Agri-structure as Infrastructure

Flood Alleviation Control by ‘Roughness’ as well as by ‘Form’

This article arises from a recent  London Forum seminar and seeks to raise awareness of engineered landuse (‘roughness’ control) to mitigate the effects of extreme flooding.  The approach was touched on by the ‘Local-Strategy’ panel, in particular by the NFU,  but, despite questions from the audience,  no financial framework was put forward to link the COST of such rural work with the flood alleviation BENEFIT accruing.

Flood Management is effectively dynamic control of water:  the two primary levers of shallow water hydraulic control are elevation and roughness.   In analysis of such hydraulic flow, elevation (and slope) assign force to flood flow, with resistance (roughness) adjusted supportively to achieve solution (of analysis) and calibration. Whilst both parameters are ‘given’ by our natural environment, for strategic/built schemes it is more usually the former which is developed for community and private resilience (levees, dams, structures, etc).

But is it defendable to focus FRM on this expensive (built, smooth and often ugly) ‘Form-based’ approach, when the natural sibling ‘Roughness’ is delegated to a mere reactive role?  Roughness grows naturally. It forms not only usefully porous capital assets, but also puts down roots to achieve self-maintenance. Roughness can be cropped for food and energy. Whilst it has to be managed and dense for good control, it does not have to be built.

So argument here is in defence of ENGINEERED roughness both for community benefit and for resilience (when river conveyance becomes over-zealous as in flood);  not forgetting that rivers are primarily  conveyors of good water which for the most part is benign – good for both life support and wellbeing.

The November 2015 WEETF seminar certainly re-examined problems and priorities of flood management, and a few (NFU) slides did indeed illustrate the helpful role landuse can have in this respect.  However the potential of the monetary mechanisms to exploit landuse good practice was not explored. In particular:-

  • Inclusion of FRM works in RDP’s (& Glastir)
  • CAP Pillar 2 definition of Flood Alleviation works as community development gain
  • (Urban corridor) Insurance sponsorship as best practice
  • Urban local authority sponsorship as best practice
  • Water Supply Industry obligation (particularly of catchments resourcing urban clean water)
  • The new Somerset Rivers Authority financial framework as good practice
  • Drainage Board/District extension (to link green storage with managed rural drainage)

It would promote the several references to the multiple benefits of strategic vegetation (pollution control, wildlife corridor, flood alleviation, water quality, etc),  if effective monetary mechanisms  could be identified which link Rural Development COST with downstream community BENEFIT . For example, in many catchments, the inverse of the Somerset formula could be applicable,   ie  the concept/mechanism of  ‘negative‘ levy (aka  RDP grant) for landowners who deliver community FRM gain.

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