NATSCI4_Flooding

Cards (43)

  • A flood is too much water in the wrong place.
  • A flood is the overflowing of water onto land that is normally dry.
  • Causes of flooding:
    1. Heavy rainfall
    2. Dam failure
    3. Storm surge
  • Tropical storm Ondoy hit the Philippines on September 26, 2009.
  • Tropical cyclones are warm-core low-pressure systems associated with a spiral inflow of mass at the bottom level and a spiral outflow at the top level.
  • Tropical cyclones form over oceans where sea surface temperatures are greater than 26 degrees Celsius.
  • Typhoons form in the western Pacific Ocean (Eastern Hemisphere).
  • Hurricanes form in the Atlantic and eastern Pacific (Western Hemisphere).
  • Cyclones form in the South Pacific and Indian Ocean.
  • Wind Signal 1 - Tropical Depression (TD) has 61 km/h or less
    Wind Signal 2 - Tropical Storm (TS) has 62-88 km/h
    Wind Signal 3 - Severe Tropical Storm (STS) has 89-117 km/h
    Wind Signal 4 - Typhoon (TY) has 118-184 km/h
    Wind Signal 5 - Super Typhoon (STY) has 185 km/h or higher
  • Cyclones in the Southern Hemisphere is where winds pass from high pressure to low pressure on the left (clockwise).
  • Cyclones in the Northern Hemisphere is where winds pass from high pressure to low pressure on the right (counter-clockwise).
  • In August 2009, there was a dam failure in Botolan, Zambales.
  • Storm surge is the abnormal rise of water generated by a storm, over and above the predicted astronomical tides.
  • A storm surge happened in Zamboanga City on November 28, 2007 due to Typhoon Mitang.
  • A storm surge happened in Panay on November 13, 2013 due to Super typhoon Yolanda.
  • The types of flooding according to location are:
    1. Coastal flooding (Shorelines)
    2. River flooding (River floodplains)
    3. Urban flooding (Paved roads & grounds)
  • Typhoon Ondoy caused both River and Urban Flooding in Metro Manila.
  • The types of flooding according to duration are:
    1. Flash flooding (upstream floods)
    2. Sheet flooding (downstream floods)
  • Flashfloods are floods of short duration with relatively high peak discharge.
  • The types of Flashfloods are:
    1. natural
    2. induced
  • Examples of induced flashfloods are:
    • Artificial damming of a river
    • breaching of dike
  • Sheet flood covers a large area and is not concentrated in a well-defined channel.
  • 243,425,000 m^3 of water were contributed by the Typhoon Ondoy in a span of 24 hours (can fill up 97,370 Olympic size swimming pools).
  • Typhoon Ondoy Flooding in the Metropolis: Contributory Factors
    • Occupation of areas along riverbanks and major floodways mainly by informal settlers
    • Indiscriminate disposal of waste/garbage
    • Inappropriate design of drain systems
    • Heavy siltation
    • Accumulation of water hyacinth
  • 2 Ways to Mitigate Flood Hazards
    1. Structural
    2. Non-structural
  • In Structural mitigation, there is the construction of physical barriers which consists of:
    • Artificial levees or dikes
    • Flood walls
    • Flood-control dams
    • Channelization
  • Artificial levees or dikes are usually built by piling soil, sand, or rocks on a cleared, level surface. Where the area beside a river or other body of water is in particular danger, levees may even be reinforced by concrete.
  • Flood walls are freestanding, permanent, engineered structure designed to prevent encroachment of floodwaters.
  • Flood-control dams keep floodwaters impounded and either release floodwaters in controlled amounts downstream to the river below or store or divert water for other uses.
  • Channelization is the straightening, deepening, widening, enlarging, clearing, or lining any existing stream channel.
  • In Non-structural mitigation, there is:
    • Land use planning/floodplain zoning
    • Flood hazard mapping
  • The symbol for Tropical Depression is D.
  • The symbol for Tropical Storm is S.
  • The symbol for Severe Tropical Storm is a hollow cyclone symbol.
  • The symbol for Typhoon is T.
  • The symbol for Super Typhoon is an all black cyclone symbol.
  • A coastal flooding happened in Tacloban City on November 10, 2013 due to Typhoon Yolanda.
  • An example of river flooding is in Marikina River.
  • An example of urban flooding is in Cainta, Rizal on September 26, 2009 due to Typhoon Ondoy