The method of evaluation flood resources sustainable utilization capacity
Zhongjing WANG1, Xuefeng WANG1, FEI ZHAO1,
Shuying GUO2, Siyi HU1, 3
1 Institute of Hydrology & Water Resources, Tsinghua University, Beijing, 100084, China
2 Hai Basin Water Resources Committee, Ministry of Water Resources, Tianjin, China
3 Nanjing Institute of Water Resources, Nanjing, China
Flood resourcification (flood resources development and utilization) is a new issue in water resources management, which aims to solve the conflict between flood and drought disaster mitigation. With a review of the history and assess the consequence of water resources development and management in Hai Basin of China, a method of evaluation flood resources development capacity and sustainable utilization ways are presented. In result, a 3-phases of capacity in history and 38.4×108m3 potential capacities of flood resources sustainable development and utilization is figured out.
From time immemorial, the flood has been regarded as disaster, the enemy of human the same as monster. A Chinese ancient wisdom named Guan Zi said. "The most mainly responsibility for a qualified administrator is to get rid of the five kinds of disaster: flood, drought, heavy storm-fog-hail-frost, disease and fire. Among these, the flood is the most harmful." Facing the flood, human being takes great pains to discharge the flood into the sea in all along. By now, how to avoid the harms of flood and to make full use of advantages of flood is the new topic in the global water shortage background, named flood resourcification.
THE CONCEPT OF FLOOD RESOURCIFICATION AND ITS UTILIZATION WAYS
With the development of human society, the water shortage and flood disaster is a worldwide confliction. Water resource is becoming the most important issue of human subsistence and sustainable development in 21st century. With a review of the history of flood, there was not only disaster brought from flood, but also freshwater, named flood sources. Plenty of studies showed that the flood is the mainly water sources for natural ecology. So, it is greatly significant for sustainable water utilization to understand the effects of flood in the nature circle and to utilize the flood water adequately.
Although there are studies about utilization of flood sources in different aspects (Tian, 2002, Li, 2003, Kang, 2003), there is still much confusion in the conception of flood resourcification. Based on solving confliction of water shortage and flood disaster, flood resourcification can definite as below. With not increased flood risk, to increase the water supply for economic system and ecological system and to improve functions of rivers, lakes and wetlands, and to recharge of groundwater by storing and detention flood inside land in all kinds of approaches both in project and in management.
This definition has such three significations: flood resourcification should not increase the risk of flood control, can be carried out by means of project and management, and has multi-objective services. Moreover, the approaches of flood resourcification are also comprehensives, such as crop structure regulation, rainfall collection, reservoir operation optimization, combination use of reservoirs- rivers-canals, actively use flood detentions to recharge groundwater etc. (Figure 1).
THE EVALUATION OF FLOOD RESOURCIFICATION ABILITY
Actually, the utilization of flood source has existed a long time since human being to use of water resources in large-scale. Irrigating, damming and some others contain the concept of flood resourcification already. However, there is still no way to evaluate the flood resourcification ability erenow. From the concept of flood resourcification, a method of evaluation current ability has been derived out as formula (1):
(1)
Where is the flood resourcification ability; is the surface runoff; is the amount of outflow of evaluation region, include that flows into the downstream and into the sea.
Hai Basin, the case study region, located in northern of China with around of 32×104km2 area, 1.2×108 population and 372×108m3 water resources. Including two large cities, Beijing and Tianjin, the Hai basin with increasing population and developing economics, water shortage is becoming a serious problem facing to the 21st century. The safety of water resources in this region has drawn a lot attention in China. Flood resourcification is expected a significant tool to increase water supply.
The primary target of flood resourcification in Hai Basin is to remain most water on land. In other words, the quantity of water entering the sea especially at the flood season may shows the flood resourcification ability in whole basin. The less water enters the sea, the higher ability flood resourcification is.
By formula (1), the difference between surface runoff and the water entering the sea shows the total of water resources remain in land. This part of water is used either directly or indirectly by dispatching, storage in reservoirs, recharging into groundwater etc. That is just the amount of flood resourcification. By the survey of surface runoff and the discharge into the sea from 1956 to 1998 (Hai river commission, 2001), a process of utilization of flood sources can be figure out as Figure 2.
