contained in the aquifers are relatively coarse which ensures sound permeability.
The single-well water outflow is measured to be 2295.44–2976.78 m
3 /d, which
implies moderate water abundance.
④ Low-level zone (<1000 m
3 /d)
The low-level zones are widely distributed, mainly on the periphery of the
medium-level zones and in the valleys between mountains. The aquifers are
lithologically complicated. According to the hydrogeological data about boreholes
ZK1, ZK3, ZK6 and ZK9, in the aquifers there are Middle Pleistocene silty gravel,
broken block stones, Late Pleistocene pebbles, gravel, coarse sand and fine sand,
and Holocene sand and gravel. The depth to water table reaches reads 44.44 m,
66.51 m, 4.36 m, 56.5 m respectively, and the aquifer thickness ranges from 54.58
to 97.04 m. The groundwater is mainly recharged by long-distance ancient and
modern river channels through infiltration and little by rivers. Due to poor permeability, the single-well water outflow is calculated to be 137.81–757.98 m
3 /d,
which denotes a low level of water abundance.
(b) Zone classification by the abundance level of confined water
The confined water is mainly distributed in the fine soil plain of the southern
alluvial-pluvial fan in the surveyed area. As hydrogeological drilling is not carried
out, according to the data from the Dachaidan hydrogeological survey report (scale:
1:20), the aquifer contains two layers: unconfined water on the top and multilayer
confined water at the bottom. According to the existing drilling and pumping data,
the water-bearing capacity of the upper layer is less than 1000 m
3 /d, which indicates a low level of water abundance. It exceeds 1000 m m
3 /d in the lower layer,
which implies moderate water abundance.
– Groundwater recharge, runoff and discharge conditions
The groundwater in the study area is recharged by precipitation. With high terrain,
the northern middle and high mountainous areas serve as a main source of
replenishment as the precipitation is relatively plentiful. In bedrock mountainous
areas of different periods, hills are undulating due to great uplifts, and weathering
fissures and tectonic fissures have been formed in the rocks, which is conducive to
the infiltration replenishment by precipitation. Therefore, the mountainous areas
become the main area of groundwater replenishment and formation. In mountainous
areas at an altitude of over 3650 m (shady slope), the precipitation from late
October to early next April is often stored in the form of ice and snow. With the
arrival of summer, snow and ice smelt, and during the accompanying rainy season,
precipitation becomes the main source of replenishment to the groundwater and
surface water in mountainous areas. As the seasonal melting depth in the frozen
zone is less than 3 m, the water circulation in the upper frozen layer is greatly
limited. Given strongly cut terrain, generally the groundwater is discharged into the
valley as springs shortly after rapid runoff formation.
5.2 Northwest China
165
The single-well water outflow is measured to be 2295.44–2976.78 m
3 /d, which
implies moderate water abundance.
④ Low-level zone (<1000 m
3 /d)
The low-level zones are widely distributed, mainly on the periphery of the
medium-level zones and in the valleys between mountains. The aquifers are
lithologically complicated. According to the hydrogeological data about boreholes
ZK1, ZK3, ZK6 and ZK9, in the aquifers there are Middle Pleistocene silty gravel,
broken block stones, Late Pleistocene pebbles, gravel, coarse sand and fine sand,
and Holocene sand and gravel. The depth to water table reaches reads 44.44 m,
66.51 m, 4.36 m, 56.5 m respectively, and the aquifer thickness ranges from 54.58
to 97.04 m. The groundwater is mainly recharged by long-distance ancient and
modern river channels through infiltration and little by rivers. Due to poor permeability, the single-well water outflow is calculated to be 137.81–757.98 m
3 /d,
which denotes a low level of water abundance.
(b) Zone classification by the abundance level of confined water
The confined water is mainly distributed in the fine soil plain of the southern
alluvial-pluvial fan in the surveyed area. As hydrogeological drilling is not carried
out, according to the data from the Dachaidan hydrogeological survey report (scale:
1:20), the aquifer contains two layers: unconfined water on the top and multilayer
confined water at the bottom. According to the existing drilling and pumping data,
the water-bearing capacity of the upper layer is less than 1000 m
3 /d, which indicates a low level of water abundance. It exceeds 1000 m m
3 /d in the lower layer,
which implies moderate water abundance.
– Groundwater recharge, runoff and discharge conditions
The groundwater in the study area is recharged by precipitation. With high terrain,
the northern middle and high mountainous areas serve as a main source of
replenishment as the precipitation is relatively plentiful. In bedrock mountainous
areas of different periods, hills are undulating due to great uplifts, and weathering
fissures and tectonic fissures have been formed in the rocks, which is conducive to
the infiltration replenishment by precipitation. Therefore, the mountainous areas
become the main area of groundwater replenishment and formation. In mountainous
areas at an altitude of over 3650 m (shady slope), the precipitation from late
October to early next April is often stored in the form of ice and snow. With the
arrival of summer, snow and ice smelt, and during the accompanying rainy season,
precipitation becomes the main source of replenishment to the groundwater and
surface water in mountainous areas. As the seasonal melting depth in the frozen
zone is less than 3 m, the water circulation in the upper frozen layer is greatly
limited. Given strongly cut terrain, generally the groundwater is discharged into the
valley as springs shortly after rapid runoff formation.
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165