The document discusses design of buildings in flood prone areas. It provides background on flooding issues in India, noting that 40 million hectares are flood prone and over 645 million houses have been damaged by floods from 1953 to 2005. It then examines reasons for housing damage in floods such as flood depth, duration, soil saturation, and horizontal forces. Common house types damaged include those with mud, unburnt brick, or light materials walls and thatch or metal sheet roofs. Effects on building foundations, walls and roofs are described. Finally, flood resistant techniques like building elevation, dry floodproofing, wet floodproofing, and permanent barriers are outlined.

1. DESIGN OF BUILDINGS IN
FLOOD PRONE AREAS
ACROPOLISINSTITUTEOFTECHNOLOGYANDRESEARCH,
INDORE
DEPARTMENTOFCIVILENGINEERING
ANKIT SHAH
ASST. PROF

2. FLOOD PROBLEM IN INDIA
According to the estimates prepared by the Rashtriya
Barh Ayog (National Commission on Floods), the area
prone to floods in the country is of the order of 40
million hectares out of which about 80% can be
provided with reasonable degree of protection through
variousmeasures.
According to the data published by NDMA in National
Disaster Management Guidelines-Management of
Floods, from the year 1953 to 2005 inclusive, 6,45,49,660
houses had been damaged by floods averaging about
12,18,000houseslostperyear.
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3. REASONS FOR
DAMAGE TO
HOUSING IN
FLOODS
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The impact of floods to housing is due to several
reasons: a) Flood depth, b) Flood duration, c)
Uplift due to soil saturation and d) Horizontal
force created by flood waves or currents.
Direct flood hazard is associated with other types
of secondary hazards such as high winds or
storms, lightning, slope instability, ground
settlement, etc.
Floodwater can submerge buildings and cause
various degrees of damage from staining of walls
to structural collapse depending on flood depth
and/ or duration and type of building.

4. HOUSES TYPES USUALLY DAMAGED UDER FLOOD
• It is seen that first three wall materials are of heavy type and the last two materials are of the light weight
type. Mud and Unburnt Brickwallswhen inundated under water become soft losing theirdry strength by
evenasmuchas85%ofthedryvalueandtherefore,startcollapsingwheninundatedforlongerdurationof
time.
• Burnt Brick and Stone houses are usually constructed using mud mortar in the rural areas. The mud
mortar also becomes soft under continuous wetting under water by which the walls lose their bearing
strengthandtendtocollapseundertheirownweightortheweightoftheroof.Also,ifthewaterisflowing,
theycollapsemoreeasilyunderthedynamicpressureofwater.
• The houses made from light weight materials like GI or other Metal sheets or Grass, Leaves, Reeds,
Bambooetc.easilyfloatawayassoonastheirholdingdownportsareuprootedbytheflowingwater.

5. EFFECTS OF FLOOD ON DIFFERENT PARTS
OF BUILDING
• FOUDATION
• WALLS
• ROOF
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6. A) Foundation
Type 1- Earthen: In kutcha houses with usually bamboo and sometimestimber posts embedded
directly into the earthen plinth. Extremely vulnerable and get damaged even in low intensity
flood,thusrequiringfrequentmaintenance.
In moderate to high intensity flood, especially if accompanied by currents, earthen plinths tend
to get completely washed off and have to be rebuilt. Bamboo or timber posts in saturated soil,
especially during long duration or recurrent flood, get rotten at the base, thus weakening the
entire structure of the buildings to damage by strong wind, differential settlement, sagging of
roofingelementsanddoors,windowsandwallelementsdevelopingcracksandlosingalignment.
Frequent replacement of bamboo posts of kutcha houses is done regularly in flood-prone areas.
Thetypicalearthenplinthinmanysemi-pucca housesalsobehavessimilarly

7. A) Foundation
Type 2 – Brick perimeter: In semi-pucca houses, locally known as “dowa-
posta”, is better at resisting erosion at the sides of a building, but the infill
earth floor can experience settlement due to saturation and in prolonged
flood canbecome muddy, unusableand the mud canescape frombelow. At
the same time, scouring of soil cover of the typically shallow foundation of
theperimeterbrickwallcanresultinitsinstabilityandsettlement.

