2018 Recharge-Report

2017 GROUNDWATER RECHARGE 2018 GROUNDWATER HARGE

November 2018 A u g u s t 2 1 9

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 2018 based on USGS calculations. Estimates of total annual recharge ranged from 43,700 acre-feet at the height of the drought of record in 1956 to 2,486,000 acre-feet in 1992, as shown in Figure 2. In 2018, total estimated recharge was 1,100,000 acre-feet, which is above both the mean annual recharge of 709,000 acre-feet and the median annual recharge of 558,000 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 2018 was 11,983 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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EDWARDS AQUIFER AUTHORITY |

Caldwell

Hays

Guadalupe

Wilson

7

Comal

8

Atascosa # * EAA-Operated Recharge Structure Drainage Basin Boundary County boundaries Aquifer Zones Drainage Area Recharge Zone Artesian Zone

Blanco

Bexar

Legend

9

Kendall

San

Geronimo Creek Verde

# * # * # *

6

Miles

0 10 20 30 40 5

Gillespie

Creek

5

# * # * # * # * # * # *

Frio

Medina

Creek

Parker

# * # * # *

Bandera

Kerr

2 3 4

Seco

Creek

Uvalde

Zavala

Real

San Antonio Segment of the Balcones Fault Zone Edwards Aquifer

Figure 1. Major Drainage Basins and Edwards Aquifer Authority-Operated Recharge Structures in the

1

Edwards

Kinney

Maverick

Nueces-West Nueces River Basin Frio-Dry Frio River Basin Sabinal River Basin

Area between Sabinal and Medina River Basin Medina River Basin

Guadalupe River Basin* Blanco River Basin

and Cibolo/Dry Comal Creek Basins

Cibolo and Dry Comal Creek Basins** Area between Medina River Basin

9

4

1

7

3

8

2

6

* The current method of estimation does not attribute any net recharge to this basin. **Recharge is reported as a single basin for these two basins.

Key to Basins

5

.

2 | 2018 RECHARGE REPORT

2018

(709,000 AF)

(590,600 AF)

1933 1935 1937 1939 1941 1943 1945 1947 1949 1951 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015 2017

(1,100,000 AF)

Total Annual Recharge

Historical Mean (1934-2018)

Ten-Year Mean (2009-2018)

Figure 2. Estimated Annual Recharge for the San Antonio Segment of the Balcones Fault Zone Edwards Aquifer, 1934–2018 0

500

2500

2000

1500

1000

Thousands of Acre-Feet

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EDWARDS AQUIFER AUTHORITY |

Table 1. Estimated Annual Groundwater Recharge to the San Antonio Segment of the Balcones Fault Zone Edwards Aquifer by Drainage Basin, 1934–2018 (in thousands of acre-feet).

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

Area between Sabinal River and Medina River Basins

Cibolo Creek/ Dry Comal Creek Basin

Nueces River/ West Nueces River Basin

Frio River/ Dry Frio River Basin

Sabinal River Basin

Blanco River Basin

Medina River Basin

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

Total a 179.6

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

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

39.8 1,258.2

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 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 9.5 8.2

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

76.4 1,142.6 70.7 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

82.2 1,486.5

4 | 2018 RECHARGE REPORT

(Table 1. continued)

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

Area between Sabinal River and Medina River Basins

Cibolo Creek/ Dry Comal Creek Basin

Nueces River/ West Nueces River Basin

Frio River/ Dry Frio River Basin

Blanco River Basin

Sabinal River Basin

Medina River Basin

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 a

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

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

75.2 1,117.8

58.6

85.6

25.3

55.4

31.8

406.4

205.0

365.2 123.4

105.6

252.1

196.8

67.3 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

23.5 23.2 25.9

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

50.7 1,003.3 44.5 1,153.7 114.9 2,003.6

110.7

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

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

41.3 1,123.2 96.9 1,508.4 226.9 2,485.7

103.1 201.1

109.7 286.6

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

37.8 36.6 30.6 13.9

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

82.3 1,134.6 104.7 1,142.3

57.2 55.2

27.9 48.6

21.0 34.1

473.5 614.5

124.1 345.2

173.7 447.8 105.0 315.0 140.4

89.7 1,069.4 150.0 1,573.7

67.4

56.2

59.9

669.0

116.0

343.9

213.4

185.8 2,176.1

50.1

79.1

84.8

74.1 17.9

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

96.9 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

18.5 27.5 57.5 18.3 51.6 42.1 16.5

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

14.4

8.9

9.5

343.8

281.9

42.2

218.4

54.6

131.6

177.3

108.3 1,358.1

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EDWARDS AQUIFER AUTHORITY |

(Table 1. continued)

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

Area between Sabinal River and Medina River Basins

Cibolo Creek/ Dry Comal

Nueces River/ West Nueces River Basin

Frio River/ Dry Frio River Basin

Blanco River Basin

Sabinal River Basin

Medina River Basin

Creek Basin

Year

Total a

2016 275.7 2017 122.0 2018 360.0

247.8 52.4 95.4 17.0 316.0 57.3

184.1

77.5 72.6 66.8

110.9

186.4

86.3 1,221.0

30.4

25.0 22.8

68.8 71.1

55.0

487.0

168.0

42.9 1,100.0

Recharge statistics for the period of record 1934–2018: Median 103.0 118.0

31.5 40.9

78.2 61.1 49.6 76.9 110.0 61.6 69.6 109.0

36.6 558.0 47.5 709.0

Mean 131.0

139.0

Recharge for the period of record 2009–2018 (last ten years): Median 100.0 89.0

13.0 21.8

22.4 50.1 15.1 50.5 83.4 49.0 39.0 76.4

47.3 400.0 50.6 590.6

Mean 148.0

123.0

Data source: USGS unpublished report (April 2019). a Totals may not exactly equal sum of all basins due to rounding errors.

6 | 2018 RECHARGE REPORT

Table 2. Estimated Annual Enhanced Recharge from Edwards Aquifer Authority-Operated Recharge Structures for 2018 (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

Annual Total

160 620

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

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

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

160 620

2,018

2,018

6

6

98

150 1,725 371 1,923 112 254 246 440 889 4,141

248 4,040 1,274 4,102 206 254 640 2,412 3,649 20,336

2,315

0

0

903 1,407

772

3 0

91

0 0

0 0

251 232 217

143 643

1,097 963 1,176

1,580 12,915

2,104

0 0

0 0

0 0

0 0

0 0

49

176 966

41

479 2,160 14,631

745 5,420 21,003

647 723

1,647 2,874 334

2,775

0

0 0

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 872 b

7,515 b 3,796b 4,606 b 2,154 b/d 18,872 50 c

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

0 b

0 b

901 b 526 b 1,811 665 2,363 795

1,023 b 1,085 b/d 4,350

184 170

0

465

4,778

14,682

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

4,682 4,018

2,257

35

0

0

0

0

756

1,333

4,056

5,838

11,983

Data source: Unpublished Edwards Aquifer Authority files (2014). 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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EDWARDS AQUIFER AUTHORITY |