Experimentation and observations are leading activities within the water sciences . From a hydrological point of view, experimental basins are typical natural laboratories, which play an important role in understanding the dynamics of genetic (natural or simulated rainfall) and conditional (soil, land use, vegetation type, human activity, etc.) factors that influence the overland flow and suspended load discharges. Moreover, plot-scale experimental studies are designed to improve our understanding of the relationships between processes involving hydrological, ecological and geomorphic factors [2–5].
Regarding water balance investigations, experimental studies at a hydrological micro-scale (1 cm2 → 1 km2) allow simulations of elementary hydrological processes by means of runoff plots [5–7]. The sizes of runoff plots are: (a) microplots (i.e. one or two square meters), (b) small-scale (i.e. ∼100 m2) and (c) field plots (i.e. ∼1 ha) . Thus the results obtained are representative for a region or a certain conditional factor, and by means of extrapolation, these results can be used on the slopes of the catchment. Several types of studies can be used, such as: data modeling; assessing socio-economic impact aspects of the water resource; detection of trends and changes in runoff regimes and ecosystem responses due to human activities and climate variability . In 1986 UNESCO created the Euro-Mediterranean Network of Experimental and Representative Basins (ERB), through its International Hydrological Program (IHP), and Romania has been affiliated with this organization since 1993, through the National Institute of Hydrology and Water Management (NIHWM). Within the NIHWM, experimental hydrological research on runoff plots, in correlation with complex programs of observations and measurements, is conducted at 2 research units. The content of its activity concerns the establishment of quantitatively defined relationships of runoff and genetic and conditional factors. These basins are situated in the Curvature Subcarpathians (Figure 1). The hydrologic activity started around 1964, with the founding of the Station for the Experimental Hydrology of Voineşti, now called Voineşti Experimental Basin, and since 1984 to Aldeni [10, 11]. On the basis of data obtained from these research units, especially those related to deterministic models, numerous studies have been published [10, 12–18].
Within the Aldeni Experimental Basin and Voineşti Experimental Basin, the micro-scale study of hydrological components of the water budget is conducted using equipment that allows an estimation of the physiographic in-fluences in the region (geomorphic, climatic, soil) and anthropic intervention – land reclamation.
The objective of this paper is to present an overview about hydrometric equipment related to the hydrological field experiments research at micro-scale carried out by the National Institute of Hydrology and Water Management (Romania).
2 Material and methods
The main data used in this communication were the bibliographic and technical resources, as well as the hydrometeorological data (i.e. water discharge, rainfall). The method used in the study was based on the investigation of bibliographical resources and field observations. The mapping was made using ArcGIS Version 9.3 and the graphical representations of hydrometeorological data were performed using OriginPro version 8.5.
3 Results and discussion
3.1 Historical and geographical background
The National Institute of Hydrology and Water Management (NIHWM) began micro-scale, experimental research – with experimental plots – of the hydrological impacts of soil erosion and water balance in soil, in 1964 at the Station for Experimental Hydrology Voineşti (VES) and in 1984, at the Aldeni Experimental Basin (AEB).
3.2 Aldeni Experimental Basin
Studies in the AEB were conducted as part of comprehensive hydrologic research initiated in 1980. In the same year, the first field explorations were conducted and between 1981 and 1984, in collaboration with the present-day University of Agronomic Sciences and Veterinary Medicine of Bucharest, soil improvement activities were initiated (terracing, artificial rill and orchard planting), in order to assess, finalize and homologate the basin. Engineering works (e.g.: terraces) conducted by AEB, allowed water and suspended load discharge values determination in a modified regime.
In terms of geomorphology, AEB is situated in the Curvature Subcarpathians (45°19’30”N latitude and meridian 26°44’43”E longitude); a region characterized by intensive soil erosion – especially in the eastern part [19, 20]. Hydro-graphically, it forms part of the Slănic River Catchment, a left-side tributary of the Buzău River (Figure 1). The landscape presents torrential formations of different stages (rills, ephemeral gully, gully). The region has a moderate temperate-continental climate with „rainshadow” and dominance of dry winds coming down from the Carpathians. The mean annual precipitation of and mean annual temperature for the period 1984-2014 was 550 mm and 9.5°C respectively. In the study area, on runoff plots, the soil type is alluviosols with coluvic subtype; generally have clay content (36.5%), humus (3.28%), the phosphorus (24%) and ph = 7.2 – a neutral reaction – mildly alkaline . Actual land use is in decline (typical perennial grass), due to partial abandonment and/or unproductive land.
