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Development of the Teviot Catchment flood model
To make a realistic dynamic model, capable of accurately representing flood propagation through the catchment, it is necessary to use actual river flow data from various strategic points in the catchment. continue reading…
Modelling floods in the Teviot Catchment
The overall aim of a catchment flood model was to produce a 200 year flood hydrograph at the upstream boundary of Hawick and to show how it could be modified by NFM. The modified hydrograph could then be run in detailed models through the town. continue reading…
Catchment flood modelling
Hydrodynamic modelling provides a means to analyse processes occurring within a catchment and to test a range of scenarios which may influence future flood events. continue reading…
Bowmont Water River channel (Source: www.geograph.org.uk).
MNV consultancy has won an important contract from the Tweed Forum to study the causes of the recent adjustment of the Bowmont Water river channel and advise on future flood risk management solutions in the Bowmont Water/River Glen sub-catchment. continue reading…
A group visiting an MNV Sustainable flood management demonstration site
Floods are destructive processes which damage buildings, agricultural land and transport networks, but are also constructive processes that maintain dynamic river systems and help landscapes to evolve.
Flood management is addressed in various ways in different regions, countries and local administrative areas – the common approach being to react to major flooding incidents by building ‘hard engineering’ flood defences against water and flood debris.
The outcome can be seen in the canalisation and deepening of river channels and the widespread construction of flood banks in agricultural areas and flood walls in urban areas. Rivers react to this type of interference and in most situations will try to return to their natural forms. To prevent this, regular maintenance has to be carried out requiring an annual expenditure to repair banks, dredge channels and clear vegetation.
In many countries, the maintenance requirement is often ignored, so that many flood defences are inadequate due to increasing flood flows linked to climate change. There has therefore been a reduction in the level of protection from many flood defences due to lack of maintenance and inability to adapt to changing circumstances.
Sustainable flood management (SFM) has recently been developed as a process which uses traditional land management techniques to address the causes of the flooding problem rather than trying to protect the impacted site with civil engineering solutions.
Overall, the aim of SFM is to reduce the rate of runoff in storm events by storing water throughout the catchment in vegetation, soils, wetlands, lakes and river channels. This is because the catchment is the interface between the climate and the river networks and the condition of the catchment determines the rate of runoff and hence the downstream flooding.
Catchment management for flood control aims to use natural processes and traditional land management techniques to reduce runoff rates, while paying close attention to other requirements in the catchment such as housing, industry and transport links. A natural catchment has in-built flood defences such as soil profiles, sediment bars, channel meanders, wetlands and natural levees.
In addition, the ground cover provides further defences which intercept rainwater, protect snowpacks and remove soil water as well as helping to stabilise soils and reduce erosion. Historical land management changes, house building and industrial development have reduced the effectiveness of some of the natural flood defences however other developments such as reservoir construction have helped to reduce runoff rates.
Flood prevention schemes have traditionally been undertaken by the construction of a solid wall or embankment, a barrier that is high enough to contain the flood water, debris and sediment in the river channel. Often, this has been done on an individual site basis, with little consideration for the wider catchment – and even less attention to funding for essential and costly maintenance.
SFM gives both short and long term benefits, it is relatively cheap to implement and is self maintaining once established.
SFM addresses flooding issues by considering all changes which have impacted the natural flood defences of the catchment, aiming to restore natural flood defences in a strategic and integrated way by addressing the whole catchment. Each part of the restoration is implemented in the most effective location with prescriptions of measures used to form an effective catchment flood prevention scheme. Some SFM techniques provide short term benefits, while others provide long term benefits. Flood management needs to address the current causes of flooding by the short term techniques and also the predictions of future flooding linked to climatic change by the long term techniques. The catchment can therefore be managed so that it reacts to the type of flooding now and in the future.
In 2004 MNV (then Mountain Environments) started a project aimed at developing techniques in SFM. This included the development of a network of demonstration sites in the River Devon and River Teviot catchments in Scotland. The sites include upland and lowland sites with the techniques ranging from forest management to river restoration. Each site was selected to be as representative as possible where the landowner was willing to take part in the project and the effectiveness could be monitored. The techniques which were developed included:
• Wetland restoration
• Native woodland restoration
• Plantation forest management
• Gully woodland development
• Management of large woody debris
• Riparian woodland development
• Control of river channel erosion
• Meander restoration
Implementation of each site was undertaken in 2005-6 and since then hydrometric instrumentation has been monitoring the rainfall and flood flows at each site. As the effectiveness of most techniques will only be seen in the long term, hydraulic models of each site have been developed which quantify the effectiveness of each technique and explain how each one works.
