• Hydrographic conditions for unconfined water in the alluvial-pluvial fan
– Endowment and distribution characteristics
The Baligou alluvial-pluvial fan is situated in the surrounding area of the Chaidan
Basin. Affected by topography and landforms, there is rare precipitation and
intensive evaporation. With different depth to water table, the groundwater, especially unconfined water in the front and rear edge of the fan, receives little
replenishment from precipitation, but considerable replenishment from the
groundwater in the fine soil plain with great depth to water table. However, in the
northern bedrock mountainous areas with high altitude and abundant precipitation,
precipitation, ice and snow meltwater and bedrock fissure water form surface
runoff, and the river water flows out of the mountain and along the modern riverbed
and can recharge the groundwater through infiltration. Owning to favorable space
for groundwater existence created by thick Quaternary loose deposits in the
alluvial-pluvial fan, the water-bearing capacity is strong in the modern and ancient
channels along the axis of the alluvial-pluvial fan, which is mainly contributed by
thick aquifers.
According to the analysis of boreholes and pumping tests, within the Baligou
piedmont alluvial-pluvial fan, the water-bearing capacity of aquifers is strong in the
modern and ancient channels along the axis, and it is weakened away from these
areas. As the Reshuigou alluvial-pluvial fan is relatively small, the water-bearing
capacity of aquifers is undermined by the limited recharge of river water to the
groundwater which amounts to 513,500 m
3 /a. Vertically, as revealed in hydrogeological drilling, the aquifer in the trailing edge of the alluvial-pluvial fan mainly
consists of sandy gravel, pebbles and boulders and has great permeability due to
these coarse particles. It is 59.97 m thick (uncovered) and the static depth to water
table is 50.13 m and the single-well water outflow is 2024.35 m
3 /d. In the central
part of the alluvial-pluvial fan, the numbers read 78.40 m, 22.77 m and
5438.88 m
3 /d respectively for the aquifer that is mainly comprised of gravel and
pebbles. In the leading edge, with fine particles in the aquifer, the permeability is
gradually weakened, leading to shallow depth to water table. In the fine soil plains,
the aquifer is mainly comprised of coarse sand, fine sand, sandy loam and mild clay,
as well as gravel. It becomes interbedded with worse permeability and
water-bearing capacity, and mainly contains confined water. Hence, the characteristics of groundwater distribution in the alluvial-pluvial fan in the study area can
be summarized as follows: the water-bearing capacity does not show the
gourd-shaped distribution as in other alluvial fans, which means the water-abundant
area gradually increases from the rear edge to the central axis. It is distributed in an
irregular ellipse that extends from center to the northwest (as shown in the
hydrogeological map), and it gradually descends from a high level to a low level.
This fully demonstrates that the groundwater endowment and distribution in the
study area are strictly determined and significantly influenced by the ancient and
modern river channels.
According to the regional geotectonic analysis, during the Late Pleistocene
period, the river drainage center developed on the northern slope of the Chaidamu
162
5 Application Cases
– Endowment and distribution characteristics
The Baligou alluvial-pluvial fan is situated in the surrounding area of the Chaidan
Basin. Affected by topography and landforms, there is rare precipitation and
intensive evaporation. With different depth to water table, the groundwater, especially unconfined water in the front and rear edge of the fan, receives little
replenishment from precipitation, but considerable replenishment from the
groundwater in the fine soil plain with great depth to water table. However, in the
northern bedrock mountainous areas with high altitude and abundant precipitation,
precipitation, ice and snow meltwater and bedrock fissure water form surface
runoff, and the river water flows out of the mountain and along the modern riverbed
and can recharge the groundwater through infiltration. Owning to favorable space
for groundwater existence created by thick Quaternary loose deposits in the
alluvial-pluvial fan, the water-bearing capacity is strong in the modern and ancient
channels along the axis of the alluvial-pluvial fan, which is mainly contributed by
thick aquifers.
According to the analysis of boreholes and pumping tests, within the Baligou
piedmont alluvial-pluvial fan, the water-bearing capacity of aquifers is strong in the
modern and ancient channels along the axis, and it is weakened away from these
areas. As the Reshuigou alluvial-pluvial fan is relatively small, the water-bearing
capacity of aquifers is undermined by the limited recharge of river water to the
groundwater which amounts to 513,500 m
3 /a. Vertically, as revealed in hydrogeological drilling, the aquifer in the trailing edge of the alluvial-pluvial fan mainly
consists of sandy gravel, pebbles and boulders and has great permeability due to
these coarse particles. It is 59.97 m thick (uncovered) and the static depth to water
table is 50.13 m and the single-well water outflow is 2024.35 m
3 /d. In the central
part of the alluvial-pluvial fan, the numbers read 78.40 m, 22.77 m and
5438.88 m
3 /d respectively for the aquifer that is mainly comprised of gravel and
pebbles. In the leading edge, with fine particles in the aquifer, the permeability is
gradually weakened, leading to shallow depth to water table. In the fine soil plains,
the aquifer is mainly comprised of coarse sand, fine sand, sandy loam and mild clay,
as well as gravel. It becomes interbedded with worse permeability and
water-bearing capacity, and mainly contains confined water. Hence, the characteristics of groundwater distribution in the alluvial-pluvial fan in the study area can
be summarized as follows: the water-bearing capacity does not show the
gourd-shaped distribution as in other alluvial fans, which means the water-abundant
area gradually increases from the rear edge to the central axis. It is distributed in an
irregular ellipse that extends from center to the northwest (as shown in the
hydrogeological map), and it gradually descends from a high level to a low level.
This fully demonstrates that the groundwater endowment and distribution in the
study area are strictly determined and significantly influenced by the ancient and
modern river channels.
According to the regional geotectonic analysis, during the Late Pleistocene
period, the river drainage center developed on the northern slope of the Chaidamu
162
5 Application Cases