Geo Exam 2
What type of flooding occurred in Green Mill Run on ECU campus as Hurricane Matthew passed Greenville?
upstream
Mitigation
the process of determining how to reduce or eliminate the loss of life and property damage resulting from natural and human-caused hazards.
How is urbanization defined hydrologically
(1) the percentage of total land surface that is covered with impervious material. 60% is considered maximum urbanization. (2) the percentage of land area that is served by storm sewers. 100% is considered maximum urbanization.
1What combination of engineering and landuse planning approaches would you recommend for Greenville, such that it will survive the next BIG FLOOD EVENT better than this last one?
-Zoning ordinances for 100-year floodplain areas to prevent more development on them and to create Floodway Districts -More retention water ponds to collect excess runoff -Make ECU obey Greenville City Flooding Ordinances -Encourage people who already live there to move off the floodplain or elevate their homes/businesses -Buy Flood Insurance if your home lies in the 100-year floodplain
What are 3 impacts that increased urbanization have on flooding, especially small upstream flooding?
1) the Frequency of flooding increases. (2) the Lag Time between peak rainfall and peak discharge/flood stage decreases. (3) the Peak discharge is increases.
Hydrograph
A Plot of Lapsed Time versus Stream Stage or Stream Discharge. Also can show changes in stream stage or discharge over lapsed time.
flood
A general and temporary condition of partial or complete inundation of normally dry land areas from overflow of inland or tidal waters or from the unusual and rapid accumulation of runoff or surface waters from any source.
Stream gradient
A measure of the vertical distance that a stream channel falls over a given horizontal distance. Expressed in feet/mile or meters/kilometer.
Stream
Any permanent, channelized flow of water on the Earth's surface.
What is meant by the terms, "bank full stage," and "flood stage?"
Discharge that fills a stream channel is called BANKFULL STAGE. When discharge exceeds the BANKFULL STAGE, the excess discharge flows out onto the floodplain of the stream and the stream is said to be in FLOOD STAGE.
FEMA
Federal Emergency Management Agency
primary role of FEMA
FEMA's primary role in responding to severe Flood Events is to coordinate relief efforts and to conduct buy outs of homeowners who have lost their home. Also to educate people in floodplain areas about flood mitigation approaches and general education about floods and their effects and hazards. FEMA encourages communities to establish sound floodplain management programs that go beyond the NFIP minimum requirements, the Community Rating System was created. The Mitigation Division at FEMA is the organization responsible for working with communities to encourage them to adopt and enforce ordinances that meet or exceed the minimum floodplain management requirements of National Flood Insurance Program
What types of flooding occurred where Hardee Creek crosses NC 33 East/10th Street as a result of Hurricane Floyd?
Flash Flooding as Hurricane Floyd passed thru and then Backwater Flooding as the Tar River crested 5-7 days after the Flash Flooding.
What types of flooding occurred where Hardee Creek crosses NC 33 East/10th Street as a result of Hurricane Matthew?
Flash Flooding as Hurricane Matthew passed thru and then Backwater Flooding as the Tar River crested 7 days after the Flash Flooding.
FIRM
Flood Insurance Rate Map - FEMA Flood Maps that show the 100-year and 500-year floodplain for Determining Flood Insurance Rates for homes and businesses.
List and describe the major landuse planning approaches for flood control and mitigation. What are the pros and cons of each landuse planning approach?
Flood Ways and Flood Plain Zoning - Areas of flood plain where no new structures are allowed And old ones may be removed in order to allow floodwaters to pass more freely and unobstructed. This reduces flood levels and submergence. Relocation of Homes and Businesses - Relocate out of the 100-year Flood Plain. If your home or business is damaged by a flood, you may be required to meet certain building requirements in your community to reduce future flood damage before you repair or rebuild. Flood insurance policyholders in high-risk areas, also known as special flood hazard areas, can get up to $15,000 to help pay the costs to bring their home or business into compliance with their community's flood plain ordinance. There are four options you can take to comply with your community's flood plain management ordinance and help you reduce future flood damage. You may decide which of these options is best for you: (1) Elevation - This raises your home or business to or above the flood elevation adopted by your community. (2) Relocation - This moves your home or business out of harm's way. (3) Demolition - This tears down and removes flood-damaged buildings. (4) Floodproofing - This option is available primarily for non-residential buildings. It involves making a building watertight through a combination of adjustments or additions of features to the building that reduces the potential for flood damage. Reforestation and Re-vegetation - Reduces runoff by increasing infiltration and interception Restoration of Wetlands - Restore Wetlands in the critical 50-year and 100-year Flood Plains. Wetlands are great water absorbers!
