Man's Influence on Freshwater Ecosystems and Water Use (Proceedings of a Boulder Symposium, July 1995). IAHS Publ. no. 230, 1995. 41
Impact of human activity on hydrology: Liaoning Province, China
YIN HSUEH-CHUN General Hydrological Station of Liaoning Province, Shenyang 110003, China
Abstract The impacts of human activities on hydrological processes are examined for Liaoning Province, an economically developing region of China. The greatest impact of human activities is shown to be on sedi ment yields, with relatively minor impacts on river runoff.
INTRODUCTION
Liaoning Province is an economically developing province located in the southern part of northeast China (Fig. 1). It basically consists of three regions: the east which is mountainous and hilly, the central part which is a plain, and the west which has lower mountains and is hilly. The south of Liaoning Province faces two seas, the Bohai Sea and the Yellow Sea. Many large rivers cross the boundary of the province: the River Liao, River Hun, River Taizi, River Daling and the River Yalu. The climate is of the humid monsoon and conti nental types having the highest rainfall and hottest temperature in the same season. Mean annual temperature decreases gradually from the south to the north and varies between 4.6° and 10.2°C. Average annual precipitation varies from 400 mm in the northwest to 1200 mm in the southeast. The native rocks in the east region of Liaoning basically consist of old metamorphic rocks and granites. Palaeozoic marine deposits are distributed across most parts of the region (Yin Hsueh-Chun, 1993). The geology in the west region is mainly sandstones and conglomerates of Cretaceous age. The valley fills date from the Neozoic era (Gu Bolin et al., 1989). The dominant soil in the east region is brown forest soil and in the west region is yellow soil. Natural vegetation in the northeast mountainous area in the east region is a mix of coniferous forest and broad-leaf forest, and the forest in the rest of the region belongs to the broad-leaf type of a warm temperate zone. The average forest cover in the mountainous area of the east Liaoning region is over 45 % and this falls to about 28% in the east coast peninsula. There are 10 large reservoirs and a great many small ones which have been built in the province since new China was founded. These provide supplies of water for irriga tion and industrial use. Although considerable work such as planting trees, building level terraces, planting grass and closing forests has been done in water and soil conservation, and many positive results have been obtained, some areas with water and soil losses still exist.
CHARACTERISTICS AND VARIATIONS OF HYDROLOGICAL PROCESSES
Today, runoff and sediment yield in many basins are the result of both natural and 42 Yin Hsueh-Chun
Fig. 1 Location of the study area. human factors. In order to define characteristics and variations of natural hydrological processes, runoff and sediment stations of catchments where no influence of human activity exists were selected for analysis.
Precipitation characteristics
Annual precipitation data for more than 80 years in the east part of the province and more than 60 years in the west part, show that the ratio between maximum and minimum precipitation is 2.0-3.0 in the east and 2.5-3.5 in the west; wet years and drought years are alternate with a frequency of three to five years. Five-year moving mean values of annual precipitation show that high and low values alternate with a frequency of 10-14 years.
Annual flow characteristics of natural basins
Flow data from small representative basins are highly correlated with precipitation data. The analysis of extremes of annual runoff in the province shows that in the east part the ratios of extremes of annual runoff increase from 6:1 in the River Ai, which has the highest annual average precipitation, to 16:1 in the south and 27:1 in the north, as annual average precipitation gradually decreases, and in the west part of the province they are from 10:1 to 35:1. Impact of human activity on hydrology: Liaoning Province, China 43
Characteristics of annual sediment yields
Analysis of annual sediment yields shows that peaks occur in the same year as those of annual runoff. The ratios of the maximum to minimum annual sediment yields are 200- 800:1 in the east and 100-500:1 in the west.
IMPACT OF HUMAN ACTIVITIES ON HYDROLOGICAL PROCESSES
Hydrological processes in the province have been greatly affected by a range of human activities. Annual runoff double mass curves for Shenyang station on the River Hun and station Liaoyang on the River Taizi in the east part of the province (Fig. 2) show that human activities in the early 1950s had little influence on runoff. However, influences of human activities on runoff gradually increased over time such that in the 1970s water yield was reduced by 29.7% at Shenyang station and 19.0% at station Liaoyang. These changes relate to the construction of a large reservoir on the River Hun in 1959, and two large reservoirs on the River Taizi around 1970. Water losses reflect evaporation and seepage losses from reservoirs, as well as consumptive uses in agriculture and industry. Analysis of the precipitation-runoff relationship in the upstream basin of the River Hun, where there are no reservoir influences, showed that the coefficient of annual runoff during the last three decades has changed little. From the five-year moving mean of the annual natural runoff and measured sedi ment yields at Shenyang station on the River Hun (Fig. 3), it can be seen that values reduce between 1975 and 1982 - the minimum is about 50% of the mean value before 1964. The minimum five-year mean value till 1982 as a proportion of that before 1964 is only 12% for sediment yields; the maximum increase of sediment yields after 1986
e> / TO 2 / / ipsp P> O- / c / "J TO ' .••' ' °-7<» / << Liaoyang . / --'* W / .•' '?<>9 TO
"1 /•• / ..•• << -ifOO 3c s.-' / •' o / ./ .-• yip
JCV /' /.• *- Shenyang .' yfp /• • s S ICO / s / /
Runoff KEflM UALUE <1Q~& MA3> "1 _~i_. L r- i ! 1 ' TFj 7| -f" TlrTKI "n r II i I J 1 I 4--Ï TT-TT 1 1 "T 7" I I II T I -^ .....ii ,. , i , i,IIi I i i i ... i i1 i .,i i it i v i i i i.i __LLi i i ,i , »» 195B 55 60! ! 65 70 75 I 83 33 90 95 A TCyrO Vf.Luc cio-7-.Ko Sedinent '- 1 - T rl . ItTT-rrJ , , , 1950 55 60 65 1710 75 0 0 05 90 95 Fig. 3 Five-year moving mean graph of annual runoff and sediment yields for Shenyang station on the River Hun.
