Hello everyone and welcome back. We are going
to continue our discussion on geologic
hazards related to landslide in this lesson.
So, in this lesson, we are going to talk about
landslide hazard zoning and we are going to
look at a few mitigation strategies typically
used to address landslide hazards.
.
But before we go ahead with today’s subject
matter, let us look back at the question set
of the previous lesson. And these are the
questions. The first one that I asked was
what
are the effects of near shore bathymetry on
propagation of waves. As I discussed in the
previous lessons, if we have got a protrusion
of a land form jutting into the water and
the
bathymetry also reflects that kind of onshore
or sub area topography, then that area is
going to be affected by refraction and focusing
of the wave energy. Let me draw a sketch
to elaborate or to jog your memory about what
I mean by this thing.
..
So, let us say we have got a land surface
that is protruding into the sea, and the
bathymetry contour near shore is also reflective
of that kind of land form. So, this one
here is our coastline; this is the coastline.
So, in this particular case, the wave energy
is
going to refract, and it is going to get focused
towards the portion of the coastline that
is
protruding into the sea in this manner. And
this bending or refraction as you recall is
because of 
slowing down of the shallow water wave depending
on water depth. So, that
is one of the things that you could have.
.
.And you can have an opposite effect in areas
where the coastline geometry is of this type
and the near shore bathymetry is bathymetry
contours are of this shape. So, these are
the
bathymetry contours like in the previous sketch.
So, they are the bathymetric contours.
And as earlier, this one here is the coastline.
So, in this case, the waves are going to be
refracted away from the bay, and the bay basically
it is going to form a low energy
environment with very little wave attack near
in this particular area; in this area you
are
going to have very little wave attack.
.
So, these two sketches basically illustrate
how the near shore bathymetry affects wave
propagation. Second question what I asked
was how the problem of sedimentation due to
long shore current is mitigated.
..
Two of the measures that I discussed if you
recall are the groins and jetties. So, basically
what they are? If you look at the coast line
that is affected by near shore transport where
you want to actually limit the near shore
erosion and sedimentation; so what you are
going to have? You are going to have groins
or jetties constructed in this manner. So,
they are basically vertical narrow structures
which are going to discourage the movement
of long shore current in the immediate vicinity
of the coastline.
So, this is the coastline here that I am drawing
same kind of color coding that I was using
in the previous sketches. So, this is the
coast line, and here again you are looking
at the
plane just like the other two sketches that
I used in the previous question to answer
the
previous question. And these features here
are groins 
or jetties, and by having these in
this area, the long shore current and sedimentation
and deposition are greatly mitigated.
So, that is the measure that we discussed
in the previous lesson.
Third question that I asked was these landslides
often occur following wet weather, what
are the reasons? Following wet weather, typically
two things happen. One is water table
concept to near this slope phase, and that
actually may lead to egress or day lighting
of
the seepage near the bottom of the slope,
and this may cause erosion. So, erosional
instability is likely to cause landslide;
that is one of the aspects.
Then the second thing that happens because
of rising of water table, the effective stress
within the near surface soil layers, they
are going to greatly reduce as a result their
frictional strength if the soils are frictional,
then the frictional strength is going to be
.greatly reduced as well. So, that also is
going to lead to frequent shallow slump pits.
So,
these are basically two causes which actually
lead to landslides because of wet weather,
okay.
Then the fourth question that I gave was this.
Deforestation leads to an increase in the
frequency of landslides in hilly areas and
I asked why. Basically what happens? Because
of deforestation, two things are happening;
let us say let us look at a section of a slope.
.
Let us say you have got a slope of this type
and you have tree cover. And the roots of
these trees as they actually penetrate the
near surface soils, you could have other trees
as
well; you could have several other trees in
the area. And because of deforestation, the
binding power of the roots which actually
impart some shear strength within the soils
where the root is penetrating. So, the shear
strength because of the binding power of the
roots is going to greatly reduce. As a result,
this thing is approximated; the shear strength
because of the binding power of the roots
is given the term root cohesion.
