TSS concentration in sewers estimated from turbidity measurements by means of linear regression accounting for uncertainties in both variables.

In order to replace traditional sampling and analysis techniques, turbidimeters can be used to estimate TSS concentration in sewers, by means of sensor and site specific empirical equations established by linear regression of on-site turbidity Tvalues with TSS concentrations C measured in corresponding samples. As the ordinary least-squares method is not able to account for measurement uncertainties in both T and C variables, an appropriate regression method is used to solve this difficulty and to evaluate correctly the uncertainty in TSS concentrations estimated from measured turbidity. The regression method is described, including detailed calculations of variances and covariance in the regression parameters. An example of application is given for a calibrated turbidimeter used in a combined sewer system, with data collected during three dry weather days. In order to show how the established regression could be used, an independent 24 hours long dry weather turbidity data series recorded at 2 min time interval is used, transformed into estimated TSS concentrations, and compared to TSS concentrations measured in samples. The comparison appears as satisfactory and suggests that turbidity measurements could replace traditional samples. Further developments, including wet weather periods and other types of sensors, are suggested.     

Assessing dry weather flow contribution in TSS and COD storm events loads in combined sewer systems

Continuous high resolution long term turbidity measurements along with continuous discharge measurements are now recognised as an appropriate technique for the estimation of in sewer total suspended solids (TSS) and Chemical Oxygen Demand (COD) loads during storm events. In the combined system of the Ecully urban catchment (Lyon, France), this technique is implemented since 2003, with more than 200 storm events monitored. This paper presents a method for the estimation of the dry weather (DW) contribution to measured total TSS and COD event loads with special attention devoted to uncertainties assessment. The method accounts for the dynamics of both discharge and turbidity time series at two minutes time step. The study is based on 180 DW days monitored in 2007-2008. Three distinct classes of DW days were evidenced. Variability analysis and quantification showed that no seasonal effect and no trend over the year were detectable. The law of propagation of uncertainties is applicable for uncertainties estimation. The method has then been applied to all measured storm events. This study confirms the interest of long term continuous discharge and turbidity time series in sewer systems, especially in the perspective of wet weather quality modelling.     

CSO treatment strategy based on constituent index relationships in a highly urbanised catchment.

In urbanising catchments the variability of particulate matter (solids) and oxygen demanding constituents of wet weather and dry weather characteristics result in variable treatment effectiveness from physical unit operations and biological unit processes. Higher organic concentrations during dry weather flow are more amenable to biological unit processes while the higher inorganic loads generated largely by urban wet weather constituents and much larger flows can be more effectively treated or conditioned by physical unit operations, including ideally preceded by hydrologic controls. This study examines the relationships between total chemical oxygen demand (COD)(t), dissolved chemical oxygen demand (COD)(d), particulate chemical oxygen demand (COD)(p) and solids, measured as total suspended solids (TSS). Results also provide an index for selection and optimisation of treatment operations for combined sewer overflow (CSO) loads.     

Runoff load estimation of particulate and dissolved nitrogen in Lake Inba watershed using continuous monitoring data on turbidity and electric conductivity

Easy-to-measure surrogate parameters for water quality indicators are needed for real time monitoring as well as for generating data for model calibration and validation. In this study, a novel linear regression model for estimating total nitrogen (TN) based on two surrogate parameters is proposed based on evaluation of pollutant loads flowing into a eutrophic lake. Based on their runoff characteristics during wet weather, electric conductivity (EC) and turbidity were selected as surrogates for particulate nitrogen (PN) and dissolved nitrogen (DN), respectively. Strong linear relationships were established between PN and turbidity and DN and EC, and both models subsequently combined for estimation of TN. This model was evaluated by comparison of estimated and observed TN runoff loads during rainfall events. This analysis showed that turbidity and EC are viable surrogates for PN and DN, respectively, and that the linear regression model for TN concentration was successful in estimating TN runoff loads during rainfall events and also under dry weather conditions.     

