Further discussion on soil and water conservation effect on water resources in the Yellow River Basin – TASAE, 2004

Further discussion on the effect of soil and water conservation
on water resources in the Yellow River Basin
Mu Xing-min, Wang Fei, Li Rui, Zhang Xiao-ping(Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources,
Northwest Sci-tech University of Agriculture and Forestry, Yangling District 712100, Shaanxi Province, China)

Abstract: The area of the Yellow River Basin is 8.3% of the area of China. Its average annual total runoff is
5.80×1010 m3,or 2% of that of China. Water resources per capita in the Yellow River basin are 527 m3,or 20%
of China’s per capital amount. For climate change, soil and water conservation, and water usage of agriculture
and industry, the condition of water resources worsens. The water resources volume varies greatly between
different years and seasons. Soil loss is severe in the Yellow River Basin with average sediment content of
37.6 kg m-3. 30% of flow, or approximating 1.50×1010~2.0×1010m3 annually, is lost flushing sediment fromlower riverbed to the sea. The sources of sediment and water are different and the sediment and water comingfrom the middle reaches of the Yellow River Basin account for 10% and 70% of that of the whole basin. A
reduction of one ton of sediment erosion results in about a 3.19 to 16.15m3 reduction in water Yield, but when
flushing one ton of sediment; about 33 to 60 m3 of water is needed. This shows that soil and water
conservation practices can result in a relative increase in water resource. From 1970 to 1996, soil and water
conservation practices reduced soil loss by an averageof 1.495×108t annually in the section between

Hekou and Longmen of the Yellow River Basin. If the water used that have to flush this sediment is considered,
the water resources have increased by 4.88×109m3.
In the last half century, because of climate change and large scale human activities, such as water resources
engineering, water use of industry, agriculture, and soil and water conservation practices (SWCP), the water
resource problems in the Yellow River Basin (YRB) have become more obvious. As a result of sediment erosion
control, runoff has decreased in the YRB, and therefore its impact on water resources has become an issue of great
concerned. Cui (2002) blamed rainfall reduction and SWCP for cutting-off of flowing to the sea. Chen (2000)
considered the reason for the cutting-off of the Yellow River to be the sharp increase of water usage in the YRB, notdue to the effect of drought and precipitation decreasing. SWCP can be regarded as a fundamental measure to
resolve the water resources problems in the Yellow River if we consider comprehensively: reduction of sediment andflood; cutting down flood peak; and preventing flood and improving water quality (Mu, 1999). In this paper, thecharacteristics of water resources are shown and the effects of SWCP on sustainable utilization of water resourcesin the YRB are analyzed.

1 Characteristics and problems of water resources in the YRB
The amount and per capita volume of water resources are both very low. The lack of water resource in the
YRB in the last fifty years is not only because the water resources distribution is not temporally and spatially even,1but also because of serious water pollution, climate change and industrial and agricultural use.

1.1 The total amount of water resources in the YRB is small. The difference between watersupply and demand is great, and the cutting-off of flow occurred frequently in recent years.
1.1.1 Small amount of water resources
The Yellow River is the second longest river of China with a length of 5464 km and a basin area of 7.95*105
km2. Its upper and middle reaches area is semiarid, and the lower reaches area is semi-humid within temperatemonsoon climate zone. Its average annual precipitation is about 445mm, and precipitation decreases gradually fromsoutheast to northwest. The average annual evaporation from the water surface is about 1200mm, ranging
from1000mm in the southeast area to 1500 mm in northwest. The average annual total runoff is 5.80 *1010m3,
accounting for only 2% of that in the whole country, while the watershed basin area is 8.3%.
The average water yield for China is 2.95*105m 3.km-2 (Wang, 2003), but it is only 9.36*104m3.km-2 in the YRB,
about 1/3 of that of the whole country (Figure 1.). In some watershed, the water yield is low, such as Huangshui
River and Weihe River (Figure 1.). In some watersheds it is worse, such as Fenhe River, Jinghe River, and thecontinental river area (Figure 1.).

