Determination of a Reasonable Percentage for Ecological Water-Use in the Haihe River Basin, China1

Pedosphere 16(1): 3 3 4 2 , 2006 ISSN 1002-0160/CN 32-1315/P @ 2006 Soil Science Society of China Published by Elsevier Limited and Science Press

Determination of a Reasona.ble Percentage for Ecological Water-Use in the Haihe River Basin, China*' XIA Junl,', FENG Hua-Li3, ZHAN Che-Sheng' and NIU Cun-Wen' 'Key Laboratory of Water Cycle & Related Land Surface Processes, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Science, Beijing 100101 (China). E-mail: [email protected] 'State Key Laboratory of Water Resources & Hydi-opower Engineering Sciences, Wuhan University, Wuhan 430072 (China) Nanjing Hydraulic Research Institute, Nanjing 210029 (China) (Received June 28, 2005; revised November 16, 2005)

ABSTRACT An investigation was conducted to study problenis of determining a reasonable percentage for ecological water-use in the Haihe River Basin of China. Three key aspects for the ecological water requirement (EWR) were analyzed, involving i) the EWR for river system, ii) the EWR for wetlands and lakes, and iii) the EWR for discharge into the sea t o maintain the estuary ecological balance of the Haihe River. The Montana method and related water level-flow relationships, and the statistic approach based on hydrological records were applied to estimate different components of EWR. The results showed that the total ecological water demand in the region was about 3.47-14.56 billion m3. Considering flow regime change and uncertainty, the ecological water demand could be estimated by the hydrological frequency approach. Preliminary analysis showed that for different annual runoff under the frequencies of 20%, 50%, 75% and 95%, the ecological water demand approached 12%-50%, 18%-74%, 24%-103'%, 35%-148% and 16%-66%, respectively. By further analysis to balance ecological water-use and socioeconomic water-use, the rational percentage of ecological water-use was estimated as 35%-74%, that provides useful information t o judge whether the allocation of water resources is reasonable, and was proved to be satisfactory by comparing with the practical condition. Key Words:

ecological water requirement, ecological water-use, Haihe River Basin

The Haihe River Basin, which is the politic, economic, and cultural center of China is a very important part of North China. However, it is also an area facing crises for water resources. For instance, the water resource per capita in the basin is about 305 m3, which is only 1/7 of the national average and 1/24 of the world average. Water shortage has also resulted in serious problems of ecosystem degradation, such as drying-up of river system, shrinking of lake and wetland, and the decrease of inflow into the Bohai Sea. In order to maintain eco-environmental sustainability in the basin system, the project on the Eco-rehabilitating Plan in Haihe River Basin was proposed by the Ministry of Water Resources, China, in which the estimation of the ecological water requirement (EWR) has become an important issue in the protection of ecological environment. From the perspective of ecological and environmental protection as well as use of sustainable water resources, the studies on EWR have become a wide concern in the field of geosciences, both in China and elsewhere, and is also an important subject in the study of ecological hydrology (Liu, 2000; Xia et al. 2003; Feng, 2002). A number of studies have been conducted in the development and application of the EWR, for example, Raskin et al. (1996), Whipple et al. (1999), and Gleick (1998, 2000) have pointed out that for the sustainable use of water resources EWR should be guaranteed. Liu (2000) indicated four principles for water-use balance that natural ecology and human environment should abide by 1) waterenergy balance, 2) water-salt balance, 3) water-sand balance, and 4) regional water balance and supplyrequirement balance. Up to now, studies on. EWR have largely focused on river ecosystems (White, *lProject supported by the Natural Science Foundation of China (No. 50279049), the Knowledge Innovation Key Project of the Chinese Academy of Sciences (Nos. CXlOG-EOI-08 and KZCX2-SW-317) and the National Challenging Program of Science and Technology of China (No. 2004BA610A-01).

