WFD dictates need for holistic monitoring strategy
The European Water Framework Directive and recent technological developments are radically changing the ways in which water resources are monitored. Robin Guy, OTT Hydrometry’s Senior Technical Engineer explains.
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 necessitates a clear understanding of the complex relationships between land, air and water.
New approach to monitoring
In order to be able to meet the objectives of the WFD it has become necessary to adopt a different approach. The complete hydrological cycle for a catchment must be monitored, which means that it is now necessary to monitor precipitation, surface water, groundwater, soil moisture, vegetation levels and other factors such as land use. A need has also arisen to move away from spot measurements to continuous or semi-continuous monitoring.
In the past, remote locations have been problematic because of a lack of power and the time and cost associated with site visits. However, technological advances in recent years 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 stand alone dataloggers are able to store many 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. For example, in 1662 Sir Christopher Wren invented the first tipping bucket raingauge and this technology became the standard methodology throughout the 18th, 19th, and 20th centuries – an astonishing achievement! However, in the early part of the 21st century a new technology emerged to replace Sir Christopher’s which was able to remain accurate during intense rainfall, to require less maintenance and to provide precise data on rainfall intensity. The new device, known as ‘OTT Pluvio2’ employs a weighing measuring principle and is able to operate unattended in remote locations for long periods of time.
Many national rainfall monitoring authorities around the world are moving over to the newer technology. However, it is interesting to note that tipping bucket raingauges remain popular in many countries because of a requirement for direct comparability with historical data. Inevitably, under-reading of rainfall during high intensity precipitation will continue where this is the case.
Field water quality
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. However, here too, sensor technology has advanced considerably and it is now possible for multiparameter water quality monitors to log an array of 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.
Continuous live data
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, not only improving data quality but also helping in the continuous drive for efficiencies.
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 important advantages for stakeholders because it is now possible to display ‘live’ data on a website for the benefit of land owners, regulators, planners, developers, local residents etc. This approach was recently adopted at a major housing development in Waterlooville, Hampshire.
The proposed housing scheme included the building of 2550 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 by creating a network of ponds and swales. OTT Hydrometry has installed a number of water level, flow and rainfall monitors at the site to provide continuous performance data for all stakeholders. 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. The data is then posted to a live website to achieve community engagement through transparent and open data collection. The developers are endeavouring to show that through the measures they have put in place localised flooding will not only be mitigated but also reduced, where possible.
Studying the effects of land management practices
The new holistic approach to monitoring has been adopted within a DEFRA funded project on the outskirts of Exmoor National Park. The project has been designed to study the effects of different land management practices particularly with respect to flooding and water quality. It is anticipated that the results of this trial will inform future land management and help to develop flood risk models for the area. In addition, the monitoring regime will demonstrate best practice for compliance with the requirements of the WFD.
Penny Anderson Associates (PAA) are 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 raingauges. PAA are conducting flow gaugings at selected locations in order to develop site specific ratings, thereby allowing the generation of continuous flow data through the conversion of measured level data. In addition, Exeter University has installed water samplers that are activated by level sensors and will operate automatically at pre-defined river levels.
The project will showcase different communication methods including GSM and radio. However, satellite communication may be installed at one site for which radio and GSM are not applicable.
Peter Worrall, Technical Director at PAA says, “The establishment of the OTT monitoring network will enable us to establish accurate baseline data so that we can study the effects of agricultural practices such as stocking density and buffer strips.”
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. It is important to note, therefore, that 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.
For further information, please contact:
OTT Hydrometry Ltd
Unit 2 Magnet Business Park
14 High Hazels Road
Chesterfield S43 4UZ
Tel. 01246 573480
Fax. 01246 813873
Web site: www.ott-hydrometry.co.uk