What are major causes of stream flooding?
Heavy rains - High Intensity and/or Long Duration. Often related to tropical depression but can occur in winter when there is less vegetation to slow excess rainfall. Rapid Snowmelt - Has both local and regional effects Dam failure - Produces flash floods including Landslide Dams.
What is the Hydrologic Cycle, what is the energy source that drives it, and what are the major pathways/processes by which water is distributed/re-distributed within Earth systems?
Hydrologic Cycle = the circulation of water among the Earth's 4 major spheres (see below). Most of this circulation is driven by solar energy. However, the flow of water within a stream channel is driven by gravity. (See Notes Part I for a cartoon) Precipitation = Runoff + Infiltration + Evapo-transpiration
List and describe the major engineering approaches for flood control and mitigation. What are the pros and cons of each engineering approach?
Levées - Small ridges that are built naturally along banks of many flood-prone streams. These actually prevent flooding from small increases in stream flow. Levees are often built higher than natural levels by man to prevent all but the most severe floods from encroaching onto the flood plain. To Levée or not to Levée? (1) Reduces fertility of flood plain. (2) Prevents rapid return of flood waters to main channel. (3) Gives people along flood plain a false sense of security. (4) For large Magnitude Floods, Levees make them worse because Flood Peak or Flood Crest moves downstream like a large wave. Floodwalls - Elevated walls built to protect area behind them from flooding. These can prevent flood waters from returning immediately to main channel. Similar approach to levées. Channelization - Modification of channel by straightening, widening, clearing, deepening, and/or lining with concrete. Can cause a lot of ecological damage to a stream and its surrounding flood plain. Also impacts stream dynamics immediately upstream and downstream from the channelized portion of a stream. Also increases the frequency and magnitude of flooding downstream from the channelized portion of a stream. Storm Water Retention Ponds - Small ponds designed to temporarily retain excess surface runoff in urban areas. Dams - Flood impoundment dams are kept empty most of the time. These can mitigate the effects of flash floods. Dams have a negative impact on the river/fluvial geo and ecosystem both upstream and downstream from the dam site.
How is Stream Discharge or Flow measured
Q = V x W x D where Q = discharge (ft3/sec), V = velocity (ft/sec), W = width (ft), D = avg depth (ft)
What are the factors that control the distribution of rainfall and runoff?
Rainfall - Both intensity and duration are important along with prior moisture conditions of the ground Infiltration Rates - Depends on land cover, nature of soils, and human factors such as pavement and ORV's. Controlled by rock properties and structure and by soil texture Slope - produce greater runoff Vegetation - Slows overland runoff and enhances infiltration and reduces flood risk Landuse
What is the numero uno clue you would look for in the field in order to determine whether an area surrounding a particular stream had experienced flooding in the recent past?
Stranded debris and/or mud lines on buildings or trees or stranded sand deposits
What is the relationship between stream discharge and stream stage or gage height?
Stream Discharge is proportional to stream stage, or as Stream Stage increases so does Stream Discharge.
Base flow
Streamflow coming from ground-water seepage into a stream.
stream stage
The height of the water surface above the gage datum (zero point).
What is recurrence interval, and how is it measured?
The recurrence interval (sometimes called the return period) is based on the probability that the given event will be equalled or exceeded in any given year. Streamflow recurrence intervals are based solely on the magnitude of the annual peak flow. Ten or more years of data are required to perform a frequency analysis for the determination of recurrence intervals. More confidence can be placed in the results of a frequency analysis based on, for example, 30 years of record than on an analysis based on 10 years of record. Make sure you can use the formula, R.I. = (n + 1)/m
drainage basin/watershed
The total area drained by a stream and its system of tributaries.
Stream discharge
Volume of water passing a fixed reference point per unit time. This is a volumetric variable and is expressed cubic meters/sec or cubic feet/sec.
backwater flooding
Water that is retarded, backed up, or turned back in its course by an obstruction, such as rising water levels in the trunk stream channel of a drainage basin.
What type of flooding occurred in Greenville along the Tar River, which crested about 6-7 days After Hurricane Floyd passed?
downstream
What type of flooding occurred in Greenville along the Tar River, which crested about 7 days after Hurricane Matthew passed?
downstream
100 year flood
it is the flood elevation that has a 1 percent chance of being equaled or exceeded each year at a given location of a stream.
Upstream floods/flash floods
result from a locally intense rainfall over a small portion of a drain basin or dam failure
downstream flood
results from larger scale meteorological events that last longer and produce persistent rainfall across a whole region or large drain basin
