Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 3
Chapter 1 Introduction With a length of about 310 miles (500 kilometers), the St. Johns River is by far the longest river in Florida. Its drainage basin of 31,954 square kilometers (km2) or 12,283 square miles (mi2) represents 23 percent of the total area of Florida and occupies the northeast quadrant of the state. Two of the state’s largest urban centers lie wholly (Jacksonville) or mostly (Orlando) within the drainage basin, and 110 other municipalities exist within the basin. The population of the basin currently is about 4.4 million people (21 percent of the state’s population) and is expected to grow to more than 7.2 million people by 2030. Additional water supply demands from the increased population will not be met by further withdrawals from groundwater supplies in the basin because those supplies are reaching their sustainable limits. Moreover, a joint action plan of the three Florida water management districts responsible for water management in central Florida capped groundwater withdrawals at the level of the 2013 demand. The St. Johns River Water Management District (the District) is thus studying the feasibility of withdrawing water from the St. Johns River and its major tributary, the Ocklawaha River. The District requested that their study, called the Water Supply Impact Study (WSIS), be reviewed by a committee of the National Research Council (NRC) as it progresses. This is the third report from the NRC committee, and it focuses primarily on the work and results stemming from the hydrology and hydrodynamics workgroup of the WSIS. It also considers related activities of the wetlands workgroup and the role of stormwater management in how the hydrologic and hydrodynamic modeling results should be interpreted. The NRC committee’s statement of task is presented in Box 1-1. This report is primarily a review of Cera et al. (2010), Sucsy (2010), and Belaineh et al. (2010)—District publications/presentations describing the recent progress of the hydrology and hydrodynamics workgroup. This report also reflects knowledge gained by the committee during numerous District presentations at meetings and conversations with District staff regarding their modeling approach, and by reviewing relevant references and other outside reviews of the District’s work. Because the primary audience of this report is the District staff and outside experts, details of the hydrology and hydrodynamic modeling are not repeated here, including evidence provided by the District showing that the model simulations closely matched measured outcomes. The reader is referred to Cera et al. (2010) and SJRWMD (2008) for such information. Rather, this report focuses on the committee’s concerns about the Cera et al. (2010) report where they existed and suggests improvements for future work. The positive statements affirming the District’s approach found throughout this report reflect the committee’s best professional judgment as it analyzed the District’s attempts to do state of the science hydrologic and hydrodynamic modeling. Detailed discussion is provided 3 PREPUBLICATION COPY
OCR for page 4
4 Review of the St. Johns River Water Supply Impact Study: Report 3 Box 1-1 Statement of Task An NRC committee overseen by the Water Science and Technology Board of the National Academies will review the progress of the St. Johns River Water Supply Impact Study (WSIS). Communities in the St. Johns River watershed in east central Florida are facing future drinking water supply shortages that have prompted the St. Johns River Water Management District to evaluate the feasibility of surface water withdrawals. At the current time, drinking water is almost exclusively supplied by withdrawals from groundwater. Reliance on groundwater to meet the growing need for public supplies is not sustainable. The St. Johns River and the Lower Ocklawaha River are being considered as possible alternatives to deliver up to 262 million gallons of water per day (MGD1) to utilities for public supply. In January 2008, the District began an extensive scientific study to determine the feasibility of using the rivers for water supply, and it has requested the advice of the National Academies as the study progresses. The WSIS is composed of six major tasks, being carried out by District staff scientists aided by a suite of outside experts, each with national standing in their scientific discipline. These activities include modeling of the relevant river basins, determining what criteria should be used to evaluate the environmental impacts of water withdrawals, evaluating the extent of those impacts, coordinating with other ongoing projects, and issuing a final report. The NRC committee