Spatial scale effect of surface routing and its parameter upscaling for urban flood simulation using a grid‐based model

Urban catchments are characterized by a wide variety of complex juxtapositions and surface compositions that are linked to multiple overland flow paths. Their extremely high spatial heterogeneity leads to great sensitivity of hydrologic simulation to the scale variation of calculation units. Although extensive efforts have been made for investigating the scale effects and indicate its significance, less is understood of how routing features vary with spatial scales and further how the variation of routing features influences the hydrological response. In this paper, a grid-based distributed urban hydrological model is applied to study spatial scale effects ranging from 10 to 250 m. Two parameters are proposed to quantitatively depict the routing features of overland flow specified for impervious and pervious areas. The results show that routing features are quite sensitive to spatial resolution. Large differences among simulations exist in the infiltration amounts attributed to the combined effects of the two routing parameters, which leads to opposite effects for both total flow volume and peak flow for various rainfall events. The relationship of the key model parameters at different spatial resolutions can be explicitly expressed by corresponding routing features. With this relationship, parameters transfer among different spatial scales can be realized to obtain consistent simulation results. This study further revealed the quantitative relationship between spatial scales, routing features and the hydrologic processes, and enabled accurate and efficient simulations required by real time flooding forecasting and land-atmosphere coupling, while fully taking the advantages of detailed surface information. Plain Language Summary Given the inherent complex underlying surface compositions and overland flow paths in urban areas, underlying high spatial resolution surface data eventually become necessary. Unfortunately, high resolution modelling in urban catchment is still challenging in terms of computational restricts, proper setting up of parameters etc., due to the high spatial heterogeneity. Practical simulation requirements often limit the use of high resolution models, as in the case of real time prediction of urban flooding, the coupling of land-atmosphere processes. Therefore, it is necessary to investigate the scale effects and its mechanism, and then to explore an accommodation approach to enable precise flooding prediction with a coarse model. For grid-based and distributed hydrologic models, the mosaic method can basically eliminate the scale effects on the runoff generation process. However, the scale effects on overland flow routing remain insufficiently understood, and to help understand the scale effects, simulations were performed under five different resolutions, ranging from 10 m to 250 m, for various rainfall events. Two physical parameters are introduced to quantify the scale effects on routing features. Three variables are concurrently calculated to assess the effects on modeling outputs. The results indicate that routing features are sensitive to changes in spatial resolution, which results in opposite effects on simulation results under different rainfall conditions. In conclusion, an accommodation approach is proposed based on the affecting mechanism

Tailoring structure and properties of polyelectrolyte-based material via materials selection and post-assembly treatment

Although polyelectrolyte-base materials have demonstrated uses in a wide range of applications, controlling properties of polyelectrolyte-based materials is challenging because of their sensitivity to material and processing parameters. This dissertation focused on fundamental science of polyelectrolyte-based materials. Although polyelectrolyte-based materials like PEMs and PECs have a wide range of potential applications, the relationship between structure and properties of those materials is still not fully understood. In this work, factors that can affect the structure and properties of PEMs and PECs were studied. Based on those results, potential approaches to tailor structure and properties of polyelectrolyte-based materials can be developed.\nThe role of the chemistry and molecular weight of first layer of a PEM was studied. By changing first layer materials, PEMs showed different internal structure, mass accumulation, and surface morphology. Quartz crystal microbalance with dissipation monitoring (QCM-D) was used to monitor the PEM assembly process. First layer choice affects the total mass accumulation of the PEM as well as the stoichiometry and thickness of the PEM. PEM topography is also affected by first layer choice. Combined with the stoichiometry results, these findings indicate that the structure of a PEM is fundamentally different depending on first layer chemistry and molecular weight. Selection of appropriate first layer material is therefore an important consideration in the design of a PEM and changing first layer material may be a facile way to tailor the structure and properties of PEMs.\nAnother category of polyelectrolyte-based materials, PECs, which are formed through electrostatic interactions between oppositely charged polyelectrolytes, have garnered sustained interest for their range of potential applications. Since water plays an important role in the structure and properties of polyelectrolyte-based materials, humidity controlled dynamic mechanical analysis (DMA) was used to characterize the thermomechanical properties of dried polyelectrolytes and PECs with different thermal and humidity histories. After exposure to higher humidities (humidity tempering), both room temperature storage modulus and flexural modulus of the resulting PEC increased. Water from the humid air plasticized the PEC, increasing mobility and facilitating chain reorganization during humidity tempering, which resulted in a structure with more intrinsic electrostatic bonds (cross-links) and higher moduli. Storage conditions and relative humidity were demonstrated to influence thermal transitions and mechanical properties of PEC, which highlighted the potential of polyelectrolyte-based materials for new applications where tailoring of mechanical properties is desired

Effect of Assembly pH on Polyelectrolyte Multilayer Surface Properties and BMP‑2 Release

The effect of solution pH during layer-by-layer assembly of polyelectrolyte multilayer (PEM) coatings on properties relevant to orthopedic implant success was investigated. Bone morphogenetic protein 2 (BMP-2), a potent osteoconductive growth factor, was adsorbed onto the surface of anodized titanium, and PEM coatings prepared from solutions of poly-l-histidine and poly­(methacrylic acid) were built on top of the BMP-2. High levels of BMP-2 released over several months were achieved. Approximately 2 μg/cm² of BMP-2 were initially adsorbed on the anodized titanium and a pH-dependent release behavior was observed, with more stable coatings assembled at pH = 6–7. Three different diffusion regimes could be determined from the release profiles: an initial burst release, a sustained release regime, and a depletion regime. BMP-2 was shown to maintain bioactivity after release from a PEM and the presence of a PEM was shown to preserve BMP-2 structure. No visible change was observed in surface roughness as the assembly pH was varied, whereas the surface energy decreased for samples prepared at more basic pH. These results indicate that the initial BMP-2 layer affects PEM surface structure, but not the functional groups exposed on the surface

Effect of Temporal Resolution of Rainfall on Simulation of Urban Flood Processes

Rainfall exhibits substantial variability, and its temporal resolution considerably affects simulation of hydrological processes. This study aims to investigate the effect of the temporal resolution of rainfall (TRR) on urban flood modeling and to explore how high TRR is required. A routing-enhanced detailed urban stormwater (REDUS) model, which has four layers and accounts for complex urban flow paths, was developed and then applied to the campus of Tsinghua University, Beijing, China. For 30 rainfall events at 1-min resolution, the rainfall accuracy index (RAI) was used to describe the discrepancy of rainfall patterns by upscaling. Through hydrodynamic modelling, the effect of TRR was quantified by the relative error of flood volume and peak in typical areas. The results show that (1) flood peak is sensitive to TRR while flood volume is generally not; (2) with lower TRR, discharge peak is underestimated, and a power function is proposed to express the relationship between the effect of TRR and the characteristics of rainfall and underlying surfaces; and (3) rainfall data of 5-min resolution for urban areas smaller than 1 km2, or at least 15-min resolution for larger areas, are required to constrain the relative biases of flood peak within 10%