88
Tecnología y Ciencias del Agua
, vol. VIII, núm. 2, marzo-abril de 2017, pp. 77-91
Mao
et al.
,
The runoff variation characteristics of Dongting Lake in China
•
ISSN 2007-2422
reducing rate. Xiangtan station’s runoff from
1951 to 2011 can be divided into four stages:
1951-1955 and 1988-2002 were a wet period,
1956-1987 and 2003-2011 were dry periods.
Taoyuan station’s runoff can be divided into 6
stages: 1951-1954, 1964-1983 and 1991-2003 were
wet periods, 1955-1963, 1984-1990 and 2004-2011
were dry periods. Shimen station’s runoff can
be divided into four stages: 1951-1973 and 1980-
1983 were wet years; 1974-1979 and 1984-2011
were dry periods.
According to three bayous’ runoff cumula-
tive anomalies (figure 6), Songzikou, Taip-
ingkou, and Ouchikou stepped into the dry
stage from the 1970s and 1980s, among which,
Ouchikou’s flow reduced most early in 1971
and got worse after the 21 century so that its
slope ratio reached the sharpest. Songzikou and
Taipingkou began to reduce at 1986 and 1978,
but their curve slope ratio is flatter so the inter
annual change was less velocity. Based on the
periodical statistics data of three bayous, their
runoff can be divided into two stages. The wet
periods of Songzikou, Taipingkou was and Ou-
chikou is 1951-1985, 1951-1977 and 1951-1970,
while the dry stages are 1986-2011, 1978-2011
and 1971-2011.
The stage runoff changes are the result of
comprehensive functions of nature factors and
human activities. Based on existing research,
the climate is the main factor that leads to the
runoff change (Zhai, Ren, & Zhang, 1999); Liu,
Ji, & Wu, 2006); Wang, Wang, & Zhao, 1999)
water and soil erosion and hydraulic engineer-
ing constructions also accelerate the change to
some extent (Li, 1998). The author used wave-
let analysis to study the period of inflow and
outflow of Dongting Lake. The conclusion is as
follows: Xiangtan station’s runoff is character-
ized with multi-temporal periodicity, among
which the period of 30-40a is the most distinct.
Meanwhile, the first period of Taojiang sta-
tion’s runoff is 30-40a, the most stable period of
Taoyuan’s is 8-15a and the most obvious period
in Shimen station is 20-27a. Those periods are
identical with our stage analysis conclusion.
The wavelet analysis of three bayous’ runoff is
25-40 (Songzikou), 22-40 (Taipingkou) and 25-40
(Ouchikou), which is also in accordance with
this paper’s research. The conclusion means that
three bayous will stay in a dry period now and
move into another cycle in the next stage.
Conclusions and discussion
River runoff can reflect water quantity supplied
from precipitation, as well as the hydrological
phenomena such as watershed closure, soil
infiltration, evaporation etc. Watershed storage
change results from the comprehensive effects
of climate change, hydraulic engineering con-
struction, human activity and soil underlying
surface parameters.
Concentration period of Dongting Lake’s
runoff focuses on June-July each year. The maxi-
mum runoff appears in the late June-early July.
Due to the time of combined flood peaks com-
ing from three bayous and four rivers, floods
are usually in late July, The catchments of four
rivers come into the raining season from April
to May, after which their discharge increases
rapidly and reaches a peak in the late May
and early June with a single symmetrical. The
peak shape is approximately symmetric single.
However, three bayous’ runoff starts their wet
period in May and June and gets their peaks in
July. The flood peaks superimpose in the lake
and raise the water level. Meanwhile, the stage
of Yangtze River rises, resulting in the flood
jacking on the outflow of Dongting Lake and
increasing the lake’s flood hazard. In summary,
1996 and 1998 extraordinary floods were the
typical examples of floods superposition.
The variation coefficient of outflow and in-
flow is between 0.194 and 0.761 which is pretty
significant, especially that of three bayous. It can
explain the instability of runoff and inter annual
variation. All branches’ extreme ratio is bigger
than 0.6, particularly that of three bayous,
indicating the significant inter annual reduc-
tion. The water reduction of three bayous is the
main reason of seasonal water shortage which
aggravates the drought disaster and threatens
water supply around the lake.
