The Chui Valley has a developed river network. The river network is especially dense on the northern slopes of the Kyrgyz Ala-Too. Most of these rivers belong to the basin of the Chu River. The small rivers in the northwestern part of the ridge disappear into the waterless plain as they exit the mountains. The main water artery is the Chu River. The area of the watershed is over 50,000 km². The length of the river, along with the Joong-Aryk River, is 140 km, while within the Chui depression it is 237 km.
According to hydrographic features and conditions of runoff formation, the basin of the Chu River is divided into three parts: the upper part - from the source to the exit from the Boom Gorge, the middle part - within the Chui depression, and the lower part, covering the deserts of Kazakhstan, with predominant dispersion of runoff.
The Chu River is formed by the confluence of the Kochkor and Joong-Aryk rivers at the village of Kochkorky and flows northeast, then breaks through a narrow gorge 4-5 km long through the Kara-Koo ridge and enters the Orto-Tokoy valley, where a reservoir of the same name has been constructed. Through a tunnel about 650 m long, water from the reservoir is supplied to the river, which flows towards the western part of the Issyk-Kul basin, separated from it by a lowland strip 10 km wide. At the city of Balakchy, the river turns west and flows through a mountain valley 1.0-1.5 km wide, then enters the deep and narrow Boom Gorge, which is 22 km long and 100-150 m wide. Here, the Chu River receives as tributaries from the left side the Baydamtap, Kongorchoak, Sulu-Terek, and others. At the exit from the Boom Gorge, the largest right tributary of the Chu River, Chong-Kemin, flows into it. Further, the river enters the Chui depression and receives its second right tributary, Kichi-Kemin. From the Boom Gorge, the Chu River flows for more than 10 km in a relatively narrow valley, pressing more to the left slope so that flat terrace areas are predominantly developed along the right bank. The floodplain here is presented intermittently. Between the exit from the Boom Gorge and the town of Kemin, in the cross-section of the valley, in addition to the floodplain, there are five terraces at heights of 5, 15, 20, 65, and 80 m above the river level (M.M. Reshetkin, 1933). In the area of the town of Kemin, three lower terraces are developed on both banks of the river. Following the slopes of the terraces downstream, there is a sequential, more or less regular retreat from the river, a decrease in height, and an increasing smoothness. West of the town of Kemin, the valley of the Chu River widens significantly. The floodplain becomes significantly developed, reaching more than 1 km in width in places, and the river itself branches into wandering arms and channels. The fall of the river, according to I.S. Shchukin (1983), also decreases significantly (from 0.0098 below the exit from the Boom Gorge to 0.0040 at Tokmok and below up to the Konstantinovsky bridge). The channel of the Chu River is winding, its width at the section near Bishkek is 30-35 m. The depth of the riverbed is 0.3 - 2.1 m.
Below the city of Tokmok to the Chemuchskaya (Chumyshskaya) dam, the valley of the Chu River expands to 2-3 km, is heavily marshy, and is characterized by abundant "kara-suu" springs. The largest of them is the Red River (Kyzyl-Suu). The Red River on the left bank of the Chu River and the Black River on the right (in the Republic of Kazakhstan) are mainly fed by groundwater. Beyond the Chemuch cliffs, the Chu River continues its flow through a wide valley, which narrows beyond the ridge of Yiyk-Too. Below this ridge, the Chu River is lost in the sands of Moyun-Kum.
The Chu River belongs to rivers fed by glaciers and snow, characterized by the presence of two peaks in water level. The first, spring peak is caused by the melting of snow in the lower part of the watershed, and the second, summer peak - a longer and more powerful rise in water occurs from the melting of eternal snows and glaciers in the highlands. According to the Jal-Aryk hydropost, the average long-term annual water flow in the upper reaches is 31.0 m³/sec, and in the Chui Valley, it is 53.5 m³/sec. The maximum flow observed in the summer period is 210 m³/sec, while the minimum winter flow is 4.3 m³/sec. The lowest average annual flow of the Chu River, 45.3 m³/sec, was recorded in 1946. The highest flow of 65.5 m³/sec was noted in 1934.
The low-water period, which occurs during the cold season of the year, is generally characterized by relatively low flows and the absence of intense fluctuations in flows. During this time, the runoff is maintained almost entirely due to the inflow of groundwater into the channel network.
The waters of the Chu River are used for irrigation of the Chui Valley plain through main canals derived from the river (BChK and others). The Chu River has great hydropower potential.
In the Chui depression, the Chu River receives its numerous left tributaries. Some of them do not reach the Chu River. Most of these tributaries originate in the highlands of the northern slope of the Kyrgyz Ala-Too.
