Wang Wenmin, Wang Wenke,Chen Xuguang and Xu Min

Chang’an University

Abstract: The Northern Piedmont of Tianshan Mountain is a primary zone of economic development in Xinjiang Province, in which there is a shortage of water resources and the irrational exploitation and usage of water resources have already caused a series of side effect to the ecological environment. In order to utilize the regional water resources reasonably and realize the balanced relationship between water resources and the development of social economy and environment, it is essential to reinforce the exploitation of groundwater resources. On the basis of the researches into the regional hydrological and geological conditions, this article makes a scientific evaluation of the storage and regulation capacity of groundwater reservoirs from three aspects: the space, the supply and the project. The researches show that presently a serious problem lies in the exploitation and usage of water resources that the increasing rate of surface water usage and the neglect of the storage and regulation of groundwater reservoirs. Therefore, it is necessary to transform the ways of exploiting and using of the regional water resources. On account of the present situation and the future plan of the exploitation and usage of the regional water resources, it proposes a way to make full use of storing and regulating ability of groundwater reservoirs to increase the use of groundwater resources, which is the fundamental way to realize the appropriate exploitation and usage of groundwater resources to meet the needs of cities and towns on the lower reaches of the river, and at the same time to decrease the ecological environment side effect resulted from the overuse of the surface water. Thus, the healthy development between regional water resources and environment can be achieved.

Key Words: groundwater reservoirs, water resources, ecological environment, and the capacity of storage and regulation

Introduction:

In the arid and semiarid regions, the evaporation amount is usually several times as much as the rainfall because of the intense evaporation and scanty precipitation. Constructing the surface reservoirs bring about not only the waste of water resources but also a series of social and environmental problems, such as the occupation and salinization of land. Therefore, to construct underground reservoirs on conditioned areas is an effective resolution to water resources on arid and semiarid regions. Rivers in the Northern Piedmont of Tianshan Mountain mainly depend on the melting ice and snow for supply, so they are conspicuously seasonal. During the dry season of spring and autumn there appear to varied degrees bottlenecks in the Northern Piedmont of Tianshan Mountain. Thus, we can make full use of the storing and regulating functions of underground reservoirs to regulate the ill-distributed water resources in different seasons and to further realize the reasonable exploitation and usage of water resources.

Beginning with the hydrogeologic structure of this region, this article makes evaluation of the storage capacity of groundwater reservoirs in the Northern Piedmont of Tianshan Mountain from three aspects: the storing and regulating space, supplies and project. Then it analyzes the economic, social and environmental benefits incurring by the construction of groundwater reservoirs and finally it reaches a conclusion that constructing groundwater reservoirs in this region will be beneficial to the society, the economy and the environment.

1       General Regional Situation

The Northern Piedmont of Tianshan Mountain is located in the Eurasian interior far away from the ocean, bearing the typical arid inland basin weather. It is very dry due to the scanty precipitation and intense evaporation. For many years the average rainfall was only 150-200mm, but the evaporation amount 1000-4000mm. The water source in the area mainly depends on the melting ice snowof the high mountain. There is a little rainfall in the hilly land and plain area. All of the rivers rise in the high mountain areas, running across the ex-mountain structure through the very profound allucial fan and finally disappearing in the desert. The medium and high mountain area is the formation place of water resources and the lowland hilly structure is the runoff area and the plain the developing and vanishing area. Therefore, the rivers originated in the Tianshan Mountain flowing in front of it are the primary water sources for the economic development district in the Northern Piedmont of Tianshan Mountain. Because of the increasing demand, the shortage of water resources has already been a bottleneck restricting the regional economic development. At present the exploitation and usage of water resources are centralized in the plain area. The water is utilized directly at the outlet. The overuse of water in the upper reaches of rivers deprives the ecological water demand in the lower ones. The over exploitation of water in plain areas caused a series of ecological problems, whereas the groundwater reservoirs in the depressions of the Tianshan Mountain are ill-exploited. As a result, the effective use of the storing and regulating capacity of groundwater reservoirs in the depressions of the Mountain is a valid solution to water resources problems.

