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Poster Session R
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Basic Study on Orhon – Ongin River Diversion
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:
- Orhon river has abundant water supply which is enough for the diversion to ongin river.
- An artificial reservoir can be established at ongin river.
- The ground water aquifer in the ongin river basin and Ulaan Nurr can be recharged and conserved by the river diversion.
- Conversion of the Orhon river basin is still maintainable without any adverse effects, even if the excessive water is diverted.
An early execution of a basic study is needed for the ongin an orhon river basins taking in the following items :
- Assessment of potential of water resources in the orhon river basin.
The potential of water resources development of the orhon river basin will be assessed carefully by studying the flow regime of orhon river and the present demand for water in the region. In the process, ecological balance in the area will be carefully protected.
- Evaluation of the huydrogeolocial structure of the watershed of ongin river.
A study will be carried out concerning the hydrogeological characteristics of ongin river watershed and also, the meteorological conditions in the area to examine the system of percolation of water into ground and also the recharge storage of ground water. The protection of the ecology has a high priority ion the study.
- Estimation of the amount of exploitation water
Amount of surface water and the amount of rechargeable groundwater in the ongin river basin after the diversion from orhon river will be calculated.
- Examination of possible diversion methods
Engineering methods of diversion will be examined on the basis of the factors such as the amount of the water to be diverted, meteorological conditions, engineering geology, environment etc.
The implementation of the basic study of the basic study delineated above is necessary to decrease the influence by desertification in the ongin river basin, and to promote the regional development of the area. Moreover, this study will contribute to the socio-economic development of the other areas in Gobi, which face the same problems.
References
- Natural resources thematic maps of Mongolia, Moscow, 1981 117p.
- Hangai mountains east south part small rivers, sources and Ulaan Nurr (lake) restrotation project – 02.07.02. Ulaanbaatar, 1990 89p.
- Sh. Tsevegmid, Geogrpahy of Mongolia, Ulaanbaatar, 1969, 401p.
- G. Lkhan-Aasuren. “Orhon-88” Draft Project. Ulaanbaatar. 1988, 40p.
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