| The gully plateau region of loess plateau, which is flat and wide, is a main place of producinggrain and cash crops on loess plateau. Because of the few forests, ravines horizon, the surfacebroken, soil erosion is serious for a long time, especially gullies headward erosion. Theatrophy of the table-land direct threat to the region’s economic and social sustainabledevelopment. Gully head is not only an important part of the channel, but also a main hub oftable-land runoff. Because of the convergence of runoff, the gully head extended and widenrapidly with gravity erosion, which is the direct cause of the channel development. Thisphenomenon is called gully headward erosion, commonly known as the trench head forward.Currently, the research date about the gully headward erosion of gully plateau region of loessplateau is less for lacking of experiment and almost no special actual positioning monitoringtest, so it is difficult to know the gully head development absolutely. Therefore, this paperusing the wild washout simulation experiment is to study on the rules of gully head sedimentand evolution process, and expound the relationship between the gully headward erosion rateand slope or water flow, the relationship between sediment yield and slope or water flow, todiscuss the gravity erosion processes of gully headward erosion and analysis the geometriccharacteristics of change of gully headward erosion. All of these can provide the scientificbasis and technical support for gully head protection. The main conclusions are as follows:(1) Because of the influence of continuous water, runoff sediment concentration decreasedwith the follow-up amount of water flow increasing and prolonged time of water. On the earlyof channel development, the sediment concentration of the plot of3°and5°is fluctuantobviously, but stable on the plot of8°and12°for forming flow channel and short of gullyhead forming time. The sediment concentration increased instantaneously for the gravityerosion. When the erosion amount of a gravity erosion is bigger or number of gravity erosionis more, the sediment concentration variation coefficient is also larger. Conversely, thesmaller erosion amount or the less number, the smaller and more stable coefficient ofvariation of sediment concentration.(2) Under the test conditions, when the water flow rate is in excess of170L/min, the gravityerosion mainly occurred in the middle and last stage, namely after20min, with manycharacteristics, such as long cycle and large erosion amount. When the water flow rate islower than170L/min, initial gravity erosion occurred in prophase stage, namely0-20minutes,frequently, but less erosion amount. The number of gravity erosion is decreased with the slopeincreasing,such as the number of an average of8.4times on3°plot but1.4times for12°plot.The rank for the number of gravity erosion in different stages is the prophase stage <the laststage <the middle stage.(3) The morphological changes of gully head is affected by gravity erosion clearly. Accordingto the characters of gully head edge line horizontal projection,it mainly divided into linear model, the peak, bimodal type, arc and bent. On the basis of damage erosion surfacemorphology are divided into vertical, concave type and the type of the slope.(4) Under the condition of test flow, the rate of gully head forward reduced with theincreasing of water flow and the variation of gully head size is different on different plots.The biggest rate of gully head forward is1.51m/field, the minimum is only0.04m/field, andthe average is0.35m/field. On the downward erosion, the order is8°plot>12°plot>3°plot>5°plot.(5) Affected by the continuous water, the volume change range from0.048to0.048m3, andthe biggest volume change is5.27°x103kg on3°plot, the minimum is2.20x103kg on5°plot. In addition to3°plot, the amount of gully headward erosion increased with slopeincreasing, simulated by linear function. A quadratic function can simulated the relationshipbetween the cumulative erosion amount and the water flow... |
