Collapsing bridges, really? No, nature has her own ways

The recent floods in Bihar have taken many lives, perhaps the most tragic being a woman and her child falling off a bridge exit, a split second away from safety.



All media have reported it as a bridge collapse and attributed it to the folly of people 

(http://timesofindia.indiatimes.com/city/patna/bihar-floods-119-dead-rains-likely-to-continue-for-a-week/articleshow/60113191.cms, http://www.dailymail.co.uk/news/article-4802280/Indian-floods-Mother-child-drown-shocking-video.html). But a different scenario emerges if we take a closer look at the video. 

Given the fact that it is the only link with a safer village, we can't blame the people fleeing with their belongings across the river towards safer grounds. What alarms more is that this is not the only video on flood related deaths in the state, or other states of India, that have circulated through the internet over years (http://www.ndtv.com/india-news/bihar-floods-253-dead-1-crore-affected-as-bihars-flood-crisis-worsens-10-points-1739794) The new york times reports: "Sadly, this happens every year. Deadly flooding is part of the landscape in South Asia, and over the past two decades an average of around 2,000 people have died each year, according to the International Disaster Database in Belgium".

The video initially shows that water has risen to the level of bottom of  bridge deck, almost creating a situation like a filled outlet of a dam/barrage. With all the spans being filled, the raging flood waters had nowhere to go, except make a path of it's own. It did exactly the same: moving around the abutment, and making a tunnel on it's own through the soil under the road pavement. There seems to be no embankment protection (stone pitching) too that made things easier.

Water reaching up to bottom of deck slab

Finding no way through, water flows to the weaker end of bridge, 

exposing the soil. A tree can be seen sucked under the road.

A part of the road width caved in and it appeared like a bridge span that was mentioned by the media. It was this temporary "bridge" that was used by the hapless people to cross over to the safer side. But as the crossings took place, the diverted flood waters were undermining soil from the abutment and the approach road.

The "bridge" formed by natural tunneling (top layers of road have partially broken); 

there's no trace of concrete here

By the time the victims started crossing no one noticed that a crack was progressively developing over the  road, thanks to the waters and the thumping movement of people running over the road. The result was an inevitable catastrophe. Ultimately it is not the bridge, but the approach road that had partially collapsed.

 Moments before the victims started crossing the "bridge" a crack developing 

at end goes unnoticed. soil can be seen falling down

 Danger strikes: approach road collapses

 The abutment tip can be seen exposed here on right side of the photo, 

i.e. the bridge is intact

Taking chances with nature is not worth it

 The aftermath, a new channel for water

The photograph below shows a typical scene, similar to what happened in the video above. People and cattle are standing at the broken approach road where as the bridge and the abutment are intact.

Another flood scene, a similar situation: an intact bridge and abutment, but washed-away approach road.

Another flood scene:  washed-away railway track 

(http://indianexpress.com/article/india/bihar-floods-death-toll-climbs-to-56-69-lakh-people-affected-nitish-kumar-araria-district-4798317/)

RIP to the unfortunate souls. A question remains: how to avoid such incidents  in future? Bihar is a flood prone state. Extreme care is needed in planning the approach roads to bridges or for that matter selecting sites for bridges and designing them. The main question is, where the abutment should be and in what form it should be. 

It  may sound strange, but had there been a concrete slab (supported by strong ground), though less thicker than the bridge deck, as the initial part of approach road immediately after the bridge, the impact could have been reduced. The accident happened more because of a mistaken "bridge" than the flood itself. A more water-friendly embankment (say rubble packing with a few pipes inside, technically a gabion with multiple pipe culvert/box culvert) would have prevented a total wash out or at least would have got the people safely across. Simply put, either the soil mound (embankment) should have been properly designed, constructed and protected at ends, or the  bridges should have had an additional span or two, ensuring safer flow of water.

A pipe culvert with gabion wall protection 

(https://www.gabion1.com/gabion-pic-info-32/)

End note

Flood can't be prevented and is sometimes unpredictable, but it's impacts can be minimised.The situation in Bihar calls for stringent steps for disaster prevention and management. The first step towards a safer tomorrow is understanding the ways of nature. The river is trying to tell us: "the issue here is simple: block me and I will find another way through". No laxity can be excused, as precious lives are lost. Strict quality control and monitoring of health of bridges and roads are necessary. The one-size-fits-all concept will not work in a flood stricken sate; this necessitates an integrated approach of pavement, soil (geotechnical), structural and water resources engineering. At the same time, it is high time the people are educated on how to act in disastrous situations.