Earth Science: Geology, the Environment, and the UniverseUnit 4:
The Atmosphere and the OceansWebQuest Projects 2Venice: At the Mercy of the Sea Introduction In this WebQuest, students use Internet resources to learn how a combination
of a rise in sea level and subsidence are causing the city of Venice, Italy,
to be inundated by water from the Adriatic Sea more than 100 times per year.
Students will answer questions based on their research that will lead them through
an investigation of why this city is susceptible to this type of flooding, as
well as the effects of flooding on the population, art, and landmarks of the
city. Students will analyze and evaluate the effectiveness of several proposed
plans to stabilize the “sinking” city, and to prevent flood water
from entering the city during high water periods. Task While students are conducting research using the Internet resources provided,
they will answer a set of nine questions. Each Web site has some of the answers,
but none of the Web sites alone will address all of the questions. Students
should be able to compile information to answer the questions as they read through
each Web site. As students research the answers to the questions, they will focus on proposed
plans for protecting Venice from high water. The plans include building mobile
barriers between the Venetian Lagoon and the Adriatic Sea, and raising parts
of the city or even the entire city through various methods. Based on their
research, which will include the opinions of scientists and others, students
will formulate an opinion about the best possible approach to saving this important
city. Objectives - Describe the unique geographic location of Venice
- Define the term subsidence, and explain how this process is affecting Venice
- Describe changes in sea level worldwide, and explain how these changes
are affecting Venice
- Use numerical values to describe the rate of change of land level relative
to sea level within the past 100 years, as well as the yearly frequency of
flooding in Venice
- Explain the artistic, cultural, and architectural significance of Venice
within the world community
- Describe and compare several proposed plans for keeping water from entering
Venice during high water events
- Analyze the possible advantages and disadvantages of proposed plans for
keeping water from entering Venice during high water events
- Form an opinion, based on research and evaluation of expert opinions, about
the best approach to take to keep water from entering Venice during high water
events
Resources
Students will use the Internet links provided to learn how flooding is, and
for much of its history, has been, a problem for residents of Venice, Italy.
They will identify the reasons behind these high water events, and will be able
to describe the role of global sea level rise in the process. Students will
examine several proposed plans for keeping flood waters out of the city. They
will also identify some of the landmarks, art, and architecture that make this
city unique. Further research will lead students to analyze the proposed plans for saving
the city from the effects of rising water. Students will identify key components
of the plans, compare and analyze their effectiveness based on expert opinion,
and form their own opinions about the most effective measures to take to keep
flooding from destroying Venice. Time
Three to four class periods to answer the set of questions, develop a comparison
of the proposed plans, and form an opinion about their effectiveness. Process
As students conduct research by studying the Web sites provided, help them
focus on the information in the questions. This will provide students a sense
of direction when approaching each site. If time allows, consider allowing students
to further explore the problems other world cities are experiencing due to subsidence,
global sea level rise, or a combination of both factors. Students may want to
examine some of the plans underway to protect these areas, and compare them
to those being suggested for Venice. Students will ultimately focus their research on the proposed plans for keeping
flood waters from invading the city. Through animation, descriptions, diagrams,
and photographs, students will learn how the mobile barrier system will work.
They will study various expert opinions from those who favor this method, as
well as those which believe they system will not work. Through comparing this
system with proposals that aim to “raise” all or parts of the city,
students will develop and create a written opinion about the best possible approach
to take to protect this important city. Have students review the rubric to understand how their final product will
be evaluated. If time permits, allow students to share their opinions with other members
of the class. Students could be arranged in groups with all members of a group
sharing a similar opinion. Given time to discuss rationales, groups could present
their arguments in classroom debate. Or, students could be arranged in groups
with members of each group having different opinions. Students could then engage
in debate within small groups. Debates should be structured, monitored, and
well led for optimum effectiveness. Evaluation
You may assign ten points to each of the ten questions for a total of 100 possible
points. The answers to the questions are given below. Rate the answer to
each question using the following scale: Excellent – 9-10 points; Very
Good – 7-8 points; Good – 5-6 points; Satisfactory – 3-4 points;
Poor – 1-2 points; and Unsatisfactory – 0 points. Answers to Questions About Natural Threats to Venice and Possible
Solutions - Venice is located on an island which is in the Venetian Lagoon. The lagoon
borders the Adriatic Sea. This low-lying island is not very far above sea
level. During periods of high tide, ocean water enters the lagoon, naturally
raising the overall water level. If tides are unusually high, or are compounded
by wind, runoff from heavy rain, or storm surge, flooding can easily occur.
- Venice is sinking at a rate of one-half inch per century. The relative land
level has dropped by more than 23 inches with respect to sea level in the
last 100 years.
- Sirens alert Venice residents of impending high water, alerting shop owners
and those who live and work in businesses, restaurants, and museums in this
area to be prepared for flooding. St. Mark’s Square is only two inches
above normal high tide level, so any abnormally high tide easily affects it.
