Abstract
Stormwater represents a complex and dynamic component of the urban water cycle. Hydrologic models have been used to study pre- and post-development hydrology, including green infrastructure. However, many of these models are applied in urban environments with very little formal verification and/or benchmarking. Here we present the results of an intercomparison study between a distributed model (Gridded Surface Subsurface Hydrologic Analysis, GSSHA) and a lumped parameter model (the US Environmental Protection Agency (EPA) Storm Water Management Model, EPA-SWMM) for an urban system. The distributed model scales to higher resolutions, allows for rainfall to be spatially and temporally variable, and solves the shallow water equations. The lumped model uses a non-linear reservoir method to determine runoff rates and volumes. Each model accounts for infiltration, initial abstraction losses, but solves the watershed flow equations in a different way. We use an urban case study with representation of green infrastructure to test the behavior of both models. Results from this case study show that when calibrated, the lumped model is able to represent green infrastructure for small storm events at lower implementation levels. However, as both storm intensity and amount of green infrastructure implementation increase, the lumped model diverges from the distributed model, overpredicting the benefits of green infrastructure on the system. We performed benchmark test cases to evaluate and understand key processes within each model. The results show similarities between the models for the standard cases for simple infiltration. However, as the domain increased in complexity the lumped model diverged from the distributed model. This indicates differences in how the models represent the physical processes and numerical solution approaches used between each. When the distributed model results were used to modify the representation of impermeable surface connections within the lumped model, the results were improved. These results demonstrate how complex, distributed models can be used to improve the formulation of lumped models.
Highlights
Stormwater management is increasingly becoming integrated and interdisciplinary, and there are a growing number of hydrologic models being used to address the challenges of urban hydrology [1,2,3].Many of these models can simulate integrated surface and subsurface flow with the aim of representingWater 2018, 10, 1756; doi:10.3390/w10121756 www.mdpi.com/journal/waterWater 2018, 10, 1756 the relevant physical processes that influence the hydrologic response at varying scales [4,5]
We present the results of an intercomparison performed for distributed and lumped hydrologic models in a completely urban domain that includes green infrastructure
Gridded Surface Subsurface Hydrologic Analysis (GSSHA) is a physically-based, distributed-parameter, structured grid, hydrologic model that simulates the hydrologic response of a watershed subject to given hydro meteorological inputs
Summary
Model Intercomparison Project (DMIP) [29,30], and Intercomparison for Integrated Hydrologic Models (IH-MIP) [4,17] These studies have compared lumped and distributed models extensively, evaluating model performance and capabilities at varying scales, but few studies if any have considered the urban system that includes green infrastructure when intercomparing hydrologic models. The guiding principle of this work is like the previous studies in which different integrated hydrologic models perform standardized benchmark problems to gain an increased understanding of the representation of coupled hydrologic processes and how they can be used to inform and improve modeling schemes and systems [4,17,27]. We discuss and compare the results to provide better understanding and confidence in the use of both distributed and lumped hydrologic models to represent green infrastructure in urban environments
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