The neo-tectonic movement has formed three rows of anticline structures and east-west counter fracture^[1]: one is the anticline structure of the Northern Piedmont of Tianshan Mountain, the second Manasi anticline structures and the third Anjihai anticline structure. The three lines of structures shaped a string of goose-like structure depressions in which piled up a huge ice water gravel stratum of the Quaternary Period which became a giant groundwater reservoir. From east to west there is the groundwater reservoir of the Chaiwobu Basin, the one at the depression of mountains in Manasi River Basin, the one at the Wowate-Anjihai depression and another one at the south Dushaizi depression.

2 The Storing and Regulating Space of the Groundwater Reservoirs

The storing and regulating space of the groundwater reservoirs is the fundamental condition for constructing them, which must enjoy the following characteristics: the large storing and regulating space, the immense storage constant for aquifer, the strong permeability and transmissibility and so on. The groundwater reservoirs at the depression in the ex-mountain structure of the Northern Piedmont of Tianshan Mountain have excellent storing and regulating space, and plenty of water resources which make them good natural groundwater reservoirs.

Fig.1 The schematic diagram of the tectonic zone in the Northern Piedmont of Tianshan Mountain ^[2]

Chaiwobu Basin is semi-closed, surrounded by Tianshan Mountain in the south, Bogeda Mountain in the north, the east side of Chaiwobu Lake in the east and the Qianshui River region of the Xishan Farm in the west. The Basin north-south is long and east-west narrow. Because of the neo-tectonic movement, the Basin can be divided into three independent parts: the Wulumuqi River Basin, the Chaiwobu Lake Basin and the Aspen River basin. There are piles of unconsolidated deposits of the Quaternary Period, with the upper part pluvial gravel stratum and the lower glaciofluvial gravel stratum. The unconsolidated deposits have good permeability. The thickest water bearing layer can reach 800m, whereas the average is just 200-400m. the groundwater is the unconsolidated Quaternary pore submersible. It is calculated that the biggest storage capacity of the groundwater reservoir in the Chaiwobu Basin is 451.5×10⁸m³/a, the least 438.6×10⁸m³/a and the adjustable storage capacity12.9×10⁸m³/a^[3]. Therefore, it is a superb natural groundwater reservoir and can be used to solve the water resources problems in Wulumuqi.

The groundwater reservoirs at the depressions in the Manasi River Basin are situated between the first and the second rows, transversing the Jinggou River, the Ningjia River, the Manasi River and the Taxi River, among which the altitude of the Manasi River valley is the least and the outflow region of the groundwater reservoirs. The length of this depression is about 85km and the width 13-17km, with an area of some 1275 km². There piles up huge gravel and soil of the lower Pleistocene series and the medium Pleistocene series, with the relatively unconsolidated structure, the developed pore space. The depth of the saturation zone can reach to 380-750m, which formed a good storing space. The first row structure, the second one and the tightly-cemented gravel of the Tertiary system in the lower part have formed a closed basin-like east-west water resisting border. It is calculated that the biggest storage capacity of the groundwater reservoir at the depression of the Manasi River is 530.4×10⁸m³ and the least 510×10⁸m³. The difference between the two is the adjustable storage capacity (20.4×10⁸m³), in other words, when the groundwater level decreases 1m, it will gain the adjustable storage capacity of 2.04×10⁸m³. Therefore, the ex-mountain groundwater reservoirs in the Manasi River, made of closed water resisting border, is one with a huge storing and regulating space.

Fig.2 The north-south section sketch map of underground reservoir in Manasi River Basin ^[4]

The groundwater reservoir of the Wowate-Anjihai depressions is situated among the ex-mountain major dislocation of the Yilinharnai Mountain, the Dshanzi-Anjihai fracture and the anticline of the Anjihai, separated from the Dunan depression of by the fracture zone of Wulanbulake in the west. The east-west length of the depression is 60km and the north-south one is 6-8km with an area of some 450km².The major water bearing stratum consists of the sandstone and conglomerate of the upper and mid Pleistocene series of the Quaternary Period, with an average depth of 450m and the deepest part of 600m. It is calculated that the biggest storage capacity of the groundwater reservoir at the Wowate-Anjihai depression is 308×10⁸m³/a, the least 297×10⁸m³/a and the adjustable one 11×10⁸m³/a.The lower mudstone of the Tertiary has shaped the water resisting border of the groundwater reservoir. The groundwater reservoir in the plain region is supplied by the depression groundwater as groundwater runoffs through the Halaande water penetrating tube, the Anjihai valley and the sandy-bay section.

