生物滞留带结构层参数对道路径流滞蓄效应影响

基于非饱和土壤水分运动理论,采用数值模拟方法研究了4种降雨作用下生物滞留带结构层参数对设施积水、产流及径流调控效应的影响特性。结果表明:生物滞留带表层积水受蓄水层深度影响显著,随蓄水层深度由20 cm增加到30 cm,设施的溢流控制水量平均提高0.196 m3左右,但积水时长增加可达85 min;生物滞留带各结构层参数对穿孔管产流均有一定影响,随种植土层与砂滤层厚度比或内部储水区高度增加,穿孔管产流时刻推迟,产流峰值减小,而蓄水层深度的增加则可导致穿孔管产流时刻提前、产流峰值增大;在4种降雨作用下,5类滞留带径流量平均消减率为16.71%~37.31%,径流峰值平均消减率为41.53%~63.90%,产流平均延迟时间为97.75~166.50 min;当滞留带发生溢流时,设施的径流调控能力显著降低,且结构层参数对设施径流调控效果的影响减弱。     

Is there a limit to bioretention effectiveness? Evaluation of stormwater bioretention treatment using a lumped urban ecohydrologic model and ecologically based design criteria

In this study, we developed the urban ecohydrology model (UEM) to investigate the role of bioretention on watershed water balance, runoff production, and streamflow variability. UEM partitions the land surface into pervious, impervious, and bioretention cell fractions. Soil moisture and vegetation dynamics are simulated in pervious areas and bioretention cells using a lumped ecohydrological approach. Bioretention cells receive runoff from a fraction of impervious areas. The model is calibrated in an urban headwater catchment near Seattle, WA, USA, using hourly weather data and streamflow observations for 3 years. The calibrated model is first used to investigate the relationship between streamflow variability and bioretention cell size that receives runoff from different values of impervious area in the watershed. Streamflow variability is quantified by 2 indices, high pulse count (HPC), which quantifies the number of flow high pulses in a water year above a threshold, and high pulse range (HPR), which defines the time over which the pulses occurred. Low values of these indices are associated with improved stream health. The effectiveness of the modelled bioretention facilities are measured by their influence on reducing HPC and HPR and on flow duration curves in comparison with modelled fully forested conditions. We used UEM to examine the effectiveness of bioretention cells under rainfall regimes that are wetter and drier than the study area in an effort to understand linkages between the degree of urbanization, climate, and design bioretention cell size to improve inferred stream health conditions. In all model simulations, limits to the reduction of HPC and HPR indicators were reached as the size of bioretention cells grew. Bioretention was more effective as the rainfall regime gets drier. Results may guide bioretention design practices and future studies to explore climate change impacts on bioretention design and management.     

Modelling hydrological response to a fully‐monitored urban bioretention cell

Municipalities and agencies use green infrastructure to combat pollution and hydrological impacts (e.g., flooding) related to excess stormwater. Bioretention cells are one type of infiltration green infrastructure intervention that infiltrate and redistribute otherwise uncontrolled stormwater volume. However, the effects of these installations on the rest of the local water cycle is understudied; in particular, impacts on stormwater return flows and groundwater levels are not fully understood. In this study, full water cycle monitoring data were used to construct and calibrate a two‐dimensional Richards equation model (HYDRUS‐2D/3D) detailing hydrological implications of an unlined bioretention cell (Cleveland, Ohio) that accepts direct runoff from surrounding impervious surfaces. Using both preinstallation and postinstallation data, the model was used to (a) establish a mass balance to determine reduction in stormwater return flow, (b) evaluate green infrastructure effects on subsurface water dynamics, and (c) determine model sensitivity to measured soil properties. Comparisons of modelled versus observed data indicated that the model captured many hydrological aspects of the bioretention cell, including subsurface storage and transient groundwater mounding. Model outputs suggested that the bioretention cell reduced stormwater return flows into the local sewer collection system, though the extent of this benefit was attenuated during high inflow events that may have exhausted detention capacity. The model also demonstrated how, prior to bioretention cell installation, surface and subsurface hydrology were largely decoupled, whereas after installation, exfiltration from the bioretention cell activated a new groundwater dynamic. Still, the extent of groundwater mounding from the cell was limited in spatial extent and did not threaten other subsurface infrastructure. Finally, the sensitivity analysis demonstrated that the overall hydrological response was regulated by the hydraulics of the bioretention cell fill material, which controlled water entry into the system, and by the water retention parameters of the native soil, which controlled connectivity between the surface and groundwater.     

低影响发展的雨洪资源调控措施研究现状与展望

低影响发展(Low Impact Development,LID)作为新兴的雨洪资源调控设计策略,对城市雨水资源化利用及生态环境保护具有重要的作用.系统论述了LID的定义、产生背景、设计目标及理念;分析了LID在主要技术措施、设计方法、效果监测、模型模拟等方面的研究进展,归纳总结了LID的优点及局限性;在此基础上,分析了LID的推广及应用前景,指出实地监测、介质试验、模型模拟及其与区域可持续发展的融合研究是目前LID研究的关键问题.国外LID的雨洪资源调控技术和方法对中国城市雨水资源化利用和生态环境保护具有借鉴意义.     

