Short classes are available from Halford Hydrology that introduce aquifer testing, analyzing hydrologic data with Excel, critically assessing groundwater-flow models, and time-series analysis with SeriesSEE. Each of the short classes are described on this page.
- Aquifer-Testing Overview —Summarizes why aquifer-testing is needed and expected results for managers and technical people.
- Aquifer Testing —Introduction to single-well aquifer tests.
- Evaluating Calibration of Groundwater Models — Introduce stress-response approach, expanding objective function comparisons, and graphical approaches for evaluating groundwater-model calibration.
- Excel for Hydrology—Functions and features in Excel are presented for analyzing hydrologic data.
- Excel VBA–Accelerate hydrologic analysis—Macros for reading and writing arrays are demonstrated.
- Hydrologic Analysis with Excel —Functions and features in Excel are presented and hydrologic problems are analyzed.
- Obtaining Useful Answers from Groundwater Models—Necessary elements for developing and reporting useful groundwater models are identified and explained.
- SeriesSEE—Time series analysis and detecting small drawdowns with SeriesSEE, An Excel Add-IN
Aquifer Testing
Groundwater flow rates and storage volumes cannot be measured directly and are estimated indirectly from aquifer-test results, which are controlled field experiments. Transmissivity and storage coefficient are principal results that define behavior of groundwater system in response to pumping. Volume of water displaced or rate of water pumped are the principal controls that allow estimation of transmissivity and storage coefficient by fitting analytical or numerical solutions to observed water-level changes.
A 1-day, aquifer-test class will cover fundamental concepts of aquifer-system responses to pumping and slugging wells. Material will emphasize practical aspects of analyzing and interpreting slug test and single-well pumping aquifer tests. Field conditions and limitations will be considered for measuring water-level and discharge data. Expected ranges of aquifer properties and empirical correlations between specific capacity and transmissivity will be presented. Design, interpretation, and limitations multiple-well aquifer tests will be presented. Guidance for reporting aquifer test results will be provided.
Data will be reduced, single-well tests will be interpreted, and simple problems will be analyzed during class exercises.
Evaluating Calibration of Groundwater Models
Groundwater models frequently are calibrated to better predict changes in water levels and spring discharges from pumping. Calibration minimizes differences between measured and simulated responses, while estimating plausible hydraulic property distributions and honoring conceptual models. Water levels, water-level changes, discharges, and changes in discharge are quantifiable measures that typically can be compared formally in an objective function. Water-table altitudes greater than land surface, head-differences between wells, and transmissivities from aquifer tests are additional measures that can be compared quantitatively, albeit, with additional subjectivity and numerical difficulties. Plausibility of simulated hydraulic property estimates is difficult to quantify, but considered more easily when reduced to a vertically integrated measure such as transmissivity. Differences between numerical and conceptual models can be assessed qualitatively with integrated results and simple visualizations. An example of integrating results is summing recharge volumes between mountain ridges and valley floors. Water-level profiles are a simple visualization for comparing simulated and measured gradients. Predictive utility of calibrated models depends on agreement between measured and simulated responses and qualitative agreement between conceptual and numerical models.
The workshop will address necessary elements for evaluating calibration of groundwater models. Topics include; (1) Designing groundwater-flow models for calibration, stress-response approach, (2) Developing an objective function with additional measurements such as transmissivity observations, (3) Comprehensively visualizing model results with Excel, Model Viewer, and Google Earth. Stress-response models that simulate part of Death Valley regional groundwater-flow system will be used as examples. Presented material will be appropriate for individuals who develop or review groundwater-flow models. Examples and software for viewing water-level profiles, hydrographs, and hydraulic-property distributions are intended for individuals with experience in developing groundwater-flow models with MODFLOW.
Excel for Hydrology
Hydrologic analysis requires data, but data rarely arrives in an analyzable form. Mismatches between available and required data range from, “Well, a few tweaks…” to “What the hell is this…” The many functions and features of Microsoft Excel are well suited to eliminating these mismatches, including the latter category.
A 1-day, Excel-for-Hydrology class will introduce functions and features for wrangling disparate data sets into analyzable forms. Essential features of Excel such as conditional formatting, data validation, text to columns, remove duplicates, pivot tables, and more will be introduced. Translating 3-column data in the form of [site name, time, value] as comes from databases into individual time series by site name using MATCH and OFFSET functions, which are more versatile than a VLOOKUP function. The Solver add-in will be explained and applied with two examples, a stage-velocity index relation and superimposed Theis functions. Shading areas in XY plots with INT and MOD functions will be demonstrated along with other approaches for drawing what you want to see. Manipulating text with LEFT, MID, RIGHT, and FIND functions and formatting numbers in text strings with TEXT function will be addressed. These approaches are especially useful for exploring new data sets or reviewing reported data, where repeated analysis is less likely than during an ongoing project.
Introduced functions and features will be applied to build a hydrograph viewer, similar to PEST-HYDROS. Class attendees will participate. We will all reduce data, utilize feature, apply functions, and draw pictures together. Participants are encouraged to bring their bad data for wrangling as a class exercise.
