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The Spatio-temporal Pattern Analysis and Numerical Modeling Study on Groundwater System in Minqin Basin

Author: ZhangYanLin
Tutor: MaJinHui
School: Lanzhou University
Course: Cartography and Geographic Information Systems
Keywords: Minqin Basin spatio-temporal patterns of groundwater numerical simulation of groundwater
CLC: P641.2
Type: Master's thesis
Year: 2009
Downloads: 144
Quote: 1
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Abstract

Minqin Basin, located in the lower reaches of Shiyang River, is a typical desert oasis in arid inland river basins. Because of enough surface water supplies, the oasis was fed to be rich in water and grass and beautiful. However, in the last several decades, as a result of deforestation, canal lining and well digging, the spring water resources considerably decreased in upper reaches. And especially in 1970s, due to large-scale exploitation of water and soil resource in upper and middle reaches of Shiyang River, the surface water which flowed into Minqin Basin decreased rapidly, which made underground water be excessively exploited and the water level descend, leaving a lot of ecological problems such as lake dry up, desertification etc. At present, these problems have badly restricted the sustainable development of local economic and society and harmed to the oasis. The quantitative research on groundwater spatio-temporal dynamic law and equilibrium elements in Minqin Basin can not only give constructive suggestions to the planning and predicting of underground water resource, but also be a science guide in ecosystem restoration.Firstly, based on the geo-statistical spatial analysis and the dynamically observed data about underground water level from 1999 to 2008, the spatio-temporal patterns of underground water level in Minqin Basin were studied and the spatial heterogeneity of groundwater level in these years was discussed. Then combined with geological and hydrological information, the observed data of 2003-2008, with month as time step, was chosen to analyzed groundwater equilibrium elements. Finally, numerical simulation of groundwater flow in the basin was carried on to give a quantitative evaluation of groundwater resource of Minqin Basin. On the basis of these studies, main conclusions obtained are as follows.1.The groundwater depth in Minqin Basin descended sharply in ten years from 1999 to 2008. And the groundwater funnel area continually expanded every year, which had a trend of merging with nearby funnel area. The minimum depth of groundwater level in 1999 was 2.26m, the maximum was 27.14m, and the mean depth was 13.86m. For 2008, they are 3.55m, 31.19m and 17.29m respectively. The area with deep groundwater depth increased annually, while the area with shallow groundwater depth decreased. For example, the area ratio of the regions where groundwater depth are more than 21m increased from 6.94% in 1999 to 39.75% in 2008, while there depth less than 16m decreased from 67% to 30.65%. The declining range of groundwater level is different in different regions. In the center of the oasis where human activities frequently occurred, the maximum declining range comes to about 9m, with a mean range of 5-6m. But in the desert on the edge of the oasis, the declining range is smaller with the mean of 2-3m. In summary, the declining range is great in the upper reaches on Lang Poquan Mountains, but smaller in lake areas and southern basin.2. The spatial auto-correlation of groundwater depth increased annually during 1999-2008, and structure behavior was enhanced year by year, but the random factors had less and less impact on groundwater depth. The influence of human activities on groundwater level gradually become structure behavior rather than random. Due to continual groundwater overdraft and extensive declining of groundwater level, regional funnel formed and expanded lastingly, and the total spatial heterogeneity of groundwater and maximum correlated distance are greatly increasing, leading to the augmentation of the connectivity and frangibility of groundwater in Minqin Basin.3. The model of numerical simulation of groundwater flow in the basin is built to reflect hydrological conditions and the dynamic of groundwater level, and to obtain the basic structure of groundwater flow in studied area, giving a trend of groundwater level change. According to the calculation, the average supply in Minqin Basin during 2003-2008 is 17615.36241×10~4m~3,the average evacuation is 43544.79×10~4m~3, and the annual average overdraft is 25929.43×10~4m~3. Among them, the precipitation supply in Minqin Basin is approximately 105.4×10~4m~3/a, and the boundary inflow volume is 32334477.33m~3/a. The runoff quantity of Shiyang River is roughly 100 million cubic meters during 2003-2008, and the natural supply of Minqin Basin, the exploitable water resources, is 132334582.7310×10~4m~3/a.

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CLC: > Astronomy,Earth Sciences > Geology > Hydrogeology and Engineering Geology > Hydrogeology (groundwater hydrology ) > Groundwater Dynamics
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