So, this component of shear strength is going
to be eliminated if there is deforestation,
and as a result, the soil is going to have
less actual shear strength. So, that could
trigger
landslides because of the immediate effect
of the deforestation process. Fifth question
that I asked was which of the following would
be fast moving. Mudflow, rock creep and
rock fall.
So, this among the three mud flow rock creep
and rock fall, both mud flow and rock fall,
they are going to be fast moving instabilities
or the velocity associated with the
.movement of unstable mass is going to be
quite large. On the other hand, rock creep
is
typically a slow moving process, okay. So,
that takes care of the question set of the
previous lesson.
.
Now we move on with the subject matter of
this particular lesson. The objectives of
this
lesson are as follows. Ah at the end of this
lesson, we would like to be able to classify
landslides according to the velocity of the
unstable mass. Then we would like to be able
to list the factors affecting landslide hazard.
We would be able to provide an outline of
the procedures for landslides vulnerability
reconnaissance and landslide hazard
assessment. And we would like to be able to
list typically mitigation strategies against
landslide hazard.
..
So, with this in mind, we first look at the
landslide velocities. Some of these things
were
discussed already in the previous lesson.
I just wanted to formalize the subject a little
bit,
and we consider this table here which you
should have a look. We have got landslide;
it
could actually affect three different types
of materials rock, debris and soil. Rock is
actually going to encompass all such materials
which are classified as hard rock or soft
rock or weathered rock.
Debris on the other hand is composed both
of rock fragments which could be as large
as
boulders and fine grained material soils which
is essentially soil. Now soil on the other
hand, it is on the other end of the spectrum
in terms of grain size comprised of relatively
fine grained materials. So, at one end of
the material spectrum, we have got rock and
that
actually includes rock, hard rock as well
as weathered rock.
Then on the other end of the spectrum we have
got soil, and in between we have got both
soils. The potentially unstable mass is going
to be comprised of both soil size grains as
well as there could be blocks of rock which
is as huge as boulders and that is given the
name debris. Now the first phenomenon that
we looked at in the previous lesson was
creep, and we can have in this respect rock
creep or another process that I discussed
previously involving wetting of soils as a
result of melting of surface snow that is
called
solifluction. And because of that wetting
the soil tends to creep down slope at the
end of
every snow melt season.
.Then the third column; in the third column,
it has got two parts. You could have
rotational slide or planar slide. The rotational
slides are slumped together for all rock
debris and soil, different classes of material;
they are lumped together with the name
given slump. Planar slides typically through
rock masses are a block slide. Through
debris it is going to be debris slide, and
through soils you could have slab slide. We
discussed the characteristics of these things
in the last lesson briefly.
And then we could have flow, and flow if it
affects rock mass, then it is typically called
rock avalanche. If flow affects debris, then
we are going to call that debris flow. And
if
flow affects soil, then there could be several
different phenomenon processes associated
with that. You could have liquefaction flow
failure or you could have lowest flow;
anything of that type, or you could have mud
flow for that matter. And then finally, the
other end of this particular table, you have
got fall where you typically can have rock
fall
affecting masses or weather or jointed rock.
.
Now let us look at the velocity; let us look
at the velocity. If you go from the left to
the
right of this particular table, what you are
going to see is typically an increase in velocity
of the unstable mass. So, when you are having
creep movement, then the velocity is quite
low. On the other hand, when you have got
different types of flow or rock fall, then
the
flow could be quite high indeed. Then if we
consider the run out distance or the distance
which is affected by unstable mass or the
distance to which the unstable mass is likely
to
.travel, then the run out distance actually
increases as we go from left again to the
right of
this particular table.
So, the run out is going to be much larger
in case of liquefaction and loess flow or
mud
flow liquefaction flow or mud flow or loess
flow. On the other hand, when you are
talking about rock creep, creep movement,
then the distance which is going to be
travelled by unstable mass is going to be
quite small. Rock creep is going to affect
areas
which are typically in less than a meter in
horizontal distance we are talking about,
whereas, mud flow for example, or liquefaction
flow slide could affect several
kilometers down slope from the location where
the flow was originally triggered.
