Study On Characteristics Of Submarine Topography And Geomorphology In Minjiang Estuary

Study on the characteristics and evolution of submarine topography of Minjiang Estuary, an important port area in Fujian Province, can provide basic geographic data for the study on ecosystem of Minjiang Estuary, and as a scientifically guide for the development and protection of the region, particularly for river realignments and port construction. Furthermore, it plays a positive role in economic construction and development of west coastal zone of Taiwan Strait.Based on high density and precision multiple and single beam data, combined with regional tectonics, nearshore dynamic conditions, marine sediment distribution and historical charts, this paper systematically studies the morphological characteristics of Minjing Estuary, analyzes the topographic changes and geomorphologic evolution in recent 60 years by use of GIS techniques. Furthermore, the main factors influencing geomorphic evolution and development on Minjiang estuary are discussed. The conclusions are drawn as follows:(1) The submarine topography in study area slopes from land to sea on the whole. It can be divided into four main terrain units, bank slope and reef zone, gulf zone, modern estuary and shelf slope . The region outside of Sansha Bay and Luoyuan Bay has bigger water depth, which is strongly fluctuant in nearshore zone but gentle in offshore zone. In the Minjiang estuary and adjacent east area with smaller water depth, the topography is gentle relatively, but it turns steeper at 10~15m.(2) The submarine geomorphology in study area includes estuarine delta, tide dominated delta, submarine accumulation slope, sloping shelf plain. The sub‐geomorphological units are tidal inlet, estuary sandbar, river mouth spit, estuary side bar, scour channel, subaqueous riffle, tidal sand ridge, etc. And some avtive tidal sand ridges develop outside the Minjiang Estuary.(3) Evolution of Minjiang estuary in recent 60 years shows that the deposition zone developed in the area with weak hydrodynamic and high slit condition, while scour zone relate with strong hydrodynamics or current turning. 5 units of deposition strength of estuary could be divided including weak deposition zone, strong deposition zone, weak erosion area, strong erosion areas and stable zone. The shape of estuary keeps dynamic balance except that north and south margin area are extending offshore.(4) Regional tectonics, runoff and sediment charge of the Minjiang River, marine hydrodynamics and human activity are main factors which control or affect evolution of Minjiang Estuary. The influences of different factors on the estuarine development are in different scales. Regional tectonics plays a decisive role in geomorphic formation and basic development of the estuary. Flood and tide are the external powers that shape the estuary landform, storms and surge normally change estuary sandbar. And human behavior of dam building and groin construction which induced sediment reducing and shoreline change is main reason accounting for erosion or siltation.