Every monsoon, Nepal faces a familiar tragedy related to seasonal hazards. Houses are swept away or damaged, bridges collapse, and families lose their livelihoods. The 2026 floods have once again exposed the danger of building where rivers need room to flow. The August floods along the Bhote Koshi and Trishuli rivers caused widespread damage. Preliminary assessments show that approximately 7,570 houses were destroyed or damaged, 37 vehicular bridges and 68 suspension bridges were wrecked, and 13 hydropower projects were affected. In October, another big flood struck Budhi Gandaki, sweeping away buildings and infrastructure.
Where and how Nepal communities settle, and how local governments enforce zoning regulations and national building codes, are critical in this regard. In the steep Himalayas, intense rainfall, landslides, temporary river blockages, and glacial hazards can occasionally trigger destructive floods. Although catastrophic events such as the 2026 Bhote Koshi–Trishuli floods are difficult to predict or prevent, Nepal can reduce annual flood damage through smart settlement planning and code-compliant construction.
Understand the Floodplain Before Building on It
A floodplain is the low-lying land beside a river that becomes swamped when water levels rise. It is not just vacant land, but is part of the river flow route.
The main river flow area carries the deepest and fastest-moving water. The surrounding fringe floodplain area provides additional space for water to spread and slow down. This area can also store floodwater, support wetlands, and provide habitat for plants and wildlife. When buildings, roads, embankments, or fill material obstruct these areas, water may find a route through human settlements.
Flood risk is often described in terms of possible return periods. A 10-year flood has a 10% chance of being equaled or exceeded in any given year. For a 20-year flood, the annual probability is 5%. For a 100-year flood, it is 1%. These figures do not mean floods arrive on a fixed schedule; two major floods can occur within a few years. Assuming the annual probabilities remain constant, an area has about a 96% chance of experiencing at least one 10-year flood over 30 years. The corresponding probability is 79% for a 20-year flood and 26% for a 100-year flood. A home in a 100-year floodplain has more than a one-in-four chance of facing a flood of that magnitude or greater during a 30-year span. Moreover, return-period estimates depend on past events. With global warming, historical estimates may become less representative of current flood risk.
These hydrological calculations provide useful reference, but do not fully predict flood risk, especially in multi-hazard-prone areas of the Himalayas. Climate change, glaciers, shifting river channels, landslides, and sudden releases from landslide-dammed rivers can create hazards that flood maps meant for flatland geography fail to capture.
Match Land Use and Building Types to the Levels of Risk
Not every part of a floodplain faces the same level of risk. National and local governments should adopt land-use and zoning regulations based on flood depth, water velocity, erosion and debris impacts, and the difficulty of evacuating residents from the affected area. A three-tier zoning classification as proposed below could help local municipalities make important decisions in this regard.
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FP-3: High-hazard flow zone
This zone would cover the main river channel, active flow paths, and areas exposed to frequent or severe flooding. Permanent homes, schools, hospitals, and other vulnerable buildings should be prohibited here. River-compatible farming and riparian restoration may be allowed with engineering support. Local governments should consider relocating settlements in the most dangerous locations, providing fair compensation and suitable housing. In the United States, governments often buy out floodplain properties for allowable uses.
FP-2: Flood-storage and fringe zone
This area would accommodate uses that can tolerate occasional flooding. Wetlands, swales, rain gardens, retention and detention ponds, community forests, seasonal agriculture, sports fields, and flood-compatible parks are possible uses here. Occupiable buildings and critical facilities should be avoided when safer alternatives are available.
FP-1: Lower-risk outer zone
Development could be permitted in this zone when a site-specific assessment shows that risks can be managed. Buildings would still require appropriate floor elevations (above possible water levels), effective drainage, erosion protection, safe access, and resilient utilities.
Floodplain large-scale maps should show expected flood extent and depth, high-velocity areas, and locations prone to erosion and debris flows. Where resources allow, municipalities should also assess the 500-year flood, which has a 0.2% annual probability, especially when planning critical facilities. Interactive GIS maps that display varying floodplain risk levels would be valuable tools for both governments and the public.