So, basically what you see here is two things
depending on what type of land slide you
are looking at the speed with which the land
slide is going to move is going to be widely
different as well as the run out distance
to which the potentially unstable mass is
going to
move; that is also going to vary over a very
wide margin.
.
And as a consequence of what we discussed
in preceding slide, the typical impacts of
different classes of landslides also could
vary by a wide margin. Now you could imagine
very easily that if the landslide is relatively
slow moving, then the impact of the landslide
is going to be only on the property within
the vicinity of the area affected by landslide.
So, that could damage houses or other structures
that are within the unstable mass
constructed within the potentially unstable
mass or a highway for that matter constructed
across the mass through which the landslide
is going or moving.
.Here you can have direct or indirect economic
loss. Direct economic loss is the loss that
arises because of the damage caused to the
property directly as a result of landslide;
indirect economic loss accrues when, for instance,
a slow moving landslide causes a
temporary shutdown of a highway. And as a
result, movement of traffic is impeded in
that particular zone. So, those are indirect
loss because of slow moving landslide,
whereas direct losses because of slow moving
landslides is the direct damage that is
caused to the properties constructed within
the properties or infrastructure constructed
within the potentially unstable mass.
Fast moving landslides such as different types
of flow are translational slides or rock fall.
This could cause property damage or infrastructure
damage as well as loss of life; the
velocity for instance of a mud flow could
be as large as 100 kilometers per hour. So,
if
you are within an area through which a mud
slide is in progress, then you are totally
trapped in that area, and many lives are lost
because of that. It also is going to cause,
it is
going to damage the structures or infrastructural
facility, the facilities that are
constructed across the path of such flow slide.
So, you have got the likelihood of 
property damage as well as loss of life in
this
particular case. Likelihood of loss of life
is quite limited in the case of slow moving
landslides or slow moving slope instabilities.
Here once again you could have direct and
indirect economic loss like what we discussed
in case of slow moving landslides.
.
.Now what we have to look at is what are the
key factors that affect landslide hazards.
We
have got several main points listed here in
this particular slide that has got remarkable
influence on landslide hazard in a particular
area. The first one being geology and
geomorphology of a given area. Here we are
looking at rock or soil type underlying the
slope that we are considering, weathering
of that particular rock or soil material,
drainage
density that is crisscrossing across the area
we are considering in our landslide hazard
assessment, and relief; that means how steep
is the country side where we are trying to
assess the landslide hazard.
Second point that is of importance is historical
landslide activity. So, areas where you
have got frequent occurrence of landslide
in recorded history that area is likely to
continue as area prone to landslide hazard.
Then you have got climatic condition, hilly
areas receiving a lot of precipitation is
going to be more likely to be affected by
landslide
hazard than areas which are relatively dry;
although, even in dry areas there could be,
in
fact, in relatively dry climatic condition
also, you can have flash rainfall of great
intensity that in turn is going to lead to
the triggering of landslide in that particular
area.
So, climatic condition in a particular area
is it has got a very large influence on landslide
hazard in that particular area. Land use is
another factor that you need to include in
landslide hazard assessment. What we are looking
at here is the density of tree cover in a
given area, then whether you have got agricultural
or urban land use in the area. And for
that matter, in fact, whether or not you are
near a road cut that also is going to be going
to have a remarkable influence on the landslide
activity in a particular area.
For instance, in many areas in the Himalayas,
landslide occurrence is greatly affected by
whether or not, there is a highway passing
through that particular area, because in many
instances, what happens? During the construction
of the highway, the slopes locally are
steepened; hill slopes are steepened locally,
and those hill slopes are often prone to
landslide hazards. So, depending on whether
or not you are near the highway is going to
also influence whether you are going to be
affected by future landslides.
