【作者】 李瑜琴；

【导师】 黄春长；

【作者基本信息】 陕西师范大学 ， 自然地理学， 2009， 博士

【摘要】 本文基于详细的野外考察,在泾河上游气候敏感区选取了典型的黄土—古土壤剖面——赵家村（ZJC）剖面;在泾河中游彬县至永寿段选取程家川（CJC）剖面,在礼泉至淳化段选择了礼淳桥（LCQ）剖面,这2处剖面中均夹有全新世洪水平流沉积物,为典型的洪水沉积剖面。对ZJC和CJC剖面进行了磁化率、烧失量、CaCO₃含量、粒度和化学元素等环境代用指标的实验分析和测定。通过ZJC剖面野外沉积特征和室内实验分析,重建了全新世气候与环境演变过程,为泾河流域全新世古洪水研究提供了气候背景。对CJC、LCQ剖面鉴定识别了古洪水平流沉积层,据此恢复了泾河古洪水水位,利用水文学方法恢复了泾河万年一遇洪水洪峰流量,并通过现代大洪水和洪峰流量—流域面积关系的验证,表明古洪水洪峰流量计算结果是可靠的,使洪水记录长度由实测洪水的数十年尺度延长到万年尺度。加入古洪水数据、结合历史调查洪水资料和实测洪水数据,绘制了泾河一万年来的洪水洪峰流量—频率曲线,使百年、千年一遇洪水的获取由传统的只依据实测几十年数据来外推方法转变为内插法来实现,提高了稀遇特大洪水流量的预测精度,为泾河流域水利水电和防洪减灾等工程建设方面提供了重要的设计洪水依据。本文获得的主要结论为:1.通过ZJC剖面多种环境代用指标分析,建立了该区域全新世气候与环境演变的过程,揭示了该区域全新世黄土—古土壤的物质来源。磁化率、烧失量、CaCO₃含量、粒度成分,以及地球化学元素等指标均显示泾河流域经历了晚冰期（14700～11500 a B.P.）、早全新世（11500～8500 a B.P.）、中全新世（8500～3100 a B.P.）、晚全新世（3100 a B.P.至今）4个气候变化阶段,为泾河古洪水发生和规律机制的研究提供了气候变化背景。2.通过地层学和沉积学分析准确判定了泾河2个剖面的古洪水平流沉积层,为再现泾河全新世洪水水位及洪峰流量提供了地质证据。通过野外宏观沉积特征识别,以及室内磁化率、烧失量、CaCO₃含量、粒度的分析,准确判定CJC剖面平流沉积层共记录了5次全新世特大洪水事件。结合剖面420～450 cm地层中含有龙山文化晚期的文化遗物,以及与流域内其他剖面热释光所测年代序列对比,确定5次洪水主要发生在龙山文化晚期（4200～4000 a B.P.）。LCQ剖面记录了2次全新世特大洪水事件,地层对比发现洪水事件发生年代与CJC剖面相同。泾河两个剖面古洪水平流沉积层的准确判定,与渭河流域漆水河已有古洪水研究成果的对比,表明在全新世4200～4000 a B.P.期间黄河中游发生特大洪水事件具有普遍性。3.通过恢复古洪水水位、过流断面形态,采用水文学中的比降法计算出古洪水洪峰流量,并利用泾河现代大洪水恢复与洪峰流量—流域面积关系进行了验证。基于地层学、考古学和水文学方法,依据CJC剖面、LCQ剖面古洪水平流沉积物的单层厚度、底界高程,利用含沙率恢复古洪水水位;采用比降法,计算出泾河全新世时期的特大洪水的洪峰流量;通过现代洪痕恢复洪水和洪峰流量—流域面积关系验证,结果显示所采用水文学方法合理,计算结果可靠。4.加入古洪水数据,结合水文站实测的年最大洪峰流量、前人调查获得的历史洪水洪峰流量,建立了泾河一万年来的洪水洪峰流量—频率皮尔逊Ⅲ型曲线,不仅延长了泾河洪水数据系列的时间尺度,而且使得百年一遇、千年一遇洪水洪峰流量的获取由传统的依据几十年实测水文数据外推转变为内插来实现,提高了洪水频率的精度,该研究成果填补了泾河古洪水研究的空白,对于泾河流域的水利水电工程、防洪减灾、城市和农村生态环境建设、水资源开发利用、水污染防治都具有十分重要的实用价值。5.研究发现泾河洪水主要是暴雨洪水,龙山文化晚期（4200～4000 a B.P.）对应全新世大暖期后期的气候恶化过程,这一时期气候变率大,降水年际、年内变化大;加之,4200～4000 a B.P.的期间气候变冷,导致季风雨带的北撤,使雨带在黄河中游地区频繁活动,二者叠加共同作用是造成这一时期特大洪水发生的主要原因。本研究通过对泾河流域深入调查研究,在泾河的一级阶地全新世黄土—土壤剖面中发现古洪水沉积夹层,利用沉积地层学、地貌学、考古学等方法,确定泾河在4200～4000 a B.P.发生了特大洪水事件。利用水文学模型,计算出特大洪水的洪峰流量,大大延长了洪水水文数据序列,并建立了泾河全新世洪水频率曲线,科学、系统地提高了泾河洪水水文学计算精度,增强了泾河流域防洪减灾和水资源开发当中洪水频率分析的可靠性。本文研究成果对于泾河流域的防洪减灾、水资源开发和生态环境建设具有重要的应用价值,同时填补了泾河流域古洪水水文学研究的空白,对于泾河流域生态环境综合治理具有重要的科学意义。更多还原

【Abstract】 Based on comprehensive field survey, the ZJC profile, a typical loess-palaeosol profile, was selected and sampled in high-resolution at the sensitive climatic zone in the upper reaches of the Jinghe River. And two typical slackwater deposits profiles including CJC profile in the middle reaches from Binxian to Yongshou and LCQ profile in the reaches from Liquan to Chunhua, were sampled and studied. The proxy indicators of environment were determined and analysised by experiments with magnetic susceptibility, loss on ignition, percentage composition of calcium carbonate, particle-size distribution and chemical element in laboratory. This research deals with the study of palaeofloods with respect to climate changes over the last few millennia years.Through the analysis of macroscopical sedimentologic characteristics and physicochemical property of the ZJC profile, characteristics of the Holocene climatic variability and environmental change in the Jinghe River Bansin were reconstructed, providing the background of climatic variability for the Holocene palaeofloods occurrence. Palaeofloods slackwater deposits of the Jinghe River were identified in the CJC and LCQ profiles, which providing information on hydrologic variability and extreme floods over long-term intervals （100-10 000 yr）. Hereby the water levels and peak discharges of the extreme