Impact of ground vegetation on erosion under rain fragmented Simulated

Transcription

1 J. Basic. Appl. Sci. Res., ()2-9, 20 20, TextRoad Publication ISSN X Journal of Basic and Applied Scientific Research Impact of ground vegetation on erosion under rain fragmented Simulated Boualem Abdelkader, Mederbal Khalladi 2, Khaldi Abdelkader 2 and Belkacem Salima 2 University of Mostaganem, Algeria 2 University of Mascara, Algeria ABSTRACT Erosion is a topical problem in the world and there are many civilizations that have struck because it is a complex phenomenon that results in loss of soil Particles could be affected directly by: the upstream watershed, soil loss and gulling intense. the downstream flooding and silting of dams, the raising of river bed... etc. In Algeria, according to studies made by FAO (983, 985, 989) erosion causes a loss of top soil estimated at -6 t / ha per year. We note that most researches had converged mainly on the quantification of erosion caused by rain, this study focuses on quantifying rainfall simulation plots in the parameter, cover rate has different values to see the influence of it on the sheet erosion. The tests are conducted with a fixed intensity of 30 mm / h with different slopes on clay at intervals of 24 hours to leave the soil Clean. The basic experimental unit is a parcel of land and redesigned according to the map soil type of clay loam, a square meter ( m 2 ). We recall that the purpose of our work is to highlight the influence of cover vegetation on erosion and by having this objective, it became necessary to plant a cereal like wheat on the test plot using a cover, and is simulated whenever the latter expects the respective are 0%, 45% not forget to vary the slope (5% and 27%). KEY WORDS: erosion, infiltration, flow, concentration, Simulator. Measuring Equipment INTRODUCTION -Rain Simulator To meet the requirements of an objective of this study, we used a rainfall simulator (see photos., 2 and 3) with a spray nozzle attached to a height of 3.50 to 4 meters it is animated by a pendulum and watering a test surface of m 2. The intensity of rain varies with the angle of displacement, the latter may not only be sensitive to changes in wind, but it can also have quite erroneous results. Corresponding author: Boualem Abdelkader, University of Mostaganem, Algeria. 2

2 Boualem et al., 20 Photo. : Rainfall simulator (side view) Photo. 2: Rainfall simulator (opposite view) 2-Overview of Simulator It consists of: a metal frame that supports the sprinkler system: the gantry a sprinkler system itself, which composed of a spray nozzle (or spray) programmable; a deer protection against the wind; a bag of control and programming; a water tank; a water supply pump; a valve to regulate the flow of water discharged; a galvanized steel tank using the simulator laboratory and for the determination of the intensity; generator; a pressure gauge to set pressure. 3

3 J. Basic Appl. Sci. Res., (): 2-9, 20 Photo. 3: Characteristics of Simulator -Generator 7-Jet 2- Water Reserve 8-The case of control 3-Electric Pump 4-Valve 5-Tyau 9- Plot trial - Cover Plant - Water Manifold runoff 6-Gauge 3-Functioning Principle Sprinkling System Watering the parcel is insured by a single jet of water produced by a calibrated nozzle disposed on an arm which the mechanical system is fed by the pump that is driven by a pendulum capable of changing the scan angle along the nozzle and the area watered. The man is able to adjust the intensity of the simulated rainfall of between 20-0 mm / h by changing the angle of spray 20 to 249 degrees. All this works either manually or automatically. MATERIALS AND METHODS Measurement Method Intensity measurement Knowing the mode of the simulator used in our study, we note that it is imperative to determine in advance the intensity of which is made in a pan with m2 of sheet superimposed 4

4 Boualem et al., 20 on the test plot in our case is fixed the scanning angle of the jet that is 240 degrees. It measures the amount of simulated rainfall (Roose, 995) fell during a given time interval is one minute in our case is then converted into hours, and after several steps, we obtain an unvarying intensity of about 30 mm / h with a pressure 0.6 bars. It is necessary to check this setting before every rain, because it can vary slightly depending on how open the valve. Abbreviations and units of Measurement Q L : liquid Flow in l/s Pl c : Cumulative Rain in mm Inf: Infiltration in mm Er c : Cumulative Erosion in t / ha Simulator Features Size Rain Drops It is necessary to prove that the sizes of simulated rain drops are the same as that of natural rainfall and that by the powder method or the method of staining. Some work, particularly that of (Mazour, 992) who carried out the comparison between the diameters of raindrops natural with those two types of simulators (See Table. ). Table. : Comparison between the diameter of rain drops with those of two natural types of simulators Rain intensity (mm / h) rainfall simulator (mm) Infiltration (mm) natural rainfall (mm) RESULTS AND DISCUSSION -Case of a plot totally naked (0%) Watering the plot is done with an intensity of 30 mm / h, unchanging throughout the course of the experiment. The shape of the curves in the figures and 2 indicates that the runoff goes off respectively from the 7th and 4th minutes, which shows the influence of the stock of soil water that had suffered a bleeding-off of 6 days. As the water seeped into the soil, the latter is close to saturation and we note that the infiltration (mm) is inversely proportional to liquid flow (l/s). At the first glance, we notice that erosion increases gradually as the runoff increases up to a maximum of.54 t / ha and 8.88 t / ha respectively for slopes of 27% and 5% (high and low). 5