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1976; Bovee, 1986; Gore, 1989a, b; Hill et al, 1990; Petts, 1996). These studies were based on the characteristics of ecosystems, without any consideration of influences of the socioeconomic system. In fact, the socioeconomic-natural system is a huge and complex system with mutual influences and restrictions. Therefore, the ecological water requirement obtained from the perspective of the ecological system will only be guaranteed when it is coordinated with the water requirements for socioeconomic development. This article focuses on the Haihe River ecological water requirement for the purpose of ecological rehabilitation plan which included determining 1) the river’s basic EWR, 2) the EWR of the area’s wetlands and lakes, and 3) the requirement for water flow into the sea to maintain the estuary’s ecological balance. MATERIALS AND METHODS

Study sites The Haihe River Basin, located between 35’ and 43’ N latitude and 112’ and 120’ E longitude, fronts the Bohai Sea on the east and the Yellow River on the south, while on the west it is adjacent to Yunzhong and Taiyue Mountains, and on the north by the Mongolian Plateau. It covers an area of 318000 km2, among which mountains and plateaus comprise 189000 km2, accounting for 60% and with plains covering 129000 km2, accounting for 40%. The main characteristics of the Haihe River Basin include limited water resources, unequal rainfall distribution over time and space, and frequent occurrence of drought years; overall, it is considered an area of water-resource shortages. From 19561998, the total volume of water resources was 37.2 billion m3, and the water resource per capita was 305 m3. This accounted for only 1/7 of the average in China, 1/24 of the world average, and was far below the international water shortage criterion average of 1000 m3 per capita. Meanwhile, the average water per ha was 3375 m3, accounting for 118 of the whole country. Among the river areas of China, the average water resource per capita and per ha for the Haihe River area was the lowest (Table I). TABLE I Comparison between the average water resource per capita and per ha in the Haihe River area and other river areas in China Index ____________

Haihe River

Yangtze River

Yellow River

Huaihe River

305 3375

2 388 419225

749 6000

505 7 095

Songliao River

Zhujiang River

Average in China

1704

3 327 72 630

2 342 28 500

~

m3

Water resource per capita Water resource per ha

9915

The Haihe River Basin is an important industrial and high-technology production base, holding an important strategic position in national, economic, and social development. In 2000 the total population in the area was 126 million, accounting for 10% of the nation’s population. Also, its urban population was 36.47 million (according to recorded vital statistics), and the rate of urbanization reached 28.9%. Within the area, there were 397 people per km2 and 628 people per km2 in the plain area. In 2000 the GDP of the area was 1121.1 billion RMB Yuan (US$ 135.7 billion at US$ 1.00 = 8.26 RMB Yuan), or about 15% of the national GDP, with an average GDP per head of 8 890 RMB Yuan (US$ 1076.3), which was above the national average. Water security problem in North China becomes a major issue of sustainable developments in China (Liu and Xia, 2004; Yang et al., 2005; Zhang et al., 2005, Chen et al., 1996; Zhao et al., 1992). The ecological problems resulting from water shortage in the Haihe River area were mainly of three types. First, water from the mountains was greatly reduced and the decrease in the volume of water resources was serious. The great decrease in water from mountain water sources imposed a great threat to the cities, the ecological environment, and the socioeconomic development in the middle and lower

REASONABLE PERCENTAGE FOR ECOLOGICAL WATER-USE

35

reaches. Second, there were river degradation, reduction in water flowing into the seas, and serious siltation at the river mouth. In the five decades, from the 1950s through the 199Os, the volume of water flowing into seas were, respectively, 24.1, 16.1, 11.6, 2.69, and 6.85 billion m3 per year. The decrease in water flowing into the seas changkd the water-sand balance, leading to siltation of the riverbed and the river mouth. Third, there were reductions of wetlands, dried-up lakes, and subsidence problems from overexploitation of underground water. In the 1950s, there were 9000 km2 of wetlands in the Haihe River area, whereas in 2002 the total area of wetlands and reservoirs was only 3 852 km2. And the total water shortage consisted of an exploitation volume that exceeded 90 billion m3 (of which 47 billion m3 came from the shallow layer, and 43 billion m3 from the deep layer). The exploited area for the shallow water layer exceeded the limit by 41000 km2, while that of the deeper layer water exceeded the limit by 56000 km2, accounting for 32% and 40%, respectively.

