Ch-3 RIVER TRAINING WORKSs.-1

Hydraulic Structures II (CENG 4602) Chapter-3 Lecture Note
Chapter Three
River Training Works
3.0 Introduction
River training includes all such measures as are taken for controlling and regulating river flow
and river configuration. River training works are constructed either across a river, or along it.
River training structures include levees or embankments built along the river to contain floods,
and spurs and guide banks are constructed for altering the local flow conditions and guiding the
flow. Besides, a river can be dredged to train it for navigation purposes. A river can also be
trained by diverting its flow into a secondary channel or by executing artificial cutoffs on the
main river so as to cause reduction in flood levels. Bank protection measures are also included in
river training methods.
3.1 Objectives of River Training

River training measures aim at achieving one or more of the following objectives:
(i) Flood Protection
River floods of very small frequency inundate the fertile and thickly-populated plains adjacent to
the river, and, thus, cause considerable loss to human life, property, agriculture, and public and
private utilities. During the years of large floods, damage is likely to be several times more.
Flood control measures for thickly-populated flood plains, therefore, become essential, even if
these measures do not assure complete protection under all conditions. River training for flood
protection, also known as ‘high water training’ or ‘training for discharge,’ is achieved by one or
more of the following four methods.
(a) Construction of levees or embankments to confine water in a narrower channel,
(b) Increasing the discharge capacity of natural channels by some means such as straightening,
widening or deepening,
(c) Provision of escapes or diversion from the main channel into an auxiliary channel for water in
excess of the carrying capacity of the main channel, and
(d) Construction of reservoirs.
WU, KIOT, CIVIL ENGINEERING DEPARTMENT

(ii) Navigation
For a river to be navigable, sufficient depth and width required for navigation should be
available even at low water level in the river. River training for navigation is also known as ‘low
water training’ or ‘training for depth’. Measures to achieve adequate depth in a river for
navigation include dredging the shallow reaches of the river and using spurs to contract the river
channel, thus, increasing its depth. Sometimes, low flow is supplemented from another source to
achieve the desired depth and width. Canalization makes a non-navigable river navigable, and, is
accomplished by building a series of small dams or weirs and locks. Sharp curves along the river
need to be eliminated so that ships can move easily.
(iii) Sediment Control

River training for sediment control is also called ‘mean water training’ or ‘training for sediment’.
This type of training aims at rectification of river bed configuration and efficient movement of
sediment load for keeping the channel in a state of equilibrium. River training methods for this
purpose involve construction of such structures which would induce the desired local curvature
to the flow. Spurs and pitched islands are normally used for training the river for sediment.
(iv) Guiding the Flow
Hydraulic structures, such as canal head works, and communication structures such as bridges,
have to be protected against outflanking and the direct attack of flow. This requires training of
the river over its considerable reach by building a system of guide banks, known as Bell’s guide
banks, on one or both sides of the stream at the bridge site. The purpose of these guide banks is
to make sure that water flows between the abutments of the bridge. The spacing between these
guide banks conforms to the width required for the river to pass the design flood discharge.
Similarly, guide banks are provided to guide the flow at the weir site. Marginal bund and lateral
spurs guide the flow through the guide banks.
Sometimes the flow in a river needs to be deflected away from a bank in order to protect some
portions of the river bank or for contracting the river. This is done by constructing one or more
spurs projecting into the river from its banks.

(v) Stabilization of River Channel

Weak river banks, which are likely to cave in or get eroded, need to be protected by training
methods, such as stone pitching, lining, and so on. In some cases, the stability of the bed may
also be endangered in some reaches due to increase in the bed shear on account of local flow
conditions.
3.3 Flood Protection Methods

3.3.1 Introduction
Disaster means a catastrophe, a calamity or mishap, a grave occurrence, which causes a

serious disruption of the functioning of a society, causing widespread human, material
or environmental losses exceeding the ability of the affected society to cope using only
its resources.
Repeated disasters threaten sustainable development. In the past twenty years, earthquakes,
floods, tropical storms, droughts and other calamities have killed more than 3 million people
globally, inflicted injury, disease, homelessness and misery on one billion others and caused
damages worth millions of Dollars. Disasters destroy decades of human effort and investments,
thereby placing new demands on society for reconstruction and rehabilitation.
Disasters are either natural, such as floods, droughts, cyclones and earthquakes, or human-made
such as riots, conflicts and others like fire, epidemic, industrial accidents and environmental
fallouts. Globally, natural disasters account for nearly 80% of all disaster affected people.
According to the insurance company estimates, natural disasters represent 85% of insured
catastrophe losses. If one adds the losses in countries like Ethiopia, where most of the property of
the people, especially in the rural areas remains uninsured, the losses are astronomical.
Floods are among the most common and destructive natural hazards causing extensive damage to
infrastructure, public and private services, the environment, the economy and devastation to
human settlements. Recurring flood losses have handicapped the economic development of both
developed and developing countries.

