Building design strategies to mitigate flooding disasters

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Building design strategies to mitigate flooding disasters
Dhanashri Mirajkar1*
1Associate Professor, D. Y. Patil School of Architecture, Ambi, Pune.
*Corresponding Author: Dhanashri.Mirajkar@dyptc.edu.in, Tel: +918308542035.
A B S T R A C T
Since dawn of civilizations, human has seen many natural disasters. Ancient civilizations
always flourished on the banks of Rivers. As a result, flood always played an important role in
human lives. A world – destroying flood is a common legend in the ancient history of the
Americans, Babylonians, Indians, Persians, Polynesians and Syrians. Archaeologists in
Mesopotamia have discovered evidence of severe flooding at various levels- in particular a
stratum of clay, eight feet deep, excavated by Sir Leonard Woolley at Ur, which he identified
with the biblical flood.
The Babylonian records say that some 4,000 years old refer to a ―dark cloud‖ that
encompassed the planet and intense fire that scorched the land- all that was bright was turned
into darkness. For six days a deluge of water driven by hurricane winds swept over earth,
destroying all forms of life and changing the face of the planet.
Indus River changed dramatically around 1900 B.C. probably flooding many settlements
along the river and disrupting the Indus valley civilization. Floods played an important role in the
decline of Harappan civilization. Several individual sites like Dholavira show that floods and
rising sea levels leading to increased salinity made them uninhabitable. The Rann of Kutch, for
example, was inhabited during the Harappan era. Floods destroyed the agricultural base of the
cities. Trade and the economy were disrupted. Hundreds of villages may have been destroyed by
floods or by rivers.
In today’s context also, floods are the most common natural disasters occurring in many areas
on the earth. India has a huge coastal area as well as large flood prone areas like Bihar, Assam,
and many other states. Loss of lives and damage of properties are the outcomes of flood. The
social and economic impacts of flood are savior and cannot be avoided. Due to impacts of flood,
buildings get damaged directly. During or after the flood, degradation of building material takes
place. Flood borne substances cause the contamination of the building. A successful flood-
resistant design can overcome all these problems and building can resist flood loads over a
decades. At city level planning stage, innovative street and public realm designs can slow and
store rainwater, resulting into reduced flooding. This paper illustrates the mitigation strategies of
building design for flood prone areas. Implementing mitigation strategies for flooding disasters
can help to get a reed of loss due to flooding. The management and control of flood water
movement can prevent the loss of lives as well as assets. Good planning and management at
building design stage can help in curbing the risks of flooding. It is therefore very important that
flooding risks must be taken into account during any planning process.
Keywords: Amphibious, Debris, Disaster, Flood, Flood Resistant, Mitigation.

1. Introduction
India lies on the banks of three oceans resulting into huge coastal areas, as well as large flood
prone areas like Bihar, Assam and in many other states. These coastal areas face difficulty due to
floods almost every year. The loss of lives and property takes place due to flooding disasters
which affect social and economic life of people.
There are areas that are more susceptible to flooding than others. Poor infrastructure of the
drainage system contributes to even more flooding risks. This therefore calls for proper planning
especially for any proposals of development in areas that are prone to flooding. Following is the
list of major flood disasters took place in India.
1. In October 1943, Madras saw the worst flood to hit the city. Damage caused to life and
property was immense however estimate figure is unknown.
2. On 11 August 1979, the Machchu-2 dam situated on the Machhu river burst, thus flooding the
town of Morbi in the Rajkot district of Gujarat. Exact figure of loss of lives is unknown, but it is
estimated between 1800 and 2500 people.
3. In 1987, Bihar state of India witnessed one of its worst floods till then. Flood occurred due to
overflow of the Koshi river; which claimed lives of 1,399 humans, 302 animals and public
property worth INR ₹68 billion
4. Heavy rains across the state of Maharashtra, including large areas of the metropolis Mumbai
on 26 July 2005 killed at-least 5,000 people. Mumbai International Airport remained closed for
30 hours, Mumbai-Pune Expressway was closed for 24 hours with public property loss was
estimated at ₹550 crore .
5. June 2015 Gujarat flood: Heavy rain in June 2015 resulted in widespread flood
in Saurashtra region of Gujarat resulting in more than 70 deaths.
6. 2015 South Indian floods: Heavy rain in Nov-Dec 2015 resulted in flooding of Adyar, Cooum
Rivers of Chennai and Tamil Nadu resulting in financial loss and human lives.
8. 2016 Assam floods: Heavy rains in July-August resulted in floods affecting 1.8 million people
and flooding the Kaziranga National Park killing around 200 wild animals. [1]
1.1 What contributes to flooding?
Flooding is the overflow of excess water from a water body onto adjacent lands. FEMA (Federal
Emergency Management Agency, USA) more specifically defines a flood as ―a general and
temporary condition of partial or complete inundation of normally dry land areas from the
overflow of inland or tidal waters or the unusual and rapid accumulation or runoff of surface
waters from any source‖.
One or more water bodies can contribute to flooding at given site; like a stream, river, a bay,
a pond, an ocean, a lake or storm water; depending upon local topography and hydraulic
conditions.[2]
1.2 Most common effects of flooding
Floods have large social consequences for communities and individuals. As most people are well
aware, the immediate impacts of flooding include loss of human life, damage to property,
destruction of crops, loss of livestock, and deterioration of health conditions owing to waterborne
diseases as well as famine conditions.[2]

