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In recent decades, stream valleys have been profoundly modified by the construction of weirs and dams and by channelisation. Channelisation modifies the morphology of streams and induces changes in their energy regime and sediment transport capacity. These types of changes in the channel morphology have to be quantified to allow the implementation of management strategies to regulate sediment transfer. However, studies over an entire stream using historical comparisons remain scarce, and the associated uncertainties have not yet been resolved. In this study, the sedimentary response to channelisation on a medium time scale (42 years) of a French river known as the Ligoire is investigated. This river is the main channel of a small rural headwater catchment that has been channelised over 21 km. We have used the historical cross sections before and after channelisation and the current ones, and the objectives of this study were as follows: (1) to develop a methodology of cross section superposition and the associated uncertainties; (2) to quantify the erosion and aggradation processes in the bed and on the banks along the bed profile; and (3) to calculate a sediment budget for the entire stream and determine the relative contributions of the banks and the streambed to this budget. A comparison of the cross sections before and after the channelisation shows that the morphology of the stream has been completely altered: the main channel length was reduced by 10%, the bankfull width was increased on average by 63%, and the slopes were smoothed. A total of 60,000 m 3 of sediments was excavated during the channelisation works. Our results indicate that erosion is the dominant process: over 63% of its length, the streambed was incised by 0.41 m on average; and over 60% of its length, the banks were eroded by 0.20 m on average. The successive patterns of erosion and deposition along the stream are the result of the cumulative effects of channelisation and of the presence of weirs and artificial knickpoints in the Ligoire channel. The vertical uncertainty of the elevation of the historical cross section is an important parameter for controlling the areas and sediment budget values. Using Monte Carlo methods, we found that 1000 sediment budgets from different profile shiftings are necessary to obtain a variation coefficient below 0.1%. The overall mean stream sediment budget for the period 1970–2012 is -9358 ± 412 m 3 , with 66% originating from the banks and 34% from the streambed. Relative to the Ligoire watershed surface, the stream sediment yield is 2.71 ± 0.12 m 3 .km − 2 .y − 1 . The approach developed in this study is easily replicable and relatively cheap and provides an integrated quantified, overview of the morphological adjustments after channelisation works on a stream. [ABSTRACT FROM AUTHOR]

While soil erosion and runoff physical processes and socio-environmental impacts are widely addressed in the literature, few studies have focused on the economical dimension. However, it is essential to consider this dimension to conduct appropriate land use management policies. Erosion and runoff are known to result into on-site and off-site impacts. A fully exhaustive analysis of erosion and runoff economic costs may be difficult and ambitious due to the low availability of the data and considering that some issues are still unevaluated in the literature (cost of public policies to prevent erosion and runoff impacts, prohibition of drinking water due to turbidity, etc.). In this study, we chose to analyze the main off-site economic costs induced by these processes in two specific areas located in the northwestern European loess belt (Normandy, France). We quantified avoidance and social damages over the last 25 years through a global and retrospective analysis of financial databases provided by regional or local authorities (water agencies, departmental councils, reinsurance, drinking water companies, transport infrastructures managers) and literature review (scientific articles and technical reports). Our analysis suggested that from 1995 to 2017, the total damages cost ranged from 611 to 721 M€. Off-site avoidance damage costs accounted for almost 2/3 of the total expenditure. In the Seine-Maritime area, the mean cost was evaluated to 4 319 € yr−1 km−2 and to 868 € yr−1 km−2 in the Eure area. Even if we tried to be as exhaustive as possible some off-site economic costs remained unknown. It appeared that more research is necessary for the scientific community to get a full picture of off-site economic costs induced by erosion and runoff. • Off-site economic costs of runoff and erosion were quantified through an analysis of public expenditures. • The total avoidance damages cost ranged from 375 to 485 M€. • The total social damages cost reached 236 M€. • The mean cost of erosion and runoff off-site impacts was estimated to 868 and 4319 € yr−1 km−2. [ABSTRACT FROM AUTHOR]