Determination of Key Risk Supervision Areas around River-Type Water Sources Affected by Multiple Risk Sources: A Case Study of Water Sources along the Yangtze’s Nanjing Section

To provide a reference for risk management of water sources, this study screens the key risk supervision areas around river-type water sources (hereinafter referred to as the water sources) threatened by multiple fixed risk sources (the risk sources), and establishes a comprehensive methodological system. Specifically, it comprises: (1) method of partitioning risk source concentrated sub-regions for screening water source perimeter key risk supervision areas; (2) approach of determining sub-regional risk indexes (SrRI, which characterizes the scale of sub-regional risks) considering factors like risk distribution intensity within sub-regions, risk indexes of risk sources (RIRS, characterizing the risk scale of risk sources) and the number of risk sources; and (3) method of calculating sub-region’s risk threats to the water sources (SrTWS) which considers the positional relationship between water sources and sub-regions as well as SrRI, and the criteria for determining key supervision sub-regions. Favorable effects are achieved by applying this methodological system in determining water source perimeter sub-regions distributed along the Yangtze’s Nanjing section. Results revealed that for water sources, the key sub-regions needing supervision were SD16, SD06, SD21, SD26, SD15, SD03, SD02, SD32, SD10, SD11, SD14, SD05, SD27, etc., in the order of criticality. The sub-region with the greatest risk threats on the water sources was SD16, which was located in the middle reaches of Yangtze River. In general, sub-regions along the upper Yangtze reaches had greater threats to water sources than the lower reach sub-regions other than SD26 and SD21. Upstream water sources were less subject to the threats of sub-regions than the downstream sources other than NJ09B and NJ03.