THE TUUL RIVER WATER RESOURCES CHANGES AND WATER USE IN ULAANBAATAR CITY, MONGOLIA N.Batnasan Institute of Geography, Mongolian Academy of Sciences, P.O.Box-664, Ulaanbaatar-24, Mongolia, e-mail: [email protected] ABSTRACT Presented annual and long-term hydrological regime of the Tuul river, which is flowing through the capital city of Mongolia. Its total length is 704 km and mean annual discharge near Ulaanbaatar city is varying from 24.1 to 26.6 m3/s. In this river basin concentrating about 30 % of all population of Mongolia, and most water users, like light and heavy industry, coal gold mining and irrigated agricultural farming. Thus, the Tuul river basin is most polluted and effected river basin in Mongolia by human activities. The river water resources varies significantly over the basin and has a great differences in seasons and long-term period. Most of the annual runoff is formed during the summer period between June to September, because most (about 80%) precipitation is falling during this period. For about 140-170 days of the year, the river is covered by ice. Analyzed present situation of water use of the Ulaanbaatar city. Discussed some negative effects and possible improvements for water use in this region. Water use of the Ulaanbaatar city is continuously increasing with relation to population growth. For instance, total water use of this city in 1968 was 25000 cub.m, in 1998 increased to 170000 cub.m, and in 2010 expected to increase about 280000 cub.m., which means that, in near future the ground water resources will be not enough for water supply and we must find another solution and put more emphases on water resources management of this region. KEYWORDS: Climate, discharge, Hydrology, human activity, river flow, pollution INTRODUCTION The Tuul river is originating from western slope of Khangai mountain and flows westwards to Orkhon river, passing through the capital city Ulaanbaatar, where living about 750000 inhabitants (Figure 1). In this river basin concentrating about 30 % of all population of Mongolia, and most water users, like light and heavy industry, coal and gold mining and irrigated agricultural farming. Total length of the Tuul river is 704 km, cachment area is 49840 sq.km and mean annual discharge near Ulaanbaatar city is varying from 24.1 to 26.6 m3/s. (Surface water of Mongolia, 1999). Figure 1. Figure 1 Figure1. Location of Ulaanbaatar city, Mongolia During the last years, because of climate changes and human activities water regime of large rivers and lakes of Mongolia are considerably effected, resulting in change of natural resources availability and distribution (N.Batnasan, 2000). WATER RESOURCES FORMATION AND WATER USE IN THE ULAANBAATAR CITY The basin of this river can be divided into 3 different parts by characteristics of water resources formation, hydrological and hydro-geological regime. First part is from its origin to the upper boundary of the Ulaanbaatar city, town Nalaikh, where closed coal mining is operating for coal supplying of the Heat Plants in Ulaanbaatar and other individual users. From this point starting pollution of the river water. This part of the river basin is mostly middle or high mountainous area, with relatively high slopes. Consequently, in this part forming most river water resources and long-term mean discharge is varying 3-4.2 litre/sec.sq.km. River width is from 0.1 to 0.6 sq.km. In incoming parts of river water balance, ground water recharge is taking place, as well as precipitation and surface water flow. Second part is Ulaanbaatar city. The city is laying along the river valley. Systematic observation on the hydrological regime and water quality is began in 1946 at Zaisan station in the middle of the city. In 1980s because of consideration in importance of controlling the river water pollution have been increased number of monitoring sites installed not only in the Tuul river itself, also at the tributaries. More emphases was placed on water quality variables such as nutrients, BOD and some kinds of heavy metals. This part of the river is mostly affected by human activities. There are developed a lot of canals, small dams, pipes and other hydro- technical constructions for water supply and used water discharge. Also there operating many wells for householder’s water supply. Main central water supply ground water wells are located in the valley of the Tuul river. There are about 160 ground water supply wells in Ulaanbaatar and their total capacity is about 220300 cub.meter/day. The ground water resources are mainly recharged during July to September, and maximum is occurred in August. In winter time, the recharge is not taking place, but water use is even