And then finally, what we need to consider
whether the area is in an earthquake, whether
the area has got a lot of seismic activity
or there are frequent earthquakes in the area.
If
you have got frequent earthquakes in the area,
then also the frequency of landslide is
going to be far greater than areas which are
not affected by earthquakes, okay. So, these
.are all the key considerations when we are
going to look at the landslide hazard of a
particular region.
.
A little bit more details about those individual
components or individual points that we
summarized in the previous slide. First, we
considered geology and geomorphology in a
given area. Prime consideration in this particular
case is rock and soil type underlying the
slope underlying the area for which we are
trying to assess the landslide hazard. If
the
soil type is soft soil or rock type is soft,
less weathering resistant such as weathered
granite, phyllite, micaceous rock, saprolite,
then we are likely to have more frequent
occurrences of landslide; that is the first
point.
The second thing also you have to watch out
for is whether you have got any contractive
soil or soils or rock units that are particularly
prone to landslides such as contractive
soils, such as loess, windblown silt, loose
sand or sensitive clays. These soil units
if you
have got if you encounter in a particular
area, then those areas are likely to be more
vulnerable in terms of landslide hazard.
..
Relief of a particular area, how steep is
the slope in a given area is also going to
affect
landslide hazard. Steeper the slope, greater
usually will be the landslide hazard. That
is,
of course, I mean there is I should have a
rejoinder here at this particular point is,
because steeper terrain could also mean that
the soil or rock unit underlying that
particular slope is stronger and more resistant
to weathering. And that also in some cases
could mean that you are going to have less
frequent landslides in steeper terrain, because
steeper terrain itself could be an artifact
of strong or sound rock or soil mass.
So, what you need to look at actually in this
particular case is that one point cannot be
considered in isolation from other points.
And there is a very significant interplay
of
these individual factors that affect landslide
hazard. Then finally, we have got drainage
density in this context. In many places what
you see is this; if you have higher drainage
density; that means if you have got higher
lengths of drainage channels per unit square
kilometer of the area for which you are trying
to assess landslide hazard.
So, for instance, if you have got more number
of kilometers of drainage channels in a
given area per square kilometer, then that
particular area is typically in many cases
that
has actually is it is more stable against
the occurrence of landslides. And you could
argue
that the point that I am trying to make here
is counterintuitive, and the explanation of
this
thing is as follows. If you have got a greater
drainage density; that means a greater
amount of runoff is exceeding that particular
area as surface runoff and very little is
getting into the material underlying the slopes
in that particular area.
.And because we have seen from the previous
discussion that when the slopes become
wet or when water percolates into the slope,
then the water table rises and that all
erosional activity increases near the bottom
of the slope. And in situations where lot
of
water is carried away as surface runoff, such
percolation cannot take place. So, landslide
occurrence is often sometimes actually reduced
in areas where you have got a greater
drainage density than a similar site where
the drainage density is far less.
But again, you have to consider the interplay
of other aspects here because let us say let
us consider vegetation cover or forest cover
on a particular area. If you have got a larger
forest cover, then the drainage density is
also going to decrease, but because of the
presence of the forest cover, you have got
a less likelihood of landslide because the
penetration of roots of those trees that constitute
the forest is going to impart root
cohesion within the near surface soils. So,
you have to consider really each of these
individual points in conjunction with all
other points that we have already considered
or
we are going to consider in the next little
bit.
.
Second point that we looked at a little bit
earlier was historical landslide activity
in a
particular area and climatic condition. And
as I mentioned before, the key consideration
with respect to historical landslide activity
in a given area is this. An area affected
in
recent times by landslides is likely to be
affected again unless there is a remarkable
change in the slope geometry as a result of
the ongoing landslide activity. So, if you
have
.got an area where frequent landslide is taking
place, then you can say that you have got
a
greater likelihood of occurrence of landslide
in near future as well.
Then the second aspect here is climate and
microclimate. The second term is of interest
here is because many of the landslides activities
affect hilly areas and hilly areas very
small units of area are affected; they have
got their own microclimate. So, they have
got
their own rainfall intensity; they have got
their own snow cover or snow melt pattern,
which may be quite different from areas which
could be only a few kilometers away
from the area that that we consider, okay.