Sustainable flood management is a new and evolving process and it is expected that there will be further developments in future years. The demonstration sites have made an important first step into developing the techniques in SFM. The sites will be maintained as long term SFM sites and the hydrometric data will be used to quantify the effectiveness of each technique. In addition to the hydrology there will be a long term programme of habitat and wildlife surveys and assessments of the wider benefits such as to the local economy.
The long term operation of the demonstration sites and catchment will be essential in the continuing development of SFM. As the techniques evolve and the effectiveness is quantified there will be a much better understanding of SFM. This will lead to more widespread implementation of the techniques which will in turn result in improved long term protection against flooding.
MNV Team members Richard and Eleanor on the Glen Dey Demonstration site
Borthwick Water in flood conditions
Links between the physical characteristics of the Teviot Catchment and flooding
The Teviot river basin above Hawick is 324 km2 in area and includes three main river systems: River Teviot, Borthwick Water and Slitrig Water and two major tributary systems: Limie Cleuch and Allan Water. continue reading…
Carrying out repairs to the banks
of the River Teviot along Duke Street in Hawick – 1890
Flood causes in the Scottish Borders
Records of flooding in the Teviot catchment extend back into history and show that floods can be caused by summer thunderstorms, winter rain or snow melt and can be so severe that they result in extensive impacts to communities continue reading…
To assess the environmental factors controlling floods in Tajikistan, comparisons were made between the river flows in each river basin and the climate in different locations. The analysis identified those basins with the highest floods and produced indicative results of the main climatic controls. This enabled a further assessment to be made of the likely trends in flooding due to predicted climatic changes for Tajikistan.
Comparison of river basins
Tajikistan has eight major river basins. The Lake Karakul basin in the north east of the country is not considered within this analysis because of its remote location and dis-connection from the major river systems. The remaining seven basins are all mountain-lowland systems with the rivers generally flowing west and south west to join the major rivers flowing towards the Aral Sea. The basins can be divided into two groups according to the main sources of the rivers: firstly those fed by melt waters from glaciers and permanent snow fields at high altitudes with snow melt and rainfall at lower altitudes (Sirdaya, Zeravshan, Vakhsh and Pamir Mountains) and secondly those fed mainly by melting snow and rainfall (Sherkent, Kafirnigan and Kyzylsu).
The spatial distribution of mean annual precipitation in the country shows three distinct zones: the low precipitation northern zone, the high precipitation west and central zone and the dry eastern zone. Annual precipitation in the northern zone ranges from over 400 mm in the north and south mountain areas to less than 200 mm in the central lowlands. In the eastern zone precipitation is generally less than 400 mm per annum although extensive areas of the eastern Pamir Mountains have less than 100 mm.
Precipitation in the western and central zone shows a strong relationship with topography resulting from the rain bearing prevailing winds being from the south west. Annual totals increase steadily from around 200 mm in the extreme south to over 1600 mm in the mountains. The highest annual totals throughout the country are found along the Gissar Mountain range north of Dushanbe and, to the east of this, the Peter Primus Mountain range leading to the central Pamir glacial area including Mount Sumoni. Winter precipitation in most parts of the country falls as snow with precipitation becoming rainfall in the summer as the air temperature rises rapidly in response to continental heating.
The distribution of precipitation throughout the year contrasts between a winter maximum in the west and a summer maximum in the east. At Hushyory, in the Gissar Mountains (altitude 1351 m), precipitation increases from October reaching a maximum in March and decreases to August. Some 90% of the annual precipitation falls in the winter period with less than 10% in the summer season.
In general, precipitation at Hushyory, falls as snow from November to March with a maximum depth reached in February. In contrast, the distribution of precipitation at Murgab in the eastern Pamir (altitude 3576 m) shows a slight increase in March and April with the maximum in May followed by a decrease to November. At Murgab temperatures are low for most of the year resulting in the precipitation falling as snow from March to April and rain from May to September.
River flows are measured at 97 gauging stations throughout the country. Using selected stations from six river basins the data showed that the three west and south west rivers (Zeravshan, Kafirnigan and Vaksh) are very similar but contrast in high flows with the River Pyanj and Pamir Mountains, which have very low flood flows for the size of catchments, and the River Kyzylsu which has very high flood flows for its catchment area.
The mean maximum flows at the selected gauging stations were analysed using the specific mean annual maximum flow (mean maximum flow / catchment area). This statistic enables the maximum flows in different sized catchments to be compared. High values indicate catchments which have highly responsive flows i.e. their floods are large for the size of catchment while low values indicate catchments with flood flows which are low for the size of catchment. Specific mean annual maximum flows, derived for the period 1936-1997 show low values for the stations recording flows from the Pamir Mountains and also the western low altitude stations. Two stations on the upper Zeravshan and upper Kafinigan have high values while the station on the Kyzylsu has an extremely high value.
