4.3 Groundwater & Landscape Development

Porosity vs. Permeability

Groundwater is water stored in the spaces inside soil and rock. Two properties control how much water a material holds and how easily it moves, and the Regents tests the difference relentlessly.

• Porosity is the percentage of a material's volume that is open pore space. It controls how much water a material can hold.
• Permeability is the rate at which water passes through a material. It controls how fast water moves.

The key fact most students get wrong: for loose, rounded sediment of the same shape, porosity is independent of particle size. A box of marbles and a box of tiny beads have the same percentage of empty space, so they have the same porosity, even though the particles differ wildly in size.

Permeability, by contrast, depends strongly on particle size. Larger particles leave larger pore spaces, so water flows through coarse gravel quickly (high permeability) but creeps through fine clay slowly (low permeability), even though clay can be very porous. Sorting matters too: well-sorted sediment is more permeable because pores stay open, while poorly sorted sediment has small grains plugging the gaps between large ones.

The Water Table, Saturation, and Capillarity

Water that infiltrates the ground sinks until it fills all available pore space. This creates two zones:

• The zone of saturation, where all pores are full of water.
• The zone of aeration above it, where pores hold mostly air.

The water table is the top surface of the zone of saturation, the boundary between the two zones. It is not flat: it generally mirrors the surface topography, rising under hills and meeting the surface at lakes, springs, and wetlands. The water table drops in droughts and rises after heavy infiltration.

Capillarity (capillary action) is the upward movement of water through tiny connected pore spaces, against gravity, caused by water's attraction to surfaces. The smaller the spaces, the higher water climbs:

Note the apparent paradox: fine clay has high porosity and high capillarity but low permeability. The tiny pores hold a lot of water and lift it far, but choke the flow. This combination is a classic Regents discriminator.

The Water Cycle

The water cycle (hydrologic cycle) continuously moves water among the oceans, atmosphere, and land, driven by solar energy and gravity. Total water on Earth is conserved, it just changes form and location. The main processes:

1. Evaporation: liquid water becomes water vapor (mostly from the oceans).
2. Transpiration: plants release water vapor through their leaves (evaporation + transpiration together = evapotranspiration).
3. Condensation: vapor cools and forms cloud droplets.
4. Precipitation: rain, snow, sleet, or hail returns water to the surface.
5. Runoff: water flows over the surface into streams, lakes, and oceans.
6. Infiltration: water soaks into the ground to recharge groundwater.

Whether precipitation becomes runoff or infiltration depends on slope, soil permeability, vegetation, and how saturated the ground already is. Steep, paved, or frozen ground forces water into runoff, the link the Human Sustainability strand uses for flooding and polluted-runoff questions.

Landscape Regions of New York

A landscape region is an area with similar surface characteristics, bedrock, and elevation. New York is divided into three broad landscape types, distinguished using the ESRT Generalized Landscape Regions of New York State and Generalized Bedrock Geology maps:

• Mountains: high elevation, steep slopes, and high relief, with old, often deformed (tilted or folded) bedrock. The Adirondacks (metamorphic and igneous rock) and the Catskills (technically a dissected plateau) stand out.
• Plateaus: high but relatively flat-lying sedimentary bedrock, deeply cut by streams into steep valleys. The Allegheny Plateau covers much of southern New York.
• Plains (and Lowlands): low elevation, low relief, gentle slopes, often underlain by easily eroded rock. The Atlantic Coastal Lowlands (Long Island) and the Erie-Ontario Lowlands are examples.

Two controls shape these regions:

• Bedrock resistance and structure: resistant rock and uplifted, deformed structures stand high as mountains; weak, flat-lying rock erodes into plains.
• Climate: wet climates favor rounded, stream-carved landscapes; arid climates leave angular, steep features. New York's humid climate and Ice Age glaciers together produced its rounded uplands and broad U-shaped valleys.

Stream Drainage Patterns

The arrangement of streams across a landscape, its drainage pattern, reflects the underlying bedrock structure and slope. Three patterns are tested:

• Dendritic: a branching, tree-like pattern that forms on uniform bedrock with no strong structural control; the most common pattern.
• Radial: streams flow outward in all directions from a central high point, such as a volcano or dome.
• Trellis: streams meet at right angles where alternating bands of hard and soft tilted or folded rock channel them, common in ridge-and-valley terrain.

Reading the pattern lets you infer the geology beneath: a dendritic pattern signals uniform rock and a gentle regional slope, while a trellis pattern signals tilted layers of differing resistance. This ties surface processes back to the structural and tectonic story of the Earth's Systems strand and completes the cycle from weathering through erosion, deposition, groundwater, and the shaping of whole landscapes.