Beeville MLT_Groundwater 101_Marcus Gary

1. Groundwater Science 101:
Connecting the Principles to the Practice
November 1, 2017
Dr. Marcus Gary
Field Operations Supervisor, Edwards Aquifer Authority
Adjunct Professor, The University of Texas at Austin

4. • Vadose (unsaturated) zone – area between the land surface and the top of the
phreatic zone, the position at which the groundwater (the water in the soil's
pores) is at atmospheric pressure
• Phreatic (saturated) zone - area in an aquifer, below the water table, in which
relatively all pores and fractures are saturated with water.
• Aquifer – a consolidated or unconsolidated geologic unit (material, stratum, or
formation) or set of connected units that yields a significant (economic) quantity
of water of suitable quality to wells or springs.
• Primary porosity – the void space in a rock or geologic media that is formed when
the sediments are deposited or the igneous rock is crystallized.
• Secondary porosity – the void space in a rock or geologic media that is formed by
fracturing or dissolution. It occurs after formation of primary porocity.
• Permeability - the ease with which a porous medium (rock, soil, etc.) transmits a
fluid (water).
A few definitions to get us started:

5. What is groundwater (above and below the water table)

7. POROSITY Primary porosity is formed when the sediments
are deposited or the igneous rock is crystallized.
Secondary porosity is formed by fracturing or dissolving matter.
It occurs after the formation of the primary porosity

8. Porosity and
permeability
are related, but
different

10. GW flow is
estimated using
Darcy’s Law

12. Head gradients influence the
direction and rate of GW flow

13. Pressure Head
Elevation Head

16. Aquifer A
Aquifer B
Aquifer C
Aquitard (confining unit)
Aquitard (confining unit)
Aquitard (confining unit)
Integrating the math into a conceptual model

17. Defining major
components
• No-flow
boundaries
• Equipotential
(equal head)
• Flow Lines
(hypothetical
flow paths
• Recharge Zone
• Lateral Flow
• Discharge Zone

18. Let’s start integrating all these components into a
conceptual water balance model

20. Transmissivity is the
rate of flow under a
unit hydraulic gradient
through a unit width
of aquifer of thickness
All models are wrong,
but some are useful.
Box and Draper
(1987)

21. Creating quantitative numerical GW models
based on the principles of hydrogeology

22. GAMs are based on
conceptual models
based on hydro-
geologic observations
and hypotheses.
The numerical models
are built from these
conceptual models

24. Interformational
Flow Study
Investigating how two
adjacent karst aquifer interact

25. Previous estimates of flow
from the trinity into the edwards
• Lowry, 1955 – 53,800 ac-ft/yr
(Cibolo Creek Basin only)
• Bader, 1993 – 107,000 ac-ft/yr
(Cibolo Creek Basin only)
• Kuniansky and Holligan, 1994 – 360,000 ac-ft/yr
• LBG-Guyton and Associates, 1995 – 5,000 ac-ft/yr
(Did not include Cibolo Creek)
• Lindgren et al., 2005 (USGS MODFLOW) – 40,298 ac-ft/yr
(increased to 74,000 ac-ft/yr in updated EAA MODFLOW)
• Jones et al., 2011 (TWDB GAM) – 110,600 ac-ft/yr 25

26. Hill Country
Trinity Aquifer
GAM
Edwards Aquifer
MODFLOW/FEFLOW
Groundwater
Models
IFF
Recharge
Puente (USGS)
Recharge
HSPF
Recharge
• TWDB is developing new conceptual model for Hill Country Trinity GAM.
• EAA is coordinating efforts to create a unified approach to link the two
groundwater models via IFF quantification.

27. Interformational Flow Investigation
Study Areas and Focus Zones

28. Some Early Working Hypotheses
1. Groundwater in the Upper Glen Rose is in close vertical communication with the Edwards in
many zones (BSEACD Westbay wells indicate this in Hays County).
2. Significant amounts of discrete recharge occurs in the Upper Glen Rose upstream of the EARZ
(indicated by gain loss surveys).
3. Groundwater can flow through conduits from the Upper Glen Rose directly to the Edwards
(indicated by dye tracing in Bexar County).
4. The Upper Trinity (UGR) and Middle Trinity (LGR & CC) are the primary contributors to IFF, but
have different spatial and temporal flow characteristics, thus must be separated in the context of
IFF analyses.
5. The highest rates of groundwater flux from the Upper and Middle Trinity occurs episodically, thus
must be characterized during major recharge events.
6. Diffuse recharge varies drastically depending on antecedent conditions, both in the Edwards
and Trinity (testing at Camp Bullis).

29. Edwards Aquifer
Trinity Aquifer
Data from BSEACD multi-port
monitor well indicates that water
in the the top ~150 feet of the
Upper Trinity Aquifer has similar
water levels and geochemistry at
Edwards water.

30. Hypothesis that most flow from the Trinity to the Edwards occurs episodically

32. Nueces River Basin
Currently, EAA staff are
performing gain/loss
surveys of rivers in the
Nueces Basin.
Data will be compared
to flow values
measured during
drought conditions of
2012-2014.

35. Dye Tracing on the Nueces

36. COLLABORATIVE EFFORT
working with neighboring agencies and entities
• Trinity Glen Rose Groundwater Conservation District
• Barton Springs Edwards Aquifer Conservation District
• Nueces River Authority
• The University of Texas at Austin
• Hays Trinity Groundwater District
• U.S. Geological Survey
• Camp Bullis – Joint Base San Antonio
• Texas Parks and Wildlife
• Natural Bridge Caverns
• Cibolo Nature Center
• Bandera County River Authority and Groundwater District
• Southwest Research Institute
36

37. COLLABORATIVE EFFORT
Continuing with the Edwards/Trinity Water Research Interest Group
• Organizations from previous slide; and,
• Guadalupe Blanco River Authority
• Medina County Groundwater Conservation District
• Uvalde County Underground Water Conservations District
• Kinney County Groundwater Conservation District
• Cow Creek Groundwater Conservation District
• Hill Country Groundwater Conservation District
• Comal Trinity Groundwater Conservation District
• GMA-10
• GMA-9
• Other stakeholder groups
37

38. Whisky is for drinking and
water is for fighting!
Mark Twain