Current analysis techniques use averages and subjective parameters in calculation, completely ignoring extreme, very rare and rare events. Recent incidents demonstrate that storms can and will occur regularly, anywhere in lowland Britain. Large storms invalidate parameters such as evaporation, soil absorption, aquifer re-charging and catchment characteristics.
A far more reliable technique, calculating a maximum probable flood using probable maximum precipitation, would eliminate reference to return-periods.
This simplified analysis would determine a maximum flood level that infrastructure and sensitive conurbations could be protected against.
Current flood maps could then be adapted to provide “probability contours” between the maximum flood and annual river levels in order that real risk can be ascertained. Solutions using this approach are not susceptible to climate change, as precipitation contributing to such flooding is simply more frequent.
David J. Yendall (M), 1 Gayle Moor Close, Ingleby Barwick, Stockton-on-Tees, TS17 0QL