Rivers play a major role in the hydrography of the ridge, representing typical mountain water flows with turbulent currents and vigorous destructive activity. Despite the relatively small size of the channels of most rivers, their valleys in the mountains represent deep gorges (Shamshy, Issyk-Ata, Alamudun).
By the nature of their feeding and the location of their sources, all rivers flowing from the northern slope of the Kyrgyz Ala-Too belong to the type of glacial-snow feeding. These are the left tributaries of the Chu River - the Shamshy, Kegeti, Issyk-Ata, Alamudun, Ala-Archa, Sokuluk, Ak-Suu, Kara-Balta rivers, and others. Their sources lie at an altitude of over 3500 m, with melting glacial waters playing a major role. However, atmospheric precipitation and groundwater also participate in the formation of runoff. Rivers of this type are characterized by two peaks in flow - a spring peak associated with the melting of seasonal snows and a prolonged summer flood, which, due to the vigorous melting of glaciers, manifests itself violently, especially in July-August. High water levels in these rivers are observed for a fairly long time - from April to September.
Middle mountain rivers, whose sources are located at an altitude of 3000-3200 m, are mainly fed by atmospheric precipitation and seasonal snows, as well as groundwater. In most cases, they originate from springs that emerge along the fault line of the earth's crust or along cracks in the rocks. These include rivers on the northern slope of the Kyrgyz ridge: Kyzyl-Suu, Alchal, Taldy-Bulak, Norus, Jylamish, Kayngdy, and others. These are mainly small mountain rivers with steep falls and fast currents, no longer than 15-20 km. Floods of these rivers occur in spring with the melting of winter snows and flow violently, but briefly. In summer, they are low-water.
In rivers originating in the low mountains, foothills of the Kyrgyz ridge, water appears only in spring during precipitation, and in summer they dry up.
Most of these rivers end in blind mouths on the foothill plain of the Chui Valley. Table 10 provides hydrographic characteristics of major rivers flowing from the northern slope of the Kyrgyz ridge.
Among the left tributaries of the Chu River, the largest watercourse is the Shamshy River. In its upper reaches, it flows through a narrow gorge and exits into the Chui Valley. The Shamshy River valley is divided into three parts by the Tuyuk and Koltor ridges - the Tuyuk, At-Jailoo, and Kel-ora basins. The total length of the Shamshy River is 58 km. The area of the river's watershed is 457 km². The average annual water flow is 5.68 m³/sec, the maximum is 29.4 m³/sec, and the minimum is 1.13 m³/sec. The largest tributary of the Shamshy River is Tuyuk, which is 24 km long, with a watershed area of 132 km².
The Shamshy River forms a huge alluvial cone as it exits the mountains onto the plain, becoming low-water (diverted for irrigation and losing water through filtration into loose deposits) and partially flows into the Chu River approximately 25 km from the mountain mouth.
The Kegeti River originates from the glaciers of the Kyrgyz ridge and flows into the Chui depression. The meridional ridges of At-Jailoo and Koltor divide the Kegeti basin into three parts: At-Jailoo, Kegeti, and Koltor. The upper reaches of the river are narrow, with a rocky and rapid channel. There is a waterfall where water cascades down a 16 m high ledge. Upon exiting the mountains onto the plain, the river expands to 1 - 1.5 km and forms an alluvial cone, losing itself in the loose deposits of the Chui depression before reaching the Chu River. A significant tributary of the Kegeti River, the Koltor River, originates from under the glacier of Anastasia. The length of the river is 17 km.
The Issyk-Ata River. The source of the river is located in the glaciers of the upper reaches of Issyk-Ata. The ridges branching off from the main ridge of the Kyrgyz Ala-Too divide the rivers into several private basins, among which the most important are the basins of Issyk-Ata, Bytya, Kok-Moynoka, and Tuyuka. Due to the location of almost the entire watershed area in the high mountainous zone in the area of glaciers, the Issyk-Ata River has a well-defined glacial type of feeding.
In the mountainous part, the river receives many tributaries (Tuyuk, Bytya, etc.), while in the plain part, it has none. Many tributaries of the Issyk-Ata River are characterized by rapids, and there are waterfalls (Issyk-Ata). In summer, the waters of the river reach the lower karasuchnaya zone and partially flow into the Chu River. A small reservoir has been built on the Issyk-Ata River at the exit from the mountains onto the plain. Several irrigation canals are derived from it.
