Over the past decades, Sebeya has experienced multiple flood-related disasters that caused loss of life, destruction of property, and environmental degradation. These recurring events positioned the catchment as a national priority for research, engineering intervention, and integrated environmental management. Today, Sebeya stands as a living laboratory for Integrated Water Resources Management (IWRM) and climate-resilient engineering solutions in Rwanda.
This article, developed under TechStream Insight, explores one of the key structural interventions implemented in the catchment: the Sebeya Lateral Dyke. The discussion highlights its engineering design, strategic location, and contribution to flood and erosion risk reduction.
Flooding and Sedimentation Challenges in the Sebeya Catchment
Rubavu District is particularly susceptible to flooding because the Sebeya River acts as a natural collector of runoff and sediment from the entire upstream catchment. Intensive soil erosion in upstream areas, driven by steep slopes, land-use pressure, and human activities—results in heavy sediment loads entering the river system.
As sediments accumulate, the riverbed elevation increases, significantly reducing the river’s hydraulic capacity. During periods of intense rainfall, the reduced channel capacity causes the river to overflow its banks, leading to floods that damage homes, agricultural land, roads, bridges, and public infrastructure.
Field observations of highly turbid river flows clearly demonstrate the strong link between upstream land degradation and downstream flood severity. These realities underscore the necessity of catchment-wide management approaches rather than isolated downstream solutions.
Integrated Water Resources Management (IWRM) in Sebeya
The restoration of the Sebeya Catchment is guided by Integrated Water Resources Management (IWRM) principles, which promote the coordinated development and management of water, land, and related resources.
In practice, IWRM in Sebeya combines:
Nature-based solutions such as afforestation, reforestation, terracing, wetland protection, and soil conservation;
Engineering interventions including retention dams, diversion channels, river training works, and lateral dykes;
Policy and planning frameworks aligned with Rwanda’s National Strategy for Transformation (NST1 and NST2).
This integrated approach ensures that environmental protection, socio-economic development, and disaster risk reduction are addressed simultaneously. Stakeholder participation, long-term planning, and technical coordination are central to the sustainability of these interventions.
Engineering Solution Focus: The Sebeya Lateral Dyke
Among the engineered flood mitigation structures in the catchment, the Sebeya Lateral Dyke plays a critical role in controlling peak floods and reducing erosion impacts.
What Is a Lateral Dyke?
A lateral dyke is a hydraulic retention structure constructed parallel to a riverbank. Unlike conventional dams that obstruct the entire river flow, a lateral dyke creates an off-stream storage area. During peak flood events, part of the river discharge is diverted into this side basin, where water spreads over a wider area and flows at a reduced velocity.
Once the flood peak subsides, the stored water is gradually released back into the main river channel at a controlled rate. This mechanism significantly reduces downstream flood intensity and delays peak discharge.
Location and Design Features of the Sebeya Lateral Dyke
The Sebeya Lateral Dyke is located in Rubavu District, Western Province, near the Musabike area along the Sebeya River. It was strategically designed to protect the Mahoko commercial center and nearby households in the Kanama and Nyundo sectors—areas historically affected by severe flooding.
Key Engineering Features
Flood Attenuation: Reduces and delays peak flood discharge downstream.
Controlled Release System: Temporarily stores excess floodwater and releases it gradually.
Construction Timeline: Completed in November 2021 under the Embedding Integrated Water Resource Management in Rwanda (EWMR) project.
System Integration: Works alongside the Bukeri diversion channel, Sebeya retention dam, and riverbank retaining walls.
Structural Materials: Constructed as a robust stone and earth embankment designed to withstand fluctuating hydraulic pressures.
Mechanism
The lateral dyke constructed along the Sebeya River has an approximate length of 606.14 m and is associated with an adjacent wetland covering about 136,991.35 m². During flood events, excess water from the upstream section of the Sebeya River is diverted into this wetland.
The wetland functions as a temporary storage zone, capable of retaining floodwater for extended periods while promoting natural infiltration and groundwater recharge. By automatically diverting a portion of surplus floodwater into the wetland, the lateral dyke prevents excessive discharge from re-entering the main river channel. This mechanism allows the Sebeya River to continue flowing within its normal capacity, significantly reducing downstream flood risk.
The water stored within the wetland is gradually released back into the river system once flood conditions subside, or it remains stored until it fully infiltrates into the ground, thereby enhancing both flood attenuation and environmental sustainability.
Why Kanama and Nyundo Were Selected?
Prior to the construction of the lateral dyke, the Kanama and Nyundo sectors experienced frequent and destructive flooding during rainy seasons. Floodwaters repeatedly washed away homes, farmland, and infrastructure, and tragically caused loss of life.
Technical risk assessments conducted by the Rwanda Water Resources Board (RWB) identified Kanama as one of 14 high-risk zones along the Sebeya River requiring urgent intervention. The location was therefore selected as part of a broader, integrated flood management strategy under the EWMR Project.
Role and Benefits of the Lateral Dyke to the Sebeya Community
The primary function of the Sebeya lateral dyke is flood attenuation. By capturing and temporarily storing excess runoff during heavy rainfall events, the dyke creates a dampening effect that significantly reduces downstream flood peaks.
Socio-Economic and Environmental Benefits
Protection of Lives and Property: Substantially reduces flood-related casualties and damage.
Infrastructure Safety: Protects roads, bridges, and water supply facilities.
Agricultural Stability: Prevents erosion and prolonged inundation of fertile farmland.
Community Resilience: Enables residents to conduct daily economic activities with reduced disaster risk.
Through this intervention, flood-prone communities such as Mahoko, Kanama, and Nyundo have experienced improved safety and long-term resilience.
Read more here or get full insights on sebeya engineering structures.
TechStream Insight
Integrated catchment management is essential for effective flood and erosion control.
Lateral dykes provide a sustainable engineering solution for managing peak river flows.
Combining engineering, environmental restoration, and policy frameworks delivers lasting impact.
At TechStream Insight, we highlight practical engineering solutions that bridge technology, water, environment, and sustainability. The Sebeya Lateral Dyke stands as a strong example of how smart infrastructure can protect communities while supporting sustainable development.
Explore more engineering insights with TechStream Insight.
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