It is easy to find that there are three obvious phases in Figure 2. The 1st phase is from 1956 to 1964. In this period, after the flood disaster of year 1956, there are 23 large-scale and 47 middle-scale reservoirs constructed which service the flood resourcification ability to about 80~90×108m3. The 2nd phase is from 1970 to 1985. Considering the heavy flood disaster in August, 1963, an extensive renovation project has been carried out again in Hai Basin. Three large reservoirs, a large number of middle-scale and small-scale reservoirs as well as some other water conservancy projects are built. From about 5-year constructing, the ability of flood resourcification is increased to about 120~130×108m3. The 3rd phase is from 1990 to present. After the staring of reform and opening of China in 1980’, with the development of social economy, the ability of water supply is strengthened following the increasing demand of water resources. The ability of flood resourcification was developed to 140~150×108 m3 via all kinds of means, such as the methods of raising flood-control level, cascade flood detention and the urban rainfall collection. The stages characteristic of flood resourcification in Hai Basin is closely relative to the history of water resources development of recent 50 years (Guo et al., 2000).
THE EVALUATION OF THE POTENTIAL CAPACITY OF FLOOD RESOURCIFICATION IN HAI BASIN
Comparing with the flood resourcification ability, the potential capacity of flood resourcification can be defined as the total amount of surface runoff except of the minimum water demand in downstream (including minimum domestic, industrial, agriculture, and ecosystem water demand).
This potential capacity is impacted by two factors: water cycle and water utilization measurements. Water cycle presents the yield of flood resources in naturally condition and water utilization measurements present the water management ability in both projection and non-project.
Accordingly, the approaches of flood resourcification shown in Figure 1, each approach can drive out a way figure out its capacity of flood resourcification, such as reservoir optimum operation, actively and optimally use flood detention and storage area etc. However, it should be pay attention that the sum of potential capacity of each approach will be not the actual one of whole region.
It is easy to find that there is a conflict between storing flood in reservoir and in flood detention. Only when the flood of exceeding standard takes place, will the two potential be calculated respectively by the two methods be effective. Thus, it is difficult to evaluate the whole basin potential of flood resourcification by each approach alone. So a comprehensive method is put forward.
This method is based on the implication of flood resourcification. As mentioned above, all unused water resources, named surplus water, can be seen as the flood resources no matter whatever it is flood in general meaning or not, whatever the reason the water is remained.
The definition of surplus water is case by case with evaluation objects. In the Hai Basin, if the evaluation object is province, city or district, the surplus water as the potential of resources is the quantity of water flowing out from this province, city or district into the adjacent areas or the Bohai Sea. If the evaluation object is basin, the surplus water is the water flowing out from the basin into the next areas or the Bohai Ocean. Therefore, by analyzing the outflow amount, the potential of flood resources can be calculated from the point of view of the natural resources.
With further studying the constitution and effect of the discharge outflow, it can be divided into three parts as the normal supply water to the inflow area, a part of natural water resources in the inflow area and the ecological water in rivers or into the sea. The formula is follow:
(2)
Where is the water outflow; is the normal supply water to the downstream area and should be deducted from the amount of surplus water since it has been utilized;is the ecological water in rivers or into the sea and should be satisfied minimally; is the exactly surplus water flowing into the downstream area.
Another formula is shown followed where is regarded as the amount of outflow water without the normal supply water to the downstream area:
(3)
Taking out the minimum ecological water demand from the outflow, , the potential of flood resources, can be calculated. And then the following formula is easily to get:
(4)
If the amount of 10~20% total runoff in the area can be regarded as the minimum ecological water demand for river or sea, in simplify, is easy to figure out. In case of estimate the actual situation of ecosystem, a nearly ten-year river inflow data at the non-flood season is used as a reference of minimum ecological water to correct the amount of 10~20% total runoff as follow:
(5)
Where is annual surface runoff of recent each year; is actually outflow into sea in non-flood season of resent each year; p is 10~20%, n is the years.
This comprehensive evaluation method according to the amount of outflow is based on the ability of flood control at a certain time in the basin. When the time expresses the status of present, the result evaluated is the presently potential of flood resourcification.
It should be careful to select the evaluation area since the net outflow water is referenced. The conflict may occur in the utilization of resources and the competition may take place in evaluation of potential, since the outflow of an area may be the inflow of another area. As far as the Hai Basin is concerned, the case study region, considering the actually dispatch of water conservancy project, the province and the whole basin is regarded as the evaluation element.
According to the method mentioned above, the present status of utilization of flood resourcification for eight provinces and in Hai Basin is evaluated. The results are shown below.
