The past decades have witnessed frequent flood peak discharges increase in the Lower Yellow River (LYR). Yet no consensus for its mechanism has been achieved. Here 21 events of the peak discharge increase (PDI) in the period of 1973–2012 are analysed. It is shown that the mean increment of peak discharge increases from 810 m³/s to 1158 m³/s and the frequency also increases from once every 2 years to once every 1.5 years after the completion of Xiaolangdi (XLD) Reservoir. Afterwards, the ordinary differential equations (ODEs) along the characteristics for the discharge are derived, from which seven factors (terms I ∼ VII) that may affect the discharge variation are identified: the effects related to the longitudinal change in flow density (I), and in the product of flow density and flow area (II); the pressure terms due to river width gradient (III) and flow density (IV); the external forces (V); the momentum term due to bed deformation (VI); and the imbalanced advection (VII). Using field data of the 21 events, the bed Manning roughness is back-calculated from the ordinary discharge equation, which agrees with the documented values very well. Quantitative comparisons of the seven factors indicate that the pressure term due to the river width gradient plays a major role in promoting the PDI in most events, whereas the external forces term is the primary cause that attenuates PDI. The rest influencing factors have marginal effects with a much smaller magnitude.

By definition, Building with Nature solutions utilise services provided by the natural system and/or provide new opportunities to that system. As a consequence, such solutions are sensitive to the status of, and interact with the surrounding system. A thorough understanding of the ambient natural system is therefore necessary to meet the required specifications and to realise the potential interactions with that system. In order to be adopted beyond the pilot scale, the potential impact of multiple BwN solutions on the natural and societal systems of a region need to be established. This requires a ‘reality check’ of the effectiveness of multiple, regional-scale applications in terms of social and environmental costs and benefits. Reality checking will help establish the upscaling potential of a certain BwN measure when addressing a larger-scale issue. Conversely, it might reveal to what extent specific smaller-scale measures are suitable in light of larger regional-scale issues. This paper presents a stepwise method to approach a reality check on BwN solutions, based on the Frame of Reference method described in a companion paper (de Vries et al., 2021), and illustrates its use by two example cases. The examples show that a successful pilot project is not always a guarantee of wider applicability and that a broader application may involve dilemmas concerning environment, policy and legislation.

Hydraulic engineering infrastructure is supposed to keep functioning for many years and is likely to interfere with both the natural and the social environment at various scales. Due to its long life-cycle, hydraulic infrastructure is bound to face changing environmental conditions as well as changes in societal views on acceptable solutions. This implies that sustainability and adaptability are/ should be important attributes of the design, the development and operation of hydraulic engineering infrastructure. Sustainability and adaptability are central to the Building with Nature (BwN) approach. Although nature-based design philosophies, such as BwN, have found broad support, a key issue that inhibits a wider mainstream implementation is the lack of a method to objectify BwN concepts. With objectifying, we mean turning the implicit into an explicit engineerable ‘object’, on the one hand, and specifying clear design ‘objectives’, on the other. This paper proposes the “Frame of Reference” approach as a method to systematically transform BwN concepts into functionally specified engineering designs. It aids the rationalisation of BwN concepts and facilitates the transfer of crucial information between project development phases, which benefits the uptake, acceptance and eventually the successful realisation of BwN solutions. It includes an iterative approach that is well suited for assessing status changes of naturally dynamic living building blocks of BwN solutions. The applicability of the approach is shown for a case that has been realised in the Netherlands. Although the example is Dutch, the method, as such, is generically applicable.