Paul A. Conrads

Flood hydrology and methylmercury availability in coastal plain rivers.

Mercury (Hg) burdens in top-predator fish differ substantially between adjacent South Carolina Coastal Plain river basins with similar wetlands coverage. In the Congaree River, floodwaters frequently originate in the Blue Ridge and Piedmont regions, where wetlands coverage and surface water dissolved methylmercury (MeHg) concentrations are low. Piedmont-driven flood events can lead to downward hydraulic gradients in the Coastal Plain riparian wetland margins, inhibiting MeHg transport from wetland sediments, and decreasing MeHg availability in the Congaree River habitat. In the adjacent Edisto River basin, floodwaters originate only within Coastal Plain sediments, maintaining upward hydraulic gradients even during flood events, promoting MeHg transport to the water column, and enhancing MeHg availability in the Edisto River habitat. These results indicate that flood hydrodynamics contribute to the variability in Hg vulnerability between Coastal Plain rivers and that comprehensive regional assessment of the relationship between flood hydrodynamics and Hg risk in Coastal Plain streams is warranted.

Climate change and watershed mercury export: a multiple projection and model analysis

Future shifts in climatic conditions may impact watershed mercury (Hg) dynamics and transport. An ensemble of watershed models was applied in the present study to simulate and evaluate the responses of hydrological and total Hg (THg) fluxes from the landscape to the watershed outlet and in-stream THg concentrations to contrasting climate change projections for a watershed in the southeastern coastal plain of the United States. Simulations were conducted under stationary atmospheric deposition and land cover conditions to explicitly evaluate the effect of projected precipitation and temperature on watershed Hg export (i.e., the flux of Hg at the watershed outlet). Based on downscaled inputs from 2 global circulation models that capture extremes of projected wet (Community Climate System Model, Ver 3 [CCSM3]) and dry (ECHAM4/HOPE-G [ECHO]) conditions for this region, watershed model simulation results suggest a decrease of approximately 19% in ensemble-averaged mean annual watershed THg fluxes using the ECHO climate-change model and an increase of approximately 5% in THg fluxes with the CCSM3 model. Ensemble-averaged mean annual ECHO in-stream THg concentrations increased 20%, while those of CCSM3 decreased by 9% between the baseline and projected simulation periods. Watershed model simulation results using both climate change models suggest that monthly watershed THg fluxes increase during the summer, when projected flow is higher than baseline conditions. The present studys multiple watershed model approach underscores the uncertainty associated with climate change response projections and their use in climate change management decisions. Thus, single-model predictions can be misleading, particularly in developmental stages of watershed Hg modeling.

Simulation of salinity intrusion along the Georgia and South Carolina coasts using climate-change scenarios

