Discussion of Hydrualic Characteristics of Canal Unit Step Overfall And Box Culvert Structure

• Main Authors: Yu-Hui Wu, 吳玉輝
• Other Authors: Te-Hsing Chang
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/23991970906105993050

碩士 === 中原大學 === 土木工程研究所 === 95 === Man-made channels can be roughly classified by function into irrigation, water transfer, drainage, and dual purpose of irrigation and drainage. Hydraulic drop design may not be required for channel running on a flat area; however, the hydraulic drop is usually designed for a channel is running on an area featuring drastic topographical falls to minimize erosion to the bottom of the channel while containing the core flow. Box culvert is a structure to contract water flow, conditions including geometry, slope, and sectional shape and size of the box culvert inlet, roughness of the inner side of the box culvert, length of box culvert, depth of water, water level at the upper stream, and tail water affect the hydraulic behavior of the box culvert. These conditions can never be overlooked since a poor design of a box culvert may attract flooding and result in loss of life and property. full understanding of hydraulic characteristics of the box culvert is a must before designing one. Based on those theories disclosed and performance of experimental design of a single level drop inlet to box culvert, this study explores into hydraulic conditions of a box culvert and its experimental results and has found that: （1） It is observed that the energy dissipation effect after drop becomes more significant in the drop inlet as the inflow increases and the water flow tends to stabilize in a longer culvert pipe after the drop. （2） Design of a box culvert is correlated to multiple factors including slope, roughness, water depth, and length (L) and pipe bore height (D) etc. Therefore, the results of the present experiment indicate that when the flow increases, the inlet is submerged, the box culvert becomes a down emission gate flow type; partially full pipe, pipe tail not submerged to become the third flow type of box culver. This study achieved the measurement of correlation respectively between rectangular box culvert and circular box culvert flow vs. water level in a model experiment; the flow rates measured in the experiment are all slower than that as computed according to the box culvert and pipe culvert conditions in the experiment; the failure of the water flow to become a stabilized flow due to shorter box culvert may be the primary cause attributable to the slower flow rates measured; and the absence of full pipe was not observed in presence of larger flow. Findings indicate that it is impossible to achieve full pipe given with shorter inlet drop and hydraulic box culvert and that design flow for the box culvert was frustrated when the inlet is not submerged.