The Ministry of the Interior and Safety has developed a small stream flood warning system to reduce damages to small streams, which are estimated to be about 43% of total streams damages. This system, which was developed using a numerically-based nomograph to estimate discharge and depth, was based on rainfall estimates obtained by the McGill Algorithm for Precipitation Nowcasting by Lagrangian Extrapolation (MAPLE) because the small streams exist in unmeasured basins. Before implementing the small stream flood warning system, a study was performed to test its accuracy in estimating measured data obtained from a test basin during 2016 and 2017. Because the results of that study showed that the discharges and depths underestimated the measured data, this study was performed to establish a new nomograph using measured depth and discharge data in the test basin for two rainfall events in 2016. The evaluation results show that the new nomograph correctly represents the measured depth and discharge, and it can be used for enhancing the small stream flood warning system.