The Peinan River is situated at the southern part of a longitudinal valley in Eastern Taiwan. The effects of, and the relationship between, the natural environment and human activities on alluvial fans were surveyed, analyzed and discussed in the context of geographical location, geomorphological processes, stages of development, land uses and geological hazards in order to promote understanding of the natural mechanisms operating in the study area and to contribute to land resource planning and hazard prevention. Towns and villages located on stream terraces, such as Gau-Tair, Long-Tyan, or on elevated alluvial fans, such as jiing-Feng, Yeong-Chang, are rarely subject to geological hazards. On the other hand, those on or nearby mountain stream alluvial fans such as Guan-Shan are prone to debris flows, and those at the lower end of valley fans, such as Pei-Nan, are subject to flooding during typhoon seasons. The study also found that land use has a closer relationship to fan characteristics than it has to debris hazard. This is a result of the construction of channels and dykes.