Managing Nepal's Dudh Koshi River System for a Fair and Sustainable Future

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• Publisher: Asian Development Bank
• Year: 2019
• Print ISBN:
  9789292615505
• eBook ISBN:
  9789292615512
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

This report examines the opportunities for developing equitable and efficient means to manage water resources in the Dudh Koshi river system in Nepal. The report suggests economically and environmentally sustainable management considering challenges that involve climate change. The study proposes a strategic planning framework that covers the holistic, technical, economic, social, and environmental aspects of integrated water resources management and development of the river system. It also contributes to strategic planning from a basin-wide perspective by supporting the design of the Dudh Koshi Storage Hydroelectric Project.

CHAPTER 1
Introduction

1.1 Background

This publication reports on a study of the Dudh Koshi River System (DKRS) that aimed to develop integrated approaches to planning and developing hydropower and river diversion projects.¹ The field work was implemented over 12 months and completed in October 2016. It formed part of the knowledge and institutional support for the Water Financing Program of the Asian Development Bank (ADB) and the knowledge partnership between ADB and the UNESCO-IHE Institute for Water Education (now the IHE Delft Institute for Water Education).

The Koshi River Basin (KRB) in Nepal holds substantial water resources that have yet to be developed, despite a number of master plans and feasibility studies that were initiated in the 1980s. Development follows a project-based approach, which does not factor in other planned or proposed developments. It is now increasingly evident that more holistic strategies are needed—those that seek to incorporate river basin planning and integrate potential social, environmental, and climate change issues across multiple projects (e.g., hydro, irrigation, flood control) over the entire basin and sub-basins. Development of high-altitude hydro schemes needs to be planned carefully to address the vulnerabilities and high sensitivities of the catchments and communities.

Development actors’ knowledge gaps on water resources, including the impacts of climate change; conjunctive use of integrated water systems; and catchment management to ensure sustainability of soil and water and reduced risk from extreme climate events.

The DKRS study aims to identify key issues and requirements to achieve economically and environmentally sustainable development, and help address the impacts of climate change. The study focuses on the Dudh Koshi sub-basin, one of the main tributaries of the Koshi River System (Figure 1).

Figure 1: Dudh Koshi Sub-Basin

Note: Report findings were based on geographic information system layers from International Centre for Integrated Mountain Development.

Source: ADB. 2016. Nepal: Operational Research for the Dudh Koshi River System, Final Report. Unpublished.

As there are significant linkages and impacts of developments on the river system upstream and downstream, the study has also incorporated a hydrological analysis of the wider Koshi River System, including the upstream catchment in the People’s Republic of China (PRC), and an assessment of hydropower and irrigation development scenarios in the Sun and Dudh Koshi river systems.

The output of the DKRS study is presented as a strategic planning framework for the Koshi Basin and also to support the planning of the Dudh Koshi Storage Hydroelectric Project, thus contributing to strategic planning from a basin-wide perspective.

The study involves

(i)	a water resources assessment based on a rainfall runoff model (soil water assessment tool [SWAT]) including climate change simulations and an analysis of water resources development scenarios through a systems planning model (water evaluation and planning [WEAP]) to explore development options and their impacts and sensitivities;
(ii)	an analysis of a large-scale hydropower development focusing on seven large schemes in the Dudh Koshi, Sun Koshi, and downstream Sapta Koshi;
(iii)	an analysis of irrigation development in the eastern Terai and the potential for irrigation diversion projects from the Koshi River;
(iv)	a review of environmental and social impacts of large-scale hydropower development;
(v)	a review of integrated development planning for the DKRS, incorporating extensive stakeholder interviews and consultations to assess community perceptions on the expansion of hydropower and overall development needs; and
(vi)	an assessment of the legal and institutional framework including a review of institutional capacities and possible approaches for long-term sustainable and effective integrated water resources management.

1.2 Profile of the Koshi Basin

Water Resources

The Koshi River is the largest tributary of the Ganges. It is a transboundary river crossing the PRC, Nepal, and India. With a basin area of 87,311 square kilometers (km²) upstream of its confluence with the Ganges, it is the largest river in Nepal. Figure 2 presents a map of the larger KRB. Dixit et al. (2009) have identified six distinct geological and climatic zones in the basin: the Tibet Autonomous Region plateau, the high Himalaya, the midland hills, the Mahabharat Lekh (range), the Chure (Siwalak range), and the Terai.

Figure 2: The Koshi River Basin

Note: Based on International Centre for Integrated Mountain Development geographic information system layers.

Source: ADB. 2016. Nepal: Operational Research for the Dudh Koshi River System, Final Report. Unpublished.

There are large temporal and spatial variations in climate across the basin, driven by topographic variations and the southwest and northeast monsoons. Most precipitation (about 80%) occurs during the southwest monsoon from June to September. Precipitation generally decreases from south to north. The trans-mountain region north of the Himalayas is arid, being in the rain shadow of the mountains to the south.

