Volume 6 Issue 1
Authors: Andrés Goyburo; Jesús A. Mejía; Aníbal S. Verástegui
Abstract: Faced with the effects of climate change, forms of environmentally friendly energy production, such as hydroelectric plants, are promoted. However, the building of these structures in a riverbed represents an obstacle to the movement of migratory aquatic species. A new case involves rivers of southwestern slopes of Los Andes, inhabited by crustaceans with economic and environmental importance. Considering the proposed construction of a diversion dam for a hydroelectric plant on the Ocoña River, 120 km upstream from its mouth, from 8 sampling points, the freshwater prawn (Cryphiops caementarius) population and its corresponding intensity of migration were estimated. The results were used to make hydraulic calculations, the sizing of passage for migrating species and for hydraulic modeling using HEC-RAS software. From the collection and analysis of the samples, it was found that the population is distributed depending on altitude. The intensity of migration was found between 0.88-23.67 and 4.02-34.92 prawns.min-1 for wet and dry season respectively. The average migration intensity was 10.08 prawns. min-1. It was calculated the ratio of required space/total length specie in 0.83, equivalent to a surface density of 1.35 migrating prawns per square meters. Considering an area of 4.80 m2 and the referred migration density, it was determined for each square meter a migration rate of 6.48 prawns. min-1. The biological corridor width results in 1.56 m, and an operating water flow of 0.33 m3. s-1. The population composition and the ability of this specie to climb over surfaces, out of the water, indicated that the most suitable step is the type pool - weir. In conclusion, the work allowed defining the architecture and dimensioning of the migration passage, according to specific requirements of the specie.
Keywords: Cryphiops Caementarius; Freshwater Prawn; Migration; Fish Passage; Ecohydraulics; Hec-Ras
Authors: Chiranjeevi Rambabu A; Sibtey Hasan
Abstract: Java Sea is a very complex tidal region due to its associated intrinsic geometrical characteristics which include coastline geometry, small islands and sharply varying bottom topography. Several numerical modelling studies have been conducted to evaluate the tidal characteristics of Java Sea. The present modelling study is an attempt to enhance the representation of tidal propagation of Java Sea by performing sensitivity analysis using Delft3D. Several simulations were done with Manning (0.015, 0.018 0.02, 0.03, 0.032 and 0.035) and Chezy (50, 55, 60, 65 and 70) bottom roughness coefficients in order to enhance the model performance. In general Java Sea is shallow in nature however based on sensitivity analysis with different bottom roughness coefficients, bottom roughness coefficients map was created and applied in combination with varying spatial wind to understand its effect on tidal propagation. The model performance has been verified by comparing with observed amplitudes and phases of M2, S2, K1, O1 tidal constituents at several locations on southern and northern coast of Java Sea. The root mean square error (RMSE) between observed and modelled amplitudes were 0.05, 0.04, 0.06, 0.04 calculated for M2, S2, K1 and O1 tidal constituents respectively at northern coast. Similarly, the maximum RMS error between observed and modelled phase of 34.07 was calculated for S2 tidal constituent. Most importantly, model results clearly indicated bottom roughness coefficients of 0.02, 0.03, 0.032 and 0.035 largely influencing the semi-diurnal tidal harmonic constituents compared to diurnal tidal constituents. However, the spatial varying wind had minimal effect on amplitude and phase. The present study clearly indicates that the assessment of tidal propagation in such a shallow water environment could be enhanced through detailed sensitivity analysis.
Keywords: Java Sea; Numerical Model; Sensitivity Analysis; Tidal Propagation; Bottom Roughness; Spatial Wind