Mapping Center Pivot Irrigation Fields in South Carolina with Google Earth Engine and the National Agricultural Imagery Program

Aerial images taken during the growing seasons of 2009, 2011, 2013, 2015, and 2017 were visually inspected for evidence of irrigation. Center pivot irrigation was identified by the characteristic shape of the spans and the curved tracks left by the wheels. The author manually delineated a polygon over each agricultural area where signs of irrigation infrastructure were observed. The result is a map of 2,689 polygons covering 146,662 acres in South Carolina. Compared with the United States Department of Agriculture 2017 Census of Agriculture, the sampling results account for over 69% of total irrigated area and over 98% of area irrigated solely by center pivots. Most center pivots covered from 25 to 75 acres, while the largest center pivot extended over 300 acres. These results are an important contribution to the quantification of water use in South Carolina.

Understanding Stakeholders’ Knowledge, Awareness, and Perception of Conservation Programs in South Carolina

The increasing population and economic growth of South Carolina make it attractive for landowners to convert their land to commercial and urbanized zones. However, since ecosystems are directly affected by land use, changes in these land uses directly impact the ecosystem services (ES). Therefore, efforts to conserve ecosystems are paramount and are often supported through conservation-incentive programs. One approach for conservation programs is to provide economic incentives for landowners to retain their land as forest or agricultural land. The success of these programs eventually affects the ES recipients or “end-users,” particularly the residents. Therefore, it is important to understand the stakeholders’ perceptions toward these programs. Understanding the landowners’ perception can provide information on how to engage them to join the conservation programs. Furthermore, knowing the residents’ perception could improve the “buy-in” or support from the public for promoting conservation within the community. The stakeholders’ perception can serve as a feedback mechanism and could provide key information for improving implementation strategies for conservation programs. This study elicited the knowledge, awareness, and perception of South Carolina residents and landowners to conservation programs. Results show that while a majority are not aware of the conservation programs being implemented in the state, there is no doubt that residents and landowners know the importance of conservation and how it affects their well-being. However, since many conservation concepts use technical terminology, stakeholders have increased difficulty grasping these concepts. This poses a challenge for academics and conservation agencies to improve communication methods and better impart conservation messaging. The results also show that residents are willing to support the conservation programs; landowners are willing to participate in conservation activities, especially if they are compensated. Therefore, this emphasizes a good opportunity to establish stakeholder-driven strategies such as sustainable financing mechanisms for conservation programs.

Streamflow and Tidal Dynamics in the Lower Pee Dee Basin: Hurricane Impacts

Over past years, extreme tropical storm events along the North and South Carolina coasts—and subsequent river flooding—have warranted the need for a better understanding of the hydrologic response to these events to protect life, property, businesses, and natural and cultural resources. Our focus in this study is the Pee Dee and Waccamaw River systems, which ultimately flow into Winyah Bay near Georgetown, South Carolina. River flows, coupled with the tidal nature of these freshwater systems, are complex and difficult to predict. The objective of the work is to analyze publicly available data from gauging stations along those river system as measured during Hurricanes Matthew and Florence and Tropical Storm Bertha—three uniquely different storm systems that produced varying rainfall depth, duration, and intensity across the Pee Dee Basin. The most important factor in tidal river analysis is the location of the stagnation point , where downstream river flow exactly balances upstream tidal flow. River flow only controls water level upstream of a tidal stagnation point, while ocean tide controls the water level downstream of a tidal stagnation point. An analysis of major flooding following Hurricanes Matthew, Florence, and Tropical Storm Bertha was used to determine the river flows associated with tidal stagnation at each stream gauge active during these storms. A major limitation of the analysis was a lack of flow data for the tidal channels in Georgetown County, which resulted in uncertainty in the flow associated with stagnation and uncertainty in the role played by each of the creeks that connect the Pee Dee and Waccamaw Rivers. Ignorance of the roles of these creeks most limited understanding of the relative importance of Pee Dee and Waccamaw flow to cause stagnation near Pawleys Island and Hagley gauges on the Waccamaw River and the Socastee gauge on the Atlantic Intracoastal Waterway.

