Indexed in Scopus Compendex and Geobase Elsevier, Chemical Abstract Services-USA, Geo-Ref Information Services-USA, List B of Scientific Journals, Poland, Directory of Research Journals www.cafetinnova.org ISSN 0974-5904, Volume 06, No. 05
October 2013, P.P. 957-963
Remote Sensing Based Delineation of Depositional landforms of Modern Penner Delta in Andhra Pradesh, India K. V. SURYABHAGAVAN1 AND J. SEETHA RAMAIAH2 1
School of Earth Sciences, Addis Ababa University, P.O.Box.1176, Addis Ababa, Ethiopia. 2 College of Earth Sciences, University of Dodoma, Dodoma, P.BOX. 259, Tanzania. Email:
[email protected]
Abstract: Remote sensing based study of the depositional landforms of Modern Penner Delta in Andhra Pradesh, India revealed that deltaic plain extends to about 1425 km2 of area comprising of river channel (61 km2), levee (29 km2), estuary (10.1 km2), tidal creek (13 km2), lagoon (9 km2), dune (26 km2), spit (2 km2), palaeo sand ridges (167 km2), marsh (3.2 km2), channel bars (8.3 km2) and flood plain (1096.4 km2). A cross section of the river channel shows two terraces formed during the Holocene period due to aggradation of channels and/ or modifications in the meander patterns of channels. Occurrence of older channel sands above the present river bed at different heights perhaps is an indication of the subsidence of the riverbed or shifting of the river course. Development of different landforms provides evidence in favor of the influence of neotectonic activity. A newly opened up channel joins the tidal creek thereby forming a new distributary at downstream of Utukuru village and is likely to cause flood effect on Pallempalem village in the coming years. Iskapalli lagoon in northern part of the delta is one of the important remnants of transgression during the Holocene period with well recorded and preserved imprints of sea level oscillations and hence there is every need to protect the natural lagoon from human interference urgently. Keywords: Landforms, Penner delta, Remote sensing 1.
Introduction:
Vast potential of the deltas as hydrocarbon reservoirs has been drawing lot of attention of the scientists and technocrats towards their architecture and formation processes. During the last two million years, coastal areas have dramatically evolved worldwide due to sea level oscillations caused by the Ice Ages altering the physiography as well as the climate of deltaic environs (Abuodha 2009, Nageswara Rao et al. 2008, Diez et al. 2007). As a result, deltaic regions around the world including that of the East Indian coastal tracks have developed well, preserving the imprints of the said oscillations to a great extent. Usually, east coast deltas are progradational in nature due to barrier development and lagoon filling processes. During deltaic progradation, a number of micro sedimentary environments evolve and effect morphodynamic changes through time. Because of a high-degree of resource potential, deltas have turned into cradles of civilization over time, but at the same time, they remain as fragile ecosystems subjected to natural phenomena like sea level rise and climatic variations on one hand and cultural processes and anthropogenic pressures on the other. Therefore, in-depth studies are essential to understand various interacting processes at operation in a coastal zone (governing the dynamics of deltas). In this connection, mapping and time series analysis of
landforms are very useful. As an attempt in this direction, studies with reference to Penner River Delta on the east coast of India were taken up mainly utilizing remote sensing technology (Lilesand et al. 2008, Rao 2002, Kameswara Rao 1991). 1.1 Study Area: Penner river originates at an altitude of +1500 m MSL in Chennakesava hills of Kolar District (13 o 22′ N and 77o 41′ E) of Karnataka State in India. The river flows for about 597 km through Karnataka followed by Anantapur, Cuddapah and Nellore Districts in Andhra Pradesh State finally joining Bay of Bengal on the east coast of India (Fig.1). The river drains < 55, 213 km2 of the Precambrian terrain, of which 12% lies in Karnataka and 88% in Andhra Pradesh. The Penner delta in Nellore District exhibits a combination of many typical landforms spread over 1425 km2 of area with prominent landforms such as river, estuary, spits, tidal creeks, barrier islands, palaeo beach ridges and flood plain. The river flows from its origin due NNW over a distance of ~ 215 km and then takes a sharp turn due east within the Archaean terrain. On entering Cuddapah basin, the river meanders gently in a broad valley with flood plains on either side. The eastward trend of the river is disrupted near Gandikota where it turns northeast and continues through an irregular valley over
