Available online at www.sciencedirect.com ScienceDirect 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, India, 575025 bCentre for Earth Science Studies, Thiruvananthapuram, 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 Kayamkulam 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 Kerala. 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 Purakkad and Punnapra 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. 1516 K.G. Parvathy et al. / Aquatic Procedia 4 ( 2015 ) 1514 – 1521 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-Pallana, 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