Study of the operational management of Sariakandi fishpass

Abstract

The present study has been aimed to identify factors affecting hydraulics and impacts of Sariakandi Fishpass on fish production, fish diversity and socia-economic condition and to develop a participatory model for operation and management of that fishpass. The study has been carried out at the adjacent areas of the Sariakandi Fishpass. This is the largest fishpass of Bangladesh. This is a veltical slot type structure, with three vents composed of 16 pools (4.2mx4.8m) in each vent. Each pool has 0.7 01 opening. The velocity at pool openings has been measured by a I-D current-meter. A 3-D Acoustic Doppler Velocimeter (AD V) has been used to measure the X, Y, Z components of velocity inside the pool. A structured questionnaire survey covenng technical, institutional, socia-economic, legal and environmental issues has been conducted to gather information from different stakeholders. Focus Group Discussion (FGD) has also been conducted on other issues. Velocity in a slot largely depends on the geometry of the structure, such as Lib (L the length of each chamber and b the opening), WIb (W the width of the chamber), yolb (Yo depth of flow), Froude number, .6.h (difference in water levels between two adjacent pools), etc. Hydraulic investigation indicates that a typical flow patterns exist in a pool. The flow from the slot travels through the center of the pool to the next slot with two large recirculation zones located on either sides of the jet. Turbulence inside a pool is high, with velocity decay rate in transverse direction is higher than that of longitudinal direction. VenicaI \'elocity component changes are random. While the head differences between Jamuna and Bangali Rivers are more than a.Sm, the measured velocities at individual pool openings are found much higher than that of the tolerable limits (e.g., reaction, cruising and darting speeds) of juveniles of all local fish species and migratory fish species. There is not sufficient place where fish can take rest. This is because of insufficient length and width of the pool. The standard ratios of pool length to pool opening and pool width to pool opening should be 210 and 28, respectively so that the velocities at the pool openings become low. As a result energy dissipation inside the pool will be high and will offer more area for the fish to take rest. At the pool opening the flow appears in the form of a jet, the relationship between velocity and head difference follows a power law. The values of the measured velocities are higher than that of the theoretical one. The velocity decreases linearly with length. The flow in approaching section is always sub-critical because Froude number is less than 0.8. It states that no hydraulic jump develops at the pool length. The calculated energy dissipation rate per unit volume of the fishpass is 71.3 W/m3. It has been found from the questionnaire survey that the impacts of fishpass on socioeconomic and environment are positive. Production of threatened fish species have increased and rare fish species are found more frequently. As a result Shanon Diversity Index (SOl) is increasing. Untimely gate operation during the breeding season, sedimentation at the upstream channel of Jamuna River, ineffective law enforcement and non-participatory decision-making are adverse factors against its desired performance. Operation and management is solely done by the BWDB. About 76% respondents are dissatisfied with existing management. Eighty percent respondents have opined that coordination among different organizations is poor. However, local beneficiaries are willing to participate in the management of the fishpass. The existing management should be replaced by participatory one. The survey output is used to frame a management model where the representation of local stakeholders has been placed under lower-level Fisheries Management Groups (FMGs) and apex-body Fishpass Management Committee (FMC). There is also a Performance Monitoring and Technical Advisory Committee (PMTAC) of officials of different government agencies, LGls, NGOs and representatives of FMC to monitor beneficiaries' performances, coordinate technical assistances, and enhance interagency cooperation. Formation, composition, responsibility, legal framework, mutual accountability among these management bodies has been ensured through defined rules and regulations.