2019 Recharge Report

HYDROLOGIC DATA FACT SHEETS

GROUNDWATER RECHARGE 2019

2019 GROUNDWATER RECHARGE Recharge to the Edwards Aquifer originates as precipitation over the drainage area and recharge zone of the aquifer, or as interformational flow from adjacent aquifers. The EAA maintains a joint funding agreement with the U.S. Geological Survey (USGS) to provide surface recharge estimates for eight of the nine major drainage basins with streams that flow on to the Edwards Aquifer recharge zone (Figure 1). Recharge is estimated using a water-balance method that relies on precipitation and streamflow measurements across the region. Based on the USGS methodology, the Guadalupe River Basin does not appear to provide significant recharge to the Edwards Aquifer, so recharge is not estimated for that drainage basin. Table 1 lists estimated annual recharge by drainage basin for the period of record from 1934 through 2019 based on USGS calculations. Estimates of total annual recharge ranged from 43,700 acre-feet during the drought of record in 1956 to 2,486,000 acre-feet in 1992, as shown in Figure 2. In 2019, total estimated recharge was 492,000 acre-feet, which is below both the mean annual recharge of 706,000 acre-feet and the median annual recharge of 557,000 acre-feet for the period of record. In an effort to enhance recharge, the EAA operates four recharge dams in Medina County on the Edwards Aquifer Recharge Zone (yellow triangles in Figure 1). The total amount of enhanced recharge for each site is estimated using data from stage recorders near these structures. Enhanced recharge refers to the estimated amount of additional recharge attributable to these structures above the amount of recharge that would have occurred naturally in the absence of these structures. Table 2 shows the estimated annual enhanced recharge for each site starting in 2014. Recharge estimates in Table 2 prior to 2014 reflect total annual recharge at each dam site. The total estimated enhanced recharge for these structures in 2019 was 90.9 acre-feet. Enhanced recharge is generally a small fraction of total recharge and tends to be greater in wet years when natural recharge is also high. Recharge resulting from interformational flow in adjacent aquifers such as the Trinity Aquifer is not estimated annually. Estimates associated with interformational flow are variable and range from 5,000 to 100,000 acre-feet per year in different publications. Estimated interformational recharge is not included in recharge values provided in this report. Edwards Aquifer Authority is presently conducting an Interformational Flow Study that may help to better quantify the amount of water that may enter the Edwards Aquifer from Trinity Aquifer formations to the north.

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Figure 1. Major Drainage Basins and Edwards Aquifer Authority-Operated Recharge Structures in the San Antonio Segment of the Balcones Fault Zone Edwards Aquifer.

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Table 1. Estimated Annual Groundwater Recharge to the San Antonio Segment of the Balcones Fault Zone Edwards Aquifer by Drainage Basin, 1934–2019 (in thousands of acre-feet).

Area between Medina River and Cibolo Creek/ Dry Comal Creek Basins

Area between Sabinal River and Medina River Basins

Nueces River/ West Nueces River Basin

Cibolo Creek/Dry

Frio River/ Dry Frio River Basin

Comal Creek Basin

Blanco River Basin

Medina River Basin

Sabinal River Basin

Total a 179.6

Year 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973

8.6

27.9

7.5

19.9

46.5 71.1 91.6 80.5 65.5 42.4 38.8 54.1 51.7 41.5 50.5 54.8 51.4 44.0 14.8 33.0 23.6 21.1 25.4 36.2 25.3 16.5 55.6 95.5 94.7 88.3 57.3 41.9 43.3 54.6 50.5 44.7 59.9 55.4 68.0 68.7 87.9 97.6 6.3

21.0

28.4

19.8 39.8 42.7 21.2 36.4 11.1 18.8 57.8 28.6 20.1 46.2 35.7 40.7 31.6 13.2 23.5 17.4 10.6 20.7 24.9 10.7 76.4 70.7 33.6 62.4 49.4 18.9 16.2 22.2 66.7 34.6 19.0 49.3 46.6 39.5 22.2 33.4 82.2 9.5 8.2

411.3 176.5

192.3 157.4

56.6 43.5 21.5 20.9 17.0 23.8 50.6 34.0 11.1 24.8 30.8 16.5 16.7 26.0 31.5 13.3

166.2 142.9

138.2 108.9

182.7 146.1

1,258.2

909.6 400.7 432.7 399.0 308.8 850.7 557.8 273.1 560.9 527.8 556.1 422.6 178.3 508.1 200.2 139.9 275.5 167.6 162.1 192.0 690.4 824.8 717.1 239.4 170.7 413.2 623.5 615.2 466.5 884.7 610.5 661.6 925.3 756.4 43.7

28.8 63.5

75.7 69.3 49.5 60.3 95.1 42.3 76.0 71.1 54.2 77.7 25.6 86.1 35.5 28.4 15.7 15.1 31.6 22.1

