July 13, 2020

Likoni Pedestrian Floating Footbridge not Viable At Kilindini Harbour

Andrew Mwangura. Image: (Courtesy)


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The construction project proposal of a Pedestrian Floating Footbridge to connect the island and the mainland south could be a threat to the navigational safety of incoming or outgoing vessels through the Likoni channel.
Details of the project are scanty but marine experts have expressed concern the footbridge could be a source of ship collision risks if not well-thought for the busy Kilindini channel.
Already, the project has been handed over to an international company on May 15, 2020 and is expected to take a period of six months to complete.
The 800 metres long bridge will start at the Liwatoni on the Island side and terminate at Ras Bofu – Sultani area – on the mainland south. It will have a 150 meter gate at the centre for passage of vessels across the Likoni channel.
In addition, the scope of the project will include access roads from the existing road networks to the bridge landings on both sides of the channel including bus/matatu terminus.
The project is financed by the National Government through the Kenya National Highways Authority (KeNHA) and will be operated by the Kenya Ports Authority (KPA).
The floating bridge will comprise of a 529-meter floating section stretching from north to south of Likoni, with 54-meter approaches on either side of the floating span.
According to reports the proposed floating bridge will be a composite structure designed for pedestrians only.
The project involves the construction of pile foundations and a Bailey bridge (a short-term bridge of lattice steel designed for quick assembly from prefabricated parts) with movable main steel bridge in the middle of the channel to allow movement of ships.
This project has been awarded to China Road and Bridge Construction (CRBC).
According to KeNHA, the effective date for the commencement of the contract is May 20 this year with its completion set for six months only.
The over Sh1.4 billion (US$ 14 million) project, fully funded by the government, comes ahead of the long-awaited Likoni permanent bridge whose development reportedly remains at the design and consultancy stage with the date of beginning construction yet to be announced.
Unfortunately, those officials behind the project have remained mum without providing details of it on how it will affect maritime communication across the busy channel into Kilindini harbour.
However, it is believed the floating bridge will be connected by pins and hinges with guard rails on either side of the deck to ensure pedestrian safety.
Mombasa port being one of the busiest ports in Africa, it also has one of the treacherous bends of entry to the port at the head of the Kilindini channel that requires navigational skills to manoeuvre.

An example of floating bridge. Image: (Courtesy)

The bend and narrow deep waters entrance allows in-bound traffic consisting of vessels originating from three major directions: vessels that from the Mediterranean Sea, those from the Far East of Asia and those from Middle East – Strait of Malacca.
It is foolhardy to build a floating bridge without conducting a ship collision risk analyses, and to compare different bridge and tunnel options from a navigational safety point of view.
This approach is a computational algorithm that relies on repeated random input parameters to a model in order to obtain numerical results; typically compressed time simulations are repeated many times to obtain the distribution of an unknown probabilistic entity.
In this study, a large number of input parameters are randomly generated according to various probability distributions.
These parameters represent realistic sets of the operational conditions of the ship traffic.
The ship traffic is simulated by a fleet of vessels, representing the predicted ship traffic in the next twenty years.
The outputs are: locations of collision (pattern) and collision energy and forces.
This data is used in combination with a prognosis for expected ship traffic frequencies and the probability for various types of failure in order to obtain probabilities for collisions and collision energies exceeding a certain energy level.
The following input parameters must be used and varied in a large number of systematically conducted compressed time simulations: size and type of ship; ship speed profile; propulsion and rudder systems; met ocean data (e.g. wind and current) and bridge configuration.
Others are routes for the fleet of representative ships at the bridge crossing and in transit outside the bridge area; probability of the occurrence of technical failures and human errors and probability that failures/errors are repaired/ corrected in due time to prevent collision.
This type of bridge should be designed to withstand a collision energy that is expected at a return period of 10,000 years.
In order to be able to assess an event with this return period, simulations representing failure events and errors expected over a total period of one million years are conducted for each of the addressed bridge and tunnel options.
Given the traffic density and probability of technical failures and human errors, it is required to simulate roughly one million vessel transits in the area.
Each of these simulations is performed using the following sequence: initiate starting ship position according to routes and traffic distribution in the area. Introduce weather condition based on statistics for the area; at a given time, initiate failure (technical failure or human error) causing the ship to divert from the intended route.
If possible due to the type of failure, take evasive actions to avoid grounding or bridge collision; continue simulation until bridge collision or grounding occurs or the given repair/ correction time is reached and for each simulation, an extensive set of result variables is stored.
In case of bridge collision, these include the location on the bridge element where the collision occurred, maximum collision force and impact energy.
The simulations generate statistical data on expected collision positions along the bridge and the associated collision energy absorbed by the bridge.
Port of Mombasa is the gateway and exit point for cargo belonging to a vast hinterland of the country apart from Uganda, Rwanda, Burundi, parts of Tanzania, Democratic Republic of Congo, South Sudan, Somalia and Ethiopia.
The port is one of the largest and busiest ports in Eastern Africa and even at times economic struggles it has remained so year after year for its business with the Great Lakes countries.
In recent times, the port has been hitting 22 million tons every year with its 21 berths as well as two bulk oil jetties and dry bulks.
The port has the huge potential for options such as cold storage or warehousing which is very handy for foreign traders, especially so, when around 72 per cent of its transactions are from imports.

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