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To explore the migration differences of sediments at the front, middle, and end sections of a storm sewer when scoured by water, and further evaluate the pollution load, the scouring process of sediments at different locations of a storm sewer was simulated and mathematical models were built to calculate the scouring rate. Results show that scouring rate is affected by sediment particle size, pipeline slope, sediment thickness, and water flow velocity. As the slope increased, scouring rate at the end section increased more obviously. The scouring rate at the front section slightly decreased with increasing sediment thickness, but opposite trends were observed at the middle and end sections. When the particle size (0.33 mm–0.83 mm) and flow velocity (0.15 m/s–0.65 m/s) increased within their ranges, scouring rate increased across all three locations. Models for calculating scouring rate were established via two data fitting. The calculated values were compared with measured values at a scouring time of 1 min. Under different particle sizes, the difference between the calculated and measured values at front, middle, and end sections were in the ranges of −0.63% to 0.63%, −0.01% to 0.02%, and −0.13% to 0.16%, respectively, all of which showed good consistency.

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Ecological shallow ditch is one of the effective methods to improve non-point source pollution of farmlands. However, during winter when the temperature is low, the operation capacity of the common ecological shallow ditch (CESD) is not satisfactory. In the present study, a thermally insulated ecological shallow ditch (TESD) was constructed, and the pollutant removal efficiency of the two ecological shallow ditches (thermal-insulation type versus common type) was compared. The changes in the number of bacteria inside these two types of shallow ditches were studied, and the underlying mechanism was analysed. The results showed that the thermally insulated ecological shallow ditch could partly reduce the adverse effects of low temperature and keep the surface temperature above 10°C. After 18 days of observation in the winter, the removal rates of COD, TN and TP in the effluent were respectively 1.3 times, 2.5 times and 1.3 times higher than those of the common type, and the concentration of bacteria in each site was also higher for TESD. The oxygen content in the soil layer and filler layer in TESD increased. Moreover, TESD also demonstrated higher microbial activity and more active plant growth than the CESD.