W.J. Shepherd

Predicting combined sewer overflows chamber depth using artificial neural networks with rainfall radar data

Combined sewer overflows (CSOs) represent a common feature in combined urban drainage systems and are used to discharge excess water to the environment during heavy storms. To better understand the performance of CSOs, the UK water industry has installed a large number of monitoring systems that provide data for these assets. This paper presents research into the prediction of the hydraulic performance of CSOs using artificial neural networks (ANN) as an alternative to hydraulic models. Previous work has explored using an ANN model for the prediction of chamber depth using time series for depth and rain gauge data. Rainfall intensity data that can be provided by rainfall radar devices can be used to improve on this approach. Results are presented using real data from a CSO for a catchment in the North of England, UK. An ANN model trained with the pseudo-inverse rule was shown to be capable of predicting CSO depth with less than 5% error for predictions more than 1 hour ahead for unseen data. Such predictive approaches are important to the future management of combined sewer systems.

Comparison between InfoWorks hydraulic results and a physical model of an urban drainage system

Urban drainage systems are frequently analysed using hydraulic modelling software packages such as InfoWorks CS or MIKE-Urban. The use of such modelling tools allows the evaluation of sewer capacity and the likelihood and impact of pluvial flood events. Models can also be used to plan major investments such as increasing storage capacity or the implementation of sustainable urban drainage systems. In spite of their widespread use, when applied to flooding the results of hydraulic models are rarely compared with field or laboratory (i.e. physical modelling) data. This is largely due to the time and expense required to collect reliable empirical data sets. This paper describes a laboratory facility which will enable an urban flood model to be verified and generic approaches to be built. Results are presented from the first phase of testing, which compares the sub-surface hydraulic performance of a physical scale model of a sewer network in Yorkshire, UK, with downscaled results from a calibrated 1D InfoWorks hydraulic model of the site. A variety of real rainfall events measured in the catchment over a period of 15 months (April 2008-June 2009) have been both hydraulically modelled and reproduced in the physical model. In most cases a comparison of flow hydrographs generated in both hydraulic and physical models shows good agreement in terms of velocities which pass through the system.

Solute Retention in Storage Tanks

This paper describes the results of steady state laboratory tests of three storage tanks of different lengths. The testing procedure involved the injection of a simulated time varying pollutant concentration that is continuously measured at the inlet and outlet of the tank. The tests have been repeated over a range of discharges and surcharge levels. An initial analysis of the temporal concentration distributions (or breakthrough curves) has been undertaken and the resulting retention times are summarised. The results allow an insight into the hydraulic processes affecting soluble pollutants as they pass through a storage tank and thus may help to improve the design and operation of storage tanks. An estimation of the retention time using ±10% of the uniform flow relationship is shown to encompass all the measured data.

Experimental Quantification of Contaminant Ingress into a Buried Leaking Pipe during Transient Events

AbstractIt has been hypothesized that negative pressures caused by transients within water distribution systems may result in ingress of contaminated groundwater through leaks and hence pose a risk to public health. This paper presents results of contaminant ingress experiments from a novel laboratory facility at The University of Sheffield. An engineered leak surrounded by porous media was subjected to pressure transients resulting from the rapid closure of an upstream valve. It has been shown that a pollutant originating externally was drawn in and transported to the end of the pipe loop. This paper thus presents the first fully representative results proving the occurrence and hence, risk to potable water quality of contaminant ingress.

Spatial and temporal variability of bacterial communities within a combined sewer system

This study describes the temporal and spatial variability of bacterial communities within a combined sewer system in England. Sampling was conducted over 9 months in a sewer system with intensive monitoring of hydraulic conditions. The bacterial communities were characterized by 16S rRNA gene‐targeted terminal restriction fragment length polymorphism analysis. These data were related to the hydraulic data as well as the sample type, location, and time. Temporal and spatial variation was observed between and within wastewater communities and biofilm communities. The bacterial communities in biofilm were distinctly different from the communities in wastewater and exhibited greater spatial variation, while the wastewater communities exhibited variability between different months of sampling. This study highlights the variation of bacterial communities between biofilm and wastewater, and has shown both spatial and temporal variations in bacterial communities in combined sewers. The temporal variation is of interest for in‐sewer processes, for example, sewer odor generation, as field measurements for these processes are often carried out over short durations and may therefore not capture the influence of this temporal variation of the bacterial communities.

Quantifying the Performance of Storm Tanks at Wastewater Treatment Works

Storm tanks at Wastewater Treatment Works (WwTW) are an essential but often neglected component of the sewerage system and in combined systems they provide relief to the WwTW at the time of storm events. Historically in the UK approximately 6 times mean daily dry weather flow (DWF) is discharged to the works with approximately half the inflow – circa 3 times DWF – being discharged to the storm tanks. Once the tanks are full the excess flows are spilled, untreated, to the nearest watercourse or ocean. After the storm event has subsided and the DWF returns to normal, the storm tanks are emptied to the works with the effluents given full treatment. It may be argued that in recent years, the design philosophy for storm tanks has been static, certainly in the UK, and has not moved forward in the same way as other developments associated with integrated quantitative and qualitative modelling of sewer systems and the performance of other ancillary structures. It is common practice for the pollution retention performance of storm tanks to be omitted from regulatory guidelines and hence there is little need to understand what is actually spilled to the receiving water. The design of tanks is usually based on a volume of effluent to be stored but little is known about how the tanks retain pollution or of the subsequent impact that the spilled pollution has on the receiving waters. New legislation in Europe, in the form of the Water Framework Directive, will require all water utility companies to better understand the magnitude, volume and quality of all intermittent discharges that issue from sewerage systems into receiving waters. This approach is recommended at the integrated catchment scale and hence the contribution to receiving waters from storm tanks may form one of the major elements of pollution. This paper describes a review of current practice and presents results of an experimental programme which improves understanding of the hydraulic and pollutant retention performance of storm tanks. This is based on UKWIR research project WW22B.