Abstract:

Groundwater renewable ability in the middle and lower watershed of Anyang River are studied by analyzing the tritium concentration of water, groundwater age and mean annual renewal rate (MARR). The MGMTP is employed to reconstruct the ³H concentration of atmospheric precipitation in the study area (1953-2016), whilst the groundwater age and MARR of phreatic water and springs are assessed via Lumped Parameter Modelling (LPM) and the method developed by Le Gal La Shalle et al., respectively. The results indicate that: (1) Phreatic water and springs received atmospheric precipitation recharge over the past 20 years, and the recharge and flow condition of the unconfined groundwater extended widely due to the regional hydrogeological control. (2) The mean residence time of the Xiaonanhai spring is 23 years, associated with 3.6% of MARR and its flux has been attenuating. (3) Unconfined groundwater in the empennage of the Anyang River alluvial/proluvial fan and recharge area has considerable renewable capacity, as it received direct recharge from infiltrated atmospheric precipitation and surface water leakage. Groundwater from the middle zone of the fan to the Beijing-Hongkong-Macao highway is 40-60 years old, and is largely sourced from modern atmospheric precipitation. Nevertheless, that in frontal belt of the fan has very low renewable capacity due to its mixing nature between modern groundwater and older input, with average age not younger than 60 years. (4) Deep confined groundwater in both the eroded hills and alluvial and flood plain is very old and has thus low renewability. This indicates that protection of the Xiaonanhai spring should be increased, and considerable achievement should be obtained in short period of time. The underground water depression cone in the Anyang city urban area has been substantially shrunk by the water supply from the Middle-Route of South to North Water Transfer Project, and the restriction on groundwater exploitation.

Key words: tritium, groundwater age, groundwater renewability, middle and lower watershed of Anyang River