Dynamics of wet‐season turbidity in relation to precipitation,discharge, and land cover in three urbanizing watersheds,Oregon

Frequent intense precipitation events can mobilize and carry sediment and pollutants into rivers, degrading water quality. However, how seasonal rainfall and land cover affect the complex relationship between discharge and turbidity in urban watersheds is still under investigation. Using hourly discharge, rainfall, and turbidity data collected from six stations in three adjacent watersheds between 2008 and 2017, we examined the temporal variability of the discharge–turbidity relationship along an urban–rural gradient. We quantified hysteresis between normalized discharge and turbidity by a hysteresis index and classified hysteresis loops during 377 storm events in early, mid, and late wet season. Hysteresis loop index and direction varied by site land cover type and season. Turbidity values peaked quicker in the watersheds with higher degrees of urban development than in a less urbanized watershed. The positive relation between discharge and turbidity was highest in two downstream stations in the mid wet season, whereas it was highest in two upstream stations in the early wet season. Correlation and regression analysis showed that maximum turbidity was best explained by discharge range, and the sensitivity of turbidity to discharge change was higher in the larger downstream watershed than in the small upstream watersheds. A flashiness index was negatively associated with the slope of turbidity versus discharge, suggesting that turbidity is difficult to predict solely on the basis of discharge in flashy urban streams. This paper contributes to a deeper understanding of the spatial and temporal variation of discharge–concentration relationship in urbanizing watersheds, which can help water managers increase the resiliency of water‐related ecosystem services to impacts of climate change.     

Spatial variability of polycyclic aromatic hydrocarbon load of urban wet weather pollution in combined sewers.

In Paris, the OPUR research programme created an experimental on-site observatory of urban pollutant loads in combined sewer systems in order to characterise the dry and wet weather flows at different spatial scales. This article presents the first results on the spatial variability of the polycyclic aromatic hydrocarbon (PAH) load during wet weather flow (WWF). At the scale of a rain event, investigations revealed that (i) PAH concentrations were relatively homogenous whatever the spatial scale and were greater than those of the dry weather flow (DWF), (ii) PAH distributions between dissolved and particulate phases were constant, and (iii) PAH fingerprints exhibited a similar pattern for all catchments. Moreover, an evaluation of the contribution of DWF, runoff and erosion of sewer deposits to WWF load was established. According to the hypothesis on the runoff concentration, the contributions were evaluated at 14, 8 and 78%, respectively, at the scale of the Marais catchment. For all the catchments, the runoff contribution was found quite constant and evaluated at approximately 10%. The DWF contribution seems to increase with the catchment area, contrary to the sewer erosion contribution, which seems to decrease. However, this latter still remains an important source of pollution. These first trends should be confirmed and completed by more investigations of rain events.     

SPATIAL AND TEMPORAL CHANGES IN TOTAL SUSPENDED SEDIMENT CONCENTRATIONS IN AN OXBOW LAKE AFTER IMPLEMENTING AGRICULTURAL LANDSCAPE MANAGEMENT PRACTICES

The Wolf–Broad oxbow lake (417 ha) was evaluated by the Mississippi Department of Environmental Quality and included on the Mississippi 303(d) list of impaired waterbodies for total suspended solids (TSS). A study was undertaken for 2 years to evaluate and document changes to TSS (mg L^?1) and overall lake turbidity (NTU) through best management practice implementation. These two objectives were analysed with routine monthly surface sampling events of turbidity (Eureka Manta 2, automated data sonde) as well as 20 random samples per sampling trip for TSS from June 2008 to June 2010. Results from a non‐parametric Kruskal–Wallis analysis indicated a significant month‐by‐year effect on turbidity and TSS (chi‐squared = 76.08, p = 0.001), but reach (chi‐squared = 2.45, p = 0.784) and depth by reach (chi‐squared = 2.44, p = 0.784) did not show significant effects on turbidity. There were no significant correlations between TSS concentrations and turbidity and 2 days and 7 days summed or mean rainfall for the duration of the evaluation. Spearman correlation analysis for TSS indicated significant correlations between TSS and mean two‐day (r² = 0.62, p = 0.002) and seven‐day (r² = 0.51, p = 0.014) wind speeds. All other variables used in the analysis did not show significant correlation with TSS ( p > 0.05). This suggests that wind conditions, rather than rainfall, predict the greatest variability in TSS and turbidity in Wolf Lake. These documented correlations between lake water column TSS, turbidity and wind highlight the difficulties of demonstrating success of management practices in the short temporal period between project initiation and completion. Unmanageable environmental conditions (wind speed and direction) and limited temporal monitoring scales (1 1/2 years post‐BMP implementation) limit the possibility of demonstrating successful water‐quality improvement within a 303(d) listed waterbody such as Wolf Lake. Copyright © 2011 John Wiley & Sons, Ltd.     

