Modes of sea (saline) water intrusion around the Bohai Gulf, China
|Location||International Geological Congress,oslo 2008|
|Author||He, Qingcheng; Li, Cai|
|Holding Date||11 October 2008|
Coastal land of the Bohai Sea, in China, has been widely and deeply affected by sea (saline) water intrusion since the phenomenon was spotted in 1964 in Dalian, Liaoning Province, only 4.2 km2 then. By 2007, more than 4000 km2 has been reported and 1500 km2 is very serious. Based on data from investigations carried out in this region, we studied modes of sea (saline) water intrusion around the gulf, and discussed how to counteract sea water intrusion impacts.
Sea water intrusion and saline water (from saline aquifers) intrusion have different distributions in the study area, which reflects different geological conditions around the gulf. Sea water intrusion is mainly distributed along lower coastal planes and lower coastal valleys, like Liaodong Peninsula, Liaoxi Corridor, Qinghuangdao Peninsula and Shandong Peninsula. The second one mainly takes place in lower plane in south Laizhou Gulf, Xialiaohe Plane and lower coastal plane in east of Hebei province. Specially, the belt along east and south Laizhou Gulf has the both.
There are 4 intruding modes, each of them corresponding specific geological conditions, respectively. In lower coastal plane with huge mantlerock and continuous aquifers with high conductivities, the fresh-saline interface (generally taking 2000mg/l Cl- as indicator) marches as a sheet along the coastline. In places with old river beds, the interface takes the former river ways to move. In places with many fractures of faults, it advances inland through these natural channels. In places farer from the see and with upper saline aquifers, leakage from the upper aquifers causes deeper fresh aquifers being salted.
Intrusion situation would be much worse in the overall region in the future 10 years. Official data shows the level of Bohai Sea rises 2.5 mm annually, and would be 29mm higher in 10 years. On the other hand, most coastal areas are with the problem of land subsidence, averagely 10~20 mm/yr. The two processes eventually results in a huge relative sea level rise. Undoubtedly, their combination could make sea water intrude much faster and get more fresh water salted, unsuitable for agricultural, industrial and household use, as well as make intrusion patters more complicated. Furthermore, as more area is affected by sea water intrusion, social and economic issues probably come up, like crisis of fresh water. As global warming introduces the sea level rise and groundwater unreasonable extraction is the main reason for sea (saline) water intrusion and land subsidence, enhanced research on climate change and groundwater management is necessary.
As groundwater takes 60% or more in water supply in this region, reducing groundwater percentage is a critical measure. Surface water should be the main source for water supply. As soon as the ongoing South-North Water Transfer Project is finished and takes effect, groundwater consumption will reduce by 50%. This would be very helpful to remediate the geo-environment in this region.