will review scientific aspects of the WSIS, including hydrologic and water quality modeling, how river withdrawals for drinking water will affect minimum flows and levels in the two rivers, the impact of removing old and introducing new wastewater streams into the rivers, the cumulative impacts of water withdrawals on several critical biological targets, and the effects of sea level rise. Potential environmental impacts being considered by the District include altered hydrologic regimes in the river, increased pollutant concentrations in the rivers (e.g., sediment, salinity, nutrients, temperature), associated habitat degradation, and other direct effects on aquatic species due to the operation of the new water supply facilities. only for those issues where improvements could be made to the modeling efforts as they evolve to support water supply planning. The reader is referred to previous reports of the committee (NRC, 2009a, b) for considerable background on the basin, the origins of the WSIS, and the District’s WSIS Phase I activities. These reports are available online at http://sjrwmd.com/surfacewaterwithdrawals/NRC_Phase1Report_review.html. WATERSHED AND RIVER DESCRIPTION The St. Johns river flows in a northerly direction for most of its length—from its origins in headwater wetlands west of Vero Beach (Indian River County) until it reaches Jacksonville, where it turns east and flows another 25 miles before reaching the Atlantic Ocean at Mayport (Figure 1-1). In spite of its length, the river elevation drops only about nine meters (~30 feet) from its headwaters to the ocean (an average of about 1.1 inches per mile or less than 2 cm per km), and most of the elevation drop occurs in the upper third of the river channel. As a result, a large fraction of the river is influenced by oceanic tides, and as a whole the river is a low- gradient, slow-moving (“lazy”) river. The present river evolved from an ancient intracoastal lagoon system into a river channel that has three hydrologically distinct parts: the upper, middle, and lower St. Johns River (see Figure 1-1 for boundaries of the subbasins). 1 1 MGD = 0.645 cubic feet per second (cfs) PREPUBLICATION COPY
OCR for page 5
Introduction 5 Before drainage activities began in the early 20th century to enable the development of agriculture, the upper St. Johns basin had an extensive floodplain with large expanses of freshwater marsh and interconnected shallow lakes, and the river flow was not always in a distinct channel. Further drainage activities for flood-control in the middle of the 20th century ultimately claimed about 70 percent of the original floodplain, created several large reservoirs, and channelized parts of the river. In addition, several large areas were removed from the St. Johns basin, and runoff from these areas was pumped into manmade canals that flowed directly into the Atlantic Ocean via the Indian River Lagoon. Because of environmental concerns, wetland restoration has been underway in the upper basin since the 1980s, and several large projects are reconnecting parts of the upper drainage basin that had been transferred out of the basin by levees, canals, and pumping systems (see below). The middle St. Johns River is a relatively short segment—approximately 60 km (37 miles)—with several large lakes and springs. It generally is considered to begin above Lake Harney and end below the outlet of Lake Monroe. The basin covers about 3,120 km2 (1,200 mi2), including some heavily urbanized areas northeast of Orlando. The Econlockhatchee River is a major tributary in this segment, and several large springs also contribute to the river flow. Lakes Harney and Monroe are widened areas in the main channel of the river, and Lake Jesup is a shallow off-channel lake between Harney and Monroe. The lower St. Johns River, the longest of the three segments, is defined as the stretch of the river that is tidally influenced. It is divided into a freshwater segment, which extends down- river approximately to Green Cove Springs (river mile 48 from the ocean) and an estuarine segment, which exhibits increasing salinity as the river approaches the ocean. In turn, the freshwater segment is divided into two sub-reaches, one including Lake George, and a second including the freshwater reach downstream of the confluence of the Ocklawaha River (see Figure 1-1). With a drainage basin of 7,170 km2 (2,769 mi2)—almost one-fourth of the entire St. Johns drainage basin—the Ocklawaha River is by far the largest tributary of the St. Johns River. The river starts as a series of large, shallow lakes (Apopka, Dora, Harris, Eustis, and Griffin) to the northwest of Orlando. The Silver River, which originates at Silver Springs, near Ocala, also