Floodplains And Floodplain Management Flashcards
What are the three most common types of floods?
Riverine, coastal and shallow flooding
LIST some examples of shallow flooding.
Poor urban drainage, sheet flow, ponding
Is mudflow a form of flood?
If the mud flow is caused by a precipitation event yes, if it is just dry earth that is just a land slide type of erosion
What type of terrain is susceptible to flash floods?
Hilly or mountainous areas, with steep slopes and narrow valleys
How is the speed of flood waters measured?
Velocity
Define overbank flooding
When downstream channels recieve more water than normal, or channel is blocked by ice jam, excess water overloads the channel and flows onto the floodplain
What type of flood has caused the most flood-related depths and why?
Flash floods are most dangerous and destructive due to high-velocity flows and short warning time.
What are the 3 types of Riverine Flooding?
Overbank flooding
Flash flooding
Riverine erosion
How can river channels change with flooding?
Velocity of flood water scours the riverbank and can alter the thalweg or channel bottom geometry.
The pattern of meanders can change as the outermost curve is eroded, or undercut, and sediment deposits on the innermost curve, creating point bars.
What are the most common types of coastal flooding?
coastal storms
coastal erosion
Tsunamis are coastal flooding but are not common
What are some types of shallow flooding?
sheet flow
poor urban drainage
ponding
Where can ponding create flooding?
Depressions in flat areas where water cannot drain out are filled by excessive rains. They are a problem in glaciated areas with poor infiltration, caves and sinkholes and manmade depressions with blocked outlets.
List the types of special flood hazards.
closed basin lakes ice jams dam breaks uncertain flow paths mudflows
What are closed basin lakes?
where there is no natural outlet, or the outlet is inadequate, regulated or elevated
Describe how uncertain flow paths develop?
Stream channels can change location. Alluvial fans, developed at the base of valley rivers can have numerous channels. Alluvial fan floods are unpredictable, the floodwaters spread out over the fan and the channel can move across the fan. Dry river beds are another example of stream beds that can shift due to the loose soils that may simultaneously erode and redeposit during a flood
Why are dam breaks so dangerous?
Breach often occurs with no warning, can be on a dry day, so no time to evacuate
When does NFIP cover mudflows?
NFIP provides flood insurance coverage if mudflow or mudslide meets NFIP definition. If it is not associated with a “river, flow or inundation of liquid mud and accumulation of water on the ground preceded by a period of heavy rain”, then it is considered simply erosion and doesn’t qualify.
List beneficial functions of floodplains?
natural flood and erosion control
maintains biological diversity and provides habitat
recreational opportunity
scientific observation
What problems arise from developing in the floodplain?
flooding dynamics are altered
buildings and infrastructure are damaged
How does development worsen riverine flooding?
channel alteration, including constricting channel with bridges and culverts,
filling in the floodplain restricts the ability to store excess water
both can lead to higher flood levels, and increase in flood velocity
How does development within the watershed impact flooding?
more impervious surfaces are created , preventing absorbtion of precipitation and acceleration of runoff.
stormsewers will speed flood flows, increasing downstream flooding,
patterns of watershed development impacts timing of flows along tributaries, altering timing of peak flows and resulting in increased downstream flooding
How is coastal flooding impacted by development?
sea walls and jetties change the natural sand transport dynamics, and deplete the source of sand to support formation of dunes, and barrier beaches. Land at the end of sea walls and jetties erodes, and has adverse impacts on properties.
List the main causes of flood damages
hydrodynamic forces debris impacts hydrostatic forces soaking sediment and contamination
What are the major health and safety impacts from flooding?
Hazards from utility damage, including electrocution, gas leaks and contaminated water
Fire from electrical shortages
Garbage and mosquitoes and dead animals from flood waters
molds, mildew especially in heating ducts
mental health from stress associated to loss of time, money, property and personal possessions
Fatigue and anxiety
Young and old are especially vunerable
What are the three types of hydrodynamic force and its impacts on a buidling
frontal impact- direct impact on structure
drag effect- pull on the structure as water runs along the sides
negative pressure or eddies, suction created on the downstream side
How much flood elevation is needed to move a car?
2 feet of moving water can float a car, floods trap and kill people in cars more than anywhere else.
What velocity is considered dangerous, and why?
Water moving faster than 5 feet per second is considered high-velocity flood. The higher the velocity, the more pressure is put on a building and more erosion to stream banks that may scour a building foundation.
What is the total impact of moving water
The velocity and the depth of flooding. Shallow, fast moving waters can have as much impact as slow, deep flood water.
List some types of debris impact
anything that can float, logs, lumber, propane tanks, ice flows
Define hydrostatic forces.
Weight of standing water. The liquid pressure is the same laterally as well as vertically. The deeper the water the greater the lateral pressure, as little as three feet of standing water is enough to collapse the walls of a frame structure.
Rising groundwater can exert upwards hydrostatic force, and cause a tank or building to float of their foundation. USTs and caskets can pop out of the ground.
What are the hazards from soaking?
wet wood will swell, wall board will fall apart, household goods can mold, furniture can warp.
What historic events led to the creation of the National Flood Insurance Program?
Mississippi River Flood in 1927 led to the Flood Control Act of 1928 and 1936- major flood control structures were built to control great rivers and prevent flash flooding
What was the main reason that structural flood control measures failed to reduce flood losses?
Development in the floodplain continued
What was the major element that was emphasized in reforming the Food Control Act?
policies and programs with a non-structural focus, and not trying to control or redirect the path of floods.