Table 1. The Potential Capacity of Flood Resourcification in Hai Basin
Unit: 108m3
Year① / Rain fall
② / Surface
runoff
③ / Total discharge into the sea
④ / Discharge into sea in flood season
⑤ / Discharge into sea in non-flood season
⑥ / 15% of surface runoff
⑦ / Minima
ecological water demand
⑧ / Potential capacity
⑨
1985 / 1724 / 186.61 / 35.50 / 27.47 / 8.00 / 27.99 / 19.06 / 17.94
1986 / 1368 / 187.06 / 49.70 / 35.74 / 13.98 / 28.06 / 19.06 / 26.22
1987 / 1731 / 181.21 / 45.00 / 33.59 / 11.38 / 27.18 / 19.06 / 24.06
1988 / 1761 / 231.70 / 55.30 / 42.60 / 12.69 / 34.75 / 19.06 / 33.04
1989 / 1377 / 126.30 / 12.60 / 6.97 / 5.58 / 18.95 / 19.06 / /
1990 / 2063 / 242.99 / 61.10 / 52.10 / 9.02 / 36.45 / 19.06 / 42.58
1991 / 1693 / 216.81 / 67.30 / 59.10 / 8.26 / 32.52 / 19.06 / 49.55
1992 / 1412 / 132.20 / 6.55 / 2.87 / 3.68 / 19.83 / 19.06 / /
1993 / 1507 / 147.07 / 25.40 / 19.19 / 6.19 / 22.06 / 19.06 / 9.66
1994 / 1841 / 309.72 / 109.00 / 100.80 / 8.12 / 46.46 / 19.06 / 91.23
1995 / 1914 / 312.56 / 113.00 / 93.70 / 19.37 / 46.88 / 19.06 / 84.20
1996 / 1899 / 380.74 / 175.00 / 142.20 / 33.14 / 57.11 / 19.06 / 132.63
1997 / 1166 / 129.54 / 16.20 / 6.02 / 10.20 / 19.43 / 19.06 / /
1998 / 1752 / 207.71 / 42.80 / 36.00 / 6.78 / 31.16 / 19.06 / 26.50
average / 1668 / 213.73 / 58.18 / 47.03 / 11.17 / 32.06 / 19.06 / 38.40
By the table 1, the minima ecological water demand is the average of discharge into sea in non-flood season (row ⑥) and 15% of surface runoff (row ⑦) from 1985 to 1994. the potential capacity of flood resourcification is 1/2 of minima ecological water demand subtract from discharge into the sea in flood season (row ⑤). The average potential of flood resourcification is around 38.4×108m3.
Based on the actual water discharged into the sea of Hai Basin from 1985, the potential flood resources are calculated. Since the extraordinary flood in 1996, the amount of water discharged into the sea increased suddenly in these years. Therefore, the average value is difficult to judge the hydrological condition that is corresponding hydrological frequency year. So, by reference the hydrological frequency in each year, the potential of flood resourcification in different frequency in both whole Hai Basin and each provincial or district can be calculated as Table 2.
Table 2. The potential of flood resourcification at the present status in different frequency
Unit: 108m3
District or provincial / Frequency / Comment5% / 25% / 50% / 75% / 95%
BeiJing / 58.06 / 11.23 / 5.54 / 3.66 / 2.88 / Outflow into other
Provincials or districts
HeBei I / 55.07 / 13.00 / 6.98 / 4.85 / 3.93
ShanXi / 29.08 / 14.21 / 5.81 / 2.37 / 1.16
HeNan / 19.27 / 7.61 / 2.39 / 0.75 / 0.30
NeiMeng / 1.81 / 1.35 / 0.94 / 0.65 / 0.48
HeBei II / 417.76 / 54.54 / 4.28 / 0.34 / 0.04 / Discharge into the sea
TianJin / 120.44 / 25.26 / 3.58 / 0.51 / 0.11
LiaoNing / 3.93 / 1.91 / 0.77 / 0.31 / 0.15
ShanDong / 63.02 / 13.34 / 1.92 / 0.28 / 0.06
Basin / 1176.61 / 138.99 / 9.63 / 0.67 / 0.08
Considering the year at 50% frequency, the potential of flood resources in Hai Basin is 9.63×108m3 and in the year of 25% frequency, the potential of flood resources is 139×108m3. Corresponding to the drought year at 75% frequency, the outflow water is almost zero. Therefore, the potential of flood resourcification in Hai Basin is about between 10~140×108 m3.