Modern Flood Process And The Osl Dating And Grain-size Characteristic On Palaeoflood Deposits Of Nalinggele Watershed, Northern Of The Qinghai-tibet Plateau

The Nalinggele River is the largest continental river in Qinghai province. It causes floods in the summer easily. And the floods endanger the salt resources and industrial production of the Four Salt Lakes Region to result in serious economic loss. Meanwhile, the important water source of the Four Salt Lakes Region is the Nalinggele River. Therefore, to study the Modern flood process and the palaeoflood deposits of Nalinggele Watershed can contribute to summarizing the features of geomorphology and drainage of Nalinggele Watershed. To Reveal the rule of regional floods, and enhance the predictability of the Four Salt Lakes floods.For deploying flood resources in the future is very important. Not only can protect the salt resources of the Four Salt Lakes Region, but also can produce normally in the Four Salt Lakes’ s industry. It has obvious the benefits of both society and economy. In addition, we can get the informations of both palaeoflood and ancient climate with the OSL dating and grain-size analysis on the palaeoflood deposits. It not only provide the reference value for other watersheds near the study area, but also make an importance to both predict the trend of global changes in the near future.In this paper, I use the 3S technologies and the samples from the field work and experimental analysis to discuss the Modern flood process and the OSL dating and grain-size analysis on palaeoflood deposits of Nalinggele Watershed. And the results as follows.1. In this study, we use DEM data based on ArcGIS 10.1 experiment platform, to extract digital watershed features on the Nalinggele River Valley, from the perspective of flow accumulation’s formation and flood regulation. The results are that(1) the geomorphology features make larger of the water contributing surface area, serious of erosion process, and weak of gravity erosion process.(2) Channel features belong to a long and narrow basin shape, and the channel is tortuous. The channel gradients of main channels are smaller. Actual gully network densities are within 1.71~2.32 km/km2.(3) The geomorphology features make larger of the water contributing surface area and the amount of flow accumulation, rapid of flow formation, and the flow go into the main channel easily. However, the features of main channels are benefit to reduce the main channel flow velocity, prolong conflux time, adjusting the flood peak. And flood peak is not easy to focus.2. The analytic results of the modern flood process are that:(1) There exist 5 periods of overcast and rainy, occur within 67 days before the annual maximum peak flow. And the periods of Ⅱand Ⅲ are major of water sources of this annual maximum peak flow. The Ⅱ period of the continuous overcast and rainy starts on June 28 th, and the maximum precipitation of 1960’s is occur on July 16 th. Hence, they are respectively about 39 days and 21 days comparing with the hydrological station of mountain pass appears the annual maximum peak flow on August 6th.(2) The Nalinggele River Valley under a situation without considering about the infiltration, plants consumed, evaporation and fill in the depression, its residence time is about 34.78 days. And its concentration time is about 57.97 days. And its the maximum peak flow appeared time is about 38.65 days. At last, its the precipitation contributed percentage of the maximum peak flow composed is about 60.88. And comparing to others datum, we think the results are acceptable. And it provides the fundamental reference datum for the further researcher on the flood hydrology of this study region in the near future.3. Through interpreting different TMs of the Four Salt Lakes Region’s water areas in 2010. Some results are that:(1) The lag phase of between the highest flood level appeared and the maximum peak flow goes through the pass of the mountain is about one-and-a-half months.(2) The four salt lakes exists different both lag phase and the time of highest flood level appeared. And the order of appearing the highest flood level of both salt lake and others water are that Ya lake, Water channel, Dongtai lake and Xitai lake, Yiliping lake.4. Using the OSL dating and grain-size analysis on palaeoflood deposits of Nalinggele Watershed can have some conclusions below.(1) The pure of quartzs from a sample have the standard growth curve. The standard growth curve is linear. Regeneration dose is far from saturated. There exists a standard growth curve among the samples from NLGL A section. And the SAR+SGC method of OSL dating is suitable for the palaeofloods deposits of the Nalinggele Watershed. Whatever, some samples ages are older. These phenomenons may be cause by inadequate exposure of the grains in samples more.(2) The palaeoflood deposits have deposited under the low water energy of the sedimentary situation. And the grain-size characteristic means that they are sandy silt with positive skewness and bad sorting. Their probability cumulative curve have common feature is that “the higher rate of the slope-jumping moved components”. And with “from coarse to fine and fine to coarse” the rhythm of layer in a catastrophic palaeoflood event. The rhythm pattern may be a special rhythm under the condition of the Nainggele Watershed on the northern of the Qinghai-Tibet Plateau.(3) Form 6.0 ka B.P., there is two periods of high-frequency of catastrophic palaeoflood. They are 6.0~5.7 ka B.P. and 4.7~3.5 ka B.P..And there are 8 times catastrophic palaeoflood at least with the OSL dating and grain-size analysis.