Quantification of sewer leakage: a review.

One of the goals of the APUSS project (assessing infiltration and exfiltration on the performance of urban sewer systems) is to assess sewer exfiltration, in order to support cities and operators to define problem-oriented rehabilitation strategies. In this paper, we review various methods currently used for the estimation of exfiltration and discuss data needs and applicability for rehabilitation planning. Although each approach has its individual advantages and drawbacks, we identified pressure tests and tracer methods to have the highest potential for decision support in rehabilitation planning. With regard to future challenges (e.g., micropollutants) such methods might play a key role in integrated sewer management.     

A new sewage exfiltration model--parameters and calibration

Exfiltration of waste water from sewer systems represents a potential danger for the soil and the aquifer. Common models, which are used to describe the exfiltration process, are based on the law of Darcy, extended by a more or less detailed consideration of the expansion of leaks, the characteristics of the soil and the colmation layer. But, due to the complexity of the exfiltration process, the calibration of these models includes a significant uncertainty. In this paper, a new exfiltration approach is introduced, which implements the dynamics of the clogging process and the structural conditions near sewer leaks. The calibration is realised according to experimental studies and analysis of groundwater infiltration to sewers. Furthermore, exfiltration rates and the sensitivity of the approach are estimated and evaluated, respectively, by Monte-Carlo simulations.     

Quantification of sewer leakage by a continuous tracer method

Water authorities interested in the evaluation of the structural state of a sewer must quantify leakage to plan strategic intervention. However, the quantification of the exfiltration and the localisation of structural damage are challenging tasks that usually require expensive and time-consuming inspections. Herein, we report one of the first applications of the QUEST-C method to quantify the exfiltration in a continuously operating sewer by dosing two chemical tracers, sodium bromide (NaBr) and lithium chloride (LiCl). The method was applied at the catchment scale in a 14-year-old sewer in Rome, Italy. Preliminary laboratory tests, field measurements, and numerical simulations showed that reliable results require the QUEST-C method to be applied to sewers without lateral inflows, during periods of quasi-steady flow, and that the travel time of the NaBr tracer is minimised. Three sewer reaches were tested and the estimated exfiltration, as a fraction of the dry weather flow (DWF), increased from 0.128 in the agricultural area to 0.208 in the urban area. Although our estimates are at the lower end of the range given in the literature (0.01-0.56 DWF), the exfiltration was not negligible, and interventions should focus on the sewers in urban areas. This illustrates the capability of the QUEST-C method to guide strategic intervention at low cost and without an interruption of sewer operation. However, careful interpretation of the results is recommended for sewers with many lateral inflows, where leakage may be overestimated.     

Application of a leakage model to assess exfiltration from sewers.

The exfiltration of wastewater from sewer systems in urban areas causes a deterioration of soil and possibly groundwater quality. Beside the simulation of transport and degradation processes in the unsaturated zone and in the aquifer the analysis of the potential impact requires the estimation of quantity and temporal variation of wastewater exfiltration. Exfiltration can be assessed by the application of a leakage model. The hydrological approach was originally developed to simulate the interactions between the groundwater and surface water, it was adapted to allow for modelling of interactions between groundwater and sewer system. In order to approximate the exfiltration specific model parameters infiltration specific parameters were used as a basis. Scenario analysis of the exfiltration in the City of Dresden from 1997 to 1999 and during the flood event in August 2002 shows the variation and the extent of exfiltration rates.     

Monitoring of carbamazepine concentrations in wastewater and groundwater to quantify sewer leakage.

Monitoring of carbamazepine concentrations in wastewater and groundwater enables us to identify and quantify sewer exfiltration. The antiepileptic drug carbamazepine is hardly removed in wastewater treatment plants and not or just slightly attenuated during bank infiltration and subsoil flow. Concentrations in wastewater are generally 1000 times higher than the limit of quantification. In contrast to . many other wastewater tracers carbamazepine is discharged to the environment only via domestic wastewater. The results from this study carried out in Linz, Austria indicate an average exfiltration rate of 1%, expressed as percentage of the dry weather flow that is lost to the groundwater on the city-wide scale. This rate is lower than sewage losses reported in most other studies which attempted to quantify exfiltration on the basis of groundwater pollution. However, it was also possible to identify one area with significantly higher sewage losses. This method seems to be very suitable for the verification of leakage models used to assess sewer exfiltration on a regional scale.     