Determining the percentage of river water for the ecological water requirement This study calculated the basic EWR of the river using the Montana method (Tennant, 1976). The EWR of the wetlands was calculated by an interaction between the water level and ecology, where the ecological water in store was determined first. This was generally done according to the demands of the water volume and the level of fish and water plants. The corresponding wetland water evaporation and leakage loss were then calculated. Finally the total EWR (W,) of the wetlands as the sum of wetland water storage (W,,), wetland water evaporation (Wwe),and water leakage loss (Wwl)was obtained:

W, = W,,

+ W,, + Wwl = hs + se + hsr

(1)

where h refers t o the depth of water corresponding t o a certain water level ( m ) ,s refers t o the water surface (km’), e stands for water surface evaporation (the value adopted in the Haihe River area is 1100 mm year-l), and r stands for the rate of water leakage loss (determined as 0.15). The percentage of EWR was expressed by a range with the low limit rate [Wmin/Wm],optimal rate [Wopti/Wm] and upper limit rate [Wm,/Wm], ie.,

where Wmin,Wopti,and W,, are the minimal, optimal, and maximal EWR of the river ecosystems; W, is the annual runoff of different frequencies; and Pmin, Popti,and P,, are the minimal, optimal, and maximal percentages of EWR. For the protection objective, there was a threshold interval consisting of the minimal, optimal, and maximal EWR.

Determining the percentage of the river flow .for ecological water-use In this work the river’s ecological water-use referred t o the volume of water either supplemented artificially (e.g., waste water) into the river ecosystems or reserved for the river’s ecological system so as to attain certain ecological objectives. In view of the growth-and-decline relation between the river’s ecological water-use and socioeconomic water supply (ground water supply), the relationship between the volume of the river’s ecological wateruse and that of the socioeconomic water supply (obtained from rivers) was established. From the perspective of river water exploitation, the relation of the river’s ecosystem water balance (We)was stated as

where W is the natural river runoff volume, W1 is the domestic water supply, Wi is the industrial water supply, Wa is the agricultural water supply, and We is the river’s ecological water. These refer to the water obtained from rivers, excluding water obtained from underground. Ecological water-use refers to

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the water reserved for river ecosystems after socioeconomic water demands have been met. Therefore, rearranging Eq. 2 the actual river's ecological water-use was

we = w - w,- wi- w,

(4)

The river's ecological water-use percentage within the research period referred t o the percentage between the ecological water-use and river runoff. Thus, the percentage of the corresponding actual ecological water-use was

where Pus,is the proportion of the river's ecological water-use (in 100 million m3); W is the river runoff within the research period; Wi is the industrial water from the rivers; W, is the agricultural water from the rivers; and Wl is the domestic water from the rivers. Determining a reasonable percentage of river flow f o r ecological water-use

The percentage of the ecological water-use (percentage of actual ecological water-use) was Pus,and the threshold interval of the percentage of EWR was [Pmin,Popti, P,,,]. By comparing the percentage of the actual ecological water-use and evaluation criterion for the percentage of the EWR, it could be seen whether the actual ecological water-use could meet the demands of the river ecosystems (Table 11). TABLE I1 Evaluation principles of the percentages of ecological water-use and ecological water requirement

iJ;)

< Pminb)

P,i,

Unsustainable water-use

< Pm < P,")

Sustainable water-use

P m

> Pmax

Unsustainable water-use

~~

")Pm:the actual ecological water-use; b)Pmin: the minimum percentage for the ecological water-use; ")Pmax: the maximum percentage for the ecological water-use.

