Reed, D.W. 2002b. Extra information for flood frequency estimation. Proc. 3rd EGS Plinius Conf. Mediterranean storms, Baja Sardinia, October 2001, 333-338.
Flood frequency estimation is inherently uncertain. To reduce uncertainty, the adopted flood frequency curve must be consistent with all that is known about the flood frequency behaviour of the river. Extra information comes in many forms, including: gauged flows & levels, flood marks on structures, contemporary accounts of historical events, and palæological markers. On permeable catchments, groundwater levels present additional data. Meteorological information is also to be prized, although the depth & duration of flood-producing rainfall are famously difficult to interpret in terms of flood rarity. After discussing different kinds of ancillary information, the paper concludes with a challenge. Hydrologists are now using digital catchment data more extensively, and it will soon be possible to produce flood estimates at sites throughout a river basin. Can methods be developed to ensure that physically meaningful relationships exist between flood frequency estimates at each site?