In Nepal’s mountain valleys, a property outside the modeled 100-year flood boundary is not necessarily safe. Sudden changes in river channels, landslide dams, and debris flows can put additional areas at risk, while landslides can be even more dangerous.
Set Building Floors Above Potential Flood Levels
Where local governments permit construction in flood-prone areas, the lowest occupied floor should be raised above the expected design flood elevation. The difference between these two elevations is called freeboard. Freeboard provides an extra margin of safety in flood estimates and local variations in water levels.
Practices by the US Federal Emergency Management Agency (FEMA) and local governments offer a useful reference for Nepal. Under the National Flood Insurance Program, new residential buildings in mapped high-risk flood areas generally must have their lowest floor at or above the base flood elevation, subject to applicable regulations and with exceptions. The base flood is the flood with a 1% annual chance of being equaled or exceeded. FEMA encourages communities to adopt at least 0.30 m of freeboard. Some communities require 0.6 m or more. The exact requirement varies by local regulations, building type, and occupancy.
For Nepal, a preliminary planning standard could require the lowest occupied floor to be at least 0.6 m above the modeled design flood elevation in ordinary mapped riverine hazard areas. This is a proposed benchmark, while higher elevations may be necessary when water moves rapidly or carries large debris.
Respect Riverbank Setbacks and Comply With Building Codes
Nepal already has regulations intended to protect river corridors, yet construction continues in hazardous areas because many municipalities lack the staff, technical capacity, or political support to enforce them.
The Kathmandu Valley’s river-setback case provides an important legal precedent. In January 2026, the Supreme Court partially overturned an earlier ruling that imposed a uniform 20-metre setback along the valley’s major rivers. A 20-metre bufferis modest by international standards. Municipalities and other local governments should establish appropriate setback requirements and designate no-build zones beyond riverbanks.
Riverbank setbacks are an important part of regulations. However, a river may need a much wider corridor due to erosion, flood storage, the shape of its valley, or the river's size. In other locations, the floodplain may extend far beyond the legally prescribed buffer. Municipalities should use flood-risk maps alongside setback regulations when preparing land-use plans and create zonings accordingly before approving building permits.
Learn from International Standards
Nepal can adapt established U.S. technical standards to local conditions. American Society of Civil Engineers (ASCE) SEI 7 covers design loads, including floods, while ASCE/SEI 24-24, Flood Resistant Design and Construction, sets requirements for flood-resistant buildings, foundations, materials, utilities, and elevations. FEMA guidance offers further direction on flood mapping, building elevations, and risk reduction. Although U.S. practices cannot be transferred directly to Nepal due to Nepal's distinct economic and cultural context, international best practices remain valuable references for local adaptation.
Himalayan rivers can carry heavy sediment and large debris, and landslide dams can release sudden surges of water. Land use, zoning, and building codes must account for these specific conditions. In addition, hospitals, emergency facilities, schools, bridges, and hydropower infrastructure deserve particular attention because their failure can affect entire communities.
Insurance and lending policies can reinforce these rules. New construction in prohibited high-risk areas should not qualify for public subsidies or favorable insurance terms. Property owners, developers, and lenders should receive clear flood-risk information. Existing buildings should be evaluated for elevation, retrofitting, or relocation, with financial assistance provided where needed.
Build Forward Safely
Land in the floodplain can remain productive while reducing risk by allowing low-risk land uses. But Nepal must locate settlements more safely. Governments should stop approving construction in places where risks are well documented, and communities have repeatedly experienced them. Keeping homes out of destructive flow paths, designing bridges for realistic flood conditions, and restoring river corridors to their natural and complementary functions can prevent future losses. The goal is not to defy rivers, but to live safely alongside them.
(Dr. Ambika P. Adhikari is a distinguished fellow at the Institute for Integrated Development Studies (IIDS), Kathmandu, Nepal, and Global Futures scholar at Arizona State University, USA. Dr. Keshav Bhattarai is a Professor of Geography at the University of Central Missouri, Warrensburg, MO, USA. He researches and teaches topics in GIS, remote sensing, tourism, geography, and forest economics.)