【作者】 杨方社；

【导师】 李怀恩；

【作者基本信息】 西安理工大学 ， 环境工程， 2009， 博士

【摘要】 黄土高原是世界上水土流失最严重的地区之一,然而砒砂岩是黄土高原集中的碎屑基岩产沙区的核心,系黄河流域多沙粗沙区的重要组成部分。该区由于严重的土壤侵蚀,被喻为“世界水土流失之最”,具有“地球癌症”之称。由于砒砂岩地区恶劣的自然环境,剧烈的水土流失,给黄河下游河道造成了更加严重的泥沙淤积,引发一系列的生态环境问题。沙棘植物柔性坝是利用生物措施治理水土流失、利用自然改造自然的生物工程,是治理河流泥沙灾害的一种治本之举。因此,开展沙棘柔性坝拦沙、生态及流速场效应等方面的研究,为沙棘柔性坝的推广及规划种植提供理论依据,在理论与实践上都具有重要意义。本文基于野外试验,以沙棘植物柔性坝为核心,对沙棘柔性坝所构成的沟道生态系统的水保效应、生态水文及土壤环境效应进行了分析与研究,探索并成功应用先进的PIV法,分析与讨论了沙棘植物柔性坝对水流特性和流速场的影响与效应；运用河流动力学及泥沙运动力学理论对沙棘柔性坝的拦沙机理进行了理论分析与探讨；运用泥沙数学模型对沙棘柔性坝的拦沙效应进行了数学模拟,并根据分析结果对沙棘柔性坝的种植规划参数进行了有益的分析与讨论；最后,提出了防治砒砂岩地区水土流失的几点建议。论文取得的主要成果如下：1.在时空尺度上,从定性与定量两方面揭示了沙棘植物柔性坝的拦沙效应。具体结论为：(1)沙棘“柔性坝”对泥沙具有显著的分选拦截作用,柔性坝系与下游刚性谷坊配套使用可天然分选沟道里的泥沙一拦粗淤细,就近将粗沙过滤在坝系沟道里,细沙淤积在下游谷坊内；(2)下游谷坊还可在上游沙棘植物坝系的过滤下储蓄细沙含量较少的清水,形成一座微型水库,可作局部农业用水之用。2.根据监测的生态特性资料,(1)对沙棘柔性坝的生态学特性、土壤改良效应、沟道土壤水分特性、土壤水分时空动态变化进行了研究；(2)用地统计学方法分析了沙棘植物柔性坝沟道不同空间立面二维区域不同方向的土壤水分空间变异特征,研究了植物柔性坝对沟道土壤水分在立面区域分布格局的影响；(3)揭示了沙棘植物柔性坝优良的生态效应、土壤改良效应及对沟道径流的调控作用,证明了沙棘柔性坝对土壤水资源具有显著的调节作用。3.分析了沙棘柔性坝对水流特性的影响与阻滞效应,论证了沙棘柔性坝对水流具有很强的拦截、阻滞和雍水作用,致使雍水区流速降低,泥沙在这一区域沉降淤积。(1)揭示了坝长、株距在水流流速、水深变化中起主导作用,且坝长的优势大于种植密度；(2)水位雍高最大发生在坝前段；(3)沙棘的年际生态调查表明,坝体的阻水效应随沙棘的强势生长而增强；(4)分析还表明,植物的生长密度较小时,坝长是导致植物坝上游区水深增加的主要因素,其次是种植密度,最后是沟床坡度；(5)植物的生长密度较大时,植物的坝长依然是导致植物坝上游区水深增加的主要因素,其次是种植密度,再次是生长密度,最后是沟床坡度。4.在野外试验基地,首次探索并成功的应用了先进的流场测量技术—-一PIV法,对沙棘柔性坝流速场的分布与变化规律进行了系统的分析与研究,讨论了沙棘柔性坝的流速场特性,探明了水流能量损失主要发生在坝上游壅水区,指出泥沙优先在这一区域沉降,再次论证了沙棘柔性坝具有显著的阻水与泥沙淤积效应,为沙棘柔性坝治理水土流失提供了理论依据。具体表现为：(1)沙棘柔性坝内的流速明显小于坝前无沙棘对比区,表现出柔性坝显著的流速衰减效应；(2)柔性坝段内的横断面上流速分布易呈现出反“流舌”型态,且流速沿横向分布曲线呈现出波浪形态或者是曲折反复的“之”字型态；(3)研究结果表明将粒子图像测速这一先进技术推广应用到室外流速场的观测是完全可行的。5.运用河流泥沙动力学理论分析探讨了沙棘植物柔性坝的阻力问题,从理论上推导了沙棘植物柔性坝的糙率系数估计公式,估计了沙棘柔性坝的糙率系数,用实测资料进行了对比验证,结果良好；运用合适的输沙公式,对东一支沟沟道输沙特性作了理论探讨与分析。结果表明：(1)沙棘植物柔性坝的阻力主要由沙棘植物、沟床底及沟道边壁阻力及床面型态阻力构成,这些阻力可通过植物柔性坝的曼宁糙率系数来综合反映；(2)沙棘植物柔性坝的曼宁糙率系数大致处于0.04-0.09的范围内,并与沟床平均植物密度、淹没体积比、水力半径及植物的生长期有关,而且植物密度、淹没体积比都随着水深的变化而有所不同；(3)使用不同的输沙公式会对拦沙结果产生一定的影响。6.应用一维水沙数学模型对东一支沟沙棘植物柔性坝的拦沙效应进行了模拟。根据计算结果对沙棘植物柔性坝的规划种植参数进行了优化探讨,为沙棘植物柔性坝的规划种植提供参考。模拟结果表明：(1)植物坝的曼宁糙率越大,植物坝的拦沙效果越好；(2)植物坝单坝的拦沙率随坝长的增加而趋近于某一最大稳定值；(3)坝长越短时,淤积范围可覆盖整个坝段,坝段较长时,坝尾部易发生不同程度的冲刷,这表明设计植物坝时,坝长并非越长越好,其坝长应在合理的范围内,避免造成浪费；(4)当沟道内设置两座植物坝时,坝间沟床段易发生冲刷,双坝的综合拦沙率随坝间距的增加而减小,且逐渐趋于某一稳定值；(5)沟道内设置两座及以上植物坝时,并非一定能提高综合拦沙率,间距为零时的双坝与两坝所合成单坝的拦沙率相当；(6)双坝间有区间支流泥沙汇入时,下游坝可有效的发挥拦截区间泥沙的功能；(7)植物坝的拦沙率受沟床比降的影响,植物坝拦沙率随沟床比降的减小而增大,植物坝对粗沙的拦截效果比细沙要高得多；(8)植物坝尾部段及下游沟床易冲刷,所以在设有植物坝的沟道出口处应该采取谷坊等措施以抑制植物坝下游沟床的冲刷。7.研究表明,沙棘是治理砒砂岩地区水土流失的先锋树种,沙棘植物柔性坝是防治该区水土流失的有效生态工程措施。针对砒砂岩地区的沟道输沙特点,指出砒砂岩地区应坚持以沙棘柔性坝为主体的沟道小流域综合防治技术体系,方可根治砒砂岩地区的水土流失。更多还原

【Abstract】 Loess plateau is one of the most serious soil and water loss regions in the word, however, the soft rock region is the core of drossy rock yield sediment regions in the Loess plateau in china, and it is also an important part of much and coarse sediment regions located in Yellow River watershed. The region is called as "earth cancer" and "the most severe soil and water loss" due to severe soil erosion. The severe sediment deposition was engendered in the lower Yellow River, and a series of ecological and environmental problems was brought because of the severe soil and water loss and atrocious natural environment. The seabuckthorn flexible dam is a new biology engineering of using biology measure controlling soil and water loss and using nature reshaping nature, and is a radical measure of controlling sediment disaster in river. So, carrying out the research on effects of sediment retention and ecology and flow velocity vector field of seabuckthorn flexible dam, it can provide for the theoretic proof in spreading and planning plant of seabuckthorn flexible dam, and this is also very important and valuable in theory and practice.In this paper, seabuckthorn plant flexible dam was the core, soil and water conservation and ecology hydrology and soil environment effects of gully ecology system formed by seabuckthorn flexible dams were analyzed and studied. The presently advanced PIV(Particle Image Velocimetry) technology was exploringly and successfully employed, the impact of seabuckthorn flexible dam on flow behavior and velocity