Julie Ahern Butler. Boulder River Valley Groundwater Investigation

Boulder River Valley
Groundwater Investigation
Designing the Groundwater Flow Model
MBMG Groundwater
Investigation Program
Julie Butler, Andrew Bobst,
Luke Carlson, John Anderson
Montana AWRA Annual
Conference October 11, 2012

• Study Objectives
OUTLINE
• Building the Conceptual Model
o Field Work
o Data Analysis
• Building the Numerical Model
o Grid Design
o Calibration & Uncertainty Analysis
• Summary

PROBLEM STATEMENT
CAUSE:
Parts of the Boulder River
regularly run dry during late
summer
Senior water rights holders
unable to irrigate
EFFECTS:
Concern over current and
future groundwater
development reducing stream
flows
Interest in enhancing latersummer
flows via springtime
peak-flow diversions (aka
managed recharge)

OBJECTIVES
• Evaluate hydrogeologic effects of current and
potential future groundwater development
• Evaluate the potential for increasing late-summer
flows through managed aquifer recharge
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• Approaches
• Characterize the physical groundwater flow system
• Quantify surface-water – groundwater interactions
Conceptual model
Numerical model

• Install Wells
• 8 Bedrock Wells
• 6 Alluvial Wells
• 9 Canal Transect Wells
• Monitor
• Groundwater
• Surface Water
• Canals
• Water Quality
• Run Aquifer Tests
• 14 Sites
FIELD WORK

POTENTIOMETRIC SURFACE MAP
(MARCH, 2012)
• Gradient reflects aquifer
properties
• Observations
calibration targets
• Aquifer property estimates
prior information
monitoring site
aquifer test site

SURFACE-WATER – GROUNDWATER INTERACTIONS

Flume
Canal
Transect
DITCH LEAKAGE

Ditch @ transect
DITCH LEAKAGE
Ditch @ flume
Loss
Median: 2.2 cfs/mile
Ditch leakage recharges
groundwater & supplements
stream flow.

GEOLOGIC FRAMEWORK
GWIC (public online database):
http://mbmggwic.mtech.edu
Inventoried wells
Verified locations
Assigned altitudes
Interpreted lithologies
Imported as boreholes
Built cross sections

• Start simple
• Slowly build complexity
if it will enhance
predictions
GRID DESIGN

BOUNDARY CONDITIONS & CALIBRATION
• Boundary Conditions
o River & creeks
o Ditches
o Pumping wells
• Calibration targets
o Water levels
o Stream flow
o Groundwater-river interaction
• Parameter Estimation
o Inverse modeling
o Prior information

MODEL DOMAINS: AVOIDING THE ALL-PURPOSE MODEL
• No one model “fits all”
• Recall: model = predictive tool
o Impact of current and
potential future groundwater
development on river flow
o Impact of managed recharge
to on late-summer river flows
• Each model meets a specific
predictive objective
North
Model
Focus
Model
South
Model

Infiltration Ponds
Groundwater Monitoring Site
Surface-Water Monitoring Site
Stream
Irrigation Ditch
MODELING PURPOSE:
PREDICTION
Managed Recharge Example

UNCERTAINTY ANALYSIS
Food for thought…
All models are wrong
We must embrace uncertainty and quantify the “wrongness”
The goal is not to make “correct” predictions, but rather
to make predictions with minimum error
“A good model encapsulates what we know, and quantifies
what we don’t”

SUMMARY
• Conceptual Model Development – in progress
o ~ 90 monitoring sites calibration targets
o Strong local influence of ditch leakage
o River conditions change through space and time
• Numerical Model Development – in progress
o 3 models
o Boundary conditions to reflect aquifer recharge/discharge
o Calibrating to observations and “prior information”
• Key Principles
o Parsimony
o Tailor to the purpose
o Quantify the “wrongness”

THANK YOU
QUESTIONS???