South Carolina has experienced several droughts during the past decade. The ability to survey and monitor water use across the State has become necessary. Using an existing water use database, an end-user application was developed to query ground water and surface water users separately. Water use can easily and interactively be totaled by county boundaries, watershed boundaries, water use type, or any combination of these conditions. The application, additionally, creates output maps from the result of the queries. Hydrologists and decision-makers can use this information to evaluate the status of water resources and then provide sound management recommendations.

South Carolina, during the last century, has enjoyed an abundant supply of water that has adequately met the State’s water demands. In recent decades, however, demand has increased in response to strong regional economic development. The water supply sources have been adversely affected by more frequent and persistent droughts. The management of the State’s water resources has received, consequently, a great deal of attention and scrutiny. The use of a geographic information system (GIS) has been a major aid in a successful implementation and evaluation of new management strategies.

Drought management decisions are made on the basis of hydrological, meteorological, and water demand information. Hydrological and meteorological data are constantly monitored by gauging stations while water use information is not. In order to provide timely information to water resources managers, an interactive GIS application was developed using ArcView software. Using this application, valuable water use data are quickly displayed on a map of South Carolina showing pertinent information such as, but not limited to, geographical location, user name and phone number, and daily water use.

To prepare a comprehensive database of water users in South Carolina, information from several sources had to be compiled. Data used for this study were obtained from the South Carolina Departments of Health and Environmental Control (DHEC), Commerce (DOC), and Natural Resources (DNR).

Six databases with water use and related information were obtained from DHEC:

a) WSINV.DBF, South Carolina Public-Drinking Water Inventory, is a compilation of public supply systems.

b) METER.DBF, Meter Systems, is a listing of public supply facilities that purchase water from other systems.

c) CU_MONIT.DBF, Capacity Use Monitoring, is a compilation of ground water users in the two Capacity Use Areas: Low Country and Waccamaw.

d) CAPUSE.DBF is a support file for the CU_MONIT.DBF that contains general information on users in the capacity use areas.

e) WU_MONIT.DBF, Water Use Program, is a record of users that pump more than 100,000 gallons per day.

f) WATERUSE.DBF is a support file for the WU_MONIT.DBF that contains basic information on the Water Use Program users.

Two databases with geographic information on selected public supply systems were obtained from DOC:

g) WATDAT.DBF has attribute data associated with public-supply service areas.

h) COVERAGE ARC/INFO has service-area coverage for public supply systems by Council of Government (COG) region.

One database with information on water wells was obtained from DNR:

i) WELLTAB.DBF is an inventory of water wells in South Carolina.

These databases were compiled and used to compute an average usage of water, in million gallons per day (MGD), and to identify location of sources, types of use, and distribution of water use. To facilitate the presentation of information, the database was divided into surface water and ground water. ArcView shapefiles were created containing the water intake locations for surface water and ground water. All databases were subjected to a limited quality-control check. Filters were run on the data to isolate gross errors. In many cases the records from one database were cross-correlated with the other databases to verify the information, mostly regarding location and use type. In a few cases, errors were corrected by contacting users; and several records were deleted because the data were unusable, for example, the reported usage was zero. Overall, the best source of information was the WSINV file and the worst was the WU_MONIT file. A reason for the difference in data quality may be that information for the WSINV comes from a program that is mandatory whereas information for the WU_MONIT comes from a program that is voluntary.

A summary of the water use in South Carolina for 1950-1996 is presented in Table 1. The information from 1950 through 1991 was obtained from the previously mentioned reports and from 1992 through 1996 from DHEC files. In this table and in the report the following convention has been followed:

PS, public supply, includes water that is used mostly for drinking and household uses, although a considerable percentage may also be used for industrial and commercial purposes.

IND, industrial, includes systems that use water for industrial and commercial purposes and are self-supplied.

OTH, other purposes, includes golf-course (GC) and crop irrigation (IR), mining (MI), and most other types of water use not covered in this classification.

Power, includes systems that use water for the production of energy, such as hydroelectric power (HP), nuclear power (NP), and thermal power (TP). Although NP is a type of TP, it has been listed separately to emphasis its importance. Nearly all of the water withdrawn for these types of uses is returned to the source.

