A riverhead is the demarcation point of continuous water channel and seasonal channel, which is characterized by a criti- cal flow that can support a continuous water body. In this study, the critical support dischar...A riverhead is the demarcation point of continuous water channel and seasonal channel, which is characterized by a criti- cal flow that can support a continuous water body. In this study, the critical support discharge （CSD） is defined as the critical steady flows required to form the origin of a stream. The CSD is used as the criterion to determine the beginning of the riverhead, which can be controlled by hydro-climate factors （e.g., annual precipitation, annual evaporation, or minimum stream flow in arid season）. The CSD has a close correlation with the critical support/source area （CSA） that largely affects the density of the river network and the division of sub-watersheds. In general, river density may vary with regional meteorological and hydrological conditions that have to be considered in the analysis. In this paper, a new model referring to the relationship of CSA and CSD is proposed, which is based on the physical mechanism for the origin of riverheads. The feasibility of the model was verified using two watersheds （Duilongqu Basin of the Lhasa River and Beishuiqu Basin of the Nyangqu River） in Tibet Autonomous Region to calculate the CSA and extract river networks. A series of CSAs based on different CSDs in derived equation were tested by comparing the extracted river networks with the reference network obtained from a digitized map of river network at large scales. Comparison results of river networks derived from digital elevation model with real ones indicate that the CSD （equal to criterion of flow quantity （Qc）） are 0.0028 m3/s in Duilongqu and 0.0085 m3/s in Beishuiqu. Results show that the Qc can vary with hydro-climate conditions. The Qc is high in humid region and low in arid region, and the optimal Qo of 0.0085 m3/s in Beishuiqu Basin （humid region） is higher than 0.0028 m3/s in Duilongqu Basin （semi-arid region）. The suggested method provides a new application approach that can be used to determine the Qo of a riverhead in complex geographical regions, which can also reflect the effect of hydro-climate change on rivers supply in different regions.展开更多
Using annual nature runoff data from 1961–2000 for the Qinghai-Tibet plateau Nyangqu River, the Mann-Kendall method and wavelet transform were adopted to analyse runoff variation characteristics for the Nyangqu River...Using annual nature runoff data from 1961–2000 for the Qinghai-Tibet plateau Nyangqu River, the Mann-Kendall method and wavelet transform were adopted to analyse runoff variation characteristics for the Nyangqu River. The results show that the annual change in runoff is relatively stable and that the intra-annual distribution of the runoff is extremely uneven. The disparity in runoff between wet seasons was significant. The runoff for June-September accounted for 65% of the whole year and the highest monthly runoff accounted for 24.56%. From 1961-2000, runoff showed a significant increasing trend with an abrupt increase in 1985. The 5-8 years oscillation period of the runoff was most notable and the 10-15 years period was relatively notable. The principal periods of annual runoff for Shigatse station and Gyantse station were 5a and 7a. The second were 13a and 12 years. Increasing glacial melt water caused by rising temperatures may be the main reason for increased runoff in the Nyangqu River.展开更多
基金Under the auspices of National Natural Science Foundation of China(No.31070405)Knowledge Innovation Programs of Chinese Academy of Sciences(No.KZCX2-XB3-08)
文摘A riverhead is the demarcation point of continuous water channel and seasonal channel, which is characterized by a criti- cal flow that can support a continuous water body. In this study, the critical support discharge （CSD） is defined as the critical steady flows required to form the origin of a stream. The CSD is used as the criterion to determine the beginning of the riverhead, which can be controlled by hydro-climate factors （e.g., annual precipitation, annual evaporation, or minimum stream flow in arid season）. The CSD has a close correlation with the critical support/source area （CSA） that largely affects the density of the river network and the division of sub-watersheds. In general, river density may vary with regional meteorological and hydrological conditions that have to be considered in the analysis. In this paper, a new model referring to the relationship of CSA and CSD is proposed, which is based on the physical mechanism for the origin of riverheads. The feasibility of the model was verified using two watersheds （Duilongqu Basin of the Lhasa River and Beishuiqu Basin of the Nyangqu River） in Tibet Autonomous Region to calculate the CSA and extract river networks. A series of CSAs based on different CSDs in derived equation were tested by comparing the extracted river networks with the reference network obtained from a digitized map of river network at large scales. Comparison results of river networks derived from digital elevation model with real ones indicate that the CSD （equal to criterion of flow quantity （Qc）） are 0.0028 m3/s in Duilongqu and 0.0085 m3/s in Beishuiqu. Results show that the Qc can vary with hydro-climate conditions. The Qc is high in humid region and low in arid region, and the optimal Qo of 0.0085 m3/s in Beishuiqu Basin （humid region） is higher than 0.0028 m3/s in Duilongqu Basin （semi-arid region）. The suggested method provides a new application approach that can be used to determine the Qo of a riverhead in complex geographical regions, which can also reflect the effect of hydro-climate change on rivers supply in different regions.
基金National basic task project, No.2006FY110200Project of institute of geographic science and natural resources research No.200906003-1
文摘Using annual nature runoff data from 1961–2000 for the Qinghai-Tibet plateau Nyangqu River, the Mann-Kendall method and wavelet transform were adopted to analyse runoff variation characteristics for the Nyangqu River. The results show that the annual change in runoff is relatively stable and that the intra-annual distribution of the runoff is extremely uneven. The disparity in runoff between wet seasons was significant. The runoff for June-September accounted for 65% of the whole year and the highest monthly runoff accounted for 24.56%. From 1961-2000, runoff showed a significant increasing trend with an abrupt increase in 1985. The 5-8 years oscillation period of the runoff was most notable and the 10-15 years period was relatively notable. The principal periods of annual runoff for Shigatse station and Gyantse station were 5a and 7a. The second were 13a and 12 years. Increasing glacial melt water caused by rising temperatures may be the main reason for increased runoff in the Nyangqu River.
