Cover:

Medina Lake, September 2001.
A Water-Budget Analysis of Medina and 

Diversion Lakes and the Medina/Diversion 

Lake System, With Estimated Recharge to 

Edwards Aquifer, San Antonio Area, Texas

By Richard N. Slattery and Lisa D. Miller

U.S. Department of the Interior

U.S. Geological Survey

In cooperation with the Edwards Aquifer Authority

Scientific Investigations Report 2004–5209
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

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Although this report is in the public domain, permission must be secured from the individual copyright owners to

reproduce any copyrighted materials contained within this report.

Suggested citation:

Slattery, R.N., and Miller, L.D., 2004, A water-budget analysis of Medina and Diversion Lakes and the Medina/Diversion

Lake system, with estimated recharge to Edwards aquifer, San Antonio area, Texas: U.S. Geological Survey

Scientific Investigations Report 2004–5209, 41 p. 
iii

Contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Hydrogeologic Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Relation to Previous Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Water-Budget Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Evaporation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Surface-Water Inflow and Outflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Reservoir Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Ground-Water Outflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Measurement Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Estimated Recharge to Edwards Aquifer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figures

1–3. Maps showing: 

1. Location of the study area and upper Medina River Basin, San Antonio area, Texas . . . . . . . . . 3

2. Southern part of the upper Medina River Basin and locations of data-collection 

sites in the study area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3. Surface and shallow subsurface geology of the study area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4–6. Photographs showing: 

4. Weather station on Medina Lake, Texas, March 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

 5. Medina Irrigation Canal near Riomedina, Texas, August 2004 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

 6. Diversion Dam near Riomedina, Texas, August 2004 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

7–13. Graphs showing: 

7. Relation between Medina Lake stage and ground-water outflow (GWout) from 

Medina Lake during selected periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

 8. Relation between Medina Lake stage and ground-water outflow (GWout) from 

Diversion Lake during selected periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

9. Relation between Medina Lake stage and ground-water outflow (GWout) from 

Medina and Diversion Lakes during selected periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

10. Relation between Diversion Lake stage and ground-water outflow (GWout) to the 

Medina River between Diversion Dam and the Medina River near Riomedina 

during selected periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

11. Relation between Medina Lake stage and ground-water outflow (GWout) from the 

Medina/Diversion Lake system during selected periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

12. Ground-water outflow (GWout) from the Medina/Diversion Lake system, as 

estimated by the present (2001–02) study, and losses computed with the Lowry 

(1953) method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
iv

13. Comparison of monthly recharge to the Edwards aquifer in the study area during 

October 1995–September 2002, as estimated by the present (2001–02) study and 

computed with the Lowry (1953) method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Tables

1. Summary of lithologic and hydrologic properties of the hydrogeologic subdivisions of 

the Edwards and Trinity aquifers, San Antonio area, Texas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2. Hydrologic budget data-collection sites in the study area, San Antonio area, Texas . . . . . . . . . . . . . . . 20

3. Summary of selected water-budget periods and associated components of the water 

budget for Medina Lake, San Antonio area, Texas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4. Summary of selected water-budget periods and associated components of the water 

budget for Diversion Lake, San Antonio area, Texas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

5. Summary of selected water-budget periods and associated components of the water 

budget for the Medina/Diversion Lake system, San Antonio area, Texas . . . . . . . . . . . . . . . . . . . . . . . . . . 29

6. Relative contribution of each component of the water budget and relative part of record 

used for each water-budget computation for Medina Lake, Diversion Lake, and the 

Medina/Diversion Lake system, San Antonio area, Texas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Vertical Datum

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).
A Water-Budget Analysis of Medina and 

Diversion Lakes and the Medina/Diversion 

Lake System, With Estimated Recharge to 

Edwards Aquifer, San Antonio Area, Texas

By Richard N. Slattery and Lisa D. Miller

Abstract 

In January 2001, the U.S. Geological Survey—in cooperation with the Edwards Aquifer Authority—began a study to 

refine and, if possible, extend previously derived (1995–96) 

relations between the stage in Medina Lake and recharge to the 

Edwards aquifer to include the effects of reservoir stages below 

1,018 feet and greater than 1,046 feet above National Geodetic 

Vertical Datum of 1929. The principal objective of this present 

(2001–02) study was to estimate ground-water outflow (seepage) from Medina Lake, Diversion Lake, and from the Medina/

Diversion Lake system through the calculation of water budgets 

representing steady-state conditions over as wide a range as 

possible in the stages of Medina and Diversion Lakes. The 

water budgets were compiled for selected periods during which 

time the water-budget components were inferred to be relatively stable and the influence of precipitation, stormwater runoff, and changes in storage were presumably minimal. 

Water budgets for the Medina/Diversion Lake system 

were compiled for 127 water-budget periods ranging from 8 to 

78 days from daily hydrologic data collected during March 

1955–September 1964, October 1995–September 1996, and 

February 2001–June 2002. Budgets for Medina and Diversion 

Lakes were compiled for 14 periods ranging from 8 to 23 days 

from daily hydrologic data collected only during October 1995–

September 1996 and April 2001–June 2002. 

Linear equations were developed to relate the stage in 

Medina Lake to ground-water outflow from Medina Lake, 

Diversion Lake, and the Medina/Diversion Lake system. The 

computed mean rates of outflow from Medina Lake ranged 

from about 18 to 182 acre-feet per day between stages of 1,019 

and 1,064 feet above National Geodetic Vertical Datum of 

1929. The computed rates of outflow from Diversion Lake 

ranged from about -85 to 52 acre-feet per day. The rates of outflow from the entire lake system ranged from about 5 to 178 

acre-feet per day between Medina Lake stages of 963 to 1,064 

feet. It is assumed that all outflow from the lake system enters 

the ground-water system as recharge to the Edwards aquifer.

During the time that the stage in Medina Lake was greater 

than about 1,040 feet, Diversion Lake gained more water than it 

lost to the ground-water system and the rate of ground-water 

outflow from Medina Lake increased sharply while its stage 

was between about 1,043 and 1,045 feet. The observed outflow 

from Diversion Lake during this time decreased sharply to the 

extent that a net gain resulted—indicating that a substantial 

amount of the additional outflow from Medina Lake returned to 

Diversion Lake. When the stage in Medina Lake is at the spillway elevation of 1,064 feet, Diversion Lake appears to gain as 

much as 40 percent of the concurrent ground-water outflow 

from Medina Lake. 

An indication of water moving from the lake system into 

the ground-water system and back to the surface-water system 

was observed in the most downstream reach of the Medina 

River, between Diversion Lake and the Medina River near Riomedina. During conditions of no flow over Diversion Dam, this 

reach of the Medina River gained from about 32 to 94 acre-feet 

per day, with the gain increasing with increasing stage in Diversion Lake.

The average of the monthly recharge to the Edwards aquifer from the Medina/Diversion Lake system—as estimated by 

the present study for the October 1995–September 2002 

period—is 3,083 acre-feet, or about 56 percent of recharge 

computed for this period with a previously used (Lowry) 

method. The present study’s estimates of recharge for months 

with rising-lake stage conditions are about 44 percent of those 

computed with the previously used method, compared to about 

60 percent for months with steady or falling-stage conditions. 

For stages greater than 1,045 feet, the present study estimated 

recharge to be about 52 percent of that computed with the previously used method, compared to about 64 percent at stages 

below 1,045 feet.
2 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

Introduction

Study Area

The Medina and Diversion Lakes study area (fig. 1) is 

located in northeastern Medina County and southeastern 

Bandera County, Texas, within the 650-square mile (mi2) drainage area upstream from the U.S. Geological Survey (USGS) 

gaging station on the Medina River near Riomedina (fig. 2). 

Medina Lake straddles the Medina-Bandera County boundary 

and Diversion Lake lies behind Diversion Dam, about 5 river 

miles (mi) downstream from Medina Dam. 

Constructed in 1912 to impound water for irrigation, 

Medina Dam has a conservation pool elevation (top of spillway) 

of 1,064.2 feet (ft) above NGVD 29. When full, Medina Lake 

holds nearly 255,000 acre-feet (acre-ft) of water, within a surface area of about 6,066 acres and about 71 mi of shoreline. The 

low-head Diversion Dam impounds an additional 2,555 acre-ft 

of water when filled to its spillway elevation of 919.0 ft. Part of 

the water from Diversion Lake can be diverted at Diversion 

Dam through the Medina Irrigation Canal to the Bexar-MedinaAtascosa Water Improvement District irrigation network, 

which provides irrigation water to about 33,000 acres of farmland in the Medina River Valley (Texas Water Development 

Board, 1996). 

Hydrogeologic Setting

The Edwards aquifer is one of the most permeable and productive carbonate-rock (limestone and dolostone) aquifers in 

the United States and is the major source of public water supply 

for more than 1.6 million people in Bexar, Comal, Hays, 

Medina, and Uvalde Counties (U.S. Census Bureau, 2000). This 

aquifer supplies large quantities of water to agricultural, industrial, and recreational interests as well as to most businesses in 

the region. Spring discharge from the aquifer is vital to the 

area’s tourism economy, the survival of several threatened or 

endangered plant and animal species, and the maintenance of 

downstream water supplies.

Recharge to the Edwards aquifer occurs mainly from 

streams that originate in the upgradient catchment area and flow 

across the outcrop (recharge zone) of the aquifer (fig. 1). Most 

runoff from the catchment area infiltrates updip, unconfined 

parts of the Edwards aquifer through faults, fractures, and sinkholes that characterize this recharge zone (Small and Clark, 

2000). 

The Edwards aquifer is recharged also by ground-water 

outflow (seepage) from Medina and Diversion Lakes, individually, as well as from the Medina/Diversion Lake system as a 

whole. Recharge from this system is estimated to contribute an 

average 62,700 acre-ft of recharge annually to the Edwards 

aquifer, accounting for about 9 percent of the estimated 698,500 

acre-ft of average annual (1934–2003) recharge to the Edwards 

aquifer (Slattery, 2004).

Recharge to the Edwards aquifer in the study area is 

greatly influenced by the local hydrogeology (fig. 3; table 1, at 

end of report). Surface-water losses from the Medina/Diversion 

Lake system enter the aquifer indirectly through the Glen Rose 

Limestone of the Trinity Group or directly through porous outcrops of the Kainer Formation of the Edwards Group (Lambert 

and others, 2000). Medina Lake bottoms in the upper member 

of the Glen Rose Limestone (Small and Lambert, 1998, fig. 3), 

which comprises the relatively impermeable upper zone of the 

Trinity aquifer (Barker and Ardis, 1996, p. B42). Southern parts 

of Medina Lake abut the basal nodular member and possibly 

lower part of the dolomitic member of the Kainer Formation 

(T.A. Small, U.S. Geological Survey, retired, oral commun., 

2000), the lowermost formation of the extraordinarily permeable Edwards aquifer. Because the relation between the hydrogeologic subdivisions in the study area and the associated zones 

of differing porosity and permeability are vertically controlled 

(Small and Lambert, 1998, table 4), recharge to the Edwards 

aquifer that occurs as seepage from the Medina/Diversion Lake 

system can be related to the stage in Medina Lake. 

Whereas the contact between the upper member of the 

Glen Rose Limestone and the basal nodular member of the 

Kainer Formation is about 1,000 ft above NGVD 29, the contact 

between the basal nodular and dolomitic members of the Kainer 

Formation occurs at about 1,050 ft (Lambert and others, 2000). 

Because Medina Lake abuts the recharge zone of the Edwards 

aquifer between altitudes of about 1,000 and 1,064 ft (top of 

spillway), it is possible for water to seep from the lake into the 

aquifer so long as the stage exceeds about 1,000 ft. According 

to Lambert and others (2000, p. 17), “...the greatest losses from 

[Medina] lake to the ground-water system appear to result from 

lake stages that range from about 1,040 to 1,045 ft,” a range that 

coincides with some of the more porous and permeable parts of 

the Kainer Formation on the southern side of Medina Lake 

(T.A. Small, U.S. Geological Survey, retired, oral commun., 

2000).

From the bottom of the Medina Lake spillway to the 

approximate midpoint of Diversion Lake, where the Diversion 

Lake fault intersects Diversion Lake (fig. 3), the Medina River 

channel lies on the upper member of the Glen Rose Limestone, 

which corresponds to the upper zone of the Trinity aquifer. 

From the approximate midpoint of Diversion Lake downstream 

to the Haby Crossing fault—including the Medina River below 

Diversion Dam—the lake and river channel lie on a thin residuum of the basal nodular member, which corresponds to the 

lowermost part of the Edwards aquifer (Lambert and others, 

2000).

Relation to Previous Studies

Lowry (1953) developed curves relating the storage (and 

therefore, stage) in Medina Lake to monthly seepage losses 

from the Medina/Diversion Lake system. Based on a substantial 

amount of estimated record, Lowry’s curves originally were 

intended only as a tool for evaluating the design of a proposed 
Introduction 3

Figure 1. Location of the study area and upper Medina River Basin, San Antonio area, Texas. 

MEDINA RIVER

MEDINA COUNTY

KENDALL

BANDERA COUNTY

KERR COUNTY

COUNTY

TEXAS

San

 Antonio

BALCONES FA ULT ZO NE

KINNEY

COUNTY

UVALDE

COUNTY

MEDINA

COUNTY

BEXAR

COMAL

COUNTY

HAYS

COUNTY

KENDALL

COUNTY

BANDERA

COUNTY

KERR

COUNTY

COUNTY

29o

30'

98o

30'

99o

30o

99o

30'

Diversion 

 Dam

Medina 

 Dam

MEDINA 

 LAKE

DIVERSION

 LAKE

0 10 20 30 MILES

Upper Medina River

Basin

Study area

EXPLANATION

Edwards aquifer recharge

zone
4 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

Figure 2. Southern part of the upper Medina River Basin and locations of data-collection sites in the study area. 

Riomedina

1

18

Edwards aquifer

recharge zone

Upper Medina

River Basin

U.S. Geological Survey

data-collection station

and number—See table 2

National Weather Service

precipitation gage and

number—See table 2

EXPLANATION

0 1 2 MILES 0.5 1.5

MEDINA

 LAKE

DIVERSION

 LAKE

Medina

 Dam

Diversion

 Dam

Irrigation

Medina 

Canal

MEDINA 

RIVER

S173

18

11

10

9

8

17

16

15

14

1312

5

7

6

3

2

1

4

MEDINA COUNTY

BANDERA COUNTY

29 ̊30'

29 ̊37'30"

99 ̊
Introduction 5

Figure 3. Surface and shallow subsurface geology of the study area. 

11

0

18

11

10

9

8

17

16

15

14

1312

5

7

6

3

2

1

4

0 1 2 MILES 0.5 1.5

29 ̊30'

29 ̊37'30"

99 ̊

0 1 2 MILES 0.5 1.5

Source—Bandera County (Lambert

and others, 2000); Medina County

(Small and Clark, 2000; University

of Texas, Bureau of Economic

Geology, 1983)

EXPLANATION

Geologic unit

Devils River Formation

Alluvium

Leona Formation

Escondido Formation

Anacacho Formation (not

exposed in study area)

Austin Group

Eagle Ford Group

Buda Limestone

Del Rio Clay

Georgetown Formation

Leached and collapsed

members, undivided

Regional dense member

Grainstone member

Kirschberg evaporite

member

Dolomitic member

Basal nodular member

Upper member of the

Glen Rose Limestone

Lower member of the

Glen Rose Limestone

Facies change

Inferred fault

Primary fault

Kainer

Formation

Edwards aquifer

Cyclic and marine

members, undivided

(not exposed in study

area)

Person

Formation

Upper Cretaceous and Quaternary rocks, undivided

1

18

U.S. Geological Survey

data-collection station

and number—See table 2

National Weather Service

precipitation gage and

number—See table 2

Diversion

Medina

Lake fault

fault

Lake

Haby Crossing

fault
6 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

reservoir in the lower part of the Medina River Basin. Lowry’s 

work was adapted later by Puente (1978) to estimate annual 

recharge to the Edwards aquifer in that basin.

The USGS currently uses Puente’s (1978) adaptation of 

the Lowry (1953) method to estimate annual recharge to the 

Edwards aquifer from the Medina/Diversion Lake system 

(Slattery, 2004). The USGS procedure sums estimates of 

monthly recharge (computed with the Lowry method) to estimate annual recharge, assuming that the short-term errors cancel over the course of a typical year.

During October 1995–September 1996, the USGS conducted a study (Lambert and others, 2000) with objectives to 

better define short-term rates of recharge and to reduce the error 

and uncertainty associated with estimates of monthly recharge 

from the Medina/Diversion Lake system. As part of that study, 

the USGS developed water budgets for Medina Lake, Diversion 

Lake, and the Medina/Diversion Lake system to derive the 

amount of ground-water outflow from each of these lakes as 

well as from the entire lake system. During that period of study, 

however, the stage in Medina Lake ranged from only about 

1,018 to about 1,046 ft above NGVD 29. Consequently, the 

recharge estimates derived by the 1995–96 study (Lambert and 

others, 2000, p. 12) are considered “...valid only for a range in 

Medina Lake stage between about 1,018 and 1,046 ft above 

[NGVD 29].”

Therefore, the USGS—in cooperation with the Edwards 

Aquifer Authority (EAA)—began a study in January 2001 to 

refine and, if possible, extend the previously derived (1995–96) 

relations between Medina Lake stage and recharge to the 

Edwards aquifer to include the effects of reservoir stages below 

1,018 ft and greater than 1,046 ft above NGVD 29. The principal objective of this present (2001–02) study was to estimate 

ground-water outflow from Medina Lake, Diversion Lake, and 

from the Medina/Diversion Lake system through the computation of water budgets representing steady-state conditions over 

as wide a range as possible in the stages of Medina and Diversion Lakes.

Purpose and Scope

The purpose of this report is to summarize precipitation, 

evaporation, and surface-water data collected during February 

2001–June 2002 and provide updated water budgets for Medina 

and Diversion Lakes and the Medina/Diversion Lake system, 

including estimates of ground-water recharge from the lake 

system to the Edwards aquifer. These updated water budgets 

incorporate data collected during March 1955–September 1964 

by the USGS, the National Weather Service (NWS), and the 

Texas Water Development Board (TWDB) in addition to data 

collected by the USGS during October 1995–September 1996 

(Lambert and others, 2000).

Water-Budget Analysis

To estimate ground-water outflow from Medina and 

Diversion Lakes and from the Medina/Diversion Lake system, 

discrete water budgets were computed for selected periods over 

a range of stages in Medina and Diversion Lakes. The waterbudget equation incorporates measurable components of inflow 

and outflow to solve for (or otherwise scientifically estimate) 

unknown gains or losses, or both, from a lake or the lake system. The measurable components include: surface-water inflow 

and outflow, precipitation, evaporation, and change in storage. 

The net effect of the unknown gains and losses is represented by 

the residual of all the measurable components—or water that is 

not accounted for, including errors associated with each of the 

measurable components.

The solution to the water-budget equation is obtained 

by balancing the contribution of each component of the water 

budget for any given budget period. The overall water-budget 

equation for Medina and Diversion Lakes and the Medina/

Diversion Lake system can be written as follows:

GWout + eGWout = P + eP – E + eE + SWin + eSWin

– SWout + eSWout – ∆S + e∆S, (1)

where (all units in acre-feet per day)

GWout is ground-water outflow (loss from the lake system, 

or selected part of the lake system, assumed to 

recharge the ground-water system) minus groundwater inflow (gain to the lake system, or selected 

part of the lake system, from the ground-water 

system); 

P is precipitation on the lake;

E is evaporation from the lake surface;

SWin is surface-water inflow to the lake;

SWout is surface-water outflow from the lake;

∆S is change in lake storage; and

ei is the standard deviation around each measured term i. 

As for the previous (1995–96) study (Lambert and others, 

2000), domestic and municipal withdrawals from and discharges into Medina and Diversion Lakes were presumed negligible and are not accounted for in the water-budget analysis. 

As for the previous study, all components of ground-water 

inflow to the Medina/Diversion Lake system also were presumed negligible.

Daily precipitation, evaporation, streamflow, and reservoir 

storage were either measured directly or values were estimated 

on the basis of periodic on-site measurements. Table 2 (at end 

of report) lists the site number, USGS or NWS station number, 

station name, latitude, longitude, drainage area, station type, 

and period of record for the data-collection sites. Locations of 

the data-collection sites are shown in figure 2.

A water budget for the Medina/Diversion Lake system 

was computed using daily hydrologic data collected during 

March 1955–September 1964, October 1995–September 1996 

(Lambert and others, 2000), and February 2001–June 2002 
Water-Budget Analysis 7

(present study). Water budgets for Medina and Diversion Lakes 

were computed using daily hydrologic data collected only during the 1995–96 and 2001–02 data-collection periods. Budgets 

for the individual lakes could not be computed from the 1955–

64 data, because no streamflow data were available between the 

two lakes during that period. 

The following sections describe how each component in 

the water budget (eq. 1) was derived for the 1955–64 and 2001–

02 periods. Data from the 1995–96 study (Lambert and others, 

2000) were used as published with the exception of some evaporation data, for which missing record was estimated as 

explained under “Evaporation,” below. 

Precipitation

Daily precipitation records from the NWS site at Riomedina (site 18) were used to estimate precipitation (P) on Medina 

and Diversion Lakes during 1955–64. No other sites from 

which to compute a weighted average were active within a reasonable proximity of the lakes during this time (fig. 2, table 2). 

For 2001–02, daily precipitation data from Medina River at 

Bandera (site 1) and Riomedina (site 18) were spatially 

weighted to estimate precipitation on Medina Lake (table 2). 

The weighting of the sites was based on the spatial proximity of 

the sites relative to Medina Lake. Using points of equal distance 

between sites 1 and 18 as the delineating boundary for each site, 

it was estimated that 30 percent of the Medina Lake surface area 

was within the area covered by site 1 and that 70 percent was 

covered by site 18. Therefore, the daily precipitation at site 1 

was multiplied by 0.30 and the daily precipitation at site 18 by 

0.70. The resulting values were summed to obtain estimates of 

daily precipitation on Medina Lake. Daily precipitation 

recorded at site 18 was used as an estimate of precipitation on 

Diversion Lake.

Evaporation

For 1955–64, daily evaporation (E) from Medina and 

Diversion Lakes was estimated from monthly evaporation totals 

for the Medina Lake area from the Texas Water Development 

Board (2004).