3.3 Voineşti experimental basin
The Voineşti Experimental Basin (VEB) was created in 1963, though the first material on the research of runoff formation processes date from 1964. The goal of its creation was to establish relationships between runoff and its genetic and conditional factors, to design rainfall-runoff mathematical models, to quantify the way different topo-graphical and cultivated surfaces participate in the flow processes and to study the water balance in the soil.
The VEB is situated at an altitude of 500 m a.s.l. (45°05’07.27”N latitude and 25°15’15.43”E longitude) and it is located in the western extremity of the Curvature Sub-carpathians, on the left bank of Dâmboviţa River (Figure 1). The climate is moderate temperate-continental and the area of the VEB was characterized in the 1980-2014 period by an average multiannual rainfall depth of 806 mm. Most rainfalls occurred in the growing semester (63%), and the highest number of rainfalls events was recorded in June (12.6%) and July (12.4%). The lowest amount of precipitation was registered in the cold semester (October-March), with the lowest precipitations measured in January (5.21%) and February (5.7%). The average air temperature was 9.7°C and July was the month of the maximum temperature, with an absolute maximum of 37.3°C in 2000 (a dry year), while January is the month having the minimum temperatures (-22.6°C in 1979).
3.4 Experimental plots
Hydrological monitoring and field experiments at the micro-scale are aimed at:
determining parameters of the water balance equation, during natural and simulated rainfall;
research of runoff generation and soil erosion processes;
transfer relation of runoff coefficients from a small scale to medium scale.
Experimental plots are of two types: water balance plots and runoff plots. The observations made during natural and simulated rainfall events included rainfall quantities, water depth, water turbidity, soil temperature, and soil moisture content.
The plots area is bordered with concrete walls, collection channels composed of gutters, underground pipes, and at their lower part there are shelters containing calibration tanks with drainage installation for evacuated of collected water.
Flow rates on plots are measured with the mechanic limnigraph (water level recorded) and automatic device, such as: pressure sensor and float-operated shaft encoder water level sensor. Automatic and continuous recordings of the water level drained from the plots into calibration tanks is done by means of a limnigraph (Valdai model), with daily change diagrams (limnigrama) at AEB and VEB, pressure sensors (U20L-04 model; accuracy: ±0.1% FS; from Onset HOBO) at AEB and float-operated shaft encoder water level sensors (OTT SE 200 model; accuracy: ±0.1% FS; from OTT) at VEB, which permits the recording of any change (volumetric method and variation in spillway) of the water depth collected in the tank (that has a full capacity of 0.46 m3). The limnigraphs and float-operated shaft encoder water level sensors, record the variation in water depth both inside the tank with the help of a floater and the water depth at the spillway; tanks have a spill-way with an opening at 45°. The water discharge calculation is done through the partial volumetric method – V (through division), the relationship beingV =f (H); also, water depth measurements are conducted with the help of pressure sensors.
Water turbidity (ρ) measurement is done through the “filtering method”; the procedure consists of collecting water samples (500 ml) from tanks – for runoff plots, filtering and drying them in the oven, followed by the calculation of associated sediment losses, after one flow.
The experimental plots from AEB are runoff plots. These have:
an area of 80 m2 (20×4 m); 5.6% slope; W-E orientation; one of them is covered with perennial grass ”grassland” (RP1), while the other ”bare soil” (RP2) is devoid of grass through hoeing and the structure of the first soil horizon measuring 20 cm is modified from that of the first runoff plots, which led to a higher degree of infiltration compared to the first one (Figure 2 A,B);
a portable rainfall simulator, used for the studies concerning overland flow; this tool generates artificial rains from nozzles (ø = 1 mm), with a controlled depth, intensity and duration; the structure consists of a 2 pipe section (ø = 37 mm) from metal (length = 20 m);
three tipping bucket rain gauges (RG3-M, Onset HOBO data logger); bulk precipitation collectors (surface area ∼200 cm2; resolution: 0.2 mm; accuracy: ±1.0% FS); two of them are located at ground level and one at the height of 1.50 m (Figure 2A,B);
four capacitance sensors (EC-5 model, accuracy: ± 1-2%) to measure electrical propriety of the soil (the dielectric permittivity -𝜀) and estimation the volumetric soil water (𝜃); set in the center of the plot at the depth of 10, 20, 40 and 60 cm and 1 rugged temperature sensor (at 10 cm depth), connected to the Em5b data logger from Decagon Devices Inc.