Quantification of sewer exfiltration using the anti-epileptic drug carbamazepine as marker species for wastewater.

The anti-epileptic drug carbamazepine was used as marker species in wastewater to identify and quantify sewer exfiltration. In several studies carbamazepine turned out to be hardly removed in wastewater treatment and not or just slightly attenuated during bank infiltration. Concentrations in wastewater are generally 1000 times higher than the limit of quantification. In contrast to many other marker species a "young" drug as carbamazepine is discharged to the environment only by wastewater. The results from this study carried out in Linz, Austria indicate an average exfiltration rate, expressed as percentage of the dry weather flow that is lost on the city-wide scale, of 1%. This rate is lower than sewage losses reported in most other studies which attempted to quantify exfiltration on the basis of groundwater pollution. However, it was also possible to identify one area with significant higher sewage losses.     

Groundwater infiltration, surface water inflow and sewerage exfiltration considering hydrodynamic conditions in sewer systems

Sewer systems are closely interlinked with groundwater and surface water. Due to leaks and regular openings in the sewer system (e.g. combined sewer overflow structures with sometimes reverse pressure conditions), groundwater infiltration and surface water inflow as well as exfiltration of sewage take place and cannot be avoided. In the paper a new hydrodynamic sewer network modelling approach will be presented, which includes--besides precipitation--hydrographs of groundwater and surface water as essential boundary conditions. The concept of the modelling approach and the models to describe the infiltration, inflow and exfiltration fluxes are described. The model application to the sewerage system of the City of Dresden during a flood event with complex conditions shows that the processes of infiltration, exfiltration and surface water inflows can be described with a higher reliability and accuracy, showing that surface water inflow causes a pronounced system reaction. Further, according to the simulation results, a high sensitivity of exfiltration rates on the in-sewer water levels and a relatively low influence of the dynamic conditions on the infiltration rates were found.     

应用聚丙烯酰胺改善砂土保水性的试验研究

通过对聚丙酰胺改善砂土保水性的试验研究成果表明,施用聚丙烯酰胺可以加速土壤水分入渗,减少渗出量。抑制土壤水分蒸发,从而增强土壤的持水能力,降低土壤密度,使土壤形成良好的疏松结构。     

基于高密度电法和综合示踪法的堤坝渗漏通道联合探测方法

为准确探测堤坝渗漏通道的位置及范围,降低单一探测方法的局限性及不确定性,提出了一种基于高密度电法与综合示踪法的堤坝渗漏通道联合探测方法。抽水蓄能电站实例验证表明：综合示踪法通过多种示踪试验对高密度电法测试成果进行验证,可以有效辅助高密度电法判别低阻异常区,解决高密度电法成果解释非唯一性问题;高密度电法和综合示踪法联合进行堤坝渗漏通道探测效率高,准确性强。     

Factors influencing exfiltration processes in sewers.

Exfiltration from sewers is widespread and emerging legislation may require water service providers to identify, and rectify, its sources in sewerage systems. This paper describes exfiltration test apparatus and a series of experiments undertaken using sewage to gain a better understanding of the influence of sewage solids and sediments on leakage rates. An overview of the results obtained is given, which demonstrates that most previous estimates of exfiltration leakage rates were too high due to a lack of appreciation of the "self-repairing" action of sewage and sewage associated solids. Exfiltration rates of 0.1% of the sewer flow or 0.001 I/s have been recorded for defects up to 6 mm wide.     

简易粒子图像测速(PIV)技术开发与优化技巧

粒子图像测速(PIV)技术是一种瞬态流动平面二维速度场测试技术,在细部流场实测领域得到重视,但是成熟的PIV产品价格高昂。鉴于此,介绍了一种简易的PIV装置,主要由高速摄像机、激光发射器、柱面透镜和示踪粒子构成,以较低成本即可基本实现商业用PIV产品的功能。为了验证简易PIV性能,设计了PIV简易装置,采用Fluent软件模拟,并结合PIV技术对比分析了简易PIV装置的优缺点,同时对影响结果的粒径大小和粒子跟随性进行了优化。结果表明,简易PIV装置适宜选用玉米粉作为示踪粒子,并需要根据示踪粒子跟随性所能达到的最大进口水流速度选择高速摄像机的帧率,最终能够较好地实现流场实测,进而达到对PIV技术进行开发和优化的目的,其分析结果将为后续研究者提供参考。     

The effectiveness of selected microbial and chemical indicators to detect sewer leakage impacts on urban groundwater quality.

