Sciences de la Terre - Gestion des ressources

Cracking Lebanon's flood puzzle: climate, urbanization and hidden variables

Lebanon, famed for its diverse landscapes and Mediterranean climate, grapples with a recurring problem: road flooding. This issue disrupts daily life, poses safety risks, and burdens the economy. To address it, understanding the causes—from topography and climate to rapid urbanization—is essential.

Lebanon, a nation blessed with diverse landscapes and a vibrant Mediterranean spirit, faces a recurring adversary - road flooding. This relentless problem disrupts daily life, poses significant safety risks, and imposes a heavy economic burden. Understanding the root causes and devising effective solutions through an engineering lens is crucial to safeguarding its future.

Unveiling the labyrinth of causes:


While topography and climate change-induced rainfall undoubtedly play a role, the heart of the issue lies within urban areas. Beirut, a bustling metropolis, exemplifies this challenge. Densely populated and packed with infrastructure, it bears the brunt of flooding due to several key contributors:

Clogged Arteries: Sedimentation in the Beirut River: Construction debris and years of accumulated silt act as a chokehold on the river, hindering water flow and leading to overflows during heavy rain events. Regular dredging is vital to restore its capacity.

Impervious Surfaces: Low Soil Permeability: Urban development often replaces natural landscapes with impermeable surfaces like concrete, preventing rainwater from infiltrating the ground and increasing surface runoff. Strategic planting of water-demanding vegetation can enhance soil permeability and reduce runoff.

Outdated Infrastructure: Inadequate Drainage Systems: Existing drainage systems may not be designed to handle the intensity and volume of rainfall experienced nowadays. Implementing the Rational Method in drainage design is critical for ensuring adequate capacity and flow.

Google Earth image showing sedimentation on the Beirut River mainly due to construction debris in the Massanih, Mkalles region

Beyond the Surface: A Deeper Dive:


Beyond these broad factors, a closer examination reveals specific challenges within the Beirut River itself:

Narrowed Passage: Insufficient Channel Width: During heavy downpours, the river channel's current width may be inadequate, leading to overflows and inundation.

Overflowing Capacity: Excess Water Volume: The combined volume of river water and urban runoff can exceed the river's capacity during storms, contributing to downstream flooding.

Backwater Blues: The Backwater Effect: Obstructions or alterations in the river's flow dynamics near its mouth create a backwater effect, further hindering drainage and exacerbating flooding.

Sedimentation's Grip: Accumulation Along the Riverbed: Years of accumulated sediment buildup significantly constricts the river channel, reducing its capacity and increasing flood risks.

Green Labyrinth: Dense Vegetation: Dense vegetation at the river's mouth further obstructs flow, contributing to localized flooding.

Maintenance Mishaps: Inadequate Management Practices: Lack of regular maintenance and dredging exacerbates sedimentation issues, compounding the impact of floods.


Google Earth Image showing previously flooded road area highlighted in dark blue

Engineering the Path Forward:


Armed with a deeper understanding of these root causes, we can propose targeted solutions:

Clearing the Blockage: Regular Dredging: Regularly dredging the Beirut River, particularly near its mouth, is essential to maintain its capacity and prevent overflows. This dredged material can be treated and reused in construction projects, making it a cost-effective solution.

Unlocking the Earth's Sponge: Enhancing Soil Permeability: Strategic planting of water-demanding vegetation like trees and bushes (riparian or native species) can enhance soil permeability in flood-prone areas. This not only reduces runoff but also provides aesthetic and ecological benefits. Careful planning is crucial to avoid unintended consequences like mosquito infestations during droughts.

Enforcing Regulations: Combating Sedimentation: Implementing and enforcing stricter regulations, including fines for construction sites dumping sediment into the river, is crucial to combat further clogging and protect the river's health.

Overflow Channels: A Temporary Relief: In flood-prone areas, constructing reinforced walls adjacent to the river channel can act as overflow channels, similar to the overflow system in a swimming pool. While effective, this solution is more expensive than others.

Picture taken from Jisr el Watti, showing the retaining wall collapse

Building a Resilient Future:


As we envision the future of urban planning in Lebanon, the concept of resilience becomes paramount. Without concerted efforts towards improved urban planning and meticulous maintenance of vital infrastructure like the Beirut River, unconventional measures like navigating heavy rains in monster trucks or boats, or even regulating digital activity, might become necessary.

Addressing the complex challenge of road flooding in Lebanon requires a collaborative effort. Engineers, urban planners, environmental experts, and the community must work together to develop sustainable solutions that withstand the test of time. Ongoing research, data gathering, and regular monitoring are crucial for understanding the evolving nature of the problem and adapting strategies accordingly.

Investing in effective engineering solutions is not just about mitigating flood risks but also about building a safer, more livable future for Lebanon. By embracing innovative approaches and tailoring solutions to the country's unique environmental context, we can forge a path towards a future where road infrastructure is resilient, robust, and serves its communities effectively.