Dynamic and resuspension by waves and sedimentation pattern definition in low energy environments: guaíba lake (Brazil)

Little research has been undertaken into sediment dynamics in lakes, and most of it only analyses particular aspects such as the texture of the sediments. In this study, the characteristics of the wave field in Guaíba Lake are investigated. The parameters significant wave height (Hs), period (T) and direction of wave propagation are examined together with their relation to the resuspension of sediments at the bottom. For this purpose, the mathematical model SWAN (Simulating Waves Nearshore) has been validated and employed. The results pointed out that the highest waves modeled reached 0.55 m at a few points in the lake, particularly when winds were blowing from the S and SE quadrants with an intensity over 7 m.s-1. Generally speaking, waves follow wind intensity and direction patterns, and reach maximum height in about 1 to 2 hours after wind speed peaks. Whenever winds were stronger, waves took some 2 hours to reach 0.10 m. However, with weak to moderate winds, the waves took around 3 hours to achieve this value in significant wave height. In addition to speed and direction, wind regularity proved relevant in generating and propagating waves on Lake Guaíba. In conclusion the lake's sediment environments were mapped and classified as follows: 1) Depositional Environments (51% of the lake); 2) Transitional Environments (41%); and 3) Erosional or Non-Depositional Environments (8%). As a contribution to the region's environmental management, elements have been created relating to the concentration of suspended particulate matter. Pesquisas referentes à dinamica sedimentar em lagos s o escassas e a maioria trata da distribui o e textura dos sedimentos, sendo raras aquelas que fazem men o ao padr o de ondas e suas rela es com a ressuspens o destes sedimentos e suas consequências. Este trabalho analisa as características das ondas incidentes no Lago Guaíba (Brasil) por meio da utiliza o do SWAN (Simulating Waves Nearshore) e suas rela es com a ressuspens o de sedimentos junto ao fundo. Os resultados mostraram que as maiores ondas incidentes atingiram 0.55 m, particularmente quando de ventos do quadrante S e SE e com velocidades maiores que 7 m/s. Em termos gerais, as características das ondas seguem os padr es de intensidade e dire o dos ventos, atingindo seus máximos valores aproximadamente 1 ou 2 horas após a velocidade de pico dos ventos. Em conclus o, os ambientes de sedimenta o do lago foram mapeados e classificados da seguinte forma: 1) Ambientes Depositionais (51% da área do lago); 2) Ambientes Transicionais (41%); e 3) Ambientes Erosionais ou d