distribution was analyzed and discussed. Sediment retention mechanism of seabuckthorn flexible dam was theoretically analyzed and discussed by river dynamics and sediment transposition mechanics theory. Sediment retention effect of seabuckthorn flexible dam was effectively simulated by sediment mathematical model, and plan plant parameters of seabuckthorn flexible dam were effectively analyzed and discussed. Finally, the author provided some advice for controlling and harnessing soil and water loss of soft rock region. The main content and innovative achievements are as follows:1. On the spatio-temporal scale, sediment retention of seabuckthorn flexible dam was revealed from the qualitative and quantitative analysis. The idiographic results were:(1) seabuckthorn flexible dam had marked choice and prevention effect to sediment, sediment of gully bed was naturally chose to coarse and fine sand by joint using of flexible dam system and lower small rigid silt dam, this can make coarse sand deposit in gully and fine sand silt in lower small rigid silt dam; (2) the lower small rigid silt dam can also save clear water that has little fine sand, and form a small reservoir that can be used for local agriculture under the upper seabuckthorn flexible dam system filtration.2. By special measured ecological data, (1) ecological feature, soil improve effect, gully soil moisture characteristic and spatio-temporal dynamic variation of soil water were studied; (2) the method of geostatistics was employed to analyze the spatial variability of soil moisture in different directions in distinct vertical two-D areas in different spatial locations and the effect of plant flexible dam on the distribution of soil moisture in the vertical section of soil in gully with seabuckthom plant flexible dam; (3) the effect of excellent ecology, soil improvement and regulating gully runoff of seabuckthom flexible dam were showed, and the strikingly adjusting soil water resource through seabuckthorn flexible dam was also tested.3. The impact of seabuckthorn flexible dam on flow behavior was analyzed, and it was proved that flow velocity was slowed down in swell water area, and that sediment was deposited in the area because of very strong prevention, delay and swell water effect of seabuckthorn flexible dam on flow. These results are as follows:(1) it was revealed that dam length and plant density took the main role in flow velocity and water-depth distribution, and the role of dam length was stronger than plant density; (2) the maximum water table swelling occurred in the front of the flexible dam; (3) seabuckthorn yearly ecology investigation showed that the preventable effect of dam on flow was gradually stronger and stronger with growth of seabuckthom; (4) as the plant density is small, dam length is main reason for increasing upper water depth of seabuckthorn flexible dam, the next is plant density, and the last is gully bed slop; (5) as the plant density is big, dam length is yet main reason for increasing upper water depth of seabuckthorn flexible dam, the next is plant density, the third is growth density, and the last is gully bed slop.4. Based on field experiment, advanced velocity field measure technology-PIV was exploringly and successfully employed, the law of flow velocity distribution and variation was systematically analysed and studied, and the velocity field characteristic of seabuckthorn flexible dam was discussed in detail. It was proved up that flow energy loss was mainly occurred in the upper swell water area of seabuckthom flexible dam, and it was pointed out that sediment was firstly deposited in the area. It was again tested that seabuckthorn flexible dam had striking resistance to flow and sediment deposit effect by above those conclusions, and this can provide theoretic proof for seabuckthom flexible dam controlling soil and water loss. Respective results were as follows:(1) flow velocity in seabuckthorn flexible dam was distinctly smaller than no