The purpose of this study is to inquire and analyse the relation between traveltime (Tc) and watetshed physical characteristics surveyed such as river length (L), Lea, river main slope (s), base length of time area diagram, and storage constant (k). The results obtained in this study are as follows. The average widths of watersheds were with the range from 4.6 kilometers to 16.7 kilometers. The shape factors of main stream ranged from 0.08 to 0.37. The average slopes to main 8tream were within the range of 1.7-5.5 meter per kilometer. The relation between the base length and traveltime from S. C. S. method, Rational method, and RZIHA+KRAVEN method were derived $Tc=0.524{ imes}1.35^c$ (r=0.98), $Tc=0.628{ imes}1.339^c$, (r=0.98), $Tc=0.667{ imes}1.342^c$ (r=0.97). The base length of the time-area diagram (c) for the IUH was derived as $c=0.9(frac{L.L_{ca}}{sqrt{s}})^{0.35}$ and correlation coefficient was 0.98 which defined a high significance. The storage constant K, derived in this study was $K=8.32+0.0213{frac{L}{sqrt{s}}}$ with correlation coefficient (0.96). The relation between storage Constant and conventional formula were figured out $Tc=0.0003{ imes}3.323^k$ (r=0.97). $Tc=0.00045{ imes}3.268^k$ (r=0.99) and $Tc=0.0004{ imes}3.26^k$ (r=0.963). The base length (c) and storage constant (k) of time-Area Diagram were very important parts that determined traveltime for flood events. In the estimate of travel time for predicting flood volume, the formula of $Tc=0.524{ imes}1.35^c$ that would be available to apply the Nak - Dong river watershed area and homogeneous watershed characteristics was found.