A Multi-Reservoir Study of the Impact of Uncertainty in Pool Evaporation Estimates on Water-Availability Models

Quantifying evaporative loss from reservoirs plays a critical role in sound water-availability management plans and in reservoir management. Various methods are used to quantify reservoir evaporation; however, each method carries a degree of uncertainty that propagates to model predictions of available water within a reservoir or a reservoir network. Herein, we explore the impact of uncertainty in reservoir evaporation on model outputs of historical and future water availability throughout the five major reservoirs in the Savannah River Basin in South Carolina, USA, using four different evaporation methods. Variability in the total available water is evaluated using the United States Army Corps of Engineers (USACE) 2006 Drought Contingency Plan hydrologic model of the Savannah River Basin, which incorporates recent water-management plans and reservoir controls. Results indicate that, during droughts, reservoir evaporation plays a large role in water-availability predictions, and uncertainty in evaporative losses produces significant uncertainty in modeled water availability for extreme events. For example, the return period for an event in which the availability of water in Lake Hartwell was reduced to 50% of full pool capacity varied from 38.2 years to 53.4 years, depending on the choice of evaporation parameterization. This is a variation of 40% in the return period, depending on the choice of evaporation method.

Modeling Tidal Characteristics in a Creek-Marsh Drainage System: Implications for Stormwater Management

The traditional goal of stormwater management is to reduce the threat of flooding to life and property, and so most landscapes are engineered to maximize the speed at which the unwanted water leaves the watershed. This has been effective in landscapes with some topographic gradient. This often involves the installation of drainage ditches that disperse runoff from urban areas to receiving water bodies; in coastal areas this means a tidal creek, estuary, bay, sounds, or the coastal ocean. This practice reduces flood hazards in some cases but results in unintended effects on the natural hydrology in the watershed and downstream tidal dynamics. For low-gradient watersheds in humid climates, ditch systems also lower the water table of an area, increasing infiltration to recharge and groundwater discharge to streams (baseflow), and larger volume of freshwater delivered downstream yearround. Ditches also create unintentional avenues for the incoming tide from a tidal creek or tidally-influenced waterway to reach further inland, thus reducing the hydraulic gradient between the inland areas and the receiving water body. The combination of these effects can exacerbate compound flooding events, increasing the flood probability if high tide and storm events coincide. Additionally, coastal communities face the challenge of mitigating more complicated flood hazards while land development increases to meet the needs of a growing population. This study analyzed the tidal influence within an inland drainage ditch in the central coast of South Carolina USA that is representative of thousands of artificially-drained coastal watersheds. The ditch-creek system investigated here is 12 km long in a 753-hectare (1860-acre) watershed of Church Flats Creek, a first-order tidal system. We monitored for 13 months a 0.75-km reach of the lower ditch portion of the system, just above the relatively undisturbed tidal creek and marsh. Prior to ditching in the 1960s this system had a wetland-rich floodplain but is now partially tidal. Field data collected were stream stage (depth), discharge, tidal range, tidal volume, incoming (flood) and outgoing (ebb) tidal durations, and water table hydrograph at a location about 50 m of mid-reach of the ditch. Multiple linear regressions were performed to best predict the flood and ebb tidal durations of the system based on tidal characteristics within the ditch. The mean values were 229 ± 2.5 and 182 ± 2.1 minutes for flood and ebb tide durations, respectively and the models explained 84% (residual standard error (RSE) of 25 minutes) and 80% (RSE of 23 minutes) for the flood and ebb conditions, respectively. The models were simulated for sea levels in 1993 and 2050, and results indicate that the flood tide within the drainage ditch is predicted to increase an average of 66 minutes and the total tidal duration (flood and ebb) an average of 139 minutes by 2050. These results suggest a loss in drainage functionality as sea level rises. Increases in the duration of tidal influence will induce a lower capacity for stormwater volume than the drainage infrastructure was constructed to manage, therefore resulting in an increased frequency of compound flooding events because of the lower storage volume and decreased hydraulic gradient in the system. This study fills a knowledge gap of tidal dynamics within coastal ditch-creek systems and we urge stormwater managers to consider the unintended consequences of using traditional stormwater methods in a region that does not benefit from gravity drainage practices like in other regions.

Floodplain Geomorphology and Response to Hurricanes: Lower Pee Dee Basin, South Carolina

Undeveloped forested wetlands in the valleys of coastal plain rivers can play a large role in storing floodwater and attenuating river flooding. In the lower Pee Dee, Little Pee Dee, and Lynches Rivers, these wetlands played a large role in mitigating downstream flooding following Hurricane Florence. Wetland forest flood mitigation was most effective for large flows in the Great Pee Dee River, where flooding on former river terraces determined the course of overbank flow and the potential storage of floodwaters. Floodwater storage and attenuation of water level were less effective if larger flows were limited to the Little Pee Dee River. Large rains prior to Hurricane Matthew, and to a lesser extent Tropical Storm Bertha, caused the forested wetland to be a source of additional flow, although with little increase in peak stage.

