Assessment of an Ultrasonic Water Stage Monitoring Sensor Operating in an Urban Stream.

Georgios Poulis,Emmanouil Nikiforakis,Elias Dimitriou,Anastasios Papadopoulos,Yiannis Panagopoulos

doi:10.3390/s21144689

Abstract

The monitoring of the water stage in streams and rivers is essential for the sustainable management of water resources, particularly for the estimation of river discharges, the protection against floods and the design of hydraulic works. The Institute of Marine Biological Resources and Inland Waters of the Hellenic Centre for Marine Research (HCMR) has developed and operates automatic stations in rivers of Greece, which, apart from their monitoring role, offer opportunities for testing new monitoring equipment. This paper compares the performance of a new ultrasonic sensor, a non-contact water stage monitoring instrument, against a pressure transducer, both installed at the same location in an urban stream of the metropolitan area of Athens. The statistical and graph analysis of the almost one-year concurrent measurements from the two sensors revealed that stage differences never exceeded 7%, while the ultrasonic measurements were most of the time higher than the respective pressure transducer ones during the low flow conditions of the dry period and lower during the wet period of the year, when high flow events occurred. It is also remarkable that diurnal air temperature variations under stable hydrologic conditions had an impact on the measured stage from the ultrasonic sensor, which varied its stage measurements within a small but non-negligible range, while the pressure transducer did not practically fluctuate. Despite a slightly increased sensitivity of the ultrasonic sensor to meteorological conditions, the paper concludes that non-contact sensors for the monitoring of the water stage in rivers can be useful, especially where danger for possible damage of submersible instruments is increased.

Highlights

The water quantity and quality monitoring of surface water bodies is essential for the preservation of a healthy aquatic environment and the sustainable management of water resources [1], with transparency in data collection being crucial for the monitoring reliability [2,3]
It is worth noting that since less than 25% of the deviation data values were negative (Q1 for deviations is positive in Table 1), the majority of the ultrasonic measurements were greater than the respective pressure transducer ones
Ultrasonic measurements were for most of the time higher than the pressure transducer ones, as shown in Figure 4, especially during the dry period of the year characterized by stable, low flow hydrologic conditions in the stream, with the opposite occurring during periods of the wet season when low flow conditions alternated with higher flow events

Summary

Introduction

The water quantity and quality monitoring of surface water bodies is essential for the preservation of a healthy aquatic environment and the sustainable management of water resources [1], with transparency in data collection being crucial for the monitoring reliability [2,3]. Automatic telemetric instruments for surface water monitoring are gaining ground as they can provide early warning services, essential for pollution mitigation and preparation against extreme events [4,5]. For streams and rivers, water stage (or water level), the height or elevation of the water surface above an established datum plane, is important for designing works (bridges, embankments and levees) or for protecting communities and human property from flood inundation. Stream stages are systematically monitored by automatic sensors, devices that automatically determine, or sense, the height of the water column from the water surface to the river bed. Various types of recording methods and associated instruments are available including the traditional method of a float being on the water surface inside a stilling well, and the newer methods utilizing pressure transducers and non-contact sensors [11]

Methods

Results

Conclusion