Mapping Hazards in Nepal’s Melamchi River: Catchment to Enhance Kathmandu’s Water Security

By Asian Development Bank

This technical report assesses the string of events that triggered Nepal’s Melamchi River floods in 2021 and highlights threats to the catchment area that provides vital drinking water to Kathmandu’s fast-growing population. The report explains how floods damaged key water supply infrastructure and analyses risks posed by earthquakes, glacial lakes, and landslides, as climate change complicates conditions in the fragile Himalayas. It shows why a comprehensive catchment strategy centered on disaster risk reduction and early warning systems, plus measures to stabilize the river and control erosion, can help protect Melamchi’s critical infrastructure from future events and boost the capital’s water security.

• Language: English
• Publisher: Asian Development Bank
• Release date: Nov 1, 2023
• ISBN: 9789292704681

Book preview

MAPPING HAZARDS IN NEPAL’S MELAMCHI RIVER

CATCHMENT TO ENHANCE KATHMANDU’S WATER SECURITY

NOVEMBER 2023

Creative Commons Attribution 3.0 IGO license (CC BY 3.0 IGO)

© 2023 Asian Development Bank

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Some rights reserved. Published in 2023.

ISBN 978-92-9270-467-4 (print); 978-92-9270-468-1 (electronic); 978-92-9270-469-8 (ebook)

Publication Stock No. TCS230541-2

DOI: http://dx.doi.org/10.22617/TCS230541-2

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Cover design by Colors Print & Production, Bhotahity, Kathmandu, Nepal

Cover photo: Melamchi Headworks site after the Monsoon 2021 flood events.

(Photo by Melamchi Water Supply Development Board (MWSDB)

Edited by Sophie Hares.

CONTENTS

TABLES, FIGURES, AND MAP

Forewords

Nepal has a long history of disasters caused by earthquakes, floods, and landslides. The 2021 dual flood events, triggered by the impacts of climate change and exacerbated by vulnerable Himalayan geology, led to massive landslides and debris floods in the Melamchi River catchment area. Approximately 17 people were killed and downstream settlements and infrastructure devastated, including the headworks of the Melamchi Water Supply Project (MWSP) that was ready to be commissioned in September 2021.

The MWSP plays a central role in ensuring the drinking water security, health, and well-being of the people of the Kathmandu Valley. Damage to the long-awaited project highlighted the vulnerability of Nepal’s infrastructure and underscored the efforts of the Government of Nepal to reduce disaster risk and protect its development gains.

It is vital to ensure that all necessary measures are taken to insulate important projects like the MWSP against future catastrophic hazards, particularly as climate change takes effect.

This technical report is an important step in understanding the causes and effects of disasters like those seen in the Melamchi River catchment. It identifies the root causes of the Melamchi debris flows and lays down the groundwork for efforts to repurpose or reconstruct the critical infrastructure destroyed by the