The experimental plots of VES are:
water balance plots – for overland flow, subsurface flow and base flow monitoring have the following characteristics: eutricambisol – a type of soil with “28% clay, 21% silt, 51% sand” ; slope of 13% and N-S orientation (Table 1, Figure 3 A,B); between the plots there is one tipping bucket rainfall collector (RG3-M); six capacitance sensors (10HS model, accuracy: ± 1-2%); set in the center of the ”grassland” plot at the depth of 5, 40, 60, 80, 100 and 120 cm connected to the Em5b data logger from Decagon Devices Inc.
runoff plots – for overland flow monitoring, have similar physiographic conditions with the first category of plots, with the single remark that they have different land uses; next to the plots, there are two pluviometers (Table 1).
3.5 Hydrological monitoring and data acquisition
The observation and measurement program at AEB is carried out following the instructions and standard guidance of the NIHWM, e.g.A guide for the activity in the representative and experimental basins, Volume IV . The instructions and guidebooks are made in accordance with the recommendations of Toebes & Ouryvaev , Technical regulations, Volume III1 and Guide to Hydrological Practices, Volume I2. According to WMO (2006), this falls in the “hydrological stations for specific purposes” category, and the observation program is typical for a hydrometric station and for ”climatological and precipitation stations for hydro-logical purposes”.
The current modernization of the observation, collection and recording process of the elements necessary for a quantitative estimation of the water balance equation involves the upgrade and replacement of outdated equipment and instruments with modern equipment’s, devices and sensors. The measurements of the hydro-meteorological elements in automatic system, using the sensors, are nowadays used to compare the results with those from the classical systems for instruments’ calibration.
The modernization process focused on the development of data acquisition storage, data transfer (every 10 minutes); terminal emulation, numeric output and export functions. Transmission of hydrometeorological data is conducted through the Global System for Mobile Communications (GSM) to the NIHWM server or is downloaded from a data logger directly on a portable PC. Data transmitted through GSM from AEB are consulted for the required time interval (time taken and finish time) and can be viewed online in tabular format (such as: browser grid/data table/plain/fancy; spreadsheet .xls/zip) and downloaded.
3.6 Data processing, quality control and storage
Periodically (at the end of each month and year), after data collection – usually checked by a Hydrological Technician or Hydrologist – in printed paper and electronic format, the data are used for the hydrologic process of verification and expertise (data quality control). Afterwards, following positive solutions (validations), the data are stored in the database.
Hydrological data are used to better knowledge our water resources and disseminated through: relations updates (e.g. rainfall-runoff) (Figure 4); multiple correlations to reflect the role of various factors, research themes/projects; yearbooks of basic data (Experimental Basins Yearbook) and scientific papers.
4 Conclusions and perspectives
Experimental investigation in NIHWM is performed with experimental plots (water balance and runoff plots). The AEB and VES represent research units equipped with hydrometric instruments, designed for the experimental hydrological studies. Hydrological monitoring is currently undergoing a process of modernization due to the availability of new tools based on sensor and electronic data transfer technologies. The valorization of data acquired allows studies to be carried at micro-scale concerning the determination of the elements that make up the equation for hydric/water balance, in order to expand the application of the relation between runoff coefficients from a small scale to a medium scale. The future plans involve implementing research projects on subjects related to rainfall, runoff and sediment transport modeling, in order to substantiate the relationship between drainage and genetic and conditional factors.
The authors would like to thank the NIHWM, for allowing Ms. Gabriela MOROfiANU, currently studying for a master’s degree at the Faculty of Geography, University of Bucharest, to carry out practical activities, focused on documentation and research, in the team of the Section of Experimental Hydrology of NIHWM and for offering her the opportunity to use the facilities of the Aldeni Experimental Basin. Also, we thank two anonymous reviewers for their suggestions and comments which greatly improved the manuscript.
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About the article
Published Online: 2016-02-29
Published in Print: 2016-02-01
Citation Information: Open Geosciences, Volume 8, Issue 1, Pages 154–160, ISSN (Online) 2391-5447, DOI: https://doi.org/10.1515/geo-2016-0015.
© 2016 G. Minea and G. Moroşanu, published by De Gruyter Open.. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License. BY-NC-ND 3.0