palaeofloods with ten-millennia-year return period were reconstructed by hydrological methods, extending the time scale of floods from decades to millennia. Through the modern flood and the relation of peak discharge and drainage area, the palaeoflood discharges were tested reliable. Palaeofloods were used in combination with historical flood data （last 1 000 yr） and the gauged record （last 30-50 yr）, we drew the rating curves of the peak discharges and frequency since ten millennia years. Palaeofloods data can also provide physical evidence for the upper limits of flood events in a basin without relying on instrumental records, improving the conventional procedure involves statistical extrapolations from short gauged hydrological records documenting 30-40 year records of observed floods to the estimation of the discharges of very large, rare floods, and the discharges precision was also improved. Thus it is significant to the engineering construction of flood mitigation, water conservancy and hydropower in the Jinghe River Basin.The main results are as following: 1. Through the analysis of proxy environmental indicators of the ZJC profile, this paper revealed the Holocene loess-palaeosol material origin and established the process of the Holocene climatic and environmental changes in the Jinghe River Basin. All the indexes including magnetic susceptibility, loss on ignition, percentage composition of calcium carbonate, particle-size distribution and chemical element, revealed as many as four periods of climatic change in Holocene, they are the late glacial period （14 700-11 500 a B.P.）, the early Holocene （11 500-8 500 a B.P.）, mid-Holocene （8 500-3 100 a B.P.） and the late Holocene （3 100 a B.P. to present）. The characteristics of the Holocene climatic and environmental change in the Jinghe River Basin were reavealed from the ZJC profile, providing a climatic context of palaeofloods occurrence.2. Through stratigraphical and sedimentologic analysis, slackwater flood deposits in two profiles were identified accurately, providing geological evidence for reconstruction water level and peak discharge of the palaeofloods in the Jinghe River. Based on identification of field macroscopical sedimentary characteristics and laboratory analysis on the proxy indexes of magnetic susceptibility, loss on ignition, percentage composition of calcium carbonate, particle-size distribution, we identified five extreme floods event recorded in the CJC profile. Cultural relics in the late period of the Longshan Culture were discovered in the stratigraphy between 420 cm and 450 cm, compared with thermoluminescence dating of other profiles in the Jinghe Basin, we obtained that the extreme palaeoloods occured during the late period of the Longshan Culture （4 200-4 000 a B.P.）. The LCQ profile recorded two extreme floods, and their chronologies were similar to the CJC profile. Over the last millennium, the palaeoflood chronologies of the Jinghe River are in accord with the paleaofloods period of the Qishui River in the Weihe River Basin, so it is common that extreme floods occurred during 4 200-4 000 a B.P. in the middle reaches of the Yellow River.3. Reconstruction of water level and shape of cross-section, the peak discharge of palaeoflood were worked out by hydrological method. Through reconstruction of modern floods and the relation of peak discharge