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Flood Resilience Measures

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Flood Risk Management

Flood risk management is a top priority, exacerbated by the perception that flood risk has increased during the last two decades in many regions.

There are two hypotheses for such changing patterns:

  • Changes in climate, e.g. the sequencing of extreme wet and dry periods, leading to a greater magnitude and/or frequency of hydrological extremes (Huntington 2006); and
  • The effects of land management in changing the relationship between extreme climate events and hydrological extremes (O'Connell et al. 2007)

It is difficult to envisage interference with climate change on a regional scale but changes in land management may sometimes be feasible. However, integrating information from weather and climate impact models will enable the design of short-term strategies to risks from storms. There is much emphasis on management of the land to reduce storm runoff, harnessing peat lands and wetlands to store water and expanding salt marshes to reduce wave energy on coastal defenses. Alongside this, is the concept of identifying areas suitable for inundation and water storage to prevent flooding elsewhere.

10FloodingAustralia.jpgField research has shown that peak discharge is sensitive to the soil characteristics, and in particular the dynamics of overland flow is thought to be driven by the saturation of the upper few centimeters of the soil. This leads to the notion of altering or controlling the vegetation in susceptible river basins and changing agricultural practices. Evidence that intensive farming leads to increased runoff rates has been established, with fast, well connected flow paths clearly contributing to the 'muddy floods' observed at the local scale. As pastoral fields are often heavily compacted, infiltration rates and capacities are lower and overland flow is more likely (Gonzales-Sosa, 2010).

Deciduous woodland land cover results in a lower peak flow than coniferous forestThis may be caused by both the soil and vegetation characteristics of these two types of woodlandDeciduous trees produce large amounts of leaf litter which improves the infiltration rate of the top few centimeters of the soil (dynamic layer in model), meaning that rainfall is partitioned into the slower sub-surface pathway resulting in lower peal flowsFurthermore, deciduous trees have larger leaves, with higher interception capacities than the needles of coniferous forestsThis means that more rainfall is stored within the canopy of a deciduous forest than one consisting of coniferous trees.

Nevertheless, since there is in fact little variation with each category of land coverit seems that the soil characteristics are the most important factor in driving flood risk rather than the vegetation characteristics and emphasizes the importance of care in tillage practices to avoid compaction.

In the long term, catchment research will critically inform radical new approaches to flood-management based on the adaptation of natural systems. Examples of this are field experiments recently conducted in NE England whereby targeting runoff in fields and farm ditches and diverting the flow via bunds, diversion structures in ditches to spill and store high flows and constructing ‘Beaver dams’ placed within the channel and riparian zone management to retain the water to allow natural seepage to occur.

Further Reading

1. Flood Resistance & Resilience (United Kingdom)

2. Flood Resilient Repairs and Resistance Measures

3. Flood Resilience for UK Infrastructure

4. Bringing Flood Resilience into Practice

Flood Risk - P.B. Sayers
 Publication Date: Jul 2012 - ISBN - 9781780404561

Water, Wastewater and Stormwater Infrastructure Management - Neil S. Grigg 
Publication Date: Jul 2012 - ISBN - 9781780400334

Flood Risk and Social Justice - Zoran Vojinovic and Michael B. Abbott 
Publication Date: Mar 2012 - ISBN - 9781843393870

References

O'Connell, P. E., Ewen, J., O'Donnell, G. and Quinn, P. F. (2007) 'Is there a link between agricultural land-use management and flooding?', Hydrol. Earth Syst. Sci., 11, (1), pp. 96-107.

Huntington TG, 2006, Evidence for intensification of the global water cycle: Review and synthesis, Journal of Hydrology, 319, 83-95.

Gonzalez-Sosa E, Braud I, Dehotin J, Lassabatere L, Angulo-Jaramillo R, Lagouy M, Branger F, Jacqueminet C, Kermadi S, Michel K; (2010); Impact of land use on the hydraulic properties of the topsoil in a small French catchment, Hydro. Process. In press.

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