Summary The design of experiments which are being laid out to investigate the hydrological effects of wattle plantations in the Natal Midlands is described. The effects that wattle plantations in the Natal Midlands may have upon streamflow and water supplies constitute an important question that is coming more and more into prominence. On the one hand public allegations have been frequently made that these plantations completely dry up water supplies in the vicinity, while at the other extreme one prominent grower has gone into print to the effect that he has observed “springs running out of wattle plantations where none were ever seen before” (cited by Wicht, 1949). As in the case of the burning versus non-burning controversy that has agitated growers, there is a lack of experimental evidence. At the beginning of 1953 the Management of the Natal Tanning Extract Company Ltd. accordingly approved a project of hydrological research designed to clarify the problem. Research on the effect of vegetation on watersupplies may be either hydrometric or physical. In the former case the actual yield of water from a series of catchments is observed and measured, the catchments being treated in different ways. In the alternative, studies are made of the effect of vegetation on net rainfall, infiltration, run-off, soil moisture and so on with the object of deducing effects on water supplies. Hydrometric research must be carried on for many years before results can be obtained, as the catchments must first be gauged for a number of years before afforestation takes place in order to calibrate their behaviour under the previous conditions. After that there is further delay while the tree crop comes to maturity. In the case of wattle we are dealing with relatively a very short-term forest crop but, even so, cannot expect to obtain results from such a project for at least fifteen years. Physical research is far less laborious and could be expected to give at least some results in only one season. We have decided to follow both lines of investigation and the projects embarked upon are described below.