Environmental Engineering Reference
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Annual water budget (1990-2000 average in 10 9
m 3 ) for the upper-middle reaches of
Fig. 9.3
the Heihe River watershed
The simulation results show there was little ET from the upper soil zone.
Instead, a very high ET rate occurred in the LSZ (Fig. 9.3 ). This phenomenon is
attributable to several factors. First, the USZ is a hypothetical storage layer with a
simulated capacity of a few cm to up to 100 cm. Second, between the mountain
outlet (Yingluoxia) and middle reach outlet (Zhengyixia), soil is quite coarse and
sandy, and thus water from the USZ infiltrates to the LSZ quickly (Cheng et al.
1999 ; Pan and Qian 2001 ; and Wu et al. 2010 ). Third, consumption of groundwater
is mainly through ET in the middle reach of the watershed. Since the LSZ is
several hundred meters deep and could be mixed with groundwater zone, loss of
soil water and groundwater was simulated through the form of ET to the atmo-
sphere in this study (Cheng et al. 1999 ; Jia et al. 2005 ; Pan and Qian 2001 ; and
 
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