HYDROLOGY-MIDTERM EXAM REVIEWER

Chapter 1
Hydrology and the Hydrologic Cycle
Hydrology-A science dealing with the properties, distribution, and
circulation of water on and below the earth's surface and in the
atmosphere.
HYDROLOGY
It is the science which deals with terrestrial waters, their occurrence,
circulation and distribution on our planet, their physical and chemical
properties and their interaction with the physical and biological
environment, including the effect on them of the activity of man.
(UNESCO, 1964)
Science that deals with the processes governing the depletion and
replenishment of water resources of the land areas of the Earth, and
treats the various phases of the hydrological cycle. (WMO, 1992)
The study of water in all its forms and from all its origins to all its
destinations on the Earth. (Bras, 1990)
Deals with the natural occurrence, distribution and circulation of water
on, in and over the surface of the Earth. (Horton, 1931)
Difference between hydrology and hydraulics
Hydrology is defined as the circulation of water and its constituents
through the hydrologic cycle, or the quantification of flows that are
ultimately produced by precipitation.
Hydraulics is defined as the study of the mechanical behavior of water
in physical systems (Henry M. Morris and James M. Wiggert). In
engineering terms, hydraulics is the analysis of how surface, and/or
subsurface flows move from one point to the next.
Hydraulic analysis is used to evaluate flow in rivers, streams, storm
drain networks, water aqueducts, water lines, sewers, etc.
Hydrologists apply scientific knowledge and mathematical principles to
solve water-related problems in society: problems of quantity, quality
and availability.
The human impact on the hydrological cycle can be subdivided into
three main areas:
1. Water quantity.
2. Water quality.
3. Water ecology.
Human activities can be divided into the following categories:
1. Surface water regulation such as rivers and lakes.
2. Water abstractions and release.
3. Activities in the catchments
Human Interventions in the Hydrological Cycle
Rivers, lake, and estuary regulation
Damming, building and management of river reservoir
Lake regulation
Estuary regulation
Water abstraction and release
Surface water abstraction/release
Surface water abstraction/release
Groundwater abstraction/release
Activities in Catchment
Change in land use
Common Aquifer Types
Water Table
Alluvial Aquifer
Bedrock Aquifer (Confined or Confined)

