**6.2 Lake Biwa, Japan**

Lake Biwa is located in the central part of Japan, and it is the largest lake in Japan with a surface area of about 681 km2, water volume about 27.6 km3, average depth of 44 m and the maximum depth of 104 m. The lake extends north to south for about 65km, and there are about 40 inflow rivers with residence time of 5 years and a single outlet river, located at the southernmost end of the lake. Lake Biwa consists of a larger north basin and a smaller south basin, and it is a valuable water resource for 14 million people living in this area.

In this section, some typical lakes in the world will be discussed, and the application of the

Lake Dianchi is the sixth largest freshwater lake in China and a capital city of this province with population of 6 million is located adjacent to the lake (see Fig. 7). The lake is divided into two parts: the northern, smaller part is called Caohai, with a surface area of 7.5km2 and an average depth of 2.5 m; the larger southern and main body of the lake is called Waihai, with a surface area of 292km2 and an average depth of 4.4 m. There are more than 20 major rivers flowing into the lake from the east, south and north. The lake water has been used to support industrial development, urban drinking water, navigation, tourism and irrigation etc.

Due to the rapid growth of population and economic development in the basin (6 million in 2006, only 1.5 million in 1980), this lake has received more and more wastewater that is yielded from the catchment. In 1995, the wastewater was up to 185 million tons, among them, TP (total phosphorous) 1021 tons, TN 8981 tons, more than half of which was nonpoint source pollutants from the agricultural fertilizer or pesticide. The algal blooms have been emerged from the late 1980. The lake has been listed in the ''Three Important Lakes Restoration Act in China'' by the central government. Huge investment has been spent for the remediation, but none of them has been proved effective. The city currently faces a difficult dilemma: whereas on one hand many efforts have been undertaken to improve the local water environment, the pollution problem is still overwhelming. On the other hand, the city is growing and its dependence on the lake, though already severely problematic, is

Gray and Li (1999) reported that if Dianchi Lake is to have the high water quality as it had in the 1960s, the TP inflow through surface water should be less than 60 tons per year. Although the government has made many attempts to reduce the TP, Huang et al (2007) drew a pessimistic conclusion: ''The TP load reduction envisaged as realistic would only stabilises the lake water quality by about the year 2008; unfortunately, interventions could

This is understandable as the government does not use the strategy of SPP. Similar to Taihu lake, once the proposed strategy is used, only the clean water is allowed to enter the lake, when the water crisis is curable. The required inner dike is about 163km for the lake to implement the SPP strategy, and the construction of this levee and its associated sluice gates

Lake Biwa is located in the central part of Japan, and it is the largest lake in Japan with a surface area of about 681 km2, water volume about 27.6 km3, average depth of 44 m and the maximum depth of 104 m. The lake extends north to south for about 65km, and there are about 40 inflow rivers with residence time of 5 years and a single outlet river, located at the southernmost end of the lake. Lake Biwa consists of a larger north basin and a smaller south

basin, and it is a valuable water resource for 14 million people living in this area.

**6. Potential application of SPP strategy to other lakes in the world** 

proposed SPP strategy to these lakes will be assessed.

**6.1 Dianchi Lake, China** 

still growing (Huang et al., 2007).

**6.2 Lake Biwa, Japan** 

not return the lake to its former pristine condition.''

is only a small fraction of the cost required by other alterative.

Fig. 7. The Lake Dianchi basin in China

Fig. 8. The Biwa Lake, Japan (after Mori et al. 1984)

Novel SPP Water Management Strategy and Its Applications 257

3. The SPP strategy refers to water separation, clean water protection and prevention from external pollution. Currently in the world, all reservoirs and lakes' water are exposed to external wastewater with no countermeasures taken to protect the stored water, and the incoming river water has never been separated. Consequently, all clean lake/reservoir water has been polluted and the storage capacity is quickly lost by sedimentation. 4. In this book chapter, we discussed some typical lakes/reservoirs in China and Japan, like Sanmemxia Reservoir, China's second, third and sixth largest lakes and Lake Biwa in Japan. To solve problems in these lakes, the SPP strategy is very effective. The water quality can be restored to acceptable level in a short period and the life span of these lakes can be extended significantly. All construction needed for SPP is only an inner dike with sluice gates. The longest dike for these lakes is about 240km, and the

5. Generally, for a given catchment, there always exist threats like flood disasters (too much), droughts (too little), deterioration of water quality (too dirty) and siltation (too

6. In this book chapter, we only outlined the application of the SPP to the mentioned lakes, but in principle, the strategy is valid to all other large water bodies. Next, more detailed research like physical and/or numerical models are needed before it can be used in practice. Eventually, it is subject to the decision maker/politician's decision.