Potential changes in climate could alter interactions between environmental and societal systems and adversely affect the availability of water resources in many coastal communities. Changes in streamflow patterns in conjunction with sea-level rise may change the salinity-intrusion dynamics of coastal rivers. Several municipal water-supply intakes are located along the Georgia and South Carolina coast that are proximal to the present day saltwater-freshwater interface of tidal rivers. Increases in the extent of salinity intrusion resulting from climate change could threaten the availability of freshwater supplies in the vicinity of these intakes. To effectively manage these supplies, water-resource managers need estimates of potential changes in the frequency, duration, and magnitude of salinity intrusion near their water-supply intakes that may occur as a result of climate change. This study examines potential effects of climate change, including altered streamflow and sea-level rise, on the dynamics of saltwater intrusion near municipal water-supply intakes in two coastal areas. One area consists of the Atlantic Intracoastal Waterway (AIW) and the Waccamaw River near Myrtle Beach along the Grand Strand of the South Carolina Coast, and the second area is on or near the lower Savannah River near Savannah, Georgia. The study evaluated how future sea-level rise and a reduction in streamflows can potentially affect salinity intrusion and threaten municipal water supplies and the biodiversity of freshwater tidal marshes in these two areas. Salinity intrusion occurs as a result of the interaction between three principal forces—streamflow, mean coastal water levels, and tidal range. To analyze and simulate salinity dynamics at critical coastal gaging stations near four municipal water-supply intakes, various data-mining techniques, including artificial neural network (ANN) models, were used to evaluate hourly streamflow, salinity, and coastal water-level data collected over a period exceeding 10 years. The ANN models were trained (calibrated) to learn the specific interactions that cause salinity intrusions, and resulting models were able to accurately simulate historical salinity dynamics in both study areas. 1U.S. Geological Survey. 2Advanced Data Mining, LLC, Greenville, South Carolina. Changes in sea level and streamflow quantity and timing can be simulated by the salinity intrusion models to evaluate various climate-change scenarios. The salinity intrusion models for the study areas are deployed in a decision support system to facilitate the use of the models for management decisions by coastal water-resource managers. The report describes the use of the salinity-intrusion models decision support system to evaluate salinity-intrusion dynamics for various climate-change scenarios, including incremental increases in sea level in combination with incremental decreases in streamflow. Operation of municipal watertreatment plants is problematic when the specific-conductance values for source water are greater than 1,000 to 2,000 microsiemens per centimeter (μS/cm). High specific-conductance values contribute to taste problems that require treatment. Data from a gage downstream from a municipal water intake indicate specific conductance exceeded 1,000 μS/cm about 5.4 percent of the time over the 14-year period from August 1995 to August 2008. Simulations of specific conductance at this gaging station that incorporates sea-level rises resulted in a doubling of the exceedances to 11.0 percent for a 1-foot increase and 17.6 percent for a 2-foot increase. The frequency of intrusion of water with specific conductance values of 1,000 μS/cm was less sensitive to incremental reductions in streamflow than to incremental increases in sea level. Simulations of conditions associated with a 10-percent reduction in streamflow, in combination with a 1-foot rise in sea level, increased the percentage of time specific conductance exceeded 1,000 μS/cm at this site from 11.0 to 13.3 percent, and a 20-percent reduction in streamflow increased the percentage of time to 16.6 percent. Precipitation and temperature data from a global circulation model were used, after scale adjustments, as input to a watershed model of the Yadkin-Pee Dee River basin, which flows into the Waccamaw River and Atlantic Intracoastal Waterway study area in South Carolina. The simulated streamflow for historical conditions and projected climate change in the future was used as input for the ANN model in decision support system. Results of simulations incorporating climate-change projections for alterations in streamflow indicate an increase in the frequency of salinity-intrusion events and a shift in the seasonal occurrence of the intrusion events from the summer to the fall. 2 Simulation of Salinity Intrusion Along the Georgia and South Carolina Coasts Using Climate-Change Scenarios Introduction Adapting to future climatic change will likely present numerous challenges to water-resource managers in coastal regions of the world. The east coast of the United States falls into this category, given the large number of people living along the Atlantic seaboard and the added strain on resources as populations grows, particularly in the Southeast. Increased temperatures, changes in regional precipitation regimes, and rises in sea level may have a large effect on existing hydrological systems in coastal regions. Many of the major municipal water-supply intakes along the southeastern coast of the United States are considered to be vulnerable to anticipated changes in climate (fig. 1; Furlow and others, 2002). Four of the municipal intakes in figure 1 are along the South Carolina and Georgia coast and were analyzed for this report. Two intakes are in the Waccamaw River–Atlantic Intracoastal Waterway (AIW) area, and two are in the lower Savannah River estuary along the South Carolina and Georgia border. The balance between streamflow conditions within a coastal drainage basin and sea levels governs the characteristics and frequency of salinity intrusion into coastal rivers. Salinity intrusion into freshwater coastal rivers has been, and continues to be, one of the most important global challenges for coastal water-resource managers, industries, and agriculture (Bear and others, 1999). Major economic and environmental consequences of saltwater intrusion include the degradation of natural ecosystems and the contamination of municipal, industrial, and agricultural water supplies (Bear and others, 1999). Coastal communities need to find approaches for the sustainability of freshwater supplies while minimizing the impact on natural systems. Increases in the frequency, magnitude, and duration of salinity intrusion into the coastal rivers near the surface-water intakes could increase the vulnerability and threaten the potability of water at the four freshwater municipal intakes, as well as the biodiversity of nearby freshwater tidal marshes. Waccamaw River, AIW, and lower Savannah River, as with many major estuarine systems, supply many local and regional water-resource needs. The tidal parts of these systems supply water to the growing coastal communities along the South Carolina and Georgia coasts, provide assimilative capacity for municipal wastewater discharges, and offer recreational opportunities along the coast (figs. 2, 3). With increases in industrial and residential development along the South Carolina and Georgia coasts, there are competing, and often conflicting, demands on coastal water resources. Coastal water-resource managers need planning tools that will provide estimates of the change in the magnitude, frequency, and duration of salinity intrusion events near water intakes projected to occur in response to anticipated changes in climate. Changes in climate could affect precipitation patterns and result in changing patterns of streamflow to the coast. Climate change also could affect the rate of sea-level rise. Concerns associated with sea-level rise are not limited to the flooding of low-lying coastal areas but include effects of altered salinity-intrusion dynamics on the availability of freshwater supplies along the coast. For municipalities with water-supply intakes in tidally affected waters proximal to the freshwater-saltwater interface, the convergence of changes in hydrologic regime and sea-level rise associated with potential climate change could have a dramatic effect on salinity intrusion and freshwater availability. Fortunately, there have been extensive data collection and salinity modeling efforts for areas near water-supply intakes in the two study areas, Waccamaw River and AIW, South Carolina, and lower Savannah River, Georgia. These monitoring and modeling efforts were initiated to address various coastal water-resources issues. Although these efforts did not directly address the effects of salinity intrusion resulting from potential climate change, the data and models (with modifications) can be used by interested parties to evaluate climate-change effects. Figure 1. Vulnerability ratings for potential salinity intrusion at selected major municipal water-supply intakes along the coast of the Gulf of Mexico and the Atlantic Ocean (modified from Furlow and others, 2002). High vulnerability Medium vulnerability Low vulnerability No data EXPLANATION Salinity intrusion TEXAS LOUISIANA MISSISSIPPI ALABAMA NORTH CAROLINA

