Daniel R. Hitchcock

SWAT-BASED STREAMFLOW AND EMBAYMENT MODELING OF KARST-AFFECTED CHAPEL BRANCH WATERSHED, SOUTH CAROLINA

SWAT is a GIS-based basin-scale model widely used for the characterization of hydrology and water quality of large, complex watersheds; however, SWAT has not been fully tested in watersheds with karst geomorphology and downstream reservoir-like embayment. In this study, SWAT was applied to test its ability to predict monthly streamflow dynamics for a 1,555 ha karst watershed, Chapel Branch Creek, which drains to a large embayment and is comprised of highly diverse land uses. SWAT was able to accurately simulate the monthly streamflow at a cave spring (CS) outlet draining mostly agricultural and forested lands and a golf course plus an unknown groundwater discharging area, only after adding known monthly subsurface inputs as a point source at that location. Monthly streamflows at two other locations, both with multiple land uses, were overpredicted when lower lake levels were prevalent as a result of surface water flow to groundwater (losing streams). The model underpredicted the flows during rising lake levels, likely due to high conductivity and also a deep percolation coefficient representing flow lost to shallow and deep groundwater. At the main watershed outlet, a wide section performing as a reservoir embayment (R-E), the model was able to more accurately simulate the measured mean monthly outflows. The R-E storage was estimated by using a daily water balance approach with upstream inflows, rainfall, and PET as inputs and using parameters obtained by bathymetric survey, LiDAR, and downstream lake level data. Results demonstrated the substantial influence of the karst features in the water balance, with conduit and diffuse flow as an explanation for the missing upstream flows appearing via subsurface conveyance to the downstream cave spring, thus providing a more accurate simulation at the embayment outlet. Results also highlighted the influences of downstream lake levels and karst voids/conduits on the watershed hydrologic balance. Simulation performance of hydrology could be improved with more accurate DEMs obtained from LiDAR for karst feature identification and related modification of SWAT parameters. This SWAT modeling effort may have implications on nutrient and sediment loading estimates for TMDL development and implementation in karst watersheds with large downstream embayments that have significant changes in water level due to adjoining lakes.

Water Use and Treatment in Container-Grown Specialty Crop Production: A Review

While governments and individuals strive to maintain the availability of high-quality water resources, many factors can “change the landscape” of water availability and quality, including drought, climate change, saltwater intrusion, aquifer depletion, population increases, and policy changes. Specialty crop producers, including nursery and greenhouse container operations, rely heavily on available high-quality water from surface and groundwater sources for crop production. Ideally, these growers should focus on increasing water application efficiency through proper construction and maintenance of irrigation systems, and timing of irrigation to minimize water and sediment runoff, which serve as the transport mechanism for agrichemical inputs and pathogens. Rainfall and irrigation runoff from specialty crop operations can contribute to impairment of groundwater and surface water resources both on-farm and into the surrounding environment. This review focuses on multiple facets of water use, reuse, and runoff in nursery and greenhouse production including current and future regulations, typical water contaminants in production runoff and available remediation technologies, and minimizing water loss and runoff (both on-site and off-site). Water filtration and treatment for the removal of sediment, pathogens, and agrichemicals are discussed, highlighting not only existing understanding but also knowledge gaps. Container-grown crop producers can either adopt research-based best management practices proactively to minimize the economic and environmental risk of limited access to high-quality water, be required to change by external factors such as regulations and fines, or adapt production practices over time as a result of changing climate conditions.

