punnapra area which is south of Alleppy pier is prograding in past decade. The Punnapra-Alleppy stretch is showing accreting tendency with magnitude varying between 25 to 30 m The Purakkad area is showing erosion with magnitude varying between 50-100 m for the last decade. The retreating tendency on the immediate south side of Punnapra is the reflection of down drift erosion by the mudbank formation at Punnapra. The formation of mudbank at Punnapra leads to heavy deposition in this region and to the north side of this area. The width of beach has increased and is approximately 300 m at Galelia Junction, North Punnapra region with reference to the old seawall and width is gradually decreasing as we move more south till Kayamkulam. In some locations coastal protection measures have become irrelevant with the mudbank occurrence (seawalls at Galelia junction, Punnapra). Reappearance of mudbanks has made seawalls in many locations irrelevant.

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5. Conclusion

The formation and functions of mudbank remain unique and enigmatic along littoral waters of Kerala. Over the past centuries Alleppy coast has been witnessing the formation, dissipation, migration and disappearance of mudbanks continuously at several locations along the coast. Based on the study it is understood that the beach sediments accumulate in the mudbank region and its north and severe erosion is found along the coastal stretch south of the mudbank occurrence. The appearance and disappearance of mudbanks induce erosion and accretion along the coast. It is evident from the study that if mudbank occur constantly for a few years at a particular location beach continuously accretes. It is observed that mudbanks, south of Alleppy deserve special mention as it appears every year. Developing solid knowledge of this local phenomenon would benefit in positioning fishing harbours and implementing coastal protection measures effectively along a mudbank dominated coast.

Acknowledgement

The authors are thankful to the Director, National Centre for Earth Science Studies, Thiruvananthapuram for his encouragement and support. The authors express sincere gratitude to Vimal K.C., Project Scientist National Centre for Earth Science Studies, Thiruvananthapuram

References

CMFRI (Central Marine Fisheries Research Institute), 1984, Mudbanks off Kerala Coast. Bulletin No.31, Cochin. Kurup, P.G., 1977, Studies on the Physical Aspects of the Mudbanks along the Kerala Coast with special reference to the Purakad Mud bank. Ph.D. Thesis, University of Cochin. Mallik, T.K., Mukherji, K.K. and Ramachandran, K.K., 1988, Sedimentology of the Kerala mudbanks (Fluid muds?). Mar. Geol., 80, 99-118. Mathew, J., Wave-Mud Interaction in Mudbanks, 1992, PhD. Thesis, Cochin University of Science & Technology, Centre for Earth Science Studies, Thiruvananthapuram Noujas V, Badarees K.O., Vimal K.C., Sreekanth K and Thomas K.V. 2010, Impact Of Mudbanks On Shore Stability along Kerala Coast, In. Kerala Science Congress Proceedings. Parizanganeh, A., Lakhan V.C., Ahmad S. R., Dynamics 0f Mudbanks along a Coast Experiencing Recurring Episodes of Erosion and Accretion. Jour. of Marine Engineering, 2008, 4(7), 1/E-10/E. Ramachandran, K.K., 1989, Geochemical Characteristics of Mud bank Environment- A case study from Quilandi, West coast of India. Journal of Geological Society of India, 33, 55-63.