Integrated Physical and Ecological Management of the East River
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Integrated physical and ecological management of the Water Science & Technology: Water Supply East River J.H.W. Lee*, Z.Y. Wang** , W. Thoe* and D.S. Cheng* *Department of Civil Engineering, The University of Hong Kong, Hong Kong, China (E-mail: hreclhw@hkucc.hku.hk; wthoe@hkusua.hku.hk; dsh_cheng@yahoo.com) **Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China (E-mail: zywang@tsinghua.edu.cn) Abstract We present an independent assessment of the health and water sustainability of the East River (Dongjiang) in South China, which is the source of nearly 80% of Hong Kong’s water supply. Field measurements show that the water quality in the upper and middle reaches is generally good and well exceeds the drinking quality standard, with high bio-diversity. The streamflow of the East River Basin is satisfactorily simulated using both the distributed MIKE-SHE model and the lumped HSPF model. With an Vol 7 No 2 pp 81–91 average streamflow of 760 m3/s, the River is able to satisfy the current water demand. Using the HSPF model, the water quality is found to have deteriorated in recent years. In addition to water supply, the River also supports a variety of needs such as hydro-power generation, waste assimilation, navigation, habitat for aquatic life, and expulsion of sea water intrusion. Using the projected need of 150 m3/s for water supply, the instream flow requirement based on hydrological and water quality simulation is estimated to be 467 m3/s in 2010. This suggests that the water sustainability of the East River requires alternative strategies, which may include integrated water resources management, provision of better wastewater treatment, and water and Q soil conservation. IWA Publishing 2007 Keywords Bio-diversity; East River; instream water requirement; integrated river management; sustainability; water quality modelling Introduction East River (Dongjiang) is one of the three main tributaries of the Pearl River (Zhujiang) system, the fourth largest river system in China. It is 562 km long and has a drainage area of 35,340 km2, with an annual average precipitation of 1,750 mm and runoff of 32.4 billion m3 (Figure 1(a)). The water resources in the East River has been harnessed through three major reservoirs: Xinfengjiang, Fengshuba and Baipenzhu, which are of great importance to the flood control, power generation, irrigation, navigation, and water supply of the Guangdong province. The river is the main source of water supply for Hong Kong, Shenzhen, Dongguan, and Guangzhou. Currently, the East River provides approximately 80% of the potable water supply in Hong Kong. The population in the East River Basin has increased from about 7 million in 1985 to 10 million in 2004, and is projected to reach 12 million in 2020 (Figure 1(b)). The population growth and associ- ated anthropogenic activities have led to drastic changes in both demand and supply of water in the region. Problems such as deterioration in water quality have been reported in both the main stream as well as their associated tributaries (Wang and Zhou, 1999; Zhang and Wu, 1999; Ho and Hui, 2001). The East River Basin is dominated by forests and woodland (Figure 1(c)); urban and agricultural land use are concentrated in the middle and lower reaches, where water pollution has been associated with an increase in industrial and domestic sewage discharges (Hills et al., 1998). Total wastewater discharge in the East River is predicted to increase from 109 t/a in 1998 to about 2.3 £ 109 t/a in doi: 10.2166/ws.2007.043 81 J.H.W. Lee et al. Figure 1 The East River Basin: (a) location of key cities and hydrological stations; (b) population and wastewater loading; and (c) land use pattern in 2000 2020. The sustainability of the water resources in the East River Basin is of foremost importance to the development of Hong Kong and the Pearl River Delta. And yet, as far as we are aware, this issue has hitherto not been addressed in a comprehensive scientific investigation; field data on bio-diversity has also not been reported. In this paper we per- form an independent assessment of the river health and water sustainability based on field studies, distributed hydrological modeling using MIKE-SHE, and lumped water quality modeling using HSPF. Environmental and ecological assessment During 2004–2006, nine field investigations to the East River Basin have been carried out. The water quality is measured along the mainstream in both the dry season (April 2006) and the wet season (July 2005). In each investigation, the common water quality par- ameters (DO, pH, conductivity, temperature) are measured on site, and samples are taken for subsequent analysis for nutrients, suspended solids, and bio-diversity using standard methods. Figure 2 shows the distribution of dissolved oxygen (DO), ammonia nitrogen (NH4), nitrate (NO3), and phosphate (PO4) along the river. In general, the water quality in the East River is better than other large rivers in China. In the dry season, it can be seen that the water quality in the upper and middle reaches (e.g. above Heyuan) is generally good and well exceeds the drinking water quality (Chinese National Water Quality Grade II) standard. The DO is close to saturation and the ammonia nitrogen is negligibly small compared to the drinking water quality standard of 0.5 mg/L. Towards the river mouth, below Boluo, however, there is notable organic pollution; the DO deceases with significant increase of ammonia nitrogen and phosphate. The same spatial trend is observed in the wet season; the higher NH4 concentrations measured may be contributed by non-point pol- lution sources brought to the river by rainfall and overland flow. Also, DO concentration is about 1 to 2 mg/L lower in the wet season. NO3 and PO4 concentrations are low in both seasons. An aggregate measure of river health can be provided by a Water Quality Index (WQI, Sˇtambuk-Giljanovic´, 2003). The WQI ranges from 0 to 100, and is based on the measured values of temperature, DO, pH, conductivity, NH4 þ NO3,PO4 and TSS. 82 For each parameter, a score is given and the scores are aggregated by a weighting factor J.H.W. Lee et al. Figure 2 Measured water quality along the mainstream of the East River P 2 to obtain the river health index WQI ¼ð1=100Þð WiQiÞ , where Q ¼ score, and W ¼ weighting factor. Details of the calculation method can be found in Fan et al. (2005). In addition to water quality, the algal and benthic macro-invertebrate bio-diversity are investigated on November 2004 and July 2006 respectively for examining the impact of anthropogenic activities on river health. Figure 3(a) shows the location of the sampling sites. Among these, four sites are selected to study the species composition of epilithic diatoms (attached to rocks and stones) and their suitability for river health assessment. These include the Xinfengjiang (XFJ) and Baipuhe (BPH) near Heyuan, as well as Simeizhou (SMZ) and Xizhijiang (XZJ) near Huizhou. Figure 3(b) shows the measured WQI and the algal community diversity in terms of the Shannon-Wiener index (H; based on the number of individuals in each species). It can be seen the WQI is generally around Figure 3 (a) Location of sampling sites; (b) measured algal bio-diversity 83 80 near Heyuan but decreases to around 50 in the downstream reaches near Huizhou. However, the WQI and the algal bio-diversity do not appear to be correlated. The Shannon-Wiener diversity index falls within the typical range of 1.5–3.5; at the XFJ site below the Xinfengjiang Reservoir, the low bio-diversity is believed to be related to the reservoir operation. Further details on the algal bio-diversity measurement can be found in Fan et al. (this volume). Aquatic macro-invertebrates have been used as indicators of J.H.W. Lee stream and riparian health (Wright et al., 1989; Chutter, 1998; Karr, 1999; Smith et al., 1999). Thirteen sites have been surveyed from upstream tributaries to the lower reaches of the East River to collect benthic invertebrates and environmental data. A total of forty- et al. one insect families have been found. Figure 4 shows the taxon richness (total number of species) at each of the sites. The highest benthic bio-diversity is measured at two rela- tively pristine stations upstream; the lowest diversity is recorded at the most downstream sampling station which is characterized by high turbidity, poor water quality, silt sub- strate, and lack of insect fauna. The WQI is strongly correlated with the benthic diversity along the East River. Hydrological modelling of the East River basin In view of the scarcity of streamflow data, a physically-based distributed model, MIKE- SHE, is employed to study the spatial and temporal variation of streamflow; this is the first time that such a distributed model has been applied to the East River. MIKE-SHE incorporates the topography of the basin derived from Digital Elevation Model (DEM) and uses the spatially distributed rainfall and potential evapo-transpiration as model inputs (Abbott et al., 1986a,b). The hydrological data from eleven precipitation stations, eleven streamflow stations, and eight stations for potential evapo-transpiration are used for model calibration (1969–1973) and validation (1974–1978). The daily averaged streamflow at eleven hydrological stations is predicted; Table 1 shows the accuracy of the hydrological 2 simulationP as evaluatedP by statistical indices including the Nash-StucliffeP coefficientP R ¼ n 2= n 2 n 2= n 2 1 2 i¼1ðPi 2 OiÞ i¼1ðOi 2 OÞ and CD ¼ i¼1ðOi 2 OÞ i¼1ðPi 2 OÞ respectively, where CD ¼ coefficient of determination, and Oi and Pi ¼ daily averaged observed and predicted streamflow respectively, and O ¼ mean observed streamflow.