The PIANC InCom/EnviCom Working Group 236 was established in early 2021 to develop PIANC guiding principles for improving navigability conditions on natural or quasi-natural rivers, while maintaining morphological processes, river form, and function. A natural river system exhibits two important characteristics – 1) unregulated hydrology and 2) unconstrained morphology. In other words, both the hydrology and the morphology of the system is ‘natural’, and the river can freely respond to the environmental boundary conditions provided by the watershed.
The key objectives of the WG 236 – ‘Sustainable Management of the Navigability of Natural Rivers’ – include: 1) development of guidelines to improve and maintain the navigability in natural rivers; 2) assess the sustainability of river training works designed to improve the navigability; 3) assess the sustainability of dynamic river management (monitoring and shifting of navigation aids to adapt the navigation channel to the river dynamics); 4) highlight the technical, operational, economic and environmental considerations for navigation in free-flowing rivers compared to that in regulated rivers and canals; and 5) improve the understanding of the physical processes in natural rivers, developed with or without river training works. In some cases throughout the report applications in trained or regulated rivers are presented to demonstrate approaches or lessons learnt. However, the primary application of the Working Group remains with natural rivers.
The guidance includes a planning framework for developing a navigability improvement masterplan for a natural river system, and the integrated and adaptive management strategies that can be applied at a system scale. Specific interventions and measures have been identified that are analysed to meet the dual goals of maintaining morphological river function and improving navigability conditions. These measures include dynamic charting; morphological dredging and disposal management; temporary, adaptable, and flexible training structures (TAFTS); riverbed armouring and sediment nourishment; rock excavation; meander cutoffs and oxbow development; localized traditional river training structures; and channel closure structures. The impacts and strategies for mitigating impacts associated with some of the measures are analysed and discussed. Finally, the continual monitoring, management, and operational tools available for improving navigability in a morphologically active river system are presented. It is recognised that natural rivers will typically be more fluvially active and dynamic than systems that have used traditional methods for navigability improvements including heavily trained rivers or systems with locks and dams. These unrestricted and unconfined river systems, therefore, require new and innovative strategies to monitor the fluvial and geomorphic changes of the system to inform managers and navigators of the river.
