Mathematical modelling of tidal currents in mangrove forests

The effects of mangrove forests on the flow structure in estuaries have been studied in this paper. An existing two-dimensional depth-integrated mathematical model has been refined to include both the effects of drag force induced by mangrove trees and the blockage effects on the mass fluxes through mangrove forests. To investigate the influence of mangrove trees on the flow structure two idealised cases have been considered. These include: (i) steady channel flow, with mangrove trees distributed within the middle reach of the channel along both sides, and (ii) tidal flow in a straight creek, fringed by mangrove swamps. Comparisons of velocity profiles at a cross-section for the case of steady channel flow, and of the time series of velocities in both the creek and its floodplain for the case of tidal flow in the straight creek–mangrove swamp system, have been undertaken. Six cases of different diameters and densities of mangrove trees have been studied to examine the significance of the drag force and blockage on the flow structure in the mangrove swamp system. It was found that mangrove trees have a significant impact on the flow structure in a mangrove system. The drag force induced by the mangrove trees plays a key role, and the blockage from the mangrove trees also plays an important role when the porosity of the mangrove trees is less than 0.8. The model has also been applied to simulate tidal flows in the Merbok Estuary, Malaysia. Simulations have been undertaken, both with and without mangrove tree effects, as well as for an extreme case of complete removal of mangrove areas from flooding, termed ‘complete bunding’, to study the effects of the mangrove trees on the hydrodynamic processes in the basin. The results show that the model provides an ideal management tool for mangrove systems.