determination of ellenburger aquifer sustainability james beach lbg-guyton associates paul tybor...
Post on 28-Dec-2015
229 Views
Preview:
TRANSCRIPT
Determination of Ellenburger Aquifer Sustainability
James Beach LBG-Guyton Associates
Paul Tybor HCUWCD
Southeast Gillespie County
Minor Aquifers
Ellenburger Aquifer
Facts
• Ellenburger is the primary water supply– Fredericksburg – Irrigation– Rural
• Complex geology
• HCUWCD (1987)
• Aquifer has limits
Objectives
• Better understand the Ellenburger aquifer (SE Gillespie County)– Update and refine model– Assess long-term availability – Evaluate aquifer impact– Provide predictive tool for appropriate
planning, management and regulation
1. Data Evaluation
• Hydrostratigraphy and Structure
• Water Levels
• Hydraulic Properties
• Well Production
• Streamflow
• Water Chemistry
• Precipitation
2. Model Refinement
• Model Extent and Boundaries
• Hydrostratigraphy and Structure
• Calibration Targets
• Recharge
• Hydraulic Properties
• Pumping Allocation
• Sensitivity Analysis
3. Groundwater Availability
• Use updated model to assess:– Long term availability– Impact of increased demands– Optimize production
Modeling Basics
Groundwater Flow Modeling
Model “Cell” or “Gridblock”
Cells “Communicate”
Groundwaterflow
What Goes on In A Gridblock?
Groundwaterflow
Gridblock Accounting
• PermeabilityPermeability
• Storage valueStorage value
• ThicknessThickness
IrrigationIrrigationreturn flowreturn flow
Exchange of Exchange of water with water with
neighboring neighboring cellscells
NaturalNaturalrechargerecharge
Water Water remaining remaining in storagein storage
Water removed Water removed from storage by from storage by pumpingpumping
Geology
Faults
Stratigraphy
Glen Rose
Hensell Sand
Ellen-burger
Layer 1
Layer 2
Model Area
Ellenburger
Hensell Sand
Surface Geology
Extent of Model
New Model
Old Model
Gillespie County
Topography
Model Area
New Model
Old Model
Gillespie County All Wells
Model Area HighCapacity
Wells
HensellThickness
Hensell Sand
0
25
50
75
100
125
150
175
200
225
250
Hensell Sand Thickness (feet)
Hensell SandHensell Sand Thickness (feet)
N
Ellenburger
• Wells generally <350 feet deep
• Very deep wells have not encountered significant permeability-porosity
• Assume Ellenburger thickness of 200 feet
Groundwater Flow
Fault
Hydraulic Properties
• 3 pump testsSpecific capacity: 13 – 79 gpm/ft
Transmissivity: 25,000-38000 gpd/ft
3,500-5000 ft2/day
Hydraulic Conductivity: 22-33 ft/day
Storativity: 1x10-4
Well Capacity
20 gpm
50 gpm
Well Capacity
Ellenburger Histogram
0
100
200
300
400
500
600
1.0 3.2 10.0 31.7 100.0 316.5 1000.0
Production (gpm)
Fre
qu
ency
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Frequency
Cumulative %
Fredericksburg Pumping
Monthly Demand
Precipitation
Ellenburger Potentiometric Surface
Source: HCUWCD
Hensell Potentiometric Surface
Source: HCUWCD
Ellenburger Hydrographs:confined and unconfined responses
Hydrologic Summary Near Old Wellfield
• Water Levels in Ellenburger near old wells historically trend downward until new wells come online in the 1990s
• Both Hensell and Ellenburger water levels are typically below river levels
• Recent HCUWCD gain-loss studies and historical TWDB gain-loss studies in the Pedernales near the old wells show losses
GM-00008
1460
1470
1480
1490
1500
1510
1520
1530
1540
1550
J-40 J-50 J-60 J-70 J-80 J-90 J-00
Wat
er L
evel
Long-Term Ellenburger Water Level Trends Near Old Wells
USGS Pedernales at Fredericksburg vs Groundwater Level Near Old Wells
1480
1490
1500
1510
1520
1530
1540
1550
1560
1570
1580
J-98 J-99 J-00 J-01 J-02 J-03
Date
WL
ft A
MS
L
0
50
100
150
200
250
300
350
400
Ped
erna
les
Flow
in c
fs
GM-00010 Level (Ellenburger)
57-50-116 Level (Hensell)
USGS FredericksburgApproximate Pedernales Elevation near Old Wells
Levels of Hensell and Ellenburger Near Old Wells are Typically Below River Elevation
PEDERNALES FLOW AT FREDERICKSBURG VS. MEASURED GAIN/LOSS AT BROWN LOCATION (near old wells)
PEDERNALES FLOW AT FREDERICKSBURG VS. MEASURED GAIN/LOSS AT BROWN LOCATION
y = -0.1771x + 0.8607
R2 = 0.5752
-25
-20
-15
-10
-5
0
5
0 10 20 30 40 50 60 70 80 90
Flow (cfs)
Gai
n/L
oss
(cf
s)
Brown Flow vs GL
Linear (Brown Flow vs GL)
Source: HCUWCD gain/loss measurements
LBG-GUYTON ASSOCIATES
Intermediate-Term Ellenburger Water Level Trends Near New Wellfield
R-00074
1490
1495
1500
1505
1510
1515
1990 1992 1994 1996 1998 2000 2002 2004
Wat
er L
evel
Hydrologic Summary Near New Wellfield
• New Wellfield is near the Ellenburger outcrop on the Pedernales
• Ellenburger water level elevations at this location appear to be buffered near the river elevation
• Recent HCUWCD gain-loss studies at the Goehmann location suggest that at Ellenburger water levels at or above the river elevation the Pedernales gains, below the river elevation the Pedernales loses
Ellenburger Groundwater Level Near Ellenburger Outcrop and Pedernales River at New Wells
1475
1480
1485
1490
1495
1500
1505
1510
1515
1520
J-95 J-96 J-97 J-98 J-99 J-00 J-01 J-02 J-03 J-04 J-05
Date
WL
ft
AM
SL
57-50-329 Level(Ellenburger)
Approximate Elevation of Pedernales near New WellsPedernales Gains
Pedernales Loses
Hydrograph of Ellenburger Well Near Outcrop
Gain-Loss Data Near Outcrop
Goehmann Location Gain/Loss vs 57-50-329 Level
-4
-3
-2
-1
0
1
2
3
4
5
1480 1485 1490 1495 1500 1505 1510 1515
57-50-329 Leve l (ft AM SL)
Go
eh
ma
nn
Ga
in/L
os
s (
cfs
)
Goehmann G/L vs 57-50-329 Level
Only gains/losses greater than 10% of flow have been included.
Approximate river elevation
Modeling Periods
Steady-state
period
Calibration- Verification Prediction
Wate
r Ele
vati
on
in
Well
1940 1990 2004 2060
Observed Water LevelModel Water Level
Pre-Developme
nt Time
Simulation Periods
Time Period Stress Periods
Length
pre-1940: steady state periodprior to major pumping
1 -
1940 – 1990: calibration period 50 1 year
1990 – 2004: calibration period 180 1 month
2005 – 2060: predictive period ? ?
Path to completion
• Calibrate model
• Incorporate demands to 2060
• Simulate aquifer impacts
top related