Streamflow and nutrients from a karst watershed with a downstream embayment: Chapel Branch Creek

Understanding sources of streamflow and nutrient concentrations are fundamental for the assessment of pollutant loadings that can lead to water quality impairments. The objective of this study was to evaluate the discharge of three main tributaries, draining different land uses with karst features, as well as their combined influences on total nitrogen (TN) and total phosphorus (TP) levels in reservoir-like embayment (R-E) on a stream entering Lake Marion, South Carolina. From 2007-2009, hydrology, TN, and TP data were collected from the 1,555-ha Chapel Branch Creek (CBC) watershed. In general, monthly streamflow in all tributaries was found to be �10% of rainfall, and as little as 0.1% in the smallest tributary. The third tributary flowed into a cave system and discharged via a cave spring (CS) into the embayment while gaining a sustained groundwater flow from a second cave (GW) system. The CS flow was substantially larger than the flow measured in the other tributaries. The small amount of rainfall that became surface flow and the large flow at the cave spring indicated a significant water loss from the surface watershed to subsurface flow or a groundwater source area substantially larger than the surface watershed. Nutrient concentrations in flows from tributaries draining various land uses were not significantly different (α ¼ 0.05) for most of the locations. A simple water balance was developed to estimate the R-E outflow to Lake Marion using measured discharges from three tributaries, change in storage computed using a bathymetric survey, daily lake level changes, rainfall, and computed evaporation. Mean monthly TN and TP concentrations in the embayment were substantially lower than the observed means from the two tributary outlets and the CS into the embay- ment, indicating a loss in the embayment. The second cave system at CS, representing an unknown subsurface drainage area, was the source of nearly 50% of TP loading, over 50% of flow, and over 70% of TN loading to CBC. These results may have implications in water quality management of the CBC watershed. DOI: 10.1061/(ASCE)HE.1943-5584.0000794.

FLOW CHARACTERIZATION IN THE SANTEE CAVE SYSTEM IN THE CHAPEL BRANCH CREEK WATERSHED, UPPER COASTAL PLAIN OF SOUTH CAROLINA, USA

Karst watersheds possess both diffuse and conduit flow and varying degrees of connectivity between surface and groundwater over spatial scales that result in complex hydrology and contaminant transport processes. The flow regime and surface- groundwater connection must be properly identified and characterized to improve management in karst watersheds with impaired water bodies, such as the Chapel Branch Creek (CBC), South Carolina watershed, which has a long-term sampling station presently listed on an EPA 303(d) list for phosphorous, pH, and nitrogen. Water from the carbonate limestone aquifer of the Santee Cave system and spring seeps in the CBC watershed were monitored to characterize dominant flow type and surface-groundwater connection by measuring dissolved calcium and magnesium, total suspended solids, volatile suspended solids, alkalinity, pH, specific conductance, and stable isotopes (d 18 O, d 2 H). These measurements indicated that the conduit flow to Santee Cave spring was recharged predominantly from diffuse flow, with a slow response of surface water infiltration to the conduit. Qualitative dye traces and stage elevation at Santee Cave spring and the adjacent Lake Marion (equal to the elevation of the flooded portion of CBC) also indicated a relation between fluctuating base level of the CBC reservoir-like embayment and elevation of the Santee Limestone karst aquifer at the spring. Methods described herein to characterize the flow type and surface-groundwater connection in the Santee Cave system can be applied not only to watershed management in the Chapel Branch Creek watershed, but also to the greater region where this carbonate limestone aquifer exists.

Chapel branch creek TMDL development: integrating TMDL development with implementation

Chapel Branch Creek is a small creek draining into Lake Marion near Santee, SC. Lake Marion is an important recreational area for coastal South Carolina, and the adjacent Town of Santee receives much of its economic activity from related tourism. The creek is on the South Carolina Department of Health and Environmental Control’s (SCDHEC) list of impaired waters (2004 - 303d list) for excess nitrogen (N), phosphorus (P), chlorophyll-a, and pH. Despite being only 1600 ha, the watershed has an unusually large number of land uses with varying potential nonpoint sources of N and P: sewage effluent spraying, golf course management, highway runoff, urban and residential stormwater runoff, agriculture and some forests. Contamination of Chapel Branch Creek directly impacts the economic health of the local community. Our initial meetings with stakeholders revealed that vigorous debate has occurred for the past decade over the sources of contamination and responsibility for clean-up.

