Accurate estimation of groundwater recharge is essential for efficient and sustainable groundwater management in many semi-arid regions. In this paper, a lumped parameter model(EARTH) was established to simulate the recharge rate and recharge process in typical areas by the observation datum of weather, soil water and groundwater synthetically, and the spatial and temporal variation law of groundwater recharge in the Hebei Plain was revealed. The mean annual recharge rates at LQ, LC, HS, DZ and CZ representative zones are 220.1, 196.7, 34.1, 141.0 and 188.0 mm/a and the recharge coefficients are 26.5%, 22.3%, 7.2%, 20.4%, and 22.0%, respectively. Recharge rate and recharge coefficient are gradually reduced from piedmont plain to coastal plain. Groundwater recharge appears as only yearly waves, with higher frequency components of the input series filtered by the deep complicated unsaturated zone(such as LC). While at other zones, groundwater recharge series strongly dependent on the daily rainfall and irrigation because of the shallow water table or coarse lithology.
The preferential flow plays a vital role on the infiltration of irrigation or rainfall. The objective of this study was to quantify preferential flow in the processing of irrigation infiltration in the field scale. Tests of different initial soil water contents and irrigation intensities were conducted using Brilliant Blue FCF(C.I.42090) dye tracer in Luancheng County of the North China Plain. The results showed that the percentages of infiltration by the preferential flow for irrigation depth of 25, 50, and 75 mm were 16.67%, 43.67%, and 34.17%, with 19.72%, 61.42%, 66.64% of dyed areas in the soil profile, respectively, which indicated that preferential flow was enhanced with increasing irrigation intensity, but reduced when the irrigation intensity was over 50 mm. The percentages of preferential flow for 75 and 180 mm previous irrigation producing different initial soil water contents were 23.26% and 18.97%, with 53.23% and 39.94% of dyed areas in the soil profile, respectively. Compared with the 75 mm without previous irrigation, the results indicated that higher initial soil water contents restrained the preferential flow in the field. Therefore, intermittent irrigation and low irrigation intensity patterns, and larger depth of plowing would be suggested to reduce the preferential flow which would increase the soil water utilization efficiency and reduce pollution risk of pesticide and fertilizer to groundwater.
The record of paleo-environment in clayey aquitard pore water is much more effective relative to aquifer groundwater owing to the low permeability of clayey aquitard. Oxygen-18(18O), deuterium(D), and chemical patterns were determined in pore water samples extracted from two 500 m depth boreholes, G1 and G2, in western Bohai Bay, China. Shallow pore water samples(depth<102 m) are saline water, with the TDS(total dissolved solids) of 3.69–30.75 g/L, and deeper ones(depth=102–500 m) are fresh water, with the TDS<1 g/L. Content of major ions(i.e., Cl-, Na+, K+, Mg2+, SO2-4, Ca2+) is high in marine sediment pore water samples and gradually decrease towards to terrestrial sediment pore water, together with the Cl/Br and Sr/Ba ratios changing significantly in different sedimentary facies along the study profile, indicating that pore water may be paleo-sedimentary water and not replaced by modern water. δ18O profile and positive correlation between δ18O and Cl- of shallow saline pore water indicated diffusion as the main transport mechanism, and distinguished four transgressive layers since Late Quaternary(i.e., Holocene marine unit, two Late Pleistocene marine units and Middle Pleistocene marine unit), further supporting the finding that pore water retained the feature of paleo-sedimentary water. Climate was identified as the main influence on the isotopic signature of aquitard pore water and four climate periods were determined by δ18O profile.
