The phrase Inner Terai Valleys or Bhitri tarai (भित्री तराइ) refers to various elongated valleys in Nepa lying between the Himalayan foothills, the 600-900 metre high Chure or Siwalak Range, and the 2,000-3,000 metre high Mahabharat Range further north. Major examples are the Chitwan Valley southwest of Kathman and the parallel Dang and Deukhuri Valleys in western Nepal. (Outer Terai refers to the plains extending south of the Chure / Siwalik Hills to the border with India.)
The valleys are low-lying, hot and humid, with swamps, grasslands and forests holding a rich variety of plant and animal life. A malaria eradication campaign in the 1950s and 1960s opened the Terai to settlement by migrants from the Tibetan highlands and the Indian plains. The new settlers have changed the local environment in ways that may threaten biodiversity and contribute to increasingly severe flooding downstream in India and Bangladesh. However, the valleys continue to be areas of great natural beauty, with rich ecosystems.
The valleys are low-lying, hot and humid, with swamps, grasslands and forests holding a rich variety of plant and animal life. A malaria eradication campaign in the 1950s and 1960s opened the Terai to settlement by migrants from the Tibetan highlands and the Indian plains. The new settlers have changed the local environment in ways that may threaten biodiversity and contribute to increasingly severe flooding downstream in India and Bangladesh. However, the valleys continue to be areas of great natural beauty, with rich ecosystems.
Geology
Geologic - Tectonic map of the Himalaya, modified after Le Fort (1988).
Ma
in article: Geology of the Himalaya
The Himalayas were formed by the collision of the Indian sub-continent with Eurasia, which began about 50 million years ago and continues today. The oceanic crust in front of India slid under Eurasia, pushing up the Tibetan plateau. The Indian continental crust is also pushing under Tibet, but is partly compressed and thrust upward to form the Himalayan mountain range, extending for over 2400 km and rising as high as 8848 m at Mt. Everest Chomolangma.
The Himalayas have four tectonic subdivisions:
The Indus Suture Zone, where the Indian Plate meets the Eurasian Transhimalaya or Karakoram-Lhasa Block.
The Central Himalayan Domain, the high backbone of the Himalayas.
The Lesser Himalaya or Mahabharat Lekh, a parallel but lower range mainly made up of more recent up-thrust surface rocks of the Indian subcontinent.
The Subhimalaya, also known as the Muree and Siwaliks Formations, the foothills of the Himalayan Range, mainly composed of folded and overlapping sheets of sediment from the erosion of the Himalaya.
The Inner Terai valleys lie between the Subhimalaya and Lesser Himalaya. They hold flat plains with winding rivers that shift course from time to time, running northwest or southeast along the folds until they find a break in the Sawaliks and flow into the Outer Terai and Gangetic plain. Usually there is little difference in elevation between the Inner Terai valley floors and the plains of the Outer Terai.
Climate & Economy
Nepal topography. The green/yellow zones hold the Inner Terai valleys.
Main article: Madhesh
The Terai has a humid, subtropical climate, warm in the winter and hot (often over 40°C) in the summer. The monsoon period of torrential rains lasts from mid-June to mid-September. Most areas in the Terai get over 1,500 mm of rain in a year. In the past, the inner and outer Terai were regions of malaria-infested marshes and forests, rich in animal and insect life. The Terai formed a formidable barrier between Nepal and potential invaders from India. The indigenous Tharu, Danuwar and others had a degree of inherited resistance to malaria and populated these areas.
A successful malaria eradication campaign in the 1950s and 1960s opened the area for settlement. People migrated to the Terai from the mountains and from neighbouring India. Today more than half the population are migrants, and many towns have developed. The Inner and Outer Tarai's have become Nepal's richest economic regions, with fertile farms and forests. The Tarai is Nepal's main source of food, and a migration destination for landless hill peasants. Tarai residents have more agricultural land than other Nepalese because of the area's generally flat terrain, which is drained and nourished by several rivers. As well, the Terai has the largest commercially exploitable forests.
Environmental Issues
The well-meaning malaria eradication campaign has had unexpected consequences by opening up the Terai region to human settlement. The Inner Terai valleys are home to a rich and diverse ecosystem. Since the early 1990s, however, the forests have been increasingly destroyed because of growing demands for timber and agricultural land[1][2] This has led to concerns about the risk of losing many rare plant[3][4], animal and insect species.
