BUILDING STRUCTURES ON OR NEAR STEEP SLOPES
Benefits of Building Structures on or Near Steep Slopes
Why would you ever do this? In some instances, it is the steep slope that people want to be near. Like a ski resort or
to enjoy the beauty of a mountain area. Some of the most expensive property is found in mountainous regions just
for the recreation aspect. Other times, like in the instance of a highway, going through a mountain area it may be the
quickest route and it is worth the risk of a landslide or mudflow.
Problems with Building Structure on or Near Steep Slopes
The first and probably most obvious reason is because of the possibility of mass wasting or mass movement. This could be a
mudflow washing out the highway or a landslide burying a highway. This same hazard can affect homes and other structures
as well. Of course this is very expensive to clean up and repair. Who should pay for this clean up and repair?
Mitigation of Mass Wasting
There are a number of ways to mitigate or prevent mass wasting. One is to help water flow out of sediments so they
are less slippery and less likely to slide. A simple way to try and keep small slides off of roadways is to either spray the
slope with concrete or put up huge steel nets. Click here to see how a city in Austria built canals to help contain and
redirect a mudflow. Some of you have seen this, but it is cool to check out again.
Drainage pipes allowing water to escape
Steel netting to help prevent rock fall and landslides.
Why would people build on or near steep slopes?
There are a number of reasons for this. One is money. Often mountainous or steep slopped areas are quite valuable
and the people who own them want to sell them for monetary gain. Contractors and construction companies stand to
gain by being allowed to build on these lands. It is their business and they make lots of money doing it. Also, there are
political reasons. If politicians and bureaucrats allow for more building and access in steep sloped areas contractors
and landowners my help them be re-elected. It may be a “you help me and I will help you” relationship. Another
reason is that sometimes structures or even entire villages may be built in areas before the population is even aware
of the danger for mass wasting. Finally, in regards to highways, it is often far to expensive to build highways around
mountains. It would simply take motorists far too long to drive that distance rather than drive through the mountains.
So it is viewed as worth the risk when considering the benefits of time and money saved.
So who should be responsible for paying for the clean up or mitigation of mass wasting events?
BUILDING ON FLOODPLAINS
What is it?
First, let’s talk about what a floodplain is. If you look in the diagram below you can see that a floodplain is the flat area
on both sides of a river channel. This is the area that extra water will flow into during times of flooding. Often this
occurs in the spring or during times of high precipitation.
Benefits of Building on Floodplains
Why would anyone want to live on a floodplain or build structures on a floodplain? One reason is floodplains are so
flat it is fairly easy to build on them. This of course was done more in the past when people did not understand
exactly how a floodplain forms and some of the hazards they pose from flooding. Another reason is that when the
floodplain is actually flooded the waters typically carry silt and clay that, when deposited, help form very rich and
fertile soil. As a result, floodplains tend to make great places to farm because they are flat and have very fertile soil.
Problems with Living on Floodplains
Clearly the main problem with living on a floodplain is the actual flooding that created them. In some instances the
damage is very extensive and very expensive. In May of 2011 USAToday reports losses in Arkansas are estimated at
more than $500 million, according to the state Farm Bureau. This raises all kinds of issues. How will we pay for the
damage? Who will pay for the damage? Usually, federal tax dollars and FEMA help the victims and support cleanup.
Mitigation of Floodplain Problems
One might ask why people would take the risk of building on a floodplain. One reason is what is called recurrence
interval. This is the average amount of time that a certain sized flood occurs. Most large floods only occur on the level
of every 1000 years so people are willing to take the risk. However, there are some preventative measures people can
take to minimize damage. One is putting structures on stilts like the figure below-left. Another is building a moat
around structures to keep water out. Can you imagine being trapped by water and not able to leave until the water
recedes. Another solution is building retention ponds for excess water to flow into. These mitigation solutions cost
money and the question still is who should pay for it? We all benefit from the food grown on farms.