The only way to avoid effects of flooding is to live away from flood prone zones. Coastal plains,
flood plains, valley bottoms and the banks of stream channels are unsafe and may be described
as areas where surface water is the prime land eroding and formatting agent. Living in these
areas, for whatever reason, implies a compromise which has a concomitant increase in risk and
hence vulnerability to this type of natural hazard. [2]
In developing countries this risk is accepted as the vulnerable locations are absolutely essential
for, for example, agriculture, and communications and building materials. To avoid large fertile
food plains would be impossible. Hence in Bangladesh 30% or more of the land is subject to
regular seasonal flooding.
Following a flood incidence it is appropriate to focus to the disastrous effects by asking a series
of pertinent questions concerning the interaction of the structures and building materials with the
water. Following are the effects of flood on structures.
1. Direct damage during a flood from inundation, high velocity flow, waves, erosion
sedimentation and/or flood-borne debris as shown in FIGURE 1(A)
2. Degradation of building materials, either during the flood or sometime after the flood as
shown in FIGURE 1 (B)
3. Contamination of the building due to flood-borne substances or mold as predicted from
FIGURE 1 (C).[3]
(A) (B) (C)
FIGURE 1: DIRECT DAMAGE OF STRUCTURE [3]
2. Characteristics of a successful Flood Resist Building Design
A "successful" building will resist flood loads and other loads over a period of decades,
and will exhibit the following characteristics:
2.1 Any flood damage will be minor and easily repairable
2.2 The foundation will remain intact and fully functional following a design flood
2.3 Any breakaway enclosures below the DFE will break free without causing damage to
the elevated building, the foundation, building access structures, or utility systems
2.4 The building envelope will remain sound
2.5 Utility connections will be intact or easily restorable after a design flood
2.6 The building will be accessible and usable after a design flood. [3]

2.7 A successful Flood-resistant design requires the character of flood conditions during
the design flood, including source of flooding, flood depth, flood velocity, flood
duration, rate of rise and fall, wave effects, flood-borne debris, scour and erosion.[2]
3. How to achieve good flood resistance building design?
Flooding presents a major risk role for buildings so it is an essential role to play in managing
and reducing this risk. Flooding is a fact of modern life - we need to accept and learn to live with
this but importantly we also need to make sure we are adequately prepared. Following are the
areas of building design where utmost care can be taken to achieve a good flood proof building.
3.1 Site Development
Site development is the important aspect of flood proof design as flood affects the site at first.
3.1.1 Accessory Structure
A low cost & small structure(less than or equal to 100 sq. ft)
made up of metal, wood or plastic, as shown in FIGURE 2,
should be provided on site detached from main structure & should
be detachable. Small accessory structures must be unfinished on
the interior, constructed of flood damage-resistant materials, used
only for storage, and, if provided with electricity, the service must
be elevated above the BFE. [3]
3.1.2 Detached garages
Garages may be constructed under elevated buildings and enclosed with
breakaway walls, as shown in FIGURE 3. These structures are not walled and
roofed in the traditional sense, and can be designed to allow the free passage
of floodwaters and waves through structures. [3]
3.1.3 Fences / privacy walls
Fences and privacy walls (including walls separating one property from
another) may obstruct or divert flood flow and waves as shown in FIGURE 4.
They must be analyzed for their effects on flood conditions and the effects of
debris generated by fence/wall failure during flood events. [4]
3.1.4 Erosion control structures
Strengthening the soil to resist erosion straw or wood chips is effective in
holding the soil in place. They have the added value of increasing the organic content of the soil.
Either material should be worked into the top few inches of the soil. Place a covering of chips 1
inch (or less) as slope and soil conditions indicate. Woven burlap as shown in FIGURE 5 (C) can
FIGURE 2 ACCESSORY STRUCTURES [3]
FIGURE 4 FENCE WALL
DIVERT DEBRI [4]
FIGURE 3 GARAGE ALLOW FREE
WAY TO FLOOD WATERS [3]

