4.2 Level variation of groundwater around Qinghai Lake
Due to some residents’ wells being sealed, groundwater level was
investigated in only 14 sites among the 34 sampling sites around Qinghai
Lake (Table 2). The buried depth of the groundwater level ranged from
0.85 to 10.87 m (mean 3.97 m). The depth range was similar as that of
previous study (0.9 m-8.2 m, mean 3.80 m; Xiao et al., 2013). However,
the buried depth of groundwater level couldn’t reflect the direction of
groundwater due to the different elevation among the sampling sites. The
relative altitude between the groundwater level and the water level of
Qinghai Lake was calculated at each sampling site (Table 2). The
relative altitude of groundwater level ranged from -1.27 to 122.91 m
(mean 25.70 m). The relative altitudes of most of the groundwater level,
excluding G6 and G29, were positive values (Table 2), indicating the
groundwater level were higher than the water level of Qinghai Lake, and
most of the groundwater flowed into the lake, while the groundwater in
location G6 and G29 would be recharged by the lake water. Based on the
data of the positive altitude of groundwater level (Table 2), the
average relative altitude was calculated for each region around the lake
and were arranged: south > north > west
> east, with altitude of 46.70 m, 38.32 m, 38.04 m, and
7.58 m, respectively.
The hydraulic gradient of each groundwater was calculated based on the
relative altitude of groundwater level and the distance between sample
site and Qinghai Lake (Table 2). The hydraulic gradient ranged from
-6.20 to 43.14‰, with the average of 5.80‰. The average hydraulic
gradient of each region around the lake was in the order: south
> east > north> west, with value
of 19.70‰, 4.61‰, 4.33‰, and 1.73‰, respectively, indicating that the
driving force of groundwater at the south of Qinghai Lake was stronger
than other regions. According to the Fig. 2, fault escarpments and
lacustrine sediment terraces had been developed extensively along the
southern shore of Qinghai Lake, while the areas surrounding the lake and
rivers were overlain by alluvial and lacustrine sediments whose age
ranges from Quaternary to recent times(Fig. 2). The mountain runoff in
the diluvial and alluvial plains recharged the groundwater via
infiltration (Xiao et al. 2012).
Therefore,
the distribution and variation of groundwater level around Qinghai Lake
would be mainly related to geomorphology, terrain, groundwater aquifers,
fault, and so on (Jin et al., 2009; Xiao et al., 2012).