Principle Investigator: Prof. J.H.W. Lee
The East River, 562 km long and with drainage area of 35340 km2, is one of the three major rivers of the Pearl River system – the largest system in South China. The river is a main source of water supply for Hong Kong, Shenzhen, Guangzhou and Dongguan. It currently supplies 1 billion m3 per year to Hong Kong; and this is projected to increase to 1.4 billion m3 in 2010. The integrated management of the East River is of foremost importance in the sustainable development of Hong Kong and the Pearl River Delta. And yet an integrated understanding is lacking on key water environment issues related to river dynamics, water quality, river ecology, river-coast interaction, and trans-boundary environmental material flows.
The project proposes to carry out field investigations, basic laboratory studies and numerical modeling on watershed management, river dynamics, water quality, and river eco-system, with specific reference to the East River. A comprehensive river health index will be developed based on the following 10 indices: (1) flood disaster, (2) watershed vegetation and erosion, (3) mountain tributaries channel morphology, (4) stem river channel stability, (5) sediment transportation, (6) working index (power generation, water supply, navigation, recreation and land creation), (7) water quality, (8) habitat and biodiversity index, (9) human-induced stresses, (10) restoration.
Objectives and long-term impact
Rivers carry not just water, but just as importantly sediments, dissolved minerals and the nutrient-rich detritus of plants and animals, both dead and alive. The ever-shifting beds and banks and the ground waters below are all integral parts of rivers which are also habitat of numerous species. Internationally, many countries have taken an increasing interest in integrated river management co-ordinating various sectors of river issues. Developing countries like China now strongly emphasize their goal of flood control and environmental protection besides reducing poverty by supporting efficient and sustainable development of agriculture and light industries. Integrated river management aims at reconciling the provision of safety to the people dwelling by the river and the land and water for sustainable use, while maintaining sound river ecology (Odum, 1971, 1989). Significant advances have been made in dealing with problems related to flood control, water quality and eutrophication, channel stabilization, sediment disasters, inland navigation, watershed vegetation and erosion management, habitats and ecological restoration. Nevertheless, there is still a lack of integrated river management taking account of the river disaster reduction, watershed management, fluvial processes, river-use, human stresses and river environment and ecology simultaneously.
The objective of this project is to combine the outstanding research strengths of the mainland research team on watershed vegetation, sediment transport, river geomorphology, urban dynamics, and environmental assessment with the proven expertise of the Hong Kong team on environmental hydraulics and hydrology, ecological management and water quality modeling to develop joint research in integrated river management. This is a critical step to provide a sound scientific basis for sustainable water management.
The East River, 562 km long and with drainage area of 35340 km2, is one of the main rivers of the Pearl River system. The river is the main source of water for Hong Kong, Shenzhen, Guangzhou and Dongguan cities. The annual runoff is 32.4 billion m3. It currently supplies Hong Kong 1 billion m3 water per year and the volume of water supply will increase to 1.4 billion m3 in 2010. The river managers and scientists are challenged by many problems, soil erosion, river sediment management, channel stability, urban sewage discharge, water pollution, habitat reduction and deterioration, ecological restoration; among them water quality (in particular nutrient input) is a main concern.
The project proposes to carry out field investigations, basic laboratory studies and numerical modeling on watershed management, river dynamics, river use, water quality and river eco-system, with specific reference to the East River. A comprehensive river health index will be developed based on the following 10 indices: (1) flood disaster, (2) watershed vegetation and erosion, (3) mountain tributaries channel morphology, (4) stem river channel stability, (5) sediment transportation, (6) working index (power generation, water supply, navigation, recreation and land creation), (7) water quality, (8) habitat and biodiversity index, (9) human-induced stresses, (10) restoration.
In addition to the integrated research outcomes in the form of joint papers in good international journals, workshop monographs, this research will provide a basis for decision support systems for the sustainable development of coastal cities and marine resources. The project will take the already established links to a more effective level of collaboration, and will likely spark off additional projects and student/staff exchange in the allied fields of civil and environmental engineering, earth sciences, ecology, urban planning and environmental management.
Rivers carry not just water, but just as importantly sediments, dissolved minerals and the nutrient-rich detritus of plants and animals, both dead and alive. The ever-shifting beds and banks and the ground waters below are all integral parts of rivers which are also habitat of numerous species. On the other hand, river flood is one of the major natural disasters costing 1/3 of the total loss of natural hazards (Wang and Plate, 2002). River-use was the engine of socio-development in the past and is nowadays even more important in economic and cultural development. Towns and cities use (and misuse) rivers to carry away their wastes. Rivers also serve as conduits for commerce. The role of rivers as the sustainers of life and fertility is reflected in the myths and beliefs of a multitude of cultures. Internationally, many countries have taken an increasing interest in integrated river management coordinating various sectors of river issues. Developing countries like China now strongly emphasize their goal of flood control and environmental protection besides reducing poverty by supporting efficient and sustainable development of agriculture and light industries. Integrated river management aims at reconciling the provision of safety to the people dwelling by the river and the land and water for sustainable use, while maintaining sound river ecology (Odum, 1971, 1989). It also aims at making water use economically productive, socially equitable and environmentally sustainable.