So, what you have to look at here in this
particular respect is both climate and
microclimate of the area, and the key considerations
here are as follows. Landslide
frequency increases following wet weather
which we have already seen, and we have
also looked at the reasons why landslide frequency
would increase following wet
weather. And then some slopes are more exposed
to intense runoff than others, and these
slopes could be more susceptible to landslide.
Like for example, because of microclimate,
the amount of rainfall or amount of snow
cover that is going to precipitate on a particular
hill slope is going to vary by a very wide
margin depending on which area you are considering.
And this variation could be quite
remarkable in the sense that if you are away
from the site that you just consider only
a
few hundred meters or a few kilometers, then
the amount of rainfall that is received in
the other area in the second side is quite
different or the rainfall pattern or the
precipitation pattern is quite a bit different
from that associated with the first site that
we
considered. So, you have to really look at
very small area units in hilly areas in terms
of
micro climate in order to assess the landslide
likelihood in that particular area because
of
the variation in terms of the prevailing microclimate.
..
The third factor here the third consideration
here is land use and seismicity. And we
looked at some of these things already. It
is just a mere repetition of some of the
discussion that we had earlier. Vegetation
growth, for example, it has got very
remarkable influence on landslide likelihood
in a given area. It reduces landslide hazard
because it induces suction as well as see
when tree wants to extract water from the
soil
surface, then it actually induces suction.
And suction is nothing but negative pore water
pressure, and as you know from the discussion
that we had on effective stress, because of
suction, the effective stress is going to
increase.
And because of the increase in effective stress,
we are going to get an increase in the
shear strength within frictional material.
And this particular aspect is also supplemented
by root cohesion that we have already looked
at. So, what happens because of loss of
vegetation cover because of deforestation
man made deforestation or because of natural
wildfire? If you lose a substantial proportion
of vegetation in a given area, that increases
the likelihood of landslide hazard. And then
we have got seismicity greater seismic
activity or greater frequency; if the frequency
of earthquakes in an area is larger, then
you got greater landslide hazard as well.
..
Now we look at a simple procedure simple technique
for assessing landslide
vulnerability in a given area. What are the
considerations when you are setting up
reconnaissance program in a given area for
assessing landslide vulnerability? Now areas,
of course, all these things are quite intuitive
really. So, areas in the vicinity of steep
and
potentially unstable slopes are going to be
more vulnerable to landslides. And these areas
include slopes that are difficult to climb.
This 
is just rule of thumb; if you find a slope
difficult to climb, you can consider that
type of slope as a slope where you might get
landslide activities.
Then slopes with shallow water table where
water table is near the surface of the slope
near the slope phase, and this is evident
from growth of water loving plants. The
technical term for this thing is phreatophytes.
There are several different plants that like
to grow near the place where water is abandoned,
and they grow near the places where
ground water actually exits a slope phase
in many instances. So, their presence actually
indicates the locations of potential landslide
instability in that case.
Then thirdly, slopes exhibiting frequent instability
and that are evident from the presence
of scarps, cracks, toe bulge, and undulating
or hummocky ground surface near the toe,
tilted trees, tilted electric poles and so
on and so forth. We looked at this list of
such
anecdotic evidence of potential slope instability
earlier as well. So, if we have got slopes
that have got these characteristics, then
those slopes are vulnerable to landslides
and
areas in the vicinity of such slopes are likely
to be affected by landslides.
..
Then areas near the slopes underlain by certain
types of soil and rock; you just look at
the bed rock geology or near surface geology
map, soils map or bed rock geology map,
and then if you see occurrence or presence
of certain types of rock and soil. A list
of
which we already looked at, and that is again
indicated here in this particular slide. If
we
have got highly weathered or jointed rock
with unfavorable joint orientation, stiff
or
sensitive fine grained soils, collapsible
soils, swelling soils or any such soils you
have
got in a particular area, then those areas
are likely to be more vulnerable to landslides.