The population of the entire KRB including the parts in India and the PRC is 39.2 million, with the highest densities in the Terai. Population growth in the last decade was 23%, with the highest rates of growth in the downstream areas. The Nepal part of the KRB has 5.1 million (2001 census) residents in 18 districts.

The KRB has 3.4 million hectares (ha) of agricultural land, of which about 50% is irrigated. A number of large schemes exist in the Terai where most irrigation takes place. In the low hill areas, irrigated agriculture is about 4% of the total.

Fisheries in the KRB are an important source of livelihood for small traditional fishing families, who are scattered and not organized; and thus records are scanty. However, estimates reveal that fish production has not been commensurate with the potential productivity of the river systems; and, in some parts, fisheries are highly exploited (Yadav n. d.). The reasons for the pressure on fisheries are complex, and may include overfishing, use of inappropriate fishing methods, and construction of the Koshi barrage, which is a major constraint to fish migration.

While this study focuses on the Dudh Koshi sub-basin, the water resources of the KRB upstream of Chatara play a significant role in meeting the irrigation demands of the lowland Terai area through irrigation diversions to the Sunsari Morang area on the left bank downstream of Chatara, and from the Koshi Barrage further downstream. Interbasin transfers have been proposed from the Sun Koshi River south to the Bagmati River and to the Kamala River. It is therefore necessary to consider aspects of the Koshi Basin as a whole. The Koshi Basin has been considered at five different levels: (i) the Dudh Koshi river system; (ii) the Sun and Dudh Koshi river systems; (iii) the Nepal Koshi river systems; (iv) the larger Koshi river basin upstream of Chatera including Nepal and the PRC; and (v) the whole Koshi river basin including India, Nepal, and the PRC.

Figure 2 shows some topographic and physiographic features of the basin: the Terai plains lie in the south, bounded by the Siwalik Hills in the north, and the Mahabharat Range, which is the southern boundary of the Sun Koshi sub-basin. To the north is the area known as the Small Himalaya with elevations below 2,000 meters (m), followed by the Middle Himalaya with elevations ranging from 2,000 m to 3,000 m. Above 3,000 m is the Greater Himalaya, where vegetation is sparse, and peaks, including Mt. Everest at 8,848 m, are permanently covered with snow wherein significant glaciation occurs. To the north of the Greater Himalayas lie the Tibet Autonomous Region Himalayas and the trans-mountain region between the Himalayas and the Tibet Autonomous Region Plateau.

The DKRS is one of six major tributaries that make up the larger KRB. The Indrawati, Tama Koshi, and Dudh Koshi rivers all contribute to the Sun Koshi, which combines with the Arun and Tamur rivers to form the Sapta Koshi, just upstream of the Chatara gauging station. The Sun Koshi forms the largest part of the Sapta Koshi flows (Figure 3). The Sapta Koshi flows south across the Terai, and is a major tributary of the Ganges in India.

Figure 3: Tributaries’ Contributions to Sapta Koshi Annual Flow

Source: ADB. 2016. Nepal: Operational Research for the Dudh Koshi River System, Final Report. Unpublished.

The area of the larger KRB upstream of Chatara totals 54,100 square kilometers (km²). Of this, 48% lies in Nepal and 52% in the PRC. Most of the area in the PRC contributes to the Arun River with a small part going to the Sun Koshi via the Indrawati and Tama Koshi rivers. The Dudh Koshi has a total catchment area of 3,712 km² upstream of the gauging station at Rabuwa Bazar, and has about 22% of the overall catchment area of the Sun Koshi.

Climate

Climatic conditions vary widely across the whole KRB, influenced mainly by the southwest monsoon that brings high rainfall to the southern parts of the basin in the summer months, and the northeast monsoon that brings drier winter conditions. The northern part of the basin in the rain shadow of the Greater Himalayas during the southwest monsoon has a cold, dry climate. Generally, Nepal has four seasons: spring or pre-monsoon from April to May, summer or monsoon from June to September, post-monsoon in October to November, and winter from December to March. In the Nepal part of the KRB, annual rainfall typically r...

Table of contents

• Front Cover
• Title Page
• Copyright Page
• Contents
• Tables and Figures
• Acknowledgments
• Abbreviations
• Weights and Measures
• Executive Summary
• CHAPTER 1: Introduction
• CHAPTER 2: Hydrology and Water Resources
• CHAPTER 3: Hydropower Development
• CHAPTER 4: Irrigation
• CHAPTER 5: Environmental and Social Impacts
• CHAPTER 6: Strategies for Integrated Development of the Dudh Koshi Sub-Basin
• CHAPTER 7: Legal and Institutional Framework
• CHAPTER 8: Analysis of Hydropower Development Scenarios
• CHAPTER 9: Conclusions and Recommendations
• References
• Footnotes
• Back Cover