Evaluating the hydraulic and hydro-morphodynamic performance of blue–green infrastructure over event and long-term timescales

Abstract

To evaluate the effectiveness of blue–green infrastructure (BGI) at multiple timescales requires a modelling tool that is capable of simulating the underlying hydraulic and morphodynamic processes within BGI. In this context, this study presents a hydro-morphodynamic modelling tool for systematic assessment of the multiple benefits of BGI on flood attenuation and sediment trapping. The model combines two-dimensional shallow-water equations with an advection–diffusion equation for fine sediment transport. The model can simulate the dynamic processes of erosion, transport and deposition of non-cohesive, fine-grained suspended sediments (i.e. fine sands and silts) under the action of flow hydraulics typical of those found in BGI. To demonstrate the model capability, it is applied to two case studies, including (a) the effects of a restored floodplain and (b) the effectiveness of an urban stormwater pond. The simulation results indicate that nature-based approaches, such as floodplain restoration and stormwater ponds, are effective for attenuating flow and retaining suspended sediments. More specifically, stormwater ponds are suitable for more-frequent smaller events (< 5-year), while floodplain restoration is more effective for extreme flood events (e.g. 30 to 100-year) where more floodwaters can be stored. From a longer-term viewpoint, stormwater ponds lose their storage capacity over a period of time; they require regular maintenance to uphold their hydraulic performance. The model developed in this study is an effective tool for the evaluation of BGI at various temporal and spatial scales, and could be applied to similar cases.