Flash floods are man-made

Environmental geologist K S Valdiya lives in Uttarakhand and keeps a tab on the changing geological processes in the Himalayan region. He was recently conferred with the G M Modi Award for Innovative Science and Technology for his contribution in the fields of Himalayan geology and neotectonics. Formerly a member of the prime minister’s science advisory council, Valdiya tells Anupam Chakravartty what triggered the recent landslide in Uttarkashi

 
By Anupam Chakravartty
Last Updated: Saturday 04 July 2015

K S ValdiyaFlash floods are becoming recurrent in the Himalaya as well as in other parts of India. What are the geological processes that could trigger them?

Flash floods have little to do with geology. They are related to the rainfall pattern that has changed considerably over the years due to warming up of the atmosphere. There has been evidence that with increasing atmospheric temperature, precipitation during the rainy season is no longer uniform. In summers there is prolonged drought followed by short spells of heavy rainfall. So quick and vast is the rate of precipitation that there is not enough time for water to percolate down the soil. To worsen the situation, there is hardly any tree cover; soil is compacted to the extent that it becomes impermeable. This results in increased river discharge and flash floods.

Could this be the only cause behind the flash flood in Uttarkashi in August that the government termed the worst in 30 years?

It is entirely man-made. A river consists of a deep channel, flanked by floodways on either sides, which are extended by floodplains. Historically, people avoided floodways for building houses and only did agriculture there. But decades of human activities have destroyed the geomorphic difference between floodplains and floodways. Now, there is construction work not only on floodway, but also close to the river channel. Unlike railway lines and bridges which span the floodways, roads and bridges get easily washed away because developers are least concerned about geological structures.

Gangotri bridge in Uttarkashi damaged due to flash flood in August


First, they restrict the channel by erecting piers on it. Then, they build embankments on both sides of the river to reach from the bank. The embankments act as dams, whereas the bridges resemble open sluice gates. In mountainous regions, the developers simply construct culverts or sometimes holes to save cost. In Uttarkashi, all the construction including roads and bridges has come up on floodways and terraces. All the new townships coming up on the riverside are on the floodways. So when a river is in spate, what does it do?

Do you think increasing pressure on land in the mountain region is also the reason for devastating flash floods?

Of course, there is pressure on land. But you will not find village residents building houses on river terraces. They prefer building on the slope. Faulty planning is responsible for such landslides. In the Himalayan region, it is a standard practice to build a road on the debris of previous landslides. This saves the cost of digging or cutting the mountain. So good engineers put pressure on road contractors to build drainage system parallel to the road. But many do not have such a drainage system for the water to flow down. This causes more landslides.

Subscribe to Weekly Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.

  • It is quite informative and

    It is quite informative and eyeopener for the people and authorities to take up preventive measures. I had an opportunity to see the beauty of Uttarakashi and Himalayas while undergoing mountaineering Courses (Basic in 1979 and Advance in 1881). Now being a Geophysicist,i can the situation in a better way.

    It is the high time to minimize the man made hazards and equip to face the natural hazards for achieving sustainable development with quality ....

    Posted by: Anonymous | 7 years ago | Reply
  • It says impact of rise in

    It says impact of rise in temperature on rainfall causing flash floods -- do you have any data to substantiate this? Mr. Vaidiya getting awards does not mean what he says is 100% true. In this part of India geological formation plays vital role in flash floods with the increased population and changes in land use that destroy the protective green cover. As a result rain water flow get more momentum that help flash flood even at low rainfall.

    Dr. S. Jeevananda Reddy

    Posted by: Anonymous | 7 years ago | Reply
  • It does not require to be

    It does not require to be Prof Valdiya on the changing rainfall patterns combined with faulty building practices and deforestation to have resulted in flash floods . It is well documented and If Dr Reddy can do some homework by searching in the archives of down to earth and National science foundation statements he can find that it is a global phenomenon .What Dr Reddy says about geological formation and changes in land use is definitely correct , Himalyas are unconsolidated and the heavy precipitation combined with deforestation is causing the flash floods

    Posted by: Anonymous | 7 years ago | Reply
  • Floods are natural

    Floods are natural geological phenomenon ...which happens weather man interferes or not .....but the impact on human civilization is man made ...because we have forgotten to live in tune with nature...and are arrogantly occupying places for habitation which were geologically considered unsafe for human settlements...
    Flash floods of encroachment2010 in Leh which claimed 210 lives and other places are perfect examples
    I was myself trapped in 2010 floods.. and later i devised a mechanism of Reservoir rupture mechanism to understand the flash flooding event ....
    No plantation ....uniform heavy rainfall ....selective destruction in few channels .....traditional habitats SAFE......new habitat s in unsafe geological locations destroyed

    Flash floods is 100% natural geological phenomenon triggered by rains but impact again is man made activities in unsafe geological locations

    But dams whose life is over can also trigger flash floods ...and they can be 100% man made.??????

    Posted by: Anonymous | 7 years ago | Reply
  • Floods are natural

    Floods are natural geological phenomenon ...which happens weather man interferes or not .....but the impact on human civilization is man made ...because we have forgotten to live in tune with nature...and are arrogantly occupying places for habitation which were geologically considered unsafe for human settlements...
    Flash floods of encroachment2010 in Leh which claimed 210 lives and other places are perfect examples
    I was myself trapped in 2010 floods.. and later i devised a mechanism of Reservoir rupture mechanism to understand the flash flooding event ....
    No plantation ....uniform heavy rainfall ....selective destruction in few channels .....traditional habitats SAFE......new habitat s in unsafe geological locations destroyed

    Flash floods is 100% natural geological phenomenon triggered by rains but impact again is man made activities in unsafe geological locations

    But dams whose life is over can also trigger flash floods ...and they can be 100% man made.??????

    Posted by: Anonymous | 7 years ago | Reply
  • Uttarakhand and Union

    Uttarakhand and Union Governments,please look into the issues raised in the article.
    Dr.A.Jagadeesh Nellore(AP),India

    Posted by: Anonymous | 6 years ago | Reply
  • You and all not giving good information please give good information

    Posted by: Man Is Also Causes For Floods Give Good Information Like Points Please | one year ago | Reply