This document summarizes a presentation given on modeled available groundwater in Texas. It notes that there are 6 major aquifers designated in Texas and that modeled available groundwater volumes from the Groundwater Availability Models are used in the 16 regional water planning regions. It also discusses how pumping strategies can be evaluated against modeled available groundwater volumes over time to determine impacts on aquifer availability. Two scenarios are presented showing drought water demand and pumping amounts versus modeled available groundwater.

1. The Role of Modeled Available
Groundwater in Local Regulation
and State Planning
Presented By Bill Mullican, PG.,
to the
2015 Texas Alliance of Groundwater Districts
Groundwater Summit
San Marcos, Texas

4. 9

5. How many major
aquifers have
been designated
in Texas?

6. 199,000,000,000,000,001

7. According to a recent
scientific study published by
Johnson, McCarthy, and
Jones, what is the volume of
groundwater, in AFY,
available in Texas today?

8. 6

9. How many acronyms using the letters A, G,
and M can be utilized based on TWC Chapter
36?
GAM – Groundwater Availability Model
GMA – Groundwater Management Area
MAG – Modeled Available Groundwater
MGA – Modeled Groundwater Applications
AGM – Approved Groundwater Model, and
AMG – Attorneys for Modeled Groundwater

10. 16 Planning Regions

11. 11
Three Texas Water Plans Published since SB 1 in 1997
Six prior to SB 1 (1961, 1968, 1984, 1990, 1992, and 1997)

12. Texas Water Code Chapter 16.053 (e) & (2-a)
(e) Each regional water planning group shall submit to the
development board a regional water plan that:
(2-a) is consistent with the desired future conditions adopted
under Section 36.108 for the relevant aquifers located in the
regional water planning area as of the date the board most
recently adopted a state water plan under Section 16.051 or, at
the option of the regional water planning group, established
subsequent to the adoption of the most recent plan.

13. 31 Texas Administrative Code Chapter 357.32 (d)
RWPGs shall use modeled available groundwater volumes for
groundwater availability, as issued by the Board, and incorporate
such information in its RWP unless no modeled available
groundwater volumes are provided. Groundwater availability
used in the RWP must be consistent with the desired future
conditions as of the date the Board most recently adopted a
state water plan or, at the discretion of the RWPG, established
subsequent to the adoption of the most recent state water plan.

14. 0
2,000
4,000
6,000
8,000
10,000
12,000
1 2 3 4 5 6 7 8 9 10
Years
Scenario 1 - Drought Demands vs. MAGS
Drought Water Demand
Average Historical Use

15. 0
2,000
4,000
6,000
8,000
10,000
12,000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
Scenario 2 - Pumping + New Strategy
vs. MAG
Pumping Strategy
MAG = 10,000 AFY • Pumping in Year 1
starts at 5,500 AFY
and increases at a
rate of 100 AFY for
50 years
• WMS = 1,000 AFY
pumping starting in
Year 1
• MAG = 10,000 AFY
• Total pumping +
WMS =447,500
• Excess MAG =
47,500 AF.

16. 0
100,000
200,000
300,000
400,000
500,000
600,000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
Scenario 2 - Cumulative MAG vs
Cumulative Pumping + WMS
Cumulative MAG Cumulative Pumping + WMS