•Drainage system was done many decades ago when city population was much smaller
•Upgrading the system might require demolishing some buildings, which City Hall says is impossible
Nairobians will continue to brave floods and stagnant water during rainy seasons because City Hall does not have the massive funds needed to revamp the drainage system.
The old drainage was designed to serve less than 500,000 people but the city population have since ballooned to about five million.
Questions have been raised over the years about why Nairobi turns into pools of stagnant water whenever it rains.
In the central business district, streets like Moi Avenue often become impassable and cart pushers make make money ferrying pedestrians and their luggage.
According to City Hall, the physical planning of the city in terms of urban planning dates back to post independence days when the designs were made.
County's Executive for Water and Environment Vesca Kango explains that the designs of the drainage systems were according to the population back then.
"The planners did not foresee the factor of population increase .The design of the city and major roads leading to CBD make it hard to properly address the issue of drainage in CBD and its outskirts. The design of drainages made by our engineers many years ago does not help the situation at all and it was limited to specific areas,"she said.
Kangogo said for the designs to be upgraded and to realign the drainage systems, some buildings in the city have to be brought down but that's not possible.
The construction especially in the slums has compounded the drainage problem.
County chief officer for roads Fredrick Karanja told the Star sewer lines are designed to always flow half full.
"There is a need to invest in a storm water master plan for the entire city which is lacking. Inadequate design of storm water automatically contributes to flooding. A big investment is required to separate the storm water drainage and the sewer lines to stop the overflow especially in the CBD," he explained.
Karanja pointed out developments which have been taking place need to be kept away from riparian wayleaves.
"The storm water eventually ends up in the natural drains which are the rivers like Nairobi, Ngong and Mathare.The development done along these natural water ways interferes with capacity of the rivers to receive the storm water.Developments need to be away from the riparian wayleaves," he said.
Trade activities on road reserves like building kiosks over drainage systems, selling building materials like sand,stones, ballast and timber some of which end up in the drains have also been faulted for blocking the drains.
City residents have also been blamed for dumping solid waste in drainage systems, blocking the flow of water.
Nairobi Governor Mike Sonko has repeatedly appealed to the public to make use of litter bins and proper waste disposal but still solid waste finds its way to the drainage.
"The change starts with an individual where one uses proper disposal ways. This is a collective responsibility and residents should know the role they play in addressing the issue on illegal dumping," Kangogo said.
An attempt to address drainage was made on April 11, 2018 when Nairobi acquired flusher machines used to unblock drainage systems.
Transport CS James Macharia and Governor Sonko unveiled a Sh25 million flusher machine for unclogging drainages.
It was part of programmes funded by the World Ban under the Nairobi Metropolitan Service Improvement Project.
The project started in December 2012 and was expected to be completed by end of May, 2019.
The whole project costs around Sh500 million and Nairobi alone is allocated 75 per cent of the total amount.
"The ongoing rains have been unusually heavy and the Meteorological Department had warned of plus 50mm-100mm over the weekend .The flusher unit machines are being used to unclog culverts where there is intense blockage," Karanja said.
The Kenya Urban Roads Authority says drainage should be given first priority when roads are constructed.
Kura communications Director John Cheboi said all roads under the authority have proper drainage systems.