Improving the performance of stormwater detention basins by real-time control using rainfall forecasts

Dry detention ponds are commonly implemented to mitigate the impacts of urban runoff on receiving water bodies. They currently rely on static control through a fixed limitation of their maximum outflow rate. Real-Time Control (RTC) allows optimizing their performance by manipulation of an outlet valve. This study developed several enhanced RTC scenarios of a dry detention pond located at the outlet of a small urban catchment near Québec City, Canada. The catchment's runoff quantity and TSS concentration were simulated by a SWMM5 model with an improved wash-off formulation. The control procedures rely on rainfall detection, on measures of the pond's water height, and in some of the RTC scenarios on rainfall forecasts. The implemented RTC strategies allow a substantial improvement of the pond's performance - the TSS removal efficiency increases from 46% (current state) to about 90% - while remaining safe and taking a mosquito-breeding risk constraint into account.     

How climate proof is real-time control with regard to combined sewer overflows?

Abstract

A question arising when considering the changing climate is whether real time control (RTC) can be considered as a ‘No Regret’ measure, i.e. can RTC maintain its proven current added-value to reduce emissions from sewage systems in the future under altered rainfall patterns and often higher extreme rainfall intensities. This study explored four climate scenarios relevant for the lowland area of North-western Europe under two time horizons and proved that RTC’s performance only marginally decreased for a representative Flemish catchment under study. Based on this case study, it was found that effects of climate change will lead to, on average, 30–40% more overflow volume in 2050 and 35–65% more overflow volume in 2085. To restore the current situation, additional measures need to be taken, but RTC preserves its contribution to the reduction of overflows. The elaborated methodology is transposable to other locations provided that the necessary information is available.     

Exploring forecast-based management strategies for stormwater detention ponds

Dry detention ponds are commonly implemented to mitigate the impacts of urban runoff on receiving water bodies. They currently rely on static control through a fixed limitation of their maximum outflow rate. This study investigated the performance of several enhanced management strategies for a dry detention pond located at the outlet of a small urban catchment near Québec City, Canada. Among the enhanced scenarios studied are some previously developed real-time control (RTC) strategies, and new operating rules relying on a daily manual adjustment of the outlet gate. Both types of control make use of rainfall forecasts originating from the initial or downscaled Canadian global ensemble prediction system. Different ways of using the forecasts' ensemble spread were considered to take action. The pond performances were investigated considering three different volumetric capacities (including the existing volume). The RTC scenarios are very promising. The value of taking rainfall forecasts into account to prevent pond overflowing is demonstrated. Strategies involving only manual adjustments on a daily basis do not seem helpful.     

Laboratory analysis of the outflow and detention processes from modular tray-based blue roofs

ABSTRACT

Novel laboratory experiments were carried out to investigate the outflow process and the detention effects of a tray module of a blue roof (BR) system designed for runoff control from building roofs. The experiments revealed the outflow from the tray to decline during time, due to a number of complex dynamics occurring in proximity of the outlet orifice. The tests also showed the system to provide potential for relevant attenuation of the flow peak during inflow events (i.e. precipitation) of different magnitude. Based on regression analysis, an empirical relationship was developed for the evaluation of the tray outflow as a function of time, thus providing a tool for improved design of BRs. Finally, combination of the identified relationship with a routine for the water balance simulation of the tray was shown to describe reliably the detention process in the BR tray module.     

