Camacho inlet southern Brazil – Instability causes and user conflicts
Abstract Inlet stabilization is a common practice in Brazil, as it is worldwide. In this paper we present results of the analysis of the stabilization practices of the Camacho Inlet, located in Santa Catarina State, southern Brazil. This inlet is maintained intermittently, in accordance with a regime designed to benefit both local fishermen and rice farmers. Fishermen require this inlet to be open as a navigation channel during the fishing season; rice farmers needs it closed during the irrigation period to allow the pumping of fresh water from the Congonhas River which drains into the Camacho’s backbarrier lagoon. An additional complication arises from the tendency of this inlet to close naturally due to infilling by dune migration. Aerial images spanning a 65 year time period (1938–2003) were analyzed, demonstrating the variability in the inlet’s width between 0 (closed) and 360 m. The analysis of inlet stability and user needs indicate that an appropriate solution is the implementation of an annual inlet dredging program in the austral autumn. This would allow for the inlet to remain open from May to September and then close naturally for the rest of the year, providing for a backbarrier fresh water reservoir during the irrigation period.
Observations on the Stability St. Andrew Bay Inlets in Florida
Abstract The need for a cautious interpretation of results from an analytic method for an analysis of the stability of tidal inlets is illustrated by comparing theory with data from St. Andrew Bay in Florida's panhandle. Historically this bay was connected to the Gulf of Mexico by East Pass at the eastern end of the bay. However, following the opening of St. Andrew Bay Entrance in 1934 at the western end to serve Panama City, the flow cross-section of this channel increased while East Pass contracted gradually and eventually closed in 1998. In December 2001 East Pass was reopened by dredging a small flow-relief channel. These events provided the opportunity to apply the stability analysis to the newly-formed two-inlet one-bay system. Interpretation of the results in terms of observed inlet stability versus prediction is shown to be contingent upon knowledge of the history of channel maintenance and the morphodynamics of the bay. The illustration underscores the need to apply the method in pre-project engineering investigations of the long-term impact of opening a second inlet in a bay.
Factors Controlling Tidal Inlet Characteristics on Low Drift Coasts
New Zealand's northeast coast is characterised by low littoral drift and the numerous barrier enclosed estuaries along the shore present an excellent opportunity to examine tidal inlet processes under low littoral drift conditions. The estuaries range in area from c .1 to 98 km 2 , are micro-mesotidal and have tidal prisms ranging from c .0.8 x 10 6 to 155 X 10 6 m 3 . Tidal inlets mostly occur where Holocene sand barriers have built out towards rock headlands. The inlets generally have positional stability as a result of shelter from wave energy in the lee of rock headlands, however, morphological instability is common and temporal. Ebb tidal delta planform is controlled by the tidal discharge, degree of headland shelter and littoral supply. In situations where a rock headland provides shelter from waves, the ebb tidal delta comprises an elongate or triangular swash platform built normal to the shore in the lee of the headland. Where there is little headland shelter and the littoral drift is very low, the ebb tidal delta is poorly developed and comprises an extension of the beach bar system across the mouth of the inlet. In comparison where there is little headland shelter but the littoral drift and tidal prism are greater, a large and more classical shaped ebb tidal delta bulges out from the coast. In general the inlets can he considered as geometrically stable (i.e. have the ability to return to their initial configuration after a disturbance) because: (1) the generally low width to depth ratio (average 44) indicates that the inlet throat channels are hydraulically efficient, (2) the strong relationship between throat area and tidal prism/discharge indicates that there is a balance between inlet geometry and tidal flow through the gorge, (3) of the similarity of their throat area/tidal prism relationships and width/depth ratios to those inlets stabilized with 2 jetties on the Pacific and particularly the Atlantic coast of the USA, and (4) the high tidal prism/ littoral drift (Ω/M tot ) ratios indicate that entrance conditions are good and that the tidal current is the main mechanism for transporting sediment through the entrance. The rock headlands at the northeast coast inlets appear to act in a similar manner to jetties in directing the ebb tide jet and so forcing tidal dominance of sediment transport, creating an efficient throat profile and a geometrically stable entrance.