Author(s): Enbang Xiao; Yasuhiro Takemon; Sohei Kobayashi; Karim Ibrahim Ahmed; Tetsuya Sumi
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Keywords: Spatial and temporal variation; Hydraulic conductivity; Gravel bar; Weir removal
Abstract: Reach scale heterogeneity of riverbed hydraulic conductivity has been investigated previously, while few examined the vicinity riverbed hydraulic conductivity response to dam removal projects. In this study, CHIT(Constant Head Injection Test) method was used for in-situ estimation of hydraulic conductivity (K) in a newly created gravel bar after a weir removal project at three depths: top(0-30cm), middle(30-60cm) and deep (over 60cm). Data were used to generate the spatial and temporal variation map of K. Results showed that K has a negative relationship with the measurement depth. Low K areas are mainly distributed in the middle and deep layer at the bar head, especially at the right-bank side. As to the bar tail (line E and F) the K was over 100m/day throughout three layers. After one-month period, the overall K increased due to a small flood, however, specific site with decrease of K were found in all layers which indicates the complexity of K evolution with time. Based on detailed background and local geomorphic settings investigation, we found that the artificial impact to the original riverbed and the strong sediment sorting during bar formation could be the fundamental control of the heterogeneity of K, which implies that during removal work, proper riverbed management strategy is crucially needed for the purposes of hyporheic ecotone restoration.
Year: 2020