Water & Wastewater Treatment

WWT January 2019

Water & Wastewater Treatment Magazine

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6 | JANUARY 2019 | WWT | www.wwtonline.co.uk The Talk: opinion JAMES BROCKETT, EDITOR, WWT Becoming more resilient together Developing a more resilient water and wastewater service will require water companies to adopt both a system-wide approach and a collaborative mindset I t might be one of the key themes of the current price review for water companies in England and Wales, but one of the notable things about resilience is that it seems to mean different things to different people. For some, it's the ability to prepare for predictable challenges, such as the next drought, storm, flood or snowfall. For others, it's all about how you respond to the unpredictable: the out-of-the-blue terrorist attack, outbreak of disease, financial crash or political crisis. A third viewpoint sees resilience as not just how you avoid or resist problems, but how you rebuild from the inevitable disruption and learn lessons for the future. So what is resilience? It's all this, and more. As our cover feature makes clear in this issue of WWT, what regulator Ofwat is asking water companies to develop is 'resilience in the round' which contains a number of strands weaved together into a holistic approach. This requires thinking about water networks, assets and operations as an integrated system, and identifying possible points of weakness. An assessment of these vulnerabilities should point to the areas that need investment, reinforcement, training, and preparation. But while it's possible to come up with a framework for how to measure long-term resilience against short-term performance, it's important to remember that the way utilities apply these calculations and approaches will still vary widely. Water companies do have a number of challenges and vulnerabilities in common, but they also have issues that are specific to their geographical area, weather and existing assets, so the solutions that they come up with in the name of resilience will appear to be quite varied. However, one observation is that resilience is a challenge that cannot be addressed in isolation. Just as an individual person's resilience is stronger if they have a network of other people to rely on, any one company needs to be able to respond to a crisis by drawing on the resources of partners, whether they be local authorities, the supply chain, neighbouring companies, other utilities, volunteers and charities, or others. When you consider that many of the challenges faced by the water sector – particularly around climate change and extreme weather – are challenges that impact us all, there should be a willingness to collaborate if the sector is willing to take the lead. Customers, too, can play their part if they are educated about the risks we all face and how they can contribute to reducing them. A more resilient water and wastewater sector is in everybody's interests. SPONSORED BY TONY SIMISTER, TECHNICAL SALES MANAGER, JACOPA LTD Sewer Flow Solutions A host of technology is now available that can regulate flows in sewers, making infrastructure more resistant to the stresses of stormwater D ue to development pressures and the increasing intensity of rainfall due to climatic change the requirement for the regulation of flow in sewers, streams, rivers or any ancillary structure is becoming more commonplace. The capacity of the sewer infrastructure can be incapable of transporting the increasing volumes of storm water, or the river profile cannot contain the flood flow and treatment facilities may not be designed to cater for higher peak flows. Common types of mechanical flow control include throttle pipes, orifice plates, flumes, vortex flow control devices, variable orifice devices and weirs. Powered flow control is also available and is normally used where real time control or complex flow regulation is required. Key points to be considered in flow control design include the accuracy required and the possible need to limit flows below a critical rate. Other considerations include the material to be controlled, whether foul or surface waters, final effluent or river. Also, is upstream storage needed and are there are any limitations on the volume of the structure? Hydrostatic head and flood risks upstream and downstream also need to be considered, as does backwater risk, which affects the accuracy of the control unit. Finally, dry weather flow rates, depth of flow, and velocities must be understood to ensure sewers are self- cleansing. Flow characteristics vary depending on the control type and will affect system performance in terms of upstream storage requirement and the ability to optimise downstream capacity. Here is a summary of some of the devices commonly employed: Throttle pipes can be used to restrict flow through high frictional resistance and energy losses at both entry and exit. However, as they are designed for a specified flow rate and defined maximum upstream water level this type of control is seldom used as flow adjustment is impossible. Orifice plates are simple and cheap to install, though they will only pass the design flow once the maximum head has been reached. Further, these devices should not be used in foul sewers below a diameter of 250mm because of the danger of ragging at small diameters. The Standing Wave Flume is a common flow measurement method at many sewage treatment works and can be used with an actuated valve to create an accurate flow control system. Vortex Flow Control is designed to create an 'air core' that reduces the available aperture, limiting the flow rate. This type of control produces a unique S-shaped head/discharge curve, reaching the desired flow depth only when achieving full depth of water. The Variable Orifice Device regulates flows by varying the size of orifice available. Many can be adjusted on site and they are widely used in the UK and Ireland due to their good accuracy and ability to be adjusted to ± 30% from the design point. Variants are designed for use in foul sewers and have an automatic blockage opening capability. Many controls only provide desired flows at the maximum water level, which means downstream capacity is not fully used in the early stages of a storm so storage must be far larger, adding to scheme costs. An ožen-overlooked consideration is the 'drain down' of the system. By permitting the design flow to constantly pass throughout the head range, the time the storage structure takes to empty can be less than half that of other controls, so the system is ready for the next storm more quickly, reducing flood risk. For more info e-mail: Tony.Simister@jacopa.com or visit: www.jacopa.com

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