Study On Hydraulic Characteristics Of Chinese Sturgeon Habitat In Yangtz River

Chinese sturgeon, Acipensor sinensis, is a valuable and rare aquatic animal in China. They lost large habitat area and the key spawning ground due to the constructing of Gezhouba dam. The fish has been found in an alternative spawning ground located in a narrow reach downstream close to Gezhouba dam site, and performs natural propagation annually. This would allow one to better investigate what the hydraulic and morphologic conditions of a river can meet the requirement of Chinese sturgeon habitat. In this paper, flow characteristics of Chinese sturgeon habitat in Gezhouba reach have been studied systematically by means of the method of field measurement and three-dimensional numerical simulation. Some flow parameters meeting the fish inhabiting and spawning demand have been obtained. The main works of the paper are listed as follows:(1) Field investigation and material collection. ADCP (Acoustics Doppler current profile) technique was selected to measure the flow field of Chinese sturgeon habitat. 1204 column velocities of 12cross-sections were obtained. The measured velocities were between 0.16 to 3.35m/s.(2) The preference values of velocity and depth of Chinese sturgeon. A three -dimentional numerical model was established. This model was based on finite difference on structure grids. The flow of the habitat was simulated. The relationship of the location velocity and depth to the observed frequency of the fish in simulated flow field was studied to obtain the preference curves of velocity and depth. The velocities and depth preference rang of the fish are respectively 1.3 to 1.5m/s and 9 to 12m.(3) Flow field characteristics of Chinese sturgeon spawning ground. Spatial kinetic energy gradient (KEG), kinetic energy gradient increasing ratio and cross-section mean vorticities were selected to study the spawning ground. The spatial distributions of the three values were computed. Comparing these values on theoretic analysis, numerical analysis and correlation analysis, the cross-section mean vorticity frequency is the most sensitive value to reflect the contribution of eggs density of unit upstream spawning area. Chinese sturgeon needs mixed flow in spawning period, so that increases the chance of eggs mixing with semen and conceiving rate. Under the conditions of the flow with high vorticity frequency value the eggs would be dispersed easily in riverbed, as a result, take refuge to keep away from predators.(4) Usable weighted area (WUA) downstream of Gezhouba dam. With the conclusion of preference depth and velocity, the suitable criterions of Chinese sturgeon were set down. The habitat model has been established and used to study Chinese sturgeon habitat. The WUA increase to the maximum 3.47km~2, as the flow discharge is about 15000m~3/s.