Self-purification ability of the water body is an in1portant factor affecting the change in 'Nater quality indicators. In this study, the self purification capability was characterized hy the BOD, degradation coefficient. From January 2015 to July 2015, six monitoring sections (Chenggou,Fangcheng,Shahenan, Lanhehei,Xinfeng,and Suzhang) of the main canal in the middle route of the south to North Water Transfer Project were selected to monitor the BOD5 monthly data and to study the flow and water depth of each control gate in the canal section, the one-dimensional steady BOD5 degradation model was used to fit the BOD5 degradation coefficient of the main channel. The results showed that the degradation coefficients of BOD5, in the channel section between 0.024/d～0.054/d. The capacity of water self-purification of the main channel is relatively small compared to other areas. The seasonal change of the BOD5, degradation coefficient in the channel section was obvious. The fitting k values from January to April and July were0.028/d（p＜O.O5)，0.033/d（p〈0.05)，0.024 /d（p＜O.O5，0.039 /d(p

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[基金项目]

水体污染与治理科技重大专项(2017ZX07 l08-001）