Eindevaluatie pilot Langsdammen in de Waal : morphology and maintenance

River interventions such as the replacement of groynes by longitudinal training walls have morphological effects on different scales. Effects on the smallest scales occur almost immediately whereas effects on the largest scales manifest themselves only after decades. As discharges vary, morphological effects keep fluctuating even in the long term. Relevant scales for morphological effects of the longitudinal-training-wall pilot in the river Waal are the reach scale, the corridor scale, the cross-section scale and the depth scale. The present report evaluates effects on these scales in three steps. In the first step, expected effects are formulated based on established knowledge from previous experiences, theoretical assessments, and a numerical model study carried out before implementation of the pilot. The second step consists of analyzing hydro-morphological data from the monitoring programme of the pilot and simulating the hydro-morphological effects by a more refined numerical model than used before implementation. Conclusions are drawn in the third step, by balancing the results from data analysis and numerical modelling and by comparing these results with the expectations based on established knowledge. Additionally, experiences of Rijkswaterstaat with maintenance are reported as they are closely linked to the morphological developments in the river.