An indicator system for assessing the impact of human activities on river structure

Abstract The impact of human activities on river systems has reached a state in which they can no longer be considered to be controlled only by natural processes of the Earth but also by anthropogenic forces in many regions of world. However, most approaches for assessing the impact still consider human activities to be an external influence in the study of feedback mechanisms between human activities and river systems, and they are usually complicated and specialized. This paper aims to develop an indicator system that includes the artificial water surface ratio (AWSR), artificial water surface density ratio (AWSDR), disruption of longitudinal connectivity ratio (DLCR), artificial river ratio (ARR), sinuosity of artificial cutoff (SAC), channelization ratio (CR), artificial levee ratio (ALR), road along river ratio (RARR), artificial sediment transport ratio (ASTR) and the integrated river structure impact index (IRSII) to quantitatively assess the impact of human activities on river structure by comparing natural and anthropogenic forces in a river system. The Nanliu River basin under the dramatic impact of human activities was selected to validate the indicator system. The case results showed the Nanliu River has become an anthropogenic river according to its high IRSII value (> 0.49). The artificial water surface area and artificial sediment discharge were 2.96 (AWSR = 2.96) and 2.51 (ASTR = 2.51) times of the outcome of natural process. The river was dramatically blocked by human-made buildings (DLCR = 68.63) and artificial channel accounts for 54.23% of total length of natural river (ARR = 0.54). Within the river basin, upper and lower sub-basins in areas with a higher economic level were more affected by human activities. Future management of the Nanliu River basin should focus on restoration of river connectivity, sand mining and irrigation issues. Unlike most previous assessment methods, the approach developed in this study is simple and readily comprehensible by the public and decision makers, cost-effective for long-term monitoring and not subject to the reference condition.