An assessment report released by Rwanda Housing Authority (RHA), on August 18, has classified the districts of Nyamagabe, Karongi, Nyamasheke, Rubavu, Rusizi and Rutsiro in highest risk zone with exposure to seismics.
The classification, the housing authority said, was motivated by the need to retain structural design safety while optimising the affordability and environmental sustainability of buildings.
The zoning map shows three main areas namely the lowest risk zone, the medium risk zone, and the highest risk zone.
“The categorisation of Rwanda’s 30 districts into these three risk zones informs the upcoming revisions of the Rwanda Building Code in 2024,” reads the report.
The districts of Gasabo, Kicukiro, Nyarugenge, Bugesera, Gatsibo, Kayonza, Kirehe, Ngoma and Rwamagana have been categorized in lowest risk zone.
The districts of Nyagatare, Burera, Gakenke, Gicumbi, Musanze, Rulindo, Gisagara, Huye, Kamonyi, Muhanga, Nyanza, Nyaruguru, Ruhango, Ngororero and Nyabihu were classified into medium risk zone.
Why zoning?
The zoning will guide building design, costs and construction budgets required for projects in different districts of the country.
It will also guide on construction techniques for buildings including affordable housing as well as environmental protection.
“The classification will ensure that structures are adequately safeguarded against levels of seismic hazards and therefore safeguarding human lives and reducing economic losses as intended by Rwandan building regulations,” the report concludes.
Moreover, the report said that, changes in building code will avoid undue financial, technical, and environmental challenges by applying figures on predicted seismic risks.
“ Apply such changes reinforces the function of our building regulations as instruments that cater to the complexities of local context and ensure our structures are safe and environmentally and economically sustainable,” adds the report.
Building structures shall be designed for forces generated by a maximum credible earthquake having peak ground acceleration equal to 2.5m/s2 (meter per second squared), which has a 10 % probability of exceed in 50 years and a return period of 500 years.
Approval for such structure shall not be granted without the explicit scrutiny of the design and signature of a qualified person, says the report.
The maximum acceleration of the ground that occurs in an event of an earthquake is known as peak ground acceleration (PGA).
Peak acceleration is a measure of the maximum force experienced by a small mass located at the surface of the ground during an earthquake and it is one of the important parameters in the design of seismic resistant structures.
Rwanda’s northwestern region is part of the Albertine Rift, the western branch of the East African Rift — which extends thousands of kilometres from Ethiopia to Mozambique.
Lake Kivu was created as a result of the rifting.
Consultations about a revised master plan for Rubavu District, located in part of the Albertine Rift, began, last year, with focus on the part of the city which was most affected by last year’s volcanic earthquakes.
A kilometres-long fault line, which resulted from the volcanic eruptions emerged and cuts across through Rubavu town into Lake Kivu.
Consequently, a post-disaster government report in July 2021 advised district authorities to avoid heavy structures above or near the rift.