Erosion, sediment transport and deposition are the power of the fluvial process and also a great challenge to river managers and scientists (Lane, 1955, Wang, 1998, Wang and Lin, 2001). Watershed vegetation, including the riparian vegetation, is a fundamental controlling factor in erosion and river eco-functions (Anderson, 1978). Wang et al. (2003) developed a model of vegetation-erosion dynamics and a new theory on the vegetation process under the action of erosion and natural and human-stresses. For a watershed, vegetation and erosion may reach an equilibrium state if the circumstances maintain unchanged for a long period of time. However, the equilibrium is not stable. Ecological stresses, especially human activities, may disturb the balance and initiate a new cycle of dynamical processes (Wang and Wang, 1999). Mortality stress is defined as the stress directly causing mortality of vegetation. Volcano eruption, forest fire, debris flow, logging are examples of mortality stresses. Vigor stress is defined as the stresses causing only vigor reduction. Drought, pollution, grazing, windstorm, flooding are a few examples of vigor stresses. Under the action of vigor stresses, vegetation will ameliorate itself to fit the stressed environment. In some cases the changed vegetation can recover in a short period of time, exhibiting resilience. The resilience, re, is a function of the composition of species of the vegetation, the climate and precipitation, and the soil composition. The human-induced stresses are mathematically expressed and the differential equations of vegetation-erosion dynamics are theoretically or numerically solved. With the model calibrated with data of vegetation evolution, one may work out the so-called vegetation-erosion chart and predict the development trend of the vegetation and erosion, and roughly estimate the measures needed to permanently improve the vegetation and landscape. The vegetation of a watershed or an area may exist in three states, i.e. vegetation-developing and erosion-reducing, vegetation-deteriorating and erosion-increasing, and the transitional state between the two.
Rivers are dynamic due to the flows cutting the bed, scouring the banks and silting the floodplain and seas. All these are realized by moving sediment from one place to another. The capacity of the flow to remove sediment from one place to other places within a river section is called sediment-removing capacity (Wang et al., 2001). This capacity is the feature of unsteady, non-equilibrium flow and represents the capability of the flow to change the channel shape and location. Analysis with the measured data and numerical modeling demonstrates that the removing capacity depends mainly on the fluctuation intensity of the flow discharge and the power spectrum. The movement of a river channel within the fluvial plain is defined as the river motion. The patterns of river motion are aggradations, degradation, widening, translation, rotation, wandering, bifurcation, and migration from one channel to another channel. The speed of the river motion is given as a function of the sediment-removing capacity. The stability of a river channel is a function of the sediment-removing capacity and the river bed inertia.
The water quality is affected by the pollutants and sewage discharged into the river and the self-purification of river. The latter is in turn depends on the dilution and decomposition of pollutants. Environmental discharges undergo active jet mixing near the discharge point. Within the near field, the discharge itself generates the flow field and mixing. Numerical models have been developed to simulate the sewage jet flow and dilution in rivers and seas (e.g. Lee, 2000). Agriculture and urbanization cause eutrophication in river and estuarine waters (Wang et al., 2001). As a result the concentration of dissolved oxygen and the water quality is reduced and the eco-system is impaired (Lee et al., 1991a, b; Lee and Arega, 1999). The impaired river eco-system by various human-induced stresses can be assessed by using selected indicator species (such as macro-invertebrate) and biodiversity indices (such as the Shannon-Wiener diversity index) (Wang and Lee, 2003). Stream eco-system can be restored by employing instream structures (such as deflectors and weirs), control sediment movement to improve the substrate, reforestation to restore the plant community and reduce urban pollutant pulse (National Technical Information Service, 1999; Brookes and Shields, 1996).
The integrated river management study will be firstly conducted for the East River. The major pollutants in the East River are organic matters such as BOD, ammonia, COD, oil, and permanganate (Jin, 2001). The river system obtains the nutrients from diffuse input from the watershed (NPS) and by direct inputs to the river (PS). Point source (PS) pollution is derived from domestic sewage and industrial wastewaters; and non-point source (NPS) pollution from atmospheric deposition (precipitation), agricultural practices (fertilizers and pesticides), livestock farming (animal manure), soil erosion, among others. The NPS pollution is of greater environmental concern than PS pollution because they are ubiquitous and the task of cleanup is costly and hard to accomplish. The assessment of NPS pollution is a complex, multidisciplinary environmental problem that encompasses coupled physical and chemical processes occurring across a wide spectrum of spatial and temporal scales (Loague et al., 1998). Of special importance are the nutrient loads (total nitrogen N, total phosphorus P). High levels of these nutrients lead to eutrophication and undesirable water quality in water supplies, and may also impact downstream estuarine and coastal waters.