Spatial variability of characteristics and origins of urban wet weather pollution in combined sewers.

An experimental on-site observatory of urban pollutant loads in combined sewers was created in the centre of Paris to quantify and characterise the dry and wet weather flow in relation to spatial scale. Eight rainfall events were studied from April 2003 to May 2004. Samples were analysed for suspended solids, organic matter, nitrogen and heavy metals. Results confirm the extent of wet weather pollution. They have shown the relative homogeneity of SS and organic matter characteristics from one urban catchment area to another. Two groups of heavy metals were identified. The first one concerns Cu, which has a higher concentration in wet weather flow (WWF) than in dry weather flow (DWF), and runoff. The second includes Cd, Pb and Zn, where higher concentrations were measured in urban runoff than in WWF and DWF. A first evaluation of contribution of wastewater, urban runoff and sewer deposit erosion sources to wet weather pollution was established and has highlighted the contribution of wastewater and sewer deposits to this pollution. However, it has shown that sewer deposit erosion remains an important source of wet weather pollution at different spatial scales.     

Integrated modelling of two xenobiotic organic compounds.

This paper presents a dynamic mathematical model that describes the fate and transport of two selected xenobiotic organic compounds (XOCs) in a simplified representation of an integrated urban wastewater system. A simulation study, where the xenobiotics bisphenol A and pyrene are used as reference compounds, is carried out. Sorption and specific biological degradation processes are integrated with standardised water process models to model the fate of both compounds. Simulated mass flows of the two compounds during one dry weather day and one wet weather day are compared for realistic influent flow rate and concentration profiles. The wet weather day induces resuspension of stored sediments, which increases the pollutant load on the downstream system. The potential of the model to elucidate important phenomena related to origin and fate of the model compounds is demonstrated.     

Comparison of satellite reflectance algorithms for estimating turbidity and cyanobacterial concentrations in productive freshwaters using hyperspectral aircraft imagery and dense coincident surface observations

We analyzed 37 satellite reflectance algorithms and 321 variants for five satellites for estimating turbidity in a freshwater inland lake in Ohio using coincident real hyperspectral aircraft imagery converted to relative reflectance and dense coincident surface observations. This study is part of an effort to develop simple proxies for turbidity and algal blooms and to evaluate their performance and portability between satellite imagers for regional operational turbidity and algal bloom monitoring. Turbidity algorithms were then applied to synthetic satellite images and compared to in situ measurements of turbidity, chlorophyll-a (Chl-a), total suspended solids (TSS) and phycocyanin as an indicator of cyanobacterial/blue green algal (BGA) abundance. Several turbidity algorithms worked well with real Compact Airborne Spectrographic Imager (CASI) and synthetic WorldView-2, Sentinel-2 and Sentinel-3/MERIS/OLCI imagery. A simple red band algorithm for MODIS imagery and a new fluorescence line height algorithm for Landsat-8 imagery had limited performance with regard to turbidity estimation. Blue-Green Algae/Phycocyanin (BGA/PC) and Chl-a algorithms were the most widely applicable algorithms for turbidity estimation because strong co-variance of turbidity, TSS, Chl-a, and BGA made them mutual proxies in this experiment.     