5 J. Basic Appl. Sci. Res., (): 2-9, 20 In the case of bare soil, we note that the results recorded on an erosion are high because they have reached.54 t / ha and 8.88 t / ha respectively for slopes 27% and 5%. Hence one can conclude that the erosion is sensitive (Roose, 975; Boulaem and Mederbal, 2006) not only to vegetation, but also to changes in the slope. Rains, Infiltrations and Flows Cumulative erosion in (t/ha) Q (l/s) pl,c (mm) Inf (mm) E,r,c (t/ha) Time in mn Figure.. Curve of variation of rainfall-infiltration-discharge and the cumulative erosion over time (slope: 5% and coverage rate: 0% (bare soil). 0 2 Rains, Infiltrations and Flows 0. TEMPS(min) Cumulative erosion in (t/ha) 0.00 Time in mn 0 Figure. 2. Curve of variation of rainfall - infiltration - discharge and cumulative erosion over time (slope: 27% and coverage rate: 0% (bare soil). 2- Case of Plot Covered 45% From Figure. 3 it is noted that the runoff has not been considered to be an evident after a long wait, because no simulation had been done before, the soil was very dry, which explains a great capacity for absorption, n' is that the 6st minutes when he tripped on ground saturated with water or to waterproof follows a reduction of porosity ceases to absorb some of the simulated rainfall (mm).this allows to define the carrying capacity of infiltration of soils because the latter depends mainly on moisture. 6

6 Boualem et al., 20 In the case of Figure.4 and the view of the stock of water in the soil during the 24 hours after the previous simulation, runoff did not occur soon and that in the 4th minutes. The increased runoff and reduced infiltration, it became less important. According to the results recorded on erosion, we can say that this becomes less important because they have values reach 0.72 t / ha respectively 3.40t/ha for slopes of 5% and 27%. We can conclude that the results about the erosion are different with respect to the cover vegetative screen increases and erosion decreases (Boulaem and Mederbal, 2009). The quantities of eroded land generally correlated with that of coverage that is a protective factor. Rains, Infiltrations and Flows temps(min) Cumulative erosion in (t/ha) Q(L/S) pl,c(mm ) INF(m m) E,r,c(T/ha) Time in mn Figure. 3: Curve of variation of rainfall-infiltration-discharge and the cumulative erosion over time (slope: 5% and coverage rate: 45% Rains, Infiltrations and Flows 0. temps(min) Cumulative erosion in (t/ha) QL(L/S) PL,c(mm) Inf(mm) E,r,c(T/ha) 0.00 Time in mn 0 Figure. 4 curve of variation of rainfall - infiltration discharge and erosion accumulated over time (slope: 27% and coverage rate: 45%) 7

7 J. Basic Appl. Sci. Res., (): 2-9, 20 CONCLUSION The main concept of this study is to highlight the importance of vegetation cover with respect to the destruction of the soil under the effect of rain. In order to achieve certain objectives we used a rainfall simulator type (Orstom, 998) for the study using this device proved to be useful tines because of the possible repetition of tests. In summarizing the results found listed on the table. II. We can say that erosion is inversely proportional to vegetation cover that is the higher the rate of recovery declines more erosion increases (Boulaem and Mederbal, 2007). Table. 2: Impact of erosion of the rate of coverage with different slopes (5% and 27%). SLOPE 5% SLOPE 27% Coverage rate (%) EROSION Coverage rate (%) EROSION (t/ha) (t/ha) Our study showed that sheet erosion is important not only from a vegetative screen to another, but also for the different slopes. The vegetation in the undisturbed state is a good protective coat against erosion, in effect as a comparative study was conducted on the river in El Aoun (Algeria).The first fully wooded takes only 5.85 t / ha / year. The second partially cleared and cultivated, showed a specific degradation of 6.45 t / ha / year. Another study showed that significant water erosion under natural vegetation varies between 0.0 and 0.5 t / ha / year. It can grate moderate hatched in culture that may vary from 0. to t / ha / yr on slopes of 2-40%. Generally, the detachments of particles are moving fast in the opposite way to the density of vegetation recovery. In most cases, they automatically cause bare soil runoff and therefore the thrust and destruction of particles leaving the remains smaller, but with time they spectacular. Acknowledgment I must thank laboratory research with the University of Chlef (Laboratory of Soil Science and Soil Science) and greeting to my colleagues from the University of Mascara to know Khaldi Abdelkader and Mederbal Khalladi. REFERENCES Boualem A., Mederbal K., Silting Bouhanifia the reservoir, Algeria, Journal of Environmental Hydrology, Publication, Volume 7, June 2009.USA. Arizona. Boualem A., Mederbal. K., Mechanism of water erosion at the dam (west of Algeria). Article of the International Conference of Water Resources in the Mediterranean. Tripoli (Lebanon).-3 November. 8

8 Boualem et al., 20 Boualem, A., Mederbal K.,2007. Approach to erosion by the method of bathymetric survey in the dams of the west of Algeria: implications and prospects. International Conference on Climate Change and their impacts on coastal areas, Alexandria (Egypt), April Website: FAO., 983. Directorate for the fight against land degradation. 40 Pages FAO., 985. Protect and produce soil conservation for development. F.A.O, Rome. 40 Pages. FAO., 989. The defense of cultivated land against water erosion. FAO. 45 Pages. Italy. Mazour M., 992. The risk-factors 'érosion sheet in the watershed of Isser. Tlemcen. Algeria. Bul. Network erosion. Orstom,.998. Bulletin network erosion, 8pages. Paris. Roose E., 995. Succession to runoff and sheet erosion of various textural types of cultivated soils in non-french territory. Experiments with simulated rain fields in Soil Science, 3, 4, Roose E., 975. Erosion and Runoff in Western Algeria: Twenty years of measurements in small plots. Cyclo. Orstrom. Adiopodoum. IVORY COAST. 9