http://reply.papertrans.cn/2/117/11660/11660-31.png
http://reply.papertrans.cn/2/117/11660/11660-32.png
Submitted on: 13 September 1999.
Revised on: 14 October 1999.
Accepted on: 12 December 1999.
___________________HYDROLOGY AND EARTH SYSTEM SCIENCES
http://reply.papertrans.cn/2/117/11660/11660-34.png
http://reply.papertrans.cn/2/117/11660/11660-35.png
http://reply.papertrans.cn/2/117/11660/11660-36.png