seabuckthorn contrast area in front of flexible dam, this showed evidently reducing flow velocity in the seabuckthorn flexible dam; (2) cross section flow velocity distribution was reverse "flow tongue" shape, and cross section velocity distribution curve showed wave shape or zigzag shape in flexible dam; (3) it is completely feasible that the advanced PIV technology is used and spread in field flow velocity measure.5. Resistance of seabuckthorn flexible dam was analyzed and discussed by river sediment dynamics theory, estimation formula of flexible dam roughness was deduced, and value of flexible dam roughness was estimated, and estimated roughness was well tested and contrasted with field data; sediment transportation trait of east one branch gully was theoretically discussed and analyzed. The results showed:(1) that resistance of seabuckthorn flexible dam was comprised of seabuckthorn plant, gully bed, gully bed and riverside resistance, and bed formation resistance, the resistances were reflected by the roughness of plant flexible dam; (2) value of seabuckthorn flexible dam’s Manning roughness is probably from 0.04 to 0.09, and it is concerned with average gully bed plant density, submersed volume scale, hydraulic radius, and plant growth, and the plant density and submersed volume scale also varied with water depth of flow; (3) sediment retention result was easily affected by using different sediment transportation formula.6. The effect of sediment retention of seabuckthorn flexible dam in east one branch gully was successfully simulated by using of one dimension flow and sediment mathematical model. The plan plant parameters of seabuckthorn flexible dam were optimized and discussed according to calculated result, and some advice was provided for planning and planting of seabuckthorn flexible dam by these results. The simulated results showed:(1) Manning’s roughness of plant dam was bigger, sediment retention effect of seabuckthorn plant dam was better; (2) sediment retention rate of single plant dam would run to be some maximum stable value with dam length increase; (3) if the dam length was shorter, scope of sediment deposit would trend to the whole dam, if the dam was longer, the tail of dam was prone to be scoured, this indicated that it was not good that the dam length was longer, but the dam length was right range to avoid waste as planning plant dams; (4) as double plant dams were planned in gully, the gully bed was easily eroded, and comprehensive sediment retention rate of double dam was smaller and to be a stable value with increase of interspace between dams; (5) comprehensive sediment retention rate was not increased as two or more dams set in gully, and sediment retention effect of double dams of their zero gap was almost equal to single dam formed by two dams; (6) the lower plant flexible dam can effectively blocked interzone yielded sediment; (7) the sediment retention effect of plant dam was influenced by gully bed slop, and it get increased with gully bed slop’s fall, and the sediment retention effect of plant dam on coarse sand was more than thin sand’s; (8) because tail and lower gully bed of flexible dam was easily eroded, so some small engineering measures should be taken to confine scour of lower gully bed of plant dam at the exit of plant dam gully. 7. The research result showed that seabuckthorn is the leading small arbor for controlling soil and water loss of the soft rock region, and seabuckthorn plant flexible dam is very effective ecology engineering for control and harness of soil and water loss of it. Finally, in point of sedimeni transportation behavior of gully in the soft rock region, it was proposed that the comprehensive small watershed controll technology system should be insisted on using in gullys in the soft rock region, but the main body of the technology system had to be the seabuckthorn flexible dam, and sc soil and water loss in the soft rock region can essentially be controlled and restrained.更多还原