only accounts for 41 % of five-year mean value before 1964. The relatively rapid reduc tion of sediment yield in relation to annual runoff during the 1960s and 1970s is primarily the result of a large reservoir being built upstream of the main stream of River Hun. However, basin regulation, and water and soil conservation works in the upstream portion of the River Hun since 1980 have also been influential. Sediment yields in the later 1980s are less than nearly two decades before due to closing of the forests since 1980: River Ai 20%, River Biliu 30%, River Taizi 57%. In contrast from ten-year moving means of precipitation, runoff and sediment for the Shalizhai station on the River Dayang (Fig. 4) it can be seen that the influence of human activities on runoff is not large; the variation of sediment is more severe than that of runoff. There are two special points related to the variation of sediment yields: (a) the increase in sediment yields happens (in 1982) earlier than that of runoff (in 1985); (b) increased runoff in the later 1980s corresponds only to 82% of maximum value of moving mean of runoff in the 1960s, while the mean value of sediment yields in the later 1980s is greater than the maximum value of the moving mean of sediment yields, about 110% of the maximum. According to the survey this relates to forest denudation. Vegetation has been destroyed since 1980 and terraces have been damaged by floods. As a result, soil losses in the basin increased again. In the west part of the province, there are no large reservoirs, but a lot of water and soil conservation works have been built. In most basins in the west part, through comparison of five-year moving averages of precipitation and sediment yield (Yin Hsueh-Chun & Zhang Jixian, 1992), precipitation in the middle period in the 1980s is seen to be the same as that in the middle of the 1960s, but sediment yield in the middle of the 1980s is about 80% less than two decades earlier.
CONCLUSION
Wet and dry periods in annual precipitation are shown to be reflected in both natural Impact of human activity on hydrology: Liaoning Province, China 45
MtlftN UnLUE !»H) — pi'ecipitî tion 15UU 12BQ
COO 1 TTTTt " II 1------
1953 55 60 65 7B 75 80 83 98 95
«H"3 > Runoff 2oua r- i_ - 2003 f-
1 5 «3
63 70 75 89 05 90 95 UAL'JE (lO'V^KC) 103 1 Sedit ent 03 ^ -, 63 13 -p TTT"I_ ^
1953 55 69 63 79 75 88 85 98 95
Fig. 4 Ten-year moving mean graph of annual precipitation, runoff and sediment yields of Shalizhai station on the River Dayang. runoff and sediment yields. The influence of human activity is superimposed upon these natural cycles having a frequency of about 12 years. The influence of human activity has been to reduce runoff but only by about 6-12% in general, rising to 20-30% where the influence of large reservoirs and increasing water use in agriculture and industry exists in the east part of the province. The influence of human activity on sediment yield is much larger and more complicated. In most basins in the west part of the province sedi ment yields have been reduced by 60-80% due to many years of water and soil conserva tion. The impact of human activity in many basins in the east part of the province have caused a 20-60 % reduction in sediment yield, but in a few rivers they have caused about a 30% increase, mainly due to forest denudation. Based on the current development of forest cover in the province, it can be predicted that the sediment yield of most river basins in the 1990s will be a 40-70% reduction of that in the 1960s in the east part of the province and a 80-90% reduction in the west part of the province.
REFERENCES
Yin Hsueh-Chun ( 1993) Analysis and assessment of hydrological processes in the warm humid region of Liaoning Province: ac&se study.\n: Hydrology in Warm Humid Regions (ed. by J.S. Gladwell) (Proc. YokohamaSymp.,July 1993), 165- 174.IAHSPubl.no. 216. Gu Bolin, Yu Wenbo & Huang Xuqing (1989) Soil losses from basins in west part of Liaoning Province and its control comments. Compiled Book on Water and Soil Conservation of Liaoning (in Chinese), Shenyang. Yin Hsueh-Chun & Zhang Jixian ( 1992) Analysis of variation of sediment transport of river basins in the Liaoning Province (in Chinese). General Report of Research of General Hydrological Station of Liaoning Province.