Remote Sensing of Delta Progradation in Mahanadi Delta, Orissa
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SHORT COMMUNICATION 227 REMOTE SENSING OF DELTA PROGRADATION IN MAHANADI DELTA, ORISSA K. VINOD KUMAR and ASls BHAITACHARYA NatIOnal Remote Sensing Agency, Balanagar. Hyderabad - 500037 Email: [email protected][email protected] Mahanadi Delta is a complex delta formed due to enhanced for carrying out the study. Density level slicing the coalescence of three sub-deltas. The northern was employed to understand the depositional processes. portion of the delta i.e. Brahmani-Baitarani river mouth was monitored using IRS .. Ie LISS·3 satellite data. Results and Discussion Barrier·Lagoon type of progradation was brought out This Brahmani - Baltarani delta is considered to be the by digitalJy enhancing the satellite data. Density slicing youngest deltaic plain in comparison to the Mahanadi and technique was employed to understand the sediment the Devi deltas in the south (Bharali et a1. 1991). The diffusion pattern. This was compared with the standard Brahmani-Baitarani river system when it enters the Lower distribution pattern to understand the nature of Deltaic Plain, bifurcates into two rivers i.e. Dhamra river dispersal mechanism near the river mouth here. and Maipura Nadi. These show anomalous meandermg and compression in this stretch (Fig.l.6). Near Chandbali (2qo45 , N Latitude and 86°45' E Longitude) (Fig.I.l) the Introduction Dhamra river takes almost right-angled bend before Mahanadi delta is a complex delta formed due to the meeting the sea. Compressed meanders are seen at this coalescence of three sub-deltas formed by Brahmani stretch COinciding with the major morphostructures (Fig. 1.6). Baitarani river in the north, Mahanadi river in the centre The progradation of the coast.at these two river mouths are and Devi River in the south. It is a typical arcuate delta by barrier-lagoon formation. Two sets of beach ridges are with its apex near Cuttack though a little cuspate further traced indicating two phases of delta progradation. These north, where Baitarani and Brahmani rivers discharge. The beach ridges form strand plain with swale depositIOn. Mahanadi River is the major river draining the central The new strand plain has beach ridges numbered 10 - A to portion of this delta. From the apex. it trifurcates into 10 -G and the older strand plain has beach ridges numbered distributaries. Some of them split into two channels and join ll-A to ll-G in the Lower Deltaic Plain (Fig.I.l). The before they reach the coastal plain. The Jatadharmohan and orientation of these two sets of beach ridges with respect to Santra rivers are the other small rivers draining this deltaic the present day coast is different. The beach ridges of new plain. Mahanadi Deltaic Plain falls under tropical climate strand plain are oriented Nw -SE whereas the older set has characterized by high temperature and medium to high orientation in NE-SW direction. This indicates that the rainfall. The hot summer is during the months of March, configuration of the coast has changed over period of time. April and May. Monsoon season is from June to September Probably, a tectonic upheaval in the past along the and winter is from December to February. The hottest morphostructure (Fig.l.6) might have resulted in the month is May during which the temperature increases to development of the depression and consequently the 40°C. The coldest month is December when the minimum orientation of the coast has changed. South of Maipura Nadi, temperature is around 22°C. The relative humidity is very the present day coast has a linear configuration probably high and varies from more than 60% in March-April to 85% controlled by geological structure (Fig.!.l). An elongated in July-August. The average annual rainfall of the area is channel bar development is seen in the Dharma river. 1504 mm. August is the rainiest month and December and The sub-aqueous portion of the delta. especially the January are the driest month. One of the earliest studies of channel margin platform and prodelta slope, was brought these deltas has brought out the various landforms here out using digital image processing techniques. LISS-III data like abandoned courses, ancient beach ridges besides was digitally enhanced to bring subtle variation in the morphostructure (Sambasiva Rao et al. 1978). submarine features along the channel margin platform of the major river mouths. The general nature of the histogram Material and Methods in the land-sea interface is bimodal with two peaks. The IRS-IC LISS-III (digital data) of December, 1996 was water portion of the histogram was stretched using used for the analysis. Satellite data was geo-referenced and various techniques like linear and histogram stretching. JOUR.GEOL SOC.INOJA. YOL.64. AUG. 2004 N I N loBAR CREST/EBB SHIRO 00 2 .SWASH BARS 3.BAR BACK 4.BAR FRONT 5 .EBB SPIT 6 .RIP CURRENTS 7.LOW TlOAL FLATS a.HIGH TIDAL FLATS 9.CHANNEl BAR 10 SlRAND PLAIN (NEW) WITH BEACH RIDGES(B to 9) 11 STRANO PlAIN (OLD) WITH BEACH RIDGES !a to fl 12 MANGROVES 13 SlRAIGHT BEACH 14 COMPRESSED MEANDER LOW 15.EMERGING BAR CREST/ EBB SHIELO TURBIDITY 2.PSEUDO LEVEL SLICED OF IMAGE OF CHANNel MARGIN PLATFORM --+ flood flow ebb flow U max (maxium ri\l&r velocity) UDP-UPPER DELTAIC PLAIN LOP -LOW£R DELTAIC PLAIN CMP--CHANNEL MARGIN PLATFORM 1.LDWEA OEl.. TAlC PLAIN & CHANNEl. MARGIN PLATFORM PD-PROOELTA (.I) :c o ~ L ~~ l'A&Al.In.TOCD.