30.0 29.5
25.0

4

average annual water yield/ 10
. km

-2

26.8

19.3

20.0

15.3

14.9

15.0

13.7

9.4

10.0

9.9

8.8
6.3

5.0

17.6
15.5 15.1

4.8

4.1

2.3

2.2

0.0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

Figure 1. The water yield characteristic of the Yellow River and its branches( The Region or River Basin: 1 China, 2 Yellow River; 3 Huangshui ; 4 Taohe; 5 upstream of Lanzhou; 6 Section between Lanzhou andHekou;7 Section between Hekou and Longmen; 8 Fenhe; 9 Jinghe; 10 Beiluohe; 11 Weihe; 12 Section between Longmen andSanmenxia; 13 Yiluo; 14 Qinhe; 15 Section between Sanmenxia and Huayuankou; 16 Lower reaches of the Yellow River; 17
continental river area)

1.1.2 Average water resources per capital and per hectare in the YRB are small
The YRB is a serious lack water region. Average water quantity of cultivated land in the YRB is just 4400m3 per
2Further discussion on soil and water conservation effect on water resources in the Yellow River Basin – TASAE, 2004
hectare, only 16% of country average level. Average water resources by population is 527m3 per capita, which isabout 22% of that of the whole country (2460m3), and equivalent to 5.3%of that of the world (10000m3, 1980). Thisvalue is overestimated because some of this water is supplied the areas outside of the YRB. According to theappraisal standard of per capita water resources put forward by “International population action”(those less than
1700m3 per capita are urgent water demand countries, less than 1000m3 per capita are lack water countries, lessthan 500m3 per capita are serious lack water countries). With anticipated climate change, especially the warm anddrought trends predicted for the YRB, the water supply will likely decrease further (Jia, 2001).
1.1.3 Different between supply and demand is highWith the development of the economy, water demand has increased greatly, and the contradiction of water
resources demand and supply is greater. According to the distribution plan of water supply in the YRB, water
resources available to be exploited and utilized is only 3.70*1010m3 annually. As social economics develop andpeople’s standard of living rises, the amount of water use in the watershed has increased from 1.20*10m in the
1950s to 3.07*1010m3 at present (external supply is 1.06*1010m3). 2003 was the worst drought year since the 1950s,
when drainage supply amount was only 1.67*1010m3. The gap of water supply and demand would be 5.0*109m3
even if the Yellow River was used up completely.
According to prediction, the total water volume of demand in the watershed in 2010 will reach 5.20 *1010 m3,
but the most water volume of supply in the YRB is only 4.80*109m3. In other words, the water will not meet thedemand and there will be 4.0*109m3 shortage in average precipitation years, and it will be more in drought years(Chen, 1991; Chinese Economy and Trade committee, 2000). According to a report by the Information Center of
Ministry of Water Resources on the response and adaptation to water resources issues induced by climate change,
water supply shortage of the YRB will be from 2.1*109m3 to 1.30*1010m3 annually (Wang, 2003).
1.1.4 Ecological environmental problems induced by shortage of water resources in the YRB
Cutting-off takes place frequently in the lower reaches of the Yellow River because of exploitation of water.
Cutting-off happened in 21of 26 years between 1972 and 1998 due to decreased rainfall and increase amount ofindustry and agriculture, and domestic water demand. Cutting-off took place every year from 1990 to1998. There are
226 days of cutting-off in 1997, which is 62% of total days in the whole year, and the channel length cutting-off was
704 km. The beginning of cutting-off in that year, and its length were the maximum in the Yellow River’s history.
As surface water resources are short and the extravagant exploitation of groundwater is very serious, many3

groundwater funnels (area of depressed groundwater) have been formed in the YRB. According to the Water
Resources Bulletin of the Yellow River Basin in 2001, the largest groundwater funnel is 3370.75km2. Average funnel
center depth is 37.8m. Area of confined groundwater funnels is 2365.4 km2, and its average center depth is 77.6m.
Table 1. The characteristics of groundwater funnel in the YRB in 2000
FunnelFunnelFunnel area/km2

