Effects Of Temporal Variability

When the flow itself changes over time, does heterogeneity still dominate the spreading?

What you’re watching Transient flow with the velocity field shown as arrows, comparing two aquifers: a homogeneous one (top) where the plume stays a compact blob, and a strongly heterogeneous one (bottom, ln K var 2.0) where the plume stretches into channelized fingers — both under the same time-varying flow.

The mechanism Temporal variability — a flow field that changes through time — is a new layer on top of spatial heterogeneity. In the homogeneous aquifer the plume simply follows the changing flow and stays compact. In the heterogeneous aquifer, the same time-varying flow drives parcels through high- and low-K zones repeatedly, amplifying spreading.

Why it matters Real flow is never steady — seasons, pumping, and recharge all change it — so understanding transport means combining temporal and spatial variability, not treating flow as fixed.

IGW-NET Running both aquifers under the same transient flow, with the velocity arrows updating live, shows heterogeneity winning even when the flow itself is in motion.

How does sorption change transport when the flow is also varying in time?

What you’re watching A heterogeneous aquifer under transient flow, run with and without sorption; the sorbing case lags and tails more, its retarded parcels caught even longer in slow zones as the flow shifts.

The mechanism Sorption retards solute, and under time-varying flow that retardation interacts with the changing velocity field: retarded parcels sit in low-K zones across many flow shifts, accumulating spreading that a non-sorbing plume escapes.

Why it matters Reactive contaminants under realistic, fluctuating flow spread and tail even more than steady-flow models predict — worsening cleanup prospects.

IGW-NET Toggling sorption under the same transient flow shows how chemistry and time-variation compound — visible only because both run together.

What happens when physical, chemical, and temporal variability all act at once?

What you’re watching A comparison of aquifers with and without interacting (K and Kd) heterogeneity under transient flow; the interacting case shows the most fragmented, trapped, and spread plume.

The mechanism Each layer of variability compounds the others. Time-varying flow shuttles parcels back and forth, while the negative K–Kd coupling traps them in slow, high-sorbing zones — so the temporal motion repeatedly feeds parcels into traps they cannot easily leave.

Why it matters This is the realistic, fully-coupled picture — the regime where simplified models are least reliable and real plumes are hardest to predict or remediate.

IGW-NET Layering temporal flow onto interacting heterogeneity and watching the plume shred reveals the full complexity that previous methods simply could not show.

If the flow swings back and forth, does the plume just return to where it started?

What you’re watching A homogeneous aquifer under reversing (transient) flow; the plume swings with the flow direction but stays a coherent, compact body — its motion is largely reversible.

The mechanism With no heterogeneity, a parcel that moves out under one flow direction retraces its path when the flow reverses. The plume oscillates left and right but does not irreversibly spread — reversing flow alone is nearly reversible.

Why it matters It isolates the key insight: flow reversal by itself does not disperse a plume; something else must break the reversibility.

IGW-NET Watching the plume swing out and come back nearly intact makes the reversibility of homogeneous transport strikingly clear — the control case for what heterogeneity adds.

What breaks the reversibility — why doesn’t the plume come back?

What you’re watching A randomly heterogeneous aquifer under the same reversing flow; now the plume does not return intact — parcels are trapped in low-K pockets and left behind each time the flow swings, so the plume spreads irreversibly.

The mechanism Heterogeneity breaks the symmetry. As flow reverses, parcels follow different paths out and back through the high- and low-K structure, and some are trapped in slow zones and stranded. Each swing strands more, accumulating irreversible spreading the homogeneous case never shows.

Why it matters This is why real, seasonally-driven plumes keep spreading rather than oscillating in place — the interaction of temporal flow with heterogeneity, not either alone.

IGW-NET Comparing this with the homogeneous case — swing-and-return versus swing-and-strand — pinpoints heterogeneity as the source of irreversibility, straight from watching the two simulations side by side.

With only the physical structure varying, how much does temporal flow add?

What you’re watching A heterogeneous-K aquifer with uniform sorption under transient flow; the plume channels and traps along the K structure as the flow shifts, but the chemistry is the same everywhere.

The mechanism Physical heterogeneity alone, combined with time-varying flow, already produces channeling and trapping: parcels strand in low-K zones as the flow swings. The uniform Kd retards everything equally, shifting timing but not adding chemical contrast.

Why it matters It separates the physical contribution from the chemical one — showing how much trapping comes from K structure before chemistry is even varied.

IGW-NET Holding Kd uniform while K varies isolates the physical contribution to irreversible spreading under transient flow.

Throw everything in — varying K, varying chemistry, and changing flow. What does transport really look like?

What you’re watching A heterogeneous-K, heterogeneous-Kd aquifer under transient flow (ln Kd var 2.0): the plume is shattered into fragmented, channelized fingers, dramatically trapped and spread compared with every simpler case.

The mechanism All three layers act together: time-varying flow shuttles parcels, physical heterogeneity channels them, and chemical heterogeneity (varying Kd) traps the reactive ones in slow, high-sorbing zones. The combination produces the strongest, most irreversible spreading of any case.

Why it matters This is the closest to reality — and the hardest case for prediction and cleanup. It shows why field plumes behave in ways steady, homogeneous, non-reactive models never capture.

IGW-NET Building this fully-coupled case and watching the plume fragment is the payoff of the digital laboratory: even a single likely realization lets you see the unseen and understand fate and transport in porous media in ways previously very hard to reach.