List the 4 main accomplishments of the NFIP
insurance program as alternative to disaster relief
distributed responsibility of flood plain management to all levels of government and the private sector
set national standards
floodplain mapping program
What are non-structural flood protection measures?
regulations, to prohibit development in high hazard areas
building codes to require flood-resistant construction
acquisition and relocation of buildings in high hazard areas
modify or retrofit existing buildings
install flood waning systems
control stormwater runoff
self help to property owners
What is the Unified National Program for Floodplain Managment?
Program created under the National Flood Insurance Act 1968 to coordinate efforts of many government programs that can affect flooding or floodplain development.
Who coordinates the Unified National Program for Floodplain Managment?
The Federal Inter-agency Floodplain Management Task Force, made up of may federal agencies
How does the Task Force define “floodplain managment?”
A decision making process that aims to achieve the wise use of the nations floodplains. “Wise use” means both reduced flood losses and protection of natural resources and functions of floodplains.
What are the main goals of floodplain management?
Where permitted, development and construction measures minimize the risk to life and property from floods, and risk to natural functions from human development.
Consider all of the options and account for both the hazards and natural values before developing or implementing any action that will change the floodplain.
What are the 4 Floodplain Management Strategies
modify human susceptibility to flood damage
modify the impact of flooding
modify flooding itself
preserve and restore the natural flood waters
List 3 tools to modify human susceptibility by avoiding hazardous, uneconomic or unwise use of floodplain
zoning and buidling codes to steer development away from flood hazard areas
acquire land in floodplain to preserve open space
prepare through forecasting, warning systems and emergency plans
List 3 tools to modify the impact and assist individuals to prepare for , respond to and recover from a flood.
provide self-helpinformation
follow flood emergency measures
provide disaster assistance, insurance and tax adjustments
List 3 tools to modify flooding and control floodwater
dams, reservoirs to store upstream water
alter channels to prevent overbank flooding
divert high flow around developed land
store runoff with on-site detention
List 3 tools to preserve and restore natural resources
land use regulations to steer development away from sensitive natural areas
land acquisition , restoration of floodplains and wetlands
information and education to make people aware of natural floodplain resources and functions and how to protect them
beach nourishment and dune buidlign
What are the three most common types of flooding
riverine, coastal and shallow flooding
Which type of flooding has accounted for the most flood-related deaths in recent history
flash floods
What is a meander?
the sinous pattern developed in a stream channel on relatively flat topography
What is the major cause of coastal flooding?
storm surge, particularly in relation to high tides
What causes a tsunami?
underwater earthquakes or volcanos
List 5 types of special flood hazards
closed lake basins ice jams dam failure undefined flow paths mudflows
List 3 benefits of floodplain, in a relatively undisturbed condition, that actually contribute or could contribute to your community.
provide storage for flood waters
provide natural habitat and species diversity
provide recreational opportunities
provide opportunity for scientific study
What 2 problems result from floodplain development?
natual flood dynamics are altered, and buildings are damaged
What does watershed development do to flooding?
increase in impervious surfaces prevent absorbing rain and accelerate runoff. Development pattern can change the timing of peak runoff from tributaries and increase downstream flooding.
What is one problem with constructing seawalls to protect buildings from flooding or erosion?
Erosion will increase at the end of the wall causing exposure to buildings behind the wall. Seawalls affect the natural sand transport patterns preventing the formation of dunes and barrier beaches that are natural barriers to flood water.
What are the 5 main causes of flood damage?
hydrodynamic forces debris impacts hydrostatic forces soaking contamination and sediment
Standing water as little a _____feet deep can collapse the walls of a frame house.
Three feet
What are some health and safety hazards that accompany floods?
mold, mildew especially in air ducts fires and electrocution gas leaks anxiety water contamination
Prior to the 1960’s what was the primary way to reduce flood loss.
Build massive flood control structures.
What is the Unified National Program for Floodplain Managements definition of floodplain management?
A decision making process that aims to achieve the wise use of the nations floodplains.
What are the two primary goals of floodplain management.
Reduce the loss of life, disruption and damages caused by floods. Preserve and restore the natural floodplain resources and functions.
What are areas are conducive to flash flooding?
mountainous of hilly terrain with narrow valleys are most susceptible to flash flooding. Urban areas, downstream from dams or where ice jams occur.
Is erosion only a threat in coastal areas?
No also inland, especially along the outer banks of meandering rivers, where there are restrictions from bridges and culverts and other locations and where velocity can scour or erode a riverbank.
What is “ponding”?
shallow flooding where impervious depressions on a flat area fill with water and cannot drain out.
Are animals and plants the only beneficiaries of the “natural and beneficial functions of floodplains?
Society benefits as floodplains have recreational value, and as well as for scientific study and a source of food.
Floodplains also recharge groundwater supplies and filtering action improves water quality.
What does filling a floodplain do.
alters the natural flood dynamics, prevents storage in the riverbanks, and alters the channel geometry, possibly accelerating erosion or deposition. Increases the flood depth, and leads to overbank flooding.
Does moving sand and sand dunes affect flooding.
Sediment transport impacts flooding. It is a natural process that provides nourishment for dunes and barrier beaches. Structures that impeded sediment transport can accelerate flooding by preventing the formation of these natural flood protection.
Hydrodynamic forces are caused by _____ water and hydrostatic forces are cause by ______water.
Moving, standing
List three materials or household items that are particularly susceptible to flood damage by soaking.
wood, dry wall and household goods
What are examples of non-structural flood protection measures?
zoning that prohibits construction in flood hazard area
relocation or acquisition of flood prone property
retrofit
protection of open space, restoration of floodplain or wetlands
public education and outreach
emergency response planning
What are the Unified National Program for Floodplain Management’s four main floodplain management strategies?
Modify human susceptibilty to flood damage
Modify the impact of flooding
Modify the flooding itself
Protect and preserve natural resource
