ADCP를 활용한 제주도 자연하천의 평균유속분포 추정과 유량산정

Abstract

ADCP flow measurement data were collected between July 2011 and June 2015 from perennial streams in Jeju Island including Jungmun-stream, Gangjeong-stream, Akgeun-stream and Yeonoe-stream. Parameters that take part in Chiu's 2-dimensional velocity distribution were predicted and verified. In addition, flow was calculated and analyzed using the velocity distribution equation and conventional depth-averaged conversion factor (0.85) and the surface velocity based on ADCP measurement and mean velocity regression coefficient. The results are as follows. Based on the analysis of sectional mean velocity distribution by ADCP and computation of parameters for Chiu's 2-dimensional velocity distribution equation, the entropy coefficient (M) was 3.1136 for Jungmun-stream, 3.3459 for Gangjeong-stream, 2.7413 for Akgeun-stream and 3.597 for Yeonoe-stream. The iso-velocity curve parameter ( _urf ) was 0.4620 for Jungmun-stream, 0.4375 for Gangjeong-stream, 0.4124 for Akgeun-stream and 0.4200 for Yeonoe-stream. Flow sensitivity of the entropy coefficient (M) was evaluated within the input range of 1∼2 in the range of 1∼10 for all streams, and flow change rate was about 19%. Flow sensitivity of the iso-velocity curve parameter was evaluated within the input range of 0.1∼0.2 in the range of 0.1∼1.0, and flow change rate was about 47%. Maximum velocity (u_max) and mean velocity (u) of each stream based on ADCP measurement data, the entropy coefficient (M) and the iso-velocity curve parameter were applied to Chiu's 2-dimensional velocity distribution equation. The value between surface velocity (u_surf) calculated using the velocity distribution equation and surface velocity of ADCP was 0.9267 for Jungmun-stream, 0.9242 for Gangjeong-stream, 0.8677 for Akgeun-stream and 0.8988 for Yeonoe-stream, showing extremely high correlation. The mean error rate of flow based on ADCP velocity data was 16.01% with flow calculated using the conventional depth-averaged velocity conversion factor (0.85), 6.02% with flow calculated using the surface velocity and mean velocity regression factor, and 4.58% with flow calculated using Chiu's 2-dimensional velocity distribution equation. If surface velocity by a non-contact velocity meter is calculated as mean velocity, the error rate can be increased for large streams in the inland areas of Koera. Therefore, flow can be calculated more precisely by utilizing the velocity distribution equation that accounts for stream flow characteristics and velocity distribution instead of the conventional depth-averaged conversion factor (0.85). A future study is required to examine the process of predicting parameters related to turbulent flow characteristics of flood and calculate flood volume in natural streams, and an additional study needs to quantify parameters related to flow characteristics and velocity distribution of independent streams.