The nature of the linkage from the nutrient loads in the watersheds, through the transport in rivers, and finally to coastal waters is not straightforward. The river nutrient load is a complicated function of nutrient sources, hydro-geology, and land use. Given the complexity, much of the past research has been focused on the estimation of the average annual nutrient load of a basin. Thus, critical environmental issues such as identification of the locality most seriously affected by the NPS pollution and the temporal variation of river nutrient concentrations cannot be addressed. Moreover, only a few (e.g., Caraco and Cole, 1999; De Wit, 2000) have dealt with large river basins of the size comparable to the East River basin. In addition, there has been no comprehensive study on the dynamic interactions between surface water and groundwater in this catchment. As far as we are aware, distributed hydrological modeling has not been applied to investigate water pollution and ecological management at this regional scale.
The study team has carried out extensive field and modeling work in coastal water quality (Lee et al 1991a; Lee et al 2003) and hydrologic modeling (e.g. Jayawardena and Zhou 2000). Since 2002, pilot studies on non-point source pollution and regional hydrologic modeling have been initiated. An estimation of non-point source pollution for Hong Kong has been completed for the first time (Li et al., 2002); it was concluded that reliable river discharge is the most important factor in the estimation of river nutrient load. Due to insufficient stream flow measurements, hydrological modeling can be used to provide the flow conditions required for the estimation of nutrient load. More recently, preliminary modeling of the regional-scale hydrology of the East river basin has been attempted using the distributed physically-based hydrological modeling system MIKE SHE (Abbott et al., 1986) and the river modeling system MIKE 11. Initial results have been encouraging (see Figure 1).
Figure 1: Comparison between the observed daily streamflow (solid line) in 1987 and the MIKE SHE-MIKE 11 simulated streamflow (dashed line) at the two hydrological stations, one upstream and the other downstream, of the East river basin.
The project proposes to carry out field investigations, basic laboratory studies and numerical modeling on watershed management, river dynamics, river use and river eco-system, with specific reference to the East River. A comprehensive river health index will be developed based on the following 10 indices:
Disaster index – measured with the risk = the threatening natural event including its probability of occurrence by the value/human exposed and by the vulnerability (the lack of resistance to the damaging and destructive forces) (Kron, 2002).
Watershed vegetation and erosion index – measured with the vegetation-erosion chart and vegetation resilience (Wang et al, 2003).
Mountain tributaries river morphology - Step-pool sequence developed in mountain rivers may resist channel incision, protect riparian vegetation, stabilize the channel and provide sound habitat for biocommunity (Wang et al, 1997; Xu and Wang, 2003). The index is measured with the length of river bed with step-pool micromorphology / total length of the river.
Stem river index – Less dynamic channel provide human society and bio-community better physical environment for development. Meandering river is stable, environmental and ecological- sound channel pattern. The index is measured with the immovability 1/k (k is the river motion coefficient) + meandering river length / total length (Wang and Wu., 2001).
Sediment movement index – River channel needs a certain amount of bed load transportation to maintain balance (otherwise sediment-starvation and channel incision occur) (Wang and Lee, 2003). Less suspended load is better for the water quality and bio-community.
Working index - measured with the power generation / potential power resources + water volume diverted for irrigation and urban supply / total water resources + navigation channel length / total length + recreation water surface area / total water area. The workload on the river should maintain at a proper value. Too high working index may damage the health of the river (for instance, the flow was cut off very often in the Yellow River due to over diversion of water resources) (Wang, 1998).
Water quality – measured with the national water quality grading system (including DO, COD, BOD, heavy metals, and nutrients) (Liu et al, 2002).
Eco-index -- For the biodiversity in the river eco-system Shannon-Wiener index is employed (Krebs, 1978). For special species (fish) the habitat unit HU is employed to assess the habitat changes (USFWS, 1981).
Human-induced stresses – measured with Hs1 (agricultural area / total drainage area) + Hs2 (urbanization area / total area) + Hs3 (total reservoir capacity / total annual water) + Hs4 (channelized length / total length).
Restoration index – measured with the investment in the river restoration, structural and non-structural restoration measures for stabilization of the channel, protection of water quality and environment (including waste water treatment, erosion control and reforestation), mitigation of impact of human-activities on the river ecology (management of the river bed substrate, instream habitats and reservoir operation revised for the purpose of eco-hydraulics).