Analysis

First, in order to help define ecological recovery, the ecological water requirement and its percentage were calculated. The protection goal corresponding to the minimal ecological water requirement was the ecological threshold state in the late 1970s, and the optimal ecological water requirement was the better ecological state in the 1970s. According t o these goals, the threshold interval of the EWR corresponding t o the minimal ecological water requirement and the optimal ecological water requirement were calculated. This study followed the work of Tennant (Tennant, 1976) taking 10% of the mean annual flow as the minimal EWR, and considering the state of the actual water resources in the Haihe River area, with socioeconomic development using the 40% of the perennial average flow as the optimal EWR. Since water resources in the Haihe River Basin were scarce and water-use for most ecosystems could not be satisfied, there was no overabundance of ecosystem water resources, especially in semiarid and arid areas. Therefore, the maximal EWR was not considered. Finally, water flow into the sea for the maintenance of the estuary's ecological balance was calculated and compared from the 1950s to the 1990s. The minimal water flow into the sea in the drought period of the 1970s was used as the bottom limit, and the average water flow into the sea in the 1970s as the upper limit. RESULTS AND DISCUSSION Background

Generally, the EWR of a river system can be understood as such a part of water resources requirement

REASONABLE PERCENTAGE FOR ECOLOG1CA.L WATER-USE

37

to maintain ecological balance of river system under an ecosystem object. It is restricted by three major factors, namely, 1) ecological objectives, 2) ecological system characteristics, and 3) outside ecological factors. The so-called ecological objectives refer to human expectations of the constitution, organization, and function of the ecosystem. Obviously, with rising expectations for the ecosystem, ecological objectives will be raised to a higher level, and correspondingly the river’s ecological water requirement will change as well. Second, the river’s EWR is mainly under the influence of two kinds of natural factors. One refers to such features as the biotic communities and morphology of the river system; for example, the influences of such system-internal characteristics as species of aquatic life and riverbed formation. The other kind includes outside ecological factors such as solar radiation, temperature, and wind speed. Also under the joint influence of circulation of matter and energy within the ecological system as well as the variation of outside ecological factors, EWR varies with time and space. Third, concerning a certain river ecosystem, it has been shown that EWFL is not fixed at a certain value, but rather changes within a threshold interval until a dynamic balance of water in the ecological system is reached. The river ecosystem, as an organism, has its own self-regulation function. Therefore, the water required for the maintenance of a healthy ecosystem is not fixed a t one point, but changes within a certain range. The range of change constitutes the threshold interval of the EWR. For a certain river ecosystem, with its basic health level as a reference, the variation between threshold and satisfactory states corresponds to a certain threshold for the water requirement interval [Wmin,Wopti,W,,,], or minimal water requirement, optimal water requirement, and maximum water requirement, respectively (Fig. 1).

--

300

E

-

161 116 68.5 26.9 I

Minimal

Optimal

Maximum

1950s 1960s 1970s 1980s 1990s

Water requirement Fig. 1

Ranges in the ecological water requirement.

Fig. 2

Mean water flow t o the sea for the Haihe River from 1950s to 1990s.

The minimal water demand for the maintenance of matter and energy input and output of the ecological system is defined as the minimal water requirement (Wmin),which refers to the minimal water required for the maintenance of current constitution and function. When the ecological water volume is lower than the minimal EWR, the original constitution of the ecological system will be lost, and service functions of ecological systems will atrophy. When water volume is at the optimal level (Wo,,i) for EWR, the productive potential of’the ecosystem will be given full play. Additionally, when the water volume exceeds the maximal water requirement (Wmax),too much water may restrict the healthy development of the ecosystem. In 1976 Tennant (1976) proposed the Montana method, which has become one of the most common historic flow methods used. The relation between hydrology and biology is of great importance in the United States as well as in many other countries, and the Montana method has successfully proven the correlation between river hydrology and ecology (Whelan and Wood, 1962; Rao e t aZ., 1992). Eco-water requirement to maintain the estuary’s ecological balance could be calculated according

38

J. XIA

e t al.