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Remote Sensing Based Delineation of Depositional landforms of Modern Penner Delta in Andhra Pradesh, India
a distance of 11 km. However, the ESE course is resumed again from Jammalamadugu onwards. The river flows southeast almost parallel to the trend of the Kurnool rocks upto a distance of 35 km. Further downstream, it has a transverse course through the folded upper Cuddapahs till it comes out of the Cuddapah basin on to the Nellore plains. Within Cuddapah basin, the gradient of the river varies from one place to another averaging at 1.02 m.km-1. Meandering nature of the river is more prominent along the valleys within the eastern ranges where the rocks are usually shales and slaty shales. After traversing off Cuddapah basin at Somasila, the river crosses Sangam, Jonnavada and Nellore areas and joins Bay of Bengal ~ 16 km northeast of Nellore (80o11′E and 14o35′N). Ghosh (1992), Sinha (1996) and Singh (2000) have reported that the flow pattern of the river in different areas is controlled by local structural elements. Jayamangali, Kunderu, Sagileru, Chitravati, Papaghni and Cheyyeru are the major tributaries of Penner. While the former three join the main stream from northern side of the main river, the latter three do so from the southern side.
and channel bar deposits were delineated in Penner delta study area. The delta is cuspate in shape unlike many other deltaic coastlines (Fig. 2). Certain of these landforms were noticed to exhibit rather complex characters due to strongly operating physico-chemical and biological variables. As a result, the type of sediment deposited varied from place to place within a geomorphic unit leading to the formation of one or more micro environments within a macro environmental entity. Landforms and the material that compose them reflect their relative responses to sea-level rise since every landform offers certain degree of resistance to erosion (Thieler and Hammer-Klose 1999).
The area under study exhibits moderate tropical climate with temperatures ranging from 25-46oC in summer and 18-28o C in winter. Rainfall in the study area ranges from 600 to 900 mm a year receiving copious rainfall from southwest monsoon but scanty condensation from northeast monsoon (Srinivsa Rao et al. 2003).
The river flow downstream of Utukuru changes its course towards south hitting the banks and paves way to the erosion of top layers. This phenomenon exposed marshy land upto a depth of 1.4 m below the present day river surface having the following stratigraphic sequence (Plate-1).
2.
Levee Silty Sand 0.20m --------------------------------------------------Flood plain Clayey Sand 0.10m --------------------------------------------------Levee Silty Sand 0.30m --------------------------------------------------Flood plain Silty Sand 0.10m --------------------------------------------------Levee Silty Sand 0.30m --------------------------------------------------Channel sand Coarse Sand 0.60m --------------------------------------------------Marshy land Clay 0.60m
Material and methods:
Survey of India (SOI) Toposheets (66B/2 and 66B/3) of 1:50,000 scale pertaining to the study area were used for geo-referencing of satellite images, creation of landform features and ground truth acquisition. Satellite data of IRS-1D LISS-III of 2012 with a spatial resolution of 23.5 m and PAN data 5.8 m pertaining to Path 102 and Row 063 were merged using Principal Component Analysis approach. The satellite data were digitally rectified and processed using ERDAS Imagine 9.2 while database integration was done in ArcGIS 10.1 software. Visual interpretation techniques together with Garmin 12 Channel GPS facility were adopted in delineation of various geomorphic features and permanent spatial features such as roads network, canals, streams and tanks besides settlements. Corrections and modifications of any misinterpreted landforms were made, final thematic details transferred onto the depositional landform maps in which specific colours were assigned to each landform unit for clear distinction. 3.
Results and Discussion:
A total of eleven different depositional landforms such as river channel, estuary, flood plain, levee, mangrove swamp, paleo beach ridge, creek, dune, beach, lagoon
3.1 River Channel: The present river channel extending to 61 km2 of area is passing through coastal plains, but normal flow has been hampered by the Sangam and Nellore anicuts. Cuddapah quartzite rocks on either side of the riverbank were exposed at Sangam and Jonnavada regions restricting the width of the river. Width of the channel upstream is ~ 0.4 km at Sangam, but increased to ~ 1.0 km at Kuditipalem downstream.