The works are supported, in part, by the open fund provided by State Key Laboratory of Hydraulics and Mountain River Engineering at Sichuan University, China (SKLH-OF-1002); the open fund from Nanjing Institute of Geography and Limnology, China (2010SKL005). National Science Foundation of China (50679046 and 51061130547) and the Ministry of

Davis, J.R. and Koop K. (2006). "Eutrophication in Australian rivers, reservoirs and

Du, Y., Cai, S., Zhang, X. and Zhao, Y. (2001). Interpretation of the environmental change of

Gleick, P.H. et al . (2004). *The world's water 2004-2005. The Biennial Report on Freshwater* 

Gray, A.V., Li, W., 1999. Case study on water quality modelling of Dianchi Lake, Yunnan Province, South West China. *Water Science and Technology*, 40(2), 35–43. Hallegraeff, G.M., 1993. A review of harmful algal blooms and their apparent global

Heisler, J., Glibert, P. M., et al.. (2008). "Eutrophication and harmful algal blooms: A

Huang, D. B., Bader, H. P., Scheidegger, R., Schertenleib R., and Gujer, W. (2007).

Confronting limitations: New solutions required for urban water management in

satellite image analysis. *Geomorphology*, 41, 171-181.

scientific consensus." *Harmful Algae*, 8(1), 3-13.

Kunming City, *J. Enviro. Management*, 84, 49–61

estuaries-a southern hemisphere perspective on the science and its implications.

Dongting Lake, middle reach of Yangtze River, China, by 210Pb measurement and

maximum height of these dike is about 10m.

Science and Technology of China (2007CB714150).

Hydrobiologia, 559, 23-76.

*resources*. Island Press.

increase. *Phycologia*, 32, 79-99.

**8. Acknowledgment** 

**9. References** 

turbid). SPP strategy is effective to all these problems.

*The problems that the lake has include*: the eutrophication of the lake caused by wastewater, which led to algal blooms in the lake has started in 1980s. After that, even the percentage of domestic wastewaters treated in the basin had increased from 1.7% in 1975 to 78.2% in 2004, and the removal rates of N and P have also been improved, the chemical oxygen demand and the NO3 and PO4 concentrations in the surface layer water have not been improved as expected (Nakano, et al. 2008). The analysis shows that the lack of improvement in the water quality of the lake is that the environmental loads from nonpoint sources are unexpectedly greater than those from point sources such as domestic wastewater. Especially, N and P of agricultural origin have a great effect on the eutrophication of the lake. This citation clearly indicates that without SPP strategy, it is impossible to provide very clean water to the users with the control of point-source pollution only, as the agricultural wastewater has been increased steadily to increase the food production.

*Application of SPP strategy to the lake*: The cause of nutrophication in Biwa lake is very clear: no measured has been taken to separate the agricultural wastewater with the clean rainwater, because this lake has not had the industrial and domestic wastewaters like other lakes in the world. In other words, the water quality of lake Biwa can be improved significantly if N and P from agricultural sources are reduced significantly, but so far no any technology except SPP can reach this goal.

Currently, all N and P yielded from farm lands in the basin are collected by the lake, and eventually it mixes with the clean lake water and the mixing leads to the eutrophication in the lake. However, if the 133km inner dike is constructed along the 10m contour, then all unwanted river water with high concentration of N and P will by-pass the lake, and only the clean river flow is allowed to enter the lake. Thus the N and P level in the lake can be significantly lowered to an acceptable level, and no algal blooms will occur.
