Basic Study on Orhon – Ongin
River Diversion G. Lakhan-Aasuren, A.
Tsetsgee, M. Saandar Remote Sensing & Geoinformation Center, MGGE, Mongolia Hiroshi Yamamota, A. Hamamori International Engineering Research Institute, Tokyo, Japan Abstract Orhon-Ongin river basin area in Mongolia, which is located in Gobi area, is rich in mineral resources, such as coal, colored and rare metal. It is also suitable for mining and cattle breeding industries. And for this reason, the area is very important for the Mongolian economy. Rivers and lakes in this area have nearly dried due to climate condition and human activities. That is why we need to carry out an investigation on the water resources and the recharge and also have an ecological basic study by the using Remote Sensing. Introduction The basic study on orhon-ongin river diversion is needed because there is an inherent water shortage which is caused by the climatic conditions of the area. Therefore, it is urgent to conduct geology ecology, etc., before making any concrete decision about the diversion plan. Study Area The origin river basin and surrounding area is located in Gobi. The study area is the watershed of Orhon river and ongin river is shown in Figure 1. The study area is 99.,528 km2. With the help of satellite images an average annual surface and groundwater flow map in the scale 1:1,000,000 was created. By using this map the natural condition of the orhon-ongin river basin was described. Its desert and semi-desert ecosystem is suitable for grazing camels, sheep and goats, which are utilized as material for wool, blankets and other livestock processing. Also, this area is very rich in mineral resources, such as coal, colored and rate metals. The stock breeding and the mining industries contribute not only for the domestic use but also for export. For this reason, the area is very important for the national economy and its development desirable. However, absolute water shortage due to climate conditions is impeding such development. Furthermore, some small rivers and lakes in the South Gobi admits surroundings have dried up in the past ten years, and now the areas shows signs of desertification. Especially, ongin river and its inland lake, Ulaan Nuur, have nearly dried up and have seriously influenced the lifestock farming and the life of the residents. To maintain the comfortable life of the residents without the effects of desertification and to further develop the area, is necessary to secure water resources. The area of the ongin river basin and its surroundings mainly uses groundwater because it is difficult to obtain surface water due to extremely low precipitation. In the Hangai mountain, where the orhon-ongin river has its orngin, the precipitation is 200-325 mm, in the planes 100-200mm and in the Gobi 50 – 100mm. In the warm season, the ground surface becomes extremely hot and causes vertical turbulent air movement. Therefore, some areas receive heavy rain for a short period of time. the main characteristics of the climate in the study area is monsoon rainfall, which occurs between July and August. This area has 4 natural zones because there are geomorphological differences and therefore environmental temperature variation is high. The mean monthly temperature reaches in January a low – 18°C - 20°C compared to a high of +40°C + 45°C in July. Average annual temperatures are: -for Hangai mountains at 1800m and higher from =1°C to 1°C; -for Gobi and plane zones at 1500 m from +1°C to +4°C The study area is divided into two major basins, i.e, Arctic Ocean basin and Central Asian Inflow basin. (See Fig. 2). In the study area, the biggest river is orhon, which merges into the selenge river, that has its outflow in the Arctic Ocean basin. This river ahs its origin in Subargan Hairhan, a part of the Hangai mountain, at the height of 3179 m above the sea level. The orhon rive is the longest in Mongolia. The river’s length is 1124 km and the catchmetn area is 132,825 sq. km The major potential surface water soruce for supplementing natural rainfall is the orhon river which makes the north-western boundary tot eh study area. Highest discharge is 20-28 m3/sec, lowest 4 – 8 m3/sec and average discharge 15, 5 m3/sec from gauge. In the month of August, the river has its highest water river which is approximately m. The ongin river starts from Hangai mountains ‘south face’ collection 70 small rivers and flows into the Gobi Ulaan Nuur. The main discharge of these rivers is rainfall and snow, but snow discharge is 5 -6 times less than rain discharge. In the North West, orhon river basin and the origin of Ongi river is in the district with permanent river flow, and the underground flows layer is 10 – 50 mm/year, and in the south it is upto 5mm/year, and in ongin river basin there are two fields with difficult conditions for the formation of underground flow. The majority of the ongiin river flow are is located in the district with nonpermanent and episodic river flow. Thus, the district included in the Arctic ocean basin is in a good hydrogeological condition. A Proposal for future study The water volume of the ground water resources is limited, so that inflow and outflow are now in balance. However, the ground water potential in the area is barely enough for the demands of the residents, who pump up water by small wells in traditional sence. An excessive use of ground water by industries will the ecology of the water shed in the area. To secure water without adverse effects to the ecology system, an idea of water diversion from Orhon river, which has abundant water flows out of the country in the summer season (see figure 3), to ongin river has been prepared. To examine the possibility of the idea, a preliminary study which was names as “Orhon 88” was conducted in 1988. As conclusion of “Orhon 88” study, it was indicated that the recharge of the groundwater would be possible by the river diversion. Also, the study mentioned the following items:
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