Page 78 - 2017地大报告电子书
P. 78
2017
streambeds to recharge groundwater systems is essential to sustainable management of scarce
water resources in arid and semi-arid areas. An inverted water table (IWT) can develop under a
stream in response to the desaturation between the stream and underlying aquifer as the system
changes from a connected to disconnected status. However, previous studies have suggested that
the IWT can only occur at the bottom of a low permeability streambed in which only the vertical
flow between the stream and groundwater during disconnection was assumed. In the present
study, numerical simulations revealed that the lateral flow induced by capillarity or heterogeneity
also plays an essential role on interactions between streams and aquifers. Three pathways were
identified for the transition from connection to disconnection in homogenous systems; notably,
the lowest point of an IWT can develop not only at the bottom of the streambed but also within
the streambed or the aquifer in response to the initial desaturation at, above, or below the
interface between the streambed and aquifer (IBSA), respectively. A sensitivity analysis indicated
that in wide streams, the lowest point of an IWT only occurs at the bottom of the streambed;
however, for a stream half width of 1 m above a 6 m thick sandy loam streambed, the lowest
point occurs in the streambed as stream depth is less than 0.5 m. This critical stream depth
increases with streambed thickness and decreases with stream width. Thus, in narrow streams the
lowest point can also develop in a thick streambed under a shallow stream. In narrow streams, the
lowest point also forms in the aquifer if the ratio of the hydraulic conductivity of the streambed
to that of the aquifer is greater than the ratio of the streambed thickness to the sum of the
stream depth and the streambed thickness; correspondingly, the streambed is thin but relatively
permeable and the stream is deep. Furthermore, in heterogeneous streambed systems, two or
three pathways can simultaneously occur
and various parts of the IWT occur at
distinct positions relative to the IBSA. This
challenges the commonly held assumption
that streambed under a disconnected
stream is always fully saturated, and limits
the methods which introduce a negative or
atmospheric pressure value at the IBSA to
calculate seepage rate or assess stream-aquifer connectivity.
论文链接:https://doi.org/10.1016/j.jhydrol.2017.03.011
10.High salinity facilitates dolomite precipitation mediated by Haloferax volcanii
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