The interpretation of this is that although high flows are experienced in the Pamir rivers these flows are small in relationship to the catchment area due to the extensive area of east Pamir with very low rainfall. For the lower Zeravshan and lower Kafirnigan the low values are likely to be due to the low rainfall in the lower catchment area making little contribution to the flood flows and also significant water abstractions in these areas for irrigation purposes.
The high values in the upper Zeravshan and upper Kafirnigan are likely to be due to the high rainfall, rapid snow melt and steep river channels. In the Kyzylsu the very high value is also due to the high rainfall and rapid snow melt but this catchment also has a complex geological structure affecting the rate of runoff and groundwater contributions.
The structure is termed the Tajikistan depression and extends through the upper Vaksh valley before turning south west to include the whole of the Kyzylsu. Little surface runoff is observed on the hillslopes but strong spring flows exist lower down. Mudflows frequently occur in heavy rain indicating the presence of surface runoff in these conditions. In addition it is thought that there is a significant subsurface movement of water through the depression importing water from neighbouring catchments into the Kyzylsu.
Floods in the main river have been observed to be very high compared to other catchments and the river is highly responsive. It is thought that the flood generation process involves the build up of the groundwater stores in the permeable surrounding mountains with the sudden transition from percolation to surface runoff once the stores reach capacity. Runoff is rapid down the steep and saturated hillslopes with mudflows generated. The rivers therefore rise quickly but also fall quickly as the rain ceases and percolation starts again as the groundwater stores slowly drain through the springs.
Climatic controls
River Zeravshan
The River Zeravshan rises in the northern mountains and flows west along a deep valley some 250 km long. Mountain peaks along the northern and southern watersheds reach heights above 5000 m with the altitude of the valley bottom in the west being only 1000 m. Some small snow fields are found at high altitudes and a glacier exists in the eastern headwater catchment.
The narrowness and deepness of the valley creates numerous very steep tributary rivers, the sites of frequent debris flows. The valley is in a rain shadow to the north of the Gissar Mountains with annual totals increasing from some 100 mm in the sheltered valley bottom to over 1000 mm on the southern ridge. Over the mountains precipitation falls as snow from October to April and in the valley bottoms from November to February. The rise in river flows after the winter is delayed until April once the snows on the surrounding mountains start to melt.
The melt continues until July or early August when the river flows peak. Flows then decrease until October when the winter baseflows are reached. During the summer heavy rain storms can occur generating short lived peaks in the river flows.
The main climatic controls on flood flows in the lower Zeeravshan river basin are therefore the accumulation of winter snow, the temperature rise during the summer and the occurrence of rain storms during the peak in the snow melt. If a rainfall event occurs during mid July to late August a large flood is likely to occur in the lower catchment. Heavy rainfall and high river flows also cause frequent debris flows in the basin with the additional risk of rock debris blocking river channels and causing floods.
River Kafirnigan
The River Kafirnigan rises in the Gissar Mountain range and flows south before joining the River Pyanj in SW Tajikistan. The headwater catchments are very steep with altitudes exceeding 4700 m. In the floodplain near the confluence with the Pyanj, some 230 km to the south, the altitude is only 400 m. Precipitation in the headwater catchments is high, over 1600 mm, decreasing to less than 200 mm in the south.
Winter precipitation in the mountains is usually snow with accumulations generally forming in late December. Maximum depths of 60-100 cm are reached in early February with melt in February and March in the valley bottoms but extending into the summer on the surrounding mountains.
Rain storms are frequent events in the mountains with maximum 24 hour totals reaching 60-100 mm. River flows are very low in the winter but increase from early March as the snows melt in the mountains. Peak flows are reached in early May and then to October there is a long recession in the flows although small peaks can occur during this period in response to rainfall events. Flows through the floodplain are modified by water abstractions in the agricultural areas where extensive irrigation systems demand large amounts of water during the growing season.
The peak flows at Tartky therefore occurred in early May during both years and appear to have been due to a combination of snow melt raising the background flows with supplementary peaks caused by rainfall events in the mountains. The greatest risk of a large flood in the lower Kafirnigan is therefore likely to be during the peak in snow melt (late April to early May) if heavy rain (>20 mm in 24 hours) also occurs. If the rain was significantly greater, e.g. 60 mm in 24 hours, then this could cause a severe flood.
River Vaksh
The River Vaksh is one of the major rivers in Tajikistan draining the northern regions of the Pamir Mountains and flowing south west to join the River Pyanj. The main river and a number of its tributaries have glacial sources including the Fedchenko glacier, one of the longest glaciers in Asia. Winter snow accumulations can be widespread throughout the upper basin with extensive snowfields forming in the high mountains. In the middle sections of the basin the river flows through a deep gorge in which two reservoirs, including the 30 km long Nurek reservoir, have been constructed. Below this the valley opens out into an extensive floodplain some 30 km wide in which there are many water offtakes for irrigation systems.
