Year

2012

Degree Name

Bachelor of Environmental Science (Honours)

ANZSRC / FoR Code

050205 Environmental Management

Department

School of Earth & Environmental Science

Advisor(s)

Sam Marx

Abstract

Pattimore’s Lagoon is a small coastal lagoon connected to Lake Conjola, an ICOLL (Intermittently Closed and Open Lakes and Lagoon) on the New South Wales South Coast. Prior to 1964 it is believed that Pattimore’s Lagoon was a perched brackish wetland, undergoing a natural transition to an increasingly freshwater system, with tidal exchange limited to large spring tides and unusually high water levels in Lake Conjola. Between 1964 and1984 a number of open channel drains and canals were excavated and an artificial canal estate built along and around the original creek path. This changed the volume, shape and entrance point the canal connecting Pattimore’s Lagoon to Lake Conjola, increasing connectivity between the systems. This increased connection has had considerable effects on the tidal regime within Pattimore’s lagoon and resulted in sediment movement, vegetation changes, and a more variable salinity within the lagoon.

This research examined the types of changes that have resulted within Pattimore’s Lagoon since the 1980s due to the modifications of the tidal regime. Diatoms fossils extracted from sediment cores were used to examine changes in recent salinity and water quality conditions in the lagoon relative to its longer term state. Aerial photographs were used to map changes in vegetation, canal area, and sedimentation within Pattimore’s Lagoon. In addition, the current tidal regime of the lagoon was examined. This combined with precise surveying using differential GPS allowed for an assessment inundation of vegetation zonation around the lagoon. These changes have been assessed with respect to natural variation in Lake Conjola’s entrance condition, which results in changes in the tidal regimes of both the Estuary and Pattimore’s Lagoon.

It was found that Pattimore’s Lagoon has historically and recently been a highly variable system which experienced different salinity regimes in short periods of time. It was also proven that the development of the canal estate did increase the amount of tidal flow into Pattimore’s Lagoon, and this has had an effect on sedimentation and vegetation. The weir, which was installed to return Pattimore’s Lagoon to its pre-Canal state, has been found to have, at least partially, failed. Lastly, it was concluded that currently Pattimore’s Lagoon experiences highly variable salinities and tidal environments. The majority of vegetation around the lagoon has adapted withstand highly variable inundation frequencies and durations. It has been concluded that this is a highly complex and variable system which must be managed in context of Lake Conjola and the wider catchment.

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