Floods usually are local, short-lived events that can happen suddenly and sometimes with little or
no warning. They usually are caused by intense storms that produce more runoff than an area can
store or a stream can carry within its normal channel. Rivers can also flood its surroundings
when the dams fail, when ice or a landslide temporarily block the course of the river channel, or
when snow melts rapidly. In a broader sense, normally dry lands can be flooded by high lake
levels, by high tides, or by waves driven ashore by strong winds. Small streams are subject to
floods (very rapid increases in runoff), which may last from a few minutes to a few hours. On
larger streams, floods usually last from several hours to a few days. A series of storms might
keep a river above flood stage (the water level at which a river overflows its banks) for several
weeks.
However, all floods are not alike. Some floods develop slowly, sometimes over a period of days.
But flash floods can develop quickly, sometimes in just a few minutes and without any visible
signs of rain. Flash floods often have a dangerous wall of roaring water that carries rocks, mud,
and other debris and can sweep away most things in its path. Overland flooding occurs outside a
defined river or stream, such as when a levee is breached, but still can be destructive. Flooding
can also occur when a dam breaks, producing effects similar to flash floods.
3.3.2 Flood Mitigation Strategies:
There are two different ways to mitigate floods: -

1. Structural
2. Non- Structural
Structural measures are in the nature of physical measures and help in “modifying the floods”,
while non- structural measures are in the nature of planning and help in “modifying the losses
due to floods”.
In the structural measures we keep the water away from people and in the non-structural
measures to try to keep the people away from water. All of these works can be individually
divided into long term and short-term measures.

1. Structural Measures:
a) Embankments: Embankments have been extensively used for protection against floods of
important towns and lands. However, the embankments are now the best means of
communication in the flood-prone areas and are being recklessly used for transportation of
materials by tractors and other heavy vehicles. During floods, people shift to the embankments
for temporary shelter and often settle down there for good. Thus, embankments and their slopes
become permanent settlements to flood victims and their livestock. It messes up proper
maintenance, and embankments become susceptible to breaches during floods. Whenever there
are lapses in maintenance, the protected areas are exposed to serious flood hazards.
b) Water Shed Management: Timely cleaning, de-silting and deepening of natural water
reservoir and drainage channels (both urban and rural) must be taken up.
c) Reservoirs: The entire natural water storage place should be cleaned on a regular basis.
Encroachments on tanks and ponds or natural drainage channel share to be removed well before
the onset of rainy season.
d) Natural water retention Basins: Construction and protection of all the flood protection
embankments, ring bunds and other bunds. Dams and levees can also be constructed which can
be used as temporarily storing space which reduces the chances of lower plains getting flooded.
e) Buildings on elevated area: The buildings in flood prone areas should be constructed on an
elevated area and if necessary on stilts and platform.
However, complete flood control in terms of structural methods of flood protection are neither
economically viable nor these are environment friendly. Therefore, non-structural methods are
becoming popular in mitigating flood disaster.

2. Non Structural Measures:
a) Flood Plain Zoning: Flood plain zoning, which places restrictions on the use of land on flood
plains, can reduce the cost of flood damage. Local governments may pass laws that prevent
uncontrolled building or development on flood plains to limit flood risks and to protect nearby
property. Landowners in areas that adopt local ordinances or laws to limit development on flood
plains can purchase flood insurance to help cover the cost of damage from floods.
b) Flood Forecasting and warning: These are issued for different areas mostly by the
Meteorological department and by the State Flood Department. However, an effective Warning
System is one that can release warning in advance, i.e. 72hrs, 48hrs and 24hrs. It can change the
existing scenario substantially and render informed decision making in adopting proper measures
towards disaster preparedness, mitigation, control, planning and management. This kind of
advance warning can help the authorities for better flood preparedness and also effective flood
mitigation. Therefore, initiatives have to be taken to modernize the operation of Flood
Forecasting & Warning by adopting the state of art technology and integrating it into the forecast
and warning dissemination process.
3.3.3 Flood Preparedness
Floods, which are a natural hazard, need not become a disaster, if we are prepared and are aware
of how to deal with them. This would reduce the losses of life and minimize human suffering.
This guide lists simple things one can do to stay safe and protect one from floods.
Before flooding occurs

1. Know the route to the nearest safe shelters that you are aware off.
2. Keep the First Aid Kit ready with extra medication for snake bite and diarrhea
3. Strong ropes for tying things
4. A radio, torch and spare batteries
5. Stocks of fresh water, dry food, candles, matchbox, kerosene etc
6. Umbrellas and bamboo sticks (to protect from snakes)
7. Higher ground where people and animals can take shelter

When you hear a flood warning

1. Tune in to your radio or watch for warning and advice
2. Keep vigil of flood warning given by local authorities
3. Keep dry food and drinking water and warm clothes ready
4. Check your emergency kit
If you need to evacuate
1. Pack clothing, essential medication, valuables, personal papers etc in water proof bags to be
taken to the safe shelter.
2. Raise furniture, appliances on beds and tables
3. Put sandbags in the toilet bowl and cover all drain holes to prevent sewage back flow.
4. Do not get into water of unknown depth and current
5. Lock your house and take the recommended or known evacuation routes for your area of safe
shelter.
During Floods
1. Drink boiled water or use halogen tablet to purify water before drinking.
2. Keep your food covered
3. Do not let children remain on empty stomach
4. Use bleaching powder and lime to disinfect the surroundings
5. Avoid entering flood waters. If you need to enter then were proper foot wear.
6. Stay away from water over knee level.
After a Flood
1. Stay tuned to local radio.
2. Do not allow children to play in, or near, flood waters.
3. Stay away from drains, culverts.
4. Do not use electrical appliances.
5. Do not eat food, which has been in floodwaters.
6. Boil tap water.
7. Use halogen tablets before drinking.
8. Be careful of snake bites, snakebites are common during floods.