Air temperatures in the catchment show a characteristic regional pattern rising rapidly in the period Mach and April as continental warming occurs with a less steep rise from early May to a maximum in mid to late July. Winter snow accumulations can be deep reaching values of 60-70 cm. From April to November temperatures are usually warm enough for precipitation to fall as rain. River flows in the Vaksh start to rise in late March as the temperatures in the mountains increase and snow melt starts. Flows peak in July or early August and then fall rapidly as the temperatures decrease in the early winter season.
Flood flows on the upper Vaksh therefore appear to be closely related to air temperature, the melting of snow throughout the catchment and glacial melt in the high mountains. In recent decades most of the Pamir glaciers have been observed to be retreating in response to either a general warming or reduction in precipitation in the mountains. This could affect the flood flows as the volume of ice available for melting is reduced. In the lower catchment the reservoirs are likely to affect the flood flows.
Attenuation of moderate floods is likely in most conditions particularly because of the size of the Nurek reservoir but attenuation of the largest floods is only likely if the reservoirs were significantly drawn down before the event. Flood flows in the lowlands are also attenuated by the extensive irrigation systems and the numerous water offtakes. The Nurek reservoir is also likely to trap large amounts of coarse sediment. This will reduce downstream sedimentation problems where the low channel gradient and gentle topography can combine with large amounts of sediment to cause frequent channel switching and extensive inundation of the whole floodplain.
River Kyzylsu
The Kyzylsu is one of the smaller river basins in Tajikistan draining the western foothills of the Pamir Mountains. The mountain peaks in the north and east of the catchment rise to over 4000 m with the altitude at the confluence with the Pyanj, some 130 km to the south, only 400 m.
Precipitation in the catchment shows a steep gradient closely linked to the topography. Annual totals increase from around 400 mm in the south west to over 1200 mm in the northern mountains. Unlike many of the other river basins in Tajikistan the upper Kyzylsu has no glaciers or permanent snow fields. Winter precipitation usually falls as snow over much of the catchment with significant snow accumulations developing.
Temperatures rise rapidly in the spring with the precipitation becoming rain and the snow accumulations starting to melt. The melt season is short relative to the other river basins with the last of the snow disappearing from the mountains in June or July. River flows rise from March to late April in response to the melting snow with occasional heavy rainstorms in the spring and early summer causing peaks in the flow.
River Pyanj
The River Pyanj is the major river of Tajikistan flowing along the county’s southern border with Afghanistan. In its upper reaches the right bank tributaries drain extensive areas of the eastern and southern Pamir Mountain region. In its lower reaches it is joined by three other major Tajikistan rivers: Kyzylsu, Vaksh and Kafernigan. Precipitation is low in the upper areas of the basin but significant falls of snow in the southern mountains and glacial melt generate high flows in the spring and summer seasons.
Glacial surges are frequent which can cause blockages to the rivers and the development of lakes behind the ice dams. Also debris flows can block river channels with lakes, such as Lake Sarez, formed upstream. Outbursts from these dams such as the Bear Glacier ice dam in 1963, can cause serious downstream flooding. River flows are torrential in the narrow gorges carrying large volumes of fine and coarse sediments. As it leaves the mountain area the river flows through a broad floodplain where there is extensive deposition of the sediment load with frequent channel avulsions, switching and flooding.
River Murgab
The River Murgab at Murgab is a high altitude (3582 m) station in the very dry eastern Pamir Mountains. The station has one of the longest records of data with the river monitoring starting in 1913 and the climate monitoring starting in 1894. Being at such a high altitude the winter conditions are severe with temperatures regularly falling below –200 C. In these conditions the rivers freeze and hence winter flows are very low.
The flood flows in the River Murgab therefore appear to be closely related to the generation of snow melt when the air temperature exceeds 100 C. Flooding is not a problem at Murgab however this analysis gives an additional information about the environmental controls on floods in the high mountain areas.
Summary of environmental factors controlling flooding
| River basin | Environmental Controls |
| Zeravshan | Snow melt peaks in mid July to early August – large floods occur if heavy rain storms in this periodHigh risk of debris flows blocking river channels |
| Kafirnigan | Steep channel gradient in headwater catchmentsSnow melt peak in late April to early May – large floods occur if heavy rain storms in this period |
| Vaksh | Melt waters from high altitude snow fields and glaciers peak in July and early AugustReservoirs and water offtakes for irrigation systems attenuate floods in the lowlands |
| Kyzylsu | Steep channel gradient in the headwater catchmentsSnow melt peak in late April to early May – large floods occur if heavy rain storms in this period |
| Pyanj | Melt waters from high altitude snow fields and glaciers peak in July and early AugustLow precipitation reduces the magnitude of the flood
Flood risk from outbursts from lakes caused by glacier or debris flow dams |
| Pamir Mountains | Snow melt peaks in late July and early August |
Tajikistan weather observation station
Flooding is not a new phenomenon in Tajikistan, there is evidence from a range of sources that major floods have occurred in historical times. Landforms in the mountains and foothills supply ample evidence of extreme paleo-floods. Debris flows have occurred in most of the high mountain catchments with huge fans of material spreading over the lower valley floors. Debris flow dams are also widespread throughout the mountain valleys with the river cutting deep gorges through the dams to reveal the coarse and chaotic nature of the material.