Daily evaporation data missing from the 1995–96 record 

(Lambert and others, 2000) were estimated using daily pan 

evaporation data from the NWS site at Sea World, San Antonio, 

Tex., located about 15 mi east-southeast of Medina Lake. 

Monthly pan coefficients for the Medina Lake area from the 

Texas Water Development Board (2003) were applied to the 

pan evaporation to compute the daily evaporation for Medina 

and Diversion Lakes. Periods for which the 1995–96 evaporation data were revised included October 11–November 12, 

1995; January 19–24, and 27–28, 1996; February 7–9, 11–15, 

and 29, 1996; May 4, 13–15, and 19–24, 1996; August 4–19, 

and 21–22, 1996; and September 12–31, 1996. 

For this report, lake evaporation (E) was estimated for 

2001–02 from meteorological data collected at sites located on 

Medina and Diversion Lakes. Estimation of E also was made 

using evaporation data collected at the Texas A&M University 

(TAMU) meteorological data-collection site in San Antonio. 

The TAMU site is located about 27 mi east of Medina Lake 

(Texas A&M University, 2003).

Data collected at the Medina Lake weather station (site 11, 

fig. 4) included wind speed and direction, net radiation, 

vapor pressure, air temperature, and water temperature at 

selected depths. Data collected at the Diversion Lake weather 

station (site 16) included wind speed and direction, shortwave 

Figure 4. Weather station on Medina Lake, Texas, March 2001.
8 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

radiation, vapor pressure, air temperature, and water temperature at the water surface. 

Evaporation data for 2001–02 were calculated with the 

Bowen ratio-energy budget (BREB) (Bowen, 1926). To calculate evaporation using the BREB method, data-collection techniques and calculation methods were modified for open-water 

conditions as described by Laczniak and others (1999) and 

German (2000). Periods of missing BREB evaporation record 

were estimated using a relation between available BREB evaporation record and potential evaporation collected at the TAMU 

meteorological data-collection site.

Surface-Water Inflow and Outflow

For 1955–64, the surface-water inflow (SWin) component 

to the Medina/Diversion Lake system was computed from 

records collected at two USGS continuous-record streamflowgaging stations, Medina River near Pipe Creek (site 3) and Red 

Bluff Creek near Pipe Creek (site 4), and from streamflow estimates from the ungaged areas (fig. 2, table 2). The Red Bluff 

Creek gage (site 4) began operation in April 1956; therefore, 

from March 1955 through March 1956, the Red Bluff Creek 

drainage basin is included in the estimates of the ungaged area 

for that period. 

 For 1955–64, the surface-water outflow (SWout) component for the Medina/Diversion Lake system was computed 

using estimated and continuous record from Medina Irrigation 

Canal, site 15 (fig. 5), and from continuous record collected at 

Medina River near Riomedina, site 17 (fig. 2, table 2). Site 15 

began operation in July 1957. Prior to July 1957, flow at site 15 

was estimated on the basis of periodic observations of the water 

level in Diversion Lake, behind Diversion Dam (fig. 6). From 

March 2 to April 29, 1955, Diversion Lake stage was reported 

as below the intake to Medina Irrigation Canal; from April 29, 

1955, to April 3, 1957, Diversion Lake was reported as “dry.” 

During these periods, flow at site 15 was estimated to be zero.

Streamflow was not measured at site 12 (Medina River 

below Medina Lake) during 1955–64; therefore, the SWin and 

SWout components were computed only for the Medina/Diversion Lake system and could not be derived for the individual 

lakes.

For 2001–02, the SWin and SWout components were 

computed from records collected at four continuous-record 

streamflow-gaging stations (sites 1, 12, 15, and 17), nine periodic streamflow measuring sites (sites 2, 5–10, 13, and 14), and 

from streamflow estimates from the ungaged areas that drain 

into Medina Lake (fig. 2, table 2). Mean daily streamflow and 

miscellaneous streamflow measurements made during 2001–02 

are published in USGS Water-Data Reports (Gandara, 2002–

03).

 SWin to Medina Lake and to the Medina/Diversion Lake 

system was computed by summing the estimated daily streamflows from seven periodic streamflow measuring sites (sites 2, 

5–10) and the estimated daily streamflow from the ungaged 

areas that drain into Medina Lake (table 2). Daily streamflow at 

Medina River at English Crossing (site 2) during 2001–02 was 

estimated on the basis of a linear relation (r2 = 0.96, p-value = 

0) developed between continuous streamflow recorded at 

Medina River at Bandera (site 1) and 28 miscellaneous streamflow measurements made, primarily during lower flows, at site 

2 between 1995–96 and 2001–02. The area upstream from site 

2 accounts for about 75 percent of the Medina Lake drainage 

area. 

The EAA recorded continuous stage at Red Bluff Creek at 

FM 1283 (site 5) for some periods during May 2000–February 

2002. To determine streamflow at site 5, a stage-streamflow 

(discharge) relation was developed using stage values recorded 

by EAA and miscellaneous discharge measurements made at 

site 5 as part of the present (2001-02) study. Missing daily 

values at site 5 were estimated on the basis of periodic on-site 

measurements and a relation developed between continuous 

streamflow recorded at site 5 and at Seco Creek at Miller Ranch, 

USGS station 08201500. Daily streamflows for periodic 

measuring sites 6, 8, 9, 13, and 14 were estimated from the periodic measurements and continuous streamflow recorded at 

site 1. Daily streamflows for site 7 were estimated on the basis 

of periodic on-site measurements and continuous streamflow 

recorded at Helotes Creek at Helotes, USGS station 08181400. 

SWin from the remaining ungaged area was estimated by multiplying the ungaged area (59 mi2) by the average daily streamflow per square mile of the surrounding gaged watersheds. The 

Medina River watershed (upstream from site 1) was not 

included in this computation.

SWout from Medina Lake and SWin to Diversion Lake 

were computed by summing the daily streamflow recorded at 

the Medina River below Medina Lake gage (site 12) and the 

estimated daily discharge from Koenig Creek (site 13) and 

Nesbit Springs (site 14). Because the results of isotope analyses 

(Lambert and others, 2000, p. 33–34) indicate that Medina Lake 

is the source of most water discharging from Koenig Creek and 

Nesbit Springs, the estimated discharge from these sites (sites 

13 and 14) was included in the computed SWout from Medina 

Lake. SWout from the Medina/Diversion Lake system and from 

Diversion Lake was computed by summing streamflow at the 

Medina Irrigation Canal (site 15) and Medina River near 

Riomedina (site 17). 

For 1955–64, the Medina River contributed an average of 

about 94 percent of the total SWin to Medina Lake, for 1995–96 

about 96 percent, and for 2001–02 about 87 percent. The proportionately lower SWin contribution from the Medina River 

during 2001–02 is attributed to the higher rainfall amounts during that time, which resulted in streamflow in the normally dry 

tributaries of Medina Lake. In contrast, no flow was recorded 

in most of the tributaries during most of the 1995–96 study 

(Lambert and others, 2000). 

Reservoir Storage

Medina Lake storage for 1955–64 was obtained from published record of the USGS and stage from USGS observer 
Water-Budget Analysis 9

Figure 5. Medina Irrigation Canal near Riomedina, Texas, August 2004.

Figure 6. Diversion Dam near Riomedina, Texas, August 2004.
10 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

records that included daily to periodic stage measurements. For 

the same period, reservoir storage for Diversion Lake was estimated from periodic lake stage measurements using the TWDB 

stage-volume-area tables for Diversion Lake (Texas Water 

Development Board, 1996). Reservoir storage during the 

present study was computed from continuous lake stage 

recorded at Medina Lake and Diversion Lake, using the TWDB 

stage-volume-area tables for Medina and Diversion Lakes 

(Texas Water Development Board, 1996). Daily changes in 

lake storage (∆S) were computed as the difference between the 

amount of current-day storage and the amount of previous-day 

storage. 

Ground-Water Outflow

Ground-water outflow (GWout) was computed as the 

residual of all other terms in the water-budget equation (eq. 1). 

GWout represents water that is not accounted for by all other 

components, including any unrecognized errors. Positive values 

of GWout represent losses from the lake system or selected part 

of the lake system (either of the two lakes and [or] the Medina 

River) to the ground-water system (Lambert and others, 2000). 

Negative GWout values represent gains to the lake system or 

selected part of the lake system (including returns to the Medina 

River) from the ground-water system. 

Equations with which to compute ground-water outflow as 

a function of reservoir stage were developed for selected periods during which time the water-budget components were 

inferred to be relatively stable and the influence of precipitation, 

stormwater runoff, and changes in storage were presumably 

minimal. These periods were chosen on the basis of three main 

criteria. First, periods were selected to exclude conditions 

affected by heavy rainfall or Medina Lake stages greater than 

1,064.2 ft above NGVD 29 (top of spillway). During such conditions, error associated with high flows presumably would 

be eliminated, as would errors associated with estimates of 

stormwater runoff from ungaged watersheds. Second, periods 

of less than 7 days were not evaluated. Periods of less than 7 

days would not adequately account for the travel time of the 

water through the system and would not provide a reasonable 

sample size for the computation of the mean daily GWout on the 

basis of the variability of the data. Third, periods were selected 

that did not begin or end on days when Medina Irrigation Canal 

(fig. 2) was either beginning or ending a period of discharge. 

Water budgets for Medina and Diversion Lakes and the 

lake system were selected also so that no budget period would 

begin or end on days when the Medina Dam gates were being 

opened or closed. The selection of such periods would presumably minimize error associated with disequilibrium within the 

system. Long periods of reasonably stable conditions with slow 

but steady decreases in lake stage were divided into approximately equal periods, with each representing approximately 

equal increments of changing stage. Tables 3–5 (at end of 

report) list the resulting mean daily GWout values, as well as statistical summaries and errors computed for each of the selected 

water-budget periods.

The periods selected for the Medina Lake (table 3) and 

Diversion Lake (table 4) budgets ranged from 8 to 23 days. 

Fourteen budget periods during October 1995–September 1996, 

together equalling about 54 percent of the record, were selected 

for each lake. Fourteen budget periods also were selected from 

the April 2001–June 2002 data-collection interval, totalling 

51 percent of the record (table 6, at end of report). Owing to 

heavy runoff resulting from above-average rainfall, slightly 

less of the total 2001–02 data were used for the water-budget 

computations.

For the Medina/Diversion Lake system, 127 water-budget 

periods (table 5) were selected that ranged from 8 to 78 days. 

Sixty-nine percent of the daily values during March 1955–September 1964 were included in the water-budget computations. 

For the October 1995–September 1996 period, 72 percent of the 

daily values were included. For the February 2001–June 2002 

period, 38 percent of the daily values were included. 

The contribution of the individual components of the water 

budget were computed as a percentage of the sum of the components for Medina and Diversion Lakes and for the Medina/

Diversion Lake system. In general, the proportions of the individual components of the water budget reflect the effects of prevailing climatological influences of the period, operation of the 

lakes, and the fact that the selected periods exclude periods of 

heavy rainfall and stormwater runoff. The contribution of the 

individual budget components are summarized in tables 3–5 for 

selected budget periods and in table 6 for available periods of 

record.

For Medina Lake, ∆S, SWout, and SWin were the major 

components of the water budget, accounting for 29.1, 25.6, and 

22.6 percent of the budget, respectively. GWout accounted for 

16.7 percent, evaporation for 4.9 percent, and precipitation for 

1.1 percent. For Diversion Lake, SWin and SWout accounted for 

47.2 and 40.7 percent of the budget, respectively. GWout

accounted for 8.5 percent, ∆S accounted for 3.0 percent, and 

evaporation and precipitation less than 1 percent. For the 

Medina/Diversion Lake system (observed between 1955 and 

2002), ∆S had the greatest contribution (33.7 percent) and precipitation the least (1.3 percent). Whereas SWout and GWout 

accounted for 20.8 and 18.4 percent, respectively, of the total 

contribution, SWin was 16.4 percent and E was 9.4 percent.

Linear equations were developed during the present study 

to relate the stage in Medina Lake to the computed mean rates 

of GWout for Medina Lake (table 3), Diversion Lake (table 4), 

and the Medina/Diversion Lake system (table 5). The rates of 

GWout from Medina and Diversion Lakes were plotted against 

the corresponding Medina Lake stages, which ranged from 

1,019 to 1,064 ft above NGVD 29. Medina/Diversion Lake 

GWout values were plotted against Medina Lake stages ranging 

from 963 to 1,064 ft. The resulting water-budget equations are:

Medina Lake GWout = 

2.3411 * MedLk Stage – 2,350.5

(r2 = 0.60, p-value = <.001, standard error = 23.85), (2)
Water-Budget Analysis 11

Figure 7. Relation between Medina Lake stage and ground-water outflow (GWout) from Medina Lake during selected periods. 

y = 2.3411x – 2,350.5

R2

 = 0.60

0

20

40

60

80

100

120

140

160

180

200

1,015 1,020 1,025 1,030 1,035 1,040 1,045 1,050 1,055 1,060 1,065 1,070

AVERAGE MEDINA LAKE STAGE, IN FEET ABOVE NGVD 29

AVERAGE GWOUT, IN ACRE-FEET PER DAY

Ground-water outflow trend line

1995–96

2001–02

Medina Lake ground-water outflow

Diversion Lake GWout = 

-2.1776 * MedLk Stage + 2,261.2

(r2 = 0.69, p-value = <.001, standard error = 18.19), and (3)

Medina/Diversion Lake system GWout = 

1.1019 * MedLk Stage – 1,057.2

(r2 = 0.76, p-value = <.001, standard error = 21.79), (4)

where 

MedLk Stage is Medina Lake stage in feet above NGVD 29.

The relation for equation 2 (fig. 7) indicates that Medina 

Lake GWout increases as the stage in Medina Lake increases. 

The computed mean GWout values for Medina Lake (table 3) 

range from 18.50 to 181.60 acre-feet per day (acre-ft/d). The 

end points of the trend line resulting from the regression of 

these GWout values are 35.1 and 140.4 acre-ft/d at stages of 

1,019 and 1,064 ft above NGVD 29, respectively.

Figure 8 (eq. 3) indicates that Diversion Lake GWout

decreases as the stage in Medina Lake increases. Whereas the 

mean GWout values (table 4) range from -85.06 to 51.92 acreft/d, the trend line end points are -55.8 to 42.2 acre-ft/d, respectively. This relation indicates that Diversion Lake gains more 

water (indicated by negative GWout values) than it loses 

through ground-water outflow when Medina Lake stages are 

greater than about 1,040 ft above NGVD 29.

Figure 7 indicates that when Medina Lake stages are 

between about 1,043 and 1,045 ft above NGVD 29, the outflow 

from Medina Lake increases sharply and exceeds the expected 

GWout as determined by the ground-water outflow trend 

line—which indicates additional (greater-than-expected) loss 

between these elevations. During the time of this range of stage 

in Medina Lake, the ground-water outflow from Diversion Lake 

decreases sharply and drops below its expected GWout as determined by the trend line in figure 8—which indicates additional 

gain of water in Diversion Lake. This additional gain in Diversion Lake represents a substantial amount of the concurrent, 

additional outflow from Medina Lake. The increase in Medina 

Lake GWout between stages of about 1,043 and 1,045 ft corresponds to an interval within the lower part of the Kainer Formation that is recognized as one of the more permeable parts of the 

Edwards aquifer on the southern side of Medina Lake (Lambert 

and others, 2000).

During their 1995–96 study, Lambert and others (2000) 

observed a direct relation between the stage in Diversion Lake 

and ground-water outflow from Diversion Lake. In this relation 

(Lambert and others, 2000, fig. 7), the outflow from Diversion 

Lake increased with increasing stage. At the higher Medina 

Lake stages (1,057 to 1,064 ft above NGVD 29) observed during the present (2001–02) study, however, a substantial amount 

of the additional ground-water outflow from Medina Lake 

returned to Diversion Lake. Accordingly, the relation between 

Medina Lake stage and the outflow from Diversion Lake 

appears as an inverse relation in figure 9, as opposed to the 

direct relation between stage and ground-water outflow from 

Medina Lake. 

The negative rates of ground-water outflow in figure 9 

indicate a net gain of water in Diversion Lake from the adjacent 
12 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

Figure 8. Relation between Medina Lake stage and ground-water outflow (GWout) from Diversion Lake during selected periods. 

Figure 9. Relation between Medina Lake stage and ground-water outflow (GWout) from Medina and Diversion Lakes during selected 

periods. 

y = -2.1776x + 2,261.2

R2

 = 0.69

-150

-100

-50

50

100

150

1,015 1,020 1,025 1,030 1,035 1,040 1,045 1,050 1,055 1,060 1,065 1,070

AVERAGE MEDINA LAKE STAGE, IN FEET ABOVE NGVD 29

AVERAGE GWOUT, IN ACRE-FEET PER DAY

0

Ground-water outflow trend line

1995–96

2001–02

Diversion Lake ground-water outflow

-200

-150

-100

-50

0

50

100

150

200

250

300

1,015 1,020 1,025 1,030 1,035 1,040 1,045 1,050 1,055 1,060 1,065 1,070

AVERAGE MEDINA LAKE STAGE, IN FEET ABOVE NGVD 29

AVERAGE GWOUT , IN ACRE-FEET PER DAY

350

Ground-water outflow trend line

Medina Lake ground-water outflow

1995–96

2001–02

Medina Lake

Diversion Lake

Diversion Lake ground-water outflow

1995–96

2001–02
Water-Budget Analysis 13

ground-water system. Because this gain was influenced by 

highly variable conditions of concurrent outflow from Medina 

Lake, a specific relation between the stage in Diversion Lake 

and the ground-water outflow from Diversion Lake could not be 

isolated from the data collected during 2001–02. 

More study is required to better understand the specific 

relation between ground-water outflow from Medina Lake and 

the associated gain in Diversion Lake. However, from a net gain 

of zero in Diversion Lake when Medina Lake stages are below 

about 1,040 ft above NGVD 29, Diversion Lake appears to gain 

on average about 2.3 acre-ft/d of water for every 1 ft of Medina 

Lake stage above about 1,040 ft (fig. 8). The expected maximum gain (negative outflow) in Diversion Lake is about -56 

acre-ft/d when the expected maximum outflow from Medina 

Lake is about 140 acre-ft/d (fig. 7). It can be deduced from these 

observations that—under optimum conditions (Medina Lake 

stage at its spillway elevation of 1,064 ft)—the gain of water in 

Diversion Lake could be as much as 40 percent of the concurrent ground-water outflow from Medina Lake.

An indication of water moving from the lake system into 

the ground-water system and back to the surface-water system 

was observed during the present study in the most downstream 

reach of the Medina River in the study area. The Medina River 

between sites 16 and 17 was analyzed for selected periods when 

the stage in Diversion Lake was less than 919 ft above NGVD 

29 (top of Diversion Dam spillway). With no water spilling over 

the dam, streamflow between sites 16 and 17 is attributed to 

springflow into the streambed or seepage from adjacent canyon 

walls and hillsides that probably originates as outflow from 

Medina Lake or Diversion Lake, or both. The results of this 

analysis (eq. 5) showed that, between sites 16 and 17, the 

Medina River gained about 32 to 94 acre-ft/d and that this net 

gain (negative ground-water outflow) was dependent upon the 

stage in Diversion Lake, increasing as stage increases (fig. 10). 

Gains to the Medina River = 

-6.2082 * DivLk Stage + 5,622.1

(r2

 = 0.81), (5)

where

DivLk Stage is Diversion Lake stage in feet above NGVD 

29.

 The water-budget equation (eq. 4) developed for the 

Medina/Diversion Lake system relates the stage in Medina 

Lake to the ground-water outflow from the entire system 

(fig. 11). The computed mean GWout values range from 4.81 to 

177.55 acre-ft/d between Medina Lake stages of 963 to 1,064 ft 

above NGVD 29 (table 5). The trend line end points for GWout

from the lake system are 3.9 to 115.2 acre-ft/d at these stages, 

respectively. The GWout associated with this analysis reflects 

water loss from the lake system that is assumed to enter the 

ground-water system as recharge to the Edwards aquifer. 

It should be noted that the sum of GWout computed for 

Medina Lake (eq. 2) and for Diversion Lake (eq. 3) does not 

equal GWout computed for the entire Medina/Diversion Lake 

Figure 10. Relation between Diversion Lake stage and ground-water outflow (GWout) to the Medina River between Diversion Dam and 

the Medina River near Riomedina during selected periods. 

y = -6.2082x + 5,622.1

R2

 = 0.81

Ground-water outflow trend line

Medina River ground-water outflow

1995–96

2001–02

-150

-130

-110

-90

-70

-50

-30

-10

10

30

50

908 910 912 914 916 918 920

AVERAGE DIVERSION LAKE STAGE, IN FEET ABOVE NGVD 29

AVERAGE GWOUT, IN ACRE-FEET PER DAY
14 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

system (eq. 4). Accordingly, equation 4 should not be used to 

estimate recharge to the Edwards aquifer without considering 

the effects of the (1) internal transfer of water among the two 

lakes and the Medina River, (2) computational error associated 

with the water-budget analysis, and (3) measurement error associated with components of the water budget. Measurement error 

is discussed in the following section.

Diversion Lake appears to gain more water than it loses 

during the time Medina Lake stages are greater than about 

1,040 ft above NGVD 29 (fig. 8). Under such conditions, the 

level of Medina Lake would affect the level of Diversion Lake 

up to the spillway elevation of 919 ft. Because the level of 

Diversion Lake affects the outflow from Diversion Lake to the 

Medina River (fig. 10), it likely also affects the total groundwater outflow from the entire Medina/Diversion Lake system.

 Errors associated with the computation of GWout values 

that were used to derive equation 4 range from +1.5 to +78 acreft/d and average +35 acre-ft/d (table 5). The standard error associated with equation 4 is 21.8 acre-ft/d.

