ABSTRACT:

Benthic disturbance is carried out in the Central Indian Basin for environmental impact assessment studies. Geotechnical measurements were made on sediments collected before and after disturbing the top 10-15 cm of the seafloor. Results indicate that the water content of siliceous sediments is high due to high porosity. The comparative studies revealed increase in sediment water content after the disturbance. Shear strength showed large variations with no specific trend due to disturbance; that could affect the bearing capacity of sediments. Significant reductions in the strength values in surface (0-5 cm) sediments from the towed zone of the disturber are observed. Porosity and wet density have not shown any significant change.

INTRODUCTION

Ferromanganese nodules containing high grade metals like copper, nickel and cobalt occupy large area in the Central Indian Basin (CIB), and are associated mostly with siliceous sediments (Cronan and Moorby, 1981; Roo and Nath, 1988; Sudhakar, 1989; Valsangkar and Khadge, 1989, Khadge, 1998). They have received considerable attention as a future mineral resource (Padan, 1990). Their abundance and metal grade play an important role for making nodule mining economically viable. However, environmental impact assessment is essential to know effect of benthic disturbance on the surroundings caused due to deep-sea mining. Therefore, studies on various parameters including geotechnical properties were conducted in an area of 3000m by 200m in the cm. As the nodule mining activity involves large instruments and infrastructure, it is likely to create a set of entirely new conditions on the seafloor and benthic environment. The sediment plume caused by mining head while collecting nodules would lead to increase in density and turbidity of the bottom waters. As an UNCLOS (United Nations Convention on Law of the Sea) obligation, the environmental impact assessment studies in the Central Indian Basin are essential before nodule mining.

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