A parametric rainfall-runoff simulation model is used with point rainfall and daily potential evapotranspiration data to predict flood volume and peak rates of runoff for small drainage areas. The model is based on bulk-parameter approximations to the physical laws governing infiltration, soil moisture accretion and depletion, and surface streamflow. An objective fitting method is used for determining optimal best-fit sets of parameter values for the data available for use in predicting flood peaks for three case studies. Errors of prediction result from both errors of rainfall input and lack of model equivalence to the physical prototype. These two sources of error seem to be of the same order of magnitude for a model of the level of simplicity of that presented. Major gains in accuracy of simulation will require improvements in both data and model. The limit of accuracy of prediction of flood peaks by simulation with a bulk-parameter model using a single rain gage seems to be on the order of 25 percent.