Sustainable concepts of ecologically functional rivers challenge engineers, researchers, and planners. Advanced numerical modeling techniques produce nowadays high-precision terrain maps and spatially explicit hydrodynamic data that aid river design. Because of their complexity, however, ecomorphological processes can only be reproduced to a limited extent in numerical models. Intelligent post-processing of hydrodynamic numerical model results still enables ecological river engineering measures to be designed sustainably. We have embedded state-of-the-art concepts in novel algorithms to effectively plan self-maintaining habitat-enhancing design features, such as vegetation plantings or the artificial introduction of streamwood, with high physical stability. The algorithms apply a previously developed lifespan mapping technique and habitat suitability analysis to terraforming and bioengineering river design features. The results not only include analytical synopses, but also provide actively created, automatically generated project plans, which are optimized as a function of an efficiency metric that describes “costs per m² net gain in seasonal habitat area for target species”. To make the benefits of these novel algorithms available to a wide audience, we have implemented the codes in an open-source program called River Architect. In this contribution, we present the novel design concepts and algorithms as well as a case study of their application to a river restoration project on the Yuba River in California (USA). With River Architect, we ultimately created an objective, parameter-based, and automated framework for the design of vegetative river engineering features. In addition, we are able to define a framework for stable and ecologically viable terraforming features, but part of the planning of earthworks is still left to expert assessment. Thus, improving the algorithms to plan terraforming of permanent, self-sustaining, and eco-morphodynamic riverbed structures based on site-specific parameters is one of the future challenges.

Physical habitat losses for Pacific salmonids in California’s Central Valley motivate stream restoration. Considerable river morphodynamics affect the sustainability of habitat enhancing interventions. In addition, the presence of large dams in many river catchments causes low sediment supply. This study revises existing stream restoration techniques for their ecologically efficient and physically stable embedding in a 36-km testbed river. Ecological efficiency is evaluated in terms of a commonly used hydraulic habitat suitability index. Physical stability results from 2D hydrodynamic modelling of bed shear stress during steady flows of different flood frequencies. We differentiate between terraforming, stabilizing and maintaining stream restoration techniques, which constitute three feature layers. The first layer, terraforming, includes artificial terrain modifications such as grading or backwater creation to generate new habitat. These features require stabilization, which is provided by the second feature layer. The stabilization (layer two) is achieved by bioengineering such as placement of streamwood, angular boulders and vegetation plantings. The third feature layer has the purpose to maintain newly created habitat, e.g., through artificial gravel injections. We illustrate the application of the three-layer-approach at one major restoration site of the lower Yuba River using a self-written Python package. Ecohydraulic 2D modeling was applied to designs with incremental layer additions to evaluate newly created spawning habitat and feature sustainability. This procedure represents a pertinent way for stream restoration planning, which avoids non-sustainable habitat enhancement features and implements ecologically as well as physically sustainable features only.