to record of the literature in the Haihe River Basin (Wang, 2002). Our research showed that the EWR in Haihe River was not a simple add-on relationship of three major components, ie., river ecological base flow, ecological water requirement of the area’s wetlands and lakes, as well as its water flow into the sea. The total EWR in the basin needs to be determined by water cycle process of river system and their interactive relationship. So, the river EWR percentages refer to the proportional value between the river ecological water requirement and the annual runoff for different frequencies . The river’s ecosystem water-use as well as the water-use for daily life and industrial needs shaFe one common water source, that is, river runoff water volume. Obviously, this comes from a different water source than precipitation, and can be called runoff water source. With the on-going development of a social economy, the conflict for water resources commonly shared in daily life, industry, and the ecosystem, has become more and more prominent, even to the extent that the three uses are in a state of competition for water. An increase in river water volume required for socioeconomic development implies a decrease in water-use for the river ecosystem; in other words, the river’s ecological water-use is compelled to decrease. When the decrease reaches a certain point, it will result in the deterioration and dying-out of the river ecosystems. In certain regions, river runoff volume is limited. Since socioeconomic water-use and ecological water-use are in a growth-and-decline relationship, an increase in the volume of water allocated to socioeconomic use suggests a decrease in water-use for the river ecosystems. Such a decrease, to a certain extent, will bring about the degeneration of the river ecosystems. In the arid and semiarid areas of China, an increase in socioeconomic water-use obtained from rivers or a decrease in the ecological water-use, is one of the main factors that contributes to the deterioration of the river’s ecological environment. Contrarily, if the ecological water-use demands are continuously met, socioeconomic development will be restricted. Therefore, coordinating the relation between the two has become one of the important research subjects in the reasonable allocation of water resources. Different ecological protection objectives require different ecological water-use proportions. Therefore, before the determination of the percentage of ecological water-use, the ecological protection system objective must be determined, and then the threshold interval of the ecological water-use and its proportion can be calculated. Finally, based on the percentage of ecological water-use and considering the demands for water with socioeconomic development, the proportion of ecological water-use can be reasonably determined. This will create a winwin situation for socioeconomic development and protection of the ecological environment. The EWR is one of the intrinsic features of an ecosystem, and is an important basis and reference criterion for reasonable ecological water allocation. If only the perspective of the protection of river ecosystem is considered, the ecological service functions of river system would be more effective as the percentage would approach the optimal proportion of ecological water use Popti.However, other aspects must be considered. The socioeconomic-natural system is a huge and complex system. The degree of coordination among society, the economy, and the ecological environment will determine the possibility of its sustainable development. Nevertheless, an ecological water-use criterion that runs counter to socioeconomic development should not be put into effect. Therefore, with a consideration of the demands of socioeconomic water needs, reasonable allocation of the ecological water-use should be carried out within the threshold intervals of EWR. Large-scale agricultural development in the mid- and late 1960s, and the massive industrial development since the 1970s has brought about a rapid increase in out-of-stream water, as well as such phenomena as river-way degradation, reduction of wetlands, and a sharp decrease in the volume flow into the sea (Table 111). For the area’s ecological water-use, the 1960s was the turning point from a satisfactory state to one of deterioration. Therefore, the ultimate goal for the recovery of Haihe River water ecological environment was the state in the late 1960s and early 1970s. Corresponding to this goal there is a threshold interval for the river’s EWR.

REASONABLE PERCENTAGE FOR ECOLOG1CA.L WATER-USE

39

TABLE 111 Ecological indexes related with water in Haihe River Basin Index

1970s baseline

Present threshold

Length of dry river (km) Area for Lakes and wetlands (km2) Water flowing into the sea during drought year (m3)

< 1000 1500 2.5 billion

4 000 122 1.2 billion

Basic water requirement of river ecology From 1956 to 1990 the perennial average runoff volume of the Haihe River Basin was 22 billion m3; the calculated minimal ecological in-stream water requirement of the Haihe River River was 22 x 10' m3; and the optimal ecological water requirement was 88 x 10' m3, with the threshold interval being 2.20 to 8.80 billion m3.

