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Numerical Model of the Groundwater-Flow System Near the Southeastern Part of Puget Sound, Washington

Scientific Investigations Report 2024-5026-D-E
Prepared in cooperation with the Cities of Auburn, Milton, Puyallup, Sumner, and Tacoma; Pierce Conservation District; Pierce County Public Works; Washington State Department of Health; Washington State Department of Ecology; Thurston County Public Utility District; Cascade Water Alliance; Lakehaven Utility District; Lakewood Water District; Firgrove Mutual Water Company; Fruitland Mutual Water Company; Spanaway Water Company; Summit Water & Supply Company; and Mt. View-Edgewood Water Company
By: , , , and 
Edited by: Wendy B. Welch and Andrew J. Long
https://doi.org/10.3133/sir20245026v2

Links

  • Document: Report (10.4 MB pdf) , XML
  • Larger Work: This publication is Chapter D-E of Characterization of groundwater resources near the southeastern part of Puget Sound, Washington
  • Tables:
    • Table 1.1 (995 KB csv) - Streamflow-Routing (SFR) Package specifications by reach
    • Table 1.2 (5 KB csv) - Estimated monthly average base flow estimated for Coal, Boise, and Scatter Creeks where they enter the active model area, near the southeastern part of Puget Sound, Washington, 2005–15
    • Table 1.3 (10 KB csv) - Estimated monthly average base flow estimated for selected streams where they enter the active model area, the Buckley diversion (inflow to Lake Tapps), and outflow from Lake Tapps, near the southeastern part of Puget Sound, Washington, 2005–15
    • Table 1.4 (6 KB csv) - Monthly average water levels for American, Gravelly, Steilacoom, and Spanaway Lakes, and Lake Tapps, derived from measured and estimated values, near the southeastern part of Puget Sound, Washington, 2005–15
    • Table 1.5 (6.7 MB csv) - Measured water levels for American, Gravelly, and Spanaway Lakes, near the southeastern part of Puget Sound, Washington, 2000–18
    • Table 1.6 (637 KB csv) - Time-series records of measured and simulated hydraulic-head values (transient model version) for selected wells used, near the southeastern part of Puget Sound, Washington, 2005–15
    • Table 1.7 (398 KB csv) - Averages of measured hydraulic-head values for selected wells and corresponding simulated steady-state values, near the southeastern part of Puget Sound, Washington, 2005-15
    • Table 1.8 (291 KB csv) - Estimated and simulated monthly average base flow for selected stations, near the southeastern part of Puget Sound, Washington, 2005–15
    • Table 1.9 (9 KB csv) - Estimated and simulated base-flow values for the steady-state model version for stations with continuous records, near the southeastern part of Puget Sound, Washington, 2005–15
    • Table 1.10 (63 KB csv) - Estimated and simulated vertical hydraulic-head differences for the steady-state model version between an upper and lower model layer for selected locations, near the southeastern part of Puget Sound, Washington, 2005–15
    • Table 1.11 (8 KB csv) - Supplemental hydraulic-head targets for the steady-state model version set equal to the land surface to prevent groundwater flooding and corresponding simulated values, near the southeastern part of Puget Sound, Washington
    • Table 1.12 (199 KB csv) - Model calibration parameters showing input to the control file for the Model-Independent Parameter Estimation (PEST) program
    • Table 1.13 (12 KB csv) - Simulated groundwater budget for the calibrated transient model version, near the southeastern part of Puget Sound, Washington, 2005–15
    • Table 1.14 (5 KB csv) - Groundwater use applied to scenario 3 for the Spanaway Water Company and the City of Sumner, near the southeastern part of Puget Sound, Washington
    • Tables 1.1-1.14 (5.2 MB xlsx)
  • Data Releases:
    • USGS data release - Spatial data in support of the characterization of water resources near the southeastern part of Puget Sound, Washington
    • USGS data release - MODFLOW-NWT model to simulate the groundwater flow system near Puget Sound, Pierce and King Counties, Washington
  • Download citation as: RIS | Dublin Core

Abstract

Groundwater flow in the active model area (AMA) was simulated using a groundwater-flow model. A steady-state model version of the model simulates equilibrium conditions, and a transient model version simulates monthly variability. The model corresponds to the physical and temporal dimensions of the conceptual model and groundwater budget. The steady-state model version represents average conditions for an 11-year period (January 1, 2005–December 31, 2015), and the transient model represents monthly hydrologic variability within that period. The 13-layer model was constructed using MODFLOW-NWT with a uniformly spaced grid consisting of 416 rows, 433 columns, and cells with a horizontal dimension of 500 feet (ft) on a side.

