Why does moving water drop its sediment, and in what order do particles settle out?
Explain how deposition occurs as transporting agents lose energy, and use the Reference Tables relationship of particle size to water velocity, together with particle size, shape and density, to predict settling order and sorting.
A Regents answer on deposition and sorting: how sediment is dropped when a transporting agent slows, the Reference Tables graph of transported particle size versus water velocity, why larger and denser particles settle first, horizontal and vertical sorting, graded bedding, and how rounded versus angular shape affects settling, with worked exam questions.
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What this topic is asking
The Regents wants you to explain deposition (why a slowing agent drops its load) and to use the Reference Tables Relationship of Transported Particle Size to Water Velocity graph, plus particle size, shape and density, to predict the order in which particles settle and how sediment becomes sorted.
Why deposition happens
Reading the particle-size graph
The Reference Tables graph plots stream velocity against the largest particle size the water can transport. The pattern the Regents tests:
- Faster water transports larger particles. A high velocity can move pebbles and boulders; a low velocity can move only sand, silt and clay.
- To find the largest particle a stream can carry, read up from the velocity to the curve, then across to the particle size.
- As a stream slows, the curve tells you which particles it can no longer carry, so those are deposited first (largest first).
What controls settling order
Sorting and graded bedding
Because settling depends on size, running water sorts sediment as it slows:
- Horizontal sorting: moving away from a fast source, particles get smaller (coarse gravel near the mountain front, then sand, then silt and clay far out, as in a delta).
- Vertical sorting (graded bedding): in a single layer deposited by slowing water, the coarsest particles are at the bottom and the finest at the top.
Sorted deposits (separated by size) are the mark of water and wind; unsorted deposits (all sizes mixed) are the mark of glaciers and gravity, which drop everything together.
Try this
Q1. State why a stream deposits sediment when it slows down. [1 point]
- Cue. It loses energy, so it can no longer carry its larger particles and drops them.
Q2. State the order in which boulders, sand and clay settle out of slowing water, and explain why. [2 points]
- Cue. Boulders, then sand, then clay; larger and denser particles need more energy to stay moving, so they settle first.
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (style)1 marksPart B-1. Using the Relationship of Transported Particle Size to Water Velocity graph, which is the largest particle a stream flowing at 100 cm/s can keep transporting? (1) clay (2) sand (3) pebbles (4) boulders. Justify your choice.Show worked answer →
A 1-point Reference Tables question. The answer is (3).
On the graph, a stream velocity of about 100 cm/s can transport particles up to about the size of pebbles (the curve crosses from sand into the pebble range near this velocity). Boulders (4) need much faster water; clay (1) and sand (2) are smaller and are carried easily but are not the largest the stream can move. The trap is reading the wrong axis; read up from 100 cm/s to the curve, then across to the largest particle size carried.
Regents (style)3 marksPart C. A fast mountain stream flows onto a flat plain and slows down. (a) Explain why the stream deposits sediment as it slows. (b) State the order in which boulders, sand and clay are deposited and why. (c) Describe what graded bedding (large particles at the bottom of a layer, fine at the top) tells you about the water.Show worked answer →
A 3-point extended-response question.
(a) 1 point: as the stream slows it loses energy, so it can no longer carry its larger particles and drops (deposits) them.
(b) 1 point: boulders are deposited first (nearest, where the water is still fastest), then sand, then clay last and farthest out, because larger and denser particles need more energy to stay moving and settle first.
(c) 1 point: graded bedding shows the water was slowing (or the flow was a single event that lost energy over time), so the largest particles settled first at the bottom and progressively finer particles settled on top.
Markers reward energy loss for deposition, the largest-first settling order, and the slowing-water interpretation of graded bedding.
Related dot points
- Identify the agents of erosion (running water, glaciers, wind, waves and gravity) and use the characteristic shapes and deposits of sediment to infer which agent transported it.
A Regents answer on erosion: the agents that transport sediment (running water, glaciers, wind, waves, gravity), why running water is the dominant agent, the tell-tale evidence each agent leaves (rounded versus angular particles, scratched and grooved bedrock, V-shaped versus U-shaped valleys, sorted versus unsorted deposits), with worked exam questions.
- Describe stream behavior and drainage patterns, and use topographic (contour) maps with the Reference Tables gradient equation to calculate gradient, determine stream flow direction and read elevations.
A Regents answer on streams and topographic maps: how stream velocity changes with gradient and discharge, the inside versus outside of meanders, reading contour lines, the rule that contour lines bend upstream (V points uphill), determining flow direction, and using the Reference Tables gradient equation, with worked exam questions and a full gradient calculation.
- Distinguish physical from chemical weathering, explain the factors that control the rate of weathering (climate, surface area, rock type), and describe how weathering and other processes form soil.
A Regents answer on weathering and soil: physical (mechanical) weathering such as frost wedging versus chemical weathering such as carbonation and oxidation, how climate, surface area and rock type control the rate, why warm wet climates weather chemically faster, and how soil forms as a mix of weathered rock and organic matter, with worked exam questions.
- Explain how sedimentary rocks form by compaction and cementation or by chemical and biologic processes, and how metamorphic rocks form by heat and pressure, using the Reference Tables charts to identify each by texture and composition.
A Regents answer on sedimentary and metamorphic rocks: clastic versus chemical and biologic sedimentary rocks, compaction and cementation, the role of fossils and sorting, foliated versus nonfoliated metamorphic rocks, contact and regional metamorphism, and how to use the Reference Tables identification charts, with worked exam questions.
- Explain how landscapes are classified (mountains, plateaus, plains) by elevation, relief and structure, how climate and bedrock control landscape development, and use the Reference Tables map of New York's landscape regions.
A Regents answer on landscapes: how mountains, plateaus and plains are classified by elevation, relief and rock structure, how climate (arid versus humid) and bedrock resistance shape landscape development, stream drainage patterns, and how to use the Reference Tables Generalized Landscape Regions and Bedrock Geology maps of New York, with worked exam questions.
Sources & how we know this
- Reference Tables for Physical Setting/Earth Science (2011 edition) — New York State Education Department (2011)
- Regents Examination in Physical Setting/Earth Science — New York State Education Department (2026)