For simplicity, the amounts given in tables have been reported in million gallons per day and were rounded upward. Table 1 shows that during the mid-1950's and the 1980's there was a decrease in water use for HP. During those years, South Carolina underwent prolonged drought, which in some months became severe. This illustrates the dependency that hydropower production has on surface water availability. Another interesting point is the decrease of IND usage after 1989, when the Savannah River Site shut down its nuclear reactors.

From 1994 to 1996, the total water use in South Carolina ranged from 59 to 68 billion gallons per day. More than 98 percent of that total was used for power generation, most of which was returned to the source, a small fraction being lost to evaporation. The remaining 2 percent, approximately 1.1 billion gallons per day, were used mostly for public supply and industrial purposes. By comparison, the aggregate daily flow of the rivers in South Carolina averages 33 billion gallons (SCWRC, 1993), which shows that, in South Carolina, surface water is used, on average, almost two times before it flows into the ocean; for the nation, the average is three times. This suggests that South Carolina could be more efficient in the utilization of its water resources.

TABLE 1. Water Use in South Carolina 1950-1996

(Millions of gallons per day)

Table 2 provides a breakdown of water use by county. Excluding power generation, public supply and industry are the largest water users in South Carolina (Figure 1). Moreover, a large percentage of the public-supply demand is for industrial purposes. For example, Andrews in Georgetown County used 1.67 MGD for public supply in 1994 and had a per capita use of over 500 gpd/p. This per capita use is nearly three times the State’s average (151 gpd/p), which suggests that two-thirds of the public-supply use in Andrews was for industrial purposes. Thus, forecasting industrial use, which is related to economic growth and development, is critical. This will be accomplished by using a combination of land-use/land-cover and population-density information, which will be explained and discussed in a future report.

TABLE 2. Water use in South Carolina counties, 1994

(millions of gallons per day)

• Self-supplied population set to 19 percent of county population

Figure 1. Water use in South Carolina by type, 1994-1996.

An ArcView application was developed for hydrologists to monitor water use. A customized interface prompts for a selection between surface water use or ground water use. Next, a view of South Carolina with water intake locations is displayed in ArcView. The water intake shapefile is linked to the water use database using a one-to-many relationship. The average MGD is totaled by intake location. The water intake location table is displayed along with the water use database table.

Water intake locations may be selected and analyzed individually, by type, by county that the location is in (Figure 2), by the county that uses the water (regardless of intake location), or by river basin. The selected records are highlighted and promoted in both tables. Water use is easily totaled based on the selections. The interface provides a button to display only the records selected (Figure 3). Additionally, maps may be generated from the result of the queries. Hydrologists and decision-makers can use this information to evaluate the status of water resources and then provide sound management recommendations.

Figure 2. Selection of surface water intakes within York County.

Figure 3. Surface water intakes located in York County.

South Carolina had a reported water use of 59.4 billion gallons per day in 1994, 68.4 in 1995, and 67.4 in 1996. More than 98 percent of the use was for power generation, in which most of the water withdrawn was returned to the original source. Of the remaining, 48 percent was for public supply, 51 percent for industry, and 1 percent for other uses. Except for power generation, the reported water use is believed to be, at best, a low estimate of the actual use.

South Carolina, in 1994, had few sites where use was high (more than 20 MGD), some areas with moderate usage (from 1 to 10 MGD), and most with low use (less than 0.1 MGD). The water use appeared to be concentrated in five regions: (1) the northwest, around Greenville-Spartanburg-Rock Hill; (2) the center, around Aiken-Columbia-Florence; (3) the northeast, around Myrtle Beach-Georgetown; (4) the southeast, around Charleston; and (5) the south, around Beaufort-Hilton Head.

Currently, the ArcView Water Use Application is an efficient tool to examine these existing conditions. The application may be further enhanced with additional data layers and analysis of land use/ land cover, climatological data, and population-density. Models should be developed within in the application to forecast long-term water use availability and demand.

Water Resources Commission, 1993. South Carolina water use, four year report 1988-1991. South Carolina Water Resources Commission, 16p.

Suzanne O’Brien White

GIS Analyst

Ogden Environmental and Energy Services, Co., Inc.

3800 Ezell Road

Nashville , TN 37211

(615) 333-0630 phone

(615) 781-0655 fax

sowhite@oees.com

Joffre E. Castro, Ph.D.

Senior Hydrologist

South Carolina Department of Natural Resources

1201 Main Street, Suite 1100

Columbia, SC 29201

(803) 737-0800 phone

Castro@water.dnr.state.sc.us