Risk evaluation for the combined clogging of subsurface drainage envelopes in arid areas

Accurately assessing the clogging risk of the drainage pipe envelopes is a prerequisite for the reasonable design and proper management of subsurface drainage. However, the current assessment of clogging risk for subsurface drainage envelopes in arid areas mainly focuses on the impacts of single factors such as physical or chemical factors, with less attention given to combined physical–chemical clogging, which is more likely to occur and causes significant harm. Based on the evaluation indicators for physical and chemical clogging risks, this study utilized the entropy weight method to determine the weights of physical and chemical clogging risks, then proposed evaluation indicators for combined clogging risks and generated risk maps of physical, chemical, and combined clogging within the Xinjiang watershed. Furthermore, field excavation and sampling of subsurface drainage pipes were conducted to apply the proposed evaluation indicators for combined clogging risks and analyze the influencing factors. The results show that the combined clogging risk map based on the proposed combined clogging evaluation indicators is consistent with the actual clogging situation in the subsurface drainage system. Both physical and chemical clogging coexisted in the subsurface drainage system in Xinjiang, with a higher mass content of SiO2 than CaCO3 in the clogging substances. The combined clogging risk increased with rises in the drainage temperature and salinity. Under current conditions, the proportions of high, moderate, and low-risk areas of combined clogging risk are 22.10%, 30.37%, and 47.53%, respectively. The high-risk areas are mainly concentrated in Southern Xinjiang, which accounts for 91.7% of the high-risk area. This study can provide technical support for the prevention and control of clogging in subsurface drainage systems for saline-alkali farmland in arid areas.