HYDRAULIC AND SEDIMENT RETENTION INFLUENCE IN VEGETATION CHANGES OF GUANDU MANGROVE WETLAND

摘要

The aerial photos from 1978 to 1994 were used to analyze the temporal variations of the vegetation changes of the Guandu Natural Reserve. The results revealed that the marsh habitat, dominated by Cyperus and Phragmites, has changed into a swamp habitat, dominated by Kandelia. The coverage area of Kandelia has increased from 0.04 hectares in 1978 to 20.75 hectares in 1994. The mangrove spreads cause a significant impact upon ecosystem and flood control operations. A horizontal two-dimensional model, TABS-2, was applied in this study to simulate the hydraulic characteristics of this estuarine wetland. Four cases with different mangrove-removal rates were investigated. It is found that the w.s.e. decreases as the mangrove-removal ratio increases. When the mangrove-removal ratio of Kandelia reaches 20%, the variations of the decrease of w.s.e. of the wetland became insignificant. Significant sediment deposition occurs due to the extensive root network of Kandelia. According to the results, the average deposition is about 33 mm during a 200 year flood event. Mangrove-removal of Kandelia is able to reduce the sediment deposition rate. When the mangrove-removal rate reaches 20%, the reduction in sediment deposition is about 5 mm. When considering the factors of flood protection and sediment deposition of wetland, the optimal mangrove-removal ratio is between 10% and 20%.