Minimal and optimal ecological water requirement of selected wetlands The ecological goals, corresponding to the minimal EWR for the Haihe River wetlands, including protection of the Baiyangdian area; improveinent of the three wetlands' ecological environments of Tuanpowa, Dalangdian, and Qianqinwa; and meeting their respective EWR are shown in Table IV. TABLE IV Minimal ecological water requirements of the Haihe River wetlands in the 1970s Wetland

Coverage

Baiyangdian Tuanpowa Dalangdian Qianqinwa Total

km2 122 263 49 37 471

Ecological water store

Volume of water evaporated

1.20 1.96 0.52 0.22 3.90

1.34 2.89 0.54 0.41 5.18

Volume of water leakage loss

Total ecological water requirement

lo8 m3 0.18 0.29 0.08 0.03 0.58

2.72 5.14 1.14 0.66 9.66

Because the minimal water depth required by fisheries and water plants in Baiyangdian is 1.0 m, the water level corresponding to this depth maintaining the ecological balance was 5.9 m. The water surface coverage, the minimal ecological water store, the volume of water required for wetland evaporation and leakage loss, and the total for the annual ecological water requirement of the wetland are shown in Table IV. Utilizing Eq. 1 the ecological water requirement for the recovery of major wetlands in Table IV was calculated and summed to equal 0.97 billion m3. The ecological goal corresponding to the optimal ecological water requirement for wetlands in the Haihe River Basin is shown in Table V with the total optimal EWR being 29.6 x 10' m3. Therefore, the threshold interval was 0.97 (Table 1V)-2.96 (Table V) billion m3.

Water flow into the sea for maintenance of the estuary's ecological balance Historically, the ecological state of the Haihe River estuary did not face great problems in the early 1970s. Fig.2 shows the mean water flow into the sea for the Haihe River, by decade, from 1950s to 1990s. The minimal water flow into the sea in the drought period of the 1970s was used as the bottom limit (about 9.7 x 108m3, Table IV), and the average water flow into the sea in the 1970s (116 x 10' m3, Fig. 2) as the upper limit. As recorded in the literature (Li and Zheng, 2000), the required upper and lower limits for water flow into the sea are 11.60 and 2.50 billion m3, respectively. This meant that the threshold interval for

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TABLE V Indexes of the optimal ecological water requirement for the recovery of the Haihe River wetlands Wetland

Coverage

Baiyangdian Tuanpowa Dalangdian Qianqinwa Ningjinpo Dongdian Qingdianwa Xiqilihai Dahuangpuwa Enxianwa Total

km2 160 263 49 37 151 87 61 50 103 107 1068

Volume of ecological water store

Volume of water evaporated

4 5.26 0.25 0.19 3.02 0.52 0.31 0.25 0.82 0.86 15.48

1.76 2.89 0.54 0.41 1.66 0.96 0.67 0.55 1.13 1.18 11.75

Volume of water leakage lossa)

Total water requirement

0.6 0.79 0.04 0.03 0.45 0.08 0.05 0.04 0.12 0.13 2.33

6.36 8.94 0.83 0.63 5.13 1.56 1.03 0.84 2.07 2.17 29.56

lo8 m3

a)The rate of leakage is calculated with 0.15.

water flow into the sea for maintenance of the estuary's ecological balance was 2.50 to 11.60 billion m3. Then adding the EWR of lakes and wetlands (0.97 from Table IV and 2.96 billion m3 from Table V) a total in-stream water requirement of 3.47-14.56 billion m3 was obtained.

Percentage of ecological water-use The ecological water-use and percentage of ecological water-use for the Haihe River area between 1998 and 2002 were calculated through the determination method employed in Eq. 2, as shown in Table VI . TABLE VI Calculation of the percentage of in-stream ecological water-use for the Haihe River Basin from 1998 t o 2002 using Eq. 2 Year