CHAPTER 2-HYDROLOGY
Hydrologic Cycle-A conceptual model that describes the STORAGE
and MOVEMENT of water.
In meteorology, the term precipitation is any product of the
condensation of atmospheric water vapour that falls under gravity.
Precipitation is the basic input to hydrology.
A common unit for precipitation is mm per time unit (e.g. mm/hour,
mm/day, mm/month, mm/year).
Factors determining precipitation or the amount of atmospheric
moisture over a region:
Climate
Geography
Ocean surfaces is the chief source of moisture for precipitation.
Forms of Precipitation(DMFRHS)
Dew
Mist
Fog
Rain
Hail
Snow
Rain-the most common type of precipitation in our atmosphere.
Two Different Forms of Rain:
Showers
Drizzles
Showers-are heavy, large drops of rain and usually only last a period of
time.
Drizzles-usually last longer and are made up of smaller droplets.
Light
I=2.55mm/hr
Moderate
I=2.8-7.6mm/hr
Heavy
I>7.6mm/hr
Mist-is a bunch of small droplets of water which are in the air.
Fog-is a cloud that has formed near the surface of the Earth.
Four Main Types of Fogs(RAUE)
Radiation Fog
Advection Fog
Upslope Fog
Evaporation Fog
Dew-small drops of water which can be found on cool surfaces like
grass in the morning.
Dew Point-temperature in which condensation starts to take place or
when dew is created.
Radiation Fog: This fog forms when all solar energy exits the earth and
allows the temperature to meet up with the dew point.
Advection Fog: This type of fog forms from surface contact of
horizontal winds. This fog can occur with windy conditions.
Upslope Fog: This fog forms adiabatically. Adiabatically is the process
that causes sinking air to warm and rising air to cool. As moist winds
blow toward a mountain, it up glides and this causes the air to rise and
cool. Evaporation Fog: This type of fog forms when sufficient water
vapor is added to the air by evaporation and the moist air mixes with
cooler, relatively drier air.
Snow-is the second most common precipitation in the North East. Forms
when water vapor turns directly into ice without ever passing through a
liquid state.
Hail-is created when moisture and wind are together. Inside the
cumulonimbus clouds ice crystals form, and begin to fall towards the
Earth’s surface.
Shapes of Hail Particles
Spherical
Conical
Irregular
Graupel, also called soft hail, hominy snow, or snow pellets, is
precipitation that forms when super cooled water droplets in air are
collected and freeze on falling snowflakes, forming 2–5 mm balls of
crisp, opaque rime.
Rime-is the white opaque deposit of ice granules more or less separated
by trapped air and forms by rapid freezing of super cooled water drops
impinging on exposed objects.
Sleet-consists of transparent, globular, solid grains of ice formed by the
freezing of raindrops or freezing of largely melted ice crystals falling
through a layer of sub freezing air near the earth’s surface.
Glaze-is the ice coating, generally clear and smooth, formed on exposed
surfaces by the freezing of super cooled water deposited by rain or
drizzle.
Formation of Precipitation
Collision and Coalescence: cloud droplets of varying sizes bump into
each other, forming large droplets. The larger they grow, the heavier
they get, and the faster they fall.
Ice-Crystal Process: also known as Bergeron process. This occurs
when both ice crystals and water droplets are in the cloud.
Mechanisms of Precipitation Formation
 A moisture source must be available,
 Lifting mechanism to cool the air
 Formation of cloud elements (droplets/ice crystals)
 Growth of cloud elements
Lifting Mechanism to Cool the Air
Cyclonic Precipitation (Frontal/NonFrontal)
Convective Precipitation
Orographic Precipitation
Cyclonic precipitation is caused by the lifting of an air mass because of
the pressure difference.
Frontal Precipitation – when two air masses, because of contrasting
densities and temperatures, clash with each other, precipitation and
condensation occurs in the surface of contact.
Non-Frontal Precipitation – the moist warm air mass is stationary and
the moving cold air mass meets it. When the lifted warm air cools down
at higher altitude, precipitation occurs.
Convectional precipitation results from the heating of the earth’s
surface that causes air to rise rapidly.
Orographic Precipitation-It results when warm moist air of the ocean
is forced to rise by large mountains.
Measurement of precipitation can be done by various
devices. The measuring devices and techniques are:
1. Rain Gauges
2. Snow Gauges
3. Radars
4. Satellites
5. Scratching of snow packs
6. Water equivalent in snow packs
Rain gauge is an instrument used by meteorologists to measure the
amount of rainfall over a period of time.
There are two main types of rain gauges:
1. Non-Recording rain gauges
2. Recording rain gauges
A. Non-Recording Rain Gauges
Symon’s rain gauge – consist of a circular area of 12.7 cm diameter
connected to the funnel and the rim of the collector is set in a horizontal
plane at a height of 30.5 cm above the ground level.
B. Recording Rain Gauges-These rain gauges are also called
integrating rain gauges since they record cumulative rainfall. It is also
called accumulation rain gauges.
Three main types of recording rain gauges:
1. Tipping bucket rain gauge
2. Weighing type rain gauge
3. Float type rain gauges
Tipping bucket gauges-is used for measurement of rainfall with a least
amount of 1mm and gives out one electrical pulse for every millimeter
of rainfall.
Weighting Type gauges- consists of a storage bin, which is weighed to
record the mass.
Float Recording Gauges-The rise of float with increasing catch of
rainfall is recorded.
Weather Radar-is a type of radar used to locate precipitation, calculate
its motion, estimate its type, and forecast its future position and
intensity.
Weather Satellite-is a type of satellite that is primarily used to monitor
the weather and climate.

CHAPTER 2 PART 2
SOLVINGS
CHAPTER 3
INFILTRATION
Infiltration-Defined as the entry and movement of water through the
land surface into the substrata below.
Factors Influencing Infiltration Capacity
1. Precipitation-The amount, intensity and duration of precipitation
affect the rate of infiltration.
2. Type of Soil (structure, texture, porosity)-A loose, permeable,
sandy soil will have a larger infiltration capacity than a tight,
clayey soil.
Dry soil has more infiltration capacity than moist or saturated soil
3. Impact of raindrops – also called battance. This results to the
compaction of the soil surface.
4. Topography and morphology - a steep slope increases surface
flow at the expense of infiltration.
Steeper slope = more runoff and less infiltration
5. Degree of saturation - the infiltration rate over time will evolve
differently depending on the initial condition of the soil.
More saturation= more runoff and less infiltration
6. Soil cover - vegetation has a positive influence on infiltration.
Vegetation intercepts falling precipitation and slows it down
More vegetation = more infiltration
7. Land Use-Roads, parking lots, buildings…creates impermeable
surfaces which leads to more runoff.
8. Temperature – infiltration capacity increases with atmospheric
temperature.
9. Fluid characteristics – the turbidity of the water, especially the
clay and the colloid content is an important factor and such
 suspended particles block the fine pores and reduce its infiltration
capacity.
10. Water supply – refers to the intensity of precipitation or the
irrigation water rate.
11. Entrapped air in the unsaturated zone, which tends to
reduce infiltration – can greatly affect the hydraulic conductivity
at or near saturation
12. Freezing – freezing in winter may lock pores
13. Annual and seasonal changes – according to change in land
use pattern. Except for massive deforestation and agriculture
Infiltration rate – the rate at which the water actually infiltrates through
the soil.
Infiltration capacity - the maximum rate at which a soil is capable of
absorbing water in a given condition.
Methods of Determining Infiltration
Infiltrometers-is a device used to measure the rate of water infiltration
into soil or other porous media.
Observation in pits and ponds-
Placing a catch basin below a laboratory sample
Artificial rain simulators
Hydrograph analysis