Measurement Error

The standard deviation around each measured term i, is 

considered to be the uncertainty or error in each term i (Lee 

and Swancar, 1997). To define the standard deviation around 

measured terms, errors (e) were assigned to each hydrologic 

budget component on the basis of the method of measurement, 

accuracy and precision of the instrumentation, and presumed 

quality of the hydrologic record. Records rated as good were 

assigned a percentage error (%ei

) of +10 percent; records rated 

as fair were assigned a percentage error of +15 percent; and 

records rated as poor were assigned a percentage error of +20 

(Novak, 1985, p. 65). Records for sites 1, 2, 3, 4, and 12 were 

rated good. Records for sites 13, 14, 15, 16, and 17 were rated 

fair. Records for the remaining surface-water sites and ungaged 

area were rated poor. Precipitation data were rated fair, and 

evaporation data were assigned a percentage error (%eE) of +25 

percent (Novak, 1985, p. 65). 

On the basis of the errors of the measured terms, the 

standard deviation (+eGWout) of the residual term (GWout) was 

calculated from the square root of the sum of the squared standard deviations of the measured terms (Lee and Swancar, 

1997). The equation used to calculate +eGWout is:

+eGWout = [(%eP * P)2 + (%eE *E)2 + (%eSWin * SWin)

2

+ (%eSWout * SWout)

2

 + (%e∆S * ∆S)2]

.5, (6)

where

%eP is fractional percentage error of daily P; 

%eE is fractional percentage error of daily E;

%eSWin is fractional percentage error of daily SWin;

%eSWout is fractional percentage error of daily SWout; and

%e∆S is fractional percentage error of daily ∆S.

Figure 11. Relation between Medina Lake stage and ground-water outflow (GWout) from the Medina/Diversion Lake system during 

selected periods. 

y = 1.1019x – 1,057.2

R2

 = 0.76

0

25

50

75

100

125

150

175

200

950 960 970 980 990 1,000 1,010 1,020 1,030 1,040 1,050 1,060 1,070

AVERAGE MEDINA LAKE STAGE, IN FEET ABOVE NGVD 29

AVERAGE GWOUT , IN ACRE-FEET PER DAY

Ground-water outflow trend line

1955–64

Medina/Diversion Lake system ground-water outflow

1995–96

2001–02
Estimated Recharge to Edwards Aquifer 15

The daily +eGWout was calculated and averaged for each 

selected budget period. The average of the daily +eGWout for 

each budget period is presented in tables 3–5.

Estimated Recharge to Edwards Aquifer

Published estimates of recharge to the Edwards aquifer 

from the Medina River Basin during 1934–2003 range from 

6,300 acre-ft (1956) to 104,000 acre-ft (1960) and average 

62,700 acre-ft per year (Slattery, 2004). These estimates—

based on methodology developed by Lowry (1953) and modified by Puente (1978)—currently (2004) are used by the USGS 

to estimate annual recharge to the Edwards aquifer.

To estimate recharge to the Edwards aquifer from the 

Medina/Diversion Lake system, Lowry (1953) performed a 

mass-balance (inflow minus outflow) analysis, in which he 

attempted to account for all inflow to and outflow from Medina 

Lake and the Medina/Diversion Lake system (including evaporation from lake surfaces). Using base-flow data collected during 1930 as part of a Medina River seepage investigation, 

Lowry estimated recharge to the Edwards aquifer from Diversion Lake. Lowry concluded that: (1) recharge from Diversion 

Lake was independent of the stage in Medina Lake, and 

(2) recharge from Diversion Lake was relatively constant—

about 1,500 acre-ft per month—as long as water was stored in 

Diversion Lake. Lowry also developed a set of curves relating 

ground-water outflow from the Medina/Diversion Lake system 

to the “reservoir contents,” or storage, in Medina Lake.

Figure 12 contains two curves modified from curves 

developed by Lowry (1953) by substituting Medina Lake stage 

for Lowry’s “reservoir contents.” Lowry reported that recharge 

during rising-lake stages (increasing storage) was greater than 

recharge during falling-stages (decreasing storage) and attributed the difference to bank-storage losses during rising-lake 

stages and to return flows from bank storage during falling 

stages. The ground-water outflow trend line in figure 12 was 

determined by equation 4 and duplicates the trend line in 

figure 11. 

To compare the results of estimating recharge to the 

Edwards aquifer with the water-budget equations developed 

during the present study to those of the Lowry (1953) method, 

monthly losses from the Medina/Diversion Lake system were 

estimated with equation 4 and plotted in combination with those 

computed with the Lowry method (fig. 13). The October 1995–

September 2002 period was chosen to compare the two methods, coinciding with the beginning of the initial 1996 study and 

the end of the present (2001–02) study. The average of the 

monthly recharge rates for October 1995–September 2002—

estimated by equation 4 and plotted in figure 13—is 3,083 acreft, or about 56 percent of the 5,833 acre-ft computed with the 

Lowry method.

The greatest difference between recharge estimated by the 

present study and that computed with the Lowry method occurs 

during months with rising-lake stage conditions. The Lowry 

Figure 12. Ground-water outflow (GWout) from the Medina/Diversion Lake system, as estimated by the present (2001–02) study, and 

losses computed with the Lowry (1953) method. 

Ground-water outflow trend line—Present (2001–02) study

Losses from the Medina/Diversion Lake system, Lowry (1953)

Rising stage

Falling stage

0

50

100

150

200

250

300

350

400

450

940 950 960 970 980 990 1,000 1,010 1,020 1,030 1,040 1,050 1,060 1,070

AVERAGE MEDINA LAKE STAGE, IN FEET ABOVE NGVD 29

AVERAGE GWOUT, IN ACRE-FEET PER DAY
16 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

method assumes that about 2,200 acre-ft more recharge occurs 

during months with rising-stage conditions than during months 

with falling stage. The present study’s estimates of recharge for 

months with rising-lake stage conditions are about 44 percent of 

those computed with the Lowry method, compared to about 60 

percent for months with steady or falling-stage conditions. 

Large differences between the results of the different methods 

also occur at stages greater than about 1,045 ft above NGVD 29. 

For these stages, the present study estimated recharge to be 

about 52 percent of that computed with the Lowry method, 

compared to about 64 percent at stages below 1,045 ft.

Summary

Medina Lake and Diversion Lake are located on the 

Medina River in northeastern Medina County and southeastern 

Bandera County, Texas. The Edwards aquifer is recharged in 

part by ground-water outflow from Medina and Diversion 

Lakes, individually, as well as from the Medina/Diversion Lake 

system as a whole. This recharge is greatly influenced by the 

local hydrogeology; surface-water losses from the Medina/

Diversion Lake system enter the aquifer indirectly through the 

Glen Rose Limestone of the Trinity Group or directly through 

the Kainer Formation of the Edwards Group. Because the relation between the hydrogeologic subdivisions in the study area 

and the associated zones of differing porosity and permeability 

are vertically controlled, recharge to the Edwards aquifer that 

occurs as outflow from the lake system can be related to the 

stage in Medina Lake.

The present (2001–02) Medina Lake study was done by 

the U.S. Geological Survey—in cooperation with the Edwards 

Aquifer Authority—to refine and, if possible, extend previously 

derived (1995–96) relations between Medina Lake stage and 

recharge to the Edwards aquifer to include the effects of reservoir stages below 1,018 ft and greater than 1,046 ft above 

NGVD 29. The principal objective of this study was to estimate 

ground-water outflow from Medina and Diversion Lakes and 

from the Medina/Diversion Lake system through the calculation of water budgets representing steady-state conditions over 

as wide a range as possible in the stages of Medina and Diversion Lakes.

Water budgets were computed for the Medina/Diversion 

Lake system from daily hydrologic data collected during March 

1955–September 1964, October 1995–September 1996, and 

February 2001–June 2002. Budgets for Medina and Diversion 

Lakes were computed from daily hydrologic data collected only 

during October 1995–September 1996 and April 2001–June 

2002. Water budgets were compiled for selected periods (within 

these data-collection intervals) through a range of lake stages, 

during which time the water-budget components were inferred 

to be relatively stable and the influence of precipitation, stormwater runoff, and changes in storage were presumably minimal. 

Figure 13. Comparison of monthly recharge to the Edwards aquifer in the study area during October 1995–September 2002, as estimated 

by the present (2001–02) study and computed with the Lowry (1953) method. 

Total monthly recharge

Lowry (1953) method

Medina Lake stage

FEB

JUNE

OCT

FEB

JUNE

OCT

FEB

JUNE

OCT

FEB

JUNE

OCT

FEB

JUNE

OCT

FEB

JUNE

OCT

FEB

OCT

JUNE

1995 1996 1997 1998 1999 2000 2001 2002

SEPT

950

1,000

1,050

1,100

1,150

1,200

AVERAGE MEDINA LAKE STAGE,

IN FEET ABOVE NGVD 29 PER MONTH 

0

2,000

4,000

6,000

8,000

10,000

12,000

TOTAL MONTHLY RECHARGE, IN ACRE-FEET PER MONTH

Present (2001–02) study
References Cited 17

Linear equations were developed from the observed relations between the stage in Medina Lake and ground-water 

outflow from Medina Lake, Diversion Lake, and the Medina/

Diversion Lake system. The computed mean rates of outflow 

from Medina Lake ranged from about 18 to 182 acre-ft/d 

between stages of 1,019 and 1,064 ft above NGVD 29. The 

computed rates of outflow from Diversion Lake ranged from 

about -85 to 52 acre-ft/d between these same Medina Lake 

stages. The rates of outflow from the entire lake system ranged 

from about 5 to 178 acre-ft/d between Medina Lake stages of 

963 to 1,064 ft above NGVD 29. It is assumed that all outflow 

from the lake system enters the ground-water system as 

recharge to the Edwards aquifer.

During the time that the stage in Medina Lake was greater 

than about 1,040 ft, Diversion Lake gained more water than it 

lost to the ground-water system and the rate of outflow from 

Medina Lake increased sharply while its stage was between 

about 1,043 and 1,045 above NGVD 29. The observed outflow 

from Diversion Lake during this time decreased sharply to the 

extent that a net gain resulted—indicating that a substantial 

amount of the additional outflow from Medina Lake returned to 

Diversion Lake. When the stage in Medina Lake is at the spillway elevation of 1,064 ft, Diversion Lake appears to gain as 

much as 40 percent of the concurrent ground-water outflow 

from Medina Lake. 

An indication of water moving from the lake system into 

the ground-water system and back to the surface-water system 

was observed in the most downstream reach of the Medina 

River, between Diversion Lake and the Medina River near Riomedina. During conditions of no flow over Diversion Dam, this 

reach of the Medina River gained from about 32 to 94 acre-ft/d, 

with the gain increasing with increasing stage in Diversion 

Lake.

To compare the results of estimating recharge to the 

Edwards aquifer with water-budget equations developed during 

the present study to those of a previously used (Lowry) method, 

monthly losses from the Medina/Diversion Lake system were 

estimated for the October 1995–September 2002 period. The 

average of the monthly recharge rates estimated for this period 

is 3,083 acre-ft, or about 56 percent of the monthly recharge 

computed with the previously used method.

The greatest difference between recharge estimated by the 

present study and that computed with the previously used 

method occurs during months with rising-lake stage conditions. 

(The previously used method assumes that about 2,200 acre-ft 

more recharge occurs during months with rising-stage conditions than during months with falling stage.) The present 

study’s estimates of recharge for months with rising-lake stage 

conditions are about 44 percent of those computed with the previously used method, compared to about 60 percent for months 

with steady or falling-stage conditions. For stages greater than 

1,045 ft above NGVD 29, the present study estimated recharge 

to be about 52 percent of that computed with the previously 

used method, compared to about 64 percent at stages below 

1,045 ft.

References Cited 

Ashworth, J.B., 1983, Ground-water availability of the Lower 

Cretaceous formations in the Hill Country of south-central 

Texas: Texas Department of Water Resources Report 273, 

173 p.

Barker, R.A., and Ardis, A.F., 1996, Hydrogeologic framework 

of the Edwards-Trinity aquifer system, west-central Texas: 

U.S. Geological Survey Professional Paper 1421–B, 61 p.

Bowen, I.S., 1926, The ratio of heat losses by conduction and 

by evaporation from any water surface: Physics Review, 

v. 27, p. 779–787.

Choquette, P.W., and Pray, L.C., 1970, Geologic nomenclature 

and classification of porosity in sedimentary carbonates: 

American Association of Petroleum Geologists Bulletin, 

v. 54, no. 2, p. 207–250.

Dunham, R.J., 1962, Classification of carbonate rocks according to depositional texture, in Classification of Carbonate 

Rocks Symposium: American Association of Petroleum 

Geologists Memoir 1, p. 108–121.

Gandara, S.C., 2002, Water resources data, Texas, water year 

2001—Volume 5. Guadalupe River Basin, Nueces River 

Basin, Rio Grande Basin, and intervening coastal basins: 

U.S. Geological Survey Water-Data Report TX–01–5, 344 p.

Gandara, S.C., 2003, Water resources data, Texas, water year 

2002—Volume 5. Guadalupe River Basin, Nueces River 

Basin, Rio Grande Basin, and intervening coastal basins: 

U.S. Geological Survey Water-Data Report TX–02–5, 382 p.

German, E.R., 2000, Regional evaluation of evapotranspiration 

in the Everglades: U.S. Geological Survey Water-Resources 

Investigations Report 00–4217, 48 p.

Holt, C.L.R., Jr., 1956, Geology and ground-water resources of 

Medina County, Texas: Texas Board of Water Engineers 

Bulletin 5601, 278 p.

Inden, R.F., 1974, Lithofacies and depositional model for a 

Trinity Cretaceous sequence, Central Texas, in Aspects of 

Trinity Division Geology, a Symposium on the Stratigraphy, 

Sedimentary Environments, and Fauna of the Comanche 

Cretaceous Trinity Division (Aptian and Albian) of Texas 

and Northern Mexico: Baton Rouge, La., School of Geoscience, Louisiana State University, Geoscience and Man, 

v. 8, p. 37–52.

Laczniak, R.J., DeMeo, G.A., Reiner, S.R., Smith, J.L., and 

Nylund, W.E., 1999, Estimates of ground-water discharge as 

determined from measurements of evapotranspiration, Ash 

Meadows area, Nye County, Nevada: U.S. Geological 

Survey Water-Resources Investigations Report 99–4079, 

70 p.

Lambert, R.B, Grimm, K.C., and Lee, R.W., 2000, Hydrology, 

hydrologic budget, and water chemistry of the Medina Lake 

area, Texas: U.S. Geological Survey Water-Resources 

Investigations Report 00–4148, 53 p.

Lee, T.M., and Swancar, Amy, 1997, Influence of evaporation, 

ground water, and uncertainty in the hydrologic budget of 
18 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

Lake Lucerne, a seepage lake in Polk County, Florida: U.S. 

Geological Survey Water-Supply Paper 2439, 61 p.

Lowry, R.L., Jr., 1953 Hydrologic report—Medina River above 

the Applewhite Dam site: Unpublished report prepared for 

San Antonio City Water Board, 43 p.

Maclay, R.W., and Small, T.A., 1976, Progress report on geology of the Edwards aquifer, San Antonio area, Texas, and 

preliminary interpretation of borehole geophysical and laboratory data on carbonate rocks: U.S. Geological Survey 

Open-File Report 76–627, 65 p.

Novak, C.E., 1985, WRD data reports preparation guide: U.S. 

Geological Survey, 199 p.

Puente, Celso, 1978, Method of estimating natural recharge to 

the Edwards aquifer in the San Antonio area, Texas: U.S. 

Geological Survey Water-Resources Investigations Report 

78–10, 34 p.

Rose, P.R., 1972, Edwards Group, surface and subsurface, central Texas: Austin, University of Texas, Bureau of Economic 

Geology Report of Investigations 74, 198 p.

Slattery, R.N., 2004, Recharge to and discharge from the 

Edwards aquifer in the San Antonio area, Texas, 2003: 

accessed August 26, 2004, at URL

http://tx.usgs.gov/reports/dist/dist-2004-01/

Small, T.A., and Clark, A.K., 2000, Geologic framework and 

hydrogeologic characteristics of the Edwards aquifer outcrop, Medina County, Texas: U.S. Geological Survey WaterResources Investigations Report 00–4195, 10 p.

Small, T.A., and Lambert, R.B., 1998, Geologic framework and 

hydrogeologic characteristics of the outcrops of the Edwards 

and Trinity aquifers, Medina Lake area, Texas: U.S. Geological Survey Water-Resources Investigations Report 97–4290, 

17 p.

Stricklin, F.L., Smith, C.I., and Lozo, F.E., 1971, Stratigraphy 

of Lower Cretaceous Trinity deposits of central Texas: Austin, Tex., University of Texas, Bureau of Economic Geology 

Report of Investigations 71, 63 p.

Texas A&M University, 2003, Agriculture program, TexasET, 

San Antonio weather station: accessed September 22, 2003, 

at URL 

http://texaset.tamu.edu/

Texas Water Development Board, 1996, Volumetric survey 

of Medina Lake and Diversion Lake: Texas Water Development Board publication prepared for Bexar-MedinaAtascosa Counties Water Control and Improvement District 

No. 1, 14 p.

Texas Water Development Board, 2003, Monthly pan coefficients used in ThEvap, quadrangle 809: accessed October 6, 

2003, at URL 

http://hyper20.twdb.state.tx.us/Evaporation/pancoef.txt

Texas Water Development Board, 2004, Monthly lake surface 

evaporation in inches, annual total evaporation in inches, 

quadrangle 809: accessed March 1, 2004, at URL 

http://hyper20.twdb.state.tx.us/Evaporation/evap.html

U.S. Census Bureau, 2000, State and county quickfacts—

Bexar, Comal, Hays, Medina, and Uvalde Counties, Texas, 

population, 2000: accessed October 4, 2004, at URL 

http://quickfacts.census.gov/qfd/states/48000.html 

University of Texas, Bureau of Economic Geology, 1983, 

Geologic atlas of Texas, San Antonio sheet: Austin, Tex., 

scale 1:250,000.
Table 1 19

Table 1

Table 1. Summary of the lithologic and hydrologic properties of the hydrogeologic subdivisions of the Edwards and Trinity aquifers, San 

Antonio area, Texas (modified from Lambert and others, 2000). 

[Hydrogeologic subdivisions modified from Maclay and Small (1976); groups, formations, members, and thicknesses modified from Holt (1956), Stricklin and 

others (1971), Rose (1972), Inden (1974), and Ashworth (1983); lithology modified from Dunham (1962); and porosity type modified from Choquette and Pray 

(1970). AQ, aquifer; CU, confining unit; *, not exposed in the study area; gal/min, gallons per minute] 

Hydrogeologic

subdivision

Group, formation,

or member

Hydrologic

function

Thickness

(feet) Lithology Fieldidentification

Cavern

development

Porosity/permeability

and well yields

Lower Cretaceous

I

Edwards aquifer

Georgetown Formation Karst AQ;

not karst

CU

2–20 Reddish-brown, gray to 

light-tan, marly

 limestone

Red-brown to gray marly 

limestone; Kingena 

wacoensis

None Low porosity/low 

permeability

II

Devils River Formation

Edwards Group

Person Formation

Cyclic and

marine 

members,

undivided

AQ 0–10 Mudstone to packstone; 

miliolid grainstone; 

chert

* Many subsurface; 

might be 

associated with 

earlier karst 

development

Laterally extensive; both 

fabric and not fabric/

water-yielding

III Leached and

collapsed 

members,

undivided

AQ 70–90 Crystalline limestone; 

mudstone to 

grainstone; chert; 

collapsed breccia

Bioturbated iron-stained 

beds separated by 

massive limestone 

beds; stromatolitic 

limestone

Extensive lateral

development; 

large rooms

Majority not fabric/one of the 

most porous and 

permeable 

IV Regional 

dense

member

CU 16–20 Dense, argillaceous

mudstone

Wispy iron-oxide stains Very few; only 

vertical fracture 

enlargement

Not fabric/low permeability; 

vertical barrier

V

Kainer Formation

Grainstone

member

AQ 50–60 Miliolid grainstone; 

mudstone to 

wackestone; chert

White crossbedded

grainstone

Few caves Not fabric/recrystallization 

reduces permeability

VI Kirschberg

evaporite

member

AQ 50–60 Highly altered 

crystalline limestone; 

chalky mudstone; 

chert

Boxwork voids, with 

neospar and travertine

frame

Probably extensive 

cave development

Majority fabric/one of the 

most porous and 

permeable

VII Dolomitic

member

AQ 110–140 Mudstone to grainstone; 

crystalline limestone; 

chert

Massively bedded, light 

gray; Toucasia 

abundant

Caves related to 

structure or 

bedding planes

Mostly not fabric; some 

bedding-plane fabric/

water-yielding

VIII Basal 

nodular

member

Karst AQ;

not karst

CU

50–60 Shaly, fossiliferous, 

nodular limestone; 

mudstone; miliolid

grainstone

Massive, nodular, and 

mottled; abundant 

gastropods and 

Exogyra texana

Large lateral caves at 

surface

Fabric; stratigraphically 

controlled/large conduit 

flow at surface; no 

permeability in subsurface

Upper 

zone 

Trinity 

aquifer

Trinity Group

Glen Rose Limestone 

Upper 

member 

CU; 

evaporite 

beds AQ

350–500 Yellowish-tan, thinly 

bedded limestone 

and marl

Stair-step topography;

alternating limestone 

and marl; Orbitolina 

minuta

Some surface cave 

development

Some water production at 

evaporite beds/relatively 

impermeable (0–20 gal/

min)
20 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

Table 2

Table 2. Hydrologic budget data-collection sites in the study area, San Antonio area, Texas.