Hydrology and Water Quality of Chapel Branch Creek Watershed with Karst Topography, SC

Understanding watershed hydrology and the concentrations of nutrients in stream waters are fundamental considerations for assessing water quality loadings for a pollutant impairing the water body. In this study, supported by SC DHEC’s 319 Grant Program, hydrology and phosphorus (TP) data collected from a 1,555 ha, mixed land use, Chapel Branch Creek (CBC) watershed were analyzed for a near three-year (2007-09) period. The main objectives of the study were to evaluate the flows and TP concentrations of three main tributaries draining different land uses with karst features and their combined influences on total phosphorus (TP) levels in downstream flooded CBC embayment. In general (except for two months), monthly stream flow was found to be less than 10% of incoming rainfall at one tributary (SL2), and with as little as 0.1% at the 2nd smaller tributary (SL1). A third tributary flowed into a cave system and entered the embayment from a cave spring (CS). Monthly flow measured at the cave spring (CS) outlet included a sustained base flow, and was substantially higher than the flow measured at the two other tributaries (SL1 and SL2). This sustained flow originated from a stream within a second cave connected to the cave spring. These values strongly suggest that there was a significant loss of water from the watershed to subsurface flow, possibly in dissolution channels associated with the karst features. Total phosphorus (TP), concentrations were highest at SL1 with the wastewater irrigation on its land, followed by SL2 with primary influence of town storm water and highway runoff, and smallest concentrations at the cave spring (CS). A simple water balance was developed to estimate the outflow from the downstream embayment of the creek to the lake based on the measured inputs from those three major tributaries, change in storage computed using a bathymetric survey and daily water level changes at Lake Marion, rainfall, and computed evaporation. Monthly TP concentrations measured in the embayment for the 2007-09 period were above the water quality standard of 0.06 mg/L for 12 out of 22 months. However, the mean monthly value in the embayment was substantially lower than the mean values of grab and automated samples observed at each of the main tributaries, indicating a loss in the embayment due to various processes in the water body and sediment-water interface. This information was critical for both the hydrologic and water quality modeling as well as source area identification and estimates of TP loading including developing a Total Maximum Daily Load (TMDL) that are complicated on this karst dominated, mixed land use Chapel Branch watershed.

Application of SWAT Model on Chapel Branch Creek Watershed with a Karst Topography, SC

SWAT, a widely used GIS-based basin scale model to characterize the hydrology and water quality for large, complex watersheds as a function of land use, soils, topography, management practices and their interactions with variability in climate, has not been fully tested on watersheds on karst topography. In this study, SWAT was used to evaluate monthly stream flow dynamics for a 1,555 ha mixed land use Chapel Branch Creek (CBC) watershed with karst features draining to Lake Marion near Santee, SC. In order to apply the SWAT model for simulating the hydrology, efforts were first made to calibrate the stream flows at three in-stream subwatersheds draining to the downstream flooded portion of the CBC at the edge of the Lake Marion using three years (2006-09) of climatic data across the watershed. The watershed was delineated into 31 smaller subwatersheds and 472 HRUs using the ArcView SWAT2003 model with DEMs for topography, SSURGO data base for soils, NAIP2005 imagery for land use, and other field observations. Out of the three main in-stream locations used for the flow calibration, the first one at the Cave Spring CS outlet (1089 ha) drained mostly agricultural and forested lands and a golf course besides an unknown subsurface area for groundwater discharging at this point. Land use draining the second one at SL-2 (550 ha) was comprised of mostly developed area of Town of Santee, highways and roads, and some agricultural and forested lands some of which had karst features characterizing the sinkholes and depressions and loosing streams. The third subwatershed drained an area of 63 ha containing a part of a golf course receiving effluents from a wastewater treatment plant within it. The model was able to capture the monthly streamflow at the cave spring (CS) outlet only after adding a known monthly baseflow as a point source at that location with a limited data. The monthly flow at the SL-2 location was over-predicted for the months with high and normal rainfall as expected as a result of loosing streams during lower lake levels. The model under-predicted the flows during high lake levels likely due to high conductivity and deep percolation coefficient used to lose flow to shallow groundwater and out of the system, respectively. The model validated at the main outlet of the watershed performing as a reservoir embayment was able to capture the measured monthly outflows during the wet periods. The measured monthly outflows of the flooded reservoir like embayment at the outlet were estimated by using a daily water balance approach with bathymetric survey and LIDAR data to obtain the volume of the embayment. This result showed the significance of the watershed karst features in the water balance with conduit and diffuse flow as a possible explanation for the missing flow from the SL-2 station that apparently appeared downstream at the cave spring as ground water flow, indicating a need to modify SWAT for accounting karst features for an accurate water balance. Secondly, the results also reflected on the effects of interactions of lake levels and voids/conduits of the karst features on the hydrology of the study watershed. These results may have large implication on estimates of nutrient and sediment loadings including TMDL development.

