Inner Terai Valleys of Nepal
The Inner Terai Valleys of Nepal comprise several elongated river valleys in the southern lowland Terai part of the country. These tropical valleys are enclosed by the Himalayan foothills, viz the Mahabharat Range and the Sivalik Hills farther south. These valleys are part of the Terai-Duar savanna and grasslands ecoregion. They are filled up with coarse to fine alluvial sediments. The Chitwan Valley and the Dang and Deukhuri Valleys are some of the largest Inner Terai Valleys. Malaria was prevalent in this region until the late 1950s. Since its eradication, the area became a  viable destination for large-scale migration of people from the hills who transformed the area from virgin forest and grassland to farmland. Geology. The Inner Terai valleys lie between the Sivalik Hills and Mahabharat Range. They hold flat plains with winding rivers that shift their courses from time to time, running northwest or southeast along the axis of the Sivalik Hills. Climate. The Terai has a humid, subtropical climate. The mean annual rainfall at the Rampur weatherstation in Chitwan was between 1995 and 2006. More than 80% of the total annual rainfall occurs during the monsoon season from June to  September. Average temperatures ranged from in January to in June. In the past, the inner and outer Terai were a formidable barrier between Nepal and potential invaders from India because marshes and forests were infested by anopheline mosquitos that transmitted virulent strains of malaria, especially during the hot spring and rainy summer monsoon. History. Until the mid 18th century, the Terai was divided into several smaller kingdoms, and the forests were little disturbed. After the unification of Nepal in the late 1760s, the rulers granted large areas of fertiIe land and forest resources to members of the royal family, officials , priests and selected groups of the society. The beneficiaries of these grants had the right to collect revenues from cultivated land and forest products. They appointed tax collectors who were also responsible for reclamation of land and establishment of settlements. In the late 1920s, the Rana rulers ordered the clearing of forests and extraction of timber for export to India in order to collect revenues. Cleared areas were subsequently used for agriculture. Tharu people have been living in the Terai for many centuries, and reputedly had an innate resistance to malaria. After malaria was eradicated using DDT in the mid-1950s , people from the hills migrated to the Terai. Timber export continued to 1969. In 1970, the king granted land to loyal ex-army personnel in the districts of Jhapa, Sunsari, Rupandehi and Banke, where seven colonies were developed for resettling about 7,000 people. They acquired property rights over uncultivated forest and waste land, thus accelerating the deforestation process in the Terai. 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 This has led to concerns about the risk of losing many rare plant, animal and insect species. The valleys also mitigate the severity of floods on the Gangetic plains. During heavy rainfall forests absorb water. During floods, rivers overflow their banks and flood adjacent forests. Later the forests gradually release water back into the rivers. Deforestation reduces this buffering effect. It also accelerates soil erosion, causing downstream rivers to silt up and overflow their banks. The frequency and severity of flooding in the Gangetic plain and  Bangladesh has steadily increased in recent years. Deforestation of the Terai appears to be one of the major causes. The Indian and Nepalese governments are cooperating in measures including construction of barrages and dams in the Terai, such as the Koshi Barrage. 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. Valleys. The major Inner Terai Valleys are listed from west to east. Click on the  terrain and satellite imagery links to see vegetation, rivers, topography, roads and towns. Western Terai. Markers at valleys "Jogbudha" (J), "Surkhet" (S), "Dang" (A) and "Deukhuri" (E) terrain satellite Surkhet Valley. The Surkhet Valley is situated in the Surkhet district, mid-western Nepal. The valley is about above sea level, forming an ellipse about east-west by north-south. It is drained by the Bheri River, a tributary of the Karnali. The district is the homeland of the Raji people. Tharu people from Dang settled in the valley since at least the 19th century. Imagery of "Surkhet" (S): terrain satellite  Dang and Deukhuri Valleys. Both valleys are located in the Dang Deukhuri District of the Rapti Zone in mid-western Nepal. The Dang Valley lies between the Mahabharat Range in the north and the Churia Range in the south. It forms a nearly plain within a local drainage basin of less than . It is drained by the Babai River, and is one of the largest Inner Terai valleys. The Deukhuri Valley is southeast of the Dang Valley and extends about in WNW-ESE direction with a maximum width of . It forms a nearly plain within a drainage basin of . The  valley is drained by the West Rapti River. The Mahendra Highway passes through the Deukhuri Valley. Both valleys are settled by Tharu people. Imagery of Dang (A) and Deukhuri (E): terrain satellite Central Terai. Chitwan Valley. The Chitwan Valley () encompasses the districts of Nawalpur, Chitwan and Makwanpur in the Narayani Zone of central Nepal. It is long and roughly wide. The cities of Bharatpur, Ratnanagar and Hetauda are in the valley. It is drained by the Rapti River flowing from the Mahabharat Range near Hetauda, then west down the valley to join the Narayani River west of Meghauli. The Narayani  is also called Gandaki further upstream and Gandak in India. Imagery of "Chitwan" (C): terrain satellite The Chitwan National Park, Nepal's first national park established in 1973, was declared a World Heritage site by UNESCO in 1984. It contains the largest and least disturbed natural Sal hill forest and associated communities. Its fauna comprises Bengal tiger, Indian leopard, great one-horned rhinos, wild Asian elephant, gaur, golden monitor lizard, gharial and marsh crocodile. Eastern Terai. Kamala Valley. The Kamala Valley, also called Udayapur Valley is in Udayapur district in southeastern Nepal. It is about long and between and wide . It is drained by the Triyuga river flowing east to join the great Koshi River. This valley lies between the Mahabharat Range to the north and the Sivalik Hills to the south, with an average elevation of about . The mouth of the valley opens onto a rectangle of land where the Triyuga meets the Koshi river above the Koshi Barrage. It was designated the Koshi Tappu Wildlife Reserve 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 a Ramsar Site. Imagery of Kamala valley: terrain satellite Traditionally, the Kamala Valley was primarily inhabited by the Dhanwar people (or Danuwar), but there is a fast-growing population of migrants from the Nepali hills and from India.