Upstream of many of these dams sediments have accumulated forming relatively flat fertile areas which have been farmed for generations. Also down the mountain valleys there are numerous bench type features formed by huge debris flows filling valley bottoms to enormous depths. These bench features are often the only remains of the events as the rivers have gradually re-established a channel and eventually a recognisable flood plain. This process takes centuries – indicating the long history of floods in Tajikistan.
Apart from the geomorphological evidence of historical floods there is also evidence from more recent times.
Flood chronologies provide information on events over the past 100 years although in this type of data set there is always the risk of missing or inaccurate information. Data from river gauging and climate stations also quantify recent events although the localised nature of flood events in Tajikistan means that many events occur in locations where there are no stations. A flood chronology and analysis of the data are reported in more detail in the following sections.
Chronology of flood events in Tajikistan
A chronology of flood events in Tajikistan has been compiled from information provided by the Department of Hydrometeorology. The list demonstrates that flood events and mudslides have been occurring throughout the country for over 100 years with the main causes being heavy rainfall, snow melt, glacial lake outbursts and breaches of debris flow dams.
In some instances the impacts have been catastrophic, with houses, schools, bridges and roads damaged, farm land destroyed and many people and animals killed. Most floods have occurred in small headwater rivers where the steep hillslopes and river channels have concentrated the flood waters and impacted the immediate downstream areas. The locations of the floods were mapped to produce a summary of those rivers which have the highest vulnerability of flooding. This showed that the most flood prone rivers are:
Records of major floods in Tajikistan
| Date | Details of the Flood Event |
|---|---|
| 1894 | Heavy rainfall – mudslide on the River Obicrut a right bank tributary of Zeravshan affecting Aini village |
| 1894 | Flood on the Kattsay river including a devastating mudslide caused by heavy rainfall |
| 1913 | Mudslide in the River Obichagon, Varzob |
| 28th July 1934 | Heavy rainfall in Khushikat rayon – high flow (230m3/sec) in the left bank tributary of the River Varzob including a mudflow. |
| July 1945 | Flood at Sauksay, the source of the River Maksy caused by the outbreak of glacial lake – bridge demolished |
| 2nd August 1946 | Heavy rainfall in the Duamalik rayon. Discharge of water in a left bank tributary of the Takob reached 400 m3/sec |
| April 1952 | Heavy rainfall at Semiganch – high flow in rightbank tributary of the River Kafirnigan (213 m3/sec) |
| 20-27 June 1952 | Flood on the River Gurham, a tributary of the Obihingou due to the breach of debris flow dams |
| April 29th 1954 | Flood on the River Kattasay with the discharge reaching 320 m3/sec – damage caused in Istaravshan |
| May 4-5 1955 | Flood and mudflow on the River Kattasay (near Istaravshan) caused by rainfall – discharge reached 615 m3/sec – damage caused in Istaravshan |
| 1957 | Mudslides in the River Obichagon, Varzob |
| April 1959 | Floods in the Kuramin range, Aktashsay |
| June 4th 1959 | Heavy rainfall in the Takob rayon – flood and mudflow in a left bank tributary of the Varzob reached 230 m3/sec. |
| 28th July 1961 | Flood at Daray-Rovand caused by a glacial lake outburst on a Pamir river in the Vanj regon. |
| 2nd August 1961 | Flood in the river Obichagon (413 m3 /sec) a left bank tributary of the River Varzob – Gushari village destroyed |
| 2nd August 1961 | Heavy rainfall resulted in a flood on the river Mopol, a left bank tributary of the Varzob – 400000 m3 of stones were deposed over the road and into the Varzob river |
| 1962 | Glacial lake outburst on the Gardjvindara a tributary of the river Ghunt |
| April 1963 | Flood on the River Pangazay in the Kuramin range |
| April 14th 1963 | Flood on the Urtasay Maliy river – tributary of the Zeravshan – maximum discharge166 m3/sec |
| July 27th 1964 | Flood on the river Khushikat – a left bank tributary of the Zeravshan near Aini village |
| 27th June 1964 | Flood caused by heavy rainfall on the river Orbikut a right bank tributary of the Zeravshan near Aini village |
| 28th July 1964 | Flood caused by heavy rainfall on the river Daray-Namak a tributary of the Vaksh – maximum discharge 515 m3/sec |
| 9th August 1965 | Flood caused by heavy rainfall on a tributary of the river Pyanj in the Jafar rayon 40 km above Kalaihumb – maximum discharge 315 m3/sec |
| May 6-7th 1966 | Rainfall generated flood on the Takob river a left bank tributary of the river Varzob – maximum discharge 180 m3/sec – one girl killed |
| August 23rd 1966 | Flood on the Zeravshan near Aini village in the Khushakat rayon; |