be laid on the slope and tied down with stakes to prevent lifting by wind or water. The burlap
will decompose eventually, but will remain long enough for vegetation to become well
established. [4]
(A) (B) (C)
Unprotected Protected Homes Burlap
Homes cause stop erosion
High erosion
FIGURE 5 EROSION CONTROL STRUCTURES [4]
3.1.5 Filling in site
Fill placed on sites should be similar to natural soils in the area. In many coastal areas, this
will be clean sand or sandy soils free of large quantities of clay, silt, and organic material. Non-
structural fill should not contain large rocks and debris. If the fill material is truly similar to
natural soils, its behavior under flood conditions should be similar to the behavior of natural
soils, and should not be a subject of debate. [4]
3.1.6 Ground elevations at or above the BFE
The buildings must be designed and constructed on pile or column foundations that are
embedded deep into the ground. The bottoms of the lowest horizontal supporting members must
be at or above the BFE. A 2-feet vertical clearance between the bottom of the lowest horizontal
supporting member and the ground is recommended. The soil around such buildings should be
graded to drain water away from the foundations. [4]
3.1.7 Septic systems
Septic system tanks must NOT be structurally attached to building foundations. Plumbing and
piping components must NOT be attached to or pass through breakaway wall panels. [4]

3.2 Flood proofing
Flood proofing is the process of making a building resistant to flood damage, either by taking
the building out of contact with floodwaters or by making the building resistant to any potential
damage resulting from contact with floodwaters. There are two types of flood proofing.
3.2.1 Active flood proofing
Active flood proofing, sometimes known as contingent (partial) or emergency (temporary)
flood proofing, requires human intervention to implement actions that will protect a building and
its contents from flooding. Successful use of this technique requires ample warning time to
mobilize people and equipment and flood proofing materials.
3.2.1.1 Dry active flood proofing:
Temporary flood shields or doors (on building openings), Temporary gates or panels (on
levees and floodwalls), Emergency sand bagging.
3.2.1.2 Wet active flood proofing :
Temporary relocation of vulnerable contents and equipment prior to a flood, in conjunction
with use of flood-resistant materials for the building [5]
3.2.2 Passive flood proofing
Passive flood proofing, sometimes referred to as permanent flood proofing, requires no
human intervention—the building (and/or its immediate surroundings) is designed and
constructed to be flood proof without human intervention. [5]
3.2.2.1 Dry passive flood proofing :
Waterproof sealants and coatings on walls and floors permanently installed automatic flood
shields and doors Installation of backflow prevention valves and sump pumps.
3.2.2.2 Wet passive flood proofing :
Use of flood-resistant materials below DFE Installation of flood vents to permit automatic
equalization of water level Elevation of vulnerable equipment above Design Flood Elevation.
Dry-flood proofing requires use of special sealants, coatings, components and/or equipment to
render the lower portion of a building watertight and substantially impermeable to the passage of
water as shown in Figure 6. [5]
Basic dry flood-proofing measures Basic wet flood-proofing measures
FIGURE 6 FLOOD PROOFING [5]

