The St. Johns River Water Management District in northeast Florida is studying the feasibility of withdrawing water from the St. Johns River for the purpose of augmenting future public water supply. The District requested that its Water Supply Impact Study (WSIS) be reviewed by a committee of the National Research Council (NRC) as it progresses. This third report from the NRC committee focuses on the hydrology and hydrodynamics workgroup.

The St. Johns River Water Management District is responsible for managing water resources in the St. Johns River basin, which comprises 23 percent of Florida. Approximately 4.73 million people (one-quarter of Florida's population) live in the area served by the District, which contains the growing cities of Jacksonville, Orlando, and Gainesville. In order to meet the increasing water supply needs of the District's residents and other water users, the District is considering supplementing its historical supply of groundwater with water from the St. Johns and Ocklawaha Rivers. To better understand the potential ecological impacts of such withdrawals, in 2008 the District began a large scientific study called the Water Supply Impact Study (WSIS). In late 2008, the Water Science and Technology Board (WSTB) of the National Academies was asked to review the progress of the WSIS, including such scientific aspects as hydrologic and water quality modeling and how river withdrawals will affect wetlands, biogeochemical processes, plankton, benthos, the littoral zone, fish, and wetlands wildlife in the basin. For two and a half years, the WSTB Committee has followed the activities of eight District workgroups as they modeled the relevant river basins, determined the criteria to evaluate the environmental impacts of water withdrawals, evaluated the extent of those impacts, and coordinated with other ongoing projects. The first report of the Committee reviewed the Phase 1 hydrologic and environmental assessment tools and relevant data, and made recommendations regarding proposed work for the second phase of the WSIS. The Committee's second report focused on how the District was responding to the recommendations in its first report. The third Committee report primarily evaluated the hydrologic and hydrodynamic work being performed by the District. Review of the St. Johns River Water Supply Impact Study, the fourth and final product of the Committee focuses on the ecological impact analyses conducted by the environmental workgroups, presents final thoughts about the hydrologic and hydrodynamic studies, and provides some overall perspectives on the WSIS.

The St. Johns River is the longest river in Florida, containing extensive freshwater wetlands, numerous large lakes, a wide estuarine channel, and a correspondingly diverse array of native flora and fauna. Water resource management in the river's watershed is the responsibility of the St. Johns River Water Management District (the District). The District must provide water for the region's 4.4 million residents as well as numerous industrial and agricultural users, all while protecting natural systems within the river basin. With population growth in the watershed expected to surpass 7.2 million in 2030, the District, through its water resources planning process, has begun to identify alternative sources of water beyond its traditional groundwater sources, including the potential withdrawal of 262 million gallons per day from the St. Johns River. To more comprehensively evaluate the environmental impacts of withdrawing this water from the river, the District embarked on a two-year Water Supply Impact Study (WSIS), and requested the involvement of the National Research Council. The present volume reviews the Phase I work of the WSIS and provides recommendations for improving Phase II.

The St. Johns River Water Management District is responsible for managing water resources in the St. Johns River basin, which comprises 23 percent of Florida. Approximately 4.73 million people (one-quarter of Florida's population) live in the area served by the District, which contains the growing cities of Jacksonville, Orlando, and Gainesville. In order to meet the increasing water supply needs of the District's residents and other water users, the District is considering supplementing its historical supply of groundwater with water from the St. Johns and Ocklawaha Rivers. To better understand the potential ecological impacts of such withdrawals, in 2008 the District began a large scientific study called the Water Supply Impact Study (WSIS). In late 2008, the Water Science and Technology Board (WSTB) of the National Academies was asked to review the progress of the WSIS, including such scientific aspects as hydrologic and water quality modeling and how river withdrawals will affect wetlands, biogeochemical processes, plankton, benthos, the littoral zone, fish, and wetlands wildlife in the basin. For two and a half years, the WSTB Committee has followed the activities of eight District workgroups as they modeled the relevant river basins, determined the criteria to evaluate the environmental impacts of water withdrawals, evaluated the extent of those impacts, and coordinated with other ongoing projects. The first report of the Committee reviewed the Phase 1 hydrologic and environmental assessment tools and relevant data, and made recommendations regarding proposed work for the second phase of the WSIS. The Committee's second report focused on how the District was responding to the recommendations in its first report. The third Committee report primarily evaluated the hydrologic and hydrodynamic work being performed by the District. Review of the St. Johns River Water Supply Impact Study, the fourth and final product of the Committee focuses on the ecological impact analyses conducted by the environmental workgroups, presents final thoughts about the hydrologic and hydrodynamic studies, and provides some overall perspectives on the WSIS.

Florida's Water poses fundamental questions about water sustainability in the United States' fourth largest state. Florida has long-standing water quality problems. Global climate change threatens to intensify Florida's floods and droughts, make hurricanes more common or more damaging, and eventually submerge much of low-lying Florida, including the Everglades. How can Florida meet these extraordinary challenges? And what lessons does the Florida experience hold for other states? This book fully integrates the many diverse responsibilities of water management into a readable and compelling combination of interesting narratives and deep analysis. Author Tom Swihart's unique, intimate knowledge of Florida's successes and failures in water management brings out both the novelty of Florida's water situation and the features that it has in common with other states.