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Abstract
Cau River Basin is located in the North-East of Vietnam. Its surface water has become more and more polluted due to social-economic development activities. Thus, the environ mental improvement of this river basin is one of the priorities and important tasks of the Vietnamese government.
River basin integrated management is more and more interesting because it can deal with conflicts between social-economic development and environ mental protection. The approach of river basin integrated management was used in this research to identify and prioritize interventions to improve the water quality of Cau River in Vietnam. This included building and comparing future social-economic development scenarios to the present situation of the river basin in terms of impact on water quality.
Cau River Basin covers seven provinces, but this study mainly focussed on the parts of Cau River Basin which belong to two provinces: Bac Kan and Thai Nguyen. Appropriate methods for building development scenarios for the study area in the context of few available data were proposed. Seven factors were taken into consideration to build the scenarios: population, domestic wastewater, industry, livestock, agricultural fertilizer, forest and climate change.
Fourteen scenarios were developed in order to assess the impacts of future social-economic development on the water quality of Cau River by using a river basin integrated management computer tool named GIBSI. This tool includes hydrology, soil erosion and river water quality models adapted to and calibrated for Cau River Basin. Simulations of water quality in GIBSI showed that population, domestic wastewater and industry are three factors which may have visible impacts on water quality in the future in the study area. Four other factors, namely livestock, agricultural fertilizer, forest, and climate change showed negligible impacts on water quality in the future.
A multi-criteria analysis method for this case study was proposed to compare and select the optimal scenarios among the fourteen developed scenarios. This analysis was based on three assessments: (1) taking the ideas of stakeholders about the scenarios, (2) assessing the impacts of each scenario on surface water quality in Cau River Basin, and (3) analyzing cost comparison for each scenario. Therefore, besides the assessment of the impacts of fourteen scenarios on water quality of the Cau River system, cost comparison analysis and ideas of experts and stakeholders for these scenarios were also taken into consideration. Based on weights given to water quality simulation, ideas of stakeholders and cost comparison analysis results, a score was given to ail scenarios.
As a result, three scenarios were found to have the highest scores and were selected. Interventions in these scenarios are therefore recommended in the future to improve surface water quality of Cau River Basin: (1) increase the capacity of the domestic wastewater treatment plant in Bac Kan town to 20,000 people; (2) keep the projection of domestic wastewater treatment plant for 100,000 people in Thai Nguyen City; and (3) install a treatment plant for the town of Song Cong town for 10,000 people. Besides these interventions, controls of population and industrial wastewater discharge in order to meet the standard were also recommended.
This research contributes to a systematic evaluation of the impacts of future social-economic development on surface water quality in Cau River Basin, in Bac Kan and Thai Nguyen provinces, helping the decision-makers select the optimal interventions for the management of Cau River Basin.