因行洪、引水使钉螺由垸外向垸内扩散是血吸虫病蔓延的一个重要原因，研究钉螺随水流扩散规律对控制血吸虫病的流行极为重要。首先采用模型试验和数值模拟的方法研究了侧堰分流的流场特性，在此基础上进行了钉螺随侧堰分流扩散规律的实验研究。结果表明钉螺随水流扩散后并不是均匀分布在流场内，而是集中分布在侧堰附近上下游以及回流区域。这一结论为安全有效地灭螺提供了重要的理论依据。

The diffusion of oncomelanias by flood is a main reason of schistosomiasis propagation. Therefore it is the most essential and effective way to control diffusion of oncomelanias along with flood for preventing epidemic of schistosomiasis disease. In this paper the research on the diffusion of oncomelanias along side-weir flow is carried out. The result shows that after diffusion along side-weir flow, oncomelanias do not evenly distribute at floodplain areas, but fall in the place that flow velocity is small , i.e. in the backflow areas and at boundary places of upper reaches and lower reaches of the side-weir breach. Oncomelania’ s diffusion law provides an important theory for eliminating oncomelanias.