\ft Ul lL_~IJUSTO_DI I"") tu~-.uIIT o ~1MKJfT~DUllTO-"""ON IN~TO~ 3: 4CLOUIIII 3: '""'Z ~ n ~ ~ D 6 z c 3 ENHANCED FCC OF PRODELTA (MaipIJra i'ladi mouth) H 8 rn C r o Morpho structure V: C '! z 1. COMPRESSED MEANDER :; ;;: 2 .TONAL ANOMALY 3 .ClRCULAR ANOMALY ~ r -Sea.k :;., ---..-..-....~~ .+- 1 > ;;0; S.RAW IMAGE ( UNSTRETCHEDI 6 .L1 NEAMENT AND GEOMORPHIC ANOMALY ~ :r: Fig. I. ( '( l~l'l . t1 .ll id ~llhrnalillc rnorrh()I()~: Ill';lJ' Chandb:.tll Jcprc<,siol1. parts oj' \1:l h;,lll~IJI JL'IL.l, O ri""a. SHORT COMMUNICATION 229 This resulted in saturation of land pixel and enhancement FRICTION-DOMINATED EFrLUENT (plano of water pixel. Pseudo colour level slicing was employed turbulent jet with pronouncod to density slice the image into turbidity classes. The various bed shear) colours in these density sliced image indicate the turbidity level of water during the satellite pass time. The dispersal pattern of the turbidity level indicates the type of coastal processes operating in these zones. The mapping of sub aerial depositional features along these stretches helped in understanding the coastal processes operating in these three di verse river mouths. North of Dhamra river, the shoreline is almost straight to arcuate. IRS-l C LISS-III Plan view (digital data) of December 1996 depicts the condition of this river mouth during low tide phase (0.58 m) (Fig. 1). The mouth exhibits semi- diurnal tidal condition with two hi gh U , - Maximum issuing velocity of river tides and two low tides. The tidal range typically indicates mo meso tidal set up with tidal range around 2 m. The average Fig.2. Plane jet diffusion (a/ler Davis Jr .. 1991 ). rainfall for this region is around 1504 mm (Source IMD). The wind direction in the Bay of Bengal during the time of satellite data analysis is northeast. The wind is north easterly from October to January along the coast and turns angle of approach the wave is NE during th e month of southwesterly with the development of an anti-cyclonic January. The morphology of Dhamra river and Maipura nadi circulation over the northwestern Bay in the month of mouth matches well with the typical setup in the wavc February. dominated ri ver mouth as illustrated by Davis Jr. (1992) The coast is wave dominated where the swell waves (Fig.3). approach from southwest direction, obliquely striking the The bar crest which is typical of wave dominated river shore with wave heights varying between 1 to 3 m. During mouth is seen to be oriented west to the zone of maximum the remaining months, the wave height is around 1 m and velocity (Fig.l.l). The bar crest is made up of coarser approach from the northeast direction. Apart from th is, sediments and the swash bar is made up of silt and clay with littoral drift of sand moves from southwest to northeast interbedded sands. The bar back and the bar front are made direction during the mon soon months and in the remaining up of poorly sorted sand and si It. The clays are deposited in months it moves from NE to SW (Mohanti, 1990). The the prodelta slope. The swash bar ultimately gets we lded landforms seen at this stretch like the ebb spit, bar crest etc to the shore in which the coarser sediments form th e are due to the interaction of the fluvial processes with the component of the beach ridge. The merging of swash bars coastal processes. constricts the river mouth resulting in the migration orri ver This zone may further be divided into Brahmani and mouth . The beach ridges in the New and Old Strand Plains Baitarani river mouths, which open into the sea as Dhamra indicate that in the past it was a wave-dominated coast. South river and Maipura nadi (Fig.l.I). The density sliced image of this zone, a long shore bar is seen with a northcast of low tidal and low fresh water condition shows that the southwest orientation (Fig. 1.1). The bar has been breached sediments are in suspension and turbulent (Fig.l.2). The by the rip currents because of change in bottom topography sediment distribution pattern indicates a plane jet type of at this zone.