引黄畦灌田间水沙分布规律

为探究引黄地面灌溉条件下水沙在田间的分布规律,该文于尊村引黄灌区开展田间试验,研究灌溉水流推进过程,灌溉水含沙量沿畦长方向的变化及灌水后泥沙在田面的沉积状况。结果表明,引黄灌溉水在沿畦长方向推进的过程中,随着水分下渗和水力损失,其流量减小,挟沙能力沿畦长方向逐渐减弱;挟沙水流中的较大粒径颗粒逐渐沉积,水流中携带泥沙的中值粒径逐渐减小;灌水结束后,田面沉积泥沙粉粒质量分数占70%左右,田面沉积泥沙质量沿畦长方向逐渐减小,在畦尾有增大趋势,且畦田首端和畦田尾端的沉积泥沙粒径大小及其颗粒组成却相差不大。研究结果为开发和利用畦灌蓄沙、放淤改土等黄河水沙利用技术提供一定的科学依据和理论支持。

Distribution of Yellow River's silt in field under border irrigation

Abstract: The irrigation water from Yellow River contains high content of sediments, and will greatly affect soil in irrigated field. In order to explore the water and silt distribution in the field, a field experiment was conducted in Zuncun Yellow River irrigation district from May to July, 2015. The experimental site is located in Yuncheng, Shanxi Province, China (110o50'' E, 35o03'' N). Border irrigation is the main irrigation method in the local area, and it was applied in the test field. We had set 2 border fields in the experiment and the width of the border was 1.8 and 2.7 m, respectively. The length of the border field was 300 m and the mean slope of each border was 0.1%. The unit-width discharge was 9.26 L/(s·m). The irrigation was conducted on June 19 and July 30, respectively. The test procedure included: 1) measurement of volumetric soil moisture 24 hours before and after irrigation; 2) recording of water movement and regression in each border; 3) collection of water samples and measurement of sediment concentration; 4) calculation of the sediment-carrying capacity in the sediment-laden flow; 5) analysis on the variation trend of the sediment content in irrigation water; and 6) study on the deposited sediment distribution along the border length after irrigation. The experimental apparatus included Parshall flume, ultrasonic flowmeter, time domain reflectometry, laser particle size analyzer, et al. The results showed that: 1) During the border irrigation, the distribution of soil moisture was relatively even; 2) The irrigation water flowed fast at the beginning of irrigation and the velocity of water flow decreased along the border length; 3) The sediments concentration in the water decreased by 81% from the head to the end of the border field; 4) The maximum sediment-carrying capacity of the flow was 0.005 kg/m3, far less than the sediments content in irrigation water; 5) The median diameter and the average particle size of the sediments in irrigation water decreased gradually with water flow advancing, and the bigger the diameter of sediment particle was, the sooner it deposited; and 6) The deposit sediments consisted of clay, silt and sand. The major composition of the deposited sediments was silt, and its proportion was as high as 70%. The results indicated that water infiltration and drainage reduced the water flow rate, and then hydraulic loss decreased sediment-carrying capacity of the flow. Then the suspended sediment particles in the sediment-laden flow settled down by gravity, and the deposited sediments form a dense layer in soil. On the other hand, border irrigation promoted faster flow advancement, and the dense layer greatly reduced the deep leakage. We concluded that the sediments in Yellow River could reduce the capacity of infiltration and make moisture distribution even, and Yellow River''s silt distribution in the field followed a certain pattern above. It is estimated that, in a long run, the soil texture will change under the Yellow River border irrigation. And the variation was similar at the head and end of the border. The mechanism involved in the influence of silt on soil remains to be investigated.