For ephemeral streams of the Southwest, runoff producing rainfall typically covers only a part of the watershed area. Conventional unit hydrograph techniques are not well adapted to the synthesis of hydrographs of runoff for such watersheds and flood routing methods must be modified to consider transmission losses and abrupt translatory waves. Hydrograph rise time was used as the time parameter for developing the dimensionless hydrographs. Average hydrograph rise time was found to decrease with increasing watershed size for the size watersheds analyzed. Dimensionless hydrographs developed in the paper were found to have a family of recessions based on antecedent channel moisture and the distance of dry streambed over which the runoff has traversed. Total runoff volumes for simple runoff events were found to be significantly correlated with the peak discharge for the event.