| 20th July 1967 | Flood in the Vanj rayon, 7 km above Paymasar village – caused by an outburst from the Ravak glacial lake |
| May 1968 | Flood at Say Yalmidich a left bank tributary of the Surhkob, 8 km above Gharm – cased by a break in a debris flow dam – volume of the debris flow was 100000 m3, the speed of water in the outburst was 15-20 m/sec and the height of the water was 7m – Yaldimich village was impacted |
| 1968-1969 | Heavy snow and rain resulted in debris flows throughout the country |
| May 1969 | Floods on the Pangazsay river and Aktashsay river both in the Kuramin range |
| March 16th 1987 | Flood in the Danghara valley caused by a break of the artificial water reservoir – discharge was more than 1000 m3/sec in the Sargazon river – the village of Bolo was destroyed with the loss of 53 houses (402 people made homeless), 30 people killed, many farms damaged (486 cows and 1800 poultry animals were killed, 100 ha of wheat destroyed), a bridge and a narrow-gauge railway were completely destroyed |
| Spring 1990 | Flood on a tributary of the Varzob caused by rain and snow melt – mudflow down the river Odjuk (maximum discharge of about 160 m3/sec) – all bridges were destroyed, and the road washed out |
| September 1991 | Glacial lake outburst flood (altitude 4680 m) in the headwater river of Khidojevdori in west Pamir – peak discharge was 200 m3/sec – Khidodjev village in the Roshtqala rayon suffered with 9 houses demolished and 8 damaged, the House of Culture was destroyed as well as the library, smithy, garage, warehouse, two transformers, secondary school, department of sovkhoz, all bridges were demolished, two tractors lost and cattle killed Rogun Hydro Power Plant was washed out; |
| May 8th 1993 | Heavy rainfall at Isfara caused flood with a school, factory, canal and fields all damaged – total cost of the damage was 240 M rubles |
| May 8th 1993 | Rainfall and snowmelt on the Takob river caused major flood with a peak discharge of 500 m3/sec – a road was washed out and all bridges destroyed |
| May 8th 1993 | Flood on the Varzob river caused by heavy rainfall and snowmelt – peak discharge was 1000 m3/sec – damage to all bridges above the dam, the Dushanbe-Khujand road was washed out, offtake channel supplying 3 Hydro Power Plants and water supply was damaged |
| May 8th 1993 | Mudflows in Hirmandjou rayon caused by heavy rainfall |
| April 1994 | Mudflows in Lahsh rayon caused by heavy rainfall |
| April 1996 | Mudflows in Shahriston rayon caused by heavy rainfall and snowmelt |
| April 1996 | Heavy rainfall in the Asht rayon caused a mudflow and damaged 60 houses |
| March 1997 | Mudflows in Varzob basin caused by heavy rainfall |
| July 1997 | Glacial lake outburst floods in Tojikobod rayon and West Pamir; |
| 1997-1998 | Precipitation during winter and spring was1.5 – 2 time the usual amount – in some places 3-4 times – mudflows in March, May, April, July |
| April 1998 | Heavy rainfall over the southern slope of the Gissar mountain range casued flood damage in Dushanbe, Karotegin, Darvoz, Khatlon, Dushanbe, Lahsh, Kalayhumb, Isambay, Dehavz, Iskanderqul, Gharm |
| May 1998 | Heavy rainfall caused flooding in Yahsu river (lower Karboztonak) |
| June 1998 | Heavy rainfall in Varzob and Tavildara (3 km above the settlement) – bridge destroyed, 500 m of roads damaged, 59 houses destroyed, 3500 fruit-trees demolished, 20 ha of agricultural land flooded, 140 cows and 520 sheep killed; |
| June 29th 1998 | Glacial lake outburst flood caused damage in Vomar-Dara rayon, the Rushon settlement suffered. During the same day a mudflow occurred in Iskanderqul |
| 1998 | Mudflows caused widespread damage – 144 people were killed, 7148 houses affected (1726 destroyed completely) as well as 255 schools and kindergartens, 88 hospitals and polio clinics, 1682 km of roads, 721 km of dams, 306 km of irrigation channel, 115 transformers, 96000 ha of agricultural land, 8730 cattle – the total cost of the damage was 60 million rubles |
| July 1999 | Flooding in the Kuramin range (Pangazsay river); |
| July 1999 | Heavy rainfall caused flooding in the Asht rayon – 19 people killed, 23 people injured, 728 houses damaged (316 destroyed), 2000 people left homeless, 20 bridges destroyed, 18 km of electricity transmission lines damaged, schools, hospitals, and farms were damaged |
| May 2000 | Flooding in a small right bank tributary of the Ghunt river near Varzob village – road washed out, rest home destroyed, 1 person killed |
Annual maximum flows
The annual maximum daily flows for 7 stations in Tajikistan were extracted from the hydrology Year Books. Water level data for the period 1993 to 2000 were missing at some stations because of the problems with instrumentation and damage caused by recent floods. In addition, river ratings were not carried out at most stations and so water discharge data for this period are sparse. Where possible, the discharge values for the annual maximum water level data were estimated by applying the most recent rating equation from that site.