[mi2, square miles; GWout, ground-water outflow; SWin, surface-water inflow site; P, precipitation measurement site; c, continuous record site; p, periodic 

measurement site; FM, Farm to Market; ∆S, change in storage measurement site; E, evaporation measurement site; SWout, surface-water outflow site; e, estimated 

record; --, not applicable] 

1 Evaporation estimated for this period, no data collected at site.

2 Streamflow estimated March 1955–April 1957.

Site

number

(fig. 1)

Station

 number Station name Latitude Longitude

Drainage

area

(mi2

)

Station

type

Period of record

available for GWout

computation

U.S. Geological Survey

1 08178880 Medina River at Bandera 29°43'25" 99°04'11" 328 SWin, P, c Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

2 08178990 Medina River at English 

Crossing

29°40'53" 98°58'32" 474 SWin, p Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

3 08179000 Medina River near Pipe 

Creek

29°40'31" 98°58'33" 474 SWin, c Mar. 1955–Sept. 1964

4 08179100 Red Bluff Creek near Pipe 

Creek

29°40'51" 98°57'19" 56.3 SWin, c Apr. 1956–Sept. l964

5 08179110 Red Bluff Creek at FM 1283 29°40'23" 98°57'36" 57.9 SWin, p Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

6 08179240 Bruins Creek near Pipe 

Creek

29°39'23" 98°59'17" 8.76 SWin, p Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

7 08179260 Rocky Creek near Pipe 

Creek

29°37'15" 98°59'57" 5.22 SWin, p Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

8 08179280 Cypress Creek near 

Riomedina

29°35'14" 99°00'30" 11 SWin, p Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

9 08179300 Elm Creek near Pipe Creek 29°36'15" 98°55'45" 12.7 SWin, p Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

10 08179320 Unnamed tributary at FM 

1283

29°34'44" 98°53'57" 5.44 SWin, p Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

11 08179500 Medina Lake near San 

Antonio

29°32'24" 98°56'01" 634 ∆S, E Mar. 1955–Sept. 19641;

Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

12 08179520 Medina River below 

Medina Lake

29°32'02" 98°56'06" 635 SWin, SWout, c Oct. 1995–Sept. 1996; 

Apr. 2001–June 2002

13 08179530 Koenig Creek near 

Riomedina

29°31'57 98°56'14" 3.64 SWin, SWout, p Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

14 08179700 Nesbit Springs near Mico 29°32'20 98°54'47" -- SWin, p SWout, p Jan. 2001–June 2002

15 08180000 Medina Irrigation Canal 

near Riomedina

29°30'19" 98°54'11" -- SWout, c, e2 Mar. 1955–Sept. 1964;

Oct. 1995–Sept. 1996; 

Feb. 2001–June 2002

16 08180010 Diversion Lake near 

Riomedina

29°30'36" 98°54'04" 649 ∆S, E Mar. 1955–Sept. 19641;

Oct. 1995–Sept. 19961;

Feb. 2001–June 2002

17 08180500 Medina River near 

Riomedina

29°29'53" 98°54'16" 650 SWout, c Mar. 1955–Sept. 1964; 

Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

-- -- Ungaged area -- -- 160 SWin, e Mar. 1955–Mar. 1956

-- -- Ungaged area -- -- 103.7 SWin, e Apr. 1956–Sept. 1964

-- -- Ungaged area -- -- 59.0 SWin, e Oct. 1995–Sept. 1996; 

Jan. 2001–June 2002

National Weather Service

18 417628 Riomedina 29°26'25" 98°53'50" -- P Mar. 1955–Sept. 1964;

Jan. 2001–June 2002
Table 3 21

Table 3

Table 3. Summary of selected water-budget periods and associated components of the water budget for Medina Lake, San Antonio 

area, Texas.

[In acre-feet per day except as indicated. GWout, ground-water outflow; SWin, surface-water inflow; SWout, surface-water outflow; ∆S, change in storage] 

Water-budget period

Number

of days in

budget

period

Medina

Lake

stage,

average

(feet above

NGVD 29)

GWout,

mean

GWout,

standard

deviation

GWout,

minimum

25th

percentileMedian

75th

percentile

GWout,

maximum

GWout,

+error

10/12/1995 to 10/25/1995 14 1,044.88 124.97 67.63 48.57 87.26 107.20 153.05 301.14 48.84

11/05/1995 to 11/16/1995 12 1,044.81 71.03 53.89 -13.47 51.69 64.45 86.69 205.63 25.09

11/19/1995 to 11/27/1995 9 1,044.97 54.87 29.18 2.48 33.06 65.31 68.45 103.18 23.02

11/30/1995 to 12/10/1995 11 1,044.88 85.09 63.44 -32.36 63.27 89.00 95.11 236.12 23.44

12/11/1995 to 12/21/1995 11 1,044.74 106.78 58.94 -33.34 90.79 109.35 127.18 192.87 23.62

12/28/1995 to 01/09/1996 13 1,044.43 107.83 67.15 7.73 60.73 101.78 143.25 246.36 24.53

01/10/1996 to 01/22/1996 13 1,044.05 107.43 87.39 -49.81 67.76 103.02 122.58 347.95 27.92

01/23/1996 to 02/04/1996 13 1,043.56 100.73 55.62 11.08 49.10 123.49 138.35 172.71 32.30

02/08/1996 to 02/28/1996 21 1,042.50 93.02 70.62 -82.27 71.99 94.04 124.29 287.61 44.76

03/02/1996 to 03/24/1996 23 1,041.13 97.91 64.01 -36.38 72.19 86.13 123.51 288.60 41.00

03/29/1996 to 04/08/1996 11 1,039.64 93.07 68.37 -32.86 50.80 91.06 143.76 203.57 47.29

04/15/1996 to 05/06/1996 22 1,037.76 57.17 95.10 -117.40 -15.89 45.45 112.14 300.84 65.17

07/16/1996 to 07/23/1996 8 1,026.30 18.50 42.31 -39.97 -6.70 23.79 43.51 81.79 71.61

09/08/1996 to 09/22/1996 15 1,019.61 50.55 48.15 -15.76 25.73 42.40 62.31 151.30 18.05

07/05/2001 to 07/20/2001 16 1,061.77 132.41 63.76 -2.33 100.05 121.05 196.17 220.91 84.69

07/21/2001 to 08/05/2001 16 1,060.30 143.30 46.25 76.37 109.07 138.87 175.43 219.00 80.48

08/08/2001 to 08/25/2001 18 1,058.47 157.67 172.75 -228.78 101.70 136.81 199.99 559.93 83.30

09/26/2001 to 10/06/2001 11 1,061.16 152.41 188.34 -80.61 -9.89 135.06 290.36 495.80 50.97

10/18/2001 to 10/31/2001 14 1,061.02 143.88 200.30 -63.21 -9.39 81.85 282.98 541.03 46.95

11/01/2001 to 11/14/2001 14 1,060.62 126.58 241.62 -89.14 -40.90 -25.95 296.72 560.44 42.61

01/25/2002 to 02/07/2002 14 1,064.15 122.80 172.58 -252.45 66.82 87.89 160.12 473.73 43.78

02/12/2002 to 02/27/2002 16 1,063.96 95.83 124.50 -54.18 .73 69.86 197.50 376.06 42.10

02/28/2002 to 03/14/2002 15 1,063.63 109.95 185.43 -234.32 .87 118.46 236.49 395.33 41.30

03/21/2002 to 04/06/2002 17 1,063.04 128.28 166.09 -112.07 2.20 109.23 223.52 558.68 52.44

04/09/2002 to 04/27/2002 19 1,062.71 111.64 146.69 -110.38 16.03 100.51 223.16 430.68 43.06

04/28/2002 to 05/16/2002 19 1,061.79 152.55 112.57 -61.89 100.41 140.40 240.79 327.13 73.81

05/27/2002 to 06/12/2002 17 1,059.76 140.91 119.68 -24.46 18.05 147.68 217.83 343.78 80.72

06/13/2002 to 06/29/2002 17 1,057.96 181.60 109.81 50.92 93.87 166.22 260.58 396.60 88.25
22 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

Table 3. Summary of selected water-budget periods and associated components of the water budget for Medina Lake, San Antonio 

area, Texas—Continued.

Water-budget period

Precipitation,

mean

Precipitation,

standard

deviation

Precipitation,

minimum

Precipitation,

maximum

Precipitation,

+error

Swin,

mean

Swin,

standard

deviation

Swin,

minimum

Swin,

maximum

SWin,

+error

10/12/1995 to 10/25/1995 0 0 0 0 0 132.62 19.88 103.44 163.29 13.77

11/05/1995 to 11/16/1995 0 0 0 0 0 175.54 34.41 134.24 237.20 18.24

11/19/1995 to 11/27/1995 0 0 0 0 0 170.65 26.44 135.21 202.79 18.00

11/30/1995 to 12/10/1995 3.05 10.12 0 33.57 .46 138.20 6.12 129.29 149.75 14.50

12/11/1995 to 12/21/1995 11.20 26.87 0 84.09 1.68 152.57 10.18 138.80 172.87 15.83

12/28/1995 to 01/09/1996 2.34 8.45 0 30.47 .35 119.81 12.52 104.27 140.96 12.36

01/10/1996 to 01/22/1996 0 0 0 0 0 103.75 3.80 98.90 112.17 10.70

01/23/1996 to 02/04/1996 2.00 7.21 0 26.00 .30 94.58 6.05 87.77 104.84 9.76

02/08/1996 to 02/28/1996 .93 4.28 0 19.62 .14 88.95 7.86 79.87 103.65 9.12

03/02/1996 to 03/24/1996 0 0 0 0 0 81.64 12.13 65.24 106.25 8.34

03/29/1996 to 04/08/1996 18.01 59.74 0 198.13 2.70 87.77 24.39 65.93 143.15 9.00

04/15/1996 to 05/06/1996 10.21 41.76 0 195.05 1.53 56.55 10.86 43.20 86.76 5.83

07/16/1996 to 07/23/1996 0 0 0 0 0 7.23 1.04 6.00 8.83 .75

09/08/1996 to 09/22/1996 13.45 39.28 0 151.73 2.02 96.63 52.24 43.20 210.47 9.95

07/05/2001 to 07/20/2001 0 0 0 0 0 120.75 28.40 88.40 185.58 12.44

07/21/2001 to 08/05/2001 0 0 0 0 0 65.49 10.67 52.60 85.91 6.76

08/08/2001 to 08/25/2001 12.38 48.77 0 207.25 1.86 40.44 3.68 35.85 47.37 4.16

09/26/2001 to 10/06/2001 2.65 8.77 0 29.10 .40 200.25 21.47 177.48 237.50 22.23

10/18/2001 to 10/31/2001 0 0 0 0 0 216.61 29.93 181.67 273.34 23.47

11/01/2001 to 11/14/2001 22.76 66.22 0 246.39 3.41 168.63 5.78 162.07 178.31 17.70

01/25/2002 to 02/07/2002 13.75 41.45 0 155.09 2.06 277.75 6.63 264.56 286.56 29.90

02/12/2002 to 02/27/2002 .57 2.27 0 9.08 .09 220.93 13.79 194.97 238.70 23.59

02/28/2002 to 03/14/2002 2.34 7.26 0 27.62 .35 179.74 8.59 168.69 194.29 18.74

03/21/2002 to 04/06/2002 46.64 156.37 0 635.09 7.00 175.15 12.98 162.07 197.57 18.55

04/09/2002 to 04/27/2002 12.82 37.37 0 120.81 1.92 170.78 20.91 141.57 207.77 18.00

04/28/2002 to 05/16/2002 0 0 0 0 0 110.46 15.42 91.24 138.77 11.39

05/27/2002 to 06/12/2002 5.19 16.82 0 69.71 .78 100.45 8.36 83.54 115.59 10.39

06/13/2002 to 06/29/2002 22.63 49.81 0 151.18 3.39 61.26 8.35 52.60 80.92 6.34
Table 3 23

Table 3. Summary of selected water-budget periods and associated components of the water budget for Medina Lake, San Antonio 

area, Texas—Continued. 

Water-budget period Swout,

mean

Swout,

standard

deviation

Swout,

minimum

Swout,

maximum

Swout,

+error

Evaporation,

mean

Evaporation,

standard

deviation

Evaporation,

minimum

Evaporation,

maximum

Evaporation, 

+error

10/12/1995 to 10/25/1995 226.83 41.94 148.72 258.85 34.41 53.60 20.35 22.05 83.51 13.40

11/05/1995 to 11/16/1995 68.87 1.50 67.26 70.73 10.75 42.47 24.27 10.23 96.49 10.62

11/19/1995 to 11/27/1995 68.30 1.39 67.13 70.34 10.66 27.92 16.39 6.60 62.31 6.98

11/30/1995 to 12/10/1995 66.82 .67 64.88 67.29 10.40 42.07 41.33 1.42 140.60 10.52

12/11/1995 to 12/21/1995 66.00 .92 64.98 67.04 10.28 36.54 37.39 0 119.01 9.13

12/28/1995 to 01/09/1996 64.69 .19 64.45 65.04 10.07 50.32 39.20 4.75 135.74 12.58

01/10/1996 to 01/22/1996 118.55 10.38 101.97 145.63 18.13 27.92 18.72 0 62.71 6.98

01/23/1996 to 02/04/1996 138.56 20.86 111.69 178.87 21.12 42.44 19.96 5.94 92.18 10.61

02/08/1996 to 02/28/1996 225.15 22.56 174.93 251.73 34.09 25.48 27.15 0 96.39 6.37

03/02/1996 to 03/24/1996 191.10 56.97 140.63 302.80 28.97 34.76 36.06 0 151.38 8.69

03/29/1996 to 04/08/1996 239.05 47.91 182.05 281.30 36.16 26.76 20.09 2.78 57.34 6.69

04/15/1996 to 05/06/1996 337.58 27.14 280.90 377.44 50.91 41.51 34.43 2.56 145.70 10.38

07/16/1996 to 07/23/1996 360.23 26.82 325.36 394.62 54.26 64.62 8.58 48.98 75.60 16.15

09/08/1996 to 09/22/1996 52.97 25.37 34.68 93.51 8.26 33.36 10.35 14.14 48.35 8.34

07/05/2001 to 07/20/2001 328.02 8.47 317.68 337.15 49.77 172.82 11.54 141.20 186.12 43.21

07/21/2001 to 08/05/2001 294.12 16.48 281.40 317.64 44.64 159.31 25.13 109.78 191.90 39.83

08/08/2001 to 08/25/2001 315.62 2.18 312.79 320.87 47.84 140.64 41.47 52.05 223.54 35.16

09/26/2001 to 10/06/2001 139.06 1.06 136.80 141.45 21.48 120.53 42.08 14.55 161.46 30.13

10/18/2001 to 10/31/2001 142.43 1.28 140.29 143.89 22.00 94.60 25.99 38.01 129.49 23.65

11/01/2001 to 11/14/2001 142.36 .86 140.76 142.88 21.96 72.45 22.80 31.23 115.44 18.11

01/25/2002 to 02/07/2002 149.13 8.53 138.63 164.33 23.06 55.29 22.12 15.15 99.45 13.82

02/12/2002 to 02/27/2002 135.66 .20 135.28 135.92 20.99 90.01 28.70 15.13 148.30 22.50

02/28/2002 to 03/14/2002 134.29 1.07 132.93 135.28 20.76 77.85 41.07 15.08 140.54 19.46

03/21/2002 to 04/06/2002 155.55 31.45 130.86 200.67 23.94 102.66 57.34 3.09 173.76 25.66

04/09/2002 to 04/27/2002 134.88 .34 134.41 135.51 20.84 89.71 63.29 0 226.24 22.43

04/28/2002 to 05/16/2002 330.67 106.59 132.34 486.53 50.16 85.13 42.93 25.87 161.16 21.28

05/27/2002 to 06/12/2002 346.64 93.87 203.07 475.99 52.54 118.09 54.41 32.69 232.79 29.52

06/13/2002 to 06/29/2002 385.09 25.25 374.46 471.99 58.28 105.44 38.87 37.85 188.27 26.36
24 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

Table 3. Summary of selected water-budget periods and associated components of the water budget for Medina Lake, San Antonio 

area, Texas—Continued. 

Water-budget period ∆S,

mean

∆S,

standard

deviation

∆S,

minimum

∆S,

maximum

∆S,

+error

GWout,

percent of

hydrologic

budget

Precipitation,

percent of

hydrologic

budget

Swin,

percent of

hydrologic

budget

Swout,

percent of

hydrologic

budget

Evaporation,

percent of

hydrologic

budget

∆S,

percent of

hydrologic

budget

10/12/1995 to 10/25/1995 -273 86 -445 -121 27.3 16.1 0 17.1 29.2 2.6 35.1

11/05/1995 to 11/16/1995 -7 71 -189 79 4.9 20.5 0 50.7 19.9 7.0 2.0

11/19/1995 to 11/27/1995 20 51 -60 93 4.6 16.6 0 51.7 20.7 5.0 5.9

11/30/1995 to 12/10/1995 -53 70 -249 14 5.6 22.0 .8 35.7 17.3 10.7 13.6

12/11/1995 to 12/21/1995 -46 61 -134 81 6.0 25.5 2.7 36.4 15.7 8.9 10.9

12/28/1995 to 01/09/1996 -101 76 -259 -3 10.1 24.8 .5 27.6 14.9 9.0 23.2

01/10/1996 to 01/22/1996 -150 86 -392 0 15.0 21.5 0 20.8 23.8 3.8 30.1

01/23/1996 to 02/04/1996 -185 67 -269 -56 18.5 18.6 .4 17.5 25.6 3.7 34.2

02/08/1996 to 02/28/1996 -254 70 -444 -99 25.4 13.5 .1 12.9 32.7 3.9 36.8

03/02/1996 to 03/24/1996 -242 89 -392 -38 24.2 15.1 0 12.6 29.5 5.6 37.3

03/29/1996 to 04/08/1996 -253 86 -373 -114 25.3 13.1 2.5 12.3 33.6 2.8 35.6

04/15/1996 to 05/06/1996 -370 77 -620 -220 37.0 6.6 1.2 6.5 39.0 4.0 42.7

07/16/1996 to 07/23/1996 -436 41 -510 -392 43.6 2.2 0 .9 43.4 1.0 52.5

09/08/1996 to 09/22/1996 -27 49 -118 71 4.6 20.2 5.4 38.5 21.1 4.1 10.7

07/05/2001 to 07/20/2001 -513 72 -600 -400 51.3 12.0 0 10.9 29.7 1.0 46.4

07/21/2001 to 08/05/2001 -531 48 -600 -500 53.1 13.5 0 6.2 27.8 2.4 50.2

08/08/2001 to 08/25/2001 -561 158 -1,000 -200 56.1 14.0 1.1 3.6 28.0 3.7 49.7

09/26/2001 to 10/06/2001 -209 187 -600 0 20.9 20.4 .4 26.9 18.7 5.6 28.0

10/18/2001 to 10/31/2001 -164 210 -600 0 16.4 20.8 0 31.2 20.5 3.7 23.7

11/01/2001 to 11/14/2001 -150 235 -600 0 15.0 20.0 3.6 26.6 22.5 3.6 23.7

01/25/2002 to 02/07/2002 -36 165 -400 300 9.3 19.8 2.2 44.7 24.0 3.6 5.7

02/12/2002 to 02/27/2002 -100 126 -400 0 10.0 16.5 .1 38.0 23.3 4.9 17.2

02/28/2002 to 03/14/2002 -140 192 -500 200 18.0 18.1 .4 29.6 22.1 6.8 23.0

03/21/2002 to 04/06/2002 -165 237 -600 400 21.2 17.6 6.4 24.1 21.4 7.9 22.6

04/09/2002 to 04/27/2002 -153 168 -500 0 15.3 17.3 2.0 26.4 20.9 9.8 23.6

04/28/2002 to 05/16/2002 -458 198 -700 0 45.8 13.9 0 10.1 30.2 3.9 41.8

05/27/2002 to 06/12/2002 -500 162 -700 -200 50.0 12.3 .5 8.8 30.2 4.7 43.6

06/13/2002 to 06/29/2002 -588 117 -900 -400 58.8 14.2 1.8 4.8 30.1 3.0 46.0
Table 4 25

Table 4

Table 4. Summary of selected water-budget periods and associated components of the water budget for Diversion Lake, San Antonio 

area, Texas.

[In acre-feet per day except as indicated. GWout, ground-water outflow; SWin, surface-water inflow; SWout, surface-water outflow; ∆S, change in storage]

Water-budget period

Number

of days in

budget

period

Diversion

Lake stage,

average

(feet above

NGVD 29)

GWout,

mean

GWout,

standard

deviation

GWout,

minimum

25th percentile Median 75th percentileGWout,

maximum

GWout,

+error

10/12/1995 to 10/25/1995 14 912.39 -9.95 8.65 -22.88 -12.85 -9.34 -6.94 9.18 48.21

11/05/1995 to 11/16/1995 12 914.18 -45.57 6.69 -56.58 -50.37 -46.01 -41.56 -33.77 22.50

11/19/1995 to 11/27/1995 9 914.45 -7.27 4.84 -15.19 -9.24 -4.94 -3.78 -3.08 13.40

11/30/1995 to 12/10/1995 11 913.75 -32.89 7.81 -45.50 -35.13 -32.79 -30.31 -17.05 22.85

12/11/1995 to 12/21/1995 11 911.53 -31.94 5.11 -41.52 -33.28 -30.06 -28.56 -26.12 20.08

12/28/1995 to 01/09/1996 13 911.56 -18.42 2.63 -23.34 -19.91 -17.77 -16.77 -14.41 17.31

01/10/1996 to 01/22/1996 13 911.47 -12.13 8.46 -22.62 -15.83 -14.57 -12.55 11.84 26.14

01/23/1996 to 02/04/1996 13 911.79 -9.76 7.15 -24.15 -14.53 -9.12 -6.17 5.23 30.32

02/08/1996 to 02/28/1996 21 912.38 2.77 6.31 -11.40 -.14 4.31 6.86 13.29 47.40

03/02/1996 to 03/24/1996 23 912.41 6.49 23.65 -30.61 -4.68 .10 5.94 59.94 39.73

03/29/1996 to 04/08/1996 11 913.35 -.71 18.83 -26.27 -19.32 7.58 13.99 23.27 52.04

04/15/1996 to 05/06/1996 22 913.11 27.57 7.84 12.80 22.16 27.28 33.76 42.25 68.45

07/16/1996 to 07/23/1996 8 913.57 51.92 9.16 39.30 47.28 49.89 56.63 66.37 71.39

09/08/1996 to 09/22/1996 15 909.32 22.44 10.02 11.50 14.96 17.37 31.49 41.86 10.17

07/05/2001 to 07/20/2001 16 915.47 -67.88 7.79 -83.53 -71.38 -67.99 -63.98 -54.09 77.04

07/21/2001 to 08/05/2001 16 914.87 -64.75 10.71 -87.70 -68.20 -64.36 -59.41 -47.84 70.78

08/08/2001 to 08/25/2001 18 913.94 -50.46 12.94 -71.87 -59.53 -49.57 -42.35 -27.74 72.47

09/26/2001 to 10/06/2001 11 918.49 -85.06 12.34 -99.68 -95.52 -84.97 -76.68 -63.63 40.65

10/18/2001 to 10/31/2001 14 919.10 -59.97 8.56 -72.99 -66.95 -58.65 -56.43 -46.96 37.55

11/01/2001 to 11/14/2001 14 918.16 -58.20 13.98 -85.87 -63.31 -55.83 -53.82 -26.21 39.65

01/25/2002 to 02/07/2002 14 919.13 -56.43 3.92 -62.63 -59.27 -57.23 -52.95 -50.92 38.38

02/12/2002 to 02/27/2002 16 918.43 -45.19 16.56 -76.65 -52.70 -45.50 -30.38 -24.71 35.77

02/28/2002 to 03/14/2002 15 917.32 -40.19 9.30 -58.98 -45.57 -40.54 -32.13 -27.80 34.02

03/21/2002 to 04/06/2002 17 918.87 -29.23 11.33 -53.67 -32.84 -28.20 -21.91 -12.20 35.40

04/09/2002 to 04/27/2002 19 918.96 -26.78 12.04 -56.47 -26.82 -22.35 -19.18 -16.10 33.08

04/28/2002 to 05/16/2002 19 917.14 -20.66 25.28 -57.15 -33.25 -26.53 -12.10 38.32 73.46

05/27/2002 to 06/12/2002 17 916.52 -39.17 26.36 -111.42 -48.35 -40.42 -25.17 13.57 78.07

06/13/2002 to 06/29/2002 17 917.48 -55.50 12.32 -84.44 -59.72 -56.63 -47.04 -37.30 89.15
26 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

Table 4. Summary of selected water-budget periods and associated components of the water budget for Diversion Lake, San Antonio 

area, Texas—Continued.

