Modelling pre-modern flow distances of inland waterways – a GIS study in southern Germany

Rivers form major traffic arteries in pre-modern Central Europe and accurate regional to supra-regional network models of inland navigation are crucial for economic history. However, navigation distances have hitherto been based on modern flow distances, which could be a significant source of error due to modern changes in flow distance and channel pattern. Here, we use a systematic comparison of vectorized old maps, which enlighten the fluvial landscape before most of the large-scale river engineering took place, and modern opensource geodata to deduce change ratios of flow distance and channel patterns. The river courses have been vectorised, edited and divided into comparable grid units. Based on the thalweg, meandering and braided/anabranching river sections have been identified and various ratios have been calculated in order to detect changes in length and channel patterns. Our large-scale analytical approach and Geographic Information System (GIS) workflow are transferable to other rivers in order to deduce change ratios on a European scale. The 19th century flow distance is suitable to model pre-modern navigation distances. As a case study, we have used our approach to reconstruct changes of flow pattern, flow distance and subsequent changes in navigation distance and transportation time for the rivers Altmühl, Danube, Main, Regnitz, Rednitz, Franconian and Swabian Rezat (Southern Germany). The change ratio is rather heterogeneous with length and travel time changes of the main channel up to 24% and an extensive transformation of channel morphology in many river sections. Based on published travel time data, we have modelled the effect of our change ratios. Shipping between the commercial hubs Ulm and Regensburg, to give an example, was up to 5 days longer based on pre-modern distances. This is highly significant and underlines the necessity for river-specific correction values to model supra-regional networks of pre-modern inland waterways and navigation with higher precision.Highlights:Systematic comparison of old maps and modern geodata to deduce river-specific length correction values to improve supra-regional network models of pre-modern inland navigation.Large-scale analytical approach and transferable GIS workflow for flow distance reconstruction with case studies in Southern Germany.Length changes of navigated fairways result in pre-modern period travel times up to 24% higher in corrected models.