contributes substantially to the river flow. Water from the Ocklawaha contributes significantly to the flow of the lower St. Johns River, and more than 40 percent of the surface water withdrawals being considered for water supply purposes in the current WSIS (i.e., 107 MGD out of a total of 262 MGD) is from the Ocklawaha River. Effects of this water withdrawal on the Ocklawaha River itself are not being considered in the current WSIS, although the ecological and hydrological effects on the St. Johns River of decreased flow from the Ocklawaha resulting from the withdrawal are being considered. (For further discussion of the Ocklawaha and its role in the WSIS, the reader is referred to NRC, 2009a). As a whole, the St. Johns River drainage basin has very limited topographic relief, and as a result the river has extensive riparian wetlands. In the upper basin, the wetlands primarily are marshes, but in the middle and lower basins, hardwood swamps predominate. The highest elevations within the basin (up to 150-200 feet above sea level) occur to the west of the river, mainly in the sand hill region east of Gainesville, which has numerous soft-water lakes, and in the Ocala National Forest in the northern part of the Ocklawaha River basin. Although agriculture is an important activity within the St. Johns basin, a larger fraction of the drainage basin, particularly in the middle and lower basins, is forested. Much of the upland forest is in pine plantations grown for pulp and paper production (see Table 1-1 for PREPUBLICATION COPY
OCR for page 6
6 Review of the St. Johns River Water Supply Impact Study: Report 3 FIGURE 1-1 A map showing the surface water basins of the St. Johns River, major lakes along the main stem, relevant towns and cities including Cocoa and Christmas where model simulations were run, and the location of four potential surface water withdrawal sites. SOURCE: Tom Bartol and Ed Carter, SJRWMD, personal communication, 2010. PREPUBLICATION COPY
OCR for page 7
Introduction 7 TABLE 1-1 1995 and predicted 2030 land use in the St. Johns River Basin. HSPF Land Use Group 1995 Land Use (acres) 2030 Land Use (acres) 1. Low Density Residential 263,841 4.9% 787,264 14.7% 2. Medium Density 247,710 4.6% 540,955 10.1% Residential 3. High Density Residential 78,947 1.5% 169,659 3.2% 4. Industrial and 140,282 2.6% 301,998 5.6% Commercial 5. Mining 20,515 0.4% 14,973 0.3% 6. Open and Barren Land 112,207 2.1% 58,512 1.1% 7. Pasture 505,701 9.4% 343,102 6.4% 8. Agriculture General 267,970 5.0% 148,201 2.8% 9. Agriculture Tree Crops 144,268 2.7% 72,500 1.3% 10. Rangeland 272,895 5.1% 136,985 2.5% 11. Forest 1,659,119 30.9% 1,139,307 21.2% 12. Water 286,016 5.3% 286,016 5.3% 13. Wetlands 1,374,656 25.6% 1,374,656 25.6% Total 5,374,127 100.0% 5,374,127 100.0% SOURCE: Cera et al. (2010). summary information on land use and land cover in the St. Johns basin, including its major subbasin, the Ocklawaha). Cattle grazing, horse farms, citrus groves, and vegetable production (e.g., potatoes, winter vegetables) are the major farming activities within the large and agriculturally diverse basin. Because of the extensive wetlands throughout the drainage basin, the St. Johns River is highly stained (brown) with humic color. Water in the river generally is quite hard—high in calcium, magnesium and alkalinity—as a result of inflows from groundwater and artesian springs connected to the calcareous Floridan Aquifer. Chloride concentrations also are high, even in the freshwater portions of the river, because of the influx of groundwater with high chloride levels. These characteristics provide challenges in treating the water for potable purposes. The river and its tributaries are rich in nutrients (nitrogen and phosphorus) as a result of runoff from agricultural and urban areas, as well as inflows of treated municipal wastewater. The nutrient levels promote luxurious growths of aquatic plants along the river edge and cause algal blooms in the major in-channel lakes, especially in the middle and lower St. Johns River. Upper Basin Projects Three upper basin diversion projects—Three Forks, C-1 basin, and Fellsmere—are underway to return tens of thousands of acres of land to the St. Johns River drainage basin (see Figure 1-2). The three projects were selected from a larger number of potential projects that had been investigated by the District and U.S. Army Corps of Engineers for several years prior to their approval in 1987. Federal funding for the projects was not forthcoming until 2006, when construction began, and they are expected to be completed by 2015. This timeframe is well ahead of the first anticipated water withdrawals (in 2020) considered in the WSIS. The projects involve re-diverting some of the water in the three subbasins from its current destination (the PREPUBLICATION COPY