The Alamudun River originates from the glaciers of the central part of the Kyrgyz ridge, although its average annual water flow is slightly less than that of the Issyk-Ata River. The system of ridges in the upper reaches of the Alamudun River is divided into three basins - Altyn-Tora, the Alamudun itself, and Ashuu-Tora. The basins of the tributaries of the Alamudun - Chunkurchaka and Salika are located separately. The upper reaches of the Alamudun River represent a trading valley, while downstream it becomes narrow, 30-40 m wide. The riverbed is pressed against the steep left slope of the valley. Here, there is a hot spring, Zhylyuu-Suu (Warm Springs). Further, the Alamudun River carves through the Shekuli mountains, forming a canyon-like gorge 200-300 m deep. In the foothills, the river flows calmly, forming a wide valley with terraced steps; below the dam, it forms an alluvial cone.
On the foothill plain, the river, cutting through its alluvial cone, flows in a reinforced cement-lined channel in the eastern part of Bishkek and flows into the Chu River.
The length of the Alamudun River is 77 km, and the area of its watershed is 317 km². The average annual water flow is greater than that of the Ala-Archa River and equals 6.36 m³/sec, with a maximum of 27.9 m³/sec and a minimum of 0.88 m³/sec.
The Ala-Archa River originates from under the moraine of the Big Ala-Archa Glacier and flows north. From the east, it receives glacial rivers Jindi-Suu, Top-Karagay, Teke-Tor, and Aksai, and from the west, Adygene. After the confluence with the right tributary Kashka-Suu, the river expands as it exits into the Baytyk depression. The riverbed splits into branches (below the dam). Further, the Ala-Archa River enters the foothills (Baytyk, Bosboltok), forming a wide flat valley with three terraced steps. The riverbed is pressed against the right slope of the foothills. Then, exiting the foothills, it forms an alluvial cone and flows in a reinforced gravel-lined channel and only in high-water years reaches the Chu River.
A reservoir of the same name has been built on the Ala-Archa River. Numerous main canals are derived from it, which irrigate extensive lands in the Chui Valley.
The Sokuluk River originates from numerous small glaciers of the Kyrgyz ridge. Three short ridges divide the upper reaches of the Sokuluk River into four private basins - Tuyuk-Tora, Ashuu-Tora, Kichi-Tora, and Chon-Tora. The main river among them is Chon-Tor, formed by the confluence of Chon-Gora and Kichi-Tora.
The upper basin of the Sokuluk River is characterized by significant dissection. In the middle mountains, at an altitude of about 3000 m, the valley turns into a gorge - a canyon - with steep slopes 500-700 m deep. Here, the river flows violently, foaming, with a steep fall and high speed. The Sokuluk River exits the mountains onto the plain near the village of Belogorka and flows north. In the plain, below the village of Sokuluk, the river is slightly replenished by springs - Kara-Suu and only reaches the Chu River in high-water years. The water of the river is completely diverted for irrigation and is a major source of water supply.
The Ak-Suu River, along with the Shamshy basin, is one of the most extensive basins of the Kyrgyz ridge. It is formed by the confluence of two streams - coming from the southeast, Jary-Tash, and from the southwest, Chon-Tash. Major tributaries in the mountainous part include: Jardy-Suu, Temene, Ak-Bashat, Bul-Teke, and others. In terms of water regime, in the upper and middle parts, the Ak-Suu River represents turbulent flows cascading from great heights through narrow gorges, cluttered with boulders. In the low mountains and on the foothill plain, the river loses a significant part of its water to filtration into debris layers, while the remaining water is diverted for irrigation. Only during periods of summer floods does the river reach the lower karasuchnaya zone and flow into the Chu River.
The longest river (132 km) is the Kara-Balta River. The sources of the Kara-Balta River, under the name Koy-Bashy, lie in the southwestern corner of the Kara-Balta River basin. On the left, the Kara-Balta River receives several insignificant tributaries, among which the largest is the Chon-Mazar River. Among the right tributaries, the most important is the Abla River.
Upon exiting the mountains onto the plain, main canals are diverted from the river. In the lower reaches of the river, the Kara-Balta Reservoir has been constructed.
The Ashmary River flows through the border of the Panfilov and Merken administrative districts and is a right tributary of the Kuragaty River in the Chui Valley. The flow of the river is formed from the glaciers of Ashu-Tor, Kol-Tor, Tukzh-Tor, and Baktybay. Major tributaries of the river include the Mahan, Arshaly rivers, and others. The flood season begins in May and ends in September. This is the last glacial river on the northern slope of the Kyrgyz ridge, flowing in the west along the border of Kyrgyzstan with Kazakhstan.
Among the right tributaries of the Chu River, the largest is the Chong-Kemin River. Its sources lie on the southwestern slope of the mountain ridge connecting the Kungei Ala-Too with the Zailiyskiy Alatau at an altitude of 3800 m. The Chong-Kemin River largely belongs to the Kungei Ala-Too, where its most water-rich tributaries are also located. In its lower reaches, the Chong-Kemin bends south and flows into the Chu River. The length of the Chong-Kemin is 116 km. The watershed area is 1890 km². The average annual flow at the mouth is 35.6 m³/sec, with a maximum flow in July-August of 81.7 m³/sec and a minimum in March of 7.18 m³/sec.
