Southeast Spain has a semiarid climate with highly variable rainfall from year to year. Global warming scenarios predict a decrease in rainfall in future and land-use changes may also alter run-off regimes. Water deficit has meant that various practices of floodwater farming have traditionally operated in valley floors. However, flash floods in the valley floors can also be dangerous and damaging. Many of the boqueras and other floodwater irrigation systems have been abandoned. The effects on the hydrological regime of the channel are calculated. These structures and water management practices could have an effect on the magnitude of low–moderate peak discharges, but are insignificant in high flows. Modern channel and flood management employs check dams, but these are frequently destroyed in moderate–high flows. Alternative strategies of channel management need to be sought and the use of vegetation cover to dissipate flood peaks and to reduce erosion may offer one possibility. Copyright © 2002 John Wiley & Sons, Ltd.