Flood Preparedness Planning

Flood preparedness planning is about putting in place a set of appropriate arrangements in
advance for an effective response to floods. Some of the commonly identified flood preparedness
activities are:
 Public awareness raising on flood preparedness, response and mitigation measures;
 Stockpiling of emergency relief materials i.e., food, fodder for livestock, emergency
medicines, materials for temporary shelter etc;
 Installation of community-based early warning system for issuance of timely and
effective flood warnings;
 Management of safe areas for temporary removal of people and property from a
threatened location;
 Transportation to safe areas/ evacuation centre;
 Ensuring access to health and sanitation facilities;
 Conducting drills and rehearsals.
The key to flood preparedness planning is to have a clarity and agreement on the roles and
responsibilities of relevant stakeholders such as the government line agencies, disaster
management organizations, Red Cross, voluntary groups as well as community members. Such
an arrangement is possible by forming disaster management committee and teams at various
levels to agree on set of standard operating procedures
(SOPs) defining what actions to be taken before, during and after floods. The benefits of the
flood preparedness planning are many and some of them are listed:
 Systematic arrangement and deployment of resources to reduce the impact of flood disaster;
 Vulnerable communities to get access to crucial information, such as timely flood forecasts
and warnings;
 The provision of basic needs, such as shelter and medical care, clean water, sanitation and
food during floods;
 Continued access to livelihoods, in order to minimize disruption of economic activities;
 Effective coordination among disaster management agencies to ensure efficient emergency
response during floods;
 Urgent restoration of critical infrastructure and measures to be taken to bring normalcy
immediately after the floods.

3.4 River Navigation

3.4.1 Scope and definition
In the modern times, towing through water is not only required for transporting purposes, but is
also required for recreational boating. However, boating and floating of ships through the natural
rivers is not always safe. Rapids and sandbars may create problems, and may require
considerable time to be passed. Isolated rocks, fallen trees, debris and other obstructions may
create constant hazards, and may damage or even wreck the boats, streamers, or ships being
towed through such waterways. It is, therefore, absolutely essential that all the waterways
through which the boats or ships are to be towed, must be made completely safe.
The chief requirement for navigating though a waterway is the availability of sufficient water
depth in the waterway. A minimum water depth of about 2.7 meters is generally required for
navigating safely and economically; although a depth of about 3.7 meters is generally aspired in
the final developments of a navigable waterway. Availability of lesser depth in the rivers may
completely eliminate the possibility of towing the ships through such rivers or may cause
increased unit cost of transport.
3.4.2 Various requirements of navigable waterways

There is no rigidity about the requirements of a good navigable waterway, since it al depends
upon the extent and type of traffic likely to pass through it. However, the various general
requirements are enumerated as below:
(1) Sufficient water depth is available so as to pass the more heavily loaded barges cheaply and
economically.
(2) The width of the waterway is sufficiently more than the width of the tow itself.
(3) The radii of the bends should not be sharp and should be high enough to allow the maximum
length of the ship to pass through them.
(4) The alignment of the waterway should be as straight as possible, because a highly irregular
alignment increases the circuitry or length in excess of air line distance which the barge tow
must travel. The existing channels generally have a length about 50 percent greater than the
air-line distances.

(5) The flow velocities should not be high, as they may cause substantial reduction in the true
speed for tows moving upstream and thereby increasing the time of transit and the cost of
transport per kilometer. The speed of most of the barge tows in still water is of the order of
2.8m/sec. The flow velocities of the order of 1 m/s may, therefore, cause sufficient reduction
in true speed (i.e. 2.8 – 1.0 = 1.8 m/s) and hence, should not exceed such a value.
(6) In order to minimize the transit time, the time required for the tow to pass through locks
should be minimum. In certain cases, where the lock is not large enough to accept the entire
tow, the tow is generally broken and taken through the lock in potions. This increases the
time lost in locking and thereby increasing the transit time and the cost of transport. Hence,
sufficient sized locks should be ensured for economic and better transport.
(7) Efficient and adequate terminal facilities for unloading the barges for transferring the cargo
effectively must be ensured for economic and better navigation.
3.4.3 Various measures adopted for achieving navigability
There are three basic methods which are generally adopted for improving a river for navigation.
These are:
(1) Open channel methods
(2) Lock and dam arrangements
(3) Canalization
They are described below:
(1) Open channel methods. In the open channel methods, the existing waterway is improved
to such an extent as to make navigation possible. This improvement natural waterway is
possible only if the following conditions are satisfied:
(i) Sufficient discharge is available in the river throughout the year or at least for a
reasonable portion of the year.
(ii) The existing river is having a satisfactory alignment without excessively sharp bends.
(iii) The river bed slope is reasonably flat so that the flow velocities are not excessive. (i.e.
they are within 1 m/s or so).
(iv) The river width is not too small and is such that it can be improved economically for
modern barge tows.
(v) The material of the river bed and banks should permit satisfactory treatment by one or
more of the open channel methods.

If the above requirements are approximately satisfied, the channel can be economically improved
and made fit for navigation. But if the available conditions are far too short of requirements,
open channel methods may prove to be highly uneconomical, and, therefore, should not be
considered. However, these requirements and factors may be controlled to some extent by some
suitable measures. Say for example, if the discharge in the river during lean periods is very low,
while the average annual flow is adequate, reservoirs may be constructed so as to store water and
augment the supplies during lean weather flows. Similarly, very sharp bends may be eliminated
by cut off channels, provided the resulting channel slopes remain within limits.
The various works and techniques that may be involved in improving the channel by the open
channel methods are
(a) Constructing and regulating the flow through storage reservoirs
(b) Excavation and Dredging.
(c) Contraction works
(d) Bank stabilization.
(e) Straightening the waterway by artificial cut offs.
(f) Removal of snag, debris and other obstructions
These techniques are generally required together as one of them may rarely provide the
necessary required improvement. These techniques are described below:
(a) Storage reservoirs. The storage reservoirs generally store water during high flows and can
release the required amount of water during lean-flows, so as to make downstream navigation
possible even during periods of low weather flows. However, the construction and planning of
storage reservoirs for navigation alone is not generally justified economically. Hence, reservoirs
are mostly planned under multipurpose projects, where navigation may be one purpose of that
project. Moreover, the storage reservoirs can augment low supplies for navigation, only if the
reservoir is situated at the head of a relatively short navigable reach.
This is because; as the distance from the reservoir to the navigable river-reach increases,
reservoir-releases have to be increase so as to allow for transit losses due to seepage,
evaporation, etc. The releases must also be made much in advance so as to allow for travel time
to the navigable reach and their quantity has to be sufficient even after reduction due to channel
storage.