Sewer and stormwater pipe leakage can lead to the degradation of urban groundwater quality. This groundwater may be subsequently used for public water supply and so the resulting water treatment and public health consequences can be serious. To understand the impact of sewer exfiltration on groundwater quality, suitable indicators need to be sampled and analysed for. This study examined potential sewer-derived inorganic and microbial parameters in the U.K. city of Doncaster. Sulphite reducing clostridia, faecal streptococci and boron were all detected in groundwater with reductions compared with sewer values ranging from 1 to 6 orders of magnitude for the former two, to 1 to 2 orders of magnitude decrease for boron. The correlation between these two different indicator types suggests that groundwater quality is being adversely affected by sewer leakage in the study area. The employment of several and varied indicators can better demonstrate the effect than use of single parameters.     

一维河流水团示踪试验数据的模糊线性回归

将模糊线性回归的概念引入分析河流水团示踪试验数据、确定河流水质参数的计算过程中,建立计算河流水质参数的模糊线性回归模型,利用该模型能计算出不同置信水平下水质参数的取值范围。算例验证结果表明,应用模糊线性回归模型可以有效地确定河流的水质参数,且计算过程具有一定的稳定性、可靠性和灵活性,模糊线性回归模型是分析河流水团示踪试验数据、确定河流水质参数的一种有效的途径。     

Automated streamflow measurements in high-elevation Alpine catchments

Salt dilution is a well-established streamflow measurement method in creeks, which works particularly well downstream of turbulent flow sections as the mixing of the salt tracer is enhanced. Usually, salt dilution measurements are performed manually, which considerably limits the observations of rare peak flow events. These events are particularly important for constructing robust rating curves and avoiding large uncertainties in the extrapolation of streamflow values. An additional challenge is the variability of the river cross section, especially after larger discharge events, leading to nonstationary rating curves. Therefore, discharge measurements well distributed over time are needed to construct a reliable streamflow–water level relationship and to detect changes caused by erosion and deposition processes. To overcome these two issues, we used an automated streamflow measuring systems at three different sites with contrasting hydrological and hydraulic characteristics in the Alps. This system allowed us to measure discharge at nearly maximum flow of the observation period (2020–2021) at all three sites and to detect abrupt changes in the rating curve by performing event-based salt injections. The uncertainty in the measurements was quantified, and the streamflow was compared with official gauging stations in the same catchment. Based on a very large dataset of almost 300 measurements, we were able to evaluate the reliability of the system and identify the primary sources of uncertainty in the experimental setup. One key aspect was the site selection for the downstream electrical conductivity sensors, as measurement location strongly controls the signal-to-noise ratio in the recorded breakthrough curves.     

Balancing Costs and Benefits in Selecting New Information: Efficient Monitoring Using Deterministic Hydro-economic Models

Uncertainty reduces reliability and performance of water system operations. A decision-maker can take action, accepting the present uncertainty and facing its risks, or reduce uncertainty by first obtaining additional information. Information, however, comes at a cost. The decision-maker must therefore efficiently use his/her resources, selecting the information that is most valuable. This can be done by solving the Optimal Design (OD) problem. The OD problem balances the cost of obtaining new information against its benefits, estimated as the added value of better informed actions. Despite its usefulness, the OD problem is not widely applied. Solving the OD problem requires a stochastic hydro-economic model, whereas most of hydro-economic models presently used are deterministic. In this paper we introduce an innovative methodology that makes deterministic hydro-economic models usable in the OD problem. In deterministic models, Least Squares Estimation (LSE) is often used to identify unknown parameters from data, making them, and hence the whole model, de facto stochastic. We advocate the explicit recognition of this uncertainty and propose to use it in risk-based decisions and formulation of the OD problem. The proposed methodology is illustrated on a flood warning scheme in the White Cart River, in Scotland, where a rating curve uncertainty can be reduced by extra gaugings. Gauging at higher flows is more informative but also more costly, and the LSE - OD formulation results in the economically optimal balance. We show the clear advantage of monitoring based on OD over monitoring uniquely based on uncertainty reduction.     