The Dunan depression is located between the Kuitun River and the ex-mountain structural basin. Influenced by the Tertiary protrusion, there piled up the unconsolidated sediment of the Quaternary period with the average depth of approximately 400-600m and the aquifer was mainly made of the Wusu cluster of the upper and mid-Pleistocene series with the average depth of about 100m.The groundwater in the basin between the mountains is supplied by the river leakage, the channel leakage, the ex-mountain influent steam of the storm rainfall and flood current, the side runoff of the bedrock mountain and the water penetration of the valley underrun and the ex-mountain rainoff. Then it runs through the Dushanzi-Anjihai fracture into the plain as groundwater supple. The west groundwater flows to the north, the east river to the northeast through the Wulanbulake Chase flowing down in the lower river, and a little amount of it flows to the north with the total excretory amount of 0.5411×10⁸m³/a. The large scale groundwater reservoir formed by the ex-mountain basin and the Tertiary swelling region enjoys relatively strong storing and regulating capacity, with a storage capacity of about 0.5×10⁸m³/a.Recently the Dushanzi chemical plant has constructed only water supply works in the upstream of the swell but no other exploitation. The total production volume of the groundwater at the depression is 0.5×10⁸m³/a and still enjoys a great latent capacity.

The groundwater reservoirs at the depression of the Northern Piedmont of Tianshan Mountain have such characteristics: 1) The water-resisting borders, consisting of the rock stratum of the depression basis and the round Tertiary Miocene and Pliocene series, are relatively closed.2) The Quaternary ice water gravel stratum piled in the depression has formed the primary water-bearing layer.3) The storing and regulating space is large.4) The aquifer’s great capacity for storage and its good permeability make it easy to store and regulate the water resources. All these mentioned characteristics are extremely excellent conditions for constructing the groundwater reservoirs.

3 The Adjustable Water Sources of the Groundwater Reservoir

Another necessary condition for constructing the groundwater reservoir is the adjustable water sources. And the groundwater reservoir in the Northern Piedmont of Tianshan Mountain structure has a great amount of adjustable water sources. The rivers rising from the alpine region of the Tianshan Mountain invert with the groundwater frequently when running across the ex-mountain depression, providing abundant water resources for groundwater reservoirs’ storing and regulating.

The groundwater reservoir in the Chaiwobu Basin is mainly supplied by the leakage of the bed river and the influent steam of the field irrigation and the precipitation. After running out the mountain, except a little amount led directly, a great deal of the river water is provided for the groundwater because of the strong permeating ability of the bed river on the alluvial-proluvial fan, which is the essential nourishment source of the basin groundwater. The groundwater is recharged by about 1.0579×10⁸m³/a of the river, channel and field leakage and some 0.2937×10⁸m³/a^[5] of lateral groundwater. Influenced by the function of the basal constitution, the geology and the geomorphy, the groundwater influxes from the basin environment to its centre.

The Manasi River Basin provides enough water resources for the groundwater reservoir’s storing and regulating. It is reported that the biggest yearly runoff volume of the Manasi River reached at 14.66×10⁸m³/a, the least 10.25×10⁸m³/a and the average 12.7×10⁸m³/a. by the data of the Hongshanzui hydrological station. And it is the important alimentation resource for the two groundwater reservoirs. Additionally, the Taxi River, the Ningjia River, the Jingou River and other rivers along the two sides of the Manasi River provide the ex-mountain groundwater reservoirs with ample water resources and it accounts for 32% of the flow amount of the Manasi River at the Hongshanzui mountain gap. The rich water resources in the Manasi River secure an adequate supply for the groundwater reservoir’s storing and regulating. According to the data of Kensiwate the biggest runoff volume of Manasi River is 20.19×10⁸m³/a, the least 9.357×10⁸m³/a and the average 12.19×108m3/a.The high water period is from June to October, accounting for 70% of the yearly total volume, and from November to March is the drought period. The biggest runoff volume of Taxi River is2.94×10⁸m³/a，the least 1.93×10⁸m³/a and the average flow amount 2.25×10⁸m³/a。The runoff of the Ningjia River is 0.71×10⁸m³/a.Because of the influence of the landform, the precipitation and its form are different from the south mountain region to the north plain region at the depression of the Manasi River. The precipitation in the mountain region is about 800mm and the primary form is snow. It is the major resource of the region. The ex-mountain rainfall has a limited effect on the groundwater reservoir due to its little precipitation and the yearly rainfall if under 200mm. Besides, the Manasi groundwater reservoir is supplied by the crake groundwater in the south and the lateral groundwater in the east and west.

