Spatial decline distribution of groundwater levels of confined aquifer in the whole Red River Delta, Vietnam

摘要

Monitoring and interpreting changes in groundwater levels are essential for groundwater management. However, a fairly wide groundwater monitoring network over the Red River Delta, Vietnam was not set up until 1995. This paper investigated trends and their slopes in groundwater level series (1995- 2009) in 63 observation wells for confined aquifer by the non-parametric Mann-Kendall trend test and Sen's slope estimator. The analyses revealed that groundwater levels experienced significant downward trends almost all wells and time series. Spatial distribution of different trend slope was clarified over the delta in which central and coastal areas showed more serious downward trend slopes than other areas. Trend results for 18 different time series (e.g. monthly, seasonal, annual means and so on) were quite similar regardless to time series to be studied. While annual cycle in groundwater levels were strongly associated with those in rainfall and river water levels, long-term downward trends could result from increasing groundwater withdrawal.