Tidal wetland mapping using remotely sensed data

Tidal wetland mapping using remotely sensed data

V. Shreedhara, A.N. Sherieff, M. Sabappa Reddy
Karnataka State Remote Sensing Technology Utilization Centre, Bangalore, India

C.R. Bannur
karnataka State Council for Science & Technology, Bangalore, India.

S. R. Nayak,Baldev Sahahi
Spalce Application Centre, Ahmedabad, India.

Introduction
Information on the coastal zone is essential for the regional planning, decision and policy making for futuristic development and constructive management plans. Wetland, the prime component of the coastal zone is a dynamic ecosystem having complex inter-relationship of hydrology, soil and vegetation. They are lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or land covered with shallow water. Tidal Wetlands have been recognized as a significant ecosystem which play an important role in Bio-geochemical cycle by trapping the silt and clay, recharging the groundwater and even cleansing certain toxic components from effluent water, to which they are aptly called as “Kidneys of landscape”. The tidal wetlands also provide a unique habitat for flora and fauna at different trophic level and are responsible for conserving reproductive fisheries not only by way of catch but as feeding, spawning and nursery grounds. Besides, mangroves and coral reefs are the economical and major ecosystem of the wetland. Conservation of these lands lies in their precise identification and periodically monitoring them over time and space.

Karnataka forms a part of the Malabar Coast in the West with extensive coastline running 320 kms, placed 12 30-150 00 N and 740 00 750 00 E. indented with promontories, headlands, picturesque estuaries, encompassing tidal wetlands essaying complex “Mangroves” and lengthy linear beaches. The coastal berm is narrow due to the descending western ghats, which are aboutted by the sea particularly in Uttara Kannada part of the coast. The region comes under the direct influence of the Southeswest monsoon, receiving very heavy rainfall during June to August. The climate is humid. Soil is alluvial in the plain region and Lateritic down the hilly slopes.

Nevertheless, the coast has foreseen over the period of time, the growth of undustry and urbanisation due to its natural harbors and ports in particular New Mangalore Port, which has opened new vistas in trade ad commerce, which along with the commissioning of the sea Bird has gone to deplete and destruct the virgin environment, in particular, the wetland ecosystems by way of discharging the industrial effluent into the sea, which needs a constant monitoring, to which remote sensing is an ideal tool.

Objectives:
The main objectives of the present study is :

To Map tidal wetlands through visual interpretation of satellite data.
Carry out spatial analysis of wetland features.
Contemplate the complied data to monitor the coastal environment periodically.

Methodology:
IRS LISS II FCC ( transperancy ) of cloudless data of post and premonsoon seasons where selected for the study . The base maps were prepared using Survey of India topographic sheet on 1:50,000 scale. IRS FCC dipositive were enlarged to 1:50,000 scale for detailed mapping using a very high magnification enlarger procom-II. All the tidal wetlands classes are identified and delineated based on the standard image interpretation key (SAC, 1991) with particular emphasis on the tone, texture, pattern and association of the individual features. The preliminary interpretation is followed by ground truth verification. The spatial analysis of individual category is carried out finally using the digital planimeter.

Data Used:
Standard false colour composite diapositive (FCC ) of IRS band 2,3 & 4 which in contrast to B/W image yields better discrimination of the wetlands categories, are used in the present study. Two season data of October and December 1988 has been selected based on the reproductively cycle of vegetation present in the wetland areas. The reproductive cycle of vegetation present in the wetland areas. Survey of India topographical sheets on 1:50,000 scale were used for the preparation of base maps, as said elsewhere. Ground truth data has preted map, in a formatted from.

Results & Discussions:
Utilizing the visual interpretation technique and the wetland classification key, the entire Karnataka coast has been mapped using IRS data. The salient features Karnataka coast has been mapped using IRS data. The salient features of wetlands units are discussed below and shown in Fig. 1.

Mudflat:
Mudflats are wide expanse of fine grained soft mud along the shore. They generally consist of deposits of clay, silt, ooze, etc. (King 1972). These mudflats are further classified based on their relation with tidal condition into 1) High-tide or supratidalflats, 2) Intertidal slopes & 3) subtaidal zones (Davies, 1972). Along the Karnataka creeks, on the low lying areas adjacent to the estuaries, lagoons particularly near Karwar, Tadri, Kundapur and Mulki. It is seen from the study the total area covered by mud flat is 3937 ha. & the same along the individual estuarine complex is given in Table I.

Interestingly, it is seen that total mud flat area is less along the Karnataka Coast due to the non-formation of the deltas which may be due to impediment of the sand & silt along the west flowing rivers, by the way of construction of innumerable irrigation & power dams / barrages and non-plain areas due to the descending western ghats may be ascribed to the less formation of mud flats. Added to , the agricultural practices on large scale along the estuaries encroaching the already formed mud flats, which invariable affect the spread of tidal wetlands.

