Effect of soil texture on water infiltration in soils of Jorf irrigation district, Errachidia province
To be able to improve the conveyance efficiency of water within earthen irrigation channels in small and medium irrigated areas in Morocco, the control of the infiltration behavior in the soil composing these irrigation channels is a stage impossible to circumvent. This is why this work was devoted to the study of the infiltration at the laboratory on samples of soil taken from the irrigation channels Lgdima and Hanabou located in the perimeter of Jorf which belongs to the province of Errachidia. The experimental device is composed of test-tubes out of glass containing the samples to be tested. The test-tubes were subjected to a constant water head during all the tests, which consisted of the recording of the infiltration time according to the advance of the humidification face in the test-tubes. All the samples underwent the same energy of dry compaction. In all the experiments, the infiltration measurements concerned the samples from origin soils not compacted, then compacted and finally mixed with fractions of clay according to percentages going from 5 to 25% by step of 5%.The two parameters analyzed in the experiments are the water infiltration time necessary to cross entirely the column of the soil sample contained in the test-tube, and the infiltration rate determined on the basis of the ratio between the variation of the levels of the humidification advance face and the variation of the infiltration time. The objective of this paper is to test the impact of change in the soil characteristics on the infiltration behavior, while keeping constant the other parameters such as the initial water content and the compaction degree. The results showed in a first stage of the experimentation, that the comparison between infiltration times in the same sample not compacted then compacted, allows us to get a ratio between the two times higher than 2.This shows the effect of the compaction on the deceleration of the humidification face and thus on that of the infiltration. In one second stage, the infiltration time was measured in a case where the two samples of origin soil were compacted then mixed with clay according to the proportions indicated above. The results of these tests indicated that the variation of the infiltration time is an increasing function of the clay fraction brought and it is that this variation is better represented by a second order parabolic law with coefficients of determination (R2) of 0,972 and 0,983, respectively, for Lgdima and Hanabou samples. The study of the variation of the infiltration rate I(t) versus the time t, made it possible to get in the case of the two samples, curves whose the best fit is a function power with a coefficient of determination R² ranging between 0,909 and 0,995. The equation of the infiltration rate was found to be as: , a and ß are coefficients which vary from a sample to another and from a test to another.
Key words: Infiltration, Humidification face, Clay fraction, Infiltration rate, Compaction