Air-water mass transfer and tracer gases in stormwater systems.

Reaeration is a central quality parameter for the performance of environmental systems such as ponds receiving urban and road runoff. Tracer gases can be used to measure reaeration rates in these systems. The methods comprise injection of a volatile tracer into an environmental system and subsequently measurement of the emission of the volatile tracer. The physical basis of such methods is the existence of a constant ratio between the air-water mass transfer coefficient for oxygen and the corresponding mass transfer coefficient for the volatile tracer gas. This constant ratio is often not clearly defined in the literature due to difficulties in both experimental procedures and handling of data. In this study such methods are evaluated and an experimental procedure and a corresponding data processing procedure for a general and reliable determination of mass transfer rates are presented. Propane is selected as an example of an appropriate tracer gas and the ratio between the mass transfer coefficients of oxygen and propane is determined.     

地下水示踪连通试验在水文地质勘察中的应用

地下水示踪试验广泛应用于水文地质工作中,是一项成熟的技术方法,它能有效地查明地下水流向,并通过试验获得进行地下水定量评价的水文地质参数。保定市一亩泉水源地地下水回灌工程水文地质勘察中,应用地下水示踪连通试验,查明了工程区回灌水向外流域流失的方向,获得的水文地质参数与抽水试验结论一致,为回灌区水文地质条件的研究及回灌方法的选择提供了可靠的保证。     

Identifying Uncertainty Guidelines for Supporting Policy Making in Water Management Illustrated for Upper Guadiana and Rhine Basins

In recent years, guidelines have been developed for supporting water managers in dealing with uncertainty in integrated water resources management (IWRM). Usually such guidelines have concentrated on certain aspects of processes in IWRM, notably on uncertainty associated with the modelling process and monitoring data. While this is of undisputed importance for supporting water managers in making well balanced and informed decisions, less attention has been paid to guiding policy makers in where uncertainty may emerge when considering the whole water management process. In this paper it is assessed in what way the policy makers can benefit from support in accounting for uncertainty at various stages in the water management process. Point of departure is an analysis of a broad range of uncertainty guidelines and their categorization in the water management process using a recently developed framework. Emphasis is on linking sources of uncertainty to uncertainty guidelines from an applied point of view in water management by developing a way to assist water managers to deal with uncertainty in IWRM and make informed and robust decisions. To support this, the Upper Guadiana basin in Spain and three Rhine basins are used as cases for water management issues in which it is demonstrated how water managers potentially can benefit from uncertainty guidelines in support of policy making, for instance with respect to implementation of the Water Framework Directive (WFD).     

SWAT模型径流模拟的校正与不确定性分析

为比较SUFI-2和GLUE两种常用的SWAT模型校正与不确定性分析方法的优劣,以三峡库区大宁河流域为研究对象,应用Arc SWAT 2012对大宁河流域进行径流模拟,并分别基于SUFI-2和GLUE方法进行校正和不确定性分析,进而从模型模拟结果的不确定性、拟合效果、运算效率和参数不确定性分析等方面对SUFI-2和GLUE进行比较。结果表明:SUFI-2和GLUE都可以较好地应用于大宁河流域SWAT模型的校正和不确定性分析,但SUFI-2方法能通过较少的模拟次数获得更小的模拟不确定性带以及更佳的拟合效果,而GLUE方法在参数不确定性分析方面的表现更佳。对于SWAT模型径流模拟,建议用SUFI-2方法进行校正和模拟结果不确定性分析,用GLUE方法进行参数不确定性分析。     

应用传递函数模型预报农药阿特拉津在土壤中的运移

本文首先对农药阿特拉津(Atrazine)在稳定流场饱和均质土壤中的运移进行了室内实验研究，采用易混合置换的方法，获得了示踪溶质Br-和Atrazine同步脉冲输入1h后的出流浓度动态；其次由批技术得到Atrazine的分配系数，进而获得阻滞因子，在此基础上应用传递函数模型，根据示踪溶质的迁移预报了吸附作用存在时Atrazine在土壤中的运移动态。