While recent floods in cities around the world have raised the profile of the ‘sponge city’ concept, looking ahead perhaps the whole future of rivers should receive more attention. As with other natural features the overwhelming approach of contemporary ‘development’ up to now has been to emphasise hydro power, flood-control and navigation, while the value of biodiversity and the natural features of rivers such as meanders have traditionally been neglected. Indeed, the potential benefit of annual flooding for rejuvenating natural soil fertility, well understood in some parts of the world, has been ignored. The whole subject needs a complete rethink. The UN Water Conference in March 2023 was ‘hailed as a once-in-a-generation opportunity to accelerate progress towards universal access to safe water and sanitation by 2030’. As this indicates the emphasis at the international level is very human-centred, with the natural world, including concerns about biodiversity, left trailing somewhere behind. Whether much was achieved at this ‘once-in-a-generation opportunity’ is an open question. I want to suggest that some principles might influence overall planning and futureproofing of rivers worldwide.
Protecting watersheds from unnecessary erosion must become a high priority. As I saw in Thailand twenty years ago (see my documentary film Greening of Thailand) the replacement of natural forest on watersheds can have catastrophic effects downstream. Not only do young or inappropriate trees contribute to ground instability, but increasing snow melt in many mountain areas has uncovered wastelands of unstable rock debris; the sooner these areas are vegetated the better and the natural flora of each area will be the most appropriate. Planting inappropriate (usually non-native) trees in many places has created environmental problems such as soil instability and added fire risk quite apart from the disruption of the natural flora and fauna.
With climate change leading to more disruptive weather patterns, the potential of river systems to hold additional water and regulate the flow even under extreme storms must be maximised. In upper sections of some European rivers, like the Danube, riverbank levees have been breached to allow more natural flow and for excess water to flood low-lying areas. In countries where many rivers have been straightened and the flow accelerated, authorities are now recognising that this approach is counterproductive; restoring the natural flow involving meanders is now preferred. Building on floodplains doesn’t make sense when natural flooding is likely to become more prevalent. In many countries humanity depends on harvesting river animals, especially fish, as a major protein source; restoring the natural flow will certainly enhance natural fish populations where their life cycles have not been impeded by hydro-electric dams built without mitigating structures such as fish-ladders.
Even naturally flowing rivers will not support natural biodiversity if the water is polluted. River pollution is a disgrace in many countries; satellite pictures have shown that a majority of North American rivers have changed colour in the last few decades, while rivers flowing through all the world’s industrial zones are seriously polluted – all examples of an economic model that allows polluters to escape payment for harm they cause downstream. Estuary areas are highly productive biodiversity hotspots, but they are particularly susceptible to pollution originating upstream.
While many big cities are built at river mouths the question of sea-level rise is alarming many urban planners. Tidal barrages with the dual purpose of protecting low-lying areas and generating renewable power are potentially of enormous benefit. As with some other renewable energy schemes the capital costs have so far deterred construction (such as the abandoned tidal lagoon project at Swansea Bay, South Wales) although functioning tidal power plants are operating in Brittany, France, and Sihwa Lake, South Korea, while there is a small pilot scheme at Eday in the Scottish Orkney Islands. There is no reason why sensitive design should in any way limit biodiversity considerations around these schemes. The London Barrage on the River Thames was built in the 1980s but doesn’t take advantage of the tidal flow to generate electricity, although a future replacement surely will.
As the main source of marine plastic waste is river outflow, I suggested in a previous blog (#6 Plastic Waste) that perhaps some means of intercepting plastic at the mouth of rivers (and of tributaries upstream) should be developed everywhere. Hopefully the construction of barrages could bring this additional benefit.
Finally, the natural outflow of rivers in tropical regions is often characterised by large areas of mangrove swamps and forests. These are of increasing importance protecting coastlines from storm surges and erosion as well as being rich in biodiversity, providing protected spawning areas for may coastal species. A worldwide moratorium on the conversion of mangroves should be instigated, and while some countries like Nigeria and even Egypt are showing the way I suggest that an international fund for mangrove replanting be set up. More than that perhaps a comprehensive initiative, spearheaded by UNEP should bring rivers into focus as a major element in the campaign for the UN Sustainable Development Goals.
By Edward Milner
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