Hydrologic Analysis with Excel
Hydrologic analysis requires data, but data rarely arrives in an analyzable form. Mismatches between available and required data range from, “Well, a few tweaks…” to “What the hell is this…” The many functions and features of Microsoft Excel are well suited to eliminating these mismatches, including the latter category. Hydrologic problems will be analyzed with many native and user-defined functions in Excel.
The 2-day, Hydrologic-Analysis-with-Excel class will introduce functions and features for wrangling disparate data sets into analyzable forms. Essential features of Excel such as conditional formatting, data validation, text to columns, remove duplicates, pivot tables, and more will be introduced. Translating 3-column data in the form of [site name, time, value] as comes from databases into individual time series by site name using MATCH and OFFSET functions, which are more versatile than a VLOOKUP function. The Solver add-in will be explained and applied with two examples, a stage-velocity index relation and superimposed Theis functions. Shading areas in XY plots with INT and MOD functions will be demonstrated along with other approaches for drawing what you want to see. Manipulating text with LEFT, MID, RIGHT, and FIND functions and formatting numbers in text strings with TEXT function will be addressed. These approaches are especially useful for exploring new data sets or reviewing reported data, where repeated analysis is less likely than during an ongoing project.
Hydrologic problems will include analyzing aquifer-tests, correlating geologic observations and hydraulic properties, and evaluating calibration of groundwater models. Aquifer-test analysis can cover single-well pumping tests, flow logs, slug tests, and multiple-well tests. Correlation between geologic observations and hydraulic properties covers data sets with greater than 100 aquifer-test results from Southern Nevada. Groundwater-model calibration is evaluated with an example from southern Nevada, where the objective function was expanded and many graphical techniques were applied.
Obtaining Useful Answers from Groundwater Models
Groundwater models are developed because questions need to be answered. Regional effects of developing groundwater resources on sensitive ecosystems, existing water rights, and contaminant transport are typical questions, where water managers and society at large expect useful answers. Hydrologists address these questions by developing calibrated groundwater models because problems are often too complex for simple analytical approaches. The lack of alternatives has been noted succinctly by John Bredehoeft, “… if you want to make predictions about how these systems are going to behave, this is the only tool you’ve got. This is it. You don’t have anything else.” Predictive utility depends on agreement between actual and estimated hydraulic properties at scales that are defined by posed questions.
The “Obtaining Useful Answers from Groundwater Models” seminar will address necessary elements for developing and reporting useful groundwater models. Topics will follow steps for developing a groundwater-flow model. These include developing a conceptual model, numerically approximating observed features, identifying measured quantities for calibration, distributing hydraulic properties, minimizing differences between measured and simulated quantities through calibration, testing alternative models, and answering original and ancillary questions. Effects of distributing recharge with modified Maxey-Eakin, explicitly simulating mountain blocks, MODFLOW packages, and discretization on model development will be discussed specifically. Relative merits of imposing hydrologic wishes on hydraulic property distributions with zones or pilot points and Tikhonov regularization will be demonstrated. Reporting groundwater-model results also will be discussed with an emphasis on clearly presenting simulated hydraulic properties and keeping model results relevant. Presented material will be appropriate for hydrologists, engineers, managers, lawyers, and all parties affected by groundwater-model results.
SeriesSEE
Small pumping signals can be detected reliably with water-level modeling as implemented in SeriesSEE. For example, drawdowns of less than 0.05 ft are detected routinely beneath Pahute Mesa, Nevada where environmental, barometric and tidal, fluctuations exceed 0.5 ft. Water-level models simulate environmental water-level fluctuations and pumping effects. Environmental water-level fluctuations are simulated by summing individual time-series of barometric pressure, tidal potential, and background water levels. Water levels from background wells, unaffected by pumping, are critical because they are affected by tidal potential–rock interaction, imperfect barometric coupling, seasonal trends, and climatic trends. Pumping schedules are transformed to water-level responses with superposition Theis models. Numerical experiments have confirmed that these Theis transforms closely approximate water-level responses through hydrogeologically complex aquifers.
SeriesSEE is an Excel Add-In for viewing, cleaning, and analyzing time series or geophysical logs. Bad data in series can be identified and removed either conditionally or graphically. Series can be added, subtracted, multiplied, or divided even where measurement frequencies are irregular, different, and asynchronous. Many other tools exist in SeriesSEE that facilitate rapid data reduction and the creation of water-level models.
Water-level models are created interactively with SeriesSEE in a new workbook. Synthetic water levels are simulated with a FORTRAN program where differences between synthetic and measured water levels are minimized with PEST. Model fit is defined by RMS error and evaluated graphically. Estimated drawdowns are the summation of all Theis transforms and differences between synthetic and measured water levels.
The methodology and supporting software in SeriesSEE is documented in publicly available articles (Garcia, et al, 2013) and reports (Halford, et al, 2012). The validity of simulating pumping signals in geologically complex environments was demonstrated clearly in the article, “Detecting Drawdowns Masked by Environmental Stresses with Water-Level Models.” The software SeriesSEE has been documented, validated, and distributed through a USGS Techniques and Methods report (Halford, et al, 2012). SeriesSEE is public domain software that can be adapted and used freely.