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Environmental Flow Requirements Assessment in the Halda River, Bangladesh

Aysha Akter
Department of Civil Engineering, Chittagong University of Engineering and Technology, Chittagong 4349, Bangladesh

Md. Hazrat Ali
Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM, Johor Bahru, Malaysia

Abstract/ Executive Summary:

The Halda River is located in the southeastern part Bangladesh. It originates from the Badnatali Hills range in Ramgarh Upazila in the Chittagong Hill Tracts, flows through Fatikchhari , Hathazari , Raozan and Chittagong Kotwali Upazila, and flows into the Karnafuli River at about 35 km from the Bay of Bengal. The Kaptai Dam is located upstream at a distance of 50 km from the confluence of the Halda and Karnafuli rivers. The total length of the Halda River is about 81 km, of which a 29-km reach up to Nazirhat is navigable by big boats throughout the year; small country boats can sail 16–24 km further upstream to Narayanhat. The Halda is a very turbulent tributary of the Dhurung River, which rises in the Pakshmimura ranges in the Hill Tracts, traverses the whole of Fatikchhari Upazila, runs almost parallel to the Halda in the east, and joins at Purba Dhalai about 48.25 km downstream. Environmental flows had scarcely been considered in river water management in Bangladesh. This study attempts to assess the environmental flow requirements in the Halda River, Bangladesh with a view to mitigate the environmental problems in the Halda River using the building block method. The LPIII distribution was used to estimate the expected extreme and satisfactory flows for fish habitat at Panchpukuria station and the expected extreme water levels at Panchpukuria, Narayanhat, Telpari and Enayethat stations. It was found that floods are likely to occur at least once in 2.1, 1.02, 1.75 and 1.25 years at Panchpukuria, Narayanhat, Telpari and Enayethat stations, respectively. The results of flow and water quality analyses suggest that environmental flow requirements cannot be achieved in this river throughout the year. The environmental flow requirements and conservation of fish resources could be achieved by implementing the suggestions provided in conjunction with a comprehensive awareness program, investigations and trade-off analyses being among the other suggestions.

Keywords: Environmental flow assessment; Building block method; Flow quantity and quality; Log-Pearson Type III distribution

Location: Halda river, Chittagong

Start Date:

End Date:

Program Area: Socio-economic and Policy

Commodity: Weather/Climate

Objectives:

To assess the situation of the Halda River environmental flow
To estimate the requirements and recommend ways to achieve optimum environmental flow

Methodology:

In this study, the Building Block Method (BBM) and the log-Pearson Type III (LPIII) distribution were selected to assess the environmental flow requirements in the Halda River. Since the BBM comprised the river ecosystem and hydrological analysis along with the hydraulic rating information and biological data, it could be used as a tool to reduce/eradicate the degradation of the Halda River water quality. The LPIII distribution was used to promote a consistent, uniform approach to flood flow frequency determination in the Halda River. Building block method Evaluation of environmental flow requirements by the building block method considers different blocks in addition to the mean monthly river flow. These blocks were: (i) minimum dam release, (ii) flushing, (iii) habitat maintenance, (iv) spawning, and (v) surplus for abstraction or storage. These blocks might play important roles for the Halda River. The assessment procedure involves the following steps: (1) Minimum dam release block: This flow was 70% of the mean monthly discharge, because 30% drop in flow was the generic minimal degradation level. Although, it was recommended for rivers in southern Africa, it could be considered for the Kaptai Dam release. (2) Flushing flow block: This was the most commonly used term for defining the channel maintaining flow. Such flow intends to mobilize fine sediments and the litter from the surface of highly productive algal mats. The requirements for the flushing flow described by different authors are: (a) 200% of the daily average flow; (b) twice the average monthly flows; (c) a flow rate necessary to maintain one riffle free of silt; (d) coincidence with fish breeding and migration; (e) maintenance of the productive algal mats to mobilize silt and debris; (f) flows greater than the 80th percentile; and (g) flow rates of rise and fall determined from the natural hydrograph for a duration of not more than the 90 th percentile. (3) Spawning flow block In the Montana method, the suggested percentages of mean flow for different fish habitats are: 10% (for survival or poor-quality habitat), 30% (for satisfactory or moderate habitat) and 60% (for excellent habitat). Considering the channel bed material as gravel, Hildebrand and Cannon (1993) concluded that the “minimum stream flow for spawning” could provide a suitable hydraulic condition over 80% of the available gravel at an optimum flow. Webb and Moir (2001) determined that relatively high flows are required for spawning Salmon in Girnock Burn and they found the lowest utilized flow equivalent to more than the river’s 50th percentile flow

Source of Information: Hydrological Sciences Journal – Journal des Sciences Hydrologiques, 57(2) 2012

Article Link (Online Journal): file:///C:/Users/barc/Downloads/3-22-2016_Environmen.pdf

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The expected extreme and satisfactory fish habitat (i.e. 30% of mean flow) flows at Panchpukuria station for different return periods were estimated based on the yearly maximum discharge using the log-Pearson Type III distribution, which might be helpful for the concerned authorities to take action against flood and satisfactory habitat for fish. It was also estimated that flood is likely to occur at least once in 2.1, 1.02, 1.75 and 1.25 years at Panchpukuria, Narayanhat, Telpari and Enayethat stations, respectively. There is no fixed minimum water level in the Halda River, so it can be set at 1.5 m to ensure satisfactory fish spawning in this river. The results of water quantity and quality analyses showed that both physical degradation and chemical pollution occur in the Halda River, indicating that environmental flow requirements cannot be achieved throughout the year. Nevertheless, a detailed awareness program, flow and water quality investigations and even trade-off analysis among the tasks may need to be undertaken to implement these successfully to maintain environmental flow requirements. Although, this study was undertaken for the Halda River, it would be of practical use for environmental flow requirements assessment in other rivers as well.

Knowledge Management: Journal