POTENTIAL IMPACTS OF CLIMATIC-CHANGE AND OF SEA-LEVEL RISE ON THE YIELDS OF AQUIFER, RIVER AND RESERVOIR SOURCES

Using regional statistics of daily rainfall, a simple water-balance mo del was employed to generate runoff sequences with which to simulate t he yield/storage behaviour of reservoirs in south-east England, in nor th-west England, and North Wales. Similarly sequences of recharge to a n unconfined aquifer in eastern England were the basis of deriving its yield/storage behaviour. Then, taking scenarios of the year 2030 rain fall and evaporation, provided by the University of East Anglia's Clim atic Research Unit, reductions in yield were calculated to be 5-15% be low present-day values. For direct supply reservoirs, greater percenta ge reductions in yield were found to apply to the south-east region, a s compared to the north-west. The results from the aquifer example are interpreted on a novel basis which allows an immediate comparison wit h the surface reservoir examples. Coastal sea-water intrusion was mode lled for three common geological conditions (i) the Grimsby Chalk (con fined), (ii) the Brighton Chalk (unconfined), and (iii) the Otter Vall ey Sandstone (unconfined). In all three cases the effect of a possible 0.6 m rise in mean sea level was shown to have only a marginal effect on sustainable yields, which reduced by about 1.5%. Estuarine fresh-s alt water interfaces are important to the abstraction regime of freshw ater intakes in the lower reaches of rivers. The effect of a 0.6-m sea -level rise on the saline interface location at high tide was evaluate d by hydrodynamic computational models. Only a minor inland shift of t he interface was found, less than 800 m in the Thames tideway and less than 500 m in the Lune estuary. The Severn estuary is exceptional in having its saline interface move 3.5 km landwards for the same 0.6-m r ise in mean sea level.