兰州大学机构库 >资源环境学院
天水罗裕沟流域土壤侵蚀时空格局模拟研究
Alternative TitleThe modeling of temporal-spatial pattern of soil erosion in Luoyugou watershed, Tianshui,China
马金辉
Thesis Advisor李吉均
2007-03-07
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword流体力学原理 降雨侵蚀力指标 罗裕沟流域
Abstract

天水市北郊的罗裕沟流域地处陇西黄土高原丘陵沟壑区和陇南山地的交互地带,其气候、地貌和土壤侵蚀特点在陇西黄土高原具有一定的代表性和特殊性,进行该流域土壤侵蚀时空格局的模拟研究,不仅有助于理解该区域生态水文和土壤侵蚀的过程与耦合机制,也对当地制订水土流失和生态重建规划具有一定的实践意义。本研究利用罗裕沟近20年的观察资料,在GIS平台上,采用了统计和空间分析技术,基于USLE框架的经验模型和基于物理基础的WEPP模型,模拟了罗裕沟流域土壤侵蚀的时空格局,探讨了不同因子的参数赋值方法及其对模拟结果的影响,分析了罗裕沟土壤侵蚀时空格局的原因,提出了罗裕沟流域生态恢复和水土流失治理的参考方案。主要结论如下: 
1.本研究根据流体力学原理提出了适合本区域的降雨侵蚀力指标——降雨动能,经过在径流场、小流域和中流域三种不同空间尺度,逐次、逐日和逐年三种不同时间尺度下与输沙量的相关分析,证明本研究提出的降雨侵蚀力指标比传统降雨侵蚀力指标更为有效,降雨动能是本区域土壤侵蚀的基本驱动因子; 
2.基于流域内降水量随地理位置和海拔高度而变化的特征,插值生流
域内汛期逐月的降雨动能场。通过计算月尺度下流域内逐点降雨动能与沟口输沙率的相关系数,来表示逐点降雨动能对沟口输沙的相对敏感性,表明逐点侵蚀敏感性的空间格局与野外观察的、USLE和WEPP模拟的侵蚀强度空间格局相一致; 
3.将流域内各个空间单元看作流域输沙的有限源区,利用优化算法建
立了月尺度下逐点降雨动能与沟口输沙率的非线性规划方程,依此方程中降雨动能系数与降雨动能乘积的累积值生成流域输沙贡献率分布图,显示输沙贡献大的区域仍在流域中游,且主要是山坡上坡位置,这与其他方法得出的结论有所差别; 
4.在使用USLE及其改造版时,应用GIS可以快速实现地形坡度坡长因子的计算和区域土壤侵蚀的评估。将USLE模型中的降水因子改为本研究提出的降雨动能后,可以提高模拟精度; 
5.从DEM中利用多种地形指标识别出沟沿线;基于将沟沿线作为侵蚀前地形表面的假设,计算获得沟谷逐点的深度,将其作为地质时期沟谷侵蚀强度的指标,该方法比单纯的沟谷密度法更好地表现了侵蚀强度的空间差异; 
6.WEPP模型能对常规侵蚀事件提供一个较好的预测结果,对强暴雨事件的模拟不够稳定,但当将逐事件模拟结果按年综合后,其结果和实测结果有一定的可比性,WEPP模型可用于罗裕沟流域多年降雨侵蚀时空格局的研究; 
7.模拟所用DEM的分辨率越高,模拟结果的空间分辨率提高,但在较大流域模拟时却存在很多困难。试验发现,22.5m的分辨率可以满足中等流域WEPP模型的应用需要。流域划分方案及从DEM中所获取沟系的详细程度影响着沟口输沙的模拟结果; 
8.沟道参数对模拟结果尤其对流域产沙、产水的影响很大,但不同级别的沟道对产水、产沙的敏感性不同,在桥子东沟流域1~3级支、毛沟的沟道参数对流域输沙的影响为明显; 
9.WEPP模型对土壤的有效水文传导率非常敏感,在由土壤质地计算的有效水文传导率的基础上,根据土壤结构和土地利用情况,对有效水文传导率的调整可使模拟精度提高; 
10. 罗裕沟流域土壤侵蚀的年际变化存在阶段性、周期性、弱趋势性和突变性4大特征。该流域土壤侵蚀存在三个明显不同的发展阶段,阶段性反映其存在一个6-8年的长周期,在高侵蚀高变幅阶段,侵蚀模数呈现出准三年周期特点;流域主要的侵蚀过程集中在6、7、8三个月,且主要发生于汛期少数几天的极端暴雨事件中; 
11.罗裕沟流域土壤侵蚀的空间分布具有很强的规律性。高侵蚀区出现在流域左岸中下游地区的谷坡区,其次出现在流域右岸的杂色土沟谷及其毛沟的谷坡上。在河流左岸基岩与黄土/杂色土区的交互地带存在一明显的强侵蚀带。高侵蚀区往往也是侵蚀时间变化的高敏感区。土地利用和地形坡度是控制罗裕沟流域土壤侵蚀空间格局的基本要素,而土壤等其它因素的作用则相对较小; 
12.根据国家退耕还林政策和罗裕沟流域土地利用现状,设计了三个土地利用优化结构条件下的情景模式,WEPP模拟表明,坡度大于25°基岩沟坡和坡度15~25°杂色土谷坡上的退耕还林对防治水土流失的效果非常明显。该土地利用的设计方案可作为罗裕沟退耕还林和生态恢复规划的参考。

