Estimation of Conversion Coefficient for the Surface Velocity of Irrigation Channel

Abstract

The continuous flow velocity monitoring has become a difficult and expensive task in hydrological survey due to unpredictable rainfall patterns. Therefore, the velocity measurements using a non-contact type flowmeter is more effective and easy to use. The generally used average velocity conversion factor 0.85 does not take into account the regional characteristics such as curves of a river, bed materials which consequentially affects the vertical flow characteristics. Therefore, considering the those characteristics of irrigation channels of two small reservoirs (Ssangam and Hangye reservoir), results showed that the gentle bed slope of irrigation channel of the Ssangam reservoir, has a velocity conversion factor of 1.06 and the depth-averaged velocity of V0.6, was measured to be higher compared to the surface velocity. On the other hand, velocity conversion factor of 0.83 was computed in case of Hangye reservoir with a relatively sharp bed slope, which is similar to the generally used velocity conversion factor of 0.85. This shows that the bed slope is the dominant factor in affecting the depth-wise velocity characteristics of a waterway.