Living with a large reduction in permited loading by using a hydrograph-controlled release scheme.

The Total Maximum Daily Load (TMDL) for ammonia and biochemical oxygen demand for the Pee Dee, Waccamaw, and Atlantic Intracoastal Waterway system near Myrtle Beach, South Carolina, mandated a 60-percent reduction in point-source loading. For waters with a naturally low background dissolved-oxygen concentrations, South Carolina anti-degradation rules in the water-quality regulations allows a permitted discharger a reduction of dissolved oxygen of 0.1 milligrams per liter (mg/L). This is known as the “0.1 rule.” Permitted dischargers within this region of the State operate under the “0.1 rule” and cannot cause a cumulative impact greater than 0.1 mg/L on dissolved-oxygen concentrations. For municipal water-reclamation facilities to serve the rapidly growing resort and retirement community near Myrtle Beach, a variable loading scheme was developed to allow dischargers to utilize increased assimilative capacity during higher streamflow conditions while still meeting the requirements of a recently established TMDL.As part of the TMDL development, an extensive real-time data-collection network was established in the lower Waccamaw and Pee Dee River watershed where continuous measurements of streamflow, water level, dissolved oxygen, temperature, and specific conductance are collected. In addition, the dynamic BRANCH/BLTM models were calibrated and validated to simulate the water quality and tidal dynamics of the system. The assimilative capacities for various streamflows were also analyzed.The variable-loading scheme established total loadings for three streamflow levels. Model simulations show the results from the additional loading to be less than a 0.1mg/L reduction in dissolved oxygen. As part of the loading scheme, the real-time network was redesigned to monitor streamflow entering the study area and water-quality conditions in the location of dissolved-oxygen “sags.” The study reveals how one group of permit holders used a variable-loading scheme to implement restrictive permit limits without experiencing prohibitive capital expenditures or initiating a lengthy appeals process.

The use of data-mining techniques for developing effective decision support systems: a case study of simulating the effects of climate change on coastal salinity intrusion

Abstract Natural-resource managers and stakeholders face difficult challenges when managing interactions between natural and societal systems. Potential changes in climate could alter interactions between environmental and societal systems and adversely affect the availability of water resources in many coastal communities. The availability of freshwater in coastal streams can be threatened by saltwater intrusion. Even though the collective interests and computer skills of the community of managers, scientists and other stakeholders are quite varied, there is an overarching need for equal access by all to the scientific knowledge needed to make the best possible decisions. This paper describes a decision support system, PRISM-2, developed to evaluate salinity intrusion due to potential climate change along the South Carolina coast in southeastern USA. The decision support system is disseminated as a spreadsheet application and integrates the output of global circulation models, watershed models and salinity intrusion models with real-time databases for simulation, graphical user interfaces, and streaming displays of results. The results from PRISM-2 showed that a 31-cm and 62-cm increase in sea level reduced the daily availability of freshwater supply to a coastal municipal intake by 4% and 12% of the time, respectively. Future climate change projections by a global circulation model showed a seasonal change in salinity intrusion events from the summer to the fall for the majority of events.

Tidal flow dynamics and background fluorescence of the Atlantic Intracoastal Waterway in the vicinity of Sullivan’s Island and the Isle of Palms, South Carolina, 2011-12