Other Abstract

Luoyugou watershed, located in the north suburb of Tianshui city, is the common boundary between Longxi Loess Plateau hill-ravine region and Longnan Mountains, which has remarkable representativeness and particularity in climate, terrain and soil erosion. The modelling research about space-time pattern of soil erosion in this watershed can help us not only understand the process and coupling mechanism between eco-hydrology and soil erosion, but also make optimized plans about water soil loss and ecosystem reconstruction. Using 20 years observation data of the  watershed and GIS technique of statistics and spatial analysis, this research, which is based on USLE empirical model and WEPP  physical model, simulates the space-time pattern of soil erosion, discusses the parameter evaluating method for different factors and the influence for simulating results, analyzes the reason of regional space-time pattern of soil erosion and brings forward the reference project about ecosystem reconstruction and water and soil loss. The main results of this research are:

(1) Based on hydromechanics theory, this research propose a new precipitation eroding force index fit for this region -- Precipitation Kinetic Energy Index and proves that this index is more effective than other traditional indices by correlated to sediment transferring amounts including three spatial scales of runoff plot, small watershed and middle watershed and three time scales of event, day and year. Precipitation Kinetic Energy Index is the fundamental driving force of soil erosion in this region.

(2)Based on the precipitation variation characters with geography location and elevation, the regional precipitation kinetic energy field in flood season is generated monthly by GIS spatial interpolation technique. Calculating monthly correlation coefficient between precipitation kinetic energy at each points and sediment transferring amounts at the watershed outlet, the relative sensitivity of precipitation kinetic energy to sediment transfer at the outlet is expressed in each spatial points. The result shows that the spatial pattern of erosion sensitivity at each point is consistent with the erosion and intensity field observation and simulation of USLE and WEPP.

(3)Using optimized algorithm and regarding each spatial unit in the watershed as sediment transfer limited sources, the monthly nonlinear plan equation between precipitation kinetic energy and sediment transferring ratio in the outlet is set up. The distribution map of sediment transfer contribution ratio is generated depending on the precipitation kinetic energy coefficient and accumulation value in the equation and shows that the region having the greater contribution for sediment transfer is located in the watershed middle reaches, spatially in uphill, which has some different conclusion with other methods.

(4)When running USLE and its improvement versions, using GIS can quickly calculate terrain LS index and evaluate regional soil erosion. Changing the precipitation index in USLE to the precipitation kinetic energy index proposed by this research can improve the simulation precision.

(5)The gully-edge can be recognized using several terrain indices and DEM. Based on the hypothesis that treats gully-edge as fore erosion terrain surface, the gully depth in each point can be calculated and treated as the gully erosion intensity index of geological period.

(6)WEPP can generate good forecast result for general erosion events, but for intense rainstorm events the simulation result isn’t stable. When accumulating the simulation results of each event to annually, the final result has certain commensurability by comparing with the observation data. So WEPP can be used for the space-time pattern research of multi-year precipitation erosion in Luoyugou watershed

(7)The higher resolution of DEM, the better spatial resolution will be obtained in simulation results. But while consider in bigger watershed there are some difficulties for simulation with high resolution and large amount data. The experiment finds that the 22.5m resolution of DEM can be satisfied to the application of WEPP in middle watersheds. The division plan of watershed and the detailed degree of channel getting from DEM will influence the simulation result of sediment transfer in the water outlet.

(8)The channel parameters have remarkable influence for simulation results, especially for watershed production of sediment and water. While for different channel ranks the sensitivity of production of sediment and water is different. In branch and tiny channel of first to third channel ranks in Qiaozidonggou watershed, the channel parameters have the most remarkable influence for watershed sediment transfer.

(9)WEPP is very sensitive to the soil effective hydrology conductivity. On the base of effective hydrology conductivity calculated from the soil texture, according to the soil structure and land use, the adjustment of effective hydrology conductivity can improve the simulation precision.

(10)The annual variation of soil erosion in Luoyugou watershed has four characters: gradualness, periodicity, weak tendency and sudden change. The soil erosion in this watershed has three remarkable developing stages and the gradualness shows that there is 6-8 year-long period. In intensive erosion variation period, the erosion has the three-year period. The main erosion process of this watershed is concentrated in June, July and August and happens in several days extreme rainfall events in flood season.

(11)The spatial distribution of soil erosion in Luoyugou watershed has distinct regularity. The intensive erosion region is firstly located in the slope region of middle and lower reaches in the left-shore watershed and then in the mixed soil channel and tiny channel of right-shore watershed. In the common boundary between bedrock and loess/mixed soil region in the left shore there is a remarkable intensive erosion region which is also the high sensitive area of erosion time variation. Land use and slope are the fundamental factors to control spatial pattern of soil erosion in Luoyugou watershed and other factors such as soil has relative small functions.

(12)According to the country policy about changing farming to nature plant and the land use situation of Luoyugou watershed, the three scene patterns of land use optimization are designed. The simulation of WEPP shows that, at the bedrock slope higher than 25 degree and mixed soil slope higher than 15-25 degree, the regions changing farming to nature plant have remarkable effect for preventing water soil loss. The design proposal of the land use can be the reference for the plans of changing farming to nature plant and ecology restoration in Luoyugou watershed.

URL查看原文
Language中文
Document Type学位论文
Identifierhttp://ir.lzu.edu.cn/handle/262010/240736
Collection资源环境学院
Recommended Citation
GB/T 7714
马金辉. 天水罗裕沟流域土壤侵蚀时空格局模拟研究[D]. 兰州. 兰州大学,2007.
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