Water-budget period

Precipitation,

mean

Precipitation,

standard

deviation

Precipitation,

minimum

Precipitation,

maximum

Precipitation,

+error

Swin,

mean

Swin,

standard

deviation

Swin,

minimum

Swin,

maximum

Swin,

+error

10/12/1995 to 10/25/1995 0 0 0 0 0 226.83 41.94 148.72 258.85 34.41

11/05/1995 to 11/16/1995 .11 .37 0 1.27 .02 68.87 1.50 67.26 70.73 10.75

11/19/1995 to 11/27/1995 0 0 0 0 0 68.30 1.39 67.13 70.34 10.66

11/30/1995 to 12/10/1995 .08 .26 0 .85 .01 66.82 .67 64.88 67.29 10.40

12/11/1995 to 12/21/1995 .37 .90 0 2.88 .06 66.00 .92 64.98 67.04 10.28

12/28/1995 to 01/09/1996 0 0 0 0 0 64.69 .19 64.45 65.04 10.07

01/10/1996 to 01/22/1996 0 0 0 0 0 118.55 10.38 101.97 145.63 18.13

01/23/1996 to 02/04/1996 0 0 0 0 0 138.56 20.86 111.69 178.87 21.12

02/08/1996 to 02/28/1996 0 0 0 0 0 225.15 22.56 174.93 251.73 34.09

03/02/1996 to 03/24/1996 0 0 0 0 0 191.10 56.97 140.63 302.80 28.97

03/29/1996 to 04/08/1996 .75 2.48 0 8.21 .11 239.05 47.91 182.05 281.30 36.16

04/15/1996 to 05/06/1996 .26 1.21 0 5.70 .04 337.58 27.14 280.90 377.44 50.91

07/16/1996 to 07/23/1996 0 0 0 0 0 360.23 26.82 325.36 394.62 54.26

09/08/1996 to 09/22/1996 .65 2.26 0 8.75 .10 52.97 25.37 34.68 93.51 8.26

07/05/2001 to 07/20/2001 0 0 0 0 0 328.02 8.47 317.68 337.15 49.77

07/21/2001 to 08/05/2001 0 0 0 0 0 294.12 16.48 281.40 317.64 44.64

08/08/2001 to 08/25/2001 .14 .59 0 2.51 .02 315.62 2.18 312.79 320.87 47.84

09/26/2001 to 10/06/2001 0 0 0 0 0 139.06 1.06 136.80 141.45 21.48

10/18/2001 to 10/31/2001 0 0 0 0 0 142.43 1.28 140.29 143.89 22.00

11/01/2001 to 11/14/2001 .68 2.54 0 9.49 .10 142.36 .86 140.76 142.88 21.96

01/25/2002 to 02/07/2002 .40 1.20 0 4.42 .06 149.13 8.53 138.63 164.33 23.06

02/12/2002 to 02/27/2002 0 0 0 0 0 135.66 .20 135.28 135.92 20.99

02/28/2002 to 03/14/2002 .06 .23 0 .88 .01 134.29 1.07 132.93 135.28 20.76

03/21/2002 to 04/06/2002 1.49 5.01 0 20.38 .22 155.55 31.45 130.86 200.67 23.94

04/09/2002 to 04/27/2002 .26 .80 0 3.15 .04 134.88 .34 134.41 135.51 20.84

04/28/2002 to 05/16/2002 0 0 0 0 0 330.67 106.59 132.34 486.53 50.16

05/27/2002 to 06/12/2002 0 0 0 0 0 346.64 93.87 203.07 475.99 52.54

06/13/2002 to 06/29/2002 .64 1.81 0 5.59 .10 385.09 25.25 374.46 471.99 58.28
Table 4 27

Table 4. Summary of selected water-budget periods and associated components of the water budget for Diversion Lake, San Antonio 

area, Texas—Continued.

Water-budget period Swout,

mean

Swout,

standard

deviation

Swout,

minimum

Swout,

maximum

Swout,

+error

Evaporation,

mean

Evaporation,

standard

deviation

Evaporation,

maximum

Evaporation,

minimum

Evaporation,

+error

10/12/1995 to 10/25/1995 224.31 41.47 150.48 265.32 33.65 2.02 0.39 2.58 1.16 0.50

11/05/1995 to 11/16/1995 127.71 25.75 81.18 164.34 19.16 1.42 .84 3.43 .26 .36

11/19/1995 to 11/27/1995 45.10 1.92 43.56 47.52 6.77 1.29 .98 3.44 .37 .32

11/30/1995 to 12/10/1995 131.22 8.99 116.82 148.50 19.68 1.91 2.02 6.76 .28 .48

12/11/1995 to 12/21/1995 113.40 12.05 99.00 132.66 17.01 1.54 1.35 4.73 .05 .39

12/28/1995 to 01/09/1996 93.06 4.20 87.12 99.00 13.96 1.22 .91 3.72 .15 .30

01/10/1996 to 01/22/1996 124.74 10.81 93.06 132.66 18.71 1.65 1.18 4.33 .62 .41

01/23/1996 to 02/04/1996 144.39 12.46 124.74 164.34 21.66 .78 .56 1.70 0 .20

02/08/1996 to 02/28/1996 219.50 17.76 186.12 243.54 32.92 1.04 .78 2.75 0 .26

03/02/1996 to 03/24/1996 180.18 32.09 138.60 225.72 27.03 1.09 1.28 5.44 0 .27

03/29/1996 to 04/08/1996 247.14 13.34 231.66 269.28 37.07 1.34 1.08 3.52 .17 .34

04/15/1996 to 05/06/1996 304.92 23.48 249.48 334.62 45.74 1.40 1.01 4.27 .31 .35

07/16/1996 to 07/23/1996 309.13 16.55 285.12 332.64 46.37 2.75 .62 3.56 1.48 .69

09/08/1996 to 09/22/1996 32.60 4.48 29.70 47.52 4.89 1.44 .62 3.02 .69 .36

07/05/2001 to 07/20/2001 391.79 11.74 364.32 403.92 58.77 3.48 .23 3.74 2.85 .87

07/21/2001 to 08/05/2001 365.68 13.85 338.58 382.14 54.85 3.19 .53 3.89 2.18 .80

08/08/2001 to 08/25/2001 362.34 21.76 310.86 394.02 54.35 2.77 .81 4.38 1.02 .69

09/26/2001 to 10/06/2001 228.42 31.52 194.04 263.34 34.26 2.98 .99 3.91 .38 .74

10/18/2001 to 10/31/2001 202.67 6.14 194.04 211.86 30.40 2.58 .72 3.54 1.04 .65

11/01/2001 to 11/14/2001 218.65 19.19 178.20 247.50 32.80 1.88 .64 3.04 .75 .47

01/25/2002 to 02/07/2002 204.51 10.97 190.08 225.72 30.68 1.45 .58 2.61 .40 .36

02/12/2002 to 02/27/2002 189.46 39.72 128.70 279.18 28.42 2.26 .75 3.85 .40 .56

02/28/2002 to 03/14/2002 179.39 8.43 168.30 192.06 26.91 1.81 .95 3.24 .36 .45

03/21/2002 to 04/06/2002 168.30 21.16 140.58 213.84 25.25 2.67 1.47 4.39 .08 .67

04/09/2002 to 04/27/2002 168.51 28.93 138.60 251.46 25.28 2.35 1.62 5.69 0 .59

04/28/2002 to 05/16/2002 351.92 61.67 174.24 405.90 52.79 2.04 1.05 3.94 .58 .51

05/27/2002 to 06/12/2002 378.88 34.88 308.88 459.36 56.83 2.81 1.29 5.65 .76 .70

06/13/2002 to 06/29/2002 449.11 21.50 419.76 487.08 67.37 2.71 1.00 4.89 .96 .68
28 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

Table 4. Summary of selected water-budget periods and associated components of the water budget for Diversion Lake, San Antonio 

area, Texas—Continued.

Water-budget period ∆S,

mean

∆S,

standard

deviation

∆S,

minimum

∆S,

maximum

∆S,

+error

GWout,

percent of

hydrologic

budget

Precipitation,

percent of

hydrologic

budget

Swin,

percent of

hydrologic

budget

Swout,

percent of

hydrologic

budget

Evaporation,

percent of

hydrologic

budget

∆S,

percent of

hydrologic

budget

10/12/1995 to 10/25/1995 10.46 10.67 -1.00 34.50 1.59 2.1 0 47.4 47.9 0.4 2.2

11/05/1995 to 11/16/1995 -14.58 27.06 -54.10 27.50 4.11 17.6 0 49.4 26.7 .6 5.6

11/19/1995 to 11/27/1995 29.18 7.20 22.00 41.60 4.38 4.8 0 29.8 45.2 .9 19.3

11/30/1995 to 12/10/1995 -33.34 7.54 -49.50 -24.70 5.00 12.4 0 49.3 25.1 .7 12.5

12/11/1995 to 12/21/1995 -16.64 8.23 -32.10 -7.30 2.50 13.9 .2 49.3 28.7 .7 7.2

12/28/1995 to 01/09/1996 -11.17 3.37 -18.20 -5.60 1.68 9.8 0 49.4 34.3 .6 5.9

01/10/1996 to 01/22/1996 4.29 10.62 -6.90 35.90 .89 4.6 0 47.7 45.4 .6 1.6

01/23/1996 to 02/04/1996 3.15 9.56 -15.60 18.40 1.21 3.3 0 48.7 46.7 .3 1.1

02/08/1996 to 02/28/1996 1.85 3.78 -5.20 9.00 .49 .6 0 48.7 50.0 .2 .4

03/02/1996 to 03/24/1996 3.33 8.95 -14.50 17.00 1.13 1.7 0 47.1 50.0 .3 .9

03/29/1996 to 04/08/1996 -7.98 19.50 -37.40 15.40 2.48 .1 .2 49.7 48.1 .3 1.6

04/15/1996 to 05/06/1996 3.95 6.53 -5.70 15.70 .89 4.1 0 45.1 50.0 .2 .6

07/16/1996 to 07/23/1996 -3.56 4.81 -12.50 0 .53 7.1 0 42.5 49.5 .4 .5

09/08/1996 to 09/22/1996 -2.85 18.64 -24.50 28.10 2.51 19.9 .6 28.9 46.9 1.3 2.5

07/05/2001 to 07/20/2001 .63 10.63 -10.00 30.00 .84 8.6 0 49.5 41.4 .4 .1

07/21/2001 to 08/05/2001 -10.00 13.17 -30.00 20.00 1.88 8.8 0 49.6 39.9 .4 1.4

08/08/2001 to 08/25/2001 1.11 13.23 -20.00 40.00 1.17 6.9 0 49.5 43.1 .4 .2

09/26/2001 to 10/06/2001 -7.27 22.84 -30.00 20.00 3.27 18.4 0 49.4 30.0 .6 1.6

10/18/2001 to 10/31/2001 -2.86 6.11 -10.00 10.00 .64 14.6 0 49.4 34.7 .6 .7

11/01/2001 to 11/14/2001 -19.29 12.07 -50.00 -10.00 2.89 13.2 .2 49.6 32.3 .4 4.4

01/25/2002 to 02/07/2002 0 3.92 -10.00 10.00 .21 13.7 .1 49.6 36.2 .4 0

02/12/2002 to 02/27/2002 -11.25 28.95 -70.00 30.00 3.56 11.8 0 49.4 35.3 .6 2.9

02/28/2002 to 03/14/2002 -6.67 6.17 -20.00 0 1.00 11.1 0 49.5 37.1 .5 1.8

03/21/2002 to 04/06/2002 15.29 32.62 -20.00 70.00 3.35 7.8 .4 45.2 41.8 .7 4.1

04/09/2002 to 04/27/2002 -8.95 26.44 -70.00 50.00 2.13 7.8 .1 49.3 39.5 .7 2.6

04/28/2002 to 05/16/2002 -2.63 44.33 -90.00 80.00 4.50 2.9 0 49.7 46.7 .3 .4

05/27/2002 to 06/12/2002 4.12 46.38 -90.00 80.00 5.21 5.1 0 49.1 44.9 .4 .5

06/13/2002 to 06/29/2002 -10.59 16.38 -30.00 30.00 2.47 6.1 .1 49.7 42.6 .3 1.2
Table 5 29

Table 5. Table 5Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period

Number

of days in

budget

period

Medina

Lake

stage,

average

(feet above

NGVD 29)

Diversion

Lake

stage,

average

(feet above

NGVD 29)

GWout,

mean

GWout,

standard

deviation

GWout,

minimum

25th

percentileMedian

75th

percentile

GWout,

maximum

GWout, 

+error

03/02/1955 to 03/19/1955 18 963.27 879.55 4.81 6.95 -12.94 2.66 5.95 7.07 15.77 2.45

03/22/1955 to 04/05/1955 15 964.45 872.94 6.22 7.02 -14.37 4.44 5.27 10.29 15.29 2.28

04/06/1955 to 04/20/1955 15 964.80 869.53 11.68 4.84 2.77 7.24 12.63 16.03 17.84 2.05

04/21/1955 to 05/05/1955 15 964.87 866.44 13.60 5.34 6.48 9.90 11.40 17.61 22.78 1.60

05/25/1955 to 06/20/1955 27 975.03 865.89 13.98 29.58 -82.46 8.04 17.14 31.44 57.52 3.68

06/23/1955 to 07/16/1955 24 975.05 865.89 12.75 22.55 -84.59 11.02 15.72 25.98 29.09 3.35

08/23/1955 to 09/12/1955 21 979.99 865.89 14.40 13.15 -15.67 14.57 21.20 21.60 26.51 3.35

09/13/1955 to 10/02/1955 20 979.50 865.89 18.42 17.85 -.63 .76 17.09 31.67 50.29 3.24

10/03/1955 to 10/22/1955 20 978.91 865.89 18.54 24.11 -2.15 .47 12.04 24.89 99.38 3.31

10/23/1955 to 11/11/1955 20 978.32 865.89 14.79 29.24 -44.88 -4.88 11.88 22.07 83.20 3.34

11/12/1955 to 12/01/1955 20 977.97 865.89 14.80 14.70 -1.36 -.48 14.11 21.38 42.00 2.30

12/02/1955 to 12/21/1955 20 977.53 865.89 17.03 12.38 1.73 3.17 15.89 26.25 42.50 1.95

12/22/1955 to 01/10/1956 20 977.11 865.89 20.58 14.57 3.17 5.54 18.41 30.24 50.65 2.16

01/11/1956 to 01/30/1956 20 976.65 865.89 15.35 10.70 4.02 6.80 11.00 23.24 40.67 1.78

01/31/1956 to 02/19/1956 20 976.36 865.89 24.06 51.35 -118.56 7.72 28.13 41.40 135.97 4.18

02/20/1956 to 03/10/1956 20 975.96 865.89 19.89 9.57 7.51 9.39 21.18 26.60 36.05 2.23

03/11/1956 to 03/30/1956 20 975.76 865.89 13.42 11.70 6.34 6.34 7.53 13.86 39.71 2.18

03/31/1956 to 04/19/1956 20 975.37 865.89 18.91 11.14 .61 11.18 20.60 29.27 35.77 2.74

04/20/1956 to 05/09/1956 20 974.89 865.89 22.52 16.59 -2.50 6.76 25.38 36.23 51.67 3.15

05/10/1956 to 05/29/1956 20 974.37 865.89 20.73 11.74 -4.10 14.10 19.39 25.98 47.41 3.04

05/30/1956 to 06/18/1956 20 973.65 865.89 19.31 10.79 -.56 13.94 20.98 25.51 41.87 2.94

06/19/1956 to 07/08/1956 20 972.98 865.89 17.08 12.19 -5.22 10.02 18.22 25.89 35.27 3.13

07/09/1956 to 07/28/1956 20 972.17 865.89 20.55 11.77 5.11 11.46 14.90 29.04 44.63 3.82

07/29/1956 to 08/17/1956 20 971.39 865.89 16.69 9.92 2.37 12.29 12.51 20.13 42.74 3.25

09/08/1956 to 09/27/1956 20 972.61 865.89 26.87 18.32 9.47 15.88 18.20 34.81 62.99 3.45

09/28/1956 to 10/15/1956 18 971.98 865.89 13.53 26.35 -50.41 9.60 16.36 20.64 56.25 3.09

10/16/1956 to 11/02/1956 18 971.73 865.89 15.30 17.04 -23.33 6.19 13.96 23.89 47.29 2.71

11/07/1956 to 11/26/1956 20 972.94 865.89 21.92 14.73 -.21 10.96 20.57 29.96 46.83 2.42

11/27/1956 to 12/16/1956 20 972.42 865.89 10.46 12.92 -1.32 -.37 7.49 19.60 45.35 1.54

12/17/1956 to 01/05/1957 20 972.08 865.89 15.95 11.79 -.37 7.34 14.21 26.31 39.69 1.88

01/06/1957 to 01/25/1957 20 971.67 865.89 11.32 20.87 -29.97 .36 10.20 21.94 50.00 1.98

01/26/1957 to 02/14/1957 20 971.35 865.89 14.01 9.56 -2.92 7.97 14.71 20.75 30.36 1.58

02/15/1957 to 03/10/1957 24 970.98 865.89 15.27 9.16 3.20 8.11 13.59 22.59 38.68 1.78

07/01/1957 to 07/15/1957 15 1,028.67 909.42 56.94 63.23 -46.06 19.64 47.35 98.12 166.21 28.61

07/26/1957 to 08/13/1957 19 1,025.76 913.30 145.28 27.22 101.68 125.64 153.20 165.11 188.21 50.13

08/14/1957 to 09/01/1957 19 1,023.39 913.14 113.82 36.52 48.40 86.40 120.17 140.82 188.60 49.15

09/02/1957 to 09/20/1957 19 1,021.07 913.12 68.32 77.47 -42.65 9.96 62.46 136.53 192.52 41.75

09/28/1957 to 10/08/1957 11 1,023.37 913.16 105.16 69.81 75.27 85.83 91.57 122.24 161.68 17.27

12/01/1957 to 12/19/1957 19 1,035.63 912.56 127.29 166.56 -399.89 97.56 136.54 230.94 291.09 63.46

12/28/1957 to 01/04/1958 8 1,036.74 913.76 113.08 66 11.25 69.30 113.04 152.10 225.13 43.62

05/21/1958 to 06/16/1958 27 1,060.12 916.14 123.70 124.91 -242.03 64.24 135.17 177.90 386.95 56.66

07/16/1958 to 08/03/1958 19 1,063.84 917.69 177.55 101.56 27.84 96.82 183.64 260.92 326.09 64.03

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas.

