Geomorphology and Stratigraphic Evolution of the Han River Delta

Dalrymple, Robert W.¹, Kyungsik Choi², JaeHwa Jin³, Donald I. Cummings⁴ (1) Queen's University, Kingston, ON (2) Chonnam National University, Kwangju, South Korea (3) Korean Institute of Geosciences and Mineral Resources, Daejon, South Korea (4) Geological Survey of Canada, Ottawa, ON

The Han River, which enters the NE part of Kyunggi Bay, is the largest river draining the Korean peninsula and has a sediment load of ~ten million tons/a. This fluvial input, coupled with probable onshore transport during the transgression, has allowed substantial aggradation and recent progradation, with up to 60 m of Holocene deposits within the Bay. The tidal range reaches ~10 m, with peak current speeds of 1-2 m/s. These tidal currents have sculpted the deposits into a series of giant, shore-normal tidal bars that show a southward change in morphology from very broad and flat-topped to sharp-crested in the south. This suggests that much of the Han's sediment discharge is retained in the northern part of the Bay. One of these giant tidal bars, which is 100 km in length, 20-30 km in width and up to 30 m in relief, has been studied in detail. The bar is symmetrical in its inner part, but shows a southward asymmetry in its outer half, perhaps due to a southerly directed wave flux. Overall, it becomes muddier outward. Its inner, sandy end is dissected by laterally migrating, cross-bar channels, whereas the outer part is smooth and dominated by heterolithic deposits. Seismic data indicate that the bar has formed by the coalescence of two smaller bars as the sea-level rise slowed and the Bay filled with sediment. The architecture of the outer bar is complex, with vertical-aggradation deposits beneath the crest, lateral-accretion deposits along the flanks, and seaward-dipping (prodeltaic?) strata at its seaward end.