The valleys also play an important role in mitigating the severity of floods in the Gangetic plains. In times of heavy rainfall, the forests absorb the water. In times of heavy run-off from the Himalayan watershed, the rivers spread out from their banks, flooding the forest. Later, the forests gradually release the water into the rivers that feed the Ganges. Forest removal reduces or eliminates this buffering effect. It also accelerates soil erosion, causing downstream rivers to silt up and overflow their banks.[5]
In recent years, the frequency and severity of flooding in the Gangetic plain and Bangladesh has steadily increased. Deforestation of the Terai appears to be one of the major causes[6]. The Indian and Nepalese governments are cooperating in measures including construction of barrages and dams in the Terai, such as the Koshi Barrage[7]. However, these efforts may have mixed results. They contain floodwater in the short term, but may increase the problem in the longer term by reducing water velocity in the rivers downstream, and thus accelerating silting and reducing the drainage capacity of the rivers.[8]
Geologic - Tectonic map of the Himalaya, modified after Le Fort (1988).
Ma
in article: Geology of the HimalayaThe Himalayas were formed by the collision of the Indian sub-continent with Eurasia, which began about 50 million years ago and continues today. The oceanic crust in front of India slid under Eurasia, pushing up the Tibetan plateau. The Indian continental crust is also pushing under Tibet, but is partly compressed and thrust upward to form the Himalayan mountain range, extending for over 2400 km and rising as high as 8848 m at Mt. Everest Chomolangma.
The Himalayas have four tectonic subdivisions:
The Indus Suture Zone, where the Indian Plate meets the Eurasian Transhimalaya or Karakoram-Lhasa Block.
The Central Himalayan Domain, the high backbone of the Himalayas.
The Lesser Himalaya or Mahabharat Lekh, a parallel but lower range mainly made up of more recent up-thrust surface rocks of the Indian subcontinent.
The Subhimalaya, also known as the Muree and Siwaliks Formations, the foothills of the Himalayan Range, mainly composed of folded and overlapping sheets of sediment from the erosion of the Himalaya.
The Inner Terai valleys lie between the Subhimalaya and Lesser Himalaya. They hold flat plains with winding rivers that shift course from time to time, running northwest or southeast along the folds until they find a break in the Sawaliks and flow into the Outer Terai and Gangetic plain. Usually there is little difference in elevation between the Inner Terai valley floors and the plains of the Outer Terai.
Climate & Economy
Nepal topography. The green/yellow zones hold the Inner Terai valleys.
Main article: Madhesh
The Terai has a humid, subtropical climate, warm in the winter and hot (often over 40°C) in the summer. The monsoon period of torrential rains lasts from mid-June to mid-September. Most areas in the Terai get over 1,500 mm of rain in a year. In the past, the inner and outer Terai were regions of malaria-infested marshes and forests, rich in animal and insect life. The Terai formed a formidable barrier between Nepal and potential invaders from India. The indigenous Tharu, Danuwar and others had a degree of inherited resistance to malaria and populated these areas.
A successful malaria eradication campaign in the 1950s and 1960s opened the area for settlement. People migrated to the Terai from the mountains and from neighbouring India. Today more than half the population are migrants, and many towns have developed. The Inner and Outer Tarai's have become Nepal's richest economic regions, with fertile farms and forests. The Tarai is Nepal's main source of food, and a migration destination for landless hill peasants. Tarai residents have more agricultural land than other Nepalese because of the area's generally flat terrain, which is drained and nourished by several rivers. As well, the Terai has the largest commercially exploitable forests.
Environmental Issues
The well-meaning malaria eradication campaign has had unexpected consequences by opening up the Terai region to human settlement. The Inner Terai valleys are home to a rich and diverse ecosystem. Since the early 1990s, however, the forests have been increasingly destroyed because of growing demands for timber and agricultural land[1][2] This has led to concerns about the risk of losing many rare plant[3][4], animal and insect species.
