How does water move through Earth's systems, and what controls how much soaks into the ground?
Describe the water cycle and its processes, and explain the factors that control infiltration, runoff and groundwater storage (porosity, permeability, slope, saturation and the water table).
A Regents answer on the water cycle and groundwater: evaporation, transpiration, condensation, precipitation and runoff, the factors that control infiltration versus runoff (porosity, permeability, particle size, slope, saturation, vegetation), the water table and zones of saturation and aeration, and the energy that drives the cycle, with worked exam questions.
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What this topic is asking
The Regents wants you to describe the water cycle and to explain what controls infiltration versus runoff and groundwater storage: porosity, permeability, particle size, slope, saturation and the water table. The defining contrast is porosity (how much space) versus permeability (how easily water flows through).
The water cycle
Infiltration versus runoff
When precipitation reaches the ground it either infiltrates or runs off. The balance is set by several factors:
- Porosity: the percentage of a material that is open pore space. More pore space can hold more water.
- Permeability: how easily water can pass through a material; it depends on pore size and how connected the pores are. High permeability means fast infiltration.
- Particle size and sorting: large, well-sorted particles (gravel) leave big connected pores (high permeability); fine particles (clay) have tiny pores that grip water (low permeability).
- Slope: water runs off steep slopes before it can soak in; gentle slopes favor infiltration.
- Saturation: if the ground is already saturated (pores full), more water cannot infiltrate, so it runs off.
- Vegetation: plants slow surface flow and hold soil, increasing infiltration.
Groundwater and the water table
A water-bearing layer that is permeable enough to supply water is an aquifer; an impermeable layer that blocks flow is an aquiclude (often clay).
Try this
Q1. Name the process by which plants release water vapor to the atmosphere. [1 point]
- Cue. Transpiration.
Q2. Explain the difference between porosity and permeability. [2 points]
- Cue. Porosity is the percentage of open pore space in a material; permeability is how easily water can pass through it (depending on pore size and connection).
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 A. Which factor would most increase the amount of rainfall that runs off the surface rather than soaking into the ground? (1) flat land with sandy soil (2) a steep slope with saturated clay soil (3) thick vegetation on level ground (4) dry, permeable gravel. Justify your choice.Show worked answer →
A 1-point multiple-choice question. The answer is (2).
Runoff increases on a steep slope (water flows off before it can soak in) and when the soil is saturated clay (clay has low permeability, and saturated ground cannot accept more water). Flat sandy soil (1) and dry permeable gravel (4) favor infiltration, and thick vegetation on level ground (3) slows water and promotes soaking in. The trap is choosing a permeable option; permeability and a gentle slope reduce runoff, while a steep slope plus saturated, low-permeability soil maximizes it.
Regents (style)3 marksPart C. (a) Name the process that returns water vapor to the atmosphere from plants. (b) Explain the difference between porosity and permeability. (c) A sample of well-rounded, well-sorted gravel and a sample of clay receive the same rainfall. Explain which allows water to infiltrate faster and why.Show worked answer →
A 3-point extended-response question.
(a) 1 point: transpiration (the release of water vapor from plant leaves).
(b) 1 point: porosity is the percentage of open space (pores) in a material; permeability is how easily water can pass through it (connected pores allow flow).
(c) 1 point: the gravel infiltrates faster, because its large, well-connected pore spaces give high permeability; clay has tiny pores that hold water tightly, so it has low permeability even though it can be porous.
Markers reward transpiration, the porosity-versus-permeability distinction, and the gravel-faster reasoning based on pore size and permeability.
Related dot points
- Explain how ocean surface currents form (winds, the Coriolis effect) and how they redistribute heat, moderate coastal climates and connect to density-driven deep circulation.
A Regents answer on the oceans: how prevailing winds and the Coriolis effect drive surface currents into gyres, how warm and cold currents redistribute heat and moderate coastal climates (for example the Gulf Stream), the difference between surface and density-driven deep circulation, and the link to the water specific heat on the Reference Tables, with worked exam questions.
- Describe the layered structure and composition of the atmosphere and explain how energy is transferred by radiation, conduction and convection, including how surfaces absorb and reflect insolation.
A Regents answer on the atmosphere and energy transfer: the layered structure (troposphere to thermosphere) and temperature profile on the Reference Tables, the composition (nitrogen, oxygen, trace gases), the three modes of heat transfer (radiation, conduction, convection), and how surface color and texture affect the absorption and reflection of insolation, with worked exam questions.
- Explain humidity, dewpoint and relative humidity, use the Reference Tables dewpoint and relative humidity charts from dry-bulb and wet-bulb readings, and relate cooling to condensation, cloud and precipitation formation.
A Regents answer on atmospheric moisture: the difference between dewpoint and relative humidity, how to read the Reference Tables dewpoint and relative humidity charts from the dry-bulb temperature and the wet-bulb depression, why air cooled to its dewpoint condenses, how clouds and precipitation form on condensation nuclei, and the saturation idea, 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.
- Describe how carbon cycles among the atmosphere, biosphere, hydrosphere and geosphere through photosynthesis, respiration, decomposition and combustion, and explain how human activities alter the carbon cycle.
A Regents answer on the carbon cycle: how carbon moves among the atmosphere, biosphere, hydrosphere and geosphere through photosynthesis, respiration, decomposition and combustion, the role of carbon sinks (oceans, forests, fossil fuels), and how burning fossil fuels and deforestation move stored carbon into the air, 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)