Areas near natural water courses are vulnerable
to fast moving flow slides if you expect
one such flow slide to occur in the upstream
area of that particular region, because flow
slides run out as I mentioned to great distances,
several kilometers down slope from the
location where the flow slides are originally
triggered.
..
Okay, now we are in a position to formalize
the notion of landslide hazard assessment;
what are the inputs for landslide hazard assessment.
We looked at these things earlier as
well, but let us formalize what we learnt
so far. We have to look at the geologic map
of a
given area in order to get a feel for what
kind of soil or rock type is underlying a
given
area. We have to look at the drainage features
of the given area, presence of falls and
folds, and whether the faults and folds that
we find on a given geologic map are
seismogenic or they themselves are sources
of earthquakes or not.
Then we have look at topographic map. Topographic
map is going to tell us whether a
particular area is underlain by very steep
topography; if we have got steep areas, then
typically frequency of landslide is also going
to be more. Topographic map is easily
obtained from remote sensing tools such as
satellite imagery or other terrestrial remote
sensing tools such as aerial photogrammetry
or LIDAR or IFSAR which we have already
discussed earlier in this course.
Then we have to look up the meteorological
features of a given area. We have to look
at
precipitation pattern of a given area, and
here again I want you to realize that in hilly
area, the precipitation pattern could be,
in fact, varying quite a bit from place to
place
even when the distance between these sites
are relatively small. And often what
happens? All these areas are not instrumented
so that you cannot have site specific
meteorological information from all these
sites which could have widely different
.meteorological characteristics. We also need
to look at the snow covered and snow melt
estimates from a given area in this respect.
.
Then we have to get the landslide inventory
of a particular area. We have to look at the
location and frequency of past landslides
within the area, then we have to consider
the
land use map. We have to look at in this respect
the forest cover in a given area or
whether a hill slope is open for residential
or commercial developments; whether there
are any highways or railroads constructed
across the hill slope. And there are other
information necessary such as remote sensing
images showing location of groundwater
springs or and regional seismicity. So, these
are the inputs that you need to consider for
landslide hazard assessment.
..
Now we are in a position actually to briefly
discuss the landslide hazard zoning that is
typically done by an engineering geologist.
What are the steps involved in this particular
assignment? So, what you need to do first
is to prepare a combined permanent factor
map. What is done here is to prepare a matrix
for statistical factor analysis which looks
at
all the individual factors that are responsible
for the landslide activity in a given area.
We
are going to look at an example, and that
is going to clarify this particular issue
a little bit
more.
But let me list here that what you need to
look at would include all the factors that
we
have already discussed namely geology, topography,
hydrogeology, climatic conditions,
landslide inventory, land use map seismicity
and so on and so forth. Then we have to
classify based on the information based on
the statistical factor analysis, we have to
classify the given area into high moderate
and low hazard zones.
..
Let us consider an example. Let us say you
are considering a particular area underlain
by
three different types of rocks. The first
type of rock is indicated by the orange shading,
and this is the outline of the area underlain
by rock type one. So, this thing this area
here
is rock type three I am calling it here. So,
let us maintain the same nomenclature. So,
this
is rock type three. Then the area along the
right margin of this particular map and most
of the bottom margin of the map, we have got
rock type one, and in the middle, you have
got rock type two.
Then we classify the areas underlain by these
individual rock units by the average relief
in a given area. So, for example, in this
particular case, what you have got? You have
got
A is it has got the least amount of relief;
that means the area it has got a flattest
relief or
the slopes in the area underlain by three
A is the gentlest, most gentle slope; three
B is
steeper, and three C is steeper still.
Similarly, one A is the flattest area underlain
by rock type one and one C on the other
hand is the area that is the steepest among
the areas underlain by rock type one and
similarly for rock type two. Then on this
map, we have to superpose the areas where
we
observe historical landslide activity, and
these areas could be in the form of areas
where
landslide scarps are visible. And areas which
are underlain by landslide deposits such as
deposits that get generated, because of landslides
such as debris flow, slope failure
deposits basically.
