ENVIRONMENTAL DEGRADATION AT THE DOWNSTREAM AND MOUTH OF TRA KHUC RIVER: CAUSES AND PROTECTION SOLUTIONS

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1 Vietnam -Japan Estuary Workshop 2006 August 22 nd -24 th, Hanoi, Vietnam ENVIRONMENTAL DEGRADATION AT THE DOWNSTREAM AND MOUTH OF TRA KHUC RIVER: CAUSES AND PROTECTION SOLUTIONS Abstract NGUYEN VAN SY Faculty of Hydrology and Environment, Vietnam Water Resources University 175 Tay Son, Dong Da, Hanoi, Vietnam Tra Khuc River takes the most important role on transporting the major amount of rainfall water to the sea as well as supplying water for coastal plain of Quang Ngai province. Recently, the aquatic environment at downstream and estuary area of the river has been degraded. This paper analyses the causes of the degradation and proposes combined solutions to control the process of environmental degradation in the area of which solution of improvement and innovation in water resources planning and management taking consideration of water demand for ecosystems and environmental flow is shown as an urgent one. 1. INTRODUCTION Tra Khuc River is one of the largest in Quang Ngai Province with the catchment area of km 2. About 1 million people are living in the river basin, 87% of them are in rural area. There is heavy rainfall in the upstream area so that the mean annual runoff module is 70 l/s.km 2, a high number in Vietnam. With such an abundant source of water, however, downstream area is facing with water shortage, especially at the river reaches from Quang Ngai town to the river mouth. In dry season, the depth of runoff at the cross-section near Tra Khuc bridge is very low, and water is nearly stagnant. The situation is mainly caused by diversion of Thach Nham weir. Through assessment of water use situation; assessment of water resource and ecosystem degradation; and investigation of causes and consequence of the degradation, the integrated solution that includes management, technical and institutional ones have been proposed to restrict water source depression and for exposing the requirement for investigating and assess environmental flow for downstream and estuary area of Tra Khuc River from Thach Nham weir to Cua Dai mouth. Figure 1 Map of Tra Khuc River Basin

2 Environmental flows (EF) are defined as the stream flow necessary to sustain habitats (including channel morphology and substrate), encourage spawning and the migration of fauna species to previously unpopulated habitats enable the processes upon which succession and biodiversity depend, and maintain the desired nutrient structure within lakes, streams, wetlands and riparian areas. Environmental flows may comprise elements from the full range of flow conditions, which describe long-term average flows, variability of flows including low flows and irregular flooding events. Both the principles and practice of EF are still rather new to Vietnam, with limited awareness and understanding throughout the country. The understanding of EF as indicated in project documents and environmental impact assessments was limited to the concept of single minimum flow set through hydrological calculation. The study site mentioned in this paper focuses within 108 o o Eastern longitude and 15 o o Northern latitude. 2. METHODS In order to carry out this research and withdraw the results as presented and discussed in this paper, the following methods and techniques are used: - Field investigation method to collect data, to assess the actuality of water use and exploitation, to assess water resources and environment degradation at concerned river basin. - Statistical analytical method to assess water resources, water accounting, to evaluate and forecast water source degradation in river basins. - Systematic analytical and mathematic simulation method to build up mathematic models of EF and EF management. - The expert panel method to assess environment impact and the effect of keeping alive EF of river basin. - The technique of remote sensing and geographic information system 3. RESULTS AND DISCUSSIONS 3.1 Flow change and water resources degradation at the downstream and estuary areas of Tra Khuc River- causes and consequences In dry season Thach Nham irrigation system with headwork is Thach Nham weir that locates at the main stream of Tra Khuc River, 40 km far from the sea, irrigating for nearly ha of cultivated plain land at the downstream and coastal area of Quang Ngai province. Sometimes in the dry season, amount of irrigation water is about 50 m 3 /s but the lowest water incoming flow to the weir is about 30 m 3 /s. Consequently, during 8 months of the dry season, in some periods of time, Thach Nham weir takes all the basic runoff of Tra Khuc River. Year 2003 saw severe drought in Vietnam and in other Southeast Asia countries with 64 days having no water spreading over the weir. The drought season is from April to August, especially at May, June and July. This is the time when summer-autumn crops take the largest amount of water from North and South canal systems as shown in Figure 2. Due to lacking of water overflowing the weir, the downstream reaches from Quang Ngai town to the sea is dried up severely. The river environment and ecosystem are damaged and degraded heavily. Wet cross section of the river is narrower and flow is interrupted at some reaches. Transportation by boat from river mouth to the upstream cannot be happened. There are times that people can wade cross the river at Tra Khuc Bridge section easily because water level is under their knees. The coming flow to the downstream area fast decreases so it is not enough to dilute water in the river causing severely

