Introduction to Hydrology

• Hydrology is the science of water ('Hydro' means Water and 'Logy' means Science).
• Hydrologists are scientists gathering data on precipitation, runoff, stream flow, and snowpack within hydropower plant watersheds.

Three Main Types of Hydrology

• Surface water hydrology studies water movement and distribution on Earth’s surface.
• Groundwater hydrology deals with the occurrence, movement, and quality of water beneath Earth’s surface.
• Watershed hydrology studies water behavior within a specific drainage basin or watershed.

Importance of Hydrology in Civil Engineering

• Flood control and drainage design
• Groundwater management
• Soil erosion and landslide prevention
• Climate change adaptation

Applications of Hydrology

• Flood control and management include flood forecasting and early warning systems, urban drainage design, and floodplain mapping.
• Water resources management involves reservoir & dam operation, sustainable groundwater management, and irrigation planning.
• Climate change impact assessment includes drought and water scarcity prediction, sea-level rise monitoring, and glacier & snowmelt studies.
• Desalination & water treatment includes reverse osmosis optimization and solar-powered water purification.

Difference Between Hydrology and Hydraulics

• Hydrology studies the movement, distribution, and properties of water on Earth
• Hydraulics studies the behavior of fluids (mainly water) in motion and at rest, especially in engineered systems
• Hydrology is concerned with the occurrence, circulation, and distribution of water in the atmosphere, surface, and subsurface.
• Hydraulics concerns the mechanical properties of water including pressure, flow, and resistance in channels, pipes, and other structures.
• Applications of hydrology include flood forecasting, water resource management, groundwater studies, rainfall analysis, and climate impact studies.
• Applications of hydraulics include the design of dams, irrigation systems, pipe networks, drainage systems, and water treatment plants.
• Hydrology focuses on natural water movement, while hydraulics deals with engineered flow systems.
• Both hydrology and hydraulics are important for infrastructure planning, flood control, and water supply systems.
• Hydraulics is more physics-based, while hydrology incorporates statistical and environmental factors.

Components of Hydrology

• Surface water includes rivers, lakes, and reservoirs, essential for drinking water, irrigation, and energy production.
• Groundwater is water stored in underground aquifers, crucial for wells and springs.
• Watersheds and drainage basins are land areas that channel precipitation into streams and rivers.
• Hydrological processes involve infiltration, percolation, and groundwater recharge.

Hydrologic or Water Cycle

• Evaporation is the process of liquid water transforming into water vapor (gas), primarily occurring from oceans, lakes, and rivers due to solar heating. Factors include temperature, humidity, wind speed, and water surface area.
• Condensation is the change of water vapor into liquid water droplets. As warm air rises and cools, water vapor condenses to form clouds.
• Precipitation is water released from clouds in the form of rain, snow, sleet, or hail. Cloud droplets grow large enough to overcome air resistance and fall to Earth, replenishing surface and groundwater supplies.
• Runoff is water flowing over land to bodies of water, influenced by soil saturation, land slope, and vegetation.
• Infiltration is water seeping into the ground, replenishing aquifers and soil moisture.
• Groundwater flow is underground water movement through soil and rock, stored in aquifers for extended periods.
• Collection is the accumulation of water in water bodies; Accumulated water evaporates and continues the cycle.

Importance and Benefits of the Water Cycle

• Maintains Water Availability: Replenishes groundwater through infiltration.
• Supports Life and Ecosystems: Provides essential water for plants, animals, and humans.
• Purifies Water Naturally: Evaporation removes impurities, leaving behind salts and contaminants.
• Prevents Flooding and Droughts: Runoff directs excess water, and groundwater storage maintains water availability.
• Supports Agriculture and Food Production: Rainfall nourishes crops and livestock.
• Essential for Human Health and Sanitation: Supports sanitation and hygiene.

