Can GIS Discover Footbridges?

BBC’s ‘Human Planet: Rivers – Friend and Foe’ episode had a segment on Maghalaya, India,  possibly the wettest place on earth. One year they had a record of 25 meters of rainfall in one year. Of course, this all happens during the monsoon season, leading to unbelievably flooded and fast flowing rivers.  In order to deal with the swollen rivers, residents grow and maintain ‘living bridges’ – strangler figs whose roots are encouraged across the river to establish there. These roots are maintained and curated across many lifetimes to become bridges that can withstand the raging torrents, growing stronger over time.

Wahthyllong 'living bridge', Meghalaya (copyright Timothy Allen)

Wahthyllong ‘living bridge’, Meghalaya (copyright Timothy Allen)

Wahthyllong 'living bridge', Meghalaya (copyright Timothy Allen)

Wahthyllong ‘living bridge’, Meghalaya (copyright Timothy Allen)

'Living bridge' maintenance, Meghalaya (copyright Timothy Allen)

‘Living bridge’ maintenance, Meghalaya (copyright Timothy Allen)

What I find fascinating is that it seems like care of these trees is a familial affair, with individuals passing down knowledge and duty of care for trees to their family members. However, these bridges are public property, with all members of the community contributing to their upkeep and able to cross and make use of this space.  These community bridges are public spaces, and are arterial links throughout the region permitting the flow of people, goods, and knowledge.

Tourists crossing a single beam foot bridge over the flooded Mekong River, Laos

Tourists crossing a single beam foot bridge over the flooded Mekong River, Laos

In Laos, I saw more ad hoc foot bridges used to cross the flooded Mekong river – single branches lashed together for people to shimmy gingerly across from island to island.  These bridges maintained lines of communication open around this flooded environment in the same way as in Meghalaya.

Private wire footbridge over flooded Mekong River, Laos (copyright Timothy Allen)

Private wire footbridge over flooded Mekong River, Laos (copyright Timothy Allen)

The BBC ‘Human Planet: Rivers – Friend and Foe’ episode also featured the flooded Mekong, and showed a Laotian fisherman using a more modern wire cable bridge to cross onto a private fishing island.  This is very close to where my wooden footbridge photo was taken, and in the same season as well, though my footbridge experience was obviously at a quieter part of the river.

This Laotian wire bridge was not public property though, only the individual fisherman who had erected it was allowed to cross to his private fishing island.  Unlike in Meghalaya, the footbridges in Laos are not always public spaces.  Does this have to do with the fact that the bridges are more temporary?  Or does it have more to do with the fact that the footbridges in Laos cross to private property?

These stories of small organic footbridges raise the question of how we are able to track the movement of people in wet, riverine environments in the past.  I think most people assume that rivers will be channels of transportation, with people and goods moving up and down the river more easily than on foot along the banks.  However, people would also have been criss-crossing the rivers to access resources and to visit other communities on the opposite bank.

It occurs to me, that footbridges are likely lost community spaces in the archaeological record.  Made of organic materials, occasionally long-term, but often expedient constructions, the location and use of these footbridges would be nigh-on impossible to locate.  GIS is often used to calculate least-cost paths through a landscape, but I don’t know of any uses where ideal river crossings on foot have been identified (anyone?).  What about on rivers where conditions change dramatically from one season to the next?  Presumably data could be used for different seasonal conditions, and various potential crossing locations could be identified. As in the Laotian wire bridge though, people will find ways of crossing rivers at unideal locations, if the destination is important enough.  How could we identify such potential locations in a prehistoric context?

Changing climatic conditions worsen the situation.  The Konya plain in Turkey is now a vast arid environment, and modern farming practices have caused the water table to drop dramatically.  However, during the Neolithic the area would likely have been swampy, with local rivers and streams criss-crossing the alluvial fan.  This is exactly the type of environment that would have lead to the creation of footbridges and pathways, with the changing course of the river requiring residents to cross watercourses regularly.  Did they ford them?  Did they use footbridges?

The archaeological identification of routes, roads, and paths is difficult anyways.  Landscape archaeology often identifying potential routes, or presumed routes, based on known destinations and the ‘least cost route’ between them.  Are communities and people always this logical though?  While the GIS calculated ‘least cost path’ might be alongside the river, unbeknownst to archaeologists, the community might have constructed a footbridge up- or down-stream that would have completely changed the route used on a day to day basis.  The identification of this community public infrastructure would be key to better understanding past landscapes and enhancing our GIS models.

Even if we do identify potential crossings, how do we discuss the rules of use?  Which crossings are public?  Are there private crossings?  Do you think bridges can ever be private space, or are they simply tacitly private due to the destination being private?

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