A new empirical model for stormwater TSS event mean concentrations (EMCs)

An empirical model for TSS event mean concentrations in storm weather discharges has been derived from the analysis of data sets collected in two experimental catchments (Chassieu, separate system and Ecully, combined system) in Lyon, France. Preliminary tests have shown that the values of TSS EMCs were linked to the variable X =TP ×ADWP (TP rainfall depth, ADWP antecedent dry weather period) with two distinct behaviours under and above a threshold value of X named λ: EMCs are increasing if X < λ and are decreasing if X > λ. An empirical equation is proposed for both behaviours. A specific calibration method is used to calibrate λ while the 4 other parameters of the model are calibrated by means of the Levenberg-Marquardt algorithm. The calibration results obtained with 8 events in both sites indicate that the model calibration is satisfactory: Nash Sutcliffe coefficients are all above 0.7. Monte Carlo simulations indicate a low variability of the model parameters for both sites. The model verification with 5 events in Chassieu shows maximum levels of uncertainty of approximately 20%, equivalent to levels of uncertainty observed in the calibration phase.     

海水干湿交替区氯离子对混凝土侵入作用的现场检测和分析

为研究海水干湿交替区氯离子对混凝土结构的侵入规律,本文分别对作用时间为4年多和16年多的2个海港码头干湿交替区进行多次现场检测。考虑了混凝土的表层对流区深度,运用Fick第二定律对实测氯离子侵入资料进行拟合,研究了干湿交替区不同高程纯扩散区域的表面氯离子含量和氯离子扩散系数。根据该海区潮汐特征的统计资料计算得到不同高程的海水年浸润时间比例,研究了不同码头海水年浸润时间比例与平均表面氯离子含量和平均扩散系数之间的关系。结果表明,海水年浸润时间比例在0.3～0.5之间时,平均表面氯离子含量和平均氯离子扩散系数都较大,将可能对混凝土结构造成严重的侵蚀。本文引入海水年浸润时间比例,可以将干湿交替条件下的氯离子侵入规律应用到其它海域。     

Water Quality Changes Shortly After Low‐Head Dam Removal Examined With Cultural and Microbial Source Tracking Methods

Short‐term effects of low head dam removal on water quality of urbanized stream were evaluated, focusing on fecal pollution indicators. Composite river samples were analyzed for Escherichia coli concentrations, nitrates, phosphates, turbidity and human‐specific marker (HF183) and antibiotic resistance marker (tetQ) before and after dam removal during dry weather conditions. The sampled Olentangy River water in summer before the dam removal showed poor water quality with mean E. coli concentration of 439 colony forming unit (CFU)/100 mL, mean turbidity of 10 NTU and mean nutrient concentrations of 0.61 and 0.41 mg/L for nitrate and phosphate, respectively. Surprisingly, even one month after the dam removal, E. coli numbers doubled and nitrate concentration tripled compared to pre‐removal concentrations. Although the detected HF183 concentrations were below the quantifiable levels, they did not correlate with E. coli concentrations, suggesting E. coli from other than human fecal origin. The correlation between turbidity and E. coli during dry weather further suggests E. coli accumulation in impoundment sediments and release once dam was removed. These short‐term effects of dam removal on water quality should be further evaluated, especially if recreation and other beneficial uses of water in the area are expected. Copyright © 2016 John Wiley & Sons, Ltd.     

Seasonal,Interannual, and Spatial Variability in the Concentrations of Total Suspended Solids in a Degraded Coastal Wetland of Lake Ontario