[In acre-feet per day except as indicated. GWout, ground-water outflow; SWin, surface-water inflow; SWout, surface-water outflow; DS, change in storage] 
30 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

08/04/1958 to 08/23/1958 20 1,062.66 916.68 165.39 88.41 -11.16 105.78 169.09 209.29 375.56 69.09

08/26/1958 to 09/05/1958 11 1,061.49 917.87 113.92 79.32 -23.21 57.82 120.43 184.46 222.79 51.57

01/22/1959 to 02/12/1959 22 1,064.04 919.15 130.95 95.91 -113.33 95.85 111.40 145.33 419.22 36.84

02/16/1959 to 03/09/1959 22 1,064.04 919.09 125.20 104 6.05 68.71 93.13 163.16 425.92 37.45

03/10/1959 to 03/30/1959 21 1,063.65 917.51 116.95 77.33 -53.30 73.88 114.13 154.61 293.61 39.65

04/14/1959 to 04/30/1959 17 1,063.80 915.18 125.48 121.80 -128.04 56.86 80.85 226.02 328.97 49.10

05/03/1959 to 06/04/1959 33 1,063.79 916.67 122.10 120.42 -81.50 21.82 116.28 196.85 316.89 43.82

07/28/1959 to 08/22/1959 26 1,063.53 916.93 107.42 104.87 -103.73 65.96 110.07 154.57 368.08 56.00

08/29/1959 to 09/17/1959 20 1,061.98 916.94 123.99 129.58 -25.59 6.67 122.55 207.44 357.85 53.98

11/17/1959 to 12/14/1959 28 1,062.73 918.36 129.00 125.69 -116.03 34.20 136.52 199.24 413.26 34.25

01/03/1960 to 03/20/1960 78 1,062.50 919.06 111.98 109.82 -184.99 52.13 85.24 155.70 597.57 35.86

05/20/1960 to 06/05/1960 17 1,061.53 918.71 58.08 117.80 -158.40 -6.48 54.02 115.49 282.58 56.88

06/06/1960 to 06/23/1960 18 1,060.29 918.64 38.70 32.58 -8.93 17.62 33.22 52.49 109.61 78.06

06/30/1960 to 07/14/1960 15 1,058.74 917.93 79.65 86.31 -51.33 32.33 75.58 110.07 283.63 51.65

07/24/1960 to 08/10/1960 18 1,058.88 918.16 106.52 133.26 -169.38 9.74 141.89 185.80 361.06 44.89

09/01/1960 to 09/23/1960 23 1,062.56 917.81 156.40 93.18 4.10 89.52 137.92 178.27 334.18 58.45

09/24/1960 to 10/15/1960 22 1,061.79 917.08 103.48 86.22 -12.12 42.19 70.28 159.60 286.39 48.02

11/06/1960 to 12/05/1960 30 1,063.26 919.16 103.59 113.88 -145.12 28.09 132.66 172.58 324.38 57.70

04/17/1961 to 05/12/1961 26 1,063.86 918.52 87.78 145.32 -105.10 -15.13 55.88 122.96 422.10 61.74

05/13/1961 to 06/07/1961 26 1,062.54 917.91 73.52 58.77 -27.30 36.86 69.32 115.08 182.83 66.80

07/29/1961 to 08/16/1961 19 1,063.85 917.70 109.78 91.08 -67.02 65.90 111.57 146.92 353.17 47.74

08/25/1961 to 09/11/1961 18 1,062.76 916.51 105.23 150.25 -79.01 -36.92 99.15 210.00 383.50 53.17

09/12/1961 to 10/01/1961 20 1,061.98 916.37 114.36 159.56 -50.81 49.65 82.81 119.03 754.64 52.18

10/27/1961 to 11/13/1961 18 1,060.39 917.39 143.38 87.31 -20.58 95.09 143.07 183.92 348.38 28.21

11/14/1961 to 12/13/1961 30 1,059.70 918.00 133.49 69.48 -29.38 102.37 127.45 161.81 295.11 26.92

12/27/1961 to 01/09/1962 27 1,058.91 917.57 139.44 94.59 -54.19 85.99 135.58 202.04 327.00 28.50

01/13/1962 to 01/22/1962 10 1,058.00 917.39 115.16 82.67 -47.29 87.38 133.27 170.18 206.39 40.35

01/23/1962 to 02/12/1962 21 1,057.39 917.59 109.14 130.46 -129.31 56.05 101.92 179.22 312.58 34.17

03/10/1962 to 04/01/1962 23 1,055.39 917.53 130.49 127.98 -70.16 43.27 104.99 204.46 421.91 47.51

05/04/1962 to 05/27/1962 24 1,053.43 916.31 66.85 139.31 -164.44 -37.74 58.86 164.17 331.46 58.82

06/04/1962 to 06/27/1962 24 1,051.56 915.96 54.67 133.83 -200.51 -24.32 20.04 130.30 358.47 58.54

06/28/1962 to 07/18/1962 21 1,049.58 915.84 84.07 246.91 -271.50 8.32 64.04 103.77 1,068.31 72.75

08/01/1962 to 08/26/1962 26 1,045.63 915.98 53.39 180.40 -427.85 -1.69 69.47 138.18 618.48 74.53

08/27/1962 to 09/17/1962 22 1,043.21 916.13 122.35 180.11 -175.67 51.11 96.13 136.24 744.53 60.48

09/18/1962 to 10/12/1962 25 1,041.38 915.96 66.56 117.93 -153.32 -4.26 110.22 130.69 242.50 43.50

11/03/1962 to 11/25/1962 23 1,039.89 915.64 110.98 87.40 -30.26 48.84 102.59 173.60 305.30 36.36

12/03/1962 to 12/17/1962 15 1,038.55 915.45 93.78 55.77 -16.69 65.84 116.91 124.66 179.93 30.27

12/26/1962 to 01/12/1963 18 1,037.72 915.51 82.87 117.63 -106.93 8.73 91.09 145.50 362.99 16.70

01/13/1963 to 01/30/1963 18 1,037.27 915.65 123.90 80.81 18.00 84.72 87.98 172.65 340.33 16.80

01/31/1963 to 02/15/1963 16 1,036.47 915.79 78.90 70.85 -8.71 30.78 60.31 102.76 286.94 41.18

03/12/1963 to 03/26/1963 15 1,035.25 916.10 44.43 31.52 -28.14 29.45 36.56 61.92 94.53 35.22

04/14/1963 to 04/26/1963 13 1,033.34 916.35 68.67 29.62 10.71 59.30 72.92 79.05 111.97 41.21

06/24/1963 to 07/14/1963 21 1,026.72 916.28 77.27 88.68 -134.12 30.64 79.80 110.42 237.61 43.33

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period

Number

of days in

budget

period

Medina

Lake

stage,

average

(feet above

NGVD 29)

Diversion

Lake

stage,

average

(feet above

NGVD 29)

GWout,

mean

GWout,

standard

deviation

GWout,

minimum

25th

percentileMedian

75th

percentile

GWout,

maximum

GWout, 

+error
Table 5 31

07/16/1963 to 07/29/1963 14 1,024.40 915.84 66.50 32.88 5.39 41.91 66.79 88.04 126.17 68.10

07/30/1963 to 08/20/1963 22 1,021.27 915.39 22.02 67.95 -118.87 -6.60 5.33 52.92 162.96 72.38

08/21/1963 to 09/11/1963 22 1,017.77 914.89 37.44 46.37 -86.17 16.40 48.95 69.45 99.51 62.52

10/03/1963 to 10/23/1963 21 1,012.04 914.36 34.81 51.80 -92.44 -2.92 30.12 73.00 112.79 44.21

11/11/1963 to 11/25/1963 15 1,008.76 914.88 31.68 55.14 -73.65 5.69 47.36 59.52 132.43 27.51

11/28/1963 to 12/17/1963 20 1,007.32 914.33 57.90 100.52 -243.09 22.83 67.27 103.90 233.31 18.24

12/18/1963 to 01/03/1964 17 1,006.39 913.81 62.79 31.43 11.50 45.03 54.90 81.69 134.75 15.36

01/10/1964 to 01/27/1964 18 1,004.38 914.94 47.77 59.15 -53.69 5.50 29.21 87.23 144.12 22.15

02/05/1964 to 02/28/1964 24 1,005.10 914.85 46.44 87.48 -72.63 -10.81 28.12 88.25 316.61 18.05

03/24/1964 to 04/16/1964 24 1,005.18 913.69 43.05 45.21 -41.76 21.45 38.62 70.25 143.09 24.33

04/19/1964 to 05/03/1964 15 1,004.53 913.30 45.61 30.35 -28.74 33.31 45.30 62.04 94.59 18.76

05/05/1964 to 05/28/1964 24 1,002.79 913.05 47.71 79.82 -97.41 14.25 57.65 101.15 168.15 42.84

06/17/1964 to 07/10/1964 24 997.70 913.86 23.31 55.18 -105.53 1.11 15.65 57.29 148.97 45.65

07/11/1964 to 07/30/1964 20 991.73 913.74 36.12 244.41 -324.63 -53.70 23.00 161.18 650.67 65.72

08/02/1964 to 08/15/1964 14 986.21 913.74 31.33 63.91 -97.03 -6.37 28.73 74.53 132.18 47.46

10/11/1995 to 10/28/1995 18 1,044.82 912.38 99.01 71.74 -25.62 52.01 96.37 122.49 294.62 35.40

11/30/1995 to 12/17/1995 18 1,044.83 912.97 62.23 56.63 -63.99 38.64 60.86 78.38 210.51 19.19

12/18/1995 to 01/04/1996 18 1,044.58 911.62 90.70 60.52 -74.13 65.18 94.62 123.61 184.74 20.63

01/05/1995 to 01/22/1996 18 1,044.13 911.39 93.22 88.85 -65.64 54.89 84.46 121.41 342.80 22.08

01/23/1996 to 02/09/1996 18 1,043.44 911.88 88.45 50.18 -1.24 48.35 93.43 123.05 163.60 26.23

02/10/1996 to 02/28/1996 19 1,042.44 912.40 96.03 75.78 -84.84 73.61 98.53 132.70 292.21 33.72

03/07/1996 to 03/20/1996 14 1,041.13 912.31 107.76 69.24 -5.03 70.61 88.36 138.19 284.63 32.54

03/21/1996 to 04/03/1996 14 1,040.12 913.22 107.87 67.94 -33.56 75.35 111.46 147.93 208.59 39.58

04/11/1996 to 04/24/1996 14 1,038.56 912.78 93.08 67.74 -16.21 59.43 100.51 133.60 188.01 42.38

04/25/1996 to 05/07/1996 13 1,037.19 913.29 70.50 107.79 -153.45 51.91 72.44 87.58 332.76 49.05

05/12/1996 to 05/26/1996 15 1,035.53 913.24 68.38 85.96 -89.40 18.50 83.17 131.94 195.88 47.24

06/04/1996 to 06/19/1996 16 1,032.47 913.70 71.13 75.53 -75.76 46.46 61.38 92.40 280.03 61.50

06/20/1996 to 07/05/1996 16 1,029.76 913.86 76.53 76.28 -15.20 21.03 60.76 117.54 271.55 62.95

07/16/1996 to 08/02/1996 18 1,025.43 913.57 65.17 50.37 -27.10 33.43 72.46 93.65 175.60 56.74

08/03/1996 to 08/19/1996 17 1,022.16 913.66 66.44 89.03 -145.58 30.16 59.98 88.54 260.93 59.32

09/06/1996 to 09/23/1996 18 1,019.62 909.47 63.75 49.08 -10.84 46.02 57.66 84.52 168.68 15.03

03/30/2001 to 04/14/2001 16 1,060.94 919.16 134.51 169.59 -218.23 58.36 151.51 280.77 361.65 59.00

06/22/2001 to 07/08/2001 17 1,062.80 915.21 86.52 108.71 -217.44 60.74 89.91 126.32 321.43 68.22

07/09/2001 to 07/27/2001 19 1,061.27 915.37 117.05 140.35 -84.55 38.62 128.61 210.80 375.49 74.80

07/28/2001 to 08/09/2001 13 1,059.79 914.43 131.58 132.31 -88.88 68.55 131.58 176.28 434.10 72.06

08/10/2001 to 08/25/2001 16 1,058.36 913.92 120.49 176.90 -273.57 58.60 100.51 161.45 516.95 74.58

10/26/2001 to 11/11/2001 17 1,060.75 918.61 91.66 261.32 -176.58 -108.45 -84.53 381.27 494.66 41.81

02/22/2002 to 03/14/2002 21 1,063.70 917.48 78.64 176.95 -295.06 -40.06 76.97 226.47 353.57 35.50

04/09/2002 to 04/27/2002 19 1,062.71 918.96 83.13 144.64 -128.60 -12.40 73.67 200.83 379.81 36.95

04/28/2002 to 05/16/2002 19 1,061.79 917.14 131.24 114.59 -102.19 61.22 120.71 221.63 324.21 62.63

05/30/2002 to 06/14/2002 16 1,059.52 916.67 126.15 115.09 -68.24 71.81 124.37 232.11 303.91 75.46

06/15/2002 to 06/29/2002 15 1,057.85 917.36 122.90 118.81 -.62 24.68 84.42 210.48 353.53 75.85

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period

Number

of days in

budget

period

Medina

Lake

stage,

average

(feet above

NGVD 29)

Diversion

Lake

stage,

average

(feet above

NGVD 29)

GWout,

mean

GWout,

standard

deviation

GWout,

minimum

25th

percentileMedian

75th

percentile

GWout,

maximum

GWout, 

+error
32 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period

Precipitation,

mean

Precipitation,

standard

deviation

Precipitation,

minimum

Precipitation,

maximum

Precipitation,

+error

Swin,

mean

Swin,

standard

deviation

Swin,

minimum

Swin,

maximum

Swin,

+error

03/02/1955 to 03/19/1955 0 0 0 0 0 19.32 0.40 19.01 19.80 1.93

03/22/1955 to 04/05/1955 0 0 0 0 0 18.64 2.68 17.42 27.72 1.86

04/06/1955 to 04/20/1955 .13 .49 0 1.88 .02 18.16 1.51 15.84 19.80 1.82

04/21/1955 to 05/05/1955 .06 .24 0 .94 .01 13.03 1.99 9.50 15.84 1.30

05/25/1955 to 06/20/1955 1.40 4.52 0 20.28 .21 13.49 5.05 7.52 27.72 1.35

06/23/1955 to 07/16/1955 .22 .85 0 4.09 .03 9.02 5.11 4.36 19.80 .90

08/23/1955 to 09/12/1955 .26 .82 0 2.97 .04 12.53 4.75 7.52 25.74 1.25

09/13/1955 to 10/02/1955 1.99 6.90 0 30.52 .30 7.74 .67 6.73 9.50 .77

10/03/1955 to 10/22/1955 .94 2.99 0 13.08 .14 6.25 1.82 2.97 8.32 .62

10/23/1955 to 11/11/1955 4.77 16.82 0 73.00 .72 3.29 .52 2.97 5.15 .33

11/12/1955 to 12/01/1955 1.74 7.77 0 34.76 .26 4.36 .63 3.56 5.94 .44

12/02/1955 to 12/21/1955 .15 .68 0 3.03 .02 5.78 .49 5.15 6.73 .58

12/22/1955 to 01/10/1956 0 0 0 0 0 6.97 .82 5.94 8.32 .70

01/11/1956 to 01/30/1956 2.13 6.75 0 26.36 .32 8.59 1.48 6.73 10.69 .86

01/31/1956 to 02/19/1956 1.55 3.42 0 13.46 .23 11.88 1.09 10.69 13.07 1.19

02/20/1956 to 03/10/1956 .31 1.40 0 6.25 .05 12.53 .61 11.88 13.07 1.25

03/11/1956 to 03/30/1956 .33 1.46 0 6.53 .05 12.12 .49 11.88 13.07 1.21

03/31/1956 to 04/19/1956 0 0 0 0 0 8.85 1.07 6.73 10.69 .89

04/20/1956 to 05/09/1956 2.41 7.94 0 35.37 .36 14.16 10.90 4.36 31.68 1.42

05/10/1956 to 05/29/1956 .37 1.20 0 4.94 .06 8.49 5.01 2.97 19.01 .85

05/30/1956 to 06/18/1956 .38 1.04 0 4.25 .06 1.89 .37 1.58 2.97 .19

06/19/1956 to 07/08/1956 .70 3.15 0 14.10 .11 1.49 .24 .99 1.98 .15

07/09/1956 to 07/28/1956 0 0 0 0 0 .84 .11 .59 .99 .08

07/29/1956 to 08/17/1956 0 0 0 0 0 .65 .09 .59 .79 .07

09/08/1956 to 09/27/1956 .50 1.70 0 7.27 .07 5.68 3.06 1.98 13.07 .57

09/28/1956 to 10/15/1956 1.14 4.83 0 20.48 .17 1.73 .19 1.58 1.98 .17

10/16/1956 to 11/02/1956 2.13 6.31 0 22.76 .32 7.55 5.20 3.56 25.74 .75

11/07/1956 to 11/26/1956 0 0 0 0 0 5.35 2.81 2.97 11.88 .53

11/27/1956 to 12/16/1956 0 0 0 0 0 2.41 .13 2.38 2.97 .24

12/17/1956 to 01/05/1957 1.08 3.61 0 15.09 .16 2.41 .13 2.38 2.97 .24

01/06/1957 to 01/25/1957 0 0 0 0 0 2.14 .24 1.58 2.38 .21

01/26/1957 to 02/14/1957 .64 1.37 0 4.26 .10 3.47 .94 2.38 5.15 .35

02/15/1957 to 03/10/1957 2.40 6.04 0 22.00 .36 7.44 2.13 3.56 13.07 .74

07/01/1957 to 07/15/1957 0 0 0 3.56 0 133.75 19.70 104.23 172.46 14.29

07/26/1957 to 08/13/1957 1.78 7.78 0 33.91 .27 51.88 14.00 31.68 79.48 5.25

08/14/1957 to 09/01/1957 6.41 19.22 0 64.23 .96 22.76 4.48 17.42 29.70 2.28

09/02/1957 to 09/20/1957 9.89 24.56 0 86.08 1.48 19.03 3.34 17.42 29.70 1.90

09/28/1957 to 10/08/1957 0 0 0 0 0 127.27 26.92 97.09 182.42 13.79

12/01/1957 to 12/19/1957 1.39 4.21 0 14.71 .21 482.88 80.36 383.33 627.62 53.70

12/28/1957 to 01/04/1958 0 0 0 0 0 345.27 21.68 321.01 378.25 38.22

05/21/1958 to 06/16/1958 5.10 20.73 0 103.45 .76 250.12 78.89 156.15 413.24 27.32

07/16/1958 to 08/03/1958 0 0 0 0 0 285.45 61.41 199.59 389.39 31.33

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.
Table 5 33

08/04/1958 to 08/23/1958 0 0 0 0 0 159.61 13.66 140.32 190.75 17.19

08/26/1958 to 09/05/1958 13.70 45.44 0 150.70 2.05 122.83 19.91 104.39 169.49 13.03

01/22/1959 to 02/12/1959 18.73 40.12 0 177.25 2.81 263.70 16.59 235.43 294.10 28.18

02/16/1959 to 03/09/1959 12.57 30.29 0 104.40 1.89 238.29 18.56 210.78 265.85 25.73

03/10/1959 to 03/30/1959 9.37 32.32 0 139.49 1.41 181.03 13.09 161.62 207.13 19.29

04/14/1959 to 04/30/1959 8.83 20.19 0 62.10 1.32 352.72 60.15 276.78 449.22 38.82

05/03/1959 to 06/04/1959 24.68 69.46 0 243.82 3.70 227.65 45.73 150.70 343.51 24.79

07/28/1959 to 08/22/1959 0 0 0 0 0 132.23 32.09 90.82 205.34 14.12

08/29/1959 to 09/17/1959 20.75 47.87 0 161.85 3.11 77.14 5.49 68.76 88.80 8.01

11/17/1959 to 12/14/1959 13.56 60.30 0 318.16 2.03 197.73 16.42 176.21 231.82 21.50

01/03/1960 to 03/20/1960 20.77 67.03 0 398.22 3.12 232.92 25.44 189.29 301.96 25.08

05/20/1960 to 06/05/1960 31.83 87.86 0 339.77 4.77 129.72 21.87 96.31 172.04 13.86

06/06/1960 to 06/23/1960 0 0 0 0 0 65.07 16.98 41.58 91.63 6.72

06/30/1960 to 07/14/1960 0 0 0 0 0 42.25 17.22 29.70 100.71 4.46

07/24/1960 to 08/10/1960 0 0 0 0 0 161.10 56.94 98.58 283.70 18.00

09/01/1960 to 09/23/1960 271.31 72.53 0 271.31 40.70 487.36 87.38 211.07 487.36 53.44

09/24/1960 to 10/15/1960 7.38 24.47 0 111.79 1.11 194.24 38.59 154.90 279.30 20.81

11/06/1960 to 12/05/1960 18.08 48.14 0 175.94 2.71 421.51 61.44 335.14 535.58 46.69

04/17/1961 to 05/12/1961 7.01 25.04 0 104.12 1.05 266.61 50.07 178.20 343.79 27.96

05/13/1961 to 06/07/1961 1.18 6.03 0 30.74 .18 138.81 24.03 99.00 174.24 13.97

07/29/1961 to 08/16/1961 12.31 53.67 0 233.95 1.85 181.50 37.40 130.68 251.40 18.91

08/25/1961 to 09/11/1961 0 0 0 0 0 137.39 20.21 110.88 172.83 14.05

09/12/1961 to 10/01/1961 42.75 153.62 0 671.85 6.41 115.38 24.85 87.12 175.15 11.56

10/27/1961 to 11/13/1961 31.37 75.61 0 276.79 4.70 111.10 3.71 104.94 120.78 11.11

11/14/1961 to 12/13/1961 15.41 40.57 0 146.85 2.31 114.77 5.21 108.90 124.74 11.48

12/27/1961 to 01/09/1962 3.97 14.57 0 63.41 .60 106.92 10.83 97.02 130.68 10.69

01/13/1962 to 01/22/1962 14.34 29.01 0 90.74 2.15 102.37 1.88 99.00 104.94 10.24

01/23/1962 to 02/12/1962 4.32 17.74 0 81.19 .65 84.57 9.39 71.28 104.94 8.46

03/10/1962 to 04/01/1962 23.30 52.69 0 195.51 3.50 71.80 5.95 65.34 87.12 7.18

05/04/1962 to 05/27/1962 0 0 0 0 0 54.45 12.66 39.60 79.20 5.45

06/04/1962 to 06/27/1962 1.06 5.18 0 25.36 .16 49.01 29.09 21.78 146.52 4.90

06/28/1962 to 07/18/1962 60.86 258.22 0 1,185.23 9.13 16.68 5.86 11.09 27.72 1.67

08/01/1962 to 08/26/1962 2.16 11.01 0 56.16 .32 7.58 1.24 6.14 11.88 .76

08/27/1962 to 09/17/1962 67.56 206.47 0 771.15 10.13 5.47 1.89 3.96 11.09 .55

09/18/1962 to 10/12/1962 10.08 31.27 0 140.82 1.51 6.71 3.71 3.37 19.01 .67

11/03/1962 to 11/25/1962 27.64 61.16 0 239.63 4.15 55.35 5.86 47.52 67.32 5.54

12/03/1962 to 12/17/1962 9.72 37.64 0 145.79 1.46 73.00 8.66 63.36 91.08 7.30

12/26/1962 to 01/12/1963 6.17 17.21 0 69.71 .93 62.81 4.49 57.42 69.30 6.28

01/13/1963 to 01/30/1963 18.53 42.64 0 151.28 2.78 50.49 2.65 47.52 55.44 5.05

01/31/1963 to 02/15/1963 8.15 28.90 0 115.64 1.22 44.18 2.87 39.60 47.52 4.42

03/12/1963 to 03/26/1963 1.36 5.28 0 20.46 .20 49.24 1.81 47.52 51.48 4.92

04/14/1963 to 04/26/1963 1.07 3.88 0 13.97 .16 51.48 3.61 47.52 57.42 5.15

06/24/1963 to 07/14/1963 6.10 27.97 0 128.18 .92 18.86 4.38 9.50 25.74 1.89

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period

Precipitation,

mean

Precipitation,

standard

deviation

Precipitation,

minimum

Precipitation,

maximum

Precipitation,

+error

Swin,

mean

Swin,

standard

deviation

Swin,

minimum

Swin,

maximum

Swin,

+error
34 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

07/16/1963 to 07/29/1963 0 0 0 0 0 5.15 1.22 3.37 7.52 0.51

07/30/1963 to 08/20/1963 0 0 0 0 0 8.02 12.06 2.18 53.46 .80

08/21/1963 to 09/11/1963 0 0 0 0 0 5.00 1.47 3.37 8.71 .50

10/03/1963 to 10/23/1963 1.21 5.56 0 25.47 .18 2.37 .24 2.18 2.97 .24

11/11/1963 to 11/25/1963 1.17 4.53 0 17.53 .18 10.08 2.76 8.12 17.82 1.01

11/28/1963 to 12/17/1963 8.35 17.72 0 62.74 1.25 27.01 9.21 14.65 43.56 2.70

12/18/1963 to 01/03/1964 1.96 8.07 0 33.27 .29 39.48 2.84 37.62 45.54 3.95

01/10/1964 to 01/27/1964 4.44 18.82 0 79.84 .67 33.22 2.10 31.68 39.60 3.32

02/05/1964 to 02/28/1964 7.85 25.73 0 114.50 1.18 103.37 17.08 79.20 142.56 10.34

