RESUMO
As one of the infiltration-based low-impact development (LID) measures, infiltration trenches are widely used to reduce runoff and improve water quality. The conventional analytical stochastic approach developed for use in the hydrologic design of infiltration trenches often overestimates the trench's runoff reduction performance when the infiltration rate at the bottom of the trench exceeds some high level or when the size of the trench is smaller than some threshold level. Furthermore, the appropriateness of using kernel density estimation (KDE) for rainfall event separation and frequency analysis has not been examined yet in the actual hydrologic design of LIDs. To overcome these deficiencies, an improved analytical stochastic model (ASM) was developed in this study incorporating the KDE-based rainfall event characterization and a modified formula for estimating the effective storage capacity of trenches. The calibration, verification and application of the improved ASM were systematically presented and their results were discussed. The accuracy of the improved ASM were verified by comparing the analytical results against the corresponding continuous simulation results. A large number of design cases in nine provincial capital cities of China were analyzed using the improved ASM and considering the effects of soil types, trench's storage reservoir depth, area ratio, and climate conditions. The improved ASM of infiltration trenches is useful for quickly and accurately assessing their water quantity control performances. The results indicated that the accuracy of improved ASM improved by up to 71 % in terms of R-square among the 9 study areas compared to conventional ASM. The improved ASM can be used to directly and quickly calculate the useful hydrologic performance indices for a given trench size, soil condition, area ratio and local climate condition, it can thus provide scientific guidance for the Sponge City construction in China and sustainable urban stormwater management.
RESUMO
Permeable pavements (PPs) are widely used for stormwater control in urbanized areas as they provide absorption and retention of surface runoff. Previous studies on PP systems mainly focus on non-vehicular access areas with light traffic loads where the base usually connects to native soils which allow exfiltration from the bottom. The runoff reduction performance of the PPs in vehicular access areas (PPs-VAA) featured by more complex structure with underdrain outflow control still needs in-depth investigation. In this study, an analytical probabilistic model was developed to quantify the runoff control performance of PPs-VAA taking into account the effects of climate conditions, layer configurations and varying underdrain outflows. The calibration and verification of the proposed analytical permeable pavement model for vehicular access areas (APPM-VAA) were performed by comparing the analytical results with SWMM simulation results. The model was tested in case studies in Guangzhou and Jinan, China, with humid and semi-humid climate conditions, respectively. Close agreement between the results obtained from the proposed analytical model and those from continuous simulation outputs was observed. The proposed analytical model is proved to be capable of rapidly assessing the runoff control performance of PPs-VAA; it can thus be used in the hydrologic design and analysis of permeable pavement systems in engineering practices.
RESUMO
Water quantity and quality are two key factors affecting the performance of integrated watershed management. Conventional water resources assessment of rivers often deals with water quantity and quality separately. However, how to make an objective and impartial assessment of water resources by incorporating both water quantity and quality remains unclear, especially in watersheds with significant human activity impacts and high spatiotemporal variations in flows. In such areas, the nonmonotonic relationship between the water quality and discharge rate of a river, in contrast to near-natural conditions, is often ignored. To resolve this problem, this paper develops a new framework for the integrated evaluation of water quantity and quality by incorporating a new index, namely, the water quality improvement degree (WQID). The WQID is proposed to quantify the disturbance degree of human activities to the near-natural relationship between the water quality and discharge rate of a river. The Yihe River in Northern China is selected as a case study to apply the proposed framework. The results show that the observed flow discharge rates of some abnormal months after a specific time of change-point are greater than the estimated discharges under the river's near-natural condition. The WQID values in these abnormal months are less than 1, resulting in a decrease in the modified water resources surplus (WRS*) or an increase in the modified water resources deficit (WRD*). This indicates that the WQID can take into account the near-natural law between water quantity and quality to make a more objective evaluation of integrated water resources management for the months of interest. The proposed framework can serve as a useful and reliable tool for a comprehensive assessment of the watershed management performance of a river system.
