in the northwest. The water temperature of hot spring registers 30–40 °C with the
maximum of 72 °C, and the flow of all springs totals 16.28 L/s. This indicates that
the fault controls the scale and extension direction of the Dachaidan Basin.
According to the local data, since the piedmont fault controls the thickness of the
Quaternary sediments in the basin, with the continuous uplift of the northern and
southern mountainous areas, the eroded debris in continuously accumulated in the
basin during floods. According to the data of local gravity geophysical survey, more
than 400 m thick Quaternary debris have been deposited in the central part of the
basin, which provides appropriate space for the formation and migration of
groundwater in the basin. Due to tectonic movements, the strata lithology, aquifer
structure and water distribution in the basin are also strictly controlled by topography and geomorphology. This gives rise to a convergence zone of surface water
and groundwater centered on the Dachaidan Lake.
(d) Hydrogeological conditions
• Hydrogeological overview
– Groundwater endowment conditions and distribution characteristics
The accumulation of thick loose materials in the piedmont plain area creates space
for groundwater endowment and migration. As replenishment from precipitation is
limited because of relatively low altitude, scarce precipitation and intensive evaporation, the groundwater is mainly recharged by leakage from outflow. In the
alluvial-pluvial fan, groundwater distribution shows the following characteristics:
horizontally, the highly permeable modern and ancient riverbeds contain abundant
water, while on the two sides, water is slightly less than that of the axis as particles
in aquifer are relatively small; longitudinally, the permeability is gradually weakened from the trailing edge to the leading edge as particles in the aquifer become
smaller. In short, the middle part is most abundant in groundwater, followed by the
trailing edge and then the leading edge.
– Groundwater type and water abundance
The endowment and distribution of groundwater in a region are affected and
restricted by many factors such as lithology, geology, geomorphology, hydrology
and meteorology. In other words, such factors determine the endowment conditions
and distribution characteristics of groundwater in a region. According to the
aqueous media, endowment conditions and hydraulic properties, the groundwater in
the region is divided into four types: loose rock pore water, carbonate rock
fissure-karst water, bedrock fissure water, and frozen layer water.
Loose rock pore water
According to the aquifer structure and water abundance characteristics, loose rock
pore water can be further divided into unconfined water in loose rock pores and
confined water in loose rock pores.
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159
maximum of 72 °C, and the flow of all springs totals 16.28 L/s. This indicates that
the fault controls the scale and extension direction of the Dachaidan Basin.
According to the local data, since the piedmont fault controls the thickness of the
Quaternary sediments in the basin, with the continuous uplift of the northern and
southern mountainous areas, the eroded debris in continuously accumulated in the
basin during floods. According to the data of local gravity geophysical survey, more
than 400 m thick Quaternary debris have been deposited in the central part of the
basin, which provides appropriate space for the formation and migration of
groundwater in the basin. Due to tectonic movements, the strata lithology, aquifer
structure and water distribution in the basin are also strictly controlled by topography and geomorphology. This gives rise to a convergence zone of surface water
and groundwater centered on the Dachaidan Lake.
(d) Hydrogeological conditions
• Hydrogeological overview
– Groundwater endowment conditions and distribution characteristics
The accumulation of thick loose materials in the piedmont plain area creates space
for groundwater endowment and migration. As replenishment from precipitation is
limited because of relatively low altitude, scarce precipitation and intensive evaporation, the groundwater is mainly recharged by leakage from outflow. In the
alluvial-pluvial fan, groundwater distribution shows the following characteristics:
horizontally, the highly permeable modern and ancient riverbeds contain abundant
water, while on the two sides, water is slightly less than that of the axis as particles
in aquifer are relatively small; longitudinally, the permeability is gradually weakened from the trailing edge to the leading edge as particles in the aquifer become
smaller. In short, the middle part is most abundant in groundwater, followed by the
trailing edge and then the leading edge.
– Groundwater type and water abundance
The endowment and distribution of groundwater in a region are affected and
restricted by many factors such as lithology, geology, geomorphology, hydrology
and meteorology. In other words, such factors determine the endowment conditions
and distribution characteristics of groundwater in a region. According to the
aqueous media, endowment conditions and hydraulic properties, the groundwater in
the region is divided into four types: loose rock pore water, carbonate rock
fissure-karst water, bedrock fissure water, and frozen layer water.
Loose rock pore water
According to the aquifer structure and water abundance characteristics, loose rock
pore water can be further divided into unconfined water in loose rock pores and
confined water in loose rock pores.
5.2 Northwest China
159