BUILDING DAMS UNDER INSECURE CONDITIONS
Benefits of Building Dams
Dams have to be built across natural river ways. It turns out that most river ways flow down valleys created by fault
zones. The reason for this is because the fractured rock provides a zone of weakness for the river to erode through. As
a result the dam can use the gravitational potential energy stored by the backed up water to turn a turbine and create
electricity. This electricity is obviously a great benefit to people.
Problems with Building Dams
Clearly building a dam on a river that flows down a fault zone can have tragic consequences. Even the smallest tremor along
the fault line could lead to a dam failure. This failure could kill many people and millions of dollars of damage to property.
The Teton Dam failure was the result of insufficient data collection and monitoring. The dam construction continued even
though there was some uncertainty about how strong some of the materials were and how stable the conditions were. There
was a lot of money at stake and some people claim that the companies involved wanted to move ahead and not have to
spend any extra money to fix problems. The result was the dam sprung a leak that grew larger and larger until the dam
completely failed. 11 people died and millions of dollars of damage was done. Who should pay for this? Who should pay if it is
cause by an earthquake?
Teton Dam initial failure
Teton Dam Rupture
Mitigation of Dam Problems
One obvious mitigation strategy is to build dams in areas that are as stable as possible. However, this is often hard to
do because rivers often flow down fault zones. In addition, to determine the safest location companies often have to
pay lots of money to research areas. This is something they do not like to do as it means less money in their pockets.
Some other techniques include a failure/flood warning system. This strategy is very new and many feel it does not
provide adequate time for citizens to respond. Finally, large spillways have been discussed. These are large concrete
canals that would direct excess water to areas that would not impact people or property. Critics of this technique say
that the spillways will divert some water, but much of the water will still do lots of damage. Who should pay for these
safety items or problems from dam failure? Why?
LIVING NEAR VOLCANOES
Benefits of Living Near Volcanoes
Believe it or not there are benefits. The main benefit is the fertile soils that typically form around volcanoes. The minerals in
the lava and the ash typically weather into very fertile soil that is easily and successfully formed. Another benefit is the
geothermal energy source. Scientists and engineers have developed technology to allow the “harvesting” or collecting of heat
energy from below volcanoes. This can be used to heat homes or run factories.
Rich and fertile land for farming.
Geothermal heat source
Another benefit is tourism. Hawaii, Yellowstone National Park, and Iceland are beautiful places to visit. Volcanoes are very
interesting and dramatic earth features and many people travel to these areas to witness eruptions. With this tourism the
local economy benefits greatly by all the money that tourists spend while on vacation.
Problems with Living Near Volcanoes
Obviously the problem with living near volcanoes is the threat of eruption. Lava flows, ash flows, or hot cloud flows call nuée
ardente can cause much destruction and even death. Another possible hazard is out gassing of toxic gasses. This happened in
Africa and an entire village was found dead (including animals) the morning after it happened. This happens when a volcano,
usually in or under a lake, puts out too much CO2. When CO2 levels reach 10% or higher, it is lethal and can cause death by
asphyxiation.
Mitigation of Volcano Problems
There are some strategies for helping prevent damage from volcanic eruptions. One strategy that was used in Iceland
was to spray the front of the lava flow with cool water. This caused the lava to cool and solidify and provide a dam
against the liquid lava. The engineers even tried to do it in a way to help direct the lava away from town. Another
strategy is to monitor a volcano. Increases in earthquake activity and SO2 and CO2 gas output suggest the possibility of
an eruption. However, this only works on volcanoes that scientists have instruments on and are actively monitoring.
Predicting an eruption is very difficult and not always correct. This could lead to evacuating people, but no eruption
happening. How do you think people may respond in the future? The scientists have to be certain and is very difficult
to be absolutely certain. Finally, communities can establish evacuation routes and strategies to help keep people safe
if there is an eruption.
Cool Volcano Link: check it out if you like. A list of possible nasty volcanic hazards.