The Anjihai River is the major supplier for the Wowate-Anjihai depression, with a average yearly runoff of 3.8×10⁸m³/a of which 0.711×10⁸m³/a for the depression.Besides that there is also the lateral and the rainfall alimentation. The total alimentation of the depression is 2.2×10⁸m³/a.

The groundwater reservoir of the Nandu depression accepts the vertical leakage of the Kuitun River, the Bayingou River and the Wulanbulagou River and the total leakage is about 0.7716×10⁸m³/a accounting for 11.34% of the surface runoff, 70% of the total alimentation of the depression. Including the rainfall leakage and the lateral leakage, the natural groundwater alimentation at the depression is 1.2573×10⁸m³/a and the biggest production volume is0.8173×10⁸m³/a. The qualified water is the major supplier for the towns and cities in the lower river basin.

Fig.3 Yearly runoff of the Manasi River Fig.4 Average monthly flow of the in Kensi Walt station (1958- 2000) Manasi River in Kensi Walt Station

As an important water supplier for the ex-mountain groundwater reservoir, rivers have abundant water resources. The high water period is from June to September and it is good for the groundwater reservoir’s storing and regulating. Just take Manasi River for example, its high water period is from June to August, and the runoff accounts for 70% of the total. Its drought period is from November to March.

4 The Project Measures for the Groundwater Reservoir

With the storing and regulating space and water sources, it is necessary to take some project measures in order to achieve the goal. Considering the water demand in the region, the artificial project construction must be implemented economically, properly and safely.

Because of the closed storing and regulating space of the groundwater reservoir in the Northern Piedmont of Tianshan Mountain, there is no need of the water interception project. And the major projects are the groundwater exploitation, the artificial recharge and the conveyance project. The groundwater exploitation should be distributed all over the region of

outflow and exploit groundwater collectively by the exploitation well. The groundwater replenishing project should be constructed in the area with good permeability near the mountain. When the high water period comes the flood is intercepted in the underground by using the percolation pit and well. And a complete relevant set of the conveyance project must be used to deliver the groundwater to the water-demanding region. For example, the groundwater reservoir in the ex-mountain of the Manasi River basin can be exploited in the stream channel near the mountain vent and constructed the central water supplier. The percolation pit and well are constructed at the depression near the Tianshan Mountain to increase the groundwater alimentation. In doing so, the water resource can be used effectively to solve the drought problem during the lower water period.

5 Benefit Analysis

The Northern Piedmont of Tianshan Mountain is the major economic development zone of the Xinjiang Province and the water resource is the essential element for the regional economic increase. But the utilization of the water resource in the plain has already reached high and the exploitation space is limited whereas the groundwater is not exploited completely, hence the qualified water of the groundwater reservoir’s storing and regulating resources can be delivered directly to the towns and cities in the lower river basin. It can be used as the water supplier for the towns and cities and also an emergency water resource. Therefore, the construction of the groundwater reservoir in the mountain region can not only promote the utilization ratio of the regional water resource but also solve the ecological environment problems caused by the decline of the groundwater level. In a word, constructing groundwater reservoir in this region is beneficial to the society , the economy and the environment.

6 Conclusion

The conclusion can be reached after the research: The groundwater reservoir in the ex-mountain of the Northern Piedmont of Tianshan Mountain is a excellent natural one because of the large storing and regulating space and the ample water resource. A certain set of artificial measures can animate the function of the groundwater reservoir and achieve the goal of effective use of the regional water resource, which can be beneficial to the society, the economy and the environment.