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SECTION-3 SECTION-3 Mangroves and Estuaries
PAPER-2
HYDRODYNAMIC PARAMETERS OF IMPORTANCE IN THE RESTORATION OF DEGRADED AREAS IN KRISHNA MANGROVE WETLANDS
D. Ramakrishna


ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
RESULTS AND DISCUSSION
CONCLUSION
ACKNOWLEDGEMENT
REFERENCES
STUDY AREA IN KRISHNA MANGROVES


ABSTRACT: up | previous | next | last

In mangrove wetlands, hydrodynamic processes play an important role in determining the health of the mangroves. Important causes for degradation of mangroves in Krishna wetlands is the poor pattern of tidal flushing in the mangroves due to the formation of topographically elevated areas which may be due to monsoon floods. Hence, to carry out restoration of degraded areas, tidal variation is measured in the creeks adjoining the restoration areas of Sorlagundi and Nakshatranagar. Salinity and temperature variation of the estuarine waters are measured in the area along with the tide for both post monsoon and summer seasons.

INTRODUCTION: up | previous | next | last

The mangroves of Krishna delta occupy an area of around 27,661 ha., the second largest patch of mangroves in Andhra Pradesh. The Krishna river emerges from the hills at Vijayawada, flows for about 96 kms downstream by forming a delta before it eventually empties into the sea. The Hamsaladevi distributary is the first to branch out 60 km. downstream from Vijayawada near Avanigadda and flows northward into the sea near Machilipatnam. Mangroves have been reported to be less abundant there. The Gollamattapaya and Nadimeru distributaries branch out 25km down stream from Avanigadda, and flow northward to join the sea. The main Krishna channel flows southward to join the sea near False Divi point. The abundance of mangroves is also more along the main Krishna river than the other distributaries. Mangroves are mainly prevalent around these three distributaries in tidal creeks, channels, lagoons, tidal flats and mudflats. The area has a warm, humid and tropical climate with an annual rainfall of around 110 cm.

Lakshminarayana (1992) carried out a study to plan the construction of canals for mangrove restoration based on the general hydrographic characters of the estuarine waters. Investigations included the floristic characters of the mangroves, the sedimentary geological characteristics of the surface and subsurface sediments in the mangrove environment and also chemical parameters like salinity and pH at some locations.

MATERIAL AND METHODS: up | previous | next | last

To study the hydrodynamic processes in the estuary, water level and current recorders were installed in the estuary in the creek at Sorlagundi and Nakshatranagar (See Map). The instruments have data logging facility for continuous recording of water level and water current for about a fortnight. The data is then retrieved through a computer. Salinity and temperature variations were measured in the same site over two tidal cycles using an in situ probe during post monsoon (February) and summer (May) seasons.

RESULTS AND DISCUSSION: up | previous | next | last

Fig.1 shows the water level variation in October 1998 for 15 days continuously at Sorlagundi in Krishna mangroves. This record was taken during the flood period of the river due to excessive rains in the catchment area. The water level rises to an elevation of about 1.4-m within two days due to the flood. During this 15-day period the maximum variation in water level is of the order of 1.2 m owing to the tidal component alone.

FIGURE-1 and FIGURE-2

Current speed observations were made for about 3 days during the last week of October. Fig.2. shows a typical record of the current speed variation in the river. It can be seen that the maximum velocity is of the order of 20 cm/s.

Fig.3 shows the tidal variation in the creek at Nakshatranagar over a 19-day period. It can be seen that tidal variation is only of the order of 25 cm.

FIGURE-3 and FIGURE-4

FIGURE-5 and FIGURE-6

FIGURE-7 and FIGURE-8

FIGURE-9 and FIGURE-10

FIGURE-11

CONCLUSION up | previous | next | last

In the restoration areas of Sorlagundi, the tidal amplitude is of the order of 1.2 m, while in Nakshatranagar, the tidal variation is only in the order of 25 cm. Hence, the canals for mangrove restoration should have at least a depth of 25 cm in Nakshatranagar, while it should be of the order of 1m in Sorlagundi. Salinity variation indicates the influence of fresh water even during summer at Sorlagundi and Nakshatranagar, which may be due to agricultural runoff.

ACKNOWLEDGEMENT up | previous | next | last

The author likes to express his thanks to Prof. M.S. Swaminathan for his constant encouragement and to the Executive Director and Project Director, MSSRF for providing the necessary facilities. Special thanks are due to Dr. T. Ravishankar for extending all the facilities in the field office both by way of men and material. The help extended by Dr. Sridhar at Krishna office is also acknowledged. Financial support from India-Canada Environment Facility, New Delhi is gratefully acknowledged for this work.

REFERENCES up | previous | next | last

Lakshminarayana, K., 1992. Conservation and management of the mangroves of the Krishna delta. Final Report of Research Project, Andhra University, Waltair - 530003. Financed by Department of Environment, Forests & Wildlife, Ministry of Environment and Forests, New Delhi.

STUDY AREA IN KRISHNA MANGROVES up | previous | next | last


FIGURE-12

Address: up | previous

Hydrologist,
M.S. Swaminathan Research Foundation,
Field Centre: 7-5a-2/1,
Gopalakrishna St.,
Ramaraopet,
Kakinada - 533 004.

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