This year's monsoon has arrived in Sanghar, while the actual accounting of the damage caused by the unprecedented rains and floods in October last year is still ongoing. Looking at the nature of rains and floods in recent years, monsoons, floods and disasters have gradually become synonymous in the context of Nepal.

Many floods of severe nature have occurred in Kathmandu Valley in the past. 

The 1954 flood is one of the earliest recorded floods. Which caused great damage to agriculture and infrastructure. The 1981 flood was caused by a heavy monsoon and affected some areas of Kathmandu.

The 1993 flood was one of the most devastating, killing more than 130 people and causing extensive damage. The 2002 floods inundated areas due to excessive rainfall and poor drainage systems. Floods in 2008 disrupted local communities and economic activity. 

Last October, the unprecedented rainfall in Nepal set a historic 24-hour rainfall record at 25 weather stations across the country. Kathmandu Valley catchment area Kathmandu, Bhaktapur and Lalitpur Districts is an end-mountain valley with a catchment area of ​​about 625 square kilometers at an altitude of 1200 meters to 2700 meters above sea level.

Our research shows that analyzing the underlying causes of floods and landslides and their interrelationships is not only necessary to develop effective flood management strategies, but also to evaluate current policies, institutional capacities, programs, and mitigation efforts. 

A research paper titled 'Unraveling the Causes and Impact of Increasing Flood Disaster in the Kathmandu Valley: Lessons from the Unprecedented September 2024 Floods' has been published in an international journal called Natural Hazards Research about the causes and damage caused by the floods in Kathmandu Valley and Roshi region last October. Authors as well as researchers Kabin Lamichhane, Bharat Khadka, Biplav Acharya, Kamal Vishwakarma, Sumit Adhikari, Rajan KC, Anusha Danegulu, Samana Bhattarai, Abhilasha Regmi, Mandeep Subedi participated in the said research.  

study conclusion

In the period from 2000 to 2019, analyzing the urbanization by geosatellite mapping, it has been shown that there has been a massive increase in the flood-affected population due to the two-fold increase in settlement development within 100 meters right-left of the river in the entire Kathmandu Valley (from 16.9 to 32.9 square kilometers).

Also, the width of the river should gradually increase from the upper part to the lower part, due to the encroachment/corridor construction of some rivers in the valley and the width is narrowing in the lower urban part than the upper part, the flow area is decreasing. As a result, the effect of flood seems to increase. In this context, it seems that the seriousness of the order issued by the Supreme Court last year that 40 meters should be left from the banks of the main rivers including Bagmati, Bishnumati, Manohara etc. 

In the last flood, there was a lot of damage around Nakhkhu river. Nakhkhu river in Lalitpur district has a steep slope in the upper part of the watershed. There are two mining areas (sand, gravel and stone quarrying) in this area, which is about 2 km above Tikabhairav. One falls in the sub-catchment of Lele River and the other in the main catchment of Nakhkhu. Due to the flood, the bank of the river in the upper part (Nallu) of Nakkhu River has widened and deepened.

This section is above the excavation area. On the other hand, about 2 km downstream from the mining area, the widening of the river is also seen due to the accumulation of sediments in the river bed. Excavated materials placed on the banks of the river have been washed away by the flood, and more sandy material has been added to the river. Because of this, the river seems to be filled between the excavation area and Tikabhairav. The post-flood conditions show that the riverbed material is thicker, indicating landslides, Gegran flows and the discharge of material stored by excavating the upper reaches.

Many houses collapsed or were washed away due to erosion and deepening near the river bank. One of the reasons for last year's extreme floods was the flow of large amounts of mud and rock from the tributaries to the main river. Due to the rain, the maximum water absorption capacity of the land has been exceeded and excessive runoff has occurred from the steep land, which can also be seen in connection with unscientific road excavation, land fragmentation (plotting) activities in the upper areas.

Floods can be caused by both natural and man-made causes. Natural causes include the nature of the watershed, topography, heavy rainfall, etc. In the same way, it is clear from the research that the structures that block the flow of the river in man-made activities have not been expanded or repaired in a haphazard manner and insufficient drainage system, river encroachment, unorganized settlement expansion and land use, uncontrolled sand mining and haphazard road digging in the upper reaches have made the effect of floods more intense and serious. 

During the last 3 days of October, when analyzing the amount of rain at the rain measuring center in the valley, it has been seen that the return period of some places is more than a thousand years. It refers to the rain that falls once in a thousand years according to the current measured rainfall data.

Last year's flood impact was higher than previous years. The character of rain and flood was not limited to regular inundation. Nepal's disaster management framework is weak and needs immediate improvement. Despite early warnings of heavy rains from the relevant agencies, the public is not aware of the seriousness of the impact of floods.

Due to the lack of adequate preparation and response, the impact of the disaster increased significantly. According to the National Disaster Risk Reduction and Management Authority, last October's disaster damaged more than 1 percent of the country's gross domestic product.

If the characteristics of changing rainfall and landslides are not analyzed closely, then in the future, the risk of flooding in Kathmandu Valley will increase from every angle and there is a risk of causing unimaginable damage. Plotting on steep slopes, and uncontrolled felling of hills for road construction are the major causes of excessive runoff/runoff in tributaries. However, landslides and mudslides have caused heavy damage even in the steep terrains, which are not easily drained by heavy rains and are covered with forest greenery.

Strict implementation of policy arrangements is necessary to address long-term solutions to the flood risk and impact of the valley. 

Suggestion

According to this study, sustainable and effective flood management in Kathmandu Valley requires a multi-pronged strategy based on collaboration based on the distinct characteristics and specific challenges of the region, rather than a one-sided or one-sided approach. There is an urgent need for flood management, especially community and nature-based integrated water resource management, urban planning, legal and policy reforms and strict implementation, inter-agency collaboration, strong local government and systemic reforms in disaster risk management. 

should focus on sustainable conservation and restoration based on the relationship between the valley and its water, land and communities. Establishing construction restrictions on river banks and creating urban development plans according to flood risk assessment, establishing water measurement and sediment monitoring centers, empowering local level employees through water resource and water disaster management training, and increasing community participation by using citizen science. 

Similarly, in the long-term measures, implementing a watershed management plan in the upper part, identifying a place to build a 'detention basin' (reservoir to store water for some time) in the middle part, giving an open channel to the river in the lower urban part, reviewing the laws and standards related to the flood area, as well as controlling illegal mining and determining the amount of sustainable mining.