03/24/1964 to 04/16/1964 2.11 7.70 0 34.98 .32 110.80 22.31 85.14 168.30 11.08

04/19/1964 to 05/03/1964 3.89 10.26 0 29.86 .58 96.62 16.85 71.28 126.72 9.66

05/05/1964 to 05/28/1964 10.91 26.38 0 119.30 1.64 51.98 11.72 35.64 69.30 5.20

06/17/1964 to 07/10/1964 11.44 56.06 0 274.62 1.72 13.93 4.68 8.12 25.74 1.39

07/11/1964 to 07/30/1964 .60 2.70 0 12.07 .09 5.52 1.37 3.96 7.52 .55

08/02/1964 to 08/15/1964 3.45 10.50 0 38.89 .52 3.38 .36 2.97 3.96 .34

10/11/1995 to 10/28/1995 0 0 0 0 0 130.77 22.75 103.44 175.17 6.86

11/30/1995 to 12/17/1995 6.58 20.97 0 84.09 .99 141.75 7.15 129.29 152.74 7.49

12/18/1995 to 01/04/1996 4.09 11.52 0 40.23 .61 136.05 16.33 114.21 172.87 7.09

01/05/1995 to 01/22/1996 0 0 0 0 0 104.88 3.91 98.90 112.17 5.46

01/23/1996 to 02/09/1996 1.44 6.13 0 26.00 .22 95.44 6.06 87.77 104.84 4.97

02/10/1996 to 02/28/1996 1.03 4.50 0 19.62 .15 87.41 6.49 79.87 103.65 4.52

03/07/1996 to 03/20/1996 0 0 0 0 0 81.00 8.81 70.79 106.25 4.18

03/21/1996 to 04/03/1996 6.41 18.24 0 65.81 .96 72.32 6.80 65.24 83.16 3.76

04/11/1996 to 04/24/1996 2.12 7.92 0 29.62 .32 74.98 20.47 53.12 115.43 3.88

04/25/1996 to 05/07/1996 15.44 55.68 0 200.75 2.32 49.51 4.20 43.20 55.10 2.59

05/12/1996 to 05/26/1996 0 0 0 0 0 39.01 10.48 26.61 52.83 2.03

06/04/1996 to 06/19/1996 0 0 0 0 0 20.24 4.44 14.08 30.25 1.04

06/20/1996 to 07/05/1996 13.74 42.52 0 164.55 2.06 15.17 4.02 10.22 24.31 .79

07/16/1996 to 08/02/1996 0 0 0 0 0 6.93 1.25 5.48 9.88 .37

08/03/1996 to 08/19/1996 .26 1.06 0 4.37 .04 4.91 .28 4.44 5.37 .27

09/06/1996 to 09/23/1996 11.75 38.06 0 160.48 1.76 96.97 48.06 43.20 210.47 5.03

03/30/2001 to 04/14/2001 3.89 13.46 0 54.17 .58 674.08 83.33 567.33 813.62 40.61

06/22/2001 to 07/08/2001 11.80 30.97 0 121.83 1.77 184.44 31.70 144.00 239.96 9.78

07/09/2001 to 07/27/2001 0 0 0 0 0 95.23 20.13 68.03 135.82 4.96

07/28/2001 to 08/09/2001 0 0 0 0 0 53.53 7.09 44.50 65.54 2.81

08/10/2001 to 08/25/2001 14.09 52.33 0 209.76 2.11 39.68 3.52 35.65 47.10 2.08

10/26/2001 to 11/11/2001 15.90 61.94 0 255.88 2.39 175.10 10.90 160.77 199.38 9.48

02/22/2002 to 03/14/2002 1.72 6.35 0 28.49 .26 185.37 14.10 167.51 215.03 9.91

04/09/2002 to 04/27/2002 13.07 38.13 0 122.53 1.96 169.05 20.56 140.35 205.69 9.09

04/28/2002 to 05/16/2002 0 0 0 0 0 109.81 15.20 90.76 137.59 5.75

05/30/2002 to 06/14/2002 5.16 17.37 0 69.71 .77 96.64 11.59 73.02 114.85 5.07

06/15/2002 to 06/29/2002 26.37 54.29 0 156.52 3.96 58.74 6.03 52.30 70.53 3.10

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period

Precipitation,

mean

Precipitation,

standard

deviation

Precipitation,

minimum

Precipitation,

maximum

Precipitation,

+error

Swin,

mean

Swin,

standard

deviation

Swin,

minimum

Swin,

maximum

Swin,

+error
Table 5 35

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period Swout,

mean

Swout,

standard

deviation

Swout,

minimum

Swout,

maximum

Swout,

+error

Evaporation,

mean

Evaporation,

standard

deviation

Evaporation,

minimum

Evaporation,

maximum

Evaporation,

+error

03/02/1955 to 03/19/1955 0 0 0 0 0 1.90 0.02 1.87 1.95 0.48

03/22/1955 to 04/05/1955 0 0 0 0 0 2.41 .42 2.09 3.01 .60

04/06/1955 to 04/20/1955 0 0 0 0 0 3.05 .02 3.02 3.08 .76

04/21/1955 to 05/05/1955 0 0 0 0 0 2.98 .12 2.76 3.07 .75

05/25/1955 to 06/20/1955 0 0 0 0 0 8.07 .88 6.62 8.72 2.02

06/23/1955 to 07/16/1955 0 0 0 0 0 8.98 .19 8.72 9.25 2.25

08/23/1955 to 09/12/1955 0 0 0 0 0 9.66 1.62 8.22 11.53 2.41

09/13/1955 to 10/02/1955 0 0 0 0 0 8.14 .08 7.97 8.28 2.04

10/03/1955 to 10/22/1955 0 0 0 0 0 8.14 .10 7.99 8.28 2.03

10/23/1955 to 11/11/1955 0 0 0 0 0 6.27 1.49 4.93 7.96 1.57

11/12/1955 to 12/01/1955 0 0 0 0 0 4.79 .32 3.45 4.92 1.20

12/02/1955 to 12/21/1955 0 0 0 0 0 3.40 .03 3.36 3.44 .85

12/22/1955 to 01/10/1956 0 0 0 0 0 3.05 .29 2.74 3.36 .76

01/11/1956 to 01/30/1956 0 0 0 0 0 2.71 .01 2.70 2.74 .68

01/31/1956 to 02/19/1956 0 0 0 0 0 3.71 .24 2.70 3.81 .93

02/20/1956 to 03/10/1956 0 0 0 0 0 4.63 .96 3.68 5.60 1.16

03/11/1956 to 03/30/1956 0 0 0 0 0 5.53 .03 5.47 5.54 1.38

03/31/1956 to 04/19/1956 0 0 0 0 0 6.94 .36 5.47 7.12 1.74

04/20/1956 to 05/09/1956 0 0 0 0 0 7.38 .61 6.81 8.09 1.84

05/10/1956 to 05/29/1956 0 0 0 0 0 7.80 .10 7.66 7.96 1.95

05/30/1956 to 06/18/1956 0 0 0 0 0 6.45 .41 6.21 7.63 1.61

06/19/1956 to 07/08/1956 0 0 0 0 0 7.62 1.90 6.01 9.96 1.90

07/09/1956 to 07/28/1956 0 0 0 0 0 9.45 .19 9.20 9.76 2.36

07/29/1956 to 08/17/1956 0 0 0 0 0 8.30 .37 7.96 9.16 2.07

09/08/1956 to 09/27/1956 0 0 0 0 0 6.97 .14 6.80 7.23 1.74

09/28/1956 to 10/15/1956 0 0 0 0 0 5.63 .53 5.30 6.79 1.41

10/16/1956 to 11/02/1956 0 0 0 0 0 5.11 .62 3.40 5.39 1.28

11/07/1956 to 11/26/1956 0 0 0 0 0 3.78 .05 3.71 3.88 .95

11/27/1956 to 12/16/1956 0 0 0 0 0 2.95 .39 2.74 3.70 .74

12/17/1956 to 01/05/1957 0 0 0 0 0 2.54 .31 2.02 2.74 .63

01/06/1957 to 01/25/1957 0 0 0 0 0 1.99 .02 1.95 2.02 .50

01/26/1957 to 02/14/1957 0 0 0 0 0 2.43 .32 1.95 2.66 .61

02/15/1957 to 03/10/1957 0 0 0 0 0 3.32 .89 2.58 4.39 .83

07/01/1957 to 07/15/1957 1.73 .95 .79 3.56 .26 74.34 .19 73.97 74.65 18.58

07/26/1957 to 08/13/1957 199.67 4.44 194.04 207.90 29.95 67.81 2.81 64.95 72.20 16.95

08/14/1957 to 09/01/1957 202.79 7.53 184.14 209.88 30.42 62.32 4.37 44.65 64.78 15.58

09/02/1957 to 09/20/1957 190.77 13.93 164.34 203.94 28.62 43.46 .66 42.47 44.55 10.86

09/28/1957 to 10/08/1957 17.68 9.83 13.46 47.12 2.65 32.38 8.58 27.33 45.75 8.10

12/01/1957 to 12/19/1957 66.17 46.37 21.78 126.72 9.93 19.94 .18 19.63 20.16 4.99

12/28/1957 to 01/04/1958 25.74 1.06 23.76 27.72 3.86 19.05 2.13 17.02 21.07 4.76

05/21/1958 to 06/16/1958 206.07 52.42 122.76 263.34 30.91 90.41 9.95 78.59 99.13 22.60

07/16/1958 to 08/03/1958 192.06 16.87 146.52 225.72 28.81 151.74 3.77 143.17 153.76 37.94

08/04/1958 to 08/23/1958 251.96 8.32 229.68 263.34 37.79 141.75 0.79 140.56 143.04 35.44

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.
36 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

08/26/1958 to 09/05/1958 176.58 5.93 172.26 194.04 26.49 109.72 34.79 73.31 140.23 27.43

01/22/1959 to 02/12/1959 137.25 10.14 126.72 158.40 20.59 28.05 1.17 27.00 29.30 7.01

02/16/1959 to 03/09/1959 135.42 14.90 112.86 164.34 20.31 46.09 23.45 27.03 73.75 11.52

03/10/1959 to 03/30/1959 153.31 15.31 130.68 178.20 23.00 73.20 .20 72.86 73.52 18.30

04/14/1959 to 04/30/1959 117.75 23.47 97.02 146.52 17.66 71.11 .06 70.97 71.20 17.78

05/03/1959 to 06/04/1959 130.86 51.95 43.56 233.64 19.63 83.07 11.61 78.65 113.98 20.77

07/28/1959 to 08/22/1959 203.41 25.44 160.38 223.74 30.51 123.83 2.66 117.77 125.82 30.96

08/29/1959 to 09/17/1959 187.11 7.34 176.22 209.88 28.07 113.24 4.36 110.58 123.37 28.31

11/17/1959 to 12/14/1959 117.95 12.71 102.96 146.52 17.69 41.76 5.36 36.44 47.08 10.44

01/03/1960 to 03/20/1960 129.55 11.77 74.05 156.42 19.43 41.59 13.29 24.77 54.37 10.40

05/20/1960 to 06/05/1960 254.02 42.04 186.12 308.88 38.10 103.33 21.84 89.33 136.35 25.83

06/06/1960 to 06/23/1960 351.78 29.59 308.88 394.02 52.77 134.38 .91 132.87 135.77 33.60

06/30/1960 to 07/14/1960 177.67 43.47 124.74 233.64 26.65 110.60 6.00 108.40 132.23 27.65

07/24/1960 to 08/10/1960 152.68 35.79 108.90 188.10 22.90 94.34 14.10 81.80 109.81 23.59

09/01/1960 to 09/23/1960 225.72 11.55 194.04 225.72 33.86 101.56 .26 100.82 101.56 25.39

09/24/1960 to 10/15/1960 212.04 1.21 209.88 215.82 31.81 77.05 16.49 65.83 100.78 19.26

11/06/1960 to 12/05/1960 181.83 22.44 156.42 229.68 27.27 36.30 6.25 22.56 39.20 9.08

04/17/1961 to 05/12/1961 290.22 29.19 255.42 326.70 43.53 86.96 2.04 84.41 88.88 21.74

05/13/1961 to 06/07/1961 332.49 6.67 320.76 342.54 49.87 87.57 6.31 83.15 98.04 21.89

07/29/1961 to 08/16/1961 174.97 21.36 148.50 215.82 26.25 105.70 1.23 104.96 108.50 26.43

08/25/1961 to 09/11/1961 215.38 26.53 172.26 239.58 32.31 100.02 3.37 97.06 104.36 25.01

09/12/1961 to 10/01/1961 203.64 16.99 156.42 215.82 30.55 94.47 10.03 51.90 97.22 23.62

10/27/1961 to 11/13/1961 90.86 19.45 61.38 106.92 13.63 44.06 4.61 41.19 51.31 11.02

11/14/1961 to 12/13/1961 99.82 29.15 58.21 154.44 14.97 35.45 6.52 28.05 41.18 8.86

12/27/1961 to 01/09/1962 110.66 39.56 73.26 176.22 16.60 28.77 1.18 27.83 30.44 7.19

01/13/1962 to 01/22/1962 196.02 31.98 160.38 251.46 29.40 30.13 .06 30.04 30.22 7.53

01/23/1962 to 02/12/1962 132.94 19.64 85.14 154.44 19.94 48.22 16.19 29.87 62.07 12.06

03/10/1962 to 04/01/1962 209.19 22.95 158.40 241.56 31.38 53.67 5.20 52.05 77.48 13.42

05/04/1962 to 05/27/1962 250.80 68.71 170.28 352.44 37.62 95.34 .83 93.85 96.48 23.83

06/04/1962 to 06/27/1962 257.98 121.19 100.98 399.96 38.70 87.03 .89 85.37 88.16 21.76

06/28/1962 to 07/18/1962 288.51 74.11 184.14 390.06 43.28 106.96 9.22 84.90 112.12 26.74

08/01/1962 to 08/26/1962 321.52 31.32 265.32 366.30 48.23 108.60 2.00 105.52 111.90 27.15

08/27/1962 to 09/17/1962 233.19 24.68 198.00 261.36 34.98 74.19 16.94 64.31 105.23 18.55

09/18/1962 to 10/12/1962 177.88 38.76 91.08 237.60 26.68 61.39 2.27 58.42 64.16 15.35

11/03/1962 to 11/25/1962 162.02 23.86 118.80 211.86 24.30 32.77 .38 32.27 33.43 8.19

12/03/1962 to 12/17/1962 146.52 13.78 132.66 168.30 21.98 16.78 .20 16.40 17.04 4.19

12/26/1962 to 01/12/1963 49.72 2.79 45.54 55.44 7.46 18.60 1.54 16.40 19.68 4.65

01/13/1963 to 01/30/1963 43.04 2.14 40.19 47.52 6.46 19.45 .11 19.31 19.61 4.86

01/31/1963 to 02/15/1963 200.97 58.62 77.22 257.40 30.15 29.64 2.83 19.31 31.06 7.41

03/12/1963 to 03/26/1963 166.32 10.32 132.66 180.18 24.95 47.57 .38 46.96 48.24 11.89

04/14/1963 to 04/26/1963 187.80 43.83 124.74 233.64 28.17 53.89 .30 53.40 54.29 13.47

06/24/1963 to 07/14/1963 171.41 46.31 97.02 233.64 25.71 67.93 1.92 65.13 70.21 16.98

07/16/1963 to 07/29/1963 321.33 17.73 310.86 358.38 48.20 66.30 0.94 64.80 67.74 16.58

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period Swout,

mean

Swout,

standard

deviation

Swout,

minimum

Swout,

maximum

Swout,

+error

Evaporation,

mean

Evaporation,

standard

deviation

Evaporation,

minimum

Evaporation,

maximum

Evaporation,

+error
Table 5 37

07/30/1963 to 08/20/1963 364.59 21.20 340.56 397.98 54.69 63.32 1.43 60.90 65.67 15.83

08/21/1963 to 09/11/1963 310.50 10.92 283.14 320.76 46.58 50.53 9.80 40.13 62.01 12.63

10/03/1963 to 10/23/1963 219.87 9.32 211.86 237.60 32.98 28.78 .64 27.73 29.77 7.19

11/11/1963 to 11/25/1963 131.87 44.26 89.10 201.96 19.78 20.54 .23 20.12 20.86 5.13

11/28/1963 to 12/17/1963 73.06 2.15 71.28 78.80 10.96 10.56 4.06 8.79 20.03 2.64

12/18/1963 to 01/03/1964 65.32 2.63 62.17 70.29 9.80 9.22 1.17 8.61 11.68 2.30

01/10/1964 to 01/27/1964 101.74 34.57 59.80 150.48 15.26 11.18 .10 11.07 11.39 2.79

02/05/1964 to 02/28/1964 69.19 36.23 49.50 196.02 10.38 12.29 .07 12.20 12.40 3.07

03/24/1964 to 04/16/1964 111.29 54.31 39.60 162.36 16.69 19.96 2.88 15.94 22.28 4.99

04/19/1964 to 05/03/1964 85.34 28.53 49.50 122.76 12.80 22.29 1.40 21.56 25.01 5.57

05/05/1964 to 05/28/1964 224.73 62.84 132.66 352.44 33.71 23.55 .55 22.75 24.56 5.89

06/17/1964 to 07/10/1964 226.89 81.98 66.53 322.74 34.03 33.45 1.55 31.57 36.03 8.36

07/11/1964 to 07/30/1964 327.29 53.73 211.86 372.24 49.09 31.74 1.30 29.64 34.01 7.94

08/02/1964 to 08/15/1964 241.56 66.96 126.72 336.60 36.23 27.05 .76 25.74 28.14 6.76

10/11/1995 to 10/28/1995 217.25 40.72 148.50 265.32 16.46 52.87 22.23 9.65 85.52 13.22

11/30/1995 to 12/17/1995 126.17 12.01 102.96 148.50 9.56 34.31 35.69 .99 141.35 8.58

12/18/1995 to 01/04/1996 79.53 28.49 31.68 110.88 6.03 50.16 36.30 5.41 136.76 12.54

01/05/1995 to 01/22/1996 115.61 17.84 87.12 132.66 8.76 36.88 27.39 .85 121.09 9.22

01/23/1996 to 02/09/1996 153.12 19.96 124.74 188.10 11.60 37.66 23.01 3.59 93.20 9.41

02/10/1996 to 02/28/1996 223.01 14.61 196.02 243.54 16.89 28.88 27.63 .14 96.87 7.22

03/07/1996 to 03/20/1996 176.22 28.50 142.56 221.76 13.35 45.93 41.64 3.76 151.38 11.48

03/21/1996 to 04/03/1996 238.02 17.26 215.82 269.28 18.03 34.52 25.83 4.62 91.18 8.63

04/11/1996 to 04/24/1996 272.53 27.25 229.68 304.92 20.65 38.50 28.95 9.68 109.80 9.62

04/25/1996 to 05/07/1996 322.44 10.69 304.92 338.58 24.43 41.32 37.71 5.15 146.75 10.33

05/12/1996 to 05/26/1996 274.96 59.53 213.84 370.26 20.83 60.51 8.82 44.07 77.43 15.13

06/04/1996 to 06/19/1996 400.95 8.91 392.04 423.72 30.38 56.50 13.29 40.14 86.59 14.13

06/20/1996 to 07/05/1996 429.04 3.29 423.72 435.60 32.50 41.33 8.56 30.70 58.39 10.33

07/16/1996 to 08/02/1996 348.92 40.35 285.12 407.88 26.43 62.21 13.18 30.08 81.49 15.55

08/03/1996 to 08/19/1996 374.10 40.25 302.94 409.86 28.34 57.80 12.18 29.77 81.96 14.45

09/06/1996 to 09/23/1996 37.40 12.45 29.70 73.26 2.83 37.49 12.96 16.07 69.98 9.37

03/30/2001 to 04/14/2001 150.23 6.50 138.60 162.36 11.38 69.48 33.51 23.90 129.35 17.37

06/22/2001 to 07/08/2001 399.73 17.42 356.40 415.80 30.28 151.76 28.68 70.01 183.30 37.94

07/09/2001 to 07/27/2001 312.25 128.73 77.22 403.92 23.66 177.07 14.30 144.05 195.79 44.27

07/28/2001 to 08/09/2001 294.44 108.73 61.38 382.14 22.31 160.58 26.42 111.95 194.51 40.14

08/10/2001 to 08/25/2001 362.71 23.14 310.86 394.02 27.48 138.70 42.52 53.07 227.92 34.67

10/26/2001 to 11/11/2001 215.00 17.13 194.04 247.50 16.29 86.69 22.48 49.23 121.02 21.67

02/22/2002 to 03/14/2002 185.55 15.21 168.30 237.60 14.06 81.47 36.45 15.44 143.78 20.37

04/09/2002 to 04/27/2002 168.51 28.93 138.60 251.46 12.77 92.06 64.91 0 231.83 23.02

04/28/2002 to 05/16/2002 351.92 61.67 174.24 405.90 26.66 87.18 43.98 26.45 165.11 21.79

05/30/2002 to 06/14/2002 401.07 39.94 364.32 487.08 30.38 113.94 56.95 33.45 238.44 28.49

06/15/2002 to 06/29/2002 444.71 18.66 419.76 481.14 33.69 112.84 40.07 38.80 193.16 28.21