The time series of annual maximum flows show that at most stations there were large ranges in values. There is an indication that maximum flows are increasing in the Kafirnigan, Vaksh and Kyzylsu rivers but a more clear and steady decrease at the two gauging stations on the River Zeravshan (Dupuli and Khudgif). Very high flows have been recorded at all stations throughout the period of records although none in the 1990s. This is most likely to be due to the recent damaging flows resulting in the temporary closure of the station.
An analysis was carried out of the annual maximum flow series including the 5 highest annual maximum flows at each station. Due to the loss of data this analysis excludes many of the major floods in the 1990s. The localised nature of flood events in Tajikistan is demonstrated by the highest flows at each station being recorded in different years. The second highest flows occurred in 1973 at three of the stations although, from the flood chronology, there is no record of flooding in that year.
Summary of annual maximum daily flows (m3 s-1 )
| Station/
River basin |
Period of record | Highest floods (year) | ||||
| 1 | 2 | 3 | 4 | 5 | ||
| Dupuli
Zeravshan |
1936
2000 |
875
(1942) |
832
(1953) |
801
(1952) |
800
(1950) |
794
(1968) |
| Khudgif
Zeravshan |
1962
2000 |
247
(1962) |
226
(1973) |
219
(1963) |
215
(1975) |
186
(1966) |
| Hushyory
Kafernigan |
1962
1988 |
288
(1987) |
216
(1973) |
207
(1969) |
178
(1968) |
169
(1970) |
| Tartky
Kafernigan |
1936
1992 |
1640
(1978) |
1590
(1969) |
1290
(1952) |
1160
(1979) |
1120
(1958) |
| Garm
Vaksh |
1941
1999 |
2410
(1958) |
1900
(1973) |
1830
(1956) |
1800
(1952) |
1680
(1953) |
| Karboztonak
Kyzylsu |
1947
2000 |
1590
(1972) |
1510
(1969) |
1220
(1976) |
1170
(1959) |
1100
(1966) |
| Murgab
Pamir |
1939
1992 |
107
(1959) |
105
(1966) |
101
(1957) |
99.6
(1984) |
97.7
(1976) |
24 hour maximum rainfall
The annual maximum 24-hour rainfall totals for 8 stations were extracted from the records within the Department of Hydrometeorology. Some gaps again exist in the data for the period 1993 to 2000. The time series of annual maximum 24 hour rainfall showed that at most stations there were large ranges in values. There is little indication of any trends in the data although cyclicity exists at some stations. Some very high values were recorded in the 1990s especially at Panjikent in the lower Zeravhan, and some of the south western stations.
The summary below shows the annual maximum rainfall series with the 5 highest annual maximum 24 hour rainfall totals at each station. The localised nature of rainfall events in Tajikistan is once again demonstrated by the five highest rainfall events at the 8 station being recorded in 32 different years. Three high totals occurred in 1983 and 1998, the latter year also having many instances of flooding according to the flood chronology. The table shows that large events occurred at Hushyori in the Kafirnigan river basin and at Khovaling in the Kyzylsu river basin. The dates of these events were 30th May 1951 at Hushyory, 6th March 1987 at Khovaling and 18th May 1998 also at Khovaling.