A 4-year (1993 through 1996) monitoring program examined the distribution of total suspended solids (TSS) in Cootes Paradise Marsh, a shallow (mean depth of 70 cm), degraded, drownedrivermouth marsh of Lake Ontario. Monthly meteorological and hydrographical data from 1986 through 1996 revealed a hydrologically dynamic system that exhibited large seasonal and interannual variation with respect to precipitation amount, discharge volume, and water levels; the prevailing winds were shown to be oriented along the length of the marsh. Interannual variation in TSS concentrations was inversely related to mean seasonal water levels that fluctuated 45 cm over the 11 years. In a stepwise regression analysis, planktonic chlorophyll-a concentration only explained 2% of the variation in TSS, while inorganic and non-algal organic solids explained 70% and 18%, respectively. Mean seasonal water turbidity increased significantly with mean seasonal wind speed at 17 sampling stations during 1993 and 1994. Runoff from a summer rainstorm more than doubled water turbidities at the mouth of all three creeks over the first 36 hours. In enclosure experiments, water turbidity increased proportionately with biomass of benthivorous fish (especially common carp, Cyprinus carpio). When wind and carp disturbance were compared simultaneously in the field, wind speed accounted for 41% of the variation in turbidity while presence of carp explained an additional 21%. The overall temporal and spatial distribution of TSS in the marsh reflected changes in water level, wind activities, onset of rain events, and fish disturbance that acted in concert to keep Cootes Paradise Marsh extremely turbid throughout the summer.     

Flow Events in the Negev—A Regional Quantitative Model

ABSTRACT

The provision of piped water has often been considered a major sanitation measure which will improve the general health of a given population. The associated problems of maintaining a functioning sewerage system so as to insure the quality of the piped water have received increasing recognition. From November 1978 to December 1979, and under varying meteorological conditions, water samples were drawn from ten taps of a piped water supply in an urban slum of Madras, Tamil Nadu, South India. Samples were tested for fecal coliform organisms as an indicator of fecal contamination of water at the taps. Regression analyses were performed on the data, using distance from the tap to the slum's boundary as the independent variable (x) and regressing average log concentration of fecal coliforms (y) during periods of dry and wetter weather, on x. It was found that during wet conditions there was a regression coefficient of +0.972 whereas during dry conditions the regression coefficient was +0.816. The linear regression model suggests that during wet conditions, especially, there is on-site contamination of piped water in the high population density conditions of this urban slum.     

Assessing characteristic time and space scales of in-sewer processes by analysis of one year of continuous in-sewer monitoring data

Long-term and high-frequency in-sewer monitoring opens up a broad range of possibilities to study (influences on) water quantity and quality variations. Using data from the Eindhoven wastewater system in The Netherlands both dry weather flow and wet weather flow situations have been studied. For approximately 160 dry weather days mean diurnal variations of flow and pollutant concentrations have been derived. For wet weather situations (≈ 40 storm events) peak load factors have been studied. Generally, peak load factors for all considered pollutant parameters are larger than one. Peak load factors for particulate matter are larger than for dissolved constituents. Also, the smallest catchment area consistently shows the largest mean peak factors and vice versa.     

Removal of total suspended solids and turbidity within experimental vegetated channel: optimization through response surface methodology

Vegetation plays an important role in transport and settling of suspended sediment in natural waterways. In this study, effectiveness of emergent vegetation in an open channel for the removal of Total Suspended Solids (TSS) and turbidity is empirically investigated. To this end, response surface methodology (RSM) was applied to optimize three variables of vegetated channel including flow velocity at the entrance, density of vegetation, and the length of vegetation zone. Analysis of Variance (ANOVA) was employed to verify the precision of the mathematical models and their relative parameters. Optimum values generated by RSM were compared with experimental results of percentage TSS and turbidity removal and good agreement was observed.     

Column studies to determine mercury settling in road runoff

A study was performed using a settling column to remove mercury (Hg) from road runoff. The emphasis was placed on the relationship between Hg removal and critical settling velocities, as well as the distribution of total suspended solids (TSS). The impact of rainfall characteristics and temperature on Hg removal was also discussed. Results indicated that Hg removal was significant within the initial 30 min of the settling process. The Hg removal rate increased with the decrease of critical settling velocity, and this trend became gradually significant, which could be used as an important reference for the optimization of sedimentation basin design. Hg removal at different settling times was significantly related to initial distribution of TSS. The impact of rainfall intensity on Hg removal was greater than other parameters of precipitation features, followed by rainfall. In addition, Hg removal was moderately related to temperature. The effect of antecedent dry periods on Hg removal was restricted by rainfall and rainfall intensity.