Impacts of rainfall events on runoff water quality in an agricultural environment in temperate areas

Since a rise in dissolved organic carbon (DOC) concentrations has been observed for surface waters at least over the last two decades, a change in weather conditions (temperature and precipitations) has been proposed to partly explain this increase. While the majority of DOC delivery from soils to stream occurs during rainfall events, a better understanding of the rainfall influence on DOC release is needed. This study has been conducted in Brittany, western France, on agricultural experimental plots receiving either cattle manure (CM) or pig slurry (PS) as fertilizers in accordance with local practices. Each plot was instrumented with a flow meter and an auto sampler for runoff measurements. The results show that export of DOC during high intensity events is higher than during lower intensity rainfalls. Fertilization has a noticeable impact on total organic carbon (TOC) fluxes with an increase of five to seven folds for PS and CM respectively. If TOC shock load occurs shortly after the rainfall peak, DOC maximum appears with the first flush of the event. Organic carbon (OC) is mainly under colloidal (41.2%) and soluble (23.9%) forms during the first stage of a rainfall event and a control of rainfall intensity on OC colloidal transport is suggested. These findings highlight the potential risk of receiving water quality degradation due to the increase of heavier rainfall events with climate change in temperate areas.     

低影响开发设施组合的水文模拟及不确定性分析

在海绵城市建设中,通过多种低影响开发(LID)设施的组合应用可实现对城市雨水径流的调控。针对LID设施组合的水文模拟存在高维参数估值不确定性分析的难题,以深圳环保产业园LID示范区为例,构建LID组合设施的暴雨洪水管理模型(SWMM),结合Morris筛选法与DREAM算法,对不同降雨条件下模型中不同设施、不同类型参数的灵敏度和不确定性进行分析。结果表明,位于下游的设施参数灵敏度普遍高于上游设施,排水及导水相关参数灵敏度相对较高;下游设施的排水参数后验分布峰值明显,参数不确定性小;中等强度降雨事件模拟结果的不确定性比高强度降雨事件要小。     

可渗水面积率在控规中的估算方法与设计应用

从绩效角度,1.提出“当量可渗水面积率”概念;2.通过雨水截流量比率确定可渗水面积折算系数,推算出适用于北京城区及其近郊的当量可渗水面积折算系数简表;3.提出基于绿地率指标的当量可渗水面积率估算模型,与现行控规指标体系衔接;4.给出基于当量可渗水面积率的奖励办法。案例应用表明,当设计暴雨频率P≥20%时,水环境友好设计可保证北京近郊开发后地表径流增量为0,全部就地滞蓄、再利用。     

Accumulation and wash-off characteristics of surface pollutant and identification of risk areas on urban land uses in a lakeside city,Wuxi, China

ABSTRACT

This paper selected administration and public services, residential areas, roads, green space, parking areas, industrial areas and commercial and business facilities in Wuxi city, China, to analyze the characteristics of pollution accumulation, wash-off and potential risk areas of pollutants over different urban land uses and pavement surface materials. Results showed that green space, residential areas and roads sequestrated higher pollutants than that of other land uses. Materials of masonry and cement pavement accumulated higher pollutant concentration than that on the marble and asphalt pavement. The potential risk areas of non-point source pollution were located in the old residential areas in the downtown region. The results of wash-off simulation showed that the first flushing effect was obvious during the initial period of rainfall. Eighty percent of the accumulative total nitrogen or total suspended solid could be washed-off during the first 25.6–50.2% period of the rainfall events.     

Treatment of stormwater using a detention pond and constructed filters

A stormwater treatment plant, consisting of a detention pond, a constructed filter system and a constructed wetland, has been investigated according to stormwater quality improvement, sediment and heavy metals accumulation and potential toxicity of the stormwater and sediment. The reduction of metal content in the detention pond was on average 26?–?84%. No acute toxicity in the stormwater was detected although heavy metal levels often exceeded guideline values during storm events. Pore water samples of the collected sediments were not toxic but the whole sediment was toxic when assessed with the Microtox^® Solid-phase test. The constructed filter system became clogged due to cementation of the filter substrate.     