(b) Excavation and dredging. Huge amounts of excavations are generally required for clearing
sand bars and filled channel sections in order to make it fit for navigation.
Besides the basic initial excavations, continuous desilting and proper maintenance is required in
order to keep the waterway fit for navigation. These excavations from the bed and banks of the
waterway are generally carried out by dredging by means of dredgers.
Three types of dredgers are generally used. They are:
(i) Dipper dredgers. They are merely floating power shovels and are used on small projects.
(ii) Ladder dredgers. They have an endless chain of buckets for bringing the excavated material
up to the surface. The cuttings carried by buckets are discharged on a belt conveyor which is
disposed of through a stacker conveyor at the rear of the dredger.
Since the stacker conveyors (generally called spoil stackers) are limited in length to about 100
meters or so, ladder dredgers cannot be used when the excavated material (i.e. spoils) are to be
discharged at a considerable distance from the dredge.
(iii) Suction dredgers. In these dredgers, the cuttings and water are collected in suction pipes,
and the mixture is then discharged by pumping through a pipe supported by floats (called spoil
pipe) into the desired spoil area. A line diagram of this operational process is shown in Figure
below.
Figure: Line plan of an ordinary suction dredge called Dust pan dredge.

A section dredge cannot operate in rocky or Boulder River reaches. The suction head of these
dredges is provided with jets or rotating blades so as to loosen the bed material and also with
suction openings through which the soil and water mixture enters into the suction pipe. These
dredgers can make cuts of about 10 m wide through sand bars, and various such parallel cuts can
be made in order to achieve a wider channel.
(c) Contraction works. Contraction works are those engineering works which are constructed in
order to change a wide shallow river into a narrow deep river; or to close off the river creeks
(small branches) and thus to divert the entire water into the main river. When the bed and bank
material of a river is course grained with little cohesion; a shallow wide channel, or at low water,
a number of channels will develop. Such situations may be corrected with the help of spurs or
groynes. Under the process, rivers carrying huge sediment loads can be corrected with the help
of properly placed permeable spurs called sal Balli Dykes made of sal ballies, driven at some
suitable distance center to center in rows across the river current and braced at top. The function
of permeable sal balli dykes is to slow the current and thus promote silting in the dyked area. The
concentration of flow in the narrower section also encourages deepening of channel. Several
years are allowed for the effect of the structures to develop.
Similarly, the rivers carrying a little sediment load can be corrected by properly placed
impermeable spurs or jetties which shall divert the flow, thereby confining the entire water in a
smaller width and thus deepening the same.
(d) Bank stabilization. A good navigable channel must have stable banks. When the river banks
are not stable and start caving, the river starts meandering, creating bends, which may obstruct
the path of longer barge tows. Moreover, scouring at concave banks and silting at convex banks
take place due to meandering. Hence at bends, sufficient depth will prevail at least near the
concave side. But the targets, i.e. the crossings jointing the two successive bends, will definitely
develop shallower channels with cross bars by the deposition of sediment scoured from the
upstream bend. It is in these crossings that the controlling depths for navigation occur.
Spur or groynes, when suitably and intelligently placed, may prove to be useful in bank
stabilization; because a spur placed along the concave bank shall promote silting. Banks may be
protected more easily by pitching or by revetments. The entire concave bank is generally
protected by pitching. The loosely dumped stone called apron or riprap is generally used, and it
is extended from top of bank to beyond the toe of the underwater slope. This extension of

revetment in the bed is essential so as to avoid the failure of revetment due to scour and
consequent undermining of the underwater edge of the revetment.
The revetment must be flexible so as to adopt itself to the surface on which it is placed.
Moreover the revetment must be relatively impervious so as to avoid, the washing of fines
through it. It must also be strong enough to resist the flow currents. Various types of revetments
are used. Concrete mattresses in the form of concrete blocks placed in wire meshes may
sometimes be used, when ordinary stone dumping over a graded filter is not provided due to non-
availability of stone in the nearby areas. Uncompacted asphalt paving is also finding a use in
developed countries, and is under serious investigations. Compacted asphalt paving and
monolithic concrete paving are not generally used, as they are liable to be cracked and damaged
by uplift pressures.
(e) Straightening by artificial cut-off. Since the development of a cut-off eliminates sharp
bends which are undesirable for navigation, artificial cut-offs may sometimes be used
advantageously. A pilot cut is made and allowed to develop. These cut offs have been used with
success to avoid future caving and meandering.
(f) Removal of snag, debris and other obstructions. Presence of debris, trees, isolated rocks,
and other obstructions, not only pose a direct hazard to the barge tows, but also promote the
formation of sand bars. They must, therefore, be removed effectively in order to ensure safe and
economical navigation. Different methods and equipments may be used in different cases,
depending upon the circumstances of each case. Tractors, winches, derrick barges, explosives,
etc. may be required in the process of clearing the waterway obstructions.
(2) Lock and dam arrangements. The arrangement consists of dams which create a series of
slack water pools through which the traffic can move with locks to lift the vessels from one pool
to the next. Lock and dam construction may be adopted where existing site conditions are not
favourable for adopting open channel methods described earlier. This arrangement is a second
choice to open channel methods. In this arrangement, water is required for lockages, sanitary
releases, evaporation, percolation, etc. This requirement of water is much less than that required
for open channel procedures. Hence, when the available water is less, these arrangements may
have to be adopted.