8. A) Foundation
Type3–Brickandconcrete:Usually in pucca and sometimes also in semi-
pucca houses. Relatively durable, but in high intensity flood accompanied
by currents, shallow foundations can become unstable due to scouring of
soil-cover.
Prolonged duration flood can lead to foundation settlement, thereby
causingcracksandfailuresindifferentpartsofthebuilding.

9. HOUSES TYPES USUALLY DAMAGED UNDER
FLOOD
A study of the Vulnerability Atlas of India 1997
and that revised in 2006 based on Census of
Houses in India 1991 and 2001 respectively,
gives the following house type figures which
are prone to damage or destruction during
floods:
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10. B) Walls
Type 1 – Organic/ Bamboo mat: Typically in kutcha houses; semi-pucca houses also
oftenhave
bamboo matwalls.Organicmaterials(e.g.jutestick,catkingrass)have alifespan of2-
3yearsand
bamboomat4-5years.Decaycangetaccelerated inflood.
In flood of high depth and moderate duration, the damage begins in the lower part of
wallsandhenceweakensthewallsandeventuallyresultsincompletedamage.
Flood with strong currents can detach wall panels and wash them away, leading to
partialorcompleteloss,especiallyiftheconnectionstopostsareweak.

11. B) Walls
Type 2 – CI sheet: Used in semi-pucca houses with timber
framing. Contact with water leads to corrosion and gets
aggravated in flood. The lower part of walls are particularly
vulnerable if plinth is not sufficiently above flood level or if flood
depth is high. Prolonged duration flood can cause damage to
lower end of CI sheet wall panels and timber frame. Flood with
strongcurrentcandetachandwashawaywallpanels,especiallyif
notadequatelysecuredtoframe.

12. B) Walls
Type3–Earth:Usedinkutchaandsemi-puccahouses.Various
types according to region, but not prevalent in all areas. In
monolithic construction, flood water can cause serious
damage: once the base gets affected, the entire structure is
liable to collapse, often rapidly. Earthen walls with an internal
framework, as in some parts of Sylhet district, are less
vulnerable;eveniftheearthcoveriswashedaway,thebuilding
remainsstandingandcanberepaired

13. B) Walls
Type 4 – Brick: Usually in pucca and sometimes also in
semi-pucca houses. Relatively durable, but can
experience staining, peeling of plaster and weakening of
mortar joints at lower ends if immersed in flood of high
depth and duration. Cracks may develop if settlement of
foundationoccurs

14. C) Roofs
Type 1 – Thatch: Typically in kutcha houses, made from catkin grass, rice,
wheat or maize straw with usually bamboo and sometimes reed stalk
framing. Normally has to be renewed every 2-3 years. Results in decay in
houses of low height and during flood of very high depth and duration, if
thatch comes into contact with flood water. In such conditions, if also
accompanied by strong current, thatching materials can get detached and
washedaway.
Secondary hazard often connected to flood is heavy rainfall, which can
cause damage. Strong wind can also blow away thatching materials and
damageframe.

15. C) Roofs
Type 2–CIsheet: Used in semi-pucca houses usually with timber
framing, sometimes with bamboo framing and in some cases
without any framing. Can lead to corrosion in contact with water
and vulnerable to secondary hazard of heavy rainfall
accompanyingflood.Particularlyvulnerabletostrongwind–can
crumple and get blown off, especially if connections to frame are
inadequate. During flood can offer a limited degree of rooftop
refuge.

16. C) Roofs
Type 3 – Reinforced concrete (RC): Relatively durable, used in
puccahouses canwithstand impact ofheavyrainfall andwind,
but can get weakened and may even collapse if foundation
settles or walls are damaged. Offers a high degree of rooftop
refugeduringflood.