Overview of the South Carolina State and River Basin Planning Framework

Economic development, environmental protection, and public health are critical quality-of-life issues that depend on a reliable supply of water. Increased water demand and climate variability (drought) are two major factors that have the potential to limit future water availability in the state of South Carolina. The development of a comprehensive water-resources management plan for the state is vital for ensuring that an adequate and reliable supply of water will be available to sustain all future uses. The South Carolina Department of Natural Resources (SCDNR) is tasked legislatively with developing water planning and policy initiatives in the state and has initiated a long-term process to update the state water plan, last published in 2004. One of the major recommendations in the 2004 plan was to form River Basin Councils (RBCs) in each of the major river basins in the state for the purpose of water planning. In 2014, SCDNR initiated a multiyear process to develop regional water plans that will serve as the foundation for a new state water plan. A central component of the process was the creation of a Planning Process Advisory Committee (PPAC) for the purpose of developing formal guidelines on the formation of RBCs and the development of river basin plans for the eight designated river basins in the state. The PPAC is composed of a diverse group of stakeholders and includes representation from water utilities, energy utilities, trade organizations, academia, conservation groups, agriculture, and the general public. The work of the PPAC culminated in a report, the South Carolina State Water Planning Framework, which was published in October of 2019. The river basin plans will identify current and future water availability issues and describe a management plan to address these issues to ensure that an adequate and reliable supply of water will be available for future generations. The purpose of this paper is to provide a general overview of the state’s river basin planning process.

Long-Term Ecohydrologic Monitoring: A Case Study from the Santee Experimental Forest, South Carolina

Long-term research on gauged watersheds within the USDA Forest Service’s Experimental Forest and Range (EFR) network has contributed substantially to our understanding of relationships among forests, water, and hydrologic processes and watershed management, yet there is only limited information from coastal forests. This article summarizes key findings from hydrology and water-quality studies based on long-term monitoring on first-, second-, and third-order watersheds on the Santee Experimental Forest, which are a part of the headwaters of the east branch of the Cooper River that drains into the harbor of Charleston, South Carolina. The watersheds are representative forest ecosystems that are characteristic of the low-gradient Atlantic Coastal Plain. The long-term (35-year) water balance shows an average annual runoff of 22% of the precipitation and an estimated 75% for the evapotranspiration (ET), leaving the balance to groundwater. Non-growing season prescribed fire, an operational management practice, shows no effects on streamflow and nutrient export. The long-term records were fundamental to understanding the effects of Hurricane Hugo in 1989 on the water balance of the paired watersheds that were related to vegetation damage by Hugo and post-Hugo responses of vegetation. The long-term precipitation records showed that the frequency of large rainfall events has increased over the last two decades. Although there was an increase in air temperature, there was no effect of that increase on annual streamflow and water table depths. The long-term watershed records provide information needed to improve design, planning, and assessment methods and tools used for addressing the potential impacts of hydrologic responses on extreme events; risk and vulnerability assessments of land use; and climate and forest disturbance on hydrology, ecology, biogeochemistry, and water supply.

A Comparison of the Diurnal Variation in Lake Surface Temperature for the Five Major Lakes of the Savannah River Basin

Satellite measurements of lake surface temperature can benefit several environmental applications such as estimation of lake evaporation, predictions of lake overturning, and meteorological forecasts. Using a one-dimensional lake simulation that incorporates satellite measurements of lake surface temperature, the average diurnal variation in lake surface temperature was obtained. The satellite measurements were obtained from the MODIS instrument aboard the Aqua and Terra satellites. Herein the functional form for the diurnal variation in surface temperature is presented for each of the five major lakes in the Savannah River Basin, which are located in South Carolina and Georgia: Lakes Jocassee, Keowee, Hartwell, Russell, and Thurmond. Differences in the diurnal variation in surface temperature between each of these lakes are identified and potential explanations for these differences are presented.

Stakeholder Engagement: Methods of Inclusion in South Carolina State Water Plan Decision-Making

Stakeholder engagement in natural resource planning has become increasingly important at local and state levels. Including stakeholders in decision-making can increase buy-in and public support of final regional and state recommendations. It can also lead to policy change and improved implementation outcomes resulting from these planning processes. South Carolina is developing a stakeholder-driven water plan, although it is several years away from being finalized. The methods used in this process are a departure from past efforts. Stakeholder inclusion in decision-making in the water planning process is described and analyzed in this article. The focus is on the specific phases of the process and the methods of inclusion used or those anticipated to be used. In this cycle, stakeholder involvement in decisions range from informational/advisory to consultative to decision-making.