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DIVANI CARAVEL HOTEL - ATHENS, GREECE
SEPTEMBER 7-9, 2022
Innovative water management in a changing climate
IAHR 2022 | Abstract Book
Combined measurement techniques for the monitoring of hydrologic processes
in the unsaturated zone
Efthymios Chrysanthopoulos1, Christos Pouliaris1, Ioannis Tsirogiannis2, Petros Kofakis3, Andreas Kallioras1
1 Department of Mining and Metallurgical Engineering, Laboratory of Engineering Geology & Hydrogeology, National
Technical University of Athens, Greece
email: echrysanthopoulos@metal.ntua.gr
email: pouliaris@metal.ntua.gr
email: kallioras@metal.ntua.gr
2 Department of Agriculture, University of Ioannina, Greece
email: itsirog@uoi.gr
3 Department of Agribusiness and Supply Chain Management, AUA, Greece
email: kofakis@gmail.com
1. Introduction
Soil moisture is a hydrologic parameter of paramount importance in agricultural studies, as most services in
agricultural ecosystems, such as water storage, food and fiber supply, water and climate regulation, are
associated with its spatial and temporal variability (Novick et al., 2022). In order to describe the state of water
in the soil two types of variables are required; volume of water and water potential.
This study involves the development of an integrated monitoring programme of the above parameters, by
utilizing an experimental agricultural farm of the Department of Agriculture of the University of Ioannina, in
Western Greece (Arta). The various monitoring activities include: (i) vertical and spatial distribution of the
volume and energy of water through the unsaturated zone; (ii) the continuous monitoring of groundwater level
fluctuations; (iii) the design and development of a wireless network with several end-nodes within the field,
that will facilitate the transmission of generated data from the sensors to a gateway which will act as a bridge
between the monitoring infrastructure and the remote server. The communication protocol is LoRaWAN
providing long-range, low-power consumption, low data rate and secure data transmission.
2. Monitoring of soil water content
2.1. TDR sensors
Conventional sensors for point measurements of soil moisture are installed in several locations within the field
in order to provide wide distribution of soil water content in the upper decimeters of unsaturated zone, which
is the soil water zone. However, unsaturated zone consists of several sub-zones, each of them hosting various
hydrological processes and contributing to the water balance. Complex processes, such as downward
movement of groundwater, return flow to the atmosphere via evaporation and plant root uptake (Kallioras et
al., 2016), cannot be monitored with conventional sensors, which have predominantly been made to observe a
particular process. Custom made time domain reflectometry (TDR) probes are installed at desired depths across
the unsaturated zone, offering continuous monitoring of soil water content.
2.2. Tensiometers
In contrast to the soil volumetric water content, soil water potential -which is the sum of matric forces (adhesive
and cohesive) and others (osmotic, gravitational and pressure)- is hardly measured in situ. This lack of
observations and measurements incorporates large uncertainties into hydrological models, while most of them
are based on pedotransfer functions (PTFs) to predict the parameters of water retention curve models, which
relates matric potential (Ψs) to the volumetric soil moisture content (θ), using empirical equations directed by
a limited set of soil properties.
The reasons why Ψs is rarely measured systematically may be due the fact that no single instrument can capture
the entire range of it and existing sensing systems have a lot of limitations. For the research activities of this
study, conventional tensiometers will be used for measuring matric potential up to -90 kPa, which in
combination with continuous measurements of θ, will grant a details about soil structure and hydrological
processes.
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DIVANI CARAVEL HOTEL - ATHENS, GREECE
SEPTEMBER 7-9, 2022
Innovative water management in a changing climate
IAHR 2022 | Abstract Book
2.3. Pressure plate apparatus
Apart from in situ measuring of matric potential (Ψs), the pressure plate apparatus method will be used to relate
soil moisture tension and the moisture content of soils. Due to the range measurement limitations of in situ
techniques, implementing the pressure plate apparatus method is going to facilitate the determination of
moisture – retention on large number of samples within the field. Furthermore, the compatibility of the
different methods can be demonstrated.
3. Monitoring of soil solution
3.1. Sampling lysimeters (porous suction cups)
Additionally with modern and conventional sensing technologies for soil water content monitoring, soil
solution sampling and analysis is being performed using porous suction cups installed on multi-level basis.
Their use in different studies to collect soil water for analytical purposes is wide. In addition, campaign-wise
undisturbed soil core sampling will be performed, in order obtain porewater quality profiles along the
unsaturated zone after the application of tailored water extraction techniques.
4. Data transmission facilities
According to the architecture of LoRaWAN network, the variety of sensors which are used in the experimental
field for monitoring soil water content, groundwater level fluctuations and a climate station, are considered to
be end nodes. End nodes or end devices send LoRa modulated wireless messages to the gateways. A gateway,
an antenna which receives broadcasts from end devices and send data back to end devices, is installed in the
vicinity of the field. The installed gateway is joined to a LoRaWAN Network Server, using a backhaul 4GLTE.
The Network Server manages the gateway, the end-nodes and the applications in the entire network. In that
way all the data monitored in the field are stored in a server, which facilitates their manipulation and the
correlation between them.
Some of the benefits of using LoRaWAN are the significant low power for the operation of the entire network,
the long range of signal transmission and reception compared to technologies like WiFi, Bluetooth or ZigBee
and the low cost of end nodes with the use of open-source software. In view of these assets LoRaWAN is well
suited for sensors which operate in low power mode.
In general, the application of wireless sensor networks for monitoring the majority of hydrological processes
in the area of a field offers significant benefits, such as the deep understanding of dynamic processes, which
could drive to the improvement of knowledge about the physical system. Also, the implementation of a
wireless sensor network allows multi-parametric environmental monitoring and the storage of the data on a
remote server, granting the opportunity even for real-time calculations, feeding hydrological models.
Acknowledgements
This research has been co-financed by the European Union and Greek national funds through the Operational Program Competitiveness,
Entrepreneurship and Innovation, under the call SUPPORT OF REGIONAL EXCELLENCE (project code MIS: 5047059).
References
Novick K, Ficklin D, Baldocchi D, Davis K, Ghezzehei T, Konings A, MacBean N, Raoult N, Scott R, Shi Y, Sulman B, Wood J
(2022) Confronting the water potential information gap, Nature Geoscience, 15, 158-164
Kallioras A, Khan A, Piepenbrink M, Pfletschinger H, Koniger F, Dietrich P, Schuth C (2016) Time-domain reflectometry probing
systems for the monitoring of hydrological processes in the unsaturated zone, Hydrogeology Journal, 24, 1297-1309
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