OCR for page 8
8 Review of the St. Johns River Water Supply Impact Study: Report 3 FIGURE 1-2 Upper Basin Project areas: Phase I C-1, Three Forks Conservation Area (part of C-1 Basin), and Fellsmere Water Management Area. SOURCE: Cera (2010). PREPUBLICATION COPY
OCR for page 9
Introduction 9 Indian River Lagoon) back to the St. Johns River, thus increasing flow in the river. As discussed later in this report, the additional flow is included in some of the WSIS scenarios. In addition to returning the land areas of the upper basin projects to the St. Johns River drainage basin, the projects are intended to provide (1) temporary storage for floodwaters, (2) treatment for stormwater, and (3) open water and wetland habitat for wildlife in a more natural state than the prior use of the land (mostly as pasture). In particular, the marsh conservation areas (e.g., Three Forks) will provide temporary storage for floodwaters. Water management areas (e.g., Fellsmere) are being developed on former agricultural land that experienced considerable soil subsidence and thus provide deep water storage reservoirs to be used for irrigation of remaining agricultural land. The projects will be managed by a system of weirs and pumping stations to direct the water through canals and augment flow to the St. Johns River during normal and dry periods. By reducing the freshwater diversion to the Indian River Lagoon, water quality in the lagoon will be improved (i.e., salinity will be returned to more stable and natural levels). In the WSIS hydrologic modeling studies, water inputs from operating the completed upper basin projects to the St. Johns River were provided as external time series that were produced from modeling complex management scenarios for the project structures. As discussed later, the combined mean annual contribution to flow in the St. Johns River at Cocoa and Christmas from the completed upper basin projects will be between 11 and 14 MGD. BACKGROUND ON THE HYDROLOGY AND HYDRODYNAMICS WORKGROUP Hydrodynamic and hydrology (H&H) studies undertaken for the St. Johns River WSIS are focused on developing models and linkages between models to characterize water flux through the watershed. The H&H effort has four principal parts: 1. Meteorological forcing (precipitation and potential evaporation) 2. Aquifer groundwater fluxes 3. Landscape water fluxes (watershed runoff) 4. River flows Meteorological forcing and groundwater fluxes are the top and bottom boundary conditions for non-tidal water fluxes into and out of the basin. These fluxes primarily have external controls (e.g., climate, weather, geology), but secondary feedbacks from the basin (e.g., local changes in hydraulic head and changes in the landscape that affect transpiration) also influence them. Watershed hydrologic conditions and hydrodynamic constraints on river flows provide the immediate controls on water movement for any given set of meteorological and groundwater conditions. The District separated the analysis of meteorology, groundwater fluxes and the watershed hydrological/hydrodynamic modeling into distinct components as follows: 1. Data from a fixed period of record for precipitation and estimated potential evaporation were used to quantify the atmosphere/landscape interchange required by a watershed hydrological model. 2. Steady-state groundwater flow models based on MODFLOW were used to compute groundwater base flows along the river from the surficial aquifer system and the upper Floridan aquifer. The primary purpose of the groundwater component of the WSIS was to estimate the response of the underlying aquifer to potential water withdrawals in terms of discharge and PREPUBLICATION COPY
OCR for page 10
10 Review of the St. Johns River Water Supply Impact Study: Report 3 aquifer head change, to provide boundary conditions for the mainstem hydrodynamic model, and to provide groundwater data for the water budget calculation. 3. A watershed hydrologic model called HSPF (which stands for hydrologic simulation program—Fortran) was calibrated for gauged sub-basins over the period of record (1995-2006) based on observed streamflow, rainfall, and 1995 land use conditions. 4. A hydrodynamic model of the main stem of the St. Johns River (the Environmental Fluid Dynamics Model or EFDC) was calibrated by varying bottom roughness to improve the fit of modeled flows to measured values. 