Development and Interpretation of Long-Term
Water Data: When is Long-Term Long Enough?
Peter Thibodeau, Ph.D., P.G.
David Dickson
For the 2011 Alabama Water Resources Conference
Organization
 Introduction
 The problem: Data Needs vs. Data Availability
 Approaches to address long-term water data needs
– Surface water
– Groundwater
– Post-construction validation
 Summary
The Problem: Do we have the data we need?
 Evaluation of proposed projects in undeveloped or “under-” studied
areas
 Time scale of concern – defining the frame of reference
 Available sources of information
 Technological advantages
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GIS
AutoCAD
Raw computing power
Database availability (USGS, STORET, state and
university databases)
 Once we have framed the problem, we can look
at the pathways for solving the data needs
Do we have enough data? Are they “good” data?
 “That system is designed to handle a 2-year storm. You know, that
happens 2 or 3 times a year around here”. ---name withheld
 “Typically, we evaluate stream effects on a decade time scale. You
don’t have 10 years of data for that particular stream segment, so start
collecting …” ---name withheld
 “How can you convince me that this was the storm of record, just
because it was the largest storm we have data for?” ---name withheld
What problems are we trying to answer?
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Framing the problem is essential
Don’t over-scope the solution
Statistical analysis options
Relevance to assessing impacts or flow regime changes
Ultimate goal: defendable decisions using appropriate data
When data are not available for the study area
 What streams/rivers in the area are/have
been monitored?
 Analytical approach: simple to complex
solutions
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Mathematical relationships
Land cover
Land use and GIS solutions
Streamstats
 Groundwater monitoring data
Data are available, but not the right time period
 Flow record extension techniques
– Analytical methods
– GIS methods
 Watershed adjustments for land use/cover
– GIS methods
 Similarity of watersheds
– GIS methods
 Stochastic events (storms and droughts)
 Groundwater correlations as a tertiary tool
http:Image obtained from
//www.cleanwaterpartnership.org/alabama-river-basins/
Index wells for groundwater evaluation
 Working with state agencies to ID and accept discrete wells as
representative of area conditions
 Changes in index well water levels are representative of changes for
sites within a defined area
 Used to estimate impacts and acceptable water level variations
 The “Frimpter Method” (USGS, 1981)
Trend analysis of temporal changes
 Trend analysis of regional water availability: groundwater and surface
– Temporal analysis used for water supply planning
– Spatial trends in water level changes due to development pressure
– Groundwater flow modeling analysis
Aquifer to aquifer comparisons
 Limited capabilities
 Uncertainties and heterogeneities
 Possible depending on scale of the problem
Image obtained from
USGS Scientific Investigation Report 2010-5080
Image obtained from
http://www.gsa.state.al.us/gsa/geologichazards/sinkholes/lscrops.gif
Post-Development and Validation
 Getting out of the computer
 Field observations
 Real-world validation and checks on calculations, statistical
analysis, and modeling
 Opportunity to revise and re-scale if needed
 Future use of calibrated and validated data
Project Example: Wetland Mitigation
 Greens Creek Mitigation Bank – Clay County, Florida
 Project size: ±4,400 acres
 Hydrologic improvements to restore impacted wetlands and
generate points of lift.
 Impacts to hydrology were from silviculture (bedding rows and
planted pines in historic wetlands) and ditches.
 Wetlands and groundwater were being drawn down.
 Goal was to restore site to pre-agriculture conditions.
 Challenges:
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Minimal on-site historical data
No off-site effects/impacts allowed
Economics
In a drought
Timeline
Project Example: Wetland Mitigation
 Restoration plan
– Installed piezometers to document current conditions (collected 10 months of
data prior to permitting).
– Identified target community types and selected representative communities
nearby to document proposed conditions.
– Collected representative site specific topographic data.
– Collected available historical data for region.
– Utilized computer model to design improvements.
– Defendable decision – prove hydrologic improvement for plan approval.
 Post Construction
– Collect groundwater data for 5 yrs to compare with pre-construction conditions
– Annual monitoring to measure success criteria and allow for adjustments
 Results
– Verify assumptions and validate the long-term water conditions as estimated
from permitting process.
Summary
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Framing the problem is essential to a good study
Use available data to the extent possible
Determine reliable extension methods based on specific site conditions
Surface water techniques
Groundwater methods
Validation and getting out of the computer
Defendable decisions using appropriate data
Thank You
Peter Thibodeau, Ph.D., P.G., P.H.
Cardno ENTRIX
Raleigh, North Carolina
919-999-4008
Peter.thibodeau@cardno.com
David Dickson
Cardno ENTRIX
Tallahassee, Florida
850-681-9700
David.dickson@cardno.com