a Sturdy on the Mean Velocity Distributionof Natural Stream Using Adcp

In the process of converting the observed flow to the flow rate, it is necessary to consider the suitability and reliability for applying the depth-averaged flow rate conversion factor. In particular, studies on simulating the flow velocity distribution of the river cross section due to insufficient actual flow velocity material are insufficient, and it is necessary to consider the accurate flow measurement of the natural river and the calculation process of the river flow rate.

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 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 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 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 and mean velocity of each stream based on ADCP measurement data, the entropy coefficient and the iso-velocity curve parameter were applied to Chiu's 2-dimensional velocity distribution equation. The value between surface velocity 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 Korea. 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).