Sand:
Sand is classified into various units such as beach, bar, spit. It is identified by its characteristics white colour in the image in associating atleast partly of unconsolidated material mostly of sand grade. It is seen as a thin white, linear discontinuous crescent shaped strip all along the coast, carpeted with beach vegetation & plantation.

Spit, is defined as a small point or low tongue or narrow embank,ment of land commonly consisting of sand or gravel and having one end attached to the main land and the other terminating to open water, usually the sea. The observed spits are of different sizes. The well developed spit is observed near Malpe, Bengre and Pavinkurve regions indicating the direction of littoral drift. The other spits are locatd at Mangalore, Kundapur & Bhatkal. Bars are submerged ridges of detrital sediments which are larger and less regularly shapped . They are found singly or together and internally terminated. In the present study Bars have not been identified, may be due to the submarine topography & wave pattern along the coast. Shoals are either submerged ridge, bank or bar producing shoal consisting of or covered by sand, Mud, gravel or other unconsolidated materials. Small pockets of shoals are identified in the estuaries and lagoons.

Rocky Coast / Cliff:
Any high, very steep to perpendicular or over laying face of rock or earth rising above the shore of the sea. Absence of sand, mud & water abutting the coast, ideally classify / categorize the coast as a cliffy one. In the present study the cliffed/rocky coast are commonly seen near Karwar, Malpe & Bhatkal regions and are steep & lateritic in nature. All headlands & promontories are rocky in nature and form elevated platforms.

Mangroves:
Mangroves are unique halophytes aptly adapted to saline environment, both morphologically & physiologically. They are found along rainy, inter-tropical shores on the low, flat coast lying inside the surf belt, but within the reach of the tide, colonizing especially in the bays, lagoons & estuarine regions. They may form a fairly continuous firings or be split up into a labyrinth of islets between the sluggish tidal streams run. A uniformly hot & wet climate, salt or brackish water, a soft ground deprived of air & rhythmic tidal flood are the conditions under which mangrove plants develop. Mangroves, based on the characteristic red tone are identified and delineated in association with mud flats habitats along the estuarine / brackish waters, in patches. However, the frings mangroves cannot be delineated from the adjacent agriculture plantations commonly seen along the estuarine banks/ Udupi & Karwar regions, where the growth is luxuriant & rest are scattered in thin patches along the estuaries. The total spatial distribution of Mangroves is estimated as 815 ha. & their spread in individual estuarine complex is given in Table – I. By the field study it is seen that the Mangroves found on the west coast in particular Karnataka coast are less complex when compared to east coast, wherein mangrove forest are found in abundance especially in Sunderban areas, with complex variety. About 16 different species were recorded, the dominant being Rhizophora mucronata, followed by Avicennea and Sonneratia. In order to improve the bio-diversity of the mangroves, a tidal arboretum is planned near the kundapur area where congenial environment is created for the flourish of the variety of the Taxa, to form a gene bank.

Beach Vegetation:
The beaches are carpeted with beach vegetation otherwise called as strand Vegetation, mainly consisting of berbs to arborealtrees. This vegetation is mainly observed along the Karwar & Mangalore coast, where the beaches are wide and extensive.

Beach Plantations:
All along the beaches rectangular shaped, characterized with cherry red tone features were identified as beach plantations, comprising of Casuarina, grown under afforestation programme to protect the coast. They were predominantly seen along the Mangalore Udupi, Honnavar & Karwar area.

Other Vegetation:
It comprises of swamp/marsh / coconut plantation. scrub vegetation, within the confluence of the wetland, related to the phenomenon of regression of the sea. They may be sites of older mudflats which are under the sea in the age past.

Water Bodies:
Estuaries, logoons, creeks and bays which form the major water bodies are easily identified by their characteristic blue tone. Estuaries usually defined as that part of the lower river course that is affected by the maxing of salt water with the fresh water. about 9 major estuarine complex were identified along the Karnataka coast, most of them draining parallel to the coast. lagoon is an elongated body of water lying parallel to the coast. Lagoon is an elongated body of water lying parallel to the coastling and separate from the open sea by barren islands. They are predominantly seen in the Kundapur, Mangalore and Karwar regions. Creeks are a low land water course of medium size, originating from any natural streams or Bay or a narrow inlet of sea that extends inland and are commonly seen along the coast.

Shoreland:
Features like paleomudflat, coastal dunes, coastal dune with vegetation and strandlines are classified under this category.

Paleomudflat:
They are defined as mudflats lying above high tide flats and are formed by marine deposition of the past sea level (Nayak & Sahai, 1984-85).

Coastal dunes:
Coastal dunes are defined as topographical feature of eolian origin composed of sand grains deposited down by wind from a natural sources of sad. The mode of transportation of these sand particle could not be identified but the dunes are identified based on photo characters and are extensively seen in the Kumta, Honnavar, Kundapur and Udupi regions. Denuded dunes, a small distance away in the coast which are cultivable, are classified as dunes with agriculture which are frequently seen.

