Tuesday 21 May 2019

Only (some of) her rivers run free

Let nobody doubt that free-flowing rivers are highly politicised. Reflecting on the big ticket items . . .
  • The Colorado River that carved the Grand Canyon now reduced to a dribble the fails to reach the Gulf of California
  • The Aswan Dam that drowned the Abu Simbel temple complex
  • All those Army Corps of Engineers levées on the Mississippi that have given back 500,000 hectares of Louisiana to the sea.
Or the Irish ecocrumps:
  • The Ard na Crusha hydroelectric dam that blocked the Shannon Ireland's longest river
    • and Bord na Mona stripping the adjacent bogs to allow millions of tonnes of sediment to clog the river
    • and Athlone to establish the town's landfill on the callows below the town
  • The Barrow Navigation that changed the river's natural tumble into a series of steps [Clashganny Lock R] to provide an additional energetic burden on spawning salmon
    • there are now no eels on the Barrow
. . . you'd think that humanity had changed, changed utterly the running of fresh water across the entire planet. Running is the appropriate word because rivers run, yes, but we run businesses also; and we have looked on rivers as things to be used and exploited to suit human convenience and profit. Let the chips for the {alder | bacteroides | caddis flies | damselflies | eel | figwort | gudgeon | heron . . .} fall where they may.

Now a multinational group led by geographers from McGill U, Montreal have carried out a global inventory of "free-flowing rivers" and published their work in Nature. It's paywalled but the abstract and pixellated figures are available to all. It's not just the goddamm dams that inhibit free-flow:

  1. dams, weirs and locks are just the longitudinal source-to-sea element. 
  2. There are also the levées, and berms and quays which constrain lateral flow - natural rivers spill out over the banks to inundate callows, flood-plains and riparian fields and forests. 
  3. Thirdly, there is a vital dynamic between groundwater, surface rivers and the atmosphere: oxygen maxes out at 14 ppm in cold water raise the temperature to 15°C downstream from a factory and there's a third less bio-available oxygen. 
  4. Finally, rivers are dynamic through time: thee Aughnabriskey at the bottom of our fields was rocks and puddles during the last hot summer but can become a raging torrent 2m deep after a significant spill of rain. Callows flood in the winter, depositing silt [good] but compressing the soil [ungood] with the weight of water. And there we go again: making a value judgement on a natural process to decide that it is [good] or indeed [bad] for us.

The McGilliQuanties have spent some time defining terms and applying weightings to their base metrics so they are comparable across very different rivers from 10km streamlets to the mighty rivers that feature in Sporcle quizzes: including Ob, Lena, Parana. Someone has to decide if a navigational lock is more or less inhibitory of free-flow than a mile of levée or a tonne of sediment retention. They have reduced the multivariate multidimensional statistics of free-flow status to a single value the connectivity status index CSI and then applied that to every reach of every river longer than 10km. A reach is stretch of river between two confluences (where a significant lateral inflow occurs). I guess its a feature of the granularity of the analysis to find that short (10-100km) rivers are mostly [97%] free-flowing, while half the long (500-1000km) rivers are constrained [56% free-flow] and very long rivers (>1000km) are mostly not free-flow [only 37% still free]. It takes just one Hoover [L] or Aswan or Three Gorges or Oroville to destroy the free-flow status and the longer the river the more places humanity can tromp in with steel and concrete. Dam removal prev.

Sounds better to me than I expected from prior ignorance. Then again, a lot of the remaining free-flowing rivers debouch into the Arctic and they are only being left alone because nobody lives there. But watch out for the Congo, when they can stop killing each other in rolling civil wars in Central Africa, then the human population will grow and it's only a matter of demographic time before some bright spark proposes a prestige dam for power. What's upstream from the Aswan Dam? Ethiopia is upstream and Ethiopia  wants its own dam. Tomorrow: The Water Wars

1 comment:

  1. The Okavango Delta is being threatened by proposed hyrdo plans in Zambia and many of the rivers which feed into it from the countries up north have their own challenges which are impacting the amount of water along the route and the delta itself. Increase in the population of Luanda is also impacting the delta. We are so unbelievably careless.