The slack water pools behind the dams will submerge the rapids and channel bends and thus
overcoming those problems. Further, because of their relatively large areas of cross-sections, the
velocities in these pools shall be low enough as to cause lesser reduction in true speed of the
barge tow moving upstream.
Lock and dam arrangements are suitable only on rivers bringing only a little sediment load.
This is because; highly silt laden river water shall fill up the pools rapidly. Moreover, suitable
sites for construction of small dams must be available for providing such arrangements.
(3) Canalization. A totally new channel cut is provided artificially around an otherwise
impassable obstruction or between two navigable rivers. Such a cut is generally economical only
when a short length of new channel opens a large length of existing waterways. Construction of a
new channel connection between two existing waterways is also sometimes adopted, so as to
ensure a continuous traffic way. However, canalization is a costly process, as the per kilometer
cost of canal, capable of passing modern barge tows, is normally very high, and are adopted
when very short lengths are required.
3.3 Flood Protection Methods

3.3.1 Introduction
Disaster means a catastrophe, a calamity or mishap, a grave occurrence, which causes a

serious disruption of the functioning of a society, causing widespread human, material
or environmental losses exceeding the ability of the affected society to cope using only
its resources.
Repeated disasters threaten sustainable development. In the past twenty years, earthquakes,
floods, tropical storms, droughts and other calamities have killed more than 3 million people
globally, inflicted injury, disease, homelessness and misery on one billion others and caused
damages worth millions of Dollars. Disasters destroy decades of human effort and investments,
thereby placing new demands on society for reconstruction and rehabilitation.
Disasters are either natural, such as floods, droughts, cyclones and earthquakes, or human-made
such as riots, conflicts and others like fire, epidemic, industrial accidents and environmental
fallouts. Globally, natural disasters account for nearly 80% of all disaster affected people.

According to the insurance company estimates, natural disasters represent 85% of insured
catastrophe losses. If one adds the losses in countries like Ethiopia, where most of the property of
the people, especially in the rural areas remains uninsured, the losses are astronomical.
Floods are among the most common and destructive natural hazards causing extensive damage to
infrastructure, public and private services, the environment, the economy and devastation to
human settlements. Recurring flood losses have handicapped the economic development of both
developed and developing countries.
Floods usually are local, short-lived events that can happen suddenly and sometimes with little or
no warning. They usually are caused by intense storms that produce more runoff than an area can
store or a stream can carry within its normal channel. Rivers can also flood its surroundings
when the dams fail, when ice or a landslide temporarily block the course of the river channel, or
when snow melts rapidly. In a broader sense, normally dry lands can be flooded by high lake
levels, by high tides, or by waves driven ashore by strong winds. Small streams are subject to
floods (very rapid increases in runoff), which may last from a few minutes to a few hours. On
larger streams, floods usually last from several hours to a few days. A series of storms might
keep a river above flood stage (the water level at which a river overflows its banks) for several
weeks.
However, all floods are not alike. Some floods develop slowly, sometimes over a period of days.
But flash floods can develop quickly, sometimes in just a few minutes and without any visible
signs of rain. Flash floods often have a dangerous wall of roaring water that carries rocks, mud,
and other debris and can sweep away most things in its path. Overland flooding occurs outside a
defined river or stream, such as when a levee is breached, but still can be destructive. Flooding
can also occur when a dam breaks, producing effects similar to flash floods.

3.3.2 Flood Mitigation Strategies:
There are two different ways to mitigate floods: -

1. Structural
2. Non- Structural
Structural measures are in the nature of physical measures and help in “modifying the floods”,
while non- structural measures are in the nature of planning and help in “modifying the losses
due to floods”.
In the structural measures we keep the water away from people and in the non-structural
measures to try to keep the people away from water. All of these works can be individually
divided into long term and short-term measures.
3. Structural Measures:
a) Embankments: Embankments have been extensively used for protection against floods of
important towns and lands. However, the embankments are now the best means of
communication in the flood-prone areas and are being recklessly used for transportation of
materials by tractors and other heavy vehicles. During floods, people shift to the embankments
for temporary shelter and often settle down there for good. Thus, embankments and their slopes
become permanent settlements to flood victims and their livestock. It messes up proper
maintenance, and embankments become susceptible to breaches during floods. Whenever there
are lapses in maintenance, the protected areas are exposed to serious flood hazards.
b) Water Shed Management: Timely cleaning, de-silting and deepening of natural water
reservoir and drainage channels (both urban and rural) must be taken up.
c) Reservoirs: The entire natural water storage place should be cleaned on a regular basis.
Encroachments on tanks and ponds or natural drainage channel share to be removed well before
the onset of rainy season.
d) Natural water retention Basins: Construction and protection of all the flood protection
embankments, ring bunds and other bunds. Dams and levees can also be constructed which can
be used as temporarily storing space which reduces the chances of lower plains getting flooded.

