Clast size characteristics of gravel within rivers of the Waimea Plains, Nelson

Gravel within rivers of the Waimea Plains near Nelson, New Zealand, was der ived through the Wairoa Gorge from Paleozoic-Mesozoic basement rocks to the southeast, and to a lesser extent from Pleistocene gravels to the west. A downstream reduction of mean clast size and an increase in sorting occurs i n three rivers of the Waimea Plains. Clast form is dominated by bladed clas ts, with a slight tendency with transport distance to more elongate forms. Clast sizes are apparently larger in the modern rivers than in fluvial grav els of the Last Glacial period. The smaller clast size in the Last Glacial deposits may indicate more efficient clast-size reduction in glacial as opp osed to modern-day rivers.