Preliminary study on seawater intrusion and aquifer freshening near reclaimed coastal area of Shenzhen, China

Local groundwater in coastal aquifers in Shenzhen has experienced heavy pumping since the 1980’s when Shenzhen began to expand very quickly from a fishing village to a modern city but lacked a public water supply. Meanwhile, large-scale land reclamation was carried out to meet the needs of various urbanization projects. In this paper we analyzed groundwater from a coastal aquifer system in Shenzhen and examined the evolution of groundwater chemistry over the last 20 years. The temporal changes of ionic ratios of rCa/(rHCO3+rSO4) and the relationship between sodium and chloride in the coastal area over this period of time indicate that the aquifer experienced seawater intrusion in the 1980’s but underwent gradual freshening in the 1990’s. It is speculated that seawater intrusion was induced by excessive groundwater pumping and that the aquifer freshening was caused both by a reduction in groundwater pumping and by coastal reclamation which moved the interface between fresh groundwater and saline groundwater seaward.