e) Buildings on elevated area: The buildings in flood prone areas should be constructed on an
elevated area and if necessary on stilts and platform.
However, complete flood control in terms of structural methods of flood protection are neither
economically viable nor these are environment friendly. Therefore, non-structural methods are
becoming popular in mitigating flood disaster.
4. Non Structural Measures:
a) Flood Plain Zoning: Flood plain zoning, which places restrictions on the use of land on flood
plains, can reduce the cost of flood damage. Local governments may pass laws that prevent
uncontrolled building or development on flood plains to limit flood risks and to protect nearby
property. Landowners in areas that adopt local ordinances or laws to limit development on flood
plains can purchase flood insurance to help cover the cost of damage from floods.
b) Flood Forecasting and warning: These are issued for different areas mostly by the
Meteorological department and by the State Flood Department. However, an effective Warning
System is one that can release warning in advance, i.e. 72hrs, 48hrs and 24hrs. It can change the
existing scenario substantially and render informed decision making in adopting proper measures
towards disaster preparedness, mitigation, control, planning and management. This kind of
advance warning can help the authorities for better flood preparedness and also effective flood
mitigation. Therefore, initiatives have to be taken to modernize the operation of Flood
Forecasting & Warning by adopting the state of art technology and integrating it into the forecast
and warning dissemination process.
3.3.3 Flood Preparedness
Floods, which are a natural hazard, need not become a disaster, if we are prepared and are aware
of how to deal with them. This would reduce the losses of life and minimize human suffering.
This guide lists simple things one can do to stay safe and protect one from floods.
Before flooding occurs

1. Know the route to the nearest safe shelters that you are aware off.
2. Keep the First Aid Kit ready with extra medication for snake bite and diarrhea
3. Strong ropes for tying things
4. A radio, torch and spare batteries
5. Stocks of fresh water, dry food, candles, matchbox, kerosene etc

6. Umbrellas and bamboo sticks (to protect from snakes)

7. Higher ground where people and animals can take shelter
When you hear a flood warning
1. Tune in to your radio or watch for warning and advice
2. Keep vigil of flood warning given by local authorities
3. Keep dry food and drinking water and warm clothes ready
4. Check your emergency kit
If you need to evacuate
1. Pack clothing, essential medication, valuables, personal papers etc in water proof bags to be
taken to the safe shelter.
2. Raise furniture, appliances on beds and tables
3. Put sandbags in the toilet bowl and cover all drain holes to prevent sewage back flow.
4. Do not get into water of unknown depth and current
5. Lock your house and take the recommended or known evacuation routes for your area of safe
shelter.
During Floods
1. Drink boiled water or use halogen tablet to purify water before drinking.
2. Keep your food covered
3. Do not let children remain on empty stomach
4. Use bleaching powder and lime to disinfect the surroundings
5. Avoid entering flood waters. If you need to enter then were proper foot wear.
6. Stay away from water over knee level.
After a Flood
1. Stay tuned to local radio.
2. Do not allow children to play in, or near, flood waters.
3. Stay away from drains, culverts.
4. Do not use electrical appliances.
5. Do not eat food, which has been in floodwaters.
6. Boil tap water.
7. Use halogen tablets before drinking.
8. Be careful of snake bites, snakebites are common during floods.

Flood Preparedness Planning

Flood preparedness planning is about putting in place a set of appropriate arrangements in
advance for an effective response to floods. Some of the commonly identified flood preparedness
activities are:
 Public awareness raising on flood preparedness, response and mitigation measures;
 Stockpiling of emergency relief materials i.e., food, fodder for livestock, emergency
medicines, materials for temporary shelter etc;
 Installation of community-based early warning system for issuance of timely and
effective flood warnings;
 Management of safe areas for temporary removal of people and property from a
threatened location;
 Transportation to safe areas/ evacuation centre;
 Ensuring access to health and sanitation facilities;
 Conducting drills and rehearsals.
The key to flood preparedness planning is to have a clarity and agreement on the roles and
responsibilities of relevant stakeholders such as the government line agencies, disaster
management organizations, Red Cross, voluntary groups as well as community members. Such
an arrangement is possible by forming disaster management committee and teams at various
levels to agree on set of standard operating procedures
(SOPs) defining what actions to be taken before, during and after floods. The benefits of the
flood preparedness planning are many and some of them are listed:
 Systematic arrangement and deployment of resources to reduce the impact of flood disaster;
 Vulnerable communities to get access to crucial information, such as timely flood forecasts
and warnings;
 The provision of basic needs, such as shelter and medical care, clean water, sanitation and
food during floods;
 Continued access to livelihoods, in order to minimize disruption of economic activities;
 Effective coordination among disaster management agencies to ensure efficient emergency
response during floods;
 Urgent restoration of critical infrastructure and measures to be taken to bring normalcy
immediately after the floods.

3.4 River Navigation

3.4.1 Scope and definition
In the modern times, towing through water is not only required for transporting purposes, but is
also required for recreational boating. However, boating and floating of ships through the natural
rivers is not always safe. Rapids and sandbars may create problems, and may require
considerable time to be passed. Isolated rocks, fallen trees, debris and other obstructions may
create constant hazards, and may damage or even wreck the boats, streamers, or ships being
towed through such waterways. It is, therefore, absolutely essential that all the waterways
through which the boats or ships are to be towed, must be made completely safe.
The chief requirement for navigating though a waterway is the availability of sufficient water
depth in the waterway. A minimum water depth of about 2.7 meters is generally required for
navigating safely and economically; although a depth of about 3.7 meters is generally aspired in
the final developments of a navigable waterway. Availability of lesser depth in the rivers may
completely eliminate the possibility of towing the ships through such rivers or may cause
increased unit cost of transport.
3.4.2 Various requirements of navigable waterways

There is no rigidity about the requirements of a good navigable waterway, since it al depends
upon the extent and type of traffic likely to pass through it. However, the various general
requirements are enumerated as below:
(8) Sufficient water depth is available so as to pass the more heavily loaded barges cheaply and
economically.
(9) The width of the waterway is sufficiently more than the width of the tow itself.
(10) The radii of the bends should not be sharp and should be high enough to allow the
maximum length of the ship to pass through them.
(11) The alignment of the waterway should be as straight as possible, because a highly
irregular alignment increases the circuitry or length in excess of air line distance which the
barge tow must travel. The existing channels generally have a length about 50 percent greater
than the air-line distances.

