Tame rivers to save bridges

THE creeks and rivers that run off the coastal mountain ranges of East Sepik, Madang and Morobe are some of the most untamed in the world.
In times of heavy rains, which fall around these mountain ranges often and in large volumes, the creeks and rivers increase in size so quickly and thunder down the mountains like runaway trains carrying all in their path.
The reasons are easy to see.
Between where they start at an elevated level and the sea where they end is a straight line. There is little meandering so the river in flood is gathering force every metre of the way to the sea.
This is the nightmare that greets Papua New Guinea road and bridges engineers today.
Some rivers such as Busu on the outskirts of Lae is said to be the fastest-flowing river in the southern hemisphere. Many a mangled remains of a bridge dotting its path to the seas is testament to this reputation.
To maintain its reputation, during the latest rains, the Busu carried away the only link between Lae and Nawaec.
This is where our engineers come in.
How does one build a bridge to withstand the ferocity of these untamed rivers?
In engineering and construction, an abutment is a structure built to support the lateral pressure of a bridge.
Abutments hold up a bridge and so are very critical in any bridge work. Much time and materials such as steel and concrete are expended on these parts of the bridge for good reason. They are compacted and reinforced with piles driven into the earth.
But how does one protect a bridge when the river is not just attacking the bridge foundations from its bed and all around it, when it submerges it altogether?
Damage must be done under these circumstances, regardless of how carefully a bridge has been constructed.
In the ongoing unusual rainy weather in parts of the country over recent days, a number of bridges have collapsed as the approaches were washed away by raging floodwaters. In other areas, abutments have actually sunk in causing bridges to collapse.

Quote:
“Climate change is no longer some far-off problem; it is happening here; it is happening now.” – Native American proverb

The cost of repairs and replacements will certainly run into hundreds of millions of kinas.
More unpredictable weather conditions, attributed to global climate change, are to be expected in future so engineering designs for roads and bridges will have to change. Building bridges to withstand weather conditions is an important agenda for governments around the world and, more so, in the Pacific region which is already experiencing impacts of unusual weather.
Better planning and cost analysis will be required for climate change-resilient infrastructure.
An idea comes to mind.
Our engineers must copy nature. Nature tampers the raging river by throwing things in its path to slow it down. It puts up raised landmass so that the river is forced to meander its way around them.
In that way, the nature that gives birth to the rage in the river also tames it incrementally until it becomes docile and still, even in flood.
If engineers began their bridge work many kilometres upriver from a particularly unruly river, and work to slow the turbulence of the river, that might do the trick in protecting the bridge many metres downriver.
That will certainly entail higher costs for certain but it might be worth it in the long term when a bridge does not have to be replaced after every heavy rain.
Given the extent and number of roads and bridges damaged in the recent rains, the immediate concern, of course, is to provide relief for people and enabling the temporary safe passage of goods and services.
The longer-term concern is ensuring that the damaged infrastructure is replaced, and to think outside the box to come up with ways to even direct the course of a river for many kilometres to tame it.