Summary of annual maximum 24 hour rainfall (mm )
| Station/
River basin |
Period of record | Highest rainfall (year) | ||||
| 1 | 2 | 3 | 4 | 5 | ||
| Panjakent
Zeravshan |
1930
2000 |
92.8
1999 |
76.2
1998 |
58.3
1960 |
46.8
1938 |
46.0
1980 |
| Hushyory
Kafirnigan |
1946
2000 |
114.4
1951 |
97.5
1978 |
94.2
1993 |
90.4
1999 |
89.0
1947 |
| Kurgan Tube
Vaksh |
1931
2000 |
43.6
1997 |
38.4
1963 |
38.5
1945 |
37.7
1933 |
33.6
1998 |
| Tavildara
Vaksh |
1933
1998 |
104.4
1983 |
73.2
1966 |
71.5
1988 |
69.9
1975 |
69.3
1961 |
| Chormaghzak
Vaksh |
1965
1999 |
94.6
1970 |
93.2
1984 |
90.3
1983 |
74.3
1971 |
71.8
1978 |
| Khovaling
Kyzylsu |
1933
2000 |
112.2
1998 |
106.7
1987 |
79.5
1976 |
79.2
1948 |
72.5
1974 |
| Khulab
Kyzylsu |
1931
1992 |
76.3
1983 |
62.7
1963 |
61.6
1937 |
60.9
1977 |
60.4
1991 |
| Ishkashim
Pamir |
1935
1999 |
31.8
1966 |
27.7
1940 |
27.5
1954 |
23.7
1979 |
21.9
1967 |
The chronology of flood events in Tajikistan identified snowmelt as one of the climatic factors affecting flood generation. The Department of Hydrometeorology have recently analysed their records of snow depth and temperature observations from the main climate stations. The conclusion was that over the period 1960-1990 the amounts of snow storage decreased at low altitudes but increased in the high mountains. During the same period temperatures in the mountain areas were found to increase. It is likely that the changes in snow depth are linked to the changes in temperature.
When winter temperatures in the mountains are very cold there is little moisture in the atmosphere but a global warming will increase the moisture content and hence the snowfall. Most climate change predictions for the region show a further increase in temperature of some 2-3 degrees celsius over the next 50 years. If this occurs then winter snowfall is also likely to increase but there is also a greater likelihood of more frequent snow melt events, with a greater risk of flooding in the downstream rivers.
The river gauging network in Tajikistan evolved over a period of 100 years although most developments occurred in the 1930s and from 1950 to 1979. Records in excess of 50 years exist for a significant number of the stations.
Number of stations installed in decades:
Date Number of stations
Before 1900 2
1900-1901 1
1910-1919 1
1920-1929 8
1930-1939 16
1940-1949 5
1950-1959 13
1960-1969 25
1970-1979 18
1980-1989 8
1990-1999 0
Total 97
Using the distribution of stations the density of stations in each river basin was calculated. A station density of 1 station / 1000 km2 is considered to be an appropriate mean value for the Tajikistan rivers. This value is lower than that in many European countries but is high for many mountainous Asian countries. The Syrdarya basin has a very low density (0.04 stations / 1000 km2). The Vaksh and Pyandj have moderately low densities (0.52 and 0.33 stations / 1000 km2 respectively) due to the catchments having large remote areas where it would be impractical to operate stations. The Zeravshan has the highest density of gauges (1.45 stations / 1000 km2) while the Sherkent, Kafinigan and Kyzylso have moderately high densities (1.00, 1.20 and 0.86 stations / 1000 km2 respectively).
Number of stations located within river basins:
Basin Number Area (km2) Stations / 1000km2
Syrdarya 6 140000 0.04
Zeravshan 16 11000 1.45
Sherkent 1 1000 1.00
Kafirnigan 12 10000 1.20
Vaksh 19 36000 0.52
Kyzylso 6 7000 0.86
Pyandj 37 113000 0.33
Many of the rivers within Tajikistan are steep with highly turbulent flows especially in the snow melt season. These are far from ideal conditions for carrying out river gauging but sites throughout the country were historically selected in the best available locations considering the flow measurements, protection of the instruments and gaining access to the sites. It is likely that most sites would still be considered the best available location unless the recent floods have caused significant deterioration to the river channel.
In most river channels there are considerable volumes of sediment which are highly mobile in the energetic flows. In some rivers the recent floods have caused excessive movements of the coarse sediments and also erosion of channel banks. The coarse sediments create problems at the gauging stations by frequently changing the river cross sections and the downstream controls. Fine sediments create problems with the silting up of tapping pipes, stilling wells and occasional deposition around the stage boards.
The installations at most of the gauging stations have fallen into a poor state of repair. Huts have been damaged and are no longer secure, cable ways and winches are rusted and difficult to use and the cradles on the cables are rotting and dangerous. The inventory of gauging stations identified a number of stations which were no longer operational, mainly due to recent flood damage. The list below shows the percentage of gauges in the river basins which are completely or partially working. The Vaksh (53%) and the Kyzylso (33%) have clearly suffered the most damage in the recent floods.
Number of stations completely or partly working in 2001 within river basins:
River basin Working Percentage
Syrdarya 6 100%
Zeravshan 16 100%
Sherkent 1 100%
Kafirnigan 10 83%
Vaksh 10 53%
Kyzylso 2 33%
Pyandj 34 92%
Total 79 81%