Wet-flood proofing allows the uninhabited lower portion of a building to flood, but uses
materials that will not be damaged by flooding as shown in Figure 7(b). [5]
3.3 Sealants, Flood Shields and Valves
A wide variety of materials and devices shown in FIGURE 7 have been developed to make
building walls, floors, openings, penetrations and utilities watertight during flooding. Flood
shields, panels, doors and gates are typically used to close medium to large openings in building
walls. They can be temporary closures that are installed only when a flood threatens, or they can
be permanent features that are closed manually or automatically. Key design parameters of these
barriers are their height, their stiffness (and resistance to hydrostatic forces), their method of
attachment or installation, and their seals and gaskets. As a general rule, flood shields, panels,
doors and gates should not be attached to building windows, glazing or doors. Given the
potential for large flood loads, they should be attached to exterior walls or the structural frame.
Designers planning to incorporate flood shields, panels, doors or gates into a building design are
advised to consult with engineers and vendors experienced with the design and installation of
these components. [3]
FIGURE 7 SEALANT, SHIELDS AND VALVES [3]
3.4 Flood openings
Areas below the Design Flood Elevation must be equipped
with flood openings capable of equalizing water levels and
hydrostatic loads. Openings in Foundation Walls and Walls of
Enclosures should be with special treatment. Since owners
usually want to control temperature and moisture in these
enclosed areas (and prevent rodents, birds and insects from
entering), opening covers are often employed. These covers
must not interfere with the equalization of water levels in the
event of a flood, and should be selected to minimize potential
blockage by debris. There are a variety of commercially available
covers, such as grates, louvers and grills that allow for control of the
enclosed space and the passage of flood waters as predicted in FIGURE 8. [3]
3.5 Flood resistant material
Choosing material for flood resistant structure is an important aspect in flood proof design. The
material should be able to fight against flood water effects.
FIGURE 8 FLOOD OPENINGS [3]

3.5.1 Flooring Materials
 Concrete, concrete tile, and pre-cast concrete
 Latex or bituminous, ceramic, clay, terrazzo, vinyl, and rubber sheets and tiles
 Pressure-treated (PT) or decay resistant lumber
 PT wood and cold-formed steel
3.5.2 Wall and Ceiling Materials
 Brick, metal, concrete, concrete block, porcelain, slate, glass block, stone, and ceramic
and clay tile
 Cement board, cold-formed steel, and reinforced concrete
 Polyester epoxy paint
 Decay resistant lumber
 Marine grade plywood
 Foam and closed-cell insulation
 Decay resistant wood like Black Locust (Robinia pseudoacacia), Teak (Tectona grandis),
Ipe (Tabebuia spp), California Redwood , (Sequoia sempervirens), Western
Redcedar (Thuja plicata), Loblolly Pine (Pinus taeda) , European Larch (Larix decidua),
Bald Cypress (Taxodium distichum).
3.5.3 Other
Hollow metal doors, cabinets, and foam or closed-cell insulation
3.6 Base flood elevation elements
The elements affect due to flood are those which are below base flood elevation as they
remain in direct contact with water. So it is essential to give a special attention on these
elements.
3.6.1 Access stairs and ramp
Stairs and ramps required to:
 Break away during base flood conditions without causing damage to the building or its
foundation,
 Resist flood loads and remain in place during the base flood
3.6.2 Foundation bracings
Elevated coastal home with timber cross-bracing,
Principally in the shore-perpendicular direction as
predicted in FIGURE 9.
3.6.3 Grade beams
Grade beams typically are made of wood or reinforced
concrete; they are used to tie together the columns or
foundation piles to provide additional lateral support. Grade
beams must resist flood, wave, and debris loads when
undermined. [3]
FIGURE 9 FOUNDATION BRACING [3]

