Bridge failures are caused by various reasons, but the main reason is caused by scour at bridge pier. Debris accumulation on bridge piers is an ongoing problem nowadays. The study of debris accumulation on bridge piers has done by many researchers, but not any researches have done on debris accumulation on sacrificial piles, yet. The aim of this study is to estimate the effect of debris accumulation at sacrificial pile to bridge pier scour. Experiments were performed to understand the changes and interaction of scour over a range of flow depths and velocities in various cases like single pier cases, sacrificial piles cases, debris accumulated at single pier cases, and debris accumulated at sacrificial piles cases with different diameters and thickness of debris. Maximum scour depth in presence of debris accumulation at isolated pier and sacrificial piles have been compared to the maximum scour depth without the presence of debris accumulation. New relationships have been proposed to predict the effect of debris accumulation at sacrificial piles on bridge pier scour in term of relative maximum scour depth. The results of single pier with debris showed that the scour depth increased from 10% to 60% compared to single pier without debris. In sacrificial piles with debris the results showed that scour depth increased from 8% to 100% compared to sacrificial piles without debris. Through this experimental study the debris found to be effected to bridge pier scour. It was seen that the debris effected to the effectiveness of sacrificial piles. The effect of debris accumulation at sacrificial piles to bridge pier scour should be considered. Future researches are needed to consider more about the spacing between the pile, the angle of the pier to approach flow, and the angle of flow to the pier.

The major damage of bridges at river crossing occurs during floods. Damage is caused for various reasons, the main reason being riverbed scour at bridge foundations, namely pier and abutments. Debris accumulation at bridge pier provides larger obstruction to flow than an isolated bridge pier. The presence of debris causes larger scours and sediment removal compared to the absence of debris accumulation. Debris accumulation at bridge pier effects to bridge pier scour has been studied by several researchers. But the effects of debris accumulation at sacrificial piles on bridge pier scour have not been studied, yet. The aim of this study is to estimates the effects of debris accumulated at sacrificial piles to bridge pier scour and proposes a new formula for predicting bridge pier scour depth with debris accumulated at the sacrificial piles. Experiments were performed to understand the changes and interaction of scour depth over a range of flow depths, y and flow intensities, V/V _c . Experiments were conducted in single pier scour, sacrificial piles scour, single pier with debris scour and sacrificial piles with debris scour. By comparing each of the experimental results it has been found that debris effects to bridge pier scour related to its size and thickness. Several scour depth prediction methods were compared with the results of this experimental study results. Among those formulae Melville’s formula was chosen to modify. The proposed modified Melville’s formula depth-size factor, K _yb ^′ = 1.56D was defined in this study. A new relation has been proposed to predict the effects of debris accumulation at sacrificial piles on bridge pier scour in term of relative maximum scour depth. D _e ^′ is proposed as effective pier with debris accumulated at sacrificial piles. The new proposed formula is well fitted with the experimental results. The results of experiments from the previous paper are used to analyze and the new formula is proposed.

The Seonakdong River is an impound stream whose flowrate is controlled by the Daejeo and Noksan gates. Therefore, constant natural flow of the Seonakdong River does not occur. In contrast, pollutant loadings occur constantly occurring as water flows into the river from the watershed. The Daejeo gate is located at the upstream head and the Noksan gate is at the downstream end of the Seonakdong River. The Seonakdong River is an estuarine tributary of the Nakdong River. It is a reservoir-like river used for agricultural irrigation, with the Noksan gate at the river mouth serving to prevent the intrusion of saline water. In this study, a steadystate model, QUAL2E, and an unsteady-state model, CE-QUAL-RIV1, were chosen for comparative simulations. The results of the simulations of river water quality changes were verified with respect to short-term variations of water quality due to the increasing water flow from the Daejeo gate and the discharging flow from the Noksan gate. Field measurements were performed to monitor the flowrate and water quality during the operation of the Daejeo and Noksan gates in the Seonakdong River. The general trend observed is that the water quality worsens after the opening of the gates. The reduction in water quality ranges from 3% to 38%. These results show that the gate operators should carefully select the most appropriate operating plan to obtain better water quality in the Seonakdong River. The numerical simulation shows that a discharge of 300 CMS, which is a peak inflow from the Daejeo water gate to the river, can make it possible to achieve the target water quality of the Seonakdong River if the Daejeo water gate can remain open in connection with the Noksan water gate operation.