Evaluation of performance of Active,Beautiful and Clean (ABC) on stormwater runoff management using MIKE URBAN: a case study in a residential estate in Singapore

ABSTRACT

Singapore has adopted a low impact development equivalent of stormwater management philosophy under a national program called ‘Active, Beautiful and Clean’ (ABC) employing soft-engineering techniques to manage rainfall runoff in the face of climate change and rapid urbanisation. This study makes use of the MIKE URBAN modelling tool to evaluate the performance of ABC units in a new residential precinct based on flow data collected. Calibration results show an overall good fit between the measured data and simulated results based on three goodness-of-fit stats. The runoff factors computed for scenarios with and without the presence of ABC units show an improvement in the range of 21–72%. This study demonstrates the usefulness of using a calibrated model to evaluate the performance of constructed units using measurements. It is recommended that this modelling tool be also used for evaluating water quality performance of the units as well as applying it for use in the planning and implementation process.     

Sensitivity analysis of the DRAINWAT model applied to an agricultural watershed in the lower coastal plain,North Carolina,USA

The DRAINWAT, DRAINmod for WATershed model, was selected for hydrological modelling to obtain water table depths and drainage outflows at Open Grounds Farm in Carteret County, North Carolina, USA. Six simulated storm events from the study period were compared with the measured data and analysed. Simulation results from the whole study period and selected rainfall events assured that the DRAINWAT model reasonably predicted the water table depths and drainage outflow events even though it underestimated outflows in very dry period after 24 April, 2001. The potential evapotranspiration by various calculation methods was found to be the most sensitive parameter in this study. The other three parameters (maximum surface depressional storage, Manning's channel roughness coefficient, and channel bedslope) were not significantly (α = 0.05) sensitive to the cumulative outflow as expected. The DRAINWAT model may be a useful tool for water management in flat agricultural areas with high water table if it can be calibrated properly with reliable measurements.     

Two-copula based simulation for detention basin design

This article presents a Monte Carlo simulation model based on Clayton copula to generate synthetic sequences of rainfall storms whose likelihood of occurrence is in consonance with historical records. These sequences are used as rainfall input data for the Storm Water Management Model to analyse a 3 km² watershed in the city of Granada, Spain. The objective of our study is to estimate the optimal volume of a detention basin that would solve the problem created by a downstream combined sewer system (CSS), part of which is undersized and which cannot be enlarged without considerable cost. In this model, the synthetic rainfall sequences provide multiple inputs to the CSS model, which produce a range of model outputs. Risk-based analysis of these outputs helps to quantify the variability of the CSS response. As a result, our model enables decisions based on the comparison of expected outcomes and the costs of different choices. The rainfall storms are represented as a sequence of rectangular pulses, whose occurrences are driven by a Poisson process with a given arrival rate. Both storm durations and average storm intensities are fitted as Pareto distributions and the dependence between these variables is described using Clayton copula.     

新型渗井-透水网格措施的径流调控效果研究

为更加合理地对雨水资源进行管理和调控,低影响开发(LID)措施日益成为我国许多城市"海绵化"的必然选择。透水网格被认为是一种有着良好雨洪管控效用的LID措施,然而大多情况下施工过程不尽规范,土基多采用渗透性不良的土质,这使得径流调控及渗流效益难以充分发挥,故拟以透水网格砖孔布设渗井来改善该现状。采用试验与SWMM仿真相结合的方法,研究了在6场重现期降雨作用下新型渗井-透水网格措施较透水网格在径流调控方面的改善效果,以及100年重现期降雨条件下两种措施的入渗规律。结果表明,在不同降雨场次下,新型措施较透水网格雨量径流系数降低了9. 94%～51. 09%,洪峰流量削减率提高了2. 91%～30. 42%;滞峰时间延迟效果不显著,在3 min以内;在100年重现期降雨下湿润锋迁移速率提高了73. 47%。     

Assessing the spatio-temporal climate variability in semi-arid Karamoja sub-region in north-eastern Uganda

Semi-arid areas show climatic variability on a spatio-temporal scale. There are few studies on the long-term trends and intensity of this variability from East Africa. We used National Ocean and Atmospheric Administration re-analysis climate data (1979–2009) in this study. Rainfall exhibited a non-significant long-term trend. The climate of the area is variable (coefficient of variation-CV?>35.0%) with spatio-temporal oddities in rainfall and temperature. A rise in minimum (0.9?°C), maximum (1.6?°C) and mean (1.3?°C) temperature occurred between 1979 and 2009. There were more months with climate variability indices below the threshold (<1.0) from 1979 to 1994 than between 1995 and 2009, with wetness intensity increasingly common after 2000, leading to the observed reduction in the recurrence of multi-year drought events. More extreme wet events (rainfall variability index?>2.6) were experienced between 2004 and 2009 than between 1984 and 2003. We consider that the use of spatio-temporal climatic information for timely adjustment to extreme climate variability events is essential in semi-arid areas.     

