It has long been assumed that the benefits of collecting streamflow data are greater than the costs of collection. However, factual information on the benefits of data collection programs are not available. To assess the value of one aspect of data use, the reduction in uncertainty of design storage size and the associated capital cost was determined for a range of lengths of available data. The results were applied to the 500 station data collection network in New South Wales, Australia to show that for this single use of data the benefits greatly exceed the cost of collection. ¿ American Geophysical Union 1993