The valleys also play an important role in mitigating the severity of floods in the Gangetic plains. In times of heavy rainfall, the forests absorb the water. In times of heavy run-off from the Himalayan watershed, the rivers spread out from their banks, flooding the forest. Later, the forests gradually release the water into the rivers that feed the Ganges. Forest removal reduces or eliminates this buffering effect. It also accelerates soil erosion, causing downstream rivers to silt up and overflow their banks.[5]
In recent years, the frequency and severity of flooding in the Gangetic plain and Bangladesh has steadily increased. Deforestation of the Terai appears to be one of the major causes[6]. The Indian and Nepalese governments are cooperating in measures including construction of barrages and dams in the Terai, such as the Koshi Barrage[7]. However, these efforts may have mixed results. They contain floodwater in the short term, but may increase the problem in the longer term by reducing water velocity in the rivers downstream, and thus accelerating silting and reducing the drainage capacity of the rivers.[8]
Valleys
This section describes the major Inner Terai valleys. A picture is worth a thousand words. Click on the coordinates below each valley's heading, and select a satellite or terrain view to see vegetation, rivers and landforms.
Kamala Valley
Sagarmatha zone: Udayapur district in green
26°47′N 86°41′E / 26.783, 86.683 (Kamala Valley)
The Kamala Valley is in the Udayapur district in the southeast of Nepal (Sketch map). About 30 km long and between 2 km and 4 km wide, it is drained by the Triyuga river, which runs east to feed the great Koshi River. The valley lies between the Mahabharat Lekh (Range) to the north and the Churia or Sivalik Hills to the south, with an average elevation of about 430 meters[9].
The mouth of the valley opens onto a 175 sq. km. rectangle of land where the Triyuga meets the Koshi river above the Koshi Barrage. It was designated the Koshi Tappu Wildlife Reserve[10] in 1976, and is home to the last remaining population of Wild Asian Water Buffalo in Nepal. The reserve is mostly wetlands, subject to seasonal flooding, but also includes some grasslands and small patches of riverine forest. It is the only Ramsar Site (a wetland of international significance) in Nepal.
Traditionally, the Kamala valley was primarily inhabited by the Dhanwar or Danuwar people[11], but there is a fast-growing population of migrants from the Nepali hills and from India. The main center is Gaighat (or Triyuga).
This section describes the major Inner Terai valleys. A picture is worth a thousand words. Click on the coordinates below each valley's heading, and select a satellite or terrain view to see vegetation, rivers and landforms.
Kamala Valley
Sagarmatha zone: Udayapur district in green
26°47′N 86°41′E / 26.783, 86.683 (Kamala Valley)
The Kamala Valley is in the Udayapur district in the southeast of Nepal (Sketch map). About 30 km long and between 2 km and 4 km wide, it is drained by the Triyuga river, which runs east to feed the great Koshi River. The valley lies between the Mahabharat Lekh (Range) to the north and the Churia or Sivalik Hills to the south, with an average elevation of about 430 meters[9].
The mouth of the valley opens onto a 175 sq. km. rectangle of land where the Triyuga meets the Koshi river above the Koshi Barrage. It was designated the Koshi Tappu Wildlife Reserve[10] in 1976, and is home to the last remaining population of Wild Asian Water Buffalo in Nepal. The reserve is mostly wetlands, subject to seasonal flooding, but also includes some grasslands and small patches of riverine forest. It is the only Ramsar Site (a wetland of international significance) in Nepal.
Traditionally, the Kamala valley was primarily inhabited by the Dhanwar or Danuwar people[11], but there is a fast-growing population of migrants from the Nepali hills and from India. The main center is Gaighat (or Triyuga).
Marin Khola Valley
Janakpur zone: Sindhuli district is green band in center
27°13′11″N 85°55′12″E / 27.21972, 85.92 (Marin Khola Valley)
The Marin Khola Valley is one of the smaller Inner Terai Valleys, in the central south region, Sindhulī Garhi district\. (Sketch Map\) The Kokhajor Khola, the Marin Khola and the Kyan Khola rivers join in the valley to form the Kamala river, a major tributary to the Bhurengi[12]..
The main town is Kamalamai\.
The Indian government is concerned about flooding from the Kamala river, and is funding engineering projects in an attempt to control the situation.