17. FLOOD RESISTANT BUILDING TECHNIQUES
• BuildingElevation
• DryFloodproofing
• WetFloodproofing
• PermanentBarriers
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18. A) Building
Elevation
• Significant flood resistant improvement can be obtained if the
structure has the lowest floors elevated to design flood elevation.
Design flood elevation includes wave height relative to a datum
determinedbasedonthefloodhazardmapofthearea.
• Parking garages, buildings access, and storages are permitted to be
constructed below design flood elevation if the enclosed area reach
the conditions of enclosed areas applicable to specific flood hazard
area.
• Lastly, non-residential structures and non-residential portion of
mixed use structure are permitted to have lowest floor below design
flood elevation provided that they meet requirements of dry flood
proofing.
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21. Foundation requirement for flood resistant structures
• Thefoundation of flood resistant structures needs tobe designed and constructed in such a way
that withstands design flood circumstances. It should have adequate capacity to resist flotation,
collapse, and permanent lateral movement under the critical load combinations that provided
byASCE7.
• Furthermore, the foundation design of flood resistant structures should depend on the
geotechnical characteristicsofsoilandstratabeneath the foundationandonthesoilfoundation
interaction.
• Added to that, it should take reduced structural capacity and instability due to expansion,
consolidation, liquefaction, local scour, subsidence, and erosion into account if such incidents
areexpectedtobeoccurred.

22. Foundation requirement for flood resistant structures
• Asfarasfoundationwallisconcerned,itmustwithstandfloodbornedebrisimpact,
hydrodynamic, hydrostatic, wind, soil, and other lateral load that may be imposed
duringflooddesigncondition.
• Apart from lateral loads, foundation wall shall be designed and constructed to
supportbuoyancyandverticalloadsthatimposedduringdesignloadconditions.
• Regardingpiers,piles,andcolumns,theyareusedtoraisethestructureabovedesign
floodelevationinadditiontomeetrequirementsofthefoundationoffloodresistant
structure.

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24. Use of filling
material
• When fill is used, it should be designed and constructed to
withstandfloodingconditionsfor instance scourand erosion due
to floods,quick rise anddrawdown offlood water,and prolonged
inundation.
• Fillusedinfloodhazardareasapartfromhighriskhazardareais
allowed unless it is leads to increase flood level while base flood
dischargeisoccurredanditdeclinesfloodwayconveyance.
• Lastly,fillispermittedtobeusedinhighriskhazardfloodareaif
it is not cause wave run up, ramping, or deflection of flood water
thatdamagethestructure.
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25. Anchorage and
Connections
• Anchorages and connections in the structures need to be
designed and executed to withstand the influence of vertical
loads,upliftforces,andlateralloads.
• Beams shall be connected to piles, columns, piers, and
foundation walls adequately using suitable means such as bolts
andwelds.
• Sufficient anchorages need to be installed for storage tanks,
sealed conduits and pipes, and other structures that may suffer
from lateral movement and floatation during design flood
condition.
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26. B) DRY
FLOODPROOFING
Dry floodproofing techniques essentially make the building
watertight by adding sealants to the walls, shields to the openings,
andsecondarydrainageandpumpstoremovethewaterthatseeps
insidethebuilding.
This technique is good for concrete or masonry construction with
low levels of flooding. But it does require significant levels of
maintenance.
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28. C) WET
FLOODPROOFING
Wet floodproofing techniques allow the water to enter the
structure but use flood damage resistant materials, hydrostatic
openings, and protection of key equipment and contents to limit
the damage. Wet floodproofing can be an effective and low cost
technique, however, there’s still a significant amount of post-flood
clean-upthatwillneedtobedone.
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30. D) PERMANENT
BARRIERS
The last flood resistant building technique is to place a permanent
barrieraroundthestructuretopreventfloodwatersfromreaching
it. This can be done by the use of a floodwall constructed of
concrete or masonry, or using a levee constructed of compacted
layers of soil with an impervious core. Both floodwalls and levies
do require significant maintenance. In addition, levees will require
significant amount of land as well as usable soil materials to
constructthem.
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