Assessing Spatiotemporal Nutrient Patterns for the Optimization of Wastewater Treatment Wetland System Performance

The objective of this study was to determine and evaluate spatial and temporal relationships between water quality parameters, and nutrient and solids concentrations within a constructed wastewater treatment wetland system in the Georgia Piedmont, USA. The study was designed to explore factors relating to system treatment efficiency through spatial characterization of water quality parameters and constituent concentrations, which were extremely variable over space and time. Results indicated significant relationships between temperature, dissolved oxygen concentrations, and redox potential, as well as relationships between these water quality parameters and inorganic nitrogen concentrations. Because temperature, dissolved oxygen concentration, and redox potential typically affect nitrification and denitrification, seasonal trends were evident, and significant correlations were found between these water quality parameters and inorganic nitrogen concentrations. Also, organic nitrogen and inorganic and organic phosphorus concentrations were closely correlated with solids concentrations in samples collected throughout the vegetated section of the system without any seasonal trends. Results indicated that the water column within the vegetated section generally exhibited anaerobic conditions, leading to significant removal of nitrate- nitrogen. Results also indicated that water quality parameters had little effect on solids removal percentages across the vegetated wetland section. This study demonstrated that the conditions affecting wastewater treatment in vegetated wetland systems are not only highly variable but also significantly correlated. This study also provides insight into the optimal conditions for effective water quality improvement, most specifically in terms of inorganic nitrogen removal, as well as considerations and recommendations for appropriate operations and maintenance practices.

Developing Stormwater Educational Programs for Rapidly Urbanizing Areas

Like many areas throughout the U.S., urban growth within South Carolina is occurring at a tremendous rate. As a result of environmental concerns, the Clemson University Cooperative Extension Service initiated public education programs in communities across the state. This presentation provides details about how Clemson became involved, as well as Extension’s role in implementing programs in local communities having diverse needs. The presentation describes development along with many other issues involved with developing and funding long term programs that meet regulatory requirements.

Reducing Stormwater Impacts from Coastal Development Using Ecological Strategies

Development in coastal South Carolina, USA, is occurring at a tremendous rate. Existing developed areas contribute to a significant increase in the percentage of impervious surface area per total area of land, resulting in increased stormwater runoff and decreased infiltration. The low topographic relief and shallow water table, however, present interesting challenges in stormwater management practice decision-making. Retention ponds are the typical stormwater management practice in coastal South Carolina; however, these ponds often become sources of various pollutants. Ecologically-based systems, such as constructed wetlands, vegetated buffers, and bioretention cells are examples of solutions that may be implemented to address water quality issues, specifically those associated with stormwater. This paper focuses on various proposed studies as part of a larger research program. The overall program objective is the assessment of various systems and strategies for mitigating water quality/quantity impacts due to the conversion of coastal forested areas to developed residential and commercial areas. In this paper, overarching questions include (1) what systems are effective in coastal South Carolina for stormwater management and water quality improvement between upland area land uses ( residential and commercial development) and downstream water resources (creeks, ponds, rivers, lakes), and (2) how is shallow water table hydrology (water quantity) altered and downstream water quality impacted when forested areas are converted to urban areas? This work is dedicated to understanding the impacts of polluted runoff, while identifying, implementing, and evaluating ecological stormwater management practicies and low impact development (LID) solutions to reduce potential impacts in coastal areas with shallow water tables.