61.3 54.1 33.1 56.6 84.4 33.8 74.3 78.6 52.0 45.2 20.2 70.3 27.0 26.4 30.2

47.8 46.2

63.9 76.8

227.0

9.3

9.6

50.4 89.9

29.3

30.8

151.8

139.0

116.3 66.9 29.5 72.5 79.6 55.5 17.5 41.8 17.3 15.3 50.1 20.1 105.1

191.2

103.5 36.5 64.1 47.3 80.9 72.4 41.1 41.5 18.3 27.9 21.4 61.3 166.0 128.0 108.6 266.7 109.6 15.6

93.6 58.3

152.5 129.9 155.3

79.5 19.9 55.9 24.6 12.5

7.3 3.2 3.2 7.1 0.6 1.6

102.3

4.4

42.3 10.0

11.9

4.2 4.3 2.0

7.7 3.6

3.3 2.2

4.2

133.6 300.0 158.9 128.1 151.3

65.4

129.5 294.9

175.6 190.9

397.9 268.7

1,142.6 1,711.2

223.8

61.6 64.9 57.4

96.7

57.4 89.7 69.3 16.7 35.8 78.8 44.5 30.2 83.1 60.2 68.8 81.4 74.3 9.3

77.9

88.7 85.2 47.4 39.7

127.0 105.4

104.0

160.0 110.8

46.6 27.0 57.1 83.0

4.3 5.0

23.5 10.3 61.3

24.7 21.3 51.1

126.1

16.3 23.2 37.7 30.4 66.4 30.7 35.4 39.2 49.0

97.9

104.0

115.3

169.2

134.0 137.9 176.0 113.8 141.9 212.4 144.6 256.9

78.2 64.8

66.5 57.3

82.2

130.8 119.7 112.6 263.4 108.4 190.6

198.7

120.5

84.2 81.6

99.9

113.8

155.6 154.6 286.4

82.4

104.2 211.7

123.9

237.2

1,486.5

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(Table 1. continued)

Area between Medina River and Cibolo Creek/ Dry Comal

Area between Sabinal River and Medina River Basins

Nueces River/ West Nueces River Basin

Cibolo Creek/Dry Comal Creek Basin

Frio River/ Dry Frio River Basin

Sabinal River Basin

Medina River Basin

Blanco River Basin

Creek Basins

Year 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

Total

91.1 71.8

135.7 143.6 238.6 193.0

36.1 47.9 68.2 62.7 30.9 68.6 42.6

115.3 195.9 182.0 159.5 103.7 203.1

96.2 93.4 94.5 77.7 76.7 89.4 88.3 91.3 76.8 74.4 43.9 64.7 74.7 90.4 69.9 46.9 54.0 52.8 91.4 78.5 61.1 61.7 42.3 63.3 80.3 77.1 53.4 90.0 93.7 86.6 95.5 82.8 47.7 75.2 53.6 45.6 68.2 43.3 41.6 10.8

68.1

76.9

39.1 85.9 57.9 66.7 26.3 75.2 31.8 67.3 23.5 23.2 25.9 50.7 44.5

2

138.8 47.9 97.9 49.6 85.4 18.8 22.6 31.9 11.3 165.0 136.7 170.2 229.3 290.6 38.9 34.1 36.2 10.6 86.2 21.2 28.6 193.4 101.5 175.5 12.6 4.6 35.9 84.5

195.7

973.0 894.1 952.0 502.5

150.7 102.9

54.3

191.6

69.8

73.1

72.4

128.4

201.4

266.3

1,117.8

58.6

85.6

25.3

55.4

406.4

205.0

365.2 123.4

105.6

252.1

196.8

1,448.4

19.4 79.2 32.4

21.0 20.1

90.9 42.9 18.1

44.8 62.5 16.9

422.4 420.1 197.7

85.9 40.4

8.8

105.9 188.4 308.5

186.9 192.8 473.3 117.9 255.0 421.0 586.9 52.6

50.7 42.2

148.5 173.6 405.5

259.2 267.4 270.9

1,003.3 1,153.7 2,003.6

110.7

114.9

59.2 52.6

17.0

24.9 13.5

28.5 12.3 71.8

25.5

355.5 214.4

8.4

23.6 41.3 96.9 37.8 36.6 30.6 13.9 82.3 21.0 34.1 89.7 74.1 17.9 96.9 18.5 27.5 57.5 18.3 51.6 42.1 16.5 59.9

479.3 325.2 234.1 124.6 107.1 130.0 176.9 141.5 101.4 238.4 297.5 149.8 481.9 105.5 32.6 83.6

