Longitudinal Dispersion of Pollutants in Flow through Natural Vegetation

The drag due to the vegetation affects of pollutant dispersion as it flows through vegetation. The previous research has aimed mostly at a cylinder-based model in which the vertical vegetative characteristics are homogenous. It rarely mentions natural vegetation in which the vertical vegetative characteristics undergo steep changes. Based on the laboratory measurements and observations, an empirical model is built to calculate the longitudinal dispersion coefficient for flow through natural shrubs using the multiple regression analysis method. The calculation model is developed by relating the longitudinal dispersion coefficient to plant diameter, the stem Reynolds number and the drag coefficient. The natural shrubs are chosen to examine in which the vertical characteristics make substantial changes and natural reeds in which the vertical characteristics change little. Shrubs and reeds, reeds and herbs in different cooperating ways are fixed on a flume. Then ammonia nitrogen is used as a tracer, an Acoustic Doppler as a velocity meter, and a water level sensor and multi-parameter water quality instruments to measure respectively the velocity, water level, and the pollutant concentration process curve.