Center depth/m

Position

Quality

Area

Net

Depth

Net

Yinchuan funnel

Yingchuan Plain

Confined water

450.0

-3.2

17.7

-1.3

Fengdong funnel

Guanzhong Plain

Shallow layer

22.1

2.0

26.7

1.2

Xinghua funnel

Guanzhong Plain

Shallow layer

40.3

0.1

19.8

0.3

Luqiao funnel

Guanzhong Plain

Shallow layer

9.0

-0.4

45.4

2.0

Weibin funnel

Guanzhong Plain

Shallow layer

14.0

0.5

19.6

0.3

Songyuegu funnel

Taiyuan Basin

Confined water

134.8

3.4

63.1

-3.5

Taiyuan funnel

Taiyuan Basin

Confined water

182.6

15.6

105.4

4.4

Yuncheng funnel

Yuncheng Basin

Confined water

1598.0

31.0

96.4

-0.2

Wuzhi~Wen County~Meng county

Huabei Plain

Shallow layer

920.0

10.0

22.2

0.4

Name of funnel

1.2 Temporal and spatial distribution of water resources is not even, difference between watersupply and demand increases
1.2.1 Water access is difficult because of the distribution of water resources
From the Report of the Water Resource in the Yellow River Basin in 2000 ( in Table 2), it is known that theobserved runoff and the total runoff at Huayuankou Station in the Yellow River are 4.08×1010m3 and 5.568×1010m3. There are two main water sources in the YRB; one is the upstream region of Lanzhou, the other is thesection between Sanmenxia and Huayuankou Station. Although their area is only 36% of the region upstream of
Huayuankou, while the observed runoff (actual runoff measured at gauging station) and the total runoff (observed
runoff plus water used) accounted for 86.6% and 72.4% in 2000 respectively. The two main net water consumption
areas are the section between Lanzhou and Hekou and the downstream area of Huayuankou. The observed annual
runoff in section between Lanzhou and Toudaoguai decrease to 2.29×1010m3. The region downstream of
Huayuankou is nearly an absolute water consumption place. The average observed runoff decreases from morethan 4.0×1010m3 at Huayuankou Station to about 3.3×1010m3 at Lijin Station.
Table 2. The quantity of water resource in different stations in the YRB

4

Further discussion on soil and water conservation effect on water resources in the Yellow River Basin – TASAE, 2004
(×108 m3)
Name of station

Lanzhou

Hekou

Longmen

Sanmenxia

Huayuankou

Area (×104 km2)

22.26

36.79

49.76

68.84

73.00

Observed runoff

316.90229.10283.30371.80408.40Total runoff

327.00322.90387.80499.60556.50*Based on the water Resources Report of The Yellow River Resources in 2000.

1.2.2 The water resource in the YRB changes greatly between years and seasons
The water resources change greatly in the YRB between different years. Based on the total and Observed Runoff
from 1952 to 1990 In The Yellow River, the Cv value (CV=S/X×100%; S is the standard errors; X is mean) of theannual total runoff on each station is about 0.2, and the Cv value of observed runoff is from 0.21 to 0.45. The ratio
between the maximum and minimum total runoff changed from 1.9 to 3.5, and that of observed runoff changed from
3.2 to 10.7 during that time.
The water resource in the YRB is distributed unevenly because of the monsoon. The runoff during July to
October is 58% of the whole year. Soil and water loss can occur during rainstorms, which can cause sedimentationin the riverbed and flood in lower reaches of the YRB.

1.3 The serious water pollution in the Yellow River makes the water deficit greater
Both ground and underground water resources are polluted because of the polluted discharge with no or
unqualified measurement.
According to the Report of Chinese Environment Condition in 1996, the main and branch channel reaches in the
Yellow River up to Class I and II (Class I is best, Class V is worst) of government water quality standard is 8.2% bylength, which is much lower than the average value of 32.2% of the seven largest rivers in China. The length
percentage of IV and V level of government water quality standard in the Yellow River is up to 65.4%, and the averagevalue of the seven largest rivers in China is 38.9%. This shows the serious pollution status of the Yellow River.
According to the Report of Water Pollution in the Seven Main Rivers (1997) by the National Bureau of Environment
Protection, The Yellow River took in 2.0×109t polluted water in the 1980s, and 4.2×109t in the 1990s. The content ofpolluted water will be 6.5×109t by 2010. By that same time, the polluted water taken in will be increased, so the trendof pollution will increase.
Based on the data of underground water quality monitored from observation wells in five provinces in north
China, including Xinjiang, Gansu, Ningxia, Qinghai, and Inner Mongolia, the underground water quality in 69 cities5was estimated. The results showed that no one city reached the Class I of the government underground water
quality standard, 10 cities had a standard of Class II (about 14.5% of all cities tested), 22 cities had a standard ofClass III (about 31.9%), and 37cities had a standard of Class IV & V (about 53.6%). The results showed that theunderground water in more than half of these cities was polluted badly.