(12) The flow velocities should not be high, as they may cause substantial reduction in the true
speed for tows moving upstream and thereby increasing the time of transit and the cost of
transport per kilometer. The speed of most of the barge tows in still water is of the order of
2.8m/sec. The flow velocities of the order of 1 m/s may, therefore, cause sufficient reduction
in true speed (i.e. 2.8 – 1.0 = 1.8 m/s) and hence, should not exceed such a value.
(13) In order to minimize the transit time, the time required for the tow to pass through locks
should be minimum. In certain cases, where the lock is not large enough to accept the entire
tow, the tow is generally broken and taken through the lock in potions. This increases the
time lost in locking and thereby increasing the transit time and the cost of transport. Hence,
sufficient sized locks should be ensured for economic and better transport.
(14) Efficient and adequate terminal facilities for unloading the barges for transferring the
cargo effectively must be ensured for economic and better navigation.
3.4.3 Various measures adopted for achieving navigability
There are three basic methods which are generally adopted for improving a river for navigation.
These are:
(4) Open channel methods
(5) Lock and dam arrangements
(6) Canalization
They are described below:
(2) Open channel methods. In the open channel methods, the existing waterway is improved
to such an extent as to make navigation possible. This improvement natural waterway is
possible only if the following conditions are satisfied:
(vi) Sufficient discharge is available in the river throughout the year or at least for a
reasonable portion of the year.
(vii) The existing river is having a satisfactory alignment without excessively sharp bends.
(viii) The river bed slope is reasonably flat so that the flow velocities are not excessive. (i.e.
they are within 1 m/s or so).
(ix) The river width is not too small and is such that it can be improved economically for
modern barge tows.
(x) The material of the river bed and banks should permit satisfactory treatment by one or
more of the open channel methods.

If the above requirements are approximately satisfied, the channel can be economically improved
and made fit for navigation. But if the available conditions are far too short of requirements,
open channel methods may prove to be highly uneconomical, and, therefore, should not be
considered. However, these requirements and factors may be controlled to some extent by some
suitable measures. Say for example, if the discharge in the river during lean periods is very low,
while the average annual flow is adequate, reservoirs may be constructed so as to store water and
augment the supplies during lean weather flows. Similarly, very sharp bends may be eliminated
by cut off channels, provided the resulting channel slopes remain within limits.
The various works and techniques that may be involved in improving the channel by the open
channel methods are
(a) Constructing and regulating the flow through storage reservoirs
(b) Excavation and Dredging.
(c) Contraction works
(d) Bank stabilization.
(e) Straightening the waterway by artificial cut offs.
(f) Removal of snag, debris and other obstructions
These techniques are generally required together as one of them may rarely provide the
necessary required improvement. These techniques are described below:
(a) Storage reservoirs. The storage reservoirs generally store water during high flows and can
release the required amount of water during lean-flows, so as to make downstream navigation
possible even during periods of low weather flows. However, the construction and planning of
storage reservoirs for navigation alone is not generally justified economically. Hence, reservoirs
are mostly planned under multipurpose projects, where navigation may be one purpose of that
project. Moreover, the storage reservoirs can augment low supplies for navigation, only if the
reservoir is situated at the head of a relatively short navigable reach.
This is because; as the distance from the reservoir to the navigable river-reach increases,
reservoir-releases have to be increase so as to allow for transit losses due to seepage,
evaporation, etc. The releases must also be made much in advance so as to allow for travel time
to the navigable reach and their quantity has to be sufficient even after reduction due to channel
storage.

(b) Excavation and dredging. Huge amounts of excavations are generally required for clearing
sand bars and filled channel sections in order to make it fit for navigation.
Besides the basic initial excavations, continuous desilting and proper maintenance is required in
order to keep the waterway fit for navigation. These excavations from the bed and banks of the
waterway are generally carried out by dredging by means of dredgers.
Three types of dredgers are generally used. They are:
(i) Dipper dredgers. They are merely floating power shovels and are used on small projects.
(ii) Ladder dredgers. They have an endless chain of buckets for bringing the excavated material
up to the surface. The cuttings carried by buckets are discharged on a belt conveyor which is
disposed of through a stacker conveyor at the rear of the dredger.
Since the stacker conveyors (generally called spoil stackers) are limited in length to about 100
meters or so, ladder dredgers cannot be used when the excavated material (i.e. spoils) are to be
discharged at a considerable distance from the dredge.
(iii) Suction dredgers. In these dredgers, the cuttings and water are collected in suction pipes,
and the mixture is then discharged by pumping through a pipe supported by floats (called spoil
pipe) into the desired spoil area. A line diagram of this operational process is shown in Figure
below.
Figure: Line plan of an ordinary suction dredge called Dust pan dredge.

