We have a pond in our back garden, which we have just had excavated, its
lined with fairly thick London clay, It use to hold water in as it was but
usually dried up in summer, although it hasn't dried up yet. We've had it
doubled in volume, about 10m by 10m, it is fed by rain water from the roof
of our house. Once its filled up is it likely that it will stay fairly full
give or take a few feet evap, or will it fall to the water table level which
is quite low....