The Role of Modeled Available Groundwater in

Local Regulation and State Planning

Presented By Bill Mullican, PG.,to the

2015 Texas Alliance of Groundwater DistrictsGroundwater Summit

San Marcos, Texas

Groundwater

$300

$500

$400

$100

$200

9

How many major aquifers have

been designated in Texas?

199,000,000,000,000,001

According to a recent scientific study published by Johnson, McCarthy, and Jones, what is

the volume of groundwater, in AFY, available in Texas today?

6

How many acronyms using the letters A, G, and M can be utilized based on TWC Chapter 36?

GAM – Groundwater Availability ModelGMA – Groundwater Management AreaMAG – Modeled Available Groundwater

MGA – Modeled Groundwater ApplicationsAGM – Approved Groundwater Model, and

AMG – Attorneys for Modeled Groundwater

16 Planning Regions

11

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

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.

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.

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

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 49 500

2,000

4,000

6,000

8,000

10,000

12,000

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.

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 49 500

100,000

200,000

300,000

400,000

500,000

600,000

Scenario 2 - Cumulative MAG vs Cumu-lative Pumping + WMS

Cumulative MAG Cumulative Pumping + WMS