A section dredge cannot operate in rocky or Boulder River reaches. The suction head of these
dredges is provided with jets or rotating blades so as to loosen the bed material and also with
suction openings through which the soil and water mixture enters into the suction pipe. These
dredgers can make cuts of about 10 m wide through sand bars, and various such parallel cuts can
be made in order to achieve a wider channel.
(c) Contraction works. Contraction works are those engineering works which are constructed in
order to change a wide shallow river into a narrow deep river; or to close off the river creeks
(small branches) and thus to divert the entire water into the main river. When the bed and bank
material of a river is course grained with little cohesion; a shallow wide channel, or at low water,
a number of channels will develop. Such situations may be corrected with the help of spurs or
groynes. Under the process, rivers carrying huge sediment loads can be corrected with the help
of properly placed permeable spurs called sal Balli Dykes made of sal ballies, driven at some
suitable distance center to center in rows across the river current and braced at top. The function
of permeable sal balli dykes is to slow the current and thus promote silting in the dyked area. The
concentration of flow in the narrower section also encourages deepening of channel. Several
years are allowed for the effect of the structures to develop.
Similarly, the rivers carrying a little sediment load can be corrected by properly placed
impermeable spurs or jetties which shall divert the flow, thereby confining the entire water in a
smaller width and thus deepening the same.
(d) Bank stabilization. A good navigable channel must have stable banks. When the river banks
are not stable and start caving, the river starts meandering, creating bends, which may obstruct
the path of longer barge tows. Moreover, scouring at concave banks and silting at convex banks
take place due to meandering. Hence at bends, sufficient depth will prevail at least near the
concave side. But the targets, i.e. the crossings jointing the two successive bends, will definitely
develop shallower channels with cross bars by the deposition of sediment scoured from the
upstream bend. It is in these crossings that the controlling depths for navigation occur.
Spur or groynes, when suitably and intelligently placed, may prove to be useful in bank
stabilization; because a spur placed along the concave bank shall promote silting. Banks may be
protected more easily by pitching or by revetments. The entire concave bank is generally
protected by pitching. The loosely dumped stone called apron or riprap is generally used, and it
is extended from top of bank to beyond the toe of the underwater slope. This extension of

revetment in the bed is essential so as to avoid the failure of revetment due to scour and
consequent undermining of the underwater edge of the revetment.
The revetment must be flexible so as to adopt itself to the surface on which it is placed.
Moreover the revetment must be relatively impervious so as to avoid, the washing of fines
through it. It must also be strong enough to resist the flow currents. Various types of revetments
are used. Concrete mattresses in the form of concrete blocks placed in wire meshes may
sometimes be used, when ordinary stone dumping over a graded filter is not provided due to non-
availability of stone in the nearby areas. Uncompacted asphalt paving is also finding a use in
developed countries, and is under serious investigations. Compacted asphalt paving and
monolithic concrete paving are not generally used, as they are liable to be cracked and damaged
by uplift pressures.
(e) Straightening by artificial cut-off. Since the development of a cut-off eliminates sharp
bends which are undesirable for navigation, artificial cut-offs may sometimes be used
advantageously. A pilot cut is made and allowed to develop. These cut offs have been used with
success to avoid future caving and meandering.
(f) Removal of snag, debris and other obstructions. Presence of debris, trees, isolated rocks,
and other obstructions, not only pose a direct hazard to the barge tows, but also promote the
formation of sand bars. They must, therefore, be removed effectively in order to ensure safe and
economical navigation. Different methods and equipments may be used in different cases,
depending upon the circumstances of each case. Tractors, winches, derrick barges, explosives,
etc. may be required in the process of clearing the waterway obstructions.
(2) Lock and dam arrangements. The arrangement consists of dams which create a series of
slack water pools through which the traffic can move with locks to lift the vessels from one pool
to the next. Lock and dam construction may be adopted where existing site conditions are not
favourable for adopting open channel methods described earlier. This arrangement is a second
choice to open channel methods. In this arrangement, water is required for lockages, sanitary
releases, evaporation, percolation, etc. This requirement of water is much less than that required
for open channel procedures. Hence, when the available water is less, these arrangements may
have to be adopted.

The slack water pools behind the dams will submerge the rapids and channel bends and thus
overcoming those problems. Further, because of their relatively large areas of cross-sections, the
velocities in these pools shall be low enough as to cause lesser reduction in true speed of the
barge tow moving upstream.
Lock and dam arrangements are suitable only on rivers bringing only a little sediment load.
This is because; highly silt laden river water shall fill up the pools rapidly. Moreover, suitable
sites for construction of small dams must be available for providing such arrangements.
(3) Canalization. A totally new channel cut is provided artificially around an otherwise
impassable obstruction or between two navigable rivers. Such a cut is generally economical only
when a short length of new channel opens a large length of existing waterways. Construction of a
new channel connection between two existing waterways is also sometimes adopted, so as to
ensure a continuous traffic way. However, canalization is a costly process, as the per kilometer
cost of canal, capable of passing modern barge tows, is normally very high, and are adopted
when very short lengths are required.

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Hydraulic Structures II (CENG 4602) Chapter-3 Lecture Note

3.1 Objectives of River Training

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

(iii) Sediment Control

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

(v) Stabilization of River Channel

3.3 Flood Protection Methods

Disaster means a catastrophe, a calamity or mishap, a grave occurrence, which causes a

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

3.3.2 Flood Mitigation Strategies:

There are two different ways to mitigate floods: -

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

2. Non Structural Measures:

Before flooding occurs

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

When you hear a flood warning

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

Flood Preparedness Planning

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

3.4 River Navigation

3.4.2 Various requirements of navigable waterways

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

3.3 Flood Protection Methods

Disaster means a catastrophe, a calamity or mishap, a grave occurrence, which causes a

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

3.3.2 Flood Mitigation Strategies:

There are two different ways to mitigate floods: -

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

Before flooding occurs

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

6. Umbrellas and bamboo sticks (to protect from snakes)

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

Flood Preparedness Planning

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

3.4 River Navigation

3.4.2 Various requirements of navigable waterways

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

WU, KIOT, CIVIL ENGINEERING DEPARTMENT

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