Group Activity: Environmental Impact Assessment
The State of Jalisco is proposing a dam project. Your task is to develop an Environmental
Impact Assessment (EIA)
Work in groups of three to write-up your EIA and present the results of your findings to
the rest of the class.
Each EIA needs to include the basic steps. They are:
To know more about the steps of EIA go to this link.
• SCREENING process – it has already been decided that an EIA should take place
• SCOPING stage – identify which impacts must be considered
• BASELINE STUDY – we need to know what the physical and biological environment
is like. What variables are you going to include?
• MEASURING IMPACT – detail potential significant impacts (good or bad) on
ecosystems, people and resources.
• EVALUATION OF IMPACT – magnitude of the impact, extent of the impact and
duration of the impact.
• MITIGATION stage – how can we mitigate the impact that the dam will have? Final
decision as to whether the project should go ahead or not.
Information about the project
Suggested location for the Arcediano Dam
Guadalajara is the second
largest municipality and also
the second largest urban area
in Mexico. Potable water
supplies are primarily derived
from surface water, with
about 60 percent of the 9.0
m3/sec supply coming from
the Lago de Chapala. The
National Water Commission
and the Government of the State of Jalisco estimate that there is a deficit of
approximately 3.5 m3/sec and are planning to further develop available surface supplies
through the construction of the Arcediano dam and reservoir on the Rio Santiago, just
downstream from where it meets the Rio Verde. The dam will help preserve the Lago de
Chapala by reducing demand on the lake resources and help improve and preserve the
environment within the Lerma-Chapala basin.
The Arcediano dam will have a height of approximately 120 m. The proposed reservoir
will store an estimated 440 million m3 of water and will allow the exploitation of up to
10.4 m3/sec of surface water on the Rio Santiago, directly benefiting 1.4 million people in
the State of Jalisco. Water from the reservoir will be pumped through a new aqueduct
approximately 8 km in length with an elevation change of about 560 m. A new
potable water treatment facility will provide water supplies to the urban area
surrounding Guadalajara. The dam may include turbines for electrical power generation,
although this has not been determined.
It will be built in the Oblatos-Huentitlán canyon, an area of high biodiversity, including
endemic and endangered species. In 1997 the canyon was declared a Protected Natural
Area by Guadalajara City Council subject to ecological conservation. The construction of
the dam would mean the deforestation of over 1,300 hectares of land followed by the
flooding of 800 hectares and the great loss of biodiversity including unique species.
The Santiago River, from its source in Lake Chapala to the Arcediano site, receives
wastewater from both domestic and industrial sources. A total of approximately 2,316
liters per second of untreated wastewater is discharged from the Suburban Area of
Guadalajara directly in the Rio Santiago. In Mexico, water quality is measured using a
Water Quality Index (ICA). The National Water Commission (CNA) requires untreated
water proposed as a source for drinking water purification to have an ICA value of at least
50.
Data presented by the CEAS indicate that due to the presence of excess nitrogen and
phosphates in the river basin, conditions for eutrophication will develop in the reservoir,
even when the proposed wastewater treatment plants are taken into account.
Eutrophication, or the increase of nutrients in freshwater lakes or reservoirs, provokes an
excess of phytoplankton and can cause severe deoxygenation of the water which is linked
to human health problems.
There are two communities living next to the Santiago River that would be flooded as a
result of the dam, El Salto and Juanacatlán. However money has been provided to
relocate these communities.