Adaptation to Climate Change

Problem: Even if significant reductions in global greenhouse gas emissions are achieved, some amount of climate change appears to be inevitable. Local, regional, state, and federal planning and regulation should begin to address how to adapt to these changes.

Purpose: This article presents a policy synthesis of adaptation planning issues, using California as a case study. We examine the institutional and regulatory challenges and tradeoffs that climate change poses in six particularly vulnerable areas: water resources, electricity, coastal resources, air quality, public health, and ecosystem resources. We discuss obstacles to adaptation planning and successes overcoming these barriers, and suggest how planning can incorporate adaptation.

Methods: This article presents a policy synthesis of adaptation planning issues, drawing on our recent research on California's experience and related literature. We summarize the results of six studies that draw on quantitative and qualitative information gathered through surveys, interviews, and literature review.

Results and conclusions: Planners should use forward-looking climate data that include higher water and air temperatures, sea-level rise, and increased numbers of extreme events like heat waves, floods, and wildfires when making decisions about future development, infrastructure investments, open-space protection, and disaster preparedness. Climate change will exacerbate conflicts between goals for economic development, habitat protection, and public safety, requiring stronger interagency coordination and new laws and regulations.

Takeaway for practice: Local and regional planners can help society adapt to a changing climate by using the best available science, deciding on goals and early actions, locating relevant partners, identifying and eliminating regulatory barriers, and encouraging the introduction of new state mandates and guidelines.

Research support: Partial support for this research was provided by Pacific Gas and Electric, The Nature Conservancy, and Next 10.     

排水管道泥沙淤积深度估算方法研究

运用C#编程语言实现了SWMM模型参数的自动提取,通过创建BP-人工神经网络实现了节点水深值与模型参数值之间的非线性拟合,基于模型参数率定的思路提出了一种排水管道泥沙淤积深度的估算方法,并且以G市某雨水排水系统为例,采用4场降雨数据对模型进行了校核与验证。结果表明,通过两场降雨数据的验证,对于管径为1.2~1.8 m的管道,淤积深度预测值与实测值之间的绝对误差均在4 cm以内;模拟结果和实测数据的水深峰现时间偏差均低于实测数据历时的5%,峰值的数值偏差均在3%以内;场次3和场次4两场降雨4个监测点的水深预测值与实测值的平均相对误差分别为3.35%、2.98%,2.75%、2.51%,7.39%、6.77%,5.53%、8.15%,说明该方法能够对排水管道淤积情况进行有效预测。     

Evapotranspiration from subsurface horizontal flow wetlands planted with Phragmites australis in sub-tropical Australia