Laboratory study of infiltration into two frozen engineered (sandy) soils recommended for bioretention

Infiltration of water into two frozen engineered soils of different gradation was studied in laboratory soil columns 1.2 m long and 0.1 m in diameter. Prior to testing, the soil moisture was adjusted to two levels, described by the gravimetric water content of 5% or 10%, and soils were compacted to about 80–90% of the maximum dry density and refrigerated to temperatures ranging from ?8 to ?2 °C. Water with temperatures 8–9 °C was thereafter fed on the top of columns at a constant head, and the times of water breakthrough in the column and reaching a steady percolation rate, as well as the percolation rate, were recorded. The soil water content was a critical factor affecting the thawing process; during freezing, soil moisture was converted into ice, which blocked pores, and its melting required high amounts of energy supplied by infiltrating water. Hence, the thawing of soils with higher initial water content was much slower than in lower moisture soils, and water breakthrough and the attainment of steady percolation required much longer times in higher moisture soils. Heat transfer between infiltrating water, soil ice, and frozen soil particles was well described by the energy budget equations, which constitute a parsimonious model of the observed processes. The finer grained soil and more compacted soil columns exhibited reduced porosity and required longer times for soil thawing. Practical implications of study results for design of bioretention facilities (BFs) in cold climate include the use of coarse engineered soils and fitting bioretention facilities with a drain facilitating soil drainage before the onset of freezing weather. Copyright © 2015 John Wiley & Sons, Ltd.     

Modelling of stormwater biofilters under random hydrologic variability: a case study of a car park at Monash University,Victoria (Australia)

Biofiltration systems represent an effective technology for the management of urban stormwater runoff volumes and quality. The performance of these systems, although largely dependent on their physical characteristics, is also strongly affected by the natural variability of runoff occurrence and volumes. This article presents a model that describes the statistical behaviour of the main variables involved in the water balance of a biofiltration system, given its main physical properties (filter media and vegetation types) and accounting for the natural inflow variability in terms of occurrence and water volumes. The model permits the analytical derivation of the long‐term (e.g. annual) probability density function of the soil water content in the filter media and the estimation of the main statistics of water fluxes, that is, outflow, evapotranspiration and overflow. By relating the soil water content in the filter media before inflow events to the outflow total nitrogen concentrations, the model also gives estimates of the statistics of nitrogen removal performance as a function of inflow variability. The model was tested against field data collected at a stormwater biofiltration system in Melbourne, Australia. The model could be used to rapidly assess the hydrologic and nitrogen treatment performance of alternative applications of biofiltration for stormwater management across a range of climates. Copyright © 2011 John Wiley & Sons, Ltd.     

生物滞留系统去除地表径流中的氮素研究评述

总结了近年来国内外应用生物滞留系统脱除降雨径流氮素的研究现状,从生物滞留系统脱氮效能、脱氮影响因素和脱氮机制3个方面论述了国内外主要研究进展和理论成果。提出了生物滞留系统脱氮的研究建议:加强生物滞留系统内氮素迁移转化驱动机制研究;推动生物滞留系统"宏观生境-运行效能-微生态系统"耦合响应体系研究;开展生物滞留系统功能植物关键分子生物学特征研究。     

生物滞留设施规模设计方法研究

研究提出了基于单场次降雨分析以及基于长系列降雨统计的生物滞留设施规模设计方法。针对国内市政排水设计一般采用设计重现期的概念,基于单场次降雨分析的规模设计方法用暴雨强度公式和雨型分配方法计算设计降雨过程,由设计降雨推算设施入流过程,用水量平衡法推算出流过程,用洪量削减率、洪峰削减率、洪峰延迟时间评估设计效果。基于长系列降雨统计的规模设计方法对长期日降雨量进行统计分析,得出不同降雨发生频率对应的设施入流量及处理量,用年径流总量削减率评估设计效果。     

生物滞留池的产流规律模拟研究

根据生物滞留池降雨径流观测试验数据,应用HYDRUS-1D对生物滞留池在24h不同降雨频率和不同填料层的产流规律进行模拟分析。结果表明,率定和验证后的HYDRUS-1D可用于模拟生物滞留池的产流过程;在1年一遇(P=100%)到百年一遇(P=1%)的不同频率下,传统填料的生物滞留池通过下渗的排水量占入流总量的百分比从90.7%下降到25.8%,而添加大粒径颗粒填料从88.9%下降到64.7%,说明添加大粒径填料能够显著增加下渗量,并减少溢流和积水时间,但是从延缓产流时间和洪峰削减效果(不发生溢流)方面,传统填料要优于添加大粒径颗粒的填料。     

Bioretention planter performance measured by lag and capture

Bioretention flow-through planters manage stormwater with smaller space requirements or structural constraints associated with other forms of green infrastructure. This project monitored the hydrology of four bioretention planters at Stevens Institute of Technology to evaluate the system's ability to delay runoff and fully capture small rain events. The water depth in the outflow and the volumetric water content near the inflow were measured continuously over 15 months. Rainfall characteristics were documented from an on-site rain gauge. This monitoring determined the time from the start of a rain event to the onset of outflow from each planter, which was defined as the lag. The initial moisture deficit (difference between pre-event volumetric water content and maximum measured volumetric water content), approximate runoff volume, and approximate runoff volume in the first half hour were analysed to determine their effect on runoff capture and lag. During the monitoring period, 38% of observations did not produce measurable outflow. Logistic regression determined that the initial moisture deficit and approximate runoff volume were statistically significant in contributing to a fully captured storm. Despite the large hydraulic loading rate and concrete bottom, the planters demonstrate effective discharge lag, ranging from 5 to 1,841 min with a median of 77.5 min. Volumetric water content of the media and inlet runoff volume in the first half hour were significant in modelling the lag duration. These results represent a combination of controllable and uncontrollable aspects of green infrastructure: media design and rainfall.