3 water pollution. Every time Quang Ngai sugar-mill discharges waste water to the river causing water pollution, many dead fish emerging on the surface. The situation of water shortage effects heavily on domestic water supply at the downstream area, abuses the scenery and makes difficulties for tourist development and navigation. According to investigation from the masses, in the past, Tra Khuc River at the downstream area had significant depth; water transport and fishing activities were crowded; trading from the upstream to estuary area was mainly by boats, and along the river there were water wheels turning round to take water to the fields. It can be said that the life of the people tied closely with the value of the river. But nowadays, this area is severely degraded and exhausted, the river environment and ecosystem is heavily injured and depressed. In the past, there were some special species such as grain goby, thai bai fish which have the high economic and eating cultural value in the riverine ecosystem. Those species disappear gradually with the aquatic environment depression. The people living in the area regret for the situation and desire to conserve those species. Those fishs have some characteristics such as: clearly categoried, easy to identify, easy to have sample outdoor, high in quatity, widely distributed, high economic value, easy to feed in labs and hard to vary so that those can be used as indicator for biological monitoring (Nguyen, 2006; PCQ-GI, 2000). Incoming flow to the weir Over flow through the weir (day) Figure 2 Graph of incoming to & over flow Thach Nham weir in the dry season 2003 Apart from the impact of Thach Nham weir as stated above, the exhaustion status of water resources was due to other causes such as the degradation of the surface of upstream area resulting from shortcoming and weakness of integrated river basin management. The degradation of the surface of the upstream area causing by deforestation over the few decades also changes hydrologic regime of the river in comparison with the previous time In flood season As stated above, the rainfall within Tra Khuc River basin is rather large in Vietnam. Because of deforestation in the basin, especially in upstream forest, and of the high slope, in recent year flood flow has been gathered faster then before. According to investigation at Son Giang hydrology station at present time, the flood travel duration at the station is only 4-5 hours, haft of the duration of

4 years ago. The flow have impacted heavily and caused land slide on the right riverside of up bend wing and on the left riverside of down bend wing of every bend of 9 bends in total between Thach Nham weir and the sea. Flow dynamic with the discharge of over 1000m3/s caused erosion to the river banks which composed from sand clay and weak compacted clay. In the flood season, the water level is high, the stream have deep impact onto the river banks. At upstream area of Tra Khuc River, the river bank forming stone is weak. The higher the bank section and the more river bank slope are, the higher the risk of land slope is. Among the three causes of land slide (displacement of river-bed, flow dynamic, slope process), displacement of river-bed plays the main role, slope process takes the second place. The river reaches which has all the three causes has the danger of land slide. At upstream area of Tra Khuc River, there are 8 reaches having the risk of land slide, 2 of which are reaches at An Loc village, Tinh Long commune, and reaches from 1 st village to 5 st village at Nghia Dung commune which close to the estuary. 3.2 General assessment of shortcomings in water exploitation and use in the basin According to the situation of water use and exploitation, it can be seen that there are several significant shortcomings, which needed to be solved: 1. Water demand for ecosystem and for environment at downstream reaches of Thach Nham weir was not be considered when designing Thach Nham irrigation system. 2. Water exploitation and use in the river basin are inappropriate and unsustainable, primarily, there are no reservoirs at the upstream for retain rainwater in wet season and regulate for using in the dry one. Thach Nham weir as a headwork of irrigation system has limited capacity for regulation. 3. Water in the basin has not been used effectively, reasonably. Currently, water is used mainly for irrigation and is limited for aquaculture and industrial uses so that economic efficiency is still low. Water demand for environment, ecosystem, navigation and tourism has not been taken into adequate consideration. 4. Currently, there is no integrated water resources plan and no principles for water allocation for different water users, especially for protecting aquatic environment. Consequently, there is no direction to deal with thorny problems and contradiction in water use among branches, between water use for people and for ecosystem. 5. There is no river basin organization, which takes responsibility to manage activities in Tra Khuc River basin. 3.3 Invesigation to propose solutions for reducing water sourse degradation at the downstream and estuary area Base on analysis the shortcomings, general solution including different group of measures for each stage to obtain the general target to overcome drawback, unsustainable elements in water use to restore river flow, the following solutions can be proposed: Improvement and innovation in water resources planning and management including consideration of the water demand for ecosystem and EF Renovation in planning It s necessary to make integrated water resources planning in the river basin including the component plans on water resources protection and ecosystem protection for gradually restoring water resources and maintaining EF in the river. In this plan, it should consider water demand for ecosystem and need of EF and bring it into alternatives of water exploitation and use and ecosystem protection in the river. The proposed solution in the plan and its implementation in practice will be bases for restoring the river from degradation and exhaustion. Renovation in management It s necessary to make strictly control of water exploitation and use in the main stream to stop environmental degradation at the downstream

