Tidal inlet short-term morphodynamics analysed trough the tidal prism - longshore sediment transport ratio criterion

Abstract

Longshore sediment transport and tidal prism are key factors in analyzing the stability and morphodynamics of a tidal inlet. Stablished by the Bruun theory, the ratio between the maximum spring tidal prism (P) and the annual total littoral drift (MT) is a parameter widely used to diagnose the stability condition of tidal inlets and to validate inlet morphological modeling results. However, the P/MT relationship is adequate for mid-term and long-term analysis only (i.e. weeks, months, years or decades). Depending on the wave climate, one may observe intense accretion in a tidal inlet in a time scale of hours to few days during storm events. No empirical criterion is yet known to be applicable for supporting analysis in such a short time scale. This work presents a modified approach of the traditional Bruun criterion, adapted for assessing short-term (i.e. hours or days) morphological evolution of tidal inlets. Instead of P and MT, the method here addressed considers the ratio between the tidal prism (Pi) and the longshore transport volume (MTi) integrated both over the flood period of every tidal cycle. This methodology was applied in the analysis of storm and post-storm induced morphodynamic response of a projected tidal channel, proposed to improve water quality in the Araruama Lagoon, Rio de Janeiro, Brazil. Hydro-sedimentological numerical modeling was used to simulate a scenario which encompassed three cycles of storm induced accretion and post-storm induced inlet development. Correlation was noticed between the patterns of short-term morphodynamic response and the temporal variations of the instantaneous Pi/MTi ratio. This research also presents calculations on the longshore sediment transport rate during the four seasons for the studied region.