Modeling waves and currents in muddy coastal areas, with a focus on the Suriname coastal zone

Abstract

The mudbanks in front of the coast of Suriname are an important coastal feature and play a key role in coastal evolution by governing the flow and wave characteristics. Suriname is located in the center of the Guiana basin and it is characterized by its erosional muddy coastal area. The Amazon river is supplying the Guiana basin with about 7-10 x10^8 tons of sediment every year, leading to the formation of long mudbanks that migrate along its coasts. Moreover, the trade winds, which arrive mainly from the northeast, prevent the large Amazon plume as well as the mudbanks to extend further than 30 km offshore. Hydrodynamics in Suriname are also influenced by semi-diurnal tides that acquire a tidal range of up to 2.8 m and by waves that reach up to 4 m offshore during extreme conditions.

Measures need to be taken in order to prevent coastal erosion and flooding and to compensate for the imminent sea-level rise. Although field campaigns took place in the past, the effect of the mudbanks on waves and tidal currents has not been extensively studied. A modeling approach is needed in order to understand in detail the complex dynamics that govern this coastal area. This study aims at identifying the correct tools in order to close that knowledge gap and provide a detailed analysis on the hydrodynamics of the area. More particular, SWAN-Mud and Delft3D-FLOW are used for the first time in order to study the dynamics in the coastal area of Suriname.

The state of the art numerical wave model SWAN-Mud is used in order to simulate waves in the muddy coastal area of Suriname. Particular attention is paid to the sensitivity of results to using different formulations for wave energy dissipation by mud. DELFT formulation (Kranenburg, 2011) shows that waves are severely dissipated as soon as they arrive at the mud layer: significant wave height reduces instantly, total and mud-induced dissipation increase sharply, wave energy is shifted towards larger frequencies, waves refract up to 50 degrees towards the coast (southwards) and orbital velocity decreases as a result of wave dissipation. DELFT formulation is in agreement with a previous study by Winterwerp (2007) at the Guyana coastline, but Gade formulation, which is tested as well, is found to have similar results except for the wave energy distribution (Wells and Coleman, 1981).

Furthermore, the commonly-used numerical flow model Delft3D-FLOW is used in order to simulate tidal currents in the coastal area of Suriname. The main tidal characteristics are in accordance with findings in the literature, i.e. M2 is the most dominant tidal component (Augustinus, 1978), tides arrive perpendicular to the coast, and the tidal phase does not vary significantly (Kagan and Sofina, 2014). A coupling between Delft3D-FLOW and Delft3D-WAVE does not take place, as the latter uses the regular version of SWAN that cannot take into account the mud layer. Results from Delft3D are expected to be of higher accuracy if it is coupled to SWAN-Mud. In this case, it will be possible to model erosion, transport, and deposition of mud.