Based on the river system data in the 1960s, 1980s and 2010s, the indicator system of quantitative description of river systems change characteristics was established, then the spatial-temporal changes of river systems and its relationship with urbanization in Jiaxing over the past 50 years was analyzed. Results indicated that: (1) Over the past half century, river systems of Jiaxing showed a decline trend. Specifically, the river development coefficient, river density and water surface ratio decreased by 58.91%, 28.94% and 14.09%, respectively. However, the degradation of the river systems varies in different urbanization stages. (2) In the whole urbanization process, the spatial differences of the changes of the river development coefficient and main river area length ratio were extremely large, and the spatial differences of the changes of the river density and water surface ratio were larger, but the spatial differences of the changes of the box dimension and river sinuosity were relatively small. (3) The decline trend of the river development coefficient, box dimension and river density was more significant in the urban area than that in the suburbs and outer suburbs, the decline trend of the water surface ratio was more significant in the outer suburbs than that in the suburbs and urban area, and the decline trend of the river sinuosity was more significant in the suburbs than that in the urban area and outer suburbs, but the spatial change trend of the main river area length ratio was insignificant. (4) The impacts of urbanization on river systems changes were extremely significant, and the changes of river systems were more drastic in higher urbanization level regions, but the impacts of urbanization on main river area length ratio and river sinuosity were larger than that on river development coefficient and river density.

Since 1973, the observed runoff of the uncontrolled areas of the section between Hekouzhen and Wubao of the Yellow River has remarkably decreased, or even, it had been dried up for a quarter of the years; based on the rainfall-runoff relationship between 1956 to 1972, the observed runoff decreased by 84% under the rainfall condition from 1973 to 2014. In this paper, the analysis results showed that the relationship between recharge, runoff and drainage of groundwater and in the Tianqiao spring region of the Yellow River has changed because of reservoir operation along the main stream of this section. This not only significantly reduced the spring recharge into the Yellow River on the left bank, but also increased the amount of leakage to the karst aquifer on the right bank. It is the main reason for the remarkable observed runoff reduction of the uncontrolled areas of section between Hekouzhen and Wubao of the Yellow River. In comparison of rainfall-runoff relationships in different periods, and analysis of water reducing effect of other underlying factors, such as vegetation, terraces and surface water evaporation of dams, the calculation results showed that changes of the recharge relationship between spring water and runoff resulted in runoff reduction of about 600-800 million m³ per year on average in the Yellow River.

In this study, palaeoflood hydrological and sedimentary investigations were carried out in the Yiluohe River basin. Typical loess-soil stratigraphy of the Holocene period was identified at the Longmenxia (LMX) site in the Yihe River basin. Based on the analysis of sedimentary characteristics, magnetic susceptibility and particle-size distribution, the five flood slackwater deposits were identified and interbedded into the loess-soil stratigraphy. By the stratigraphic correlation and the optically stimulated luminescence method (OSL), the four episodes of flooding events occurred at 3100-3000 a BP, 1800-1700 a BP, 770-610 a BP and 420-340 a BP, respectively, namely at the end of the mid-Holocene Climatic Optimum and the beginning of the late Holocene, the dynasties of Eastern Han to Western Jin, Song-Yuan and the Ming-Qing, respectively. These flooding events might include the AD223 and 1761 flooding events and they well corresponded to the phase of the Holocene monsoonal shift, climatic abrupt change and climatic decline. The flooding peak stages were estimated with the elevations and the depositional depths of the SWD. According to the flood peak stages and hydraulic parameters, the peak discharges were reconstructed at 14100-15800 m³/s with the slope-area method. The reconstructed peak discharges of the flooding events are much more than those of the gauged modern floods at the Longmenxia gauge station in the middle reach of the Yihe River.

Field archaeological investigations were carried out in the Jianghan Plain in the middle reaches of the Changjiang River. Based on the integrated study with a comparative analysis for characteristics of the modern flood sediments, multidisciplinary approaches such as the AMS¹⁴C and archaeological dating, micromorphology of zircon, grain size, magnetic susceptibility and geochemistry are conducted to identify paleoflood sediments archived at the Zhongqiao Site. The results indicate that three paleoflood events (i.e. 4800-4597 cal. a BP, 4479-4367 cal. a BP & 4168-3850 cal. a BP) occurred at the Zhongqiao Site. Comparisons of paleoflood deposit layers at numerous Neolithic sites show that two Holocene extraordinary paleoflood events occurred over the Jianghan Plain area at approximately 4900-4600 cal. a BP (i.e. mid-late Qujialing cultural period) and 4100-3800 cal. a BP (i.e. from late Shijiahe cultural period to the Xia Dynasty). Further analysis of the environmental background for the paleoflood occurrences suggested that there was great climate variability between approximately 5000-4500 a BP and ca 4000 a BP. These two paleoflood events were closely related with the expansion of Jianghan lakes driven by the climatic change, and influenced the rise and fall of regional Neolithic Culture. Other evidences also suggested that intensified discrepancy between social development and environmental change processes (especially the hydrological process) in the end of Shijiahe cultural period might be the key factor leading to the collapse of Shijiahe Culture. The severe extraordinary floods related to the climatic anomaly at ca 4000 a BP and political conflicts from internal or other cultural areas all accelerated the collapse of the Shijiahe Culture. These results gave us a better understanding of the climate change at ca 4000 a BP, and also provide evidence for the prehistoric flood events in the Great Yu age, which is considered to be the turning point from the Neolithic Age to the Bronze Age in China.

：Based on the empirical sediment transport equation that reflects the characteristics of "more input, more output" for sediment-laden flow rivers, a general sediment transport expression was developed, which takes into account the effects of upstream sediment input, previous cumulative erosion and sedimentation, critical water volume for sediment initiation and the differences of sediment sizes between the main stream and its tributaries. Then, sediment load equations of non-flood and flood seasons for the sub-reaches from Bayangaole to Sanhuhekou and from Sanhuhekou to Toudaoguai, as well as the whole Inner Mongolia reach from Bayangaole to Toudaoguai, were obtained based on measured data from 1952 to 2010. Furthermore, the corresponding erosion and sedimentation and the cumulative values at each river reach were calculated using the proposed sediment transport equations for the period from 1952 to 2010 according to the principle of sediment conservation. Comparisons between the calculated and measured values using the proposed sediment load equations for the sub-reaches and the whole reach show that the calculated sediment load and erosion and sedimentation and corresponding cumulative values in the non-flood and flood seasons were in good agreement with measurements; the determination coefficient R² between the calculated and measured sediment load is about 0.93 and 0.97 for the non-flood and flood season, respectively; the determination coefficient R² between calculated and measured the erosion and sedimentation for the non-flood and flood season is about 0.80 and 0.90; and the R² between the calculated and measured cumulative erosion and sedimentation is about 0.94 and 0.99. It is obvious that the agreement of cumulative erosion and sedimentation was higher than that of the corresponding annual values, and the agreement of flood seasons was higher than that of non-flood seasons. These results indicated that the proposed methods can be applied to calculate the sediment load and erosion and sedimentation in the non-flood and flood seasons; and they can provide a scientific basis for the analysis of sediment load and the long-term trend of sediment deposition in the Inner Mongolia reach of the Yellow River.