The square can be covered by four inches of water during a high water event,
forcing residents and visitors to wade through water to get from place to
place, or converge on relatively narrow wooden walkways elevated above the
square.
- Venice is on a low-lying island in a lagoon. The lagoon adjoins the Adriatic
Sea. Therefore, changes in sea level affect the water height in the lagoon.
Globally, sea level is rising, making water levels surrounding Venice slightly
higher each year. The second factor which contributes to flooding in Venice
is known as subsidence. Venice is built on ground that is a composite of poorly
consolidated sand, silt, and clay. The weight of the city, combined with the
fact that groundwater was removed from aquifers at an enormous rate in the
1900s, leads to compaction of this underlying material. As this sand, silt,
and clay compacts, the city “sinks.”
- As businesses, industries, and farming grew in and around Venice in the
1900s, groundwater was pumped from aquifers below the city for industrial
and agricultural use at an increasing rate. The removal of groundwater took
place at a higher rate than it was naturally recharged, which increased the
compaction of materials on which the city was built. While large-scale removal
of groundwater ceased in the 1970s, much damage was already done, which set
the stage for subsidence that continues today.
- Answers will vary widely. Students may mention the Marco Polo arch, which
dates around 1300 and stands in the neighborhood where Marco Polo is said
to have lived, the sarcophagus of Giovanni Priuli, a famous Venetian senator
who died in 1375, or the “Bridge of Sighs,” built in 1600 to connect
an inquisition room with a prison across one of the cities many canals.
- This system is called the MOSE system, which stands for Modulo Sperimentale
Elettromeccanico, or Electromechanical Experimental Module. The system consists
of 79 gates which will lie flat on the sea bed, out of sight and filled with
water, when not in use. When a high water event is expected, the gates will
be filled with air, which will force the seawater out and cause them to rise.
The gates will block all entrances between the Adriatic Sea and the Venetian
Lagoon, preventing flood water from entering the lagoon and causing flooding
in the city.
- Critics of the MOSE system say that the gates will not be able to block
all water entering from the Adriatic, and that increased rates of sea level
rise over the next century will soon make these very expensive gates obsolete.
Some environmentalists argue that closing the gates for long periods of time
will damage the lagoon ecosystem, as they will prevent the natural flow of
water between the sea and the lagoon necessary to flush pollutants from the
lagoon. Proponents say the gates are a good solution because they are only
activated when needed, can remain in use for short periods of time rather
than being a permanent feature, and that they can adjust easily to changes
in sea level because of their mobility.
- Currently, as has been the case in much of the history of Venice, the city
has simply been “built up” to accommodate increasingly higher
water levels. Sidewalks are raised, lower levels of buildings abandoned and
higher levels added when possible, railings and curbs are raised. Another
plan involves injecting either seawater or carbon dioxide into aquifers below
the city to “pump up” the entire city.
- Critics of the plan to build up parts of the city on a continual basis contend
that this can only go on for so long before structural stability of some buildings
becomes an issue, the proportion of raised areas to existing structures becomes
visually unappealing, and, in some cases, doorways simply become too small.
Proponents say this method has worked for much of the history of Venice, because
construction and changes can occur at a pace which stays ahead of changes
in water levels. While advocates of the plan to inject seawater or carbon
dioxide into underground aquifers say this is a low-cost solution which is
relatively easy to implement, critics say it would be impossible to uniformly
raise all parts of the city, which would lead to widespread structural instability.
Evaluating the Written Opinion Use the evaluation rubric or other means to assess each students analysis of
the proposed plans to prevent further flooding in Venice. Evaluation of the
written opinion should include self-assessment and teacher assessment. Students
may want to add a third column to the rubric to be completed after debating
their opinions with class members. Conclusion Based on Internet research, students should be able to explain the factors
that contribute to the flooding that affects Venice on a weekly basis. They
should be able to describe the unique nature of this city among world cities
based on its history, art, and architecture, and recognize the importance of
preserving Venice. Students should be able to describe and compare several proposed
plans for preventing flood waters from entering the city. Based on their research,
as well as the opinions of experts, students should be able to prepare a written
opinion about the best approach to take to save this important city for future
generations. Written Opinion Rubric
Written Opinion Rubric | Points Possible | Self-Assessment | Teacher Assessment | The statement clearly describes
the opinion of the writer. | 10 | | | The statement provides evidence,
based on research, which supports the opinion of the writer. | 10 | | | The statement clearly outlines
the approach the writer believes should be taken. | 10 | | | The statement is well-written
and its content clear and understandable. | 10 | | |
Rate each category according to the following scale:
Excellent – 9-10 points; Very Good – 7-8 points; Good – 5-6
points; Satisfactory – 3-4 points; Poor – 1-2 points; and Unsatisfactory
– 0 points. | |