Gradational Gradational Gradational Gradational Gradational Erosional Contact
The active river channel made up of sandy sediments is subjected to annual flooding that broadcasts over 400600 m wide floodplain. This surface, recognized as recent active floodplain is made up of active channel, braided bars, point bars and sandy flats. These facts indicate that evolution of Penner channel probably occurred due to continuous floodplain aggradation effected by frequent as well as extensive overbank flooding. The channel sands exhibit cross bedding, ripple marks and coarse nature typical of new channels. Channel sands are also occurring above the present river bed (To surface). Further, two terraces, designated as T 1 and T2; are noticed on the northern bank. While T2 surface occurs at a height of 5 m above river bed, T 1
International Journal of Earth Sciences and Engineering ISSN 0974-5904, Vol. 06, No. 05, October 2013, pp. 957-963
K. V. SURYABHAGAVAN AND J. SEETHA R AMAIAH
surface lies at a further height of 3 m with clear exposure just downstream of Utukuru. All these formations are perhaps an indication of the subsidence of the riverbed. Perched location of the channels and overbank spilling are likely given way to the formation of new channels. Presence of sand ridges of 30 m height above to surface also provides further evidence to the above observed facts. Thus, weather and base-level changes during the Holocene period account for the aggradation of channels and modification in their meander patterns due to neotectonics, widening and coalescing of river valleys coupled with the development of new distributaries in the river system. 3.2 Estuary: Estuary of the Penner River spreads over 10.1 km2 of area extending upto 7 km upstream the confluence. According to the classification of estuaries based on tidal ranges by Hayes (1979) and Davis (1985), Penner estuarine system represents a mesotidal (< 2m) and positive estuary. As stated by Dalrymple et al. (1992), two main categories of depositional environs, namely, fluvial and marine sediments occur in this estuary, which is formed in the seaward portion of the drowned river valley. For convenience in describing morphological changes, left and right banks of the estuary are dealt with separately. From Survey of India Toposheet (No.66B/2) for the year 1917-18, one big island is observed at the mouth of the estuary at Jeevandibba region (Fig.2). Another notable feature on the northern periphery of the estuary was the existence of a small tidal creek running almost parallel to the coastline. There were no spit developments except low water spit sands. At that time, Pallepalem village was situated 1 km away from the coastline towards north of the estuary. Field observations during the present instance indicate that right bank is presently active while left bank is slowly silting up from Pallepalem village downstream due to formation of new sandy islands that forced opening up of a new channel of 150m width into the tidal creek between Utukuru and Pallepalem villages, thereby creating a new distributary downstream Utukuru village. Because of this newly formed distributary, new Pallempalem village is under constant threat of subsidence. Tidal influence on the present estuarine environment progressively increases from November to June and accordingly the salt wedge moves inland towards the head of the estuary. Within the estuary, a number of braided islands running parallel to the river channel are existing and some more are being formed newly at barrier spits opposite river mouth due to shifting of the very mouth.
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Since 1917 till now, over 5 km2 of land got eroded from the right and left banks together whereas about 7 km2 of land was added up to the delta by way of new alluvial islands in the estuarine channel. The land coalesced to the coast near river mouth was estimated to have prograded approximately at a rate of 10 m.yr -1. 3.3 Tidal Creeks: In the study area, Upputeru creek is one of the biggest landward tidal creeks running inland to a length of 15 km across the southern margin of the delta (Fig.2). This creek was serving as a minor port at Krishnapatnam in Nellore District during the study period, but subsequently developed into a major port predominantly handling iron ore exports. Seasonally varying dynamic currents operating at the mouth have lead to the formation of a north-south bar that hampers the navigational activities of the port. Water depth in the creek varies from 1-10 m. The creek is bound all around by mangroves ranging in height from 1-3m. Southern part of the creek is bounded by palaeo sand ridges with a maximum dune height of 20 m. Kameswara Rao (1991) reported that the creek is a limited meandering type guided by a fault in the basin. As per the information gathered from local fishers, there is a drastic decrease in the fish landings from the creek in recent years due to severe pollution caused by the aquaculture farms that came up in a big way in the vicinity. Three more tidal inlets extending in length from 1 to 3 km and often shallow in nature with
