The Study of Detention-Sedimentation Pond from Viewpoint of Improving Water Quality

• Main Authors: Je-Tong Wang, 王哲通
• Other Authors: Han-Keng Lee
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/48826085108322243695

碩士 === 逢甲大學 === 土木及水利工程研究所 === 89 === Various studies have concluded one of the most important factors to affect the quality of surface water is Non-point source pollution. Non-point source pollution is a kind of water pollution caused by runoff when rainfall washes off against surfaces of the ground, and scour pollutants to water body. A detention pond is a control system for non-point source pollution. Besides having a great result of decreasing flood peak, it also has controlling effects of sediment and it reduces the concentration of pollutants in water. This thesis discusses different tracers used to discuss the detention pond, and the effects on pond conditions and hydraulic properties when the detention changes of the discharge of inflow and its properties. The series tests use Rhodamine B and Kaolin as tracers respecting to simulate the dissolved and suspended pollutants. Analysis of Rhodamine B tests can produce a series data of hydraulic properties, likes mixing conditions, hydraulic detention time, horizontal velocity, dispersion, Peclet number and dead volumes…etc. In Kaolin tests, which can calculate the removal efficiency and analyze the removal mechanism of suspended pollutants. The test results indicate that the changes of concentration of Rhodamine B are mostly effected by flush and dispersion. Most of dissolved pollutants are flush from the detention pond by out flow, only few parts are adsorbed in the walls. The concentrations of suspended pollutants are effected largely by sedimentation, and the flush effect is lesser. When inflow discharge keeps constant and changes the ratio of pond width to depth, removal efficiency of suspended pollutants is similar to variation of dead volume. The dead volume creates circular flow in the pond, and changes the flow path. The pollutants are took to bottom and cut down the distance of sedimentation and increase the removal efficiency. Through tracer studies, characters of detention pond such as hydraulics and pollutants removal efficiency can be determined.