5. Scenarios for various land use and water withdrawals were simulated with the models to estimate the effects on water levels, the magnitude of flows, and the timing peak and minimum flows throughout the basin. The above approach is a reasonable use of the state-of-the-science for hydrological modeling, and it is reasonable within the context and goals of the WSIS. However, there are several levels of ambiguity inherent in this modeling process that should be acknowledged as the District moves to use the study results to formulate management plans. These issues (described in Chapter 3) are not criticisms of the District’s approach, but rather serve as caveats to what science presently can discern; they should be considered in evaluating the model results. A primary goal of the H&H workgroup is to send relevant data to the environmental workgroups of the WSIS to facilitate their impact analyses. The Committee requested, and received in June 2010, an informal cataloguing of these data to better understand the approaches that each environmental workgroup would be using for its impact analysis. These include data on river water level and salinity (for almost all workgroups), discharge (biogeochemistry, plankton, fish, and submersed aquatic vegetation or SAV workgroups), rainfall and wetland evapotranspiration data (biogeochemistry workgroup), water age and temperature (plankton workgroup), light attenuation (SAV workgroup), and shallow well water levels along some of the MFL transects (wetlands workgroup). In general, the Committee finds these categories of data, and the necessary detail with which they will be provided, as adequate, with the exception of shallow well data for the wetlands workgroup (as described in Chapter 3). SCENARIOS TO BE MODELED The District has decided upon four potential water withdrawal points: one within the upper St. Johns River basin, two in the middle basin, and one in the Ocklawaha River, which flows into the lower St. Johns River basin. The most southern withdrawal point is at the Taylor Creek Reservoir, where 55 MGD would be withdrawn from a canal on the west side of the St. Johns River just north of State Route 520. The first middle basin location is State Route 46, at which 50 MGD would be withdrawn at the northeast end of Lake Jesup. The second middle basin site is at the Yankee Lake project, where 50 MGD would be withdrawn from an intake location already sited on a canal, on the west side of the St. Johns River north of the I-4 crossing (near the outlet of Lake Monroe). The fourth withdrawal point is planned for the Ocklawaha River basin, where up to 107 MGD would be withdrawn upstream of the Rodman Reservoir at a location just north of Route 40 (according to a recent District map). In conducting hydrologic simulations of water withdrawals and their effects on river hydrodynamics, the District considered various combinations of the four withdrawal points. In particular, the scenarios include “no withdrawal,” a “half withdrawal” that corresponds to half PREPUBLICATION COPY
OCR for page 11
Introduction 11 the allotted amount from the three main-stem locations (77.5 MGD), a “full withdrawal” that corresponds to the full allotted amount from the three main-stem locations (155 MGD), and the full withdrawal plus the Ocklawaha withdrawal (262 MGD). In addition to the amount of water withdrawn, the District is altering other variables as it develops scenarios that will reflect future conditions, including changes in land use from 1995 to 2030, changes in how the upper basin is managed, potential sea level rise, future wastewater treatment plant (WWTP) reuse, and dredging in the lower St. Johns River (although simulations that include the latter three issues were not available in time to be reviewed in this report). The three typical scenarios used in the District’s latest hydrology and hydrodynamics report (Cera et al., 2010) are (1) 1995 land use, (2) 1995 land use along with upper basin projects that put water back into the river system; and (3) 2030 land use with the upper basin projects added. For each of these scenarios, the District is simulating the “no withdrawal,” “half withdrawal” (77.5 MGD), “full withdrawal” (155 MGD), and “full withdrawal + Ocklawaha” (262 MGD) cases, for a total of 12 major simulations. It should be kept in mind that each withdrawal scenario is more complicated than is implied by the single MGD value because withdrawals are restricted during low flow periods and then increase as flows increase. For example, the amount of water withdrawn from the river into the Taylor Creek Reservoir will range from 0 to 84 MGD depending on the flow and stage conditions at State Road 50. A constant 55 MGD will be diverted from the reservoir for water supply, while a constant 11 MGD will be released from the reservoir to satisfy minimum flow requirements. Both these reservoir outflows would be cut off when the river stage at State Road 50 drops below 30.0 ft NGVD. PREPUBLICATION COPY