소하천유역의 퇴사량 변화 연구
(A) Study on the sediment variation of small stream basin
소하천유역 퇴사량 small stream basin;
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The characteristics of sediment phenomena and the sediment variation by the extension of channel box installed at the studied for Bi-Wol stream, a small stream in Sunchon area. The design frequency of the steam basin was checked with 5, 10 and 25 year and the concentration time was estimated as 15 minutes. The design floods were estimated as 4.20, 4.68 and 5.58 ㎥/s, respectively. And the hydraulic analysis for the channel box extension using an hydraulic simulation program named HEC-RAS showed minor velocity variation and detention time increase about 2.4 sec. The sediment yield of the basin was estimated as 496.7 ton/yr using Dendy-Bolton method, channel character method and the estimate for Sum-Jin river basin. The sediment load was estimated as 15.1 ton/yr using Yang formula selected from the various sediment load formulas in the facility criteria of small stream, grain size analysis and hydraulic analysis. The specific sediment yield was checked with various method by the application of sediment delivery ratio and sediment trap efficiency to the sediment yield. With the consideration of sediment delivery ratio 15∼34% and trap efficiency 0∼39%, the sediment deposit until February 2002 was too much as the accumulated sediment and the fact was checked by the field investigation as the results of stream barrier collapse. From the feasibility test of settling basin installation, a simple storage reservoir was suitable to reduce the sediment deposit in the channel box. A storage reservoir located at the close upstream of the box and sized with B × L × H=8.0m × 8.0m × 8.0m was examined. The storage of this reservoir needs 2 year period dredging with the annual occurrence assumption of 25 year frequency flood. To check the influence of reservoir installation to the channel flow, a hydraulic numerical model was applied for the typical flow with 1 day continue 25 year frequency. The stage increase of 5 cm and velocity decrease of 0.02 m/s were appeared at the channel section from the channel box to 32 m upstream site. So, it can be said that the reservoir will not make any hydraulic problem to harm the sediment control of Bi-Wol stream.