To investigate the cause of overflow in the torrential stream, the estimated peak flow of run-off and the maximum tarring capacity of the stream were measured at the upstream of Samsung-cheon located in Kwanak Aboretum during July, 1987. The results obtained from this study could be summarized as follows 1. The surveyed catchment area was 477㏊, which was 116 of the designed area (410㏊) by the plan. 2. The maximum rainfall intensity measured was 99.5㎜/hr and was almost same as the designed intensity (100㎜/hr) . 3. The surveyed run-off coefficient was 0.672 that was about twice as much as designed one(0.35). 4. The surveyed peak flow of run-off was 88.59㎥/sec, 222% as large the designed one(39.9㎥/sec). 5. The designed cross-sectional area of the stream was 17.25㎡, which was 68% of the designed one 125.43㎡. 6. The surveyed hydraulic mean radius was 0.94m, which was shorter than the designed one(1.28m). 7. The surveyed mean stream-bed gradient(0.998%) was almost the same as the designed one(1.00%). 8 The surveyed maximum velocity of flow passing through the stream was 2.87m/sec, 78.0 of the designed one(3.68m/sec). 9 The surveyed run-off capacity of the stream was 49.51㎥/sec, 53% of the designed one (93.5㎥/sec).