To study influences on the downstream, and the Gunsan harbor by setting up estuary of the Gumgang, available data which were collected from the measuring stations which were established within the river basin of which results attained are as follows: 1. The discharge can be calculated as the relationship between the discharge and precipitation in the basin is $R=4{ imes}10^{-4}p^2$ or R=P-600 2. The discharge flow in to small resevoirs in the basin can be estimated as $QR=QSfrac{PR-600}{PS-600}(frac{AR}{AS})$ 3. This daily average discharge at Kongju is 31% less than the during maximum probable discharge and that in Okcheon is 48% less than the daily maximum probable flood. 4. The maximum probable flood from the small stream in the basin can be estimated by a $Q=82.45A^{0{cdot}464}$ 5. Sediments can be computed with Qs (suspended load)=1.41 $Q^{1{cdot}42}$ and Qb (bed load)=165.2 $Q^{0{cdot}705}$. 6. By setting up the specific estuary the tidal movement will be reduced to 93.6% on the average and the sedimentation is reduced to 96.0%. Upon review of overall analysis, the dead wate level of estuary of Gumgang will completely sedimented in next 30 years, therefore, the dredging work at Gunsan harbor is reduced to 73.6%, it is considered that life length will be extended about 52years taking account the existing condition.