Siltation rate and main anthropic impacts on sedimentation of the São Luís tidal inlet - State of Maranhão, Brazil

Abstract In recent decades, intense human intervention in the coastal zone has given rise to severe siltation and erosion problems. This scenario is located the São Luís tidal inlet, formed by the mouths of the Anil and Bacanga rivers which due to various kinds of interference have been changing their sediment transport and deposition processes. With these changes in mind, this study sought to evaluate the evolution of the siltation and sedimentation rates in this area, as well as the main anthropogenic influences associated with this process. The methodology consisted in verifying the morphological evolution on the basis of the scanning and vectorization of nautical charts of 1947 and 1966, bathymetric surveys conducted in 2006, and aerial photos dating from 2011. The results show a silting up process coincident with interventions that occurred in the Anil and Bacanga river basins, with a volume of silt estimated at 8.5x106 m3, over the period from 1944 to 2011 (64 years), at a rate of 1.6 cm.yr-1. These processes are associated mainly with the construction of the Bacanga dam and land reclamation projects undertaken for the purpose of providing new areas for urban expansion. The evaluation of the results showed intense and advanced silting up of the São Luís tidal inlet, at rates proportionally greater than those of other estuaries, calling for corrective actions and the implementation of coastal management policies for this area.

摘要
近几十年来，人类对海岸带的高强度干预引发了严重的淤积与侵蚀问题。本次研究的研究区域为圣路易斯潮汐汊道（São Luís tidal inlet），该汊道由阿尼尔河（Anil）与巴坎加河（Bacanga）的河口共同发育形成，受各类人类活动干扰，其泥沙输运与沉积过程已发生显著改变。基于上述变化背景，本研究旨在评估该区域的淤积演化过程与沉积速率，同时解析与此过程相关的主要人为影响因素。
本研究采用的方法包括：对1947年、1966年的海图进行扫描与矢量化处理，结合2006年开展的水深测量数据以及2011年的航空影像，验证研究区的地貌演化过程。研究结果显示，淤积过程与阿尼尔河、巴坎加河流域内实施的人类干预活动存在显著关联；1944年至2011年（共64年）间，该区域的淤积量估算为8.5×10⁶ 立方米，年均淤积速率达1.6厘米·年⁻¹。上述淤积过程主要与巴坎加河大坝的修建以及为城市扩张拓展用地而实施的围填海工程密切相关。结果评估表明，圣路易斯潮汐汊道已出现高强度且程度较深的淤积现象，其淤积速率显著高于其他河口，亟需采取整治措施并针对该区域制定并实施海岸管理政策。