💧 IGW-NET · Quick Tutorial 7 of 31

Tutorial 7: Transient Modeling

Set up a transient simulation with time-varying stresses, initial conditions, and storage parameters. Analyze time-series at observation wells.

IGW-NET Tutorial 7 Prereq: MAGNET4WATER account 2 sections

This tutorial covers

  1. Transient Regional Model — Fort Custer, Michigan
  2. What's Next

1Transient Regional Model — Fort Custer, Michigan

Step 1 — Load the Steady-State Model

Click Save/Load Load to load the regional model from Tutorial 1. This steady-state solution will serve as the initial condition for the transient simulation — the water level distribution at time zero, before any stress changes occur.

Step 2 — Run the Steady-State Baseline

Click Submit to submit the model for simulation in steady-state mode first. This establishes the equilibrium condition that the transient model will depart from.

Step 3 — Enable Transient Mode

Click Settings to open the Default Attributes menu. In the Simulation Settings tab, check the box next to 'Transient'. Configure the simulation parameters: Start Date (when the simulation begins), Time Step (how finely time is discretized — e.g., daily, weekly, monthly), and Simulation Length (total duration to simulate). Choose the 'Parent' option as the initial condition for head — this uses the steady-state solution as the starting water levels.

Step 4 — Apply a Stress Change

In the Aquifer Attributes tab, change the recharge multiplier to 0.1 — reducing recharge to 10% of the steady-state value. This simulates a drastic reduction in recharge — representing severe drought, urbanization covering recharge areas with impervious surfaces, or climate change reducing precipitation. The aquifer must now respond to receiving far less water than it was accustomed to.

Step 5 — (Step numbering note: Step 5 is configuration)

Review all settings — transient mode enabled, time step and duration configured, initial conditions set from the steady-state parent, recharge reduced to 10%. The model is ready to simulate the aquifer's response to stress.

Step 6 — Re-Submit for Transient Simulation

Click Submit to re-submit the model for transient simulation. IGW-NET's streaming visualization now shows a movie — water levels declining over time as the aquifer drains. Areas with thin saturated thickness or low storage respond fastest. Areas near rivers or lakes may be buffered by surface water exchange.

Step 7 — View Time-Varying Results

Watch the results evolve in the IGW-NET modeling environment. The plan view shows head contours changing at each time step. Areas of rapid decline become immediately visible — these are the vulnerability hotspots. You can step forward and backward through time, pause, or let the animation play continuously.

Step 8 — Save or Publish

Save or publish the transient model for future use. The entire time history is available for replay and further analysis.

Transient simulation results showing the regional model at a later time step with water levels significantly declined from the initial steady-state condition, particularly in areas far from surface water features. Head contours have shifted, flow patterns have changed, and areas of vulnerability are visible.
Figure 1: Transient results — water levels declining over time as recharge drops to 10% of steady-state. Areas far from rivers show the most dramatic decline. The flow pattern reorganizes as the aquifer drains.
Transient simulation settings showing the Default Model Input Parameters dialog with Transient checkbox enabled, Start Date, Time Step, and Simulation Length configured, and Recharge multiplier set to 0.1
Figure 2: Transient simulation settings — Transient mode enabled, time step and duration configured, initial condition from parent (steady-state), and recharge multiplier reduced to 0.1 (10% of baseline).

Key Concepts

Initial conditions matter: A transient simulation needs a starting point. Using the steady-state solution as the initial condition ensures the model begins in equilibrium — any changes you observe are due to the stress change, not numerical artifacts from a poorly initialized model.

Storage controls the response rate: How fast water levels decline depends on the storage coefficient (specific yield for unconfined, specific storage for confined). High storage = slow response (the aquifer has a large "buffer"). Low storage = fast response (small buffer, quick decline). This is why clay-rich confining layers respond differently than sandy unconfined aquifers.

Multipliers for scenario testing: The recharge multiplier (0.1 in this example) is a powerful tool for "what-if" analysis. Try 0.5 (50% reduction), 0.1 (90% reduction), or even 2.0 (doubled recharge) to explore the aquifer's sensitivity. Each scenario produces a different time history — revealing how resilient or vulnerable the system is to different levels of stress.

Streaming visualization = time as a movie: In IGW-NET, the transient simulation streams as an animation — compute one time step, render it, discard from memory, move to the next. A 50-year simulation uses the same memory as a 1-day simulation. You watch the aquifer evolve in real time — the most intuitive way to understand dynamic systems.

2What's Next

With transient modeling mastered, continue the learning path:

Tutorial 8: Calibration — match your transient model to time-series observations from monitoring wells
Tutorial 9: Synthetic Model — generate heterogeneous aquifers and explore how heterogeneity affects transient response
Tutorial 10: Aquifer Layers — add geological complexity with multiple distinct layers