2.1.1 Groundwater Abstraction
Consumptive water use is a management tool in SWAT that removes water
from a basin. Water removed for consumptive use is designed to be lost
from the system. SWAT allows water to be removed from a shallow aquifer,
deep aquifer, reach, or pond within any subbasin in the watershed
selectively. Consumptive water use varies from month to month. For each
month in the year, an average daily volume of water is removed from the
source and is specified (Neitsch, Arnold, Kiniry & Williams, 2005). A
shallow aquifer composed of sand, gravel, and clay is distributed
throughout South Korea. The aquifer has good porosity with adequate
nutrients for cultivation so that it is mainly used as a major source of
groundwater (Park, Lee, Koo & Kim, 2016). Thus, monthly groundwater use
was applied to be removed from a shallow aquifer using consumptive water
use tool in SWAT.
The National Groundwater Information Center updates annual groundwater
use report which provides groundwater abstraction (GA) information with
three types: agricultural, industrial, and domestic. Based on the
report, the annual use data in study area from 1976 to 2015 were
collected and they were monthly averaged in 10-year periods (the 1980s,
the 1990s, the 2000s, the 2010s) so that SWAT could simulate GA scenario
periodically. Figure 2 illustrated the monthly and annual groundwater
use of the Geum River basin corresponding to the four decades. The
annual groundwater use has gradually increased since the 1980s, appeared
to have 107.6% increase rate in the 2010s compared with the 1980s. The
monthly use was highly concentrated in June, July, and August. This
pattern coincided with the precipitation trend of South Korea, in which
most rainfall occurs in Summer. The groundwater use database has been
constructed in subbasin unit for every decade. Figure 3 shows the
spatial increment of groundwater use in every decade compared with the
1980s. Middle and Northern part of the target catchment showed
relatively higher increase of groundwater use.
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