Human Impact on the Hydrologic Cycle

• Urbanization: Reduces natural infiltration, increasing surface runoff and flood risks.
• Deforestation: Disrupts rainfall patterns and reduces water retention in soil.
• Agriculture: Alters natural water distribution.
• Pollution and Climate Change: Contaminates water bodies and impacts precipitation patterns, worsening weather conditions.

Stages of the Hydrologic Cycle

• Evapotranspiration: total losses of water from vegetation.
• Evaporation is from the soil, and transpiration is from the plants.
• Precipitation is the total amount of water falling in a given area: rain, hail, or snow.
  • Orographic: Involves moist air mass rising on the windward side of a mountain.
  • Convectional: The land warms up and heats the air above it.
  • Frontal: The moist air mass rises on the windward side of a mountain.
• Infiltration: the process of precipitation absorbed into subsurface soils and rocks.
• Percolation: movement of water through soil.
• Surface and Subsurface Runoff: precipitation that did not absorbed into the soil.
  • Surface runoff, otherwise known as overland flow.
  • Subsurface runoff flows below the surface and remains above the water table.

Factors Affecting Infiltration and Percolation

• Soil texture and structure are how water enters soil is transmitted downward, and must be fairly rapid.
• Conditions at the soil surface, this is whether the subsoil drainage is excellent or have sealed pores due to turbid.
• Soil moisture content affects the rate in high and dry soils.
• Type of vegetative cover affects how the entry is protected.
• Soil temperature affects whether the soil is impermeable to water.
• Human Activity on Soil Surface causes compaction.

Runoff

• Occurs when rain does not seep into soil, which proceeds to bodies of water.

Types of Runoff

• Surface Runoff is the unconfined flow of water over ground surfaces.
  • Hortonian flow causes excess water into the soil.
  • Saturation-Excess causes excess water due to land being too saturated.
• Subsurface Runoff occurs where water flows though soil layers.

Watersheds and Drainage

• Watersheds capture several forms of precipitation and water sources including snow, and funnels it all towards a common outlet including rivers, etc.

Main sources of water

• Rainwater - can be sustainable. Challenges can include contamination.
• Groundwater - can be well-protected. Challenges can include depletion over usage.
• Surfacewater - can be easy to store, but is vulnerable to contamination.

Watershed Information

• They help to absorb the risk of flood. Watersheds especially play a vital role in impacting nearby heavy communities.
• It is essential for ecosystems with various wildlife and the like.
• They supply freshwater that enables management for water resources for drinking and other water uses and needs
• Well-Known watersheds in the Philippines consist of
  • Cagayan
  • Angat
  • Ilog
  • Agusan
  • Bicol

Watershed Delineation

• Is identifying and marking the boundaries of all land area, where waters converge into single outlets.
• Drainage is the land area that drains into a specific outlet.

Important of Watershed Delineation

• Defines boundaries of all watersheds.
• Accurately flood forecasts more vulnerable areas.
• It is essential for water resources management.
• Provides information to create hydrological water models.

Sub-Basins

• Sub basins are typically localized hydrological areas.

Importance of Sub Basin Analysis

• Localized water and flood management
• Assess soil and water quality.
• Plays a role in ecosystem protection

Physical Properties Determination

• Topography measures the slope and elevation of land affecting water
• Land Use is a measure of urbanization for water response
• Vegetation impacts are important for water retention

Soil Types

• Clay Soil tends to retain water longer, and has high erosion qualities in heavy rain.
• Loam Soil has a balance of silt, sand, and clay. Is ideal for agriculture.
• Sandy Soil has high permeability but tends to not retain water.

Applications of Water Projects

• In general, water projects essential in hydrological modeling, agricultural development, infrastructure planning, and environmental conservation

Factors Affecting the Hydrological Cycle

• Surface and Natural (Factors)
  • Climate
  • Type of Surface
  • Vegetation
  • Soil Type
• Human (Factors)
  • Deforestation
  • Industrialization
  • Urbanization
  • Buildings