Modeling the geomorphic response to early river engineering works using CAESAR-Lisflood

Abstract

Landscape Evolution Models (LEMs) simulate the movement of water and sediment over the landscape. Although much progress has been made in the development of LEMs, few have been tested in rivers subject to anthropogenic impacts that produce high energy flows, transporting large amounts of sediment and causing significant geomorphic changes. As such, it remains uncertain if LEMs are useful and stable under relatively short term ‘extreme’ geomorphic conditions. To shed light on this topic we use a LEM (CAESAR-Lisflood) and historical documents to develop a detailed reach scale model of the Kander river (Switzerland). This model was used to simulate the unintended impacts of engineering works, occurring in 1714, that deviated the Kander river into a lake and resulted in a large decrease in base level of the river. In 10 years, the model simulates knickpoint propagation that rapidly erodes 2.5 million m3 of sediment and produces a remarkable 27 m of channel erosion. Simultaneously, the model develops the formation of a delta via frequent avulsions. Model testing is performed by comparing model predictions against historical observations of channel incision, knickpoint location, and delta spatial extent. Overall, model error is low and the model remained stable as results do not contain erratic erosion or deposition. Importantly the model suggests that downstream processes occurring at and near the delta have an effect on upstream channel erosion. We also recommend that studies replicating historic landscape changes with LEMs reduce uncertainty in hydrological inputs.