1.4 Soil loss in the middle reaches of the Yellow River is so severe that the water consumption
for flushing sediment in the lower Yellow River is great
Soil loss in the middle reaches of the YRB is severe. The area of soil loss in the loess plateau is up to 2.12×105
km2. The sediment load in the Yellow River is about 1.6×109t, of which 90% comes from the middle loess plateau. The
average in stream sediment content at Huayuankou Station is about 37.6 kg•m-3. The content of first class branches,such as Huangfuchuan River, Kuye River, Wuding River, North Luo river, and Weihe River, are 283, 139, 92.0, 195,
119, and 54.5 kg•m-3 respectively. The sediment content at Wenjiachuan Station in the kuye River is up to 1700 kg•m-3(July 10th 1958). The average soil loss in the section between Shenmu and Wenjiachuan in the Kuye River watershedis 4.0 ×104 kg•m-3•a-1,and it was 1.0 ×105 kg•m-3•a-1 in 1959.
The serious soil loss in the middle YRB causes high sediment content in the stream. The limited runoff andgentle channel in the lower YRB make great sedimentation in the riverbed and reservoirs, which makes the Yellow
River well known as a hanging river on the ground with a wide alluvial flat. The riverbed is nearly 22m and 13m
higher than Xinxiang City and Kaifeng City. The riverbed is raising 10cm annually. To reduce the risk of flood and tolower the riverbed, about 1.5×1010 to 2.0×1010m3 of water is used to flush the sediment into the sea (30% of thewhole water resources in the YRB). This lost water is more than the irrigation volume (1.55×1010 m3 ) of the wholebasin in the 1980s. It is more than the annual 1.30-1.40×1010 m3 of water from Yangtze River Basin to the YRB by
the middle route of South-North Water Diversion of China (You, 2002).

2 The effect of SWCP on the water resource of the Yellow River
2.1 SWCP in the middle reaches of the YRB reduce water resource slightly
In the YRB, water and sediment comes from different areas. 50% of runoff and 9% of sediment of the Yellow
River come from the upriver region of Hekou (51.3% of the whole basin area) respectively. More than 90% of thesediment comes from the middle reaches of the Yellow River, so the section between Hekou and Tongguan Stationis the main sediment source area. Therefore, the section between Hekou and Longmen amounts to 15% of the6

Further discussion on soil and water conservation effect on water resources in the Yellow River Basin – TASAE, 2004
whole basin, but the runoff and sediment account for 12.5% and 56% respectively.
Since the runoff from the middle reaches of the YRB only account for about 10% of the total, SWCP there haveless effect on the runoff but more effect on sediment discharge. From 1970 to 1996, SWCP decreased the averageannual runoff by about 3.58×108 m3, about 5.52% and 0.64% of total runoff of middle reaches and upper region of
Huayuankou station respectively. At the same time, 1.495×108t of sediment was decreased, which is 21% of theaverage sediment yield of the middle reaches region (6.925×108t). Compared with the maximum experimental
sediment yield (8.208×108t), the decrease in the sediment ratio is 18.2%.

2.2 SWCP can increase water resources relatively by decreasing water used for flushingsediment
2.2.1 Water yield losses associated with retaining sediment is far less than that due to water lost in sediment
discharge in the lower Yellow River
The water required to flush 1 ton of sediment from the lower reaches of the Yellow River is between 33 m3 and60 m3 (Liu, 2002), which equals 4.5~30 times the water required to reduce sediment erosion at the source during theflood season and 2~20 times the mean annual cost. In general, the SWCP can increase the water resources in the
Yellow River comparatively.
Table 3. The runoff cost of retained sediment in the section between Hekou and Longmen
Unit：m3・t-1
Name of branch