The Marin Khola valley is one of the areas of Nepal inhabited by Hayu people, who also live in the valleys of the Rosi Khola and the Sun Kosi north of the Mahabharat range.[13]
Chitwan Valley
Natayani zone: the Chitwan district is yellow area to the west
Main article: Chitwan Valley
27°41′N 84°26′E / 27.683, 84.433 (Chitwan Valley)
The Chitwan Valley is in central Nepal in the Narayani Zone. It is 150 km long and roughly 30-48 km wide, the largest of the inner Terai valleys. (Sketch Map) The cities of Bharatpur, Hetauda, and Ratnanagar are in the valley.
The Narayni and East Rapti rivers join in the valley. The Naryani is the main river and life line of the Chitwan Valley, flowing from the Himalayan Glaciers with tributaries Kaligandaki, Trishuli, Seti, Madi, Marshangdi, Budhi Gandaki and Draudi. The Naryani is also known as the Gandaki River in India. The Rapti river flows from the Mahabharat Lekh (range) and enters the Chitwan valley from Hetuda, joining the Naryani west of the Meghauli.
The Chitwan National Park[14] is one of the most important sub-tropical parks on the Indian subcontinent with good populations of the endangered Bengal tiger, great one-horned rhinos, gangetic dolphin, wild Asian elephant, gaur, golden monitor lizard and gharial crocodile. In 1963 the southern two-thirds of the park were declared a Rhino Sanctuary, with a moratorium on hunting and the relocation of 22,000 people from the Chitwan valley. Since then, wildlife populations and ecosystems have been rebounding in this area. In 1973 Chitwan became Nepal’s first National Park. The unique ecosystems prompted UNESCO to declare the park a World Heritage site in 1984.
Surkhet Valley
Bheri Zone districts. Surkhet is the purple band in the center
28°36′N 81°38′E / 28.6, 81.633 (Surkhet Valley)
The Surkhet Valley[15] is in the mid-west of Nepal, in the Surkhet district (Sketch map), with an average elevation of 700 meters above sea level. The valley is elliptically shaped, about 9 km east-west and 6 km north-south. It is drained by the Bheri River[16].
Birendranagar is the main population center in the valley. Historically, Birendranagar and the surrounding area of Surkhet were the lands of the Tharu and local Rajhi people. However the region has seen increased migration from the surrounding mountain regions as well as other parts of the country.
Deukhuri and Dang Valleys
Rapti zone: Dang Deokhuri district in south west
28°7′N 82°17′E / 28.117, 82.283 (Deukhuri and Dang Valleys)
The parallel Deukhuri and Dang Valleys are in the Rapti zone of mid-western Nepal, in the Dang Deokhuri district (Sketch map).
The larger Deukhuri Valley is drained by the West Rapti river, running to the north east[17]. Tulsipur is the main center in the Deukhuri valley.
To the south of Deukhari valley, separated by a range of hills, is the narrow Dang Valley. The Dang valley is drained by the Babai river[18], which also runs towards the north east. The city of Tribhuvannagar is in the center of the Dang valley. The Babai river breaks through the Chure Hills into the Royal Bardia National Park (Map). This park is the largest and most undisturbed wilderness area in the Terai. About 70% of the park is covered with forest with the balance a mixture of grassland, savannah and riverine forest.
Jogbudha Valley
Mahakali zone: Dadeldhura district is the yellow area towards the south
29°10′N 80°20′E / 29.167, 80.333 (Jogbudha Valley)
The Jogbudha Valley is in the far west of Nepal, in the Dadeldhura district of the Mahakali zone (Sketch map). The rivers of this relatively small and largely undeveloped valley empty into the Mahakali or Sarda River, which flows from the Greater Himalayas and defines part of the western border of Nepal with Uttarakhand, India.
To the south of this valley, in the Outer Terai, is the Suklaphanta Wildlife Reserve[19], home of the largest herd of swamp deer in the world, and listed by UNESCO as a World Heritage Site in 1984.
Janakpur zone: Sindhuli district is green band in center
27°13′11″N 85°55′12″E / 27.21972, 85.92 (Marin Khola Valley)
The Marin Khola Valley is one of the smaller Inner Terai Valleys, in the central south region, Sindhulī Garhi district\. (Sketch Map\) The Kokhajor Khola, the Marin Khola and the Kyan Khola rivers join in the valley to form the Kamala river, a major tributary to the Bhurengi[12]..
