Year

2017

Degree Name

Master of Engineering Research

Department

School of Civil, Mining and Environmental Engineering

Abstract

The natural flow regime is vulnerable to both climate variability and human activities. Therefore, understanding the hydrological alteration and the effects of climate and human factors is crucial for future water resources management and environmental sustainability. Dongting Lake, the second largest freshwater lake in China, is characterized by rapid changing hydrological conditions suffering from both climate and human impacts. The aim of this thesis is to examine the extent to which natural flow regimes have been changed in Dongting Lake under the combined effects of climate and human impacts, as well as to quantify the respective effects of climatic variabilities and human activities on streamflow.

The Indicators of Hydrologic Alteration are used to investigate the pre- and post-dam hydrologic changes in flow magnitude, frequency, duration, timing and rate of change at the annual, quarterly, monthly, weekly and daily scales. Results show that the natural flow regime in Dongting Lake has been changed noticeably following the regulations of Three Gorge Dam (TGD) and Gezhouba Dam (GD), and the changes become more significant after the regulation of TGD. The lake has suffered from long-term water resource losses with remarkably reduced annual flow after the impounding of the two dams. From January to March, the monthly flow has become marginally higher than the natural situation, while it is substantially dampened in the remaining nine months. There are minor magnitude increases in the daily, weekly, monthly and quarterly minimum flows, while significant decreases are identified in extreme high flow at various time scales. Besides, the timing of extreme water conditions, frequency and duration of high and low pulses have also been modified to different extents. Furthermore, the rates of both hydrograph rise and fall have been significantly reduced following TGD, whereas flow has become flashier with more frequent hydrograph reversals.

The Budyko-based decomposition and runoff sensitivity methods are used to quantitatively assess the respective impact of climatic variations and human activities on streamflow alteration over the five study regions. The two methods yield very close results that indicate that both climate and human activities are the combined driving factors that change the streamflow. During the first-impacted period (1982-2002), streamflow over Xiangjiang, Zishui, Yuanjiang, and the Whole basin increased to various extents while streamflow over Lishui decrease slightly. Climate change or variability acts as a decisive role in contributing 59.5%~72.3% of the total changes in annual streamflow, while human activities accounts for 27.7%~40.5%. During the second-impacted period (2003-2014), streamflow over all the five regions show a decrease resulted from both climate and human impacts, with human-induced and climate-induced changes in annual streamflow contributing 57.3%~72.2% and 27.8%~42.7% of the overall changes in annual streamflow, respectively.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.