The Water Cycle: Runoff and Infiltration

The Water Cycle: Runoff and Infiltration

• Water Cycle Components: Water exists in three states: liquid (rivers, lakes, oceans), solid (ice, snow), and vapor (air moisture, clouds). The water cycle involves these states changing and moving.
• Water Movement: Precipitation (rain, snow, sleet, hail) falls to Earth. Water can collect, runoff, infiltrate the ground, or be absorbed by plants/animals. Evaporation and transpiration return water to vapor form, completing the cycle.
• Runoff Defined: Runoff is water that flows across the land surface due to excess precipitation. It cannot be absorbed. It eventually reaches streams, rivers, and then the ocean.
• Infiltration Defined: Infiltration is the process of water soaking into the ground. It moves into soil pores and rock cracks. Gravity and capillary action pull the water downward.

Runoff in the Water Cycle

• Runoff Trigger: Runoff occurs when rainfall exceeds the ground's ability to absorb it.
• Runoff Path: Water from runoff travels downhill through various channels—ditches, creeks, ravines—eventually joining rivers and lakes, flowing towards the ocean.
• Runoff Factors:
  • Soil Type: Impermeable surfaces (concrete, granite) lead to more runoff. Saturated ground also creates runoff.
  • Precipitation Type & Rate: Heavy rainfall or rapid snow melt causes more runoff.
  • Topography: Steep slopes lead to quicker runoff.
  • Vegetation: Dense vegetation promotes infiltration.
• Runoff Process: Water accumulates as precipitation, flows across land surfaces to lower elevation, collects in waterways, and ends up in oceans. Parts evaporate, infiltrate, or get used by plants and animals.
• Runoff Outcomes: Runoff can cause erosion (moving materials) and deposition (dropping materials). It transports pollutants, which can harm ecosystems.

Effects of Runoff

• Erosion and Deposition: Runoff moves soil, rocks, and nutrients. This can damage farms.
• Pollution Transport: Runoff carries pollutants from various sources into waterways, harming aquatic life.
• Sedimentation: Runoff can deposit sediment in lakes and estuaries.
• Algae Blooms: Nutrients transported by runoff can lead to harmful algae blooms.

Infiltration in the Water Cycle

• Infiltration Defined: Infiltration is water seeping into the ground.
• Infiltration Conditions: Porosity (water holding capacity) and permeability (water flowing rate) are crucial for infiltration.
• Infiltration Factors:
  • Soil Type: Porous and permeable soils lead to more infiltration.
  • Vegetation: Plant roots and organic matter aid infiltration.
  • Slope and Elevation: Shallow slopes and low-lying areas facilitate infiltration.
  • Temperature: Warmer soil leads to faster infiltration than frozen soil.

Infiltration Process

• Water moves into the soil, filling pore space and cracks.
• Gravity and capillary action drive the downward movement.
• Infiltrated water replenishes groundwater and creates aquifers.
• Eventually, water reaches an area where the ground is fully saturated (water table).

Rate of Infiltration

• Infiltration Rate: Measured in inches per hour and depends on soil type and conditions.
• Influences:
  • Grain size (larger, less tightly packed = faster)
  • Vegetation (roots and organic matter)
  • Slope (shallow = slower)
  • Rainfall rate (slower rain = better absorption)

Infiltration Examples

• Impermeable Materials: Granite, concrete. These materials obstruct water absorption.
• Permeable Materials: Limestone (can create aquifers). Sand (high porosity and permeability). Clay (High porosity, low permeability).

This quiz explores the fundamental concepts of the water cycle, focusing on the processes of runoff and infiltration. You will learn about the various forms of water, how it moves through the environment, and the significance of these processes in natural ecosystems. Test your understanding of these key components of hydrology.