Shiwang,
Yunyan

Hunhe

Xinshui,
Wuding r,
Xianchuan

Pianguan, Lanyi,
Sanchuan, Tuwei,
and Weifen

Zhujiachuan, Yanhe,
Qingshui, Quchan,
Qingjian, and Kuye

Qiushui, Huangfuchuan,
Gushanchuan, Jialu

Terrace

1

7.20

6.02

3.13

3.08

2.37

2.26

Reforestation

2

7.17

6.20

3.08

3.27

2.61

2.23

Grass-planting

3

7.19

5.85

2.90

2.78

2.39

2.24

Average (1+2+3)/3

7.19

6.02

3.04

3.04

2.46

2.24

Dam

1.45

2.00

1.84

2.09

1.87

2.13

Flood period

7.34

2.46

2.34

3.01

2.08

2.04

Average annual

16.15

5.34

3.91

4.07

3.21

3.19

Water erosion is the main form of erosion in the Loess Plateau. SWCP not only decrease the erosion, but also
decrease the runoff. If we consider the associated runoff volume lost by retaining one ton of sediment (called the
Runoff cost of Retained Sediment , RRS), the RRS between different SWCP and different regions varies greatly. The
RRS in the section between Hekou and Longmen is shown in Table 3 (Wang, 2004). In the regions with severe soil
7

loss, such as Qiushui River, Huangfuchuan River, Gushanchuan River, and Jialu River, the RRS of SWCP is lower.
The RRS of practices on the slope (terrace, reforestation, and grass-planting) is about 2.2m3.t-1, and it is very near to
the RRS of check dam practices in the channel. In Shiwangchuan River, Yunyan River and Hunhe River, the soil andwater losses are small, but the differences of RRS between different practices are big. This average RRS on theslope accounts for 7.19 m3.t-1 while only 1.45 m3.t-1 in the channel. The mean RRS is from 2.04 m3.t-1 to 7.34 m3.t-1
during flood season, and the mean annual RRS is from 3.19 m3.t-1 to 16.15 m3.t-1. That is, if the soil and water losses
in mid-areas are controlled on the spot, when 1 ton of sediment is controlled, the surface runoff will be reduced by
3.19 m3 to 16.15m3.
2.2.2 Estimate of comparative water resource increase from SWCP in the section between Hekou andLongmen
When estimating the water resource change from SWCP in the YRB, the water reduced by SWCP must be
considered. A comparative increase results because the water saving not having to flush sediment from the lower
reaches is greater than the reduction in runoff decreased by SWCP. Taking the example of the section between
Hekou and Longmen, the amount of water and sediment of different periods in the control areas reduced by SWCP
is showed in Table 4. The amount of reduced sediment is 1.495×108t from 1970 to 1996. If the water lost for
flushing sediment is 35 m3.t-1, the annual water lost for flushing sediment is 5.23×109 m3. This improves exploitablewater resources by 4.88×109m3 which accounts for 75.1% and 8.76% of total runoff in the section between Hekou
and Longmen, and the upper area of the Huayuankou Station respectively. This means that, if the balance of waterand sediment in the whole basin is considered, SWCP in the section between Hekou and Longmen, can increase
markedly the amount of water resources of the basin.
Table 4. The water resource increase estimation of different stage
Runoff detained

Water reduction for sedimentretainedflush *

VolumePercentage

Percentage

1***

2****

108 m3%%108t

108 m3

1970-1979 3.352

5.17

0.60

1.458

1980-1989 3.521

5.42

0.63

1990-1996 3.993

6.15

1970-1996 3.580

5.52

Stage

VolumeWater increase relatively**

Sediment

Percentage

Percentage

1***

2****

108 m3%%51.03447.682

73.47

8.57

1.398

48.91845.397

69.95

8.16

0.72

1.688

59.07355.080

84.87

9.90

0.64

1.495

52.33148.750

75.12

8.76

Note: *The average annual water for flushing sediment is 35 m3・t-1; **The water increased relatively is the difference between the watersaving from for sediment flushing and the runoff detained. ***Percentage of the section between Hekou and Longmen;
8Further discussion on soil and water conservation effect on water resources in the Yellow River Basin – TASAE, 2004****Percentage of upper Huayuankou area

