Journal of Geographical Sciences ›› 2016, Vol. 26 ›› Issue (6): 694-706.doi: 10.1007/s11442-016-1293-0

• Research Articles • Previous Articles     Next Articles

Degrading river network due to urbanization in Yangtze River Delta

Longfei HAN1(), Chaogui LEI1,*, Liu YANG1, Xiaojun DENG1, Chunsheng HU1,2, Guanglai XU2()   

  1. 1. School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China
    2. College of Territorial Resources and Tourism, Anhui Normal University, Wuhu 241000, Anhui, China
  • Received:2015-11-12 Accepted:2015-12-15 Online:2016-06-15 Published:2016-07-08
  • Contact: Chaogui LEI E-mail:hanlf.nju@gmail.com;xuyp305@163.com
  • About author:

    Author: Han Longfei (1988-), PhD Candidate, specialized in urban hydrology. E-mail: hanlf.nju@gmail.com

  • Supported by:
    National Natural Science Foundation of China, No.41371046;The Commonwealth and Specialized Program for Scientific Research, Ministry of Water Resources of China, No.201201072, No.201301075;Natural Science Foundation of Jiangsu Province, No.BK20131278

Abstract:

Evolution of river systems under the background of human activities has been a heated topic among geographers and hydrologists. Spatial and temporal variations of river systems during the 1960s-2010s in the Yangtze River Delta (YRD) were investigated based on streams derived from the topographic maps in the 1960s, 1980s and 2010s. A list of indices, drainage density (Dd), water surface ratio (WSR), ratio of area to length of main streams (R), evolution coefficient of tributaries (K) and box dimension (D), were classified into three types (quantitative, structural, and complex indices) and used to quantify the variations of stream structure. Results showed that: (1) quantitative indices (Dd, WSR) presented decreasing trend in the past 50 years, and Dd in Wuchengxiyu, Hangjiahu and Yindongnan have decreased most, about 20%. Structurally, the Qinhuai River basin was characterized by significant upward R, and K value in Hangjiahu went down dramatically by 46.8% during the 1960s-2010s. Decreasing tendency in D was found dominating across the YRD, and decreasing magnitude in Wuchengxiyu and Hangjiahu peaks for 7.8% and 6.5%, respectively in the YRD. (2) Urbanization affected the spatial pattern of river system, and areas with high level of urbanization exhibited least Dd (2.18 km/km2), WSR (6.52%), K (2.64) and D (1.42), compared to moderate and low levels of urbanization. (3) Urbanization also affected the evolution of stream system. In the past 50 years, areas with high level of urbanization showed compelling decreasing tendency in quantitative (27.2% and 19.3%) and complex indices (4.9%) and trend of enlarging of main rivers (4.5% and 7.9% in periods of the 1960s-1980s and the 1980s-2010s). In the recent 30 years, areas with low level of urbanization were detected with significant downward trend in Dd and K. (4) Expanding of urban land, construction of hydraulic engineering and irrigation and water conservancy activities were the main means which degraded the river system in the YRD.

Key words: stream structure, spatial and temporal change, urbanization, Yangtze River Delta