and catchment area, the results were verified. From sedimentological evidence of floodwater elevations reached by past floods, water level of palaeoflood were reconstructed by riverload during the late period of the Longshan Culture. Baesd on the methodology of Stratigraphy, Archaeology, Hydrology and referred to 1/10000 terrain map, shape of cross-sections was restored and regulated, other parameters including channel roughness and slope of river bed were determined, adopting slope-area method and hydraulic calculations, peak discharges of extreme palaeofloods during the Holocene were received. The modem extraordinary floods were reconstructed from floodmarks by slope-area method. The error of the calculated results was less than 5%, and rationality of application the slope-area method was verified. Relation between peak discharge and catchment area tested that the calculated peak discharges of palaeofloods were reasonable and credible.4. Taking advantage of palaeoflood discharge data, together with gauged data and historical flood infromation, applying procedure of the Pearson curves in Hydrology, peak discharge-frequency curves of the Jinghe River have been established, which prolonging flood data timeseries of the Jinghe River. The method of design flood calculation altered extrapolation into interpalation, improving the precision of flood frequency, reducing unnecessary funds waste. This research fills the domestic gap of palaeoflood in the Jinghe River, and it is very valuable to the engineering construction of flood mitigation, water conservancy and hydropower, development and utilization of water resources, eco-environmental construction between urban and rural areas, water pollution control in the Jinghe River Basin.5. The research discovered that floods mainly resulting from rainstorm of the Jinghe River Basin were highly sensitive to climate change, and Holocene extreme palaeofloods occurred in the late period of Longshan Culture （4 200-4 000 a B.P.）. Extreme floods were unequivocally related to anomalous weather （rainfall） conditions in the late Megathermal of the Holocene. Climatic instability, uneven distribution of annual precipitation within a year, change of intensity of summer monsoon, monsoonal rain-belt moving to the north and activating frequently in the middle reaches of the Yellow River during 4 200-4 000 a B.P., which are the main reasons to the extreme floods in the period.Through field survey, the palaeoflood deposits were found and analyzed on T₁ terrace of the Jinghe river. Using stratigraphy, physiognomy and archaeology, it is certain that the extreme palaeoflood events happened in the period of 4 200-4 000 a B.P. since 11 500 a B.P., respectively. Then the peak discharges of palaeofloods were calculated by the hydrological model, which greatly prolonged the flood data series of the Jinghe River. And the flood rating curves were established to improving the reliability to the engineering construction of flood mitigation, water conservancy and hydropower in this basin. This research results are not only practical to the flood mitigation, water resources exploitation and eco-environmental construction, but also fill in the blank of the palaeoflood hydrological study in the Jinghe River Basin, which are of great scientific significance to the comprehensive improvement of the eco-environment of the basin.更多还原