The main town is Kamalamai\.
The Indian government is concerned about flooding from the Kamala river, and is funding engineering projects in an attempt to control the situation.
The Marin Khola valley is one of the areas of Nepal inhabited by Hayu people, who also live in the valleys of the Rosi Khola and the Sun Kosi north of the Mahabharat range.[13]
Chitwan Valley
Natayani zone: the Chitwan district is yellow area to the west
Main article: Chitwan Valley
27°41′N 84°26′E / 27.683, 84.433 (Chitwan Valley)
The Chitwan Valley is in central Nepal in the Narayani Zone. It is 150 km long and roughly 30-48 km wide, the largest of the inner Terai valleys. (Sketch Map) The cities of Bharatpur, Hetauda, and Ratnanagar are in the valley.
The Narayni and East Rapti rivers join in the valley. The Naryani is the main river and life line of the Chitwan Valley, flowing from the Himalayan Glaciers with tributaries Kaligandaki, Trishuli, Seti, Madi, Marshangdi, Budhi Gandaki and Draudi. The Naryani is also known as the Gandaki River in India. The Rapti river flows from the Mahabharat Lekh (range) and enters the Chitwan valley from Hetuda, joining the Naryani west of the Meghauli.
The Chitwan National Park[14] is one of the most important sub-tropical parks on the Indian subcontinent with good populations of the endangered Bengal tiger, great one-horned rhinos, gangetic dolphin, wild Asian elephant, gaur, golden monitor lizard and gharial crocodile. In 1963 the southern two-thirds of the park were declared a Rhino Sanctuary, with a moratorium on hunting and the relocation of 22,000 people from the Chitwan valley. Since then, wildlife populations and ecosystems have been rebounding in this area. In 1973 Chitwan became Nepal’s first National Park. The unique ecosystems prompted UNESCO to declare the park a World Heritage site in 1984.
Surkhet Valley
Bheri Zone districts. Surkhet is the purple band in the center
28°36′N 81°38′E / 28.6, 81.633 (Surkhet Valley)
The Surkhet Valley[15] is in the mid-west of Nepal, in the Surkhet district (Sketch map), with an average elevation of 700 meters above sea level. The valley is elliptically shaped, about 9 km east-west and 6 km north-south. It is drained by the Bheri River[16].
Birendranagar is the main population center in the valley. Historically, Birendranagar and the surrounding area of Surkhet were the lands of the Tharu and local Rajhi people. However the region has seen increased migration from the surrounding mountain regions as well as other parts of the country.
Deukhuri and Dang Valleys
Rapti zone: Dang Deokhuri district in south west
28°7′N 82°17′E / 28.117, 82.283 (Deukhuri and Dang Valleys)
The parallel Deukhuri and Dang Valleys are in the Rapti zone of mid-western Nepal, in the Dang Deokhuri district (Sketch map).
The larger Deukhuri Valley is drained by the West Rapti river, running to the north east[17]. Tulsipur is the main center in the Deukhuri valley.
To the south of Deukhari valley, separated by a range of hills, is the narrow Dang Valley. The Dang valley is drained by the Babai river[18], which also runs towards the north east. The city of Tribhuvannagar is in the center of the Dang valley. The Babai river breaks through the Chure Hills into the Royal Bardia National Park (Map). This park is the largest and most undisturbed wilderness area in the Terai. About 70% of the park is covered with forest with the balance a mixture of grassland, savannah and riverine forest.
Jogbudha Valley
Mahakali zone: Dadeldhura district is the yellow area towards the south
29°10′N 80°20′E / 29.167, 80.333 (Jogbudha Valley)
The Jogbudha Valley is in the far west of Nepal, in the Dadeldhura district of the Mahakali zone (Sketch map). The rivers of this relatively small and largely undeveloped valley empty into the Mahakali or Sarda River, which flows from the Greater Himalayas and defines part of the western border of Nepal with Uttarakhand, India.
To the south of this valley, in the Outer Terai, is the Suklaphanta Wildlife Reserve[19], home of the largest herd of swamp deer in the world, and listed by UNESCO as a World Heritage Site in 1984.
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