The model was calibrated to measured values of water levels in wells and lakes and estimated base flow for selected streamflow measurement stations, commonly referred to as streamgages. Model calibration was accomplished using a combination of manual and automatic methods, including the Model-Independent Parameter Estimation (PEST) program that adjusted model input parameters with the aim of minimizing the difference between estimated and model-simulated values of hydraulic head and base flow.

Model boundary conditions consist of all simulated groundwater inflow to and outflow from the AMA. For example, a stream reach that simulates a gain from or loss to groundwater is a boundary condition that allows water to exit or enter, respectively, the groundwater system. Other boundary conditions include springs, seeps, precipitation recharge, groundwater exchange with lakes and Puget Sound, and groundwater pumping. A comparison of the estimated groundwater budget to that simulated by the steady-state model version indicates that the relative percentages of total inflow or total outflow for six major categories of boundary conditions are similar for the two budgets.

The model was used to simulate three suites of scenarios of potential drought and water-use changes. Scenario 1 suite consisted of the steady-state model version that was run with 0, 15, 20, and 25 percent reduction of precipitation recharge to assess the corresponding reductions in base flow with decreasing recharge. The last simulation for the scenario 1 suite consisted of the transient model version simulating 3 years of consecutive seasonal drought, defined by the months of May through September, to assess the corresponding base-flow reductions. Scenario 2 suite consisted of the steady-state model version with all simulated groundwater use removed, compared with a simulation that includes current groundwater use to evaluate changes to potentiometric surfaces and base flows. Scenario 3 suite consisted of a transient model version of the model that simulated pumping increases for four different categories of water-supply wells (compared to no pumping increases) to evaluate resulting reductions in base flow. Although, these scenarios provide examples of model applications and useful insights, many other scenarios could be simulated. A description of how to download the model is described in the body of this report.

Uncertainty is associated with most model inputs. Groundwater levels, lake levels, and land-surface altitudes are relatively certain; other model inputs are far less certain, including precipitation recharge, base flow, hydraulic properties, water use, and the three-dimensional structure of subsurface hydrogeologic units. Models are useful not because of high levels of accuracy of all model inputs, but because they combine the best information and estimates available, thereby providing the best predictions available related to physical processes.

The model described in this report simulates groundwater flow on a regional scale, which has inherent limitations for simulating hydrologic scenarios at local scales. Model structures and inputs were generalized to be consistent with this regional scale. For example, the actual groundwater system has much greater heterogeneity of hydraulic conductivity than is possible within the model’s degrees of freedom. Variations in hydraulic gradients over distances less than 500 ft cannot be simulated. The distances between model features, such as a pumping well and a stream, must be placed at 500-ft intervals and are co-located if both features are within the same model cell.

Suggested Citation

Long, A.J., Wright, E.E., Fuhrig, L.T., and Bright, V.A.L., 2024, Numerical model of the groundwater-flow system near the southeastern part of Puget Sound, Washington, v. 2 of Welch, W.B., and Long, A.J., eds., Characterization of groundwater resources near the southeastern part of Puget Sound, Washington, 2 chap. (D–E): U.S. Geological Survey Scientific Investigations Report 2024–5026–D–E, [variously paged; 103 p.], https://doi.org/10.3133/sir20245026v2.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Preface
  • Acknowledgements
  • Executive Summary
  • Introduction to Chapters D and E
  • Glossary
  • Chapter D. Numerical Model Construction and Calibration
  • Introduction
  • Design and Construction
  • Model Calibration and Sensitivity
  • References Cited
  • Chapter E. Numerical Model Results
  • Introduction
  • Groundwater Budgets
  • Scenario Simulations
  • Model Limitations and Potential Refinements
  • References Cited
  • Appendixes 1–3
Publication type Report
Publication Subtype USGS Numbered Series
Title Numerical model of the groundwater-flow system near the southeastern part of Puget Sound, Washington
Series title Scientific Investigations Report
Series number 2024-5026
Chapter D-E
DOI 10.3133/sir20245026v2
Year Published 2024
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Washington Water Science Center
Description Report: 103 p.; 14 Tables; 2 Data Releases
Country United States
State Washington
Other Geospatial Puget Sound
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details