5 3.3.2 Improvement and development institution related to protecting water ecosystem and EF management Water use management in river basin is infected. It is necessary to organize management system that with available necessary policy for management. Policy relating to management and control of water resources degradation It is necessary for investigating and proposes policy to have management and control water resources degradation status in the river basin. Policy relating to EF Investigation on EF and propose policy relating to EF management is very necessary. It creates legislation bases to take out water demand for environment to consider in planning alternated for water exploitation and use of river basin as well as improving existing water development structures in order to meet requirement of EF as in water resources management policy of America, Australia, and South Africa etc, in recent decades Engineering solutions including complement, improvement of existing and proposals of new water resources development structures to meet the demand of and maintain EF For regulated river as Tra Khuc River, the engineering or technical solutions are indispensable and they also can be called construction ones. The targets of construction are water resources development structures those may be divided into three categories: (i) existing; (ii) under construction and (iii) new ones. Content of these solutions as in the table below: Type of Content of solution structures Existing water resources development structures Small reservoir in the upper stream like Cu Va reservoir Thach Nham weir/irrigation system Under construction structure Nuoc Trong dam/reservoir - To assess requirements to maintain EF in the down stream of the dams - To upgrade and modify to add regulated sluice for the down stream. - To adjust reservoir operation to meet irrigation requirement and EF demand - To assess requirements to maintain EF in the down stream of the weir - To upgrade and modify to add regulated sluice for the down stream. - To operate head intake and the regulated sluices with consideration of meeting EF for the downstream reaches of the river. Nuoc Trong reservoir is at beginning stage of construction. But it s volume is limited. The water demand of ecosystems at the downstream was not mentioned in the design. - To assess requirements to maintain EF in the downstream of the dam - To modify the regulation sluice to ensure that it can supply adequate water for the downstream and EF demands - To operate reservoir to meet irrigation requirement and EF demand Proposed new water resources development structures More reservoirs Result of capacity assessment of Nuoc Trong reservoir shows that it can not in the upstream, meet water demands of all users at the downstream including requirements to such as Son Ha maintain EF in the down stream of the river. So it is important to propose new reservoir structures or system that can provide additional volumes and work together with all available structures in the basin to retain water in rainy season and to operate based on procedure of integrated water resources management that including water demand of EF for the downstream reaches of the river Institutional solutions such as river basin management and protection, capacity buildings; training and educating for raising awareness These non-engineering solutions include:

6 - To improve and renovate in water resources planning and management taking into consideration of water demand for ecosystem and for EF. - To improve and develop institutions and policies relating to water sources and EF. - To carry out river basin management for reducing degradation of the watershed surface - To train and educate for strengthening ability on EF assessment and apply it s results into production practice. - Educating to raise the awareness of protecting water resources and ecosystem. 4. CONCLUSIONS The outcome and shortcomings stated above set up the need of orienting the way to investigate and to solve the problems for managers and scientists. Some main issues need to be focused on in the near future are: 1. Reviewing sufficiently and comprehensively about effective and reasonable water use for all water demands based on principles of integrated water resource management and criterion of sustainable development adjusting to suit with the next period. 2. Investigating and proposing solution for effective and reasonable water use in the river basin. 3. Investigating and proposing solution to overcome the degradation, exhaustion of water sources and ecosystem and environment regression at downstream area currently for sustainable socioeconomic development at Quang Ngai province. 4. Establishing plan for water resource integrated use at the river basin (river basin planning) and river basin administration. 5. REFERENCES Nguyen, V. S. (2006). The opinion of water ecosystem health and environment supervision- the example of application identity creatures to oversee environment at upstream area of Tra Khuc River. Journal of Water Resources and Environmental Engieering, Water Resources University, Vol. 12, pp Nguyen, V. T. (2005). Water Resources degradation and exhaustion at river basins in Vietnam, the causes and control methods. Environment Resources Magazine, Ministry of Environment and Natural Resources, Vol. 3 [29], March, pp Nguyen, V. T. (2006). Impact of water use and exploitation on the variation of river flow in Vietnam. Journal of Water Resources and Environmental Engineeing, Water Resources University, Vol. 10, pp The People s Committee of Quang Ngai Province in Collaboration with Geology Institute (PCQ-GI, 2000). The report of investigation and assessment land slide along Tra Khuc River system and - solutions to prevent and reduce the loss, 116p