4. Floating houses
Float house is a Canadian and American term for a house on a float (raft), a rough house may
be called a shanty boat. In Western countries, houseboats tend to be either owned privately or
rented out to holiday-goers, and on some canals in Europe, people dwell in houseboats all year
round.
4.1 Need of Floating Houses in India
India has a huge coastal area as well as large flood prone areas like Bihar, Assam and in many
other states where almost every year, public face difficulty due to floods and loss of lives and
property takes place. In case, the principle of construction of floating houses is adopted in which
the houses would rise during floods and subside down during dry conditions, loss of lives and
property can be avoided. Simple techniques based on telescopic arrangements should be
designed for requirements. Therefore, research and development can be taken up as model
projects for developing such designs. In the starting, life line buildings in the flood prone areas
can be constructed with such techniques. These buildings will function even during period when
they remain cut off due to floods and have no external electricity and water. In the islands and
coastal areas, such houses will certainly be adopted sooner or later and thus Indian architects and
designers should start getting expertise in this field to design such houses. Floating houses can
also be built for tourists who would love to stay in such houses and India can generate
considerable revenue from the same.
4.2 Basic Principle of Construction
Generally there are two basic principles for making floating
houses. First is the pontoon principle, shown in FIGURE 10, in
which one makes a solid platform, lighter than the water and the
other based on the ship in which a hollow concrete box is created
which is open on the top. The pontoon principle has the benefit of
its use in shallow water, compared to the hollow concrete box while
the concrete box has the benefit of higher space utilization within as
a part of the building. Both type of floating houses are connected
with a flexible connection to the quay, so the houses can rise with
the water when the tide changes. When needed the floating system
can be moved elsewhere at short notice without leaving any scar to
the environment. Instead a new house can be placed in to old one
which makes it the most sustainable and durable way to build.
FIGURE 10 PANTOON PRINCIPLE

4.3 Services
Providing services in a floating house is a challenge which includes water supply, electricity
and toilets. Therefore, green building concept has to be followed in the floating houses which use
non-conventional resources for energy, make use of waste products, and recycles the water. Net
zero energy buildings are more useful as they do not require additional energy from external
source and total energy demand is met from onsite generation power. Normally solar panels are
provided for the energy requirements. Due to aesthetic requirements as well energy efficiency,
roof garden is also becoming popular. Other measures like incinolets (toilets which use electric
heat) to burn waste, geothermal pond loops into the floor, and filtration unit for drinking water
collected from rainstorms.
5. Water Gates
Water Gate flood wall is designed to contain & stop heavy
water flow due to severe flooding. Water gates are quick & easy
to deploy to prevent heavy flood water from reaching the
property. Quick Dam water gate is self-rising flood barrier that
is quick & easy to use to contain large flood waters as predicted
in FIGURE 11.
6. Conclusion.
The occurrence of flood causes a hazard to human as well as non-human communities along
the river corridor. The immediate impact of flooding include loss of human lives, damage of
property, destruction of crops, loss of livestock and deterioration of health conditions owing to
waterborne diseases. The loss of lives and properties affect social and economic life of people.
The only way to avoid effects of flood is to live away from flood prone zones. Due to scarcity of
land in developing countries, this risk is accepted. Also the vulnerable locations are absolutely
essential as River basins provide fertile crescents, ease in communication and transportation and
availability of many other resources.
Buildings and infrastructures are the major areas which get affected due to flooding disasters.
Direct damage, degradation and contamination are the effects of flooding on building structures.
Buildings can resist flood and over a period of decades only if they are designed to mitigate the
flooding disasters.
The paper has illustrated the strategies for achieving good flood resistant building design. Site
development, flood proofing, sealants, flood shields, valves, flood openings, use of flood
resisting materials and base flood elevation elements are the areas which should be taken care at
design stage. These strategies can help to achieve a good flood resistant building structure which
can mitigate flooding disasters. Paper also discussed about floating houses and water gates which
are useful in flood prone areas.
The paper gives direct guidelines for designing in flood prone areas. By using these guidelines
and strategies it is possible to mitigate flooding disasters saving on loss of lives and buildings,
resulting into stable social and economic life.
FIGURE 11 WATER GATE

7. Bibliography
1. https://en.wikipedia.org/wiki/Floods_in_India
2. Jones, Christopher P. PE, Flood Resistance of the Building Envelope
(http://www.adit.org.il/site/includes/Admin/Articles/PDF/Flood Resistance of the
Building Envelope.pdf)
3. Technical Bulletin 5, Free of Obstructions, Federal Emergency Management Agency,
USA
4. Homeowner’s guide for flood, debris, and erosion control, Riverside fire department,
office of emergency management, Guided by PWD, Los Angeles
5. Linham, Matthew M., Nicholls, Robert J., Flood Proofing, University of
Southampton www.climatetechwiki.org/content/flood-proofing
8. Acknowledgement
1. Mr. Sojwal Pohekar
2. Mrs. Priti Mahajan