Semester : BE - 5th Civil-A

Subject : Hydrology & Water Resources EngineeringCode : 2150602

Presentation On : Flood Management

Prepared by : Eddy Ankit Gangani

eddygangani@gmail.com

What is Flood ?

What is Flood Management ?

Types of flood

Causes Of Flood

Flood : A flood is anexcess of water (or mud) onland that's normally dryand is a SITUATIONwherein the inundation iscaused by high flow, oroverflow of water in anestablished watercourse, suchas a river, stream, or drainageditch; or ponding of water ator near the point where therain fell.

This is a unpredictable -duration type -natural andinevitable event.

According to Duration : Slow-Onset Flooding

Rapid-Onset Flooding

Flash Flooding

According to Location : Coastal Flooding

Storm surge

Arroyos/Mud Flooding

River Flooding

Urban Flooding

1. Riverine Floods: The majority of floods recorded globally are due to rivers overflowing as aresult of long-lasting precipitation in the river basin. Melting snow and ice can also contributeto flooding.

2. Flash Floods : Flash floods generally occur due to local high-intensity precipitation in hilly ormountainous areas. The short warning time makes them difficult to predict. Dischargesduring flash floods are often much higher than normal flows in water courses. Flash floods areparticularly dangerous on steep slopes.

3. Coastal Floods : Areas along the coast may be flooded due to tsunamis, hurricanes or/andunusually high tides. Also long-term phenomena like subsidence and sea-level rise can lead tothe gradual encroachment of the sea.

4. Urban flooding : The urban area is paved with roads etc and the discharge of heavy rain can’tabsorbed into the ground due to drainage constraints leads to flooding of streets, underpasses,low lying areas and storm drains

5. Stagnant and Urban Floods: Extreme rainfall in towns and cities combined with blocked drainscan cause severe flooding. This often occurs in urban areas, where a large percentage of thesurface is impermeable.

6. Lake and Canal Floods : High levels of precipitation or long-lasting inflows from streams cancause a substantial rise in water levels of lakes and canals that lack sufficient drainagecapacity. Also, long periods of drought can cause man-made (peat) embankments to becomeunstable and fail – resulting in flooding.

Uncontrolled unplanned urbanization - Unauthorized colonies , Poor Water and Sewerage Management

Deforestation + Population pressure

Lack of Flood Control Measures

Lack of attention to the nature of hydrological system

Slope Failures

Type of River

Intensity of Rainfall

Topography

Sedimentation of River/Reservoir

Obstructions in River flow

Contraction in River

Seismic effects

Mitigation Measures

Mitigation Measures

Flood plain zoningFlood forecastingFlood proofingMathematical modelingResponse planningModifying loss burden

Reservoirs-Flood gatesLeveesFlood wallFloodwaysFlood bypassWatershedCut-offRain Water HarvestingChannel improvementDrainage improvementWatershed management

Reservoirs & Flood gates -Reservoirs can moderate the intensity and timing of theincoming flood.

Floodgates are used to control the flow of water and canbe a part of flood prevention.

Floodgates are often incorporated into reservoir, river,stream, levee, or storm surge systems.

Water flow can be either partially restricted orcompletely stopped, depending on the water level anddesired effect.

Expensive & potential error .

Levees - A levee is a barrier built to keep a river, orother waterway away from people orsensitive habitats.

Important considerations

First, it is important not to remove too muchfloodplain storage. Excess removal could restrictflood waters and slow drainage upstream.Second, levees are designed to protect an areafrom a certain flood level and storm intensity. Ifthese levels are exceeded, a levee may beovertopped or may fail completely.Third, in order for a levee to continue functioningproperly and provide security for those behind it, alevee should be regularly inspected andmaintained.

Floodwall -

When construction space is low thena flood wall is implemented to protectlow lying area.

Does not reduce the flood flow but

reduce spilling

Acts as a retaining wall

Section : Rectangular trapezoidal

Sheet piling

Mitigation Measures

• Cut-off -To have highvelocity of water flowalong a straight path

To avoid ox bowlake

Does not reduce the

flood flow but reduce

spilling

Mitigation Measures

• Watershed Management -

Long term effect

Examples ; AfforestationContour farmingCheck damsGullyingBank protectionDiversion drains

Mitigation Measures

• Flood ways -Low lying are(depressions ) along the river course is known as floodways.

Connected to natural channel or artificial channel

Temporary storage

Can be used for agriculture other than flood.

Do not reduce the flood flow but reduce

spilling

Mitigation Measures

• Flood plain zoning- Oftentimes floodplain management is not

contained in a single comprehensivedocument, but instead is incorporatedinto other rules, guidelines, orregulations, including:

• Floodplain Management Ordinance• Encourage appropriate development• Community Master Planning• Flood Hazard Zoning• Open Space Preservation Ordinance• Education and Outreach• Emergency Management Program• Mapping Program or GIS

Mitigation Measures

• Flood forecasting -

For emergency evacuation

Flood forecasting through range of hydrodynamic/ snowmelt / flood routing models.

Flood warnings

CWC National Flood Forecasting Network

Mitigation Measures

• Flood proofing - Combination of structural change

& emergency action.

Water proofing materials on windows

Water tight closure on doors

Example : use of flood wall or levees on periphery of building

Indirect DamageDirect

Damage

Flood Damage Analysis

• clean-up costs• disruption to transport services ( disbility to providecommunity services)• disruption to utilities • disruption to public & emergency services• economic impacts of health issues

• damage to building • external damage (pools, gardens, fences, shedcontents)• motor vehicles• infrastructure (roads, bridges and other services)• clean-up costs for individual home owners• loss of stock• cost of re-instatement or rebuilding of houses and buildings.

Tangible Damage

Non-monetary losses -variability

-Loss of life & cattle-- Loss of health

-Loss caused by social distress

-Loss due to hindrance in development work-Physical ailments

Flood Damage Analysis

Intangible Damage

Where applicable, the best practices described in here should be taken into ac-count, in particular on:

Integrated river basin approach Public awareness, public participation and insurance Research, education and exchange of knowledge Retention of water and non-structural measures Land use, zoning and risk assessment Structural measures and their impact Flood emergency Prevention of pollution