Major tributaries include the Kalmak-Suu, Orto-Kayindy, Kashka-Suu, Tegirmenty rivers, and others.
In the upper part, the valley of the Chong-Kemin forms an extensive trough, the right bank of which is composed of moraines of lower Quaternary age. The slopes are steep, especially the left one; below, for 5 km, the river carves a gorge up to 600 m deep, then the valley widens again near the village of Shabdan. Below, the valley narrows again and flows into the Chu River.
One of the right tributaries of the Chu River is the Kichi-Kemin River. It originates from the southern slope of the Zailiyskiy ridge, flows southwest, does not reach the Chu River, and is completely diverted for irrigation. The upper reaches are in a narrow gorge, widening in the middle (up to 50-70 m). The length of the river is 81 km, and the watershed area is 514 km². The average annual flow is 2.10 m³/sec, with a maximum of 9.63 m³/sec (July) and a minimum of 0.46 m³/sec (February). Major tributaries of Kichi-Kemin include Kyr-Tabylgy (length 19 km), Sasyk-Bulak (15 km), and others.
To regulate the flow of the Chu River and its tributaries, several large reservoirs and many small ponds (Orto-Tokoy, Chemuch, Lower Ala-Archa, etc.) have been constructed. The Tash-Otkol Reservoir has been built in the channel of the Chu River. An 8 hydroelectric power plant cascade has been constructed on the Chu River and in the Big Chui Canal. They are part of the Bishkek energy system. Currently, the reservoirs are being developed for recreational and sports purposes.
In the Chui depression, an extensive system of irrigation facilities has been created. Initially, the Boroldoy and Krasnorechensky main canals were built. Then, 18 km from Bishkek, the Atbashinsky Canal (60 km long) was constructed. Since 1940, the construction of the BChK (Big Chui Canal) began; the Western BChK stretches 175 km from the village of Keng-Bulun (west of the city of Tokmok) through the outskirts of Bishkek to Merke. Its width is 10-15 m, and the depth is 5-6 m. A 70 km section of the canal was built during the Great Patriotic War using the method of people's construction. The construction of the remaining part of the canal was completed in 1958. The Eastern BChK begins east of the city of Tokmok. It stretches 100 km to Bishkek, where it ends by discharging into the Ala-Archa River. A number of main canals, including Krasnorechensky, Atbashinsky, and others, require renovation. Due to siltation and destruction of the walls, the carrying capacity of these canals has decreased. They are usually laid in loess-like silty clays, whose unreinforced walls are easily washed away.
In addition to surface waters, the Chu River receives so-called "karasuchnye" tributaries, which originate from springs that form at the ends of alluvial cones and along the Chu River itself, starting from the east of the city of Tokmok. The largest of them is the Red River, collecting waters from many springs, with a length of 50 km. The average annual flow is 2.5-3.5 m³/sec. On the right bank of the Chu River is the Black River, also mainly fed by groundwater.
Below the line of groundwater discharge, the Chui Valley is cut by a network of gullies that collect and carry "karasuchnye" waters. The flow of such "karasuchnye" rivers is calm, the banks are marshy, and ponds have been created along the gullies. Some of the water is diverted for irrigation, while less reaches the Chu River.
A significant portion of groundwater is used in the national economy, primarily in agriculture for irrigation.
Groundwater in the foothill fringe and most of the foothill plain is of good drinking quality. Below the karasuch zone, they are somewhat mineralized. In some places in the lower part of the depression, they sometimes cause soil salinization. However, this does not diminish the immense importance of groundwater in the Chui depression for supplying water to settlements, primarily the city of Bishkek. The water supply of Bishkek is currently provided by groundwater from the Baytyk depression, located at significant depths (up to 80-90 m). The reserves of groundwater from the alluvial cones of the Ala-Archa and Alamudun rivers can fully meet the needs of the city of Bishkek.
Through numerous discharges, both longitudinal and transverse, deep waters emerge in the Kyrgyz ridge in the form of mineral-thermal springs, which are used for therapeutic purposes. Most of these springs are located on the northern slopes of the ridge. The Kara-Balta thermal springs in the upper reaches have a temperature of 20-28°. The Alamudun springs emerge from cracks in the granites on the left bank of the Alamudun River south of Bishkek; their temperature is 29.5-33°. Numerous springs in the Issyk-Ata gorge also emerge from granites with temperatures of 36-55°. They serve as a hydrotherapy resort. In the valley of the Kyzyl-Suu River, there is a spring of the same name with a temperature of 20-23° and others.