The Gnangara Groundwater System meets about 50% of all water needs for the Perth–Peel region of Western Australia (population 1.7 million). Much of the water is contained in an unconfined aquifer which occurs in coastal sand dunes and supports ecologically-important throughflow wetlands. The system has been subject to significant climate change since about 1975, although the persistent and unidirectional nature of the change was not recognised for some time. As well as climate, groundwater levels are affected by land use (e.g. plantation forestry, urbanisation) and land management (e.g. how plantations and stormwater are managed) as well as by the amount of groundwater abstraction from each of several inter-connected aquifers. Land, water and forests are managed by different government agencies with their own policy objectives. Maintaining groundwater levels within an agreed range of values to protect the wetlands requires informed and early adaptation by these agencies as well as a supportive community. Adaptation was hampered because there was little or no experience of managing groundwater for climate change and the causes of declining levels were neither clear nor agreed. Even when target water level decisions were agreed, their achievement required the cooperation of parties with different priorities. This paper examines some of the lessons learned from this experience and the current approach to manage the land, water and forest resources to meet multiple objectives in a system that is undergoing transitional change rather than reaching a new equilibrium. Climate change impacts have been progressive and the concept of a system that can respond in a resilient manner after a temporary perturbation is not an appropriate concept in this example. Climate adaptation involves significant social and institutional change as well as biophysical changes to make the most of a changing system.
Widespread flooding occurred in December 1982 and in spring 1983 in the central and southern Mississippi River basin. The first series of storms, December 2-7, caused severe flooding along many streams in Illinois, Missouri, and Arkansas. Much of the three-State area experienced recordbreaking 24-hour rainfall amounts that caused some streams to exceed previously known flood heights and discharges; in many cases the recurrence interval of peak discharges exceeded 100 years. The second series of storms, December 24-29, caused severe flooding in Louisiana and moderate flooding in Mississippi. Peak discharges on some streams exceeded the 100-year recurrence interval. Damages exceeded $200 million and 25 persons died as a result of the December storms. Western Tennessee was on the fringes of both storms and received only minor flooding. During April 4-8, 1983, as much as 17 inches of rain fell in parts of southern Mississippi and southeastern Louisiana. In some areas, 24-hour amounts exceeded 5 inches, causing peak discharges to exceed the recurrence interval of 100 years at 20 streamflow gaging stations. In May 1983 heavy and intense rains caused major flooding in the Big Black River and Pearl River basins in Mississippi.
Introduction Previous investigations Acknowledgments Description of study area Location and setting St. Johns River Hydrogeology Surficial aquifer t Water-table zone Semiconf ining beds Limestone unit Appraisal of the interconnection between the St. Johns River and the limestone unit Hydraulic relations 17 Water-quality relations
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