Strand line:
It is an ancient shorelines, refers collectively to the assemblage of various features characteristics of former coastal areas. It is observed all around karwar and Honnavar coast, featuring like a lineament in the image.

Other Features:
They include saltpans, Aquaculture ponds, Islands, high water and low water line.

Salt pans:
An undrained usually small & shallow, rectangular, man-made depression or hollow in which saline water accumulates & evaporate leaving salt deposits. These features are very well delineated in the image based on their characteristic features & vast stretches of them are identified along the Tedri and Kali estuaries.

Islands:
Many tiny offshore Islands are clearly visible near Maple, Kundapur, Bhatkal, Honnavar & Karwar regions. Estuarine islands locally called as “kudrus” which are generally muddy, low and flat often support good growth of mangroves, coconut plantation and agriculture were also identified in this category.

High water & Low water line:
Water at the maximum & minimum level reached during the tidal cycle is coined as high and low water line, which can be demarked by the analysis of satellite data.

Conclusion:
It is evident from the present study, the usefulness of 1:50,000 scale, albeit with certain limitations. the information culminated is very informative & resourceful for the planners & decision makers, in taking constructive measures to conserve and apt management of the coastal environment. As been said earlier, tidal wetlands are very unique ecosystems by itself, interfacing land & water, none others to it can speak about the their resources potentiality, need continues monitoring & inventory for maintaining the eco-balance. The studies were useful in identifying vulnerable points along estuaries where afforestation of mangroves are being presently carried out by the Udupi regions of the coast Along with brackish water aquaculture sites were too demarcated to carry out pisciculture activities as a socioeconomic measure near the Kumta & Ankola regions of Uttara Kanada coast. Marine regressions over the period of time is indicated by the presence of place-mud flats, strandlines & lagoons identified by the studies.

References:

Davies J.L., 1972: Geographical variation in coastal Development, Oliver & Boyd, Edinburgh.

King C.A.M. 1972: Beaches & Coasts. 2nd Edition. University of Nottingham Edward Arnold, London.

Nayak. S.R. & Sahahi, B., 1985: Coastal Morphology: A case study of the gulf of Kambhat (Cambay). Int. Jurn. Remote Sensing, 6 (3 & 4), 559-567.

SAC, 1991: Manual for mapping of Coastal Wetlands/land forms & shore line changes using satellite date.

Sheikh M.G., Nayak S.R, Shah, P.M. & Jambusarai B.B. 1985: Coastal land form mapping around the Gulf of Khambhat using landsat TM data. Jurn, Ind. Society of Remote sensing, Vol. 17. No. 1.

Table – 1

NON – VEGETATED WETLANDS						VEGETATED WETLANDS					WATER BODIES					SHORE LAND		OTHER FEATURES
Estuarine Complex	Mudflat	Sand	Beach	Shoa	Rocky coast	Mangroves	Beach Veg.	Bach plant	Other veget	Estuary	Langoon	Kayal back	Creek	Water body	Coastal dune	Coastal with veg.Dune	Place flats	Salt pan	Aqua. Ponds	Islan
KALI	1032.50	7.5	337.5	20.00	125.00	37.5	2.5	27.5	32.5	1395.00	-	227.5	-	-	262.5	-	-	67.5	-	110.00
BELEKERI TADRI – GANGAVALLI	354.50	10.0	267.5	22.5	12.5	57.5	-	-	27.5	267.5	12.5	-	205.0	-	-	1545.0	-	1212.5	5.0	42.5
AGHNASHNI SHARAVATHI	1587.5	10.0	47.5	42.5	-	85.0	-	-	357.5	2883.5	-	-	90.0	-	347.5	155.0	-	415.0	242.5	450.0
VENKATAPUR	160.0	-	330.0	-	47.5	17.5	10.0	-	15.0	60.0	10.	-	17.5	-	-	-	-	-	-	147.5
SHIROOR BAINDOORHOLE	102.5	-	394.5	-	-	80.0	-	-	2.5	372.5	30.0	-	77.5	-	-	20.0	-	-	-	-
CHAKRAHALADIKOLLUR	4.27.5	7.50	412.5	52.50	-	312.50	5.0	-	12.50	1805.0	485.0	-	-	-	-	35.0	-	-	-	495.0
SITASWARNAKODI UDIYAVARA	67.5	-	530.0	40.00	-	77.50	-	-	10.00	1705.0	-	-	-	-	35.0	-	-	-	-	428.5
MULKIPAVANJE	107.5	7.5	377.5	10.00	-	125.0	5.0	10.0	5.0	455.0	-	35.0	87.5	7.5	42.5	-	15.0	-	-	-
GURPUR NETRAVATHI	97.5	480	516.2	100.0	-	22.5	5.0	152.5	57.5	2078.5	37.5	335.0	45.0	92.5	-	-	-	-	-	297.5
	3937.0	522.50	3213.20	287.50	185.00	815.00	27.50	190.00	520.00	11022.0	575.0	597.5	522.5	100.0	687.5	1875.0	15.0	1695.0	247.5	1971.0