Research papersA modified portable rainfall simulator for soil erosion assessment under different rainfall patterns
Introduction
The search for sustainable use of soil resources is one of the main motivations for the study on erosion and the development of conservation practices that mitigate this natural process commonly accentuated by anthropic action. The world demand for food, fiber and fuel and the increase in areas with agricultural production and pastures have intensified erosion (Merten and Minella, 2013).
The erosive process is associated with large-scale factors, such as global warming (Lal et al., 2011), and with the characteristics of rainfall, climate, management, topography, as well as soil types and cover (Hamanaka et al., 2019), and is considered a global concern because it degrades the natural resources of soil and water, leading to major economic losses. In countries of tropical climate, water erosion is the main cause of losses in the agricultural yield of food crops, resulting in increased production cost and environmental contamination (Andrade et al., 2011).
Soil losses can be generated with natural rainfall or through rainfall simulators, which are tools used in hydrogeomorphological or hydrological studies, in the field and in the laboratory (Askoy et al., 2012), related to runoff, infiltration and sediment loss due to use, cover and management in different soil classes (Sarasty et al., 2017, Boulange et al., 2019). These devices make it possible to simulate rainfall with different characteristics (precipitation duration and intensity) and have been used to evaluate soil erodibility (Mhaske et al., 2019) and the impact of revegetation (Askoy et al., 2012), besides generating information that validates conservation practices and models for estimating soil losses, provided that they have characteristics similar to those of natural rainfall, such as drop diameter and kinetic energy (Munster et al., 2006). In addition to being simple, portable and economical (Mhaske et al., 2019), the simulators should have low water consumption (Iserloh et al., 2012), precise control of precipitation intensity and provide a relationship between simulated/natural rainfall kinetic energy and uniformity above 75% (Alves Sobrinho et al., 2008).
According to the form of production of the drops (Morin et al., 1967), rainfall simulators are classified into two categories, being equipped with drippers, composed of capillary tubes, or with nozzles, which operate with a wide range of precipitation intensity and drop diameter, enabling the formation of a more random drop falling pattern, similar to that of natural rain. The simulator developed by Alves Sobrinho et al. (2008), called InfiAsper, operates with two pressurized nozzles and is one of the most used devices in Brazil to simulate rainfall with constant precipitation pattern, according to previous calibration (Carvalho et al., 2015, Panachuki et al., 2015, Valim et al., 2016, Almeida et al., 2018, Marques et al., 2019, Moraes et al., 2019). However, as natural rainfall events are variable in space and time (Assouline, 2009), the natural process of soil loss is best reproduced when the simulators have mechanisms for varying the intensity during the occurrence of precipitation (Nielsen et al., 2019). According to Alavinia et al. (2019), rainfalls simulated with constant intensity do not represent the characteristics of natural rainfalls, leading to significant differences in the results of soil losses.
The combination of different precipitation intensities during rainfall is called a rainfall pattern (Luo et al., 2020) and is considered one of the main factors that influence soil erosion (Huihui et al., 2016). Rainfall pattern classified as delayed, when the peak of precipitation intensity occurs on the final third of the rain (Flanagan et al., 1988), tends to generate higher rates of soil loss and runoff volume considering that the highest intensity occurs in water-saturated soil (Wang et al., 2016, Sofia et al., 2019). Therefore, the possibility of adapting and updating the original control panel of InfiAsper with the application of a rotation microcontroller, to obtain different pre-set rainfall patterns, is a fundamental improvement in its operation and, consequently, in the quality of the obtained data. The study was conceived based on the hypothesis that the variation in the shutter disc rotation in the rainfall simulator InfiAsper (Alves Sobrinho et al., 2008) makes it possible to change precipitation intensity and obtain different rainfall patterns with no simultaneous alteration in the shutter opening. Thus, the objective of this study was to evaluate whether the variation in the shutter disc rotation, associated with its opening, enables the obtaining of different rainfall patterns in the rainfall simulator InfiAsper.
Section snippets
Material and methods
The rainfall simulator used in this study was the InfiAsper, developed by Alves Sobrinho et al., 2002, Alves Sobrinho et al., 2008), composed of five independent modules, which facilitate transport and operation in the field (Fig. 1). It has two fixed spray nozzles (Veejet 80.150 model), which must be positioned at 2.30 m height from the ground during operation (Fig. 2a). The nozzles are located above the shutter’s overlapping discs (Fig. 2b), whose rotation is defined by the input frequency of
Precipitation intensity, water consumption and efficiency
With the tested rotations (140, 200, 260, 400, 600 and 800 rpm) and disc openings (33, 44, 56 and 60 mm), the device showed PI ranging from 0.7 to 123.4 mm h−1, Cw from 0.02 to 2.53 L min−1 and Ew from 41.2 to 56.8% (Table 1). These results indicate the ability of the equipment to apply rains with different PI values, which resembles natural events that normally do not present constant intensity.
These values indicate that InfiAsper is more efficient and requires lower water volume than the 13
Conclusions
The installation of electronic components in the InfiAsper control panel makes it possible to vary shutter rotation during its operation according to previous programming, enabling the simulation of rainfalls with different rainfall patterns. Rainfalls with PI peaks of 110 mm h−1 and duration of 40 min were adequately simulated by the device, with uniformity above 75%. It is possible to simulate other rainfall patterns, with different PI and duration, by changing the settings on the device’s
CRediT authorship contribution statement
Pietro Menezes Sanchez Macedo: Conceptualization, Methodology, Investigation, Data curation, Writing - review & editing. Marinaldo Ferreira Pinto: Methodology, Writing - original draft, Writing - review & editing. Teodorico Alves Sobrinho: Validation, Writing - review & editing. Nivaldo Schultz: Writing - original draft, Funding acquisition. Thiago Altamir Rodrigues Coutinho: Investigation, Data curation. Daniel Fonseca de Carvalho: Conceptualization, Methodology, Validation, Resources, Writing
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We thank the Federal Rural University of Rio de Janeiro, specifically the PPGA-CS/UFRRJ. We acknowledge the Conselho Nacional de Desenvolvimento Científico e Tecnológico – Brasil (CNPq) for the financial support (Process 422394/2018-1). This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.
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