Georgia s Aquifers. USGS Fact Sheet

Transcription

1 Georgia s Aquifers USGS Fact Sheet

2 2005 Groundwater Use by Aquifer Withdrawal (mgd) % 17.5% 7.6% 6.0% 9.2% 4.3% 60% 50% 40% 30% 20% 10% 0% Percent of Withdrawal 86.5% of groundwater was withdrawn from Coastal Plain aquifers in southern Georgia (Floridan, Cretaceous, Claiborne, Clayton) 13.5% of groundwater was withdrawn from crystalline rock and Paleozoic rock aquifers in northern Georgia Floridan Cretaceous Claiborne Clayton Crystalline Rocks Paleozoic Rocks Aquifer Withdrawal (mgd) % of Withdrawal Data from USGS SIR

3 2005 Groundwater Use by Principal Aquifer USGS SIR

4 2005 Groundwater Withdrawals USGS SIR

5 Percentage of 2005 Water Withdrawals from Groundwater USGS SIR

6 Metropolitan North Georgia Water Planning District 6

7 Water Use in the Metropolitan North Georgia Water Planning District n Within the Metro Water District, including both surface and groundwater, almost 888 average annual day (AAD)-MGD of permitted water supply is available n Groundwater accounts for less than 1 percent of the water supply within the Metro Water District n Over the 2035 planning horizon, it is expected that the percentage of groundwater use will remain about constant n The City of Roswell (Fulton County) plans to continue to use a combination of groundwater and surface water sources 7

8 Groundwater Use in the Metropolitan North Georgia Water Planning District 8

9 Groundwater Use in the Metropolitan North Georgia Water Planning District Bartow County USGS SIR Cherokee County Rockdale County 9

10 Priori&zed Aquifers for Determina&on of Sustainable Yields Paleozoic Rock Aquifer Dougherty Plain Upper Floridan Aquifer Crystalline Rock Aquifer Coastal Plain Aquifers 10

11 Groundwater in the Crystalline Rock Aquifer USGS Water Supply Paper

12 Groundwater Storage in the Crystalline Rock Aquifer USGS Water Supply Paper

13 Permitted Groundwater Withdrawals from the Crystalline Rock Aquifer 13

14 Projected Groundwater Availability from the Crystalline Rock Aquifer Estimated 40 mgd from 280 Wells Area will support one or more wells yielding 100 gpm Area eliminated from consideration due to potential point source pollution GGS Open File Report

15 Piedmont and Blue Ridge Water Budget Basins Blue Ridge Basin Piedmont Basin 315 mi mi 2 15

16 Chattahoochee River Helen Gauge and USGS Well 16MM03 16

17 Base Flow Component of Total Stream Flow USGS Circular

18 Chattahoochee River Helen Gauge and USGS Well 16MM03 18

19 Sustainable Yield of the Crystalline Rock Aquifer is Related to Streamflow n September is usually the month of lowest stream flow in Georgia n Constraining groundwater use to mean September stream flow or base flow minus a percentage of the stream flow (Tennant threshold) would maintain opportunities for surface water use during a month of low stream flow n Others managing groundwater resources in crystalline rock aquifers of the eastern United States with hydrogeology similar to the Georgia Piedmont and Blue Ridge have used 20% of the stream flow or base flow metric as a sustainable yield 19

20 Net Groundwater Available Based on Total Stream Flow 20

21 Net Groundwater Available Based on Stream Base Flow 21

22 Sustainable Yield of the Crystalline Rock Aquifer n More groundwater is available from the crystalline rock aquifer than is currently being withdrawn n It might be difficult to find sufficient waterbearing fractures in the crystalline rock aquifer to develop the full range of sustainable yield n Because it might be difficult to find sufficient water-bearing fractures planning for use of groundwater should focus on the lower-end of the sustainable yield range 22

23 Sustainable Yield of the Crystalline Rock Aquifer n Net groundwater availability in the 163 squaremile Piedmont study basin was 0.6 to 2.1 mgd, or to mgd/mi 2 n Net groundwater availability in the 315 squaremile Blue Ridge study basin was 10.3 to 19.1 mgd, or to mgd/mi 2 n If the availability of groundwater is similar to that in the in the Piedmont and Blue Ridge study basins, the availability of groundwater from the crystalline rock aquifer in the Piedmont and Blue Ridge of Georgia may be in the range of 141 to 361 mgd, more than current withdrawals 23

24 Paleozoic Rock Aquifers Knox/Shady Dolomites Conasauga Limestone Well or Spring etowahwaterbank.com 24

25 Permitted Groundwater Withdrawals from Paleozoic Rock Aquifers 25

26 Northwestern Georgia Model Boundary and Current Groundwater Withdrawals 26

27 Northwestern Georgia Model Grid 27

28 Northwestern Georgia Model Boundary and Simulated Withdrawals 28

29 Northwestern Georgia Model Layers 29

30 Coosawattee River Pine Chapel Gauge and USGS Well 07KK64 30

31 Coosawattee River Pine Chapel Gauge and USGS Well 07KK64 31

32 Sustainable Yield of Paleozoic Rock Aquifers n Dry-year stream baseflow was simulated with no groundwater withdrawals and plotted as cubic feet per second (CFS) versus the day of the year n Simulated dry-year baseflow minus 10% of simulated average year baseflow was plotted as CFS versus the day of the year n The difference between the two plots was the sustainable yield envelope for an average year n Baseflow with groundwater withdrawals was simulated to fall within the envelope to determine the sustainable yield for an average year 32

33 Average Year Sustainable Yield Paleozoic Rock Aquifer Sustainable Yield of 70 MGD Increased from Current 15 MGD Simulated Dry-Year Baseflow with No Groundwater Withdrawals Simulated Baseflow with Groundwater Withdrawals of 70 Million Gallons per Day Sustainable Yield Envelope Simulated Dry-Year Baseflow Minus 10% of Average-Year Baseflow 33

34 Sustainable Yield Paleozoic Rock Aquifer n The sustainable yield envelope for a dry year was the simulated dry-year baseflow with no groundwater withdrawals minus 10% of the simulated dry-year baseflow n Baseflow with groundwater withdrawals was simulated to fall within the envelope to determine the sustainable yield for a dry year n Less baseflow and less groundwater recharge from surface water is available during a dry year than during an average year n 10% of the dry year baseflow was smaller than 10% of the average year baseflow so that the dry-year sustainable yield envelope was smaller than the average year sustainable yield envelope 34

35 Dry Year Sustainable Yield Paleozoic Rock Aquifer Sustainable Yield of 27 MGD Increased from Current 15 MGD Simulated Dry-Year Baseflow with No Groundwater Withdrawals Simulated Baseflow with Groundwater Withdrawals of 27 Million Gallons per Day Sustainable Yield Envelope (smaller than average year) Simulated Dry-Year Baseflow Minus 10% of Dry-Year Baseflow (which is smaller than 10% of average-year baseflow and results in a smaller envelope for sustainable yield) 35