1. A Groundwater Perspective on Surface Water Resources for GMA12
Dan Opdyke, PhD, PE Water Resources Branch
May 10, 2007

2. Greenthroat darter (Etheostoma lepidum)
Why is TPWD here?
Responsibility to protect fish and wildlife resources in Texas
Provide input to GMAs, not to tell GMAs what to do
We are available to assist GMAs

3. Importance of Springs and Baseflows
Support unique aquatic environments, including rare species
Serve as a barometer of local aquifer conditions
Relatively inexpensive means of monitoring groundwater
Provide important baseflows to rivers
Baseflows
Dependent on aquifer discharge
Important component of natural flow regime
Support habitats during dry periods

4. State of Springs Contributions by Brune in 1970’s
Fern Pool – April ‘04
State of Springs
Contributions by Brune in 1970’s
Of 281 historically significant springs, 65 had failed completely
Of 31 large springs, only 17 remained
Fern Pool – Oct. ‘06

5. Springs in GMA12

6. GMA12 Model Results What does the Future Hold?
Key Points to Remember for Discussion
10,000’ view
Looking for gross effects, not splitting hairs
Looking at entire QC-SP-CW model
Model provided by URS on 4/27/07
No changes made by TPWD
Boundary conditions drive the model

7. GMA12 Location
Milam
Queen City Sparta
Carrizo-Wilcox

8. Central QC-SP-CW Model
Nacogdoches
Milam
De Witt

9. Boundary Conditions Recharge (diffuse): direct infiltration
Reservoir Leakage: leakage through bottom of reservoir
ET: evapotranspiration
Stream Leakage: leakage through bottom of rivers and streams
General Head Boundaries: represent interaction with younger strata and horizontally adjacent models
Drains: represent areas with very shallow water tables, e.g., wetlands
Wells: represent pumping

10. Water Balance Recharge Reservoir Leakage Net Stream Leakage Wells ET
Net GHB
Drains
1 Sparta
2 Weches
3 Queen City
4 Reklaw
5 Carrizo
IMPERMEABLE
6 Upper Wilcox/Calvert Bluff
7 Middle Wilcox/Simsboro
8 Lower Wilcox/Hooper
Arrows denote direction of positive values

19. Question
What is the potential future interaction between the QC-SP-CW aquifer and rivers, streams, and lakes?

20. This water must come from somewhere

21. GW → SW Terms Recharge Reservoir Leakage Net Stream Leakage Wells ET
Net GHB
Drains
1 Sparta
2 Weches
3 Queen City
4 Reklaw
5 Carrizo
IMPERMEABLE
Net GW→SW = - Reservoir Leakage
6 Upper Wilcox/Calvert Bluff
7 Middle Wilcox/Simsboro
8 Lower Wilcox/Hooper

22. GW → SW Terms Recharge Reservoir Leakage Net Stream Leakage Wells ET
Net GHB
Drains
1 Sparta
2 Weches
3 Queen City
4 Reklaw
5 Carrizo
IMPERMEABLE
Net GW→SW = - Reservoir Leakage - Net Stream Leakage
6 Upper Wilcox/Calvert Bluff
7 Middle Wilcox/Simsboro
8 Lower Wilcox/Hooper

23. GW → SW Terms Recharge Reservoir Leakage Net Stream Leakage Wells ET
Net GHB
Drains
1 Sparta
2 Weches
3 Queen City
4 Reklaw
5 Carrizo
IMPERMEABLE
Net GW→SW = - Reservoir Leakage - Net Stream Leakage + Drains
6 Upper Wilcox/Calvert Bluff
7 Middle Wilcox/Simsboro
8 Lower Wilcox/Hooper

25. What does 128 cfs look like? 128 cfs ≈ 93,000 ac-ft/yr ≈ 83 MGD
For comparison:
Brazos River near Highbank (1965 – present) average flow: 2700 cfs median flow: 1000 cfs 25th %-ile: 460 cfs
City of Waco projected demands: 24,876 ac-ft/yr (Table 4A-20 of 2006 RWP)
Falls
Milam
Robertson

26. TPWD Groundwater Management Goal: Maintain Streamflows
Region K example: Region K determined that “groundwater availability values from the GAM runs were to maintain 90 percent of the streamflow contribution from the aquifer compared to a no pumpage run during the worst drought of record year.”

27. Proposed DFC Metric: Streamflows
Streamflows are gauged in many locations and often have a long period of record.
Streamflows have a direct impact on the environment.
Surface water rights have been authorized contingent on the historical streamflow record
Streamflows are a highly visible characteristic of the Texas landscape

28. Recommendations (in order of increasing difficulty)
Consider impacts to surface water during DFC deliberations
Include quantitative impacts to surface water in DFC definitions
Improve the GAMs in their representation of GW/SW interaction

29. Questions?