.And those are indicated by these solid shaded
areas. So, these are landslide deposits
landslide areas. And what you have to do?
In this particular case in order to simplify
our
life, I just considered here a two-factor
example. And here what I am considering just
the
effect of rock type and the effect of steepness
of a given area on the landslide hazard. In
addition to it, if you have got other factor
such as rainfall or hydro geological factors,
then you have to include those factors on
top of the factors that I am considering here,
okay. So, then what we do out of the data
presented on these on a map like this and
after
we superpose the area that are affected by
recent landslide activities.
.
Then we prepare a matrix such as that presented
here. For example, here we have got
three different rock types and three different
slope classes as we have seen earlier. For
instance, if we consider rock type one, for
slope class 0 to 25 percent; by 25 percent
what
I mean is that if you move horizontally by
100 meters, then the vertical drop is going
to
be 25 percent. So, a slope which is between
0 to 25 percent grade underlain by rock type
one, there you have got 0 hectare of land
mass affected by landslide out of 3557 hectare
of land underlain by rock type one which is
categorized in slope class 0 to 25 and so
on
and so forth.
You have to complete this matrix for all the
different rock types and all the different
slope classes, and then you have to construct
you have to express the proportion of area
in a given category that is covered by landslide
deposits as a ratio of the area underlain
by landslide deposits to the total area which
is within that particular category. For
.example, for rock type two for slope class
25 to 50, you are going to have a proportion
of
657 divided by 4048 as the number. And then
you have to classify these proportions by
some statistical means in order to get the
areas that are classified to be of 
high moderate
or low landslide hazards, and the steps here
are given on this particular slide.
.
So, here near the bottom you can see a double
summation and x ij x subscript ij in this
particular case represents the individual
observations or all those individual proportions
that we got from the matrix of tables that
we had before. And x j bar represents the
mean
for a given type of rock and then you are
going to minimize basically the double
summation which is shown in that particular
equation there.
And by minimizing actually by adjusting the
bins in which you classify the proportions
that are considered highly hazardous from
those that are considered moderately
hazardous; by adjusting the interclass boundaries,
you want to minimize the double
summation that is observed in the previous
equation there. So, this is basically the
factor
analysis that you are going to perform for
a given area, and that gives you areas sub
classified as zones of high moderate and low
landslide hazards.
..
Mitigation strategies include avoidance. So,
if we have got an area which is characterized
by large likelihood of landslide or highly
hazardous with respect to landslide hazard.
You avoid that area for any development or
construction. Avoidance could be ensured by
having requirement for having carrying property
insurance and taxation for developing
an area and land use restrictions. Then there
many jurisdictions affect grading ordinance
which restrict possibilities of alteration
of slopes or performing excavation near a
particular slope. Then you can also have stabilization
measures or structural measures
such as flattening of slopes, reinforcing
of slopes, and installing a forest cover in
an area
to avoid possible landslide instabilities.
.
.Okay, that brings us pretty much to the end
of this particular lesson. So, what we learnt
in this lesson are the following. We looked
at velocities of different classes of landslides.
We looked at factors affecting landslide hazards.
We gave a very brief outline of the
procedures for landslide vulnerability, reconnaissance
and landslide hazard assessment.
And we then looked at typical mitigation strategies
against landslide hazard.
.
So, we wrap up this particular lesson with
a question set. The first one being list the
typical impacts of mudflow, how far would
the anticipated area of its influence extend
from the location of trigger. Second question,
why landslide inventory is an important
factor in landslide hazard assessment; third
one, explain the following terms, permanent
factor map and grading ordinance. And finally,
which of the following could cause loss
of life, loess flow, rock creep and solifluction,
okay. So, try to answer these questions at
your leisure, and I am going to provide you
with my solutions when we meet with the
next lesson; so until then bye for now.
Thank you.
.
