ABSTRACT

Shalini, G.; Karapurkar, D.; Ramakrishnan, R.; Hegde, V.S., and Korakoppa, M.M., 0000. Sand bypassing across tropical river mouths: Implications for the provenance of beach sands, west coast of India.

The current notion is that, due to high energy, sand bypassing does not occur across the river mouths in tropical coasts, so the area between two river mouths, or between a river mouth and headland or between two headlands, is defined as a cell for sediment budget studies. Contrary to this general notion, heavy mineral compositions from beaches between the Gangolli and the Sita-Swarna rivers and north of the Panchagangavali (locally also called as Gangolli, henceforth refered to as Gangaolli) River along the west coast of India indicate sand bypassing the estuarine mouth from south of the Sita-Swarna River. This heavy mineral study of beaches of the Sita-Swarna and Gangolli estuary indicated two generations of ilmenites: one contributed by the modern fluvial system and another from recycled and offshore sources. Two generations of rutiles and zircon are also suggestive of recent origin and recycled sources from older cycles. The presence of both low-Mg and high-Mg hornblende in the beach sands suggests contribution from felsic and mafic rocks, respectively, while minerals like kyanite and garnet of pyrope type in the sands of the Sita-Swarna and Gangolli beaches are characteristic of granulite and khondalitic sources. The absence of such rocks in the Sita-Swarna and Gangolli catchment, the presence of rocks with such minerals in the Netravati catchment south of the Sita-Swarna River, and ilmenite-magnetite probably derived from St. Mary’s Island to the southwest of the Sita-Swarna River all imply sand bypassing from the adjacent beaches brought by the alongshore current crossing the Sita-Swarna, Malpe (Udyavara), Mulki, and Netravati-Gurpur rivers.