Introduction to Hydrology

Introduction to Hydrology

• Hydrology is the science of water, dealing with its occurrence, circulation, and distribution in the Earth's atmosphere and lithosphere.
• It is a branch of Earth science focused on water in streams, lakes, rainfall, snowfall, snow, ice, and subsurface water in soil and rocks
• Hydrology is an applied science, often classified as scientific hydrology (academic aspects) and engineering/applied hydrology (engineering applications).
• Engineering hydrology deals with water resource estimation, studying processes like precipitation, runoff, evapotranspiration, and strategies to combat floods and droughts.
• Hydrologists help solve water-related problems using their knowledge and oversee activities to protect the water environment

Hydrologist Tasks

• Design and operation of hydraulic structures
• Water Supply
• Wastewater treatment and disposal
• Irrigation/Drainage
• Hydropower generation
• Flood control/Navigation
• Erosion/Sediment control

Hydrologic Engineering Design

• Provides a service and the level of service and acceptable risk of failure must be determined
• Is constrained by cost and site
• Occurrence, timing, and water amount are vital aspects from an engineering perspective
• Lack or excess of water can cause problems

Hydrology vs. Hydraulics

• Hydrology relies on observations generalized to practice (e.g., estimating maximum rainfall or streamflow from a storm)
• Hydraulics begins with basic principles and then approximates for practice (e.g., determining flow depth in a channel or working with manmade systems)
• Surface water hydrology provides inputs like maximum flow rate for hydraulics

Hydrologic Cycle

• The water cycle involves continuous water circulation in the Earth-atmosphere system
• Key processes are evaporation, transpiration, condensation, precipitation, and runoff
• The total water amount in the cycle remains constant, but its distribution changes

Evaporation

• Physical state of water changes from a liquid to a gaseous state
• Affected by solar radiation, temperature, vapor pressure, wind, and atmospheric pressure.
• It occurs from raindrops, free water surfaces, vegetation, soil, rocks, and snow

Condensation

• The process by which water vapor turns into liquid form
• Water vapor condenses on airborne particles and forms fog or clouds
• Cooled air or increases in the amount of vapor in the air to saturation point, can cause condensation

Precipitation

• Any form of water particles falling from the atmosphere to the ground.

Interception

• Interception interrupts the movement of water in the events of transportation of water leading to streams.
• Occurs via vegetal cover or depression storage like puddles and land formations

Infiltration

• Physical process that involves the movement of water through the boundary where the atmosphere meets the soil.
• Is related to soil surface conditions, porosity, and soil profile permeability

Percolation

• Movement of water through the soil layers from gravity and capillary forces.

Transpiration

• Biological process where water inside plants is transferred to the atmosphere, mostly during the day.

Runoff

• Flow from a drainage basin/watershed that appears in surface streams.
• Composed of precipitation falling on the stream, surface runoff, subsurface runoff, and groundwater runoff from deep percolation

Storage

• Water is stored in the atmosphere, on the earth's surface, and the ground

Weather Basics - Meteorology

• Meteorology studies the atmosphere and its phenomena, especially the weather
• Weather is a mix of conditions that vary over time and location
• Most weather occurs in the troposphere
• Weather can be categorized as wind, precipitation, temperature, sunshine, humidity, pressure, what kind of clouds exist, and visibility

First Set of Weather Elements

• The sun heats the Earth unevenly, causing air pressure changes and wind

Climate

• Climate is the average weather conditions in a specific location over a long period
• Climate is determined by rainfall, temperature, latitude, elevation, and ocean currents

Climate of the Philippines

• Tropical and maritime, characterized by high temperature, high humidity, and abundant rainfall.
• The mean annual temperature (excluding Baguio) is 26.6°C; January is the coolest (25.5°C) and May is the warmest (28.3°C)
• Latitude has little effect on the variation of temperature.
• Altitude has a big impact on temperature, like Baguio with 18.3°C with an elevation of 1,500 meters.
• Humidity is high, ranging from 71% in March to 85% in September

Rainfall in the Philippines

• The is the climatic factor in the Philippines
• Annual rainfall varies from 965 to 4,064 mm annually,
• High rainfall occurs in Baguio City, eastern Samar and Surigao.
• Minimum rainfall occurs in Cotabato.
• General Santos City rainfall is 978 millimeters

Seasons in the Philippines

• Rainy (June-November) and dry (December-May)
• Dry season has cool (December-February) and hot (March-May) seasons.

Climate Types

• I: Two main seasons (dry from November-April, wet the rest of the year)
• II: No dry season, maximum rain from December-February
• III: Short (1–3 month) dry season, maximum rain
• IV: Evenly distributed rainfall

Climate Influences

• Typhoons greatly influence the Philippines' climate and weather
• Most come from the Marianas and Caroline Islands, moving northwestward and sparing Mindanao
• The movements follows a northwesterly, sparing Mindanao, and making the southern Philippines desirable for agriculture and industrial development