Flood and risk management

data requirements for practical flood modelling: Topographical data

• Digital Elevation Model (DEM)

• Geological data/map which is tradaitional obtained from gauging stations and ground based surveys

• River bathymetry

• Land use data/map

data requirements for practical flood modelling: Hydrometric data

• rainfall measurements/predictions

• river stage

• river discharge

• tidal level

data requirements for practical flood modelling: Flood data

• flood depth

• flood extent

What is flooding?

Flooding is an overflow of water that submerges land that is usually dry

What are the different type of floods? and the causes

Flooding can be caused by many different reasons and processes and therefore there are many different types of floods e.g. river flooding, coastal flooding, surface water flooding and groundwater flooding

Explain and describe river/fluvial flooding

• River floods occur when water levels rise over the top of river banks and cause damage or obstruction to nearby areas.

• River floods can be cause by heavy rain from extreme storms, persistent rainfall over the same area for extended periods of time, combined rainfall and snowmelt in the spring, ice jam, catastrophic floods caused by natural dam failures.

Explain and describe coastal flooding

• Coastal flooding is the inundation of normally dry land area along the coast with seawater which affects communities situated close to the sea

• Coastal flooding is caused by topical cyclones such as typhoons and hurricanes, storm surge which is an abnormal rise in water level in coastal areas over and above the regular astronomical tide caused by wind or waves or low atmospheric pressure, high tide, tsunami

Explain and describe surface water/pluvial flooding

• surface water flooding occurs after periods of heavy rainfall where excess water cannot efficiently drain away

• surface water flooding is caused by heavy rainfall and limited drainage capacity

• threatening more people and properties than any other forms of flooding in the UK

Extreme surface water /pluvian flooding can:

• rapidly propagate across connected urban and catchment systems, generating fast onset debris laden flows

• create inland tsunamis to inundate streets and destroy buildings within minutes causing severe disruption and potentially death

Explain and describe groundwater flooding

• groundwater flooding occurs when the water table in permeable rocks rises to enter basements/cellars or come up above ground surface, causing damage to property and infrastructure

• groundwater flooding is caused by periods of abnormally high rainfall and can happen in a range of geographical settings e.g. areas of outcrop chalk and river valleys underlain with permeable superficial deposits.

compare river flooding to groundwater flooding

Groundwater flooding occurs much slower than river flooding, it will usually happen weeks or months after heavy or prolonged rainfall.

Explain and describe sewer flooding

• Sewer flooding is when sewage or foul water leaks from the sewage systems through pipes, drains, manholes or floods up through toilets, sinks or showers inside buildings

• Sewer flooding is caused by the failure of the sewerage system, blockage in drainage pipes, insufficient capacity of the sewerage system to take the amount of sewerage and /or water entering the system

Can sewerage flooding be dangerous?

Sewerage can be a dangerous type of flood due to the high level of bacteria that would be spread

Explain and describe reservoir flooding

• Reservoir flooding is the uncontrolled release of abundant water from a reservoir

• Reservoir flooding is caused by prolonged periods of heavy/intense rainfall, improper maintenance, overtopping of the dam, a leak or crack in the dam or embankment structure, slope instability

What are the impacts of flooding?

• floods can be considered distaters as some impacts includes threatening peoples lives, damaging properrty and infrastructure, disrupting traffic and other infrastcture systems, disrupting businesses

What are benefits of flooding?

• distributing rich soil/sediment

• spreading nutrients to water

• maintaining/improving ecosystems

• recharging groundwater

Flood risk calculation

probability of flood x consequences or damages caused by the event

Why is flood risk calculations needed?

the probability of flood hazard and risk is needed for design, planning and development control to match the Flood Estimation Handbook for factors such as populaton protection, prevent urban and sewer flooding and to maintain reservoir and dam safety

Flood risk management

As flooding involved complex human and natural processes thereis no simple solution to mitigate flood impact and manage flood risk. However effective flood risk management strategies may include integrating grey-blue-green solutions together with disaster management schemes.

What is grey (Structured) flood protection infrastructure?

grey infrastructure refers to human made structures using hard building materials in terms of flood protection including barriers and dams

Define Nature Based Solutions (NFM)

• Nature flood management involves techniques such as restoration, enhancement and alteration of natural features to reduce runoff and manage flood water. These techniques are designed to work in natural hydrological and morphological processes, features and characteristics to manage the sources and pathways of flood waters.

Benefits of Nature based solutions NFM

• reduces erosion

• improves soil and water quality

• providing carbon storage

• increasing biodiversity

What are some actual nature based solutions?

• implementations of more responsible environmental practices

• connect water through integrated urban water management with a focus on nature based solutions/ effective use of blue and green infrastructure to create multiple benefits and positive social consequences

What are some non structural measures

• As structural measures can never 100% eliminate the risk of flooding, non structural measures are also put in place

• Non structure measures include land use regulations, flood forecasting and warming, flood proofing and general disaster prevention and preparation systems.