increasing, which leads to considerably decreasing ground water table and damaging the Tuul river hydrological system. During the last years in low water period (May, June) often observed cutting up rivers in some places near the Ulaanbaatar city, which is never happened before. Also, during the end of 1980s, where happened dry periods in most parts of Mongolia, central water supply system could not operate normally, because of considerably decreasing of the ground water table. Third part is from down boundary of the city to the end of this river, which is about 524 km in length. In this part dominates steppe landscape with low slope. Ground water recharge is decreased considerably. Long-term mean of river discharge is varying from 0.5 to 1 litre/sec.sq.km. There are no significant tributaries which could affect the river water quantity and quality. Urbanization and population density is low. The major point pollution sources here is number of gold mining activities carried out in the region of Zaamar town. WATER RESOURCES VARIABLITY The river water resources varies significantly over the basin and has a great differences in seasons and long-term period. Most of the annual runoff is formed during the summer period between June to September (Figure 2), because most precipitation is falling during this period. For about 140-170 days of the year, the river is covered by ice. 100 100 90 90 80 80 70 70 60 60 50 50 P, mm 40 40 Q, m3/s 30 30 20 20 10 10 0 0 1 2 3 4 5 6 7 8 9 10 P1-Ulaanbaatar P2-Terelj Q1-Ulaanbaatar Figure 3. Annual distribution of the Tuul river discharge (Q, m3/s) and precipitaion (P1, P2, mm) in the river basin Investigation results shows that the Tuul river water recharged by the ground water during high and autumn low water period, which is resulting in increasing river discharge along the river. In contrast, during spring low water period the river water feeds the ground water, in the result the river discharge decreases along the river. Long-term variation of precipitation and river discharges shows that, there are some similarities in decreasing and increasing periods (Figure 4). In the Tuul river basin the precipitation is decreased during 1970s and increasing from beginning of 1980s until mid of 1980s and again reducing untill 1990, after that increased, which has same trends as a river discharges. This indicates that, the precipitation is considerably effecting into the formation of river water resources. 500 90 450 80 400 70 350 60 300 50 mm 250 m3/s 40 P, 200 Q, 150 30 100 20 50 10 0 0 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 P1-Ulaanbaatar P2-Terelj Q-Ulaanbaatar Figure 3. Long-term variation of the Tuul river discharges (Q) and precipitation (P1, P2) in the basin CONCLUTION Water use of the Ulaanbaatar city is continuously increasing with relation to population growth. For instance, total water use of this city in 1968 was 25000 cub.m, in 1998 increased to 170000 cub.m, and in 2010 expected to increase about 280000 cub.m., which means that, in near future the ground water resources will be not enough for water supply and we must find another solution and put more emphases on water resources management of this region. Certainly, there are number of reasons for decreasing water resources both in surface water and ground water. In the background affect of climate change, also affecting the human activities and mismanagement of natural resources in the river basin, specially in the head water basin. Uncontrolled cutting of forests in large water resources formation area and forest fires are often occurred in many watershed areas. It is clear that, if decrease forested area, than also decreasing moisture contents of that region, which resulted in decreasing of ground water and river discharges. Also effecting, land degradation, over grazing of pasture and soil erosion because of increasing density of population and large amount of livestock near the city. REFERENCES Batnasan N, (1998), Hydrologycal systems, water regime and natural development of Greet Lakes in Gobi Desert region, Ph.D. Dissertation in Geographical Science, Library of the Center for Science and Technology of Mongolia, Ulaanbaatar, p.263 Batnasan N, (2000), Hydrological systems of Gobi Desert’s Great Lakes Basin and their Environmental Responses to Climate Change. In Abstract volume of the 29th International Geographical Congress, 14-18 August 2000, Seoul, Korea. Batima P, (1998), River water chemical composition and quality assessment, Ph.D. Dissertation in Geographical Science, Library of Science and Technology of Mongolia, Ulaanbaatar, p.138 Myagmarjav, B and G.Davaa, Surface Water of Mongolia, (1999), Ed:, Ulaanbaatar, pp.9.1- 9.55 .