54.6

131.2 315.2 566.1

1,123.2 1,508.4 2,485.7

103.1 201.1

109.7 286.6

226.9

78.5

29.6 29.5 34.7 11.4 57.0 72.5 30.8 33.1 66.2 70.6 31.7

60.8 45.1 62.4

90.9 55.6 51.1 14.7

447.6 538.1 531.3 324.3

151.5 147.6

92.0

9.4

209.1 214.8 136.8 123.0 126.7 207.3 112.2 424.5 147.2

208.4 201.4

144.2 240.9

1,134.6 1,142.3

104.7

57.2 55.2

27.9 48.6

473.5 614.5

124.1 345.2

173.7 447.8 105.0 315.0 140.4

1,069.4 1,573.7

150.0

67.4

56.2

669.0

185.8

2,176.1

116.0

343.9

213.4

50.1

79.1

84.8

764.0 201.6

45.5

60.2

9.0

5.0

5.1

11.2

471.8

474.4

104.0

406.4

227.6

306.1

2,162.3

48.2 58.5

44.5 30.3

5.9 1.8

9.8

9.6 7.3

22.8 26.4

212.9 210.9 813.5 112.0 313.5 182.6 107.2

13.5

135.4

104.9

31.5

186.3

81.4

148.2

15.3 78.3 67.7 19.8

13.7 82.6 26.7 32.8

1.0 8.9 0.5 4.9

2.0

3.0 3.9 3.3 0.4

15.3 32.2 28.7

14.4

2.8

9.5

14.4

8.9

343.8

281.9

42.2

218.4

54.6

131.6

177.3

108.3

1,358.1

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(Table 1. continued)

Area between Medina River and Cibolo Creek/ Dry Comal

Area between Sabinal River and Medina River Basins

Nueces River/ West Nueces River Basin

Cibolo Creek/Dry Comal Creek Basin

Frio River/ Dry Frio River Basin

Sabinal River Basin

Medina River Basin

Blanco River Basin

Creek Basins

Year 2016 2017 2018 2019

Total

275.7 122.0

247.8

52.4 17.0 57.3 27.2

184.1

77.5 72.6 66.8 86.8

110.9

186.4

86.3 55.0 42.9 39.1

1,221 487.0 1,100

95.4 316 91.8

30.4 168 40.6

25.0 22.8 35.2

68.8 71.1 81.0

360 90.6

492

Recharge statistics for the period of record 1934–2019: Median 102 116 31.2 76.3

61.4 61.9

48.8 69.2

77.4 109

37.2 47.4

557 706

Mean

130

139

40.7

110

Recharge for the period of record 2010–2019 (last ten years): Median 106 93.6 22.1 36.5

60.7 53.1

23.9 41.8

70.0 81.9

47.3 51.8

490 619

Mean

151

129

24.3

86.1

Data source: USGS letter report (April 10, 2020). a Totals may not exactly equal sum of all basins due to rounding.

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Figure 2. Estimated Annual Recharge for the San Antonio Segment of the Balcones Fault Zone Edwards Aquifer, 1934–2019.

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Table 2. Estimated Annual Enhanced Recharge from Edwards Aquifer Authority-Operated Recharge Structures for 2019 (measured in acre-feet).

Parker (April 1974)

Middle Verde (April 1978)

San Geronimo (November 1979)

Seco (October 1982)

Year 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019

Annual Total

160 620

--- --- --- ---

--- --- --- --- ---

--- --- --- --- --- --- --- ---

160 620

2,018

2,018

6

6

98

150

248

2,315

1,725

0

4,040 1,274 4,102

0

371

903

772

1,923

1,407

3 0

112 254 246 440 889

91

0 0

206 254 640

0 0

251 232 217

143 643

1,097

2,412 3,649 20,336

963

1,580 12,915

2,104

4,141

1,176

0 0

0 0

0 0

0 0

0 0

49

176 966

41

479

745

647 723

1,647 2,874

2,160 14,631

5,420 21,003

2,775

0

0 0

334

508

842 164

159

0

5

18

79

51

880

1,028

0

0

0

0

0

2,941 a 1,469 a/b

2,154 b 1,160 b 1,371 b 657 b/d 1,511 0 b

1,579 b

7,515 b 3,796b

14,189 b 7,297 b 7,901 b 4,422 b/d 26,544 1,314 21,993 50 b/c

872 b

0 b

0 b

50 c

901 b 526 b

1,023 b 1,085 b/d

4,606 b 2,154 b/d 18,872

1,811

4,350

665

184 170

0

465

2,363

4,778

14,682

795

0 0

0 0

58

853

0

0

0

5,998

2,091

7,268

10,645

26,002

2.6 630 10 1.0 0.6 759 419

2.5 31 4.5 51

0

0

5

0.1

28

688

1,356

1,324

4,375

6,171

13,226

1.0

0

16

0 0 0

98 0.4 319

150 1.0

0

38.0 816 747

1,116 7,079 8,799

1,163 1,776 4,056 14.7 0

4,682 4,018 5,838 76.2 0

2,257

35

0

0

756

1,333

11,983

0

0

90.9

Data source: Unpublished Edwards Aquifer Authority files (2020). a = Written communication from USGS, San Antonio Subdistrict Office. b = Determined by linear-regression analysis using rainfall data and historical recharge data. c = Linear-regression analysis indicates zero recharge; however, one recharge event was observed that was estimated to have recharged 50 acre-feet. d = Part of 2001 recharge estimate provided by HDR Engineering, Inc. (unpublished report). --- = Years prior to construction of recharge structure.

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