2.3 Other effects of SWCP on water resources
2.3.1 Increasing the soil water capability and reducing the water lost as flood
It is shown that, in the gully loess area, compared with natural basins, the ability to capture rainstorm water is
45~98% (the average is 77%). When the average intensity of the rain is less than 4mm.h-1, runoff will be cut by
40~50%(Mu, 1999), while it will be reduced by 45~55% when the average intensity of the rain is 4~10mm.h-1.
SWCP can improve infiltration, make rainstorm water change into available soil water resources and decrease thewater loss due to sheet flow.
2.3.2 Improving water quality
In addition to soil degradation resulting from surface soil and soil nutrient losses, soil and water losses also
induce water pollution through adding organic matter, mineral and sediment into water. Although this kind of pollution
has no serious negative effects on field irrigation, it can cause or worsen eutrophication of the water body. The
organic carbon, nitrogen and phosphorous of cultivated soil are 5.73 g.kg-1, 0.56 g.kg-1 and 0.66g.kg-1 in the sloping
land of the loess plateau respectively (Guo, 2003). If the average sediment content of flow is 40kg.m-3, theconcentration of phosphorous will reach as high as 0.026mg.l-1,which is worse than Class 1 of the government water
quality standard. In cropland with vegetation and fertilization, soil nutrient content is even worse, and the pollution
caused by soil and water losses is more serious because chemicals such as pesticide, and herbicide and so on, areapplied widely to agricultural production. If SWCP are carried out, contamination will decrease and the water will
improve.
2.3.3 SWCP can reduce the sedimentation of reservoirs, and spatial and temporal distribution and use ofwater resources
Soil erosion is the main reason for reservoir sedimentation. The average annual sedimentation rate in China is
2.3%, which is higher than that of Algeria (1.8%), Japan (1.02%) and USA (0.24%)(Qian, 1991). 601 of the large andmiddle reservoirs have been built since 1950 with a total capacity of 5.23×1010 m3. About 20.8% of this capacity waslost by the end of 1989 (Floods and Drought Disasters Committee of the Yellow River basin and northwest part
China, 1996). SWCP can prevent the sedimentation of reservoirs thus resolving the problem of water resources
shortage.

9References:
1 Cui Shu-qiang. Influence of water discharge cut-off of Huanghe on environment of its delta. Marine Sciences, 2002,26(7):42-46.
2 Chen Ji-wei, Mu Xing-min. Rootstock of water discharge cut-off of Huanghe and science and technology countermeasure. Journal of
Natural Resources, 2000,15(1):31-35.
3 Mu Xing-min, Li Rui. Strategic status of soil and water conservation on solving water problems in China. Bulletin of Soil and Water
Conservation, 1999,19(3):1-5.
4 Wang Shou-rong, Zhu Chuan-hai, Cheng Lei et al. Global water cycle and water resources. Beijing: Meteorological Press,
2003:119-142.
5 Jia Shao-feng, Zhang Shi-feng. Annalysis on the water supply capacity of the Yellow River Drainage Basin. Journal of Natural
Resources, 2001,16(6):547-551.
6 Chen Jia-qi. Water resources of China. See：Qian Zheng-ying. Water conservancy of China. Beijing: Hydraulic and Electric Power
Press，1991.
7 Chinese Economy and Trade committee. Problems of water resources in the Yellow River and its countermeasure.
http://www.drccu.gov.cn, 2000
8 You Xing-tian, Zhu He. The discharge varaiation in the two main rivers of China during the recent half century and the relationship withthe south-to-north water transfer project. Advances in Earth Sciences, 2002,17(6):811-817.
9 Wang Fei. Quantitative evaluation on the human activity effect on the regional soil erosion. Doctoral degree thesis. Yangling:
Northwestern Sci-tech University of Agriculture and Forestry, 2004.
10 Liu Xiao-yong, Li Tian-hong, Zhao Ye-an et al. Water demand for sediment transport in the lower The Yellow River. Journal of Basic
Science and Engineering, 2002,10(3): 253-262.
11 Mu Xing-min, Wang Wen-long. Effect of the soil and water conservation in the hilly-gully region of tableland on the runoff in
sub-catchment. Journal of Hydraulic engineering , 1999,(2):71-75.
12 Guo Sheng-li, Liu Wen-zhao, Shi Zhu-ye, et al. Soil nutrients distribution and its relation to landform and vegetation at small
watershed in semiarid area. Agricultural Research in Arid Areas，2003,21(4):40-43.
13 Qian Zhen-ying. Water conservancy of China. Beijing: Hydraulic and Electric Power Press，1991:87-131.
14 Floods and Drought Disasters Committee of the Yellow River basin and northwest part China. Zhengzhong: Yellow River Water
Conservancy Press, 1996:226-243.

10