Local surface water available ~~~~

Volume of surface water resources

Volume of ecological water-use

Percentage of ecological water-use

79.95

42

-

-

20.16 5.59

16 6

-

-

~

10' 1998 1999

109.75 107.91

189.70 92.00

2000 2001 2002

105.02 84.11 81.55

125.18 89.70 64.08

%

m3

In 1998, a year of moderate water flow, the volume of surface water resources were abundant, the percentage of ecological water-use was 42% (Table VI), and the demands for water in the river ecosystems were basically met. During the drought years of 1999 and 2002, the volume of surface water resources decreased markedly, but without any marked reduction in local surface water available, which was maintained around 10 billion m3. In 1999 and 2002, the local surface water available exceeded the total volume of surface water resources, with exploitation rates of 117% and 127%, respectively. The in-stream water mainly discharged waste water, and the river ecosystem greatly deteriorated. However, in 2000 and 2001, another two drought years, because the surface water need was relatively less, there were portions for ecological water-use, accounting for 16% and 6%, respectively. Thus, the percentage of ecological water-use in 2000 was around the threshold of EWR, meaning it could basically be satisfied. Confronted with outside interferences, ecosystems have the ability of self-regulation. However, when the intensity of interference exceeds a certain limit, and the duration of interference accumulates to a certain amount, ecosystems lose their flexibility and their ability of counteraction, self-maintenance,

41

REASONABLE PERCENTAGE FOR ECOLOGICAL WATER-USE

and self-regulation. Water shortages over a long time can be seen as a kind of interference. During 1999 to 2002, the volume of the river's ecological water-use in the Haihe River Basin was very small, meaning for four consecutive years the ecological water-use requirement could hardly be met. This was a major factor in the degeneration of the service function of the Haihe River Basin ecosystem, and a deterioration of the river system. Therefore, the allocation of ground-water resources was not reasonable, and different water-use plans were needed for years of moderate water flow. Table VII showed that the percentage of ecological water demand changed according to differing annual runoff. Based on the mean annual runoff from 1956 to 1998, the percentage of ecological water demand was 16%-66%. TABLE VII Percentage of ecological water-use requirement for different levels of annual runoff based on mean annual maximum runoff in the Haihe River Basin from 1956 to 1998 Frequency of annual runoff

Surface water resources

Ecological water requirement and percentage Minimal requirement

Percentage

Optimal requirement

Percentage

%

10' m3 294.00 196.00 142.00 98.20 220.00

10' m3 34.7

%

10' m3 145.6

%

20 50 75 95

Mean

12 18 24 35 16

50 74 103 148 66

From the results of Table VII, in a wet year, the minimum water requirement accounted for 12% of the total water resources, however, in a severe dry year it was 35%. Thus, the minimum percentage of ecological water demand in Table VII varied between 12% and 35% for different amounts of runoff. It is generally accepted that the ecosystem has a self-adaptation ability to disturbances of a changing environment. However, t o avoid the risks of ha-ving a water deficit in the river ecosystem, 35% of the water resources in a severe dry year were proposed as the lowest rational percentage for the minimum ecological water demand. This minimum was set only according t o the ecological water demand and did not take into consideration the socioeconomic water demand. However, for the highest amount, that is the most suitable percentage of ecological water demand, socioeconomic water-use should be considered. For wet and severe dry years, the optimal ecological water demand varied between 50% and 148%. Thus, in a severe dry year, the percentage was much larger than 100%. This meant that even if all water resources were used for the ecological aspect, it still could not meet the optimal ecological water demand. In fact, it was impossible t o allocate all of the freshwater in the river for ecological use. So a tradeoff between ecological water-use and socioeconomic water-use was necessary t o maximize the ecosystem and socioeconomic system. Taking all these factors into account, 50% of the mean annual runoff was decided as the highest volume for optimal ecological water demand. Thus, the percentage changed t o between 35% and 74%. So, the percentage of ecological water-use is a good tool to judge whether the allocation of water resources is reasonable or not in some areas, and can then be used t o evaluate the sustainable exploitation issues of river basins as references. Results were proved to be satisfactory by comparing with the practical condition. REFERENCES Bovee, K. D. 1986. Development and Evaluation of Habitat Suitability Criteria for Use in the Instream Flow Incremental Methodology. US. Fish and Wildlife Service, Washington, D.C. Instream Flow Information Paper No. 21. Biological Report 86(7). 235pp.

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