To effectively plan site-specific studies to understand the connection between wastewater effluent and shellfish beds, data are needed concerning flow dynamics and background fluorescence in the Atlantic Intracoastal Waterway near the effluent outfalls on Sullivan’s Island and the Isle of Palms. Tidal flows were computed by the U.S. Geological Survey for three stations and longitudinal water-quality profiles were collected at high and low tide. Flows for the three U.S. Geological Survey stations, the Atlantic Intracoastal Waterway by the Isle of Palms Marina, the Atlantic Intracoastal Waterway by the Ben M. Sawyer Memorial Bridge at Sullivan’s Island, and Breach Inlet, were computed for the 53-day period from December 4, 2011, to January 26, 2012. The largest flows occurred at Breach Inlet and ranged from -58,600 cubic feet per second (ft3/s) toward the Atlantic Intracoastal Waterway to 63,300 ft3/s toward the Atlantic Ocean. Of the two stations on the Atlantic Intracoastal Waterway, the Sullivan’s Island station had the larger flows and ranged from -6,360 ft3/s to the southwest (toward Charleston Harbor) to 8,930 ft3/s to the northeast. Computed tidal flow at the Isle of Palms station ranged from -3,460 ft3/s toward the southwest to 6,410 ft3/s toward the northeast. The synoptic water-quality study showed that the stations were well mixed vertically and horizontally. All fluorescence measurements (recorded as rhodamine concentration) were below the accuracy of the sensor and the background fluorescence would not likely interfere with a dyetracer study. Introduction Proposed changes in water-quality limits for fecal coliform may have potential effects on the open shellfish beds (those beds where harvesting is allowed) near the effluent outfalls of the Sullivan’s Island and the Isle of Palms wastewater treatment plants (fig. 1). A number of alternative study approaches can be used to better understand the potential connections between wastewater effluent and the shellfish bed, including dye-tracer studies, sediment sampling for wastewater indicators, and thermal plume tracking. To effectively plan such studies, data are needed concerning the flow dynamics and background fluorescence of the Atlantic Intracoastal Waterway near the effluent outfalls on Sullivan’s Island and the Isle of Palms in South Carolina. Tidal flow dynamics of the Atlantic Intracoastal Waterway, located on the landward side of the barrier islands along the South Carolina coast, are quite complex because of reversing tidal flows, interconnected tidal creeks, multiple connections between barrier islands and the Atlantic Ocean, wetting and drying of extensive tidal marshes, and semidiurnal tides with a 5to 7-foot (ft) vertical range. Often, flows in these systems are characterized by large, bidirectional tidal excursions during the flood and ebb tides and by small residual (net) flows over the tidal cycle. Dye fluorometry is an established method for tracing the movement of water in many hydrologic settings. When used as a tracer, the concentration of a dye is directly proportional to its fluorescence. Background fluorescence can interfere or enhance the fluorescence of the dye, thereby causing overestimation of the movement and dispersion of the dye (Hartel and others, 2007). Elevated background fluorescence can be caused by optical brighteners commonly found in the effluent of wastewater treatment plants and septic tanks. Optical brighteners have the ability to fluoresce and interfere with the measurement of rhodamine dye used as a hydrologic tracer. Other sources of background fluorescence include naturally occurring humic substances that produce the “blackwater” of coastal waters, synthetic organic compounds that can reach the water during rainfall runoff, and various by products from pulp and paper production (Hartel and others, 2007). The U.S. Geological Survey (USGS), in cooperation with the South Carolina Department of Health and Environmental Control, initiated a data-collection effort in 2011 to measure the tidal flow dynamics and background fluorescence in the 2 Tidal Flow Dynamics and Background Fluorescence of the Atlantic Intracoastal Waterway

The Evolution and Development of Improved Data Collection Methods and Mobile Networks for the Observation of Inland Hurricane Storm Surge

1U.S. Geological Survey, 415 National Center, Reston, VA 20192; PH 703-6485305; email rrmason@usgs.gov 2U.S. Geological Survey, Stephenson Center, Suite 129, 720 Gracern Road, Columbia, SC 29210; PH 803-750-6140; email pconrads@usgs.gov 3U.S. Geological Survey 3916 Sunset Ridge Road, Raleigh, N.C. 27607; PH 919571-4017; email jrobbins@usgs.gov 4U.S. Geological Survey, Peachtree Business Center, Suite 130, 3030 Amwiler Road, Atlanta GA 30360; PH 770-903-9127; email bemccall@usghs.gov 5U.S. Geological Survey, 6000 “J” Street, Placer Hall, Sacramento, CA 95819; PH 916-278-3227; ceberenb@usgs.gov

Using "big data" to optimally model hydrology and water quality across expansive regions

This paper describes a new divide and conquer approach that leverages big environmental data, utilizing all available categorical and time-series data without subjectivity, to empirically model hydrologic and water-quality behaviors across expansive regions. The approach decomposes large, intractable problems into smaller ones that are optimally solved; decomposes complex signals into behavioral components that are easier to model with sub-models; and employs a sequence of numerically optimizing algorithms that include time-series clustering, nonlinear, multivariate sensitivity analysis and predictive modeling using multi-layer perceptron artificial neural networks, and classification for selecting the best sub-models to make predictions at new sites. This approach has many advantages over traditional modeling approaches, including being faster and less expensive, more comprehensive in its use of available data, and more accurate in representing a systems physical processes. This paper describes the application of the approach to model groundwater levels in Florida, stream temperatures across Western Oregon and Wisconsin, and water depths in the Florida Everglades.