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period Swout,

mean

Swout,

standard

deviation

Swout,

minimum

Swout,

maximum

Swout,

+error

Evaporation,

mean

Evaporation,

standard

deviation

Evaporation,

minimum

Evaporation,

maximum

Evaporation,

+error
38 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period ∆S,

mean

∆S,

standard

deviation

∆S,

minimum

∆S,

maximum

∆S,

+error

GWout,

percent of

hydrologic

budget

Precipitation,

percent of

hydrologic

budget

Swin,

percent of

hydrologic

budget

Swout,

percent of

hydrologic

budget

Evaporation,

percent of

hydrologic

budget

∆S,

percent of

hydrologic

budget

03/02/1955 to 03/19/1955 9.62 7.47 -2.41 30.00 1.34 13.5 0 54.2 0 5.3 27.0

03/22/1955 to 04/05/1955 10.00 9.26 0 40.00 1.00 16.7 0 50.0 0 6.5 26.8

04/06/1955 to 04/20/1955 3.56 4.45 -3.33 10.00 .40 31.9 .3 49.7 0 8.3 9.7

04/21/1955 to 05/05/1955 -3.62 4.40 -10.00 0 .37 40.8 .2 39.1 0 9.0 10.9

05/25/1955 to 06/20/1955 -7.16 30.28 -46.67 83.33 2.15 31.7 3.2 30.6 0 18.3 16.2

06/23/1955 to 07/16/1955 -12.50 22.42 -30.00 80.00 1.92 29.3 .5 20.7 0 20.7 28.8

08/23/1955 to 09/12/1955 -11.27 15.86 -20.00 20.00 1.89 29.9 .5 26.0 0 20.1 23.4

09/13/1955 to 10/02/1955 -16.83 18.30 -50.00 0 1.68 34.7 3.7 14.6 0 15.3 31.7

10/03/1955 to 10/22/1955 -19.50 24.55 -100.00 0 1.95 34.7 1.8 11.7 0 15.3 36.5

10/23/1955 to 11/11/1955 -13.00 24.61 -66.67 40.00 1.90 35.1 11.3 7.8 0 14.9 30.9

11/12/1955 to 12/01/1955 -13.50 14.12 -43.33 0 1.35 37.8 4.4 11.1 0 12.2 34.4

12/02/1955 to 12/21/1955 -14.50 12.25 -40.00 0 1.45 41.7 .4 14.1 0 8.3 35.5

12/22/1955 to 01/10/1956 -16.67 14.75 -46.66 0 1.67 43.5 0 14.7 0 6.5 35.3

01/11/1956 to 01/30/1956 -7.33 10.90 -36.67 0 .73 42.5 5.9 23.8 0 7.5 20.3

01/31/1956 to 02/19/1956 -14.33 50.81 -126.67 126.67 3.47 43.3 2.8 21.4 0 6.7 25.8

02/20/1956 to 03/10/1956 -11.67 9.52 -26.67 0 1.17 40.6 .6 25.6 0 9.4 23.8

03/11/1956 to 03/30/1956 -6.50 11.92 -33.33 0 .65 35.4 .9 32.0 0 14.6 17.2

03/31/1956 to 04/19/1956 -17.00 11.39 -33.33 0 1.70 36.6 0 17.1 0 13.4 32.9

04/20/1956 to 05/09/1956 -13.33 11.39 -36.67 0 1.33 37.7 4.0 23.7 0 12.3 22.3

05/10/1956 to 05/29/1956 -19.67 10.86 -50.00 0 1.97 36.3 .6 14.9 0 13.7 34.5

05/30/1956 to 06/18/1956 -23.50 11.05 -46.67 -3.33 2.35 37.5 .7 3.7 0 12.5 45.6

06/19/1956 to 07/08/1956 -22.50 11.54 -40.00 0 2.25 34.6 1.4 3.0 0 15.4 45.5

07/09/1956 to 07/28/1956 -29.17 11.84 -53.33 -13.33 2.92 34.2 0 1.4 0 15.8 48.6

07/29/1956 to 08/17/1956 -24.33 9.92 -50.00 -10.00 2.43 33.4 0 1.3 0 16.6 48.7

09/08/1956 to 09/27/1956 -27.67 17.74 -63.33 -6.67 2.77 39.7 .7 8.4 0 10.3 40.9

09/28/1956 to 10/15/1956 -16.30 25.15 -60.00 46.67 2.59 35.3 3.0 4.5 0 14.7 42.5

10/16/1956 to 11/02/1956 -10.74 21.71 -46.67 46.67 1.81 37.5 5.2 18.5 0 12.5 26.3

11/07/1956 to 11/26/1956 -20.00 13.64 -40.00 0 2.00 42.9 0 10.5 0 7.4 39.2

11/27/1956 to 12/16/1956 -11.00 13.03 -46.67 0 1.10 39.0 0 9.0 0 11.0 41.0

12/17/1956 to 01/05/1957 -15.00 12.16 -40.00 0 1.50 43.1 2.9 6.5 0 6.9 40.6

01/06/1957 to 01/25/1957 -11.17 20.89 -50.00 30.00 1.78 42.5 0 8.0 0 7.5 42.0

01/26/1957 to 02/14/1957 -12.33 9.86 -30.00 3.33 1.27 42.6 1.9 10.6 0 7.4 37.5

02/15/1957 to 03/10/1957 -8.75 8.33 -26.67 0 .88 41.1 6.4 20.0 0 8.9 23.5

07/01/1957 to 07/15/1957 .74 65.14 -108.08 74.85 15.11 21.3 0 50.0 .6 27.8 .3

07/26/1957 to 08/13/1957 -359.10 20.85 -381.20 -291.21 35.97 17.6 .2 6.3 24.2 8.2 43.5

08/14/1957 to 09/01/1957 -349.77 39.12 -431.20 -259.77 35.04 15.0 .8 3.0 26.8 8.2 46.2

09/02/1957 to 09/20/1957 -273.63 83.83 -389.77 -149.77 27.42 11.3 1.6 3.1 31.5 7.2 45.2

09/28/1957 to 10/08/1957 -27.95 47.41 -99.77 33.57 3.46 33.9 0 41.0 5.7 10.4 9.0

12/01/1957 to 12/19/1957 270.87 199.51 97.46 897.43 27.72 13.1 .1 49.9 6.8 2.1 28.0

12/28/1957 to 01/04/1958 187.40 68.48 79.02 312.61 19.36 16.4 0 50.0 3.7 2.8 27.1

05/21/1958 to 06/16/1958 -164.96 199.20 -419.15 446.00 24.87 14.7 .6 29.8 24.5 10.8 19.6

07/16/1958 to 08/03/1958 -235.90 156.50 -477.72 -11.59 24.16 17.0 0 27.4 18.4 14.6 22.6

08/04/1958 to 08/23/1958 -399.49 86.27 -610.67 -219.20 41.86 14.8 0 14.3 22.5 12.7 35.7

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued. 
Table 5 39

08/26/1958 to 09/05/1958 -263.69 87.35 -418.30 -117.98 30.14 14.2 1.7 15.3 22.1 13.7 32.9

01/22/1959 to 02/12/1959 -13.81 73.20 -200.15 199.77 3.21 22.1 3.2 44.5 23.2 4.7 2.3

02/16/1959 to 03/09/1959 -55.85 108.35 -400.23 -.23 5.73 20.4 2.0 38.8 22.1 7.5 9.1

03/10/1959 to 03/30/1959 -153.05 74.86 -318.13 -17.48 16.21 17.0 1.4 26.4 22.3 10.7 22.3

04/14/1959 to 04/30/1959 47.21 149.40 -190.50 409.26 12.07 17.4 1.2 48.8 16.3 9.8 6.5

05/03/1959 to 06/04/1959 -83.70 154.51 -469.57 209.96 13.04 18.2 3.7 33.9 19.5 12.4 12.5

07/28/1959 to 08/22/1959 -302.42 125.60 -601.13 -1.14 30.30 12.4 0 15.2 23.4 14.2 34.8

08/29/1959 to 09/17/1959 -326.46 131.69 -564.82 -198.12 33.12 14.6 2.4 9.1 22.0 13.3 38.5

11/17/1959 to 12/14/1959 -77.42 109.81 -285.71 133.54 12.55 22.3 2.3 34.2 20.4 7.2 13.4

01/03/1960 to 03/20/1960 -29.43 83.24 -300.00 300.14 4.24 19.8 3.7 41.1 22.9 7.3 5.2

05/20/1960 to 06/05/1960 -253.88 100.53 -400.53 -34.70 25.44 7.0 3.8 15.6 30.6 12.4 30.6

06/06/1960 to 06/23/1960 -459.79 46.52 -500.53 -400.53 46.01 3.7 0 6.2 33.5 12.8 43.8

06/30/1960 to 07/14/1960 -325.67 81.37 -478.11 -198.01 33.10 10.8 0 5.7 24.1 15.0 44.3

07/24/1960 to 08/10/1960 -192.44 140.61 -497.99 2.02 19.75 15.1 0 22.8 21.6 13.3 27.2

09/01/1960 to 09/23/1960 -.74 126.05 -406.52 -.74 40.98 12.6 21.8 39.2 18.2 8.2 .1

09/24/1960 to 10/15/1960 -190.96 75.05 -406.38 -73.00 20.30 13.2 .9 24.7 27.0 9.8 24.3

11/06/1960 to 12/05/1960 117.87 115.16 1.24 301.25 11.90 11.8 2.1 47.9 20.7 4.1 13.4

04/17/1961 to 05/12/1961 -191.35 166.11 -603.63 -4.35 19.34 9.4 .8 28.7 31.2 9.4 20.6

05/13/1961 to 06/07/1961 -353.58 62.70 -470.17 -203.63 35.54 7.4 .1 14.1 33.7 8.9 35.8

07/29/1961 to 08/16/1961 -196.65 74.70 -310.49 -10.88 20.20 14.1 1.6 23.2 22.4 13.5 25.2

08/25/1961 to 09/11/1961 -283.24 148.28 -601.75 -101.76 28.41 12.5 0 16.3 25.6 11.9 33.7

09/12/1961 to 10/01/1961 -254.34 71.47 -401.74 -101.75 25.89 13.9 5.2 14.0 24.7 11.5 30.8

10/27/1961 to 11/13/1961 -135.84 63.09 -228.34 4.95 14.81 25.8 5.6 20.0 16.3 7.9 24.4

11/14/1961 to 12/13/1961 -138.57 55.86 -228.19 5.16 14.70 24.8 2.9 21.4 18.6 6.6 25.8

12/27/1961 to 01/09/1962 -167.97 102.60 -370.69 -3.97 17.01 25.0 .7 19.2 19.8 5.2 30.1

01/13/1962 to 01/22/1962 -224.61 62.45 -297.95 -131.33 22.98 16.9 2.1 15.0 28.7 4.4 32.9

01/23/1962 to 02/12/1962 -201.40 136.49 -433.39 2.09 20.59 18.8 .7 14.6 22.9 8.3 34.7

03/10/1962 to 04/01/1962 -298.25 115.31 -566.79 -136.97 29.95 16.6 3.0 9.1 26.6 6.8 37.9

05/04/1962 to 05/27/1962 -358.54 167.32 -736.53 -103.18 36.00 8.1 0 6.6 30.4 11.5 43.4

06/04/1962 to 06/27/1962 -349.61 150.68 -667.70 -101.01 35.01 6.8 .1 6.1 32.3 10.9 43.7

06/28/1962 to 07/18/1962 -402.00 152.31 -600.05 -1.00 40.22 8.8 6.3 1.7 30.1 11.2 41.9

08/01/1962 to 08/26/1962 -473.78 177.51 -1,000.05 2.00 47.84 5.5 .2 .8 33.2 11.2 49.0

08/27/1962 to 09/17/1962 -356.70 111.33 -564.67 -134.36 35.79 14.2 7.9 .6 27.1 8.6 41.5

09/18/1962 to 10/12/1962 -289.05 101.32 -401.05 -101.05 28.96 10.9 1.6 1.1 29.1 10.0 47.3

11/03/1962 to 11/25/1962 -222.77 90.79 -401.03 -101.03 22.33 18.1 4.5 9.1 26.5 5.4 36.4

12/03/1962 to 12/17/1962 -174.36 53.75 -267.72 -101.02 17.49 18.2 1.9 14.2 28.5 3.3 33.9

12/26/1962 to 01/12/1963 -82.20 113.33 -365.57 101.13 11.47 27.4 2.0 20.8 16.4 6.2 27.2

01/13/1963 to 01/30/1963 -117.38 58.54 -232.16 -32.16 12.02 33.2 5.0 13.5 11.5 5.2 31.5

01/31/1963 to 02/15/1963 -257.18 82.10 -398.85 -65.55 26.01 12.7 1.3 7.1 32.5 4.8 41.5

03/12/1963 to 03/26/1963 -207.72 38.77 -265.53 -132.24 21.06 8.6 .3 9.5 32.2 9.2 40.2

04/14/1963 to 04/26/1963 -257.80 65.48 -332.22 -132.22 26.07 11.1 .2 8.3 30.3 8.7 41.5

06/24/1963 to 07/14/1963 -291.65 102.40 -510.45 -101.29 29.30 12.2 1.0 3.0 27.1 10.7 46.1

07/16/1963 to 07/29/1963 -448.98 36.54 -500.41 -380.43 45.08 7.3 0 0.6 35.4 7.3 49.4

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period ∆S,

mean

∆S,

standard

deviation

∆S,

minimum

∆S,

maximum

∆S,

+error

GWout,

percent of

hydrologic

budget

Precipitation,

percent of

hydrologic

budget

Swin,

percent of

hydrologic

budget

Swout,

percent of

hydrologic

budget

Evaporation,

percent of

hydrologic

budget

∆S,

percent of

hydrologic

budget
40 A Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, San Antonio Area, Texas

07/30/1963 to 08/20/1963 -441.91 83.19 -617.01 -300.33 44.36 2.4 0 .9 40.5 7.0 49.1

08/21/1963 to 09/11/1963 -393.46 47.15 -469.82 -286.53 39.50 4.7 0 .6 39.0 6.3 49.4

10/03/1963 to 10/23/1963 -279.88 48.17 -351.36 -170.71 28.25 6.1 .2 .4 38.8 5.1 49.4

11/11/1963 to 11/25/1963 -172.83 66.48 -282.16 -87.32 17.85 8.6 .3 2.7 35.8 5.6 46.9

11/28/1963 to 12/17/1963 -106.17 97.86 -265.31 184.68 12.78 20.5 3.0 9.5 25.8 3.7 37.5

12/18/1963 to 01/03/1964 -95.89 28.31 -141.84 -48.49 10.61 22.9 .7 14.4 23.8 3.4 34.9

01/10/1964 to 01/27/1964 -123.04 90.22 -272.25 7.86 14.28 14.9 1.4 10.3 31.7 3.5 38.3

02/05/1964 to 02/28/1964 -16.70 82.38 -186.63 89.87 7.34 18.2 3.1 40.4 27.0 4.8 6.5

03/24/1964 to 04/16/1964 -61.39 98.30 -224.46 112.21 10.20 12.3 .6 31.8 31.9 5.7 17.6

04/19/1964 to 05/03/1964 -52.73 52.74 -122.74 -2.72 5.41 14.9 1.3 31.5 27.8 7.3 17.2

05/05/1964 to 05/28/1964 -233.10 112.07 -423.22 -76.51 23.84 8.1 1.8 8.8 38.0 4.0 39.4

06/17/1964 to 07/10/1964 -258.28 138.10 -430.94 50.26 26.48 4.1 2.0 2.5 40.0 5.9 45.5

07/11/1964 to 07/30/1964 -389.03 251.38 -1,033.11 -49.78 38.95 4.6 .1 .7 41.4 4.0 49.2

08/02/1964 to 08/15/1964 -293.11 107.52 -416.45 -143.11 29.37 5.2 .6 .6 40.3 4.5 48.9

10/11/1995 to 10/28/1995 -238.36 99.81 -443.00 -27.40 26.15 13.4 0 17.7 29.4 7.2 32.3

11/30/1995 to 12/17/1995 -74.37 58.42 -273.70 -15.80 9.03 14.0 1.5 31.8 28.3 7.7 16.7

12/18/1995 to 01/04/1996 -80.26 66.52 -216.50 72.70 11.42 20.6 .9 30.9 18.0 11.4 18.2

01/05/1995 to 01/22/1996 -140.82 86.79 -398.90 -3.60 15.17 19.0 0 21.3 23.5 7.5 28.7

01/23/1996 to 02/09/1996 -182.33 55.80 -256.90 -53.00 20.02 15.8 .3 17.1 27.4 6.7 32.7

02/10/1996 to 02/28/1996 -259.48 69.70 -443.00 -93.50 26.69 13.8 .1 12.6 32.0 4.1 37.3

03/07/1996 to 03/20/1996 -248.91 78.72 -395.30 -136.50 25.57 16.3 0 12.3 26.7 7.0 37.7

03/21/1996 to 04/03/1996 -301.69 59.02 -407.00 -194.40 33.15 14.2 .8 9.5 31.3 4.5 39.7

04/11/1996 to 04/24/1996 -327.01 63.66 -438.60 -217.50 34.64 11.5 .3 9.3 33.7 4.8 40.5

04/25/1996 to 05/07/1996 -386.45 78.12 -622.00 -318.10 39.06 8.0 1.7 5.6 36.4 4.7 43.6

05/12/1996 to 05/26/1996 -364.84 123.22 -583.60 -158.90 39.03 8.5 0 4.8 34.0 7.5 45.2

06/04/1996 to 06/19/1996 -508.34 82.48 -734.10 -355.50 51.35 6.7 0 1.9 37.9 5.3 48.1

06/20/1996 to 07/05/1996 -517.99 76.41 -724.70 -436.30 52.29 7.0 1.3 1.4 39.2 3.8 47.4

07/16/1996 to 08/02/1996 -469.37 50.05 -576.50 -402.00 47.52 6.8 0 .7 36.6 6.5 49.3

08/03/1996 to 08/19/1996 -493.16 94.97 -695.10 -285.10 49.75 6.7 0 .5 37.5 5.8 49.5

09/06/1996 to 09/23/1996 -29.92 47.68 -130.60 67.10 7.87 23.0 4.2 35.0 13.5 13.5 10.8

03/30/2001 to 04/14/2001 323.75 187.54 0 600.00 33.06 9.9 .3 49.7 11.1 5.1 23.9

06/22/2001 to 07/08/2001 -441.76 110.18 -600.00 -90.00 45.50 6.8 .9 14.5 31.3 11.9 34.6

07/09/2001 to 07/27/2001 -540.53 60.41 -610.00 -400.00 54.24 9.4 0 7.7 25.1 14.3 43.5

07/28/2001 to 08/09/2001 -533.08 60.33 -620.00 -400.00 54.50 11.2 0 4.6 25.1 13.7 45.4

08/10/2001 to 08/25/2001 -568.13 162.61 -1,000.00 -200.00 58.09 9.7 1.1 3.2 29.2 11.2 45.7

10/26/2001 to 11/11/2001 -202.35 259.07 -650.00 0 20.94 11.7 2.0 22.3 27.3 11.0 25.7

02/22/2002 to 03/14/2002 -158.57 185.24 -500.00 200.00 19.26 11.4 .2 26.8 26.8 11.8 22.9

04/09/2002 to 04/27/2002 -161.58 168.66 -530.00 0 17.39 12.1 1.9 24.6 24.5 13.4 23.5

04/28/2002 to 05/16/2002 -460.53 172.55 -650.00 -20.00 50.29 11.5 0 9.6 30.9 7.6 40.4

05/30/2002 to 06/14/2002 -539.38 113.64 -670.00 -320.00 60.22 9.8 .4 7.5 31.3 8.9 42.1

06/15/2002 to 06/29/2002 -595.33 125.52 -930.00 -410.00 60.30 9.0 1.9 4.3 32.7 8.3 43.7

Table 5. Summary of selected water-budget periods and associated components of the water budget for the Medina/Diversion Lake 

system, San Antonio area, Texas—Continued.

Water-budget period ∆S,

mean

∆S,

standard

deviation

∆S,

minimum

∆S,

maximum

∆S,

+error

GWout,

percent of

hydrologic

budget

Precipitation,

percent of

hydrologic

budget

Swin,

percent of

hydrologic

budget

Swout,

percent of

hydrologic

budget

Evaporation,

percent of

hydrologic

budget

∆S,

percent of

hydrologic

budget
Table 6 41

Table 6

Table 6. Relative contribution of each component of the water budget and relative part of record used for each water-budget 

computation for Medina Lake, Diversion Lake, and the Medina/Diversion Lake system, San Antonio area, Texas.

[GWout, ground-water outflow; P, precipitation; SWin, surface-water inflow; SWout, surface-water outflow; E, evaporation; ∆S, change in storage] 

1 Percentage of sum of all water-budget components. 

2 Percentage of total GWout period of record. 

GWout period of record

Percentage of water budget1

components of total water budget

Percentage

of days in

period

budgeted GW 2 out P SWin SWout E ∆S

Medina Lake 10/01/1995 to 09/30/1996 16.9 1.0 24.4 26.2 5.2 26.5 53.6

04/20/2001 to 06/30/2002 16.5 1.3 20.8 25.0 4.6 31.8 51.0

Average 16.7 1.1 22.6 25.6 4.9 29.1 52.3

Diversion Lake 10/01/1995 to 09/30/1996 7.3 .1 45.2 42.5 .5 4.4 53.6

04/20/2001 to 06/30/2002 9.8 .1 49.2 39.0 .5 1.6 51.0

Average 8.5 .1 47.2 40.7 .5 3.0 52.3

Medina/Diversion Lake System 03/01/1955 to 04/18/1957 36.3 1.9 18.4 0 11.7 31.7 84.0

06/30/1957 to 09/30/1964 14.4 1.8 17.9 25.8 8.5 31.6 54.9

10/01/1995 to 09/30/1996 12.8 .7 13.3 30.4 6.8 36.1 72.1

02/26/2001 to 06/30/2002 10.2 .8 15.9 26.8 10.6 35.6 38.4

Average 18.4 1.3 16.4 20.8 9.4 33.7 62.4
Prepared by the Texas District Office:

U.S. Geological Survey

8027 Exchange Drive

Austin, TX 78754–4733

Information regarding water resources in Texas is available at URL

http: //tx.usgs.gov/