Sensor and sensibility
Robin Guy explains how technological advances have benefited the complete monitoring that's required under the WFD.The European Water Framework Directive (WFD) aims to promote sustainable water use and to protect water resources. This relates to surface and ground water quantity, quality and ecological status and takes into consideration the likely impacts of climate change.
As a result, a holistic approach to the protection of water resources has developed - Integrated Catchment Management (ICM). This aims to protect water resources at source by avoiding diffuse and point source pollution, by minimising incidents of unconstrained flooding and drought, and by enhancing biodiversity.
A catchment is defined as the land area from which all water drains to a single watercourse. Consequently, the management of catchments requires an understanding of the relationships between land, air and water.
To meet the WFD's objectives a different approach is needed. The complete hydrological cycle for a catchment must be monitored, which means it is now necessary to monitor precipitation, surface water, groundwater, soil moisture, vegetation levels and land use. A need has also arisen to move from spot measurements to continuous or semi-continuous monitoring.
In the past, remote locations have been problematic because of a lack of power. Recent technological advances have resulted in a far greater proportion of monitoring data being collected automatically in the field and transferred remotely; this has coincided with a greater requirement for field data as a result of the WFD.
Low power standalone dataloggers can store thousands of records without the need for mains power - and where a continuous power supply is required, this can often be provided by a solar- or wind-powered charger.
Communication technology has advanced beyond all recognition in recent years. As a result, a choice of highly effective and reliable wireless communications options exist, most of which are relatively low in cost and power requirement. These include GPRS, SMS, radio and satellite.
Sensor technology has also advanced to support the move to remote monitoring. Sensors are now more accurate, more reliable, less prone to drift and consequently require less frequent service and/or calibration. In 1662, Sir Christopher Wren invented the first tipping bucket rain gauge which became the standard methodology until the end of the 20th century. However, in the early 21st century a new technology emerged that remained accurate during intense rainfall; required less maintenance; and provided precise data on rainfall intensity. Called OTT Pluvio2, the device employs a weighing measuring principle and can operate unattended in remote locations for long periods of time.
Many national rainfall monitoring authorities are moving over to the newer technology. Historically water quality measurements in remote locations have been undertaken with spot measurements using portable instruments and kits or by taking samples to a laboratory for in-depth analysis. Here too sensor technology has advanced and it is now possible for multiparameter water quality monitors to log water quality parameters almost continuously for several weeks without any requirement for maintenance or recalibration.
Automatic water samplers have also enhanced monitoring capability, by taking water samples at pre-set intervals and storing them for subsequent analysis. The latest samplers can be activated by changes in local preset parameters, for example breeches of flow or level thresholds signifying a major event, thereby enhancing our understanding of water quality changes with variable flow regimes. The ability to monitor a catchment continuously means that the pollution prevention and hydrological objectives of the WFD are more easily met. Continuous monitoring enables the rapid detection of point source pollution and provides an opportunity to take remedial action before serious damage occurs.
Similarly, if water level or flow data reaches pre-set low or high alarms, it becomes possible to minimise the effects of flooding and drought. The provision of real time data also assists resource management ensuring that underperforming or faulty sites can be targeted and rectified immediately.
One of the key advantages of continuous monitoring over spot data is that it records peaks and troughs, providing much greater insight into the cause and effects of changes in a catchment. Continuous long-term data also enables more accurate identification of diffuse pollution. New communications technologies combined with continuous monitoring also offer advantages for stakeholders as it is now possible to display live data on a website.
This approach was adopted at a major housing development in Waterlooville, Hampshire. The scheme included building 2,550 homes, which would have a large potential effect on local drainage and flooding. However, Sustainable Urban Drainage Systems (SUDS) have been established to try and mitigate against any potential for flooding.
OTT Hydrometry has installed water level, flow and rainfall monitors at the site to provide continuous performance data. The main objective is to ensure that the development at Waterlooville will not increase the risk of flooding, affect the water quality or harm the ecology of the receiving watercourses. Data is posted to a live website to achieve community engagement through open data collection.
The new holistic approach to monitoring has been adopted within a Defra-funded project on the outskirts of Exmoor National Park. The project is designed to study the effects of different land management practices particularly with respect to flooding and water quality. This trial is expected to inform future land management and help to develop flood risk models for the area. And the monitoring regime will demonstrate best practice for compliance with the requirements of the WFD.
Penny Anderson Associates (PAA) is managing the project, which has established a catchment-wide monitoring network consisting of the latest OTT instruments such as water level monitors, doppler water velocity meters and automatic rain gauges. PAA is conducting flow gaugings to develop site specific ratings, thereby allowing the generation of continuous flow data through the conversion of measured level data.
Also, Exeter University has installed water samplers that are activated by level sensors and will operate automatically at river levels. The project will showcase communication methods including GSM and radio. Satellite communication may be installed at one site.
The Waterlooville and Exmoor projects are good examples of the new WFD prompted approach to monitoring. However, the new catchment monitoring requirements, coupled with recent technological advances, will result in the generation of much greater volumes of data.
Data will only contribute to the catchment management plan if it is representative and interpreted correctly, so a level of expertise is often necessary when establishing and managing a monitoring network.
Robin Guy is senior technical engineer
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