There is a need for different interventions to curb floods from River Nyabarongo that continue to damage major bridges and roads.

River Nyabarongo, the longest River in Rwanda, starts from the confluence of Mbirurume and Mwogo rivers in the western province and ends up at its confluence with the River Akanyaru , emptying into the River Akagera River, one of the largest rivers that drain into Lake Victoria.

River Nyabarongo serves as a tributary of the Nile River and provides goods and services such as a source of drinking water, irrigation, and fishery to the Rwandese communities.

However, it is currently facing heavy pollution from mining, encroachment, landslides, unsustainable agriculture, and domestic and industrial wastes leading to floods that block transport on the Kigali-Southern province road, Muhanga-Ngororero road among others as happened last week.

The Nyabarongo floods have also been affecting water transport that uses boats blocking cooperation among districts such as Muhanga, Gakenke, Rulindo and Ngororero.

According to Rwanda Water Resources Board, studies are being carried out to inform infrastructure developers in charge of planning and designing to build bridges and road sections that are resilient to floods caused by this River.

The recent floods paralyzed the main bridge over River Nyabarongo that connects the City of Kigali and the Southern province.

The damage happened after a few years, having been rehabilitated and heightened by some metres but still ended up failing to become resilient to floods.

Currently, there are worries that the bridge might collapse as it is sinking and officials announced that rehabilitation works are only possible when the rainy season ends.

"The floods from River Nyabarongo have been worsening at an unprecedented rate and we need interventions that can help reduce the floods and also carry out studies to guide engineers on bridges that are resilient,” Davis Bugingo the Flood Management and Water Storage Development Division Manager at Rwanda Water Resources Board (RWB) told The New Times.

The causes of the floods in River Nyabarongo, he said, include soil erosion and mining activities occurring in the river’s catchments.

"There has been a drastic change in land use and settlements in the river’s catchments areas. The main interventions in these catchment areas that are needed to curb floods are mainly preventing soil erosion,” he said.

The lower catchment area of the river is essentially covered by the districts of Gakenke, Muhanga, Rulindo, Kamonyi, Gicumbi, Gasabo, Nyarugenge, Gatsibo, Rwamagana, and Kayonza.

Some small areas of the catchment are located in the districts of Kicukiro and Burera.

The upper catchment area of the river is within the Nile Basin and runs south to north in the western part of Rwanda.

More than 745,000 hectares of agricultural land in Rwanda potentially loses its topsoil every year and the country loses more than Rwf800 billion annually due to soil erosion.

The eroded soil and sediments are washed away and deposited into different rivers including Nyabarongo.

"The river starts from the districts such as Ngororero, Rutsiro, Muhanga, Huye, and others. Mining activities including illegal mining are dominant in these districts and they are polluting the river. When the river is full of sediments and soil, they block water flow, and cause floods,” he said.

He said that other interventions that are needed but still not fully embraced include rainwater harvesting.

Bugingo said that while such sustainable interventions have not yet been scaled up, they are working with RTDA on studies to save the Nyabarongo bridge that is sinking due to floods.

"There are sensors or data monitoring equipment that are being installed on rivers to predict flood impact in terms of water levels or peak flow to be able to guide planners such as RTDA in road construction and infrastructure in general,” he said.

Since last week, vehicles were using one side of Kigali-Southern province road that connects Nyarugenge district and Kamonyi district as the other side was sinking.

In 2016, due to floods, transport on this road was halted for three days.

Urgent rehabilitation needed on Nyabarongo bridge

Imena Munyampenda, the Director General at Rwanda Transport Development Agency said that the side of the bridge on River Nyabarongo needs urgent rehabilitation but said that it could be done when the rainy season ends as floods decrease.

"The floods destroyed underneath part of the bridge. We will soon embark on rehabilitation works,” he said.

The bridge could be heightened by two metres but there is also $80 million to renovate the road from Giticyinyoni area to Kabgayi hospital in Muhanga district which will also work on the bridge.

The tender to build the road is expected to be launched next year.

The road will have four lanes from Kigali to Bishenyi beyond Ruyenzi area in Kamonyi district.

Meanwhile, if floods persist to paralyse the Nyabarongo bridge that is sinking, he said passengers could be advised to use the Kigali-Bugesera-Nyanza road although its construction is yet to be completed.