The balance between evapotranspiration (ET) loss and rainfall ingress in treatment wetlands (TWs) can affect their suitability for certain applications. The aim of this paper was to investigate the water balance and seasonal dynamics in ET of subsurface horizontal flow (HF) TWs in a sub-tropical climate. Monthly water balances were compiled for four pilot-scale HF TWs receiving horticultural runoff over a two year period (Sep. 1999-Aug. 2001) on the sub-tropical east-coast of Australia. The mean annual wetland ET rate increased from 7.0 mm/day in the first year to 10.6 mm/day in the second, in response to the development of the reed (Phragmites australis) population. Consequently, the annual crop coefficients (ratio of wetland ET to pan evaporation) increased from 1.9 in the first year to 2.6 in the second. The mean monthly ET rates were generally greater and more variable than the Class-A pan evaporation rates, indicating that transpiration is an important contributor to ET in HF TWs. Evapotranspiration rates were generally highest in the summer and autumn months, and corresponded with the times of peak standing biomass of P. australis. It is likely that ET from the relatively small 1 m wide by 4 m long HF TWs was enhanced by advection through so-called “clothesline” and “oasis” effects, which contributed to the high crop coefficients. For the second year, when the reed population was well established, the annual net loss to the atmosphere (taking into account rainfall inputs) accounted for 6.1-9.6 % of the influent hydraulic load, which is considered negligible. However, the net loss is likely to be higher in arid regions with lower rainfall. The Water Use Efficiency (WUE) of the wetlands in the second year of operation was 1.3 g of above-ground biomass produced per kilogram of water consumed, which is low compared to agricultural crops. It is proposed that system level WUE provides a useful metric for selecting wetland plant species and TW design alternatives to use in arid regions where excessive water loss from constructed wetlands can be problematic. Further research is needed to accrue long-term HF TW water balance data especially in arid climatic zones.     

Contamination of headwater streams in the United Kingdom by oestrogenic hormones from livestock farms

Most studies of hormonal activity in rivers have focused on inputs from sewage treatment works (STW), and their consequences for endocrine disruption in fish. It is possible that livestock is contributing to this hormonal activity in rivers. This study represents a search for evidence of steroid hormone contamination in streams associated with livestock farms. The majority of the 10 sites selected were streams running through dairy farms, although some examples of beef, sheep and pigs were included. Passive water samplers (Polar Organic Chemical Integrative Samplers-POCIS) were deployed up- (control) and down-stream of the farms for 3 to 10 weeks (mean=39 days) during the period November 2004 to January 2005. At one site, water samples were also taken automatically during rainfall events. All samples were solvent-extracted. Total oestrogenic activity in concentrates of the extracts was analysed using the Yeast Estrogen Screen (YES) calibrated against 17beta-oestradiol (E2), while oestrone (E1), E2 and 17alpha-ethinylestradiol (EE2) were analysed by liquid chromatography-mass spectrometry (LC-MS/MS). Stream water from the entirety of only one rainfall event was sampled directly, but this revealed background activity (E2 equivalents) of 0-0.3 ng/l, rising to a transient peak of 9.4 ng/l. Average oestrogenic activity at this site as estimated from the POCIS samplers was 1.8-2.7 ng E2 equiv./l. Estimated average oestrogenic activity across all sites (with one exception) lay in the range 0-26.5 ng E2 equiv./l (mean=2.0 ng/l; S.D.=5.1), based on the POCIS samples. The outlier was 292 ng/l, and this could not be specifically linked with livestock rearing. 92% of monitoring stations (at least one on each farm) contained some oestrogenic activity, and activity was higher at downstream sites in 50% of cases. Although no EE2 was detected analytically in any stream, E1 and E2 were almost ubiquitous, with E2 equivalents ranging from 0.04 to 3.6 ng/l across all sites. Furthermore, steroid concentrations downstream of livestock were higher than upstream in 60% of cases, more markedly so than for the YES data. In several cases, activity upstream was greater than downstream, and this tended to be associated with higher activity than could be accounted for by the hormone analyses. Both the YES and chemical analytical data suggest that fish in headwater streams on or near some livestock farms may be at risk of endocrine disruption.     

A frost decay exposure index for porous,mineral building materials

The disintegrative process of freezing and thawing of porous, mineral materials represents a significant challenge in the design and construction of building enclosures. In this paper, we present a simple method for assessing the relative potential of a climate to accelerate frost decay based on multi-year records of daily air temperatures and rainfall, with special emphasis on masonry. Distributions of 4-day rainfall prior to days with freezing events provide quantitative information on the geographically dependant frost decay risk in porous, mineral building materials in a given climate. Data from 168 weather stations in Norway are analysed, using weather data from the reference 30-year period 1961–1990.