Stream Table: Erosion & Deposition

What this investigation asks

A stream can erode upstream material, transport it, and deposit it where the flow slows. This investigation separates those stages through a stream table, sediment measurements, and a settling comparison. Begin by identifying what the selected record measures: float travel, collected sediment, channel change, or particle settling. The goal is to connect each outcome to the flow and grain conditions rather than assuming that the amount of sand moved must increase in direct proportion to every increase in measured surface speed.

Design and measure the comparison

Change slope while retaining flow supply, run time, sand sample, and channel geometry. Use float timing to estimate surface motion and collect the deposited sediment under the specified procedure. Compare the mass transported as well as the velocity. Sediment movement has a threshold and a nonlinear response to the modeled water forcing, so a modest speed change can accompany a much larger transported amount. Keep surface-float velocity distinct from the depth-averaged flow quantity in the model; they are not interchangeable readings even when both are expressed in distance per time.

Connect the record to the model

Follow the channel into slower or still water to explain deposition and sorting. Grain size, density, and shape influence settling, so the simplest larger-first pattern applies under matched material assumptions. The bend comparison relates faster outer-bank flow to erosion and slower inner-bank conditions to deposition. Retain the location and time interval when interpreting a changed bank or deposit. A sediment pile records accumulated transport and settling over a run, not the instantaneous carrying capacity at every upstream position or a complete history of the physical stream system.

Interpret the evidence and its limits

Use the course's flow and sediment assumptions to explain an observed contrast while distinguishing the tabletop scale from a natural river. Channel evolution can change conditions during a run, making a later reading different from the initial geometry. A settling trial and an erosion trial isolate different parts of the process. Report which measurement supports the threshold, transport, or deposition claim, and identify a controlled comparison that could test another factor. Do not promote a matched-model trend into a universal field erosion prediction independent of grain composition, geometry, discharge, and the observation interval.

Reference conditions and quantities

For the specified Ideal straight-channel case at slope 2% and supply 30 mL/s, the course depth-averaged speed reference is 0.1717433364 m/s, while the surface speed is 0.2020509840 m/s. These are different model quantities for the same setup. Retain which speed the float estimates before comparing a surface observation with an average-flow calculation.

Use the record to test your explanation

Write a prediction before collecting the comparison, naming the quantity that should change and the condition you will alter. Keep a reference run and vary one factor at a time when the question calls for a controlled test. Record the selected apparatus settings, units, and measurement interval. Where an activity supplies Ideal and Real modes or seeded variation, retain that identity with each record rather than mixing incompatible runs in one calculation.

Separate an instrument reading or counted observation from the model relationship used to explain it. Keep raw values alongside derived results so another student can reconstruct the argument. A graph needs labeled axes and a stated comparison range. If a result differs from a reference, inspect the conditions, rounding, and measurement procedure before changing the explanation.

For a classroom discussion, compare claims supported by the same evidence and identify an additional measurement that would distinguish competing accounts. Finish with a claim, the relevant observations, and reasoning tied to this course's model. State a specific limitation instead of assigning a general error label to every disagreement.

Related investigations

Review flowing